The present invention relates to methods for the operation of an engine to enable the use of new fuel compositions having physical properties that differ from traditional fuels.

Background of the Invention

The pursuit for fuel alternatives to conventional fossil fuels is primarily driven by the need for a 'clean' emissions fuel coupled with low production costs and wide availability. Much attention is paid to the environmental impact of fuel emissions. Research into alternative fuels focuses on fuels that will reduce the amount of particulate matter and oxides produced by fuel combustion as well as fuels that reduce the non-combusted fuel and C0 ₂ emissions and other products of combustion.

Fuel alternatives for complete or partial replacement of traditional fuels have not become widely used.

One major disadvantage with the complete replacement of traditional fuels, and in particular fuels for compression ignition engines (diesel fuels), with a renewable replacement fuel, relates to the perceived problems associated with the low cetane index of such fuels. Such fuels present problems for achieving ignition in the manner required for efficient operation of the engine.

The present applicant has developed new fuel compositions for use in compression ignition (diesel) engines with an improved emissions profile without a major adverse impact on fuel efficiency and/or engine performance. The fuel composition comprises methanol and water, and low levels of additional components (referred to as additives). One additive that may be present in the fuel is dimethyl ether. The fuel is introduced into the combustion chamber of the engine. According to some embodiments, a fumigant comprising an ignition enhancer, such as dimethyl ether, is fumigated into the intake air stream of the compression ignition engine prior to compression and introduction of the methanol water fuel, referred to as the "main fuel" or "traditional diesel replacement fuel".

The applicant has recognised that further improvements are desired in the operation of diesel or compression ignition engines to facilitate the use of methanol-water fuels in such engines. This would make the use of methanol-water fuels even more attractive as a replacement for traditional diesel fuel. Summary of the Invention

The diesel engine fuel comprising methanol and water is much more fluid, or less viscous, than traditional diesel fuels. This low viscosity fuel creates a greater likelihood of leakage from, and friction within, the engine. The applicant has found that it is possible to cool the fuel prior to introduction of the fuel into the combustion chamber to obtain a sufficient increase in the viscosity of the fuel to enable operation of the methanol-water fuel in a conventional compression ignition engine, in place of traditional diesel fuel. The step of cooling a fuel, and introducing a cooled fuel into a compression ignition engine, is counterintuitive in the field of compression ignition engine operation. Whilst cooling of the fuel will typically be required to achieve the desired viscosity levels, it is recognised that in some countries or regions, such cooling will only be required at some times of the year, when the temperatures are higher. At other times of the year, the prevailing temperatures may not require cooling to take place. Accordingly, a temperature measurement and control step is utilised to ensure that temperature control (e.g. cooling) takes place only when required.

Accordingly, the work of the applicant has led to the development of a range of related processes, systems and uses that address the differences between the viscosity of methanol-based fuels and traditional diesel fuel in the operation of a compression ignition engine. In accordance with one aspect, there is provided a process for operating a compression ignition engine, the process comprising: measuring the temperature of a fuel comprising methanol and water prior to its introduction into the combustion chamber of the compression ignition engine; and controlling the temperature of the fuel to control the viscosity of the fuel prior to its introduction into the combustion chamber of the compression ignition engine.

The temperature control will typically involve cooling of the fuel to increase the viscosity of the fuel. The degree of cooling may be that required to achieve the desired degree of increase in the viscosity of the fuel.

In accordance with a second related aspect, there is provided a process for operating a compression ignition engine, the process comprising: cooling a fuel comprising methanol and water, introducing intake air into the combustion chamber of the engine, introducing the cooled fuel into the combustion chamber of the engine, and igniting the fuel/air mixture to thereby drive the engine.

The fuel compositions of embodiments of the invention are set out in the detailed description below.

The process may further comprise the steps of:

Fumigating the intake air stream with a fumigant comprising an ignition enhancer, and/or preheating the intake air stream.

According to some embodiments, the process comprises the step of fumigating the intake air stream with a fumigant comprising an ignition enhancer. The fumigant may comprise dimethyl ether.

Also provided by the applicant are a series of systems, or apparatus, suitable for performing the processes of the present application.

In accordance with a third aspect, there is provided a system comprising: a compression ignition engine; and a control system for measuring the temperature of a fuel prior to its introduction into the compression ignition engine and adjusting the temperature of the fuel following measurement and prior to introduction of the fuel into the compression ignition engine.

The control system suitably comprises a cooling system, since cooling is the typical mechanism that will be required for adjusting the temperature of the fuel to the required temperature to achieve the desired viscosity.

In accordance with a fourth related aspect, there is also provided a system comprising: a fuel storage unit; a compression ignition engine; and a cooling system positioned to cool fuel from the fuel storage unit prior to its introduction into the compression ignition engine.

The cooling system may be positioned in the fluid pathway between the fuel storage unit and the compression ignition engine, such that in operation, the cooling system cools the fuel from the fuel tank prior to the fuel being introduced into the compression ignition engine. The cooling system may form a component of the fuel storage unit - for example, it may be coupled directly with the fuel storage unit in a manner that enables the fuel exiting the fuel storage unit to be cooled prior to introduction into the compression ignition engine. The cooling system may alternatively form a component of the compression ignition engine - for example, the engine may include a modification that effects cooling of the fuel prior to it entering the combustion chamber of the engine. In other embodiments, the system may not include a fuel storage unit (for example, the fuel may be directed from a fuel supplier directly to the engine, without storage in a fuel storage unit). Such examples are within the scope of the present application unless expressly excluded. The system may further comprise a control system for measuring the temperature of the fuel, and controlling the operation of the cooling system. The controller may operate to control the (fuel) cooling system to control the fuel temperature to be within a pre-set temperature range. The pre-set temperature range may be a range that corresponds to a target viscosity for the fuel. In accordance with fifth aspect, there is provided a power generation process comprising: cooling a fuel comprising methanol and water, powering a compression ignition engine by igniting the cooled fuel to generate power; - treating engine exhaust to recover exhaust heat and/or water from the engine, and redirecting the heat and/or water for further use.

The power generation process may further comprise: preheating an inlet air stream of the compression ignition engine, and/or fumigating the inlet air stream with an ignition enhancer. The power generation process may include both the pre-heating and fumigation steps.

In some embodiments, the process for operating a compression ignition engine may comprise: measuring the temperature of a fuel comprising methanol and water prior to introduction into the combustion chamber of the compression ignition engine; controlling the temperature of the fuel to control the viscosity of the fuel prior to introduction into the combustion chamber of the compression ignition engine; - introducing intake air into the combustion chamber of the engine, and igniting the fuel/air mixture to thereby drive the engine.

The controlling step typically comprises changing the temperature of the fuel prior to its introduction into the combustion chamber of the compression ignition engine. This change is made in response to the temperature measured in the measuring step. If the measured temperature is not within a target range set for the fuel, being a temperature that provides a target viscosity, then the temperature is changed to bring the fuel temperature within the target temperature range.

The step of controlling the temperature typically comprises cooling the fuel prior to introduction into the combustion chamber of the compression ignition engine.

In accordance with this process, the corresponding system may comprise: a compression ignition engine; and a control system for measuring the temperature of a fuel prior to its introduction into the compression ignition engine and adjusting the temperature of the fuel following measurement and prior to introduction of the fuel into the compression ignition engine.

The system will typically comprise a cooling system as described above. The system may comprise a fuel storage unit. In the alternative, fuel from a fuel source may be directed to the compression ignition engine without the use of an

intermediate fuel storage unit.

The control system may operate to cool the fuel if the fuel temperature is outside a pre-set range that corresponds to a target viscosity range for the fuel. If the incoming fuel is already with in the required temperature range, the temperature is not adjusted. If the incoming fuel is not within the target range, it may be cooled through operation of the fuel cooling system prior to the fuel being introduced into the compression ignition engine.

The present application further relates to the use of temperature adjustment to modify the viscosity of a fuel comprising methanol and water prior to introduction of the fuel into a compression ignition engine. In some embodiments, the temperature adjustment is cooling.

The present application further provides for the use of temperature adjustment of a methanol-based fuel, and the inclusion of water in the fuel, to modify the viscosity of the methanol-based fuel to fall within a range suited to the operation of a compression ignition engine. The temperature adjustment is preferably cooling.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

Figure 1 is a schematic diagram of the system in accordance with one embodiment of the invention including a fuel storage unit, cooling unit, and compression ignition engine;

Figure 2(a) is a depiction of Stribeck curve showing the friction coefficient as a function of film thickness, noting that film thickness is proportional to the product of entrainment speed and viscosity at a constant load;

Figure 2(b) is a schematic illustration of the mini traction machine (MTM) used for performing friction measurements performed in the Experimental section, operated under low load. Friction is measured between the ball and disk that rotate at different speeds.

Figure 3 is a graph showing viscosity measurements performed in the Experimental section (measured in mPas) for methanol-water mixtures shown as a function of (a) % methanol (linear scaling), and (b) temperature (log-linear scale). The lines are empirical fits to the data.

Figure 4 presents the results of the study into tribological properties for methanol- water systems tested using a ball-on-disc tribometer (as illustrated schematically in Figure 2(b)). The friction coefficient is measured between stainless steel contacts as a function of entrainment speed (top graph) and (lubricant viscosity x entrainment speed) (bottom graph).

Figure 5 is a graph showing the friction coefficient (log scales) measured between stainless steel contacts as a function of (lubricant viscosity x entrainment speed) at 4°C. The line is an empirical fit to the data. The stars in the graph indicate estimates for the friction coefficient at 500 mm/s for 70% methanol (30% water) using the viscosity at -15°C and -30°C, respectively.

Figure 6 is a graph of the friction coefficient (at 500 mm/s) versus temperature for 100% methanol, compared to 70% methanol:30% water. The data presented to the left of the solid vertical line (indicated by the left-pointing arrow) is based on the data of Figure 5, and the data presented to the right of the vertical line is based on the measured friction coefficient using the tribometer.

Detailed Description The processes and systems described herein relate to processes and systems that enable the use of methanol-water fuels in compression ignition (CI) engines.

Details regarding the engine operation once the fuel is supplied to the engine are set out in the applicant's co-pending applications PCT/AU201 1/001530, PCT/AU201 1/001531 , and PCT/AU2013/000555, the entirety of which is incorporated herein by specific reference. These co-pending applications describe the composition of suitable methanol-water fuels, how the compression ignition engine can be operated and controlled, the recovery and reuse of heat and water generated during the operation of the engine, and how to generate a fumigant and main fuel composition from a pre-fuel for use in the engine, amongst other related matters.

The present application focuses on ways to modify the use of a compression ignition engine to enable the use of methanol-water fuel, which at typical climatic temperatures have a lower viscosity than traditional diesel fuel. This involves the use of a cooling step to cool the fuel, prior to delivery or supply of the fuel into the engine to power the engine.

Underlying theory

When faced with the problem of a low viscosity fuel, the natural approach in the art is to increase the viscosity of the fuel through the use of additives. The approach of the present applicant is a new way to address low viscosity fuel, involving the use of a preliminary step of cooling the fuel prior to introduction of the fuel into the engine. The applicant has examined the impact that temperature, and the methanol and water content, has on the viscosity of fuel compositions. Although it is known that viscosity of liquids tends to increase when cooled, it would not have been anticipated that a combination of methanol and water, each being of very low viscosity, would have a sufficiently high viscosity increase to enable substitution for diesel fuel in a conventional compression ignition engine. In fact, the laboratory work reported below has shown that mixtures of methanol and water, up to 50:50 methanokwater content, , have a viscosity that approaches or exceeds twice the viscosity of the methanol alone at the same temperature, through the range -30 to + 30 deg C. Moreover, at reduced temperatures, the viscosity of the mixture within this compositional range results in an even greater viscosity increase, which brings the viscosity into the diesel engine fuel viscosity range. It should be noted that although such ratios of methanol to water are particularly suited based on viscosity, when balancing the viscosity factors with other factors such as engine operation and engine emissions, the methanokwater ratio of the fuel may fall slightly outside this range. Suitable fuel compositions are described in further detail below.

Components of the system The core components of the system are schematically illustrated in Figure 1 . As shown in Figure 1 , the system comprises an optional fuel storage unit (1 ), a cooling system (2), and a compression ignition engine (3). The three components are in fluid

communication, with the cooling system located in the fluid pathway between the fuel storage unit and the compression ignition engine. It is noted that, in some cases, fuel may be delivered directly from a fuel producer to the engine without an intervening fuel storage unit, so the fuel storage unit may not be present in all embodiments of the invention. Fuel storage unit

The fuel storage unit may be of any configuration suitable for storage of fuel. The fuel storage unit may be in the form of a fuel storage tank or tanks. The fuel storage unit may be fixed in one location, transportable, or may form part of an integrated vehicle such as a train or marine vessel. The shape, size, configuration and construction may be of any type known in the art for fuel storage.

Cooling system

The cooling system may be of any type capable of cooling the fuel prior to

introduction of the fuel into the combustion chamber of the compression ignition engine. The cooling system may be in the form of a chiller. Chillers are used to provide chilled water or other fluids for air conditioning systems, and for other industrial applications. The chiller may comprise a compressor. The compressor may be of any suitable type, such as a centrifugal compressor, reciprocating compressor, or screw compressor. The cooling system may comprise one or a series of chillers. When multiple chillers are used, these may be in series or parallel. The cooling unit may operate in a continuous cooling mode for cooling of the fuel as it passes through the cooling unit and then into the engine, or it may operate in a batch process. Continuous cooling is preferred.

The cooling system, or chiller, may be powered by any suitable technique. Examples include chillers powered by external electricity, chillers powered by the compression ignition engine, and chillers using engine coolant waste heat. In the case of chillers powered by the compression ignition engine itself, the chiller may be driven via a shaft or any other arrangement powered by the compression ignition engine. In the case of chillers using engine coolant, the evaporating or chilling medium is evaporated at low temperature with the vapour (e.g. methanol vapour) being adsorbed onto a suitable medium, such as activated carbon. When the adsorbent is near saturation, hot coolant (for example, an engine coolant at about 100-130 ^° C,) is used to drive off the adsorbed vapour to restart the cooling cycle.

Cooling refers to the obtaining of a temperature reduction in the fuel from the pre- cooled temperature to a cooled temperature, prior to the introduction of the fuel into the engine. Direct, or indirect use of waste exhaust gas heat via heat exchange may also be used to provide the input thermal energy at a sufficiently high temperature, to drive any suitable cooling cycle used to cool the fuel. In some embodiments, the cooling system may comprise evaporation of a

component of the fuel to cause a temperature decrease in the remaining fuel. In other embodiments, the cooling system effects cooling without changing the fuel composition. Expressed another way, in such embodiments, the cooling system effects cooling while maintaining the fuel composition. Such cooling systems may be ones operating by heat exchange, or by operation of a chiller, such as by a heat adsorbent material that can be regenerated.

The degree of cooling required may vary depending on the extent of viscosity increase required, and depending on the prevailing atmospheric or seasonal conditions. The degree of cooling will also depend on the relative proportions of water to methanol in the fuel. The dimethyl ether content of the fuel, if any, can also have an impact.

As examples, the fuel may be cooled by at least 2 ^° C, such as at least 3 ^° C, at least 4 ^° C, at least 5 ^° C, at least 6 ^° C, at least 7 ^° C, at least 8 ^° C, at least 9 ^° C, at least 10 ^° C, at least 1 1 ^° C, at least 12 ^° C, at least 13 ^° C, at least 14 ^° C, at least 15 ^° C, at least 20 ^° C, at least 25 ^° C, at least 30 ^° C, at least 40°C, at least 50°C, at least 60°C, or more. The temperature of the fuel prior to cooling is measured at the point prior to the cooling operation taking place. If the fuel is passed through a fluid conduit prior to cooling, according to an embodiment, the pre- cooled temperature is measured in the fluid conduit prior to cooling taking place. If the fuel is stored in a fuel storage tank prior to cooling, according to an embodiment, the pre-cooled temperature is measured in the fluid conduit prior to cooling taking place. The temperature of the fuel following cooling may be measured following cooling and prior to the fuel being introduced into the engine. According to an embodiment, this may be measured just prior to the fuel being introduced into the engine. There may a change in temperature in the fuel following the cooling step and introduction into the engine - that is, the fuel may increase in temperature between the cooling step and the point of entry into the engine. It is required that the fuel does not return to the pre-cooled temperature, to obtain the benefit of the present invention.

According to embodiments, the fuel is cooled to a temperature of 15°C or less, or 10 ^° C or less prior to introduction into the engine. According to embodiments, the fuel may be cooled to a temperature of 8 ^° C or less, 6 ^° C or less, 4 ^° C or less, 2 ^° C or less, 0 ^° C or less, - 2 ^° C or less, -4 ^° C or less, -6 ^° C or less, -8 ^° C or less, -10 ^° C or less, -12 ^° C or less, -14 ^° C or less, -16 ^° C or less, -18 ^° C or less, or -20 ^° C or less. A suitable cooled fuel temperature to obtain significant benefits in the process and system is around - 10 ^° C or less. It will be appreciated that the process and system are subject to a trade-off between the energy required to refrigerate the methanol water fuel, and the heat energy produced. The coefficient of performance (COP), being the measure of refrigeration energy/heat energy, may be in the region of around 0.6-0.7, depending on the temperature of the fuel prior to and following cooling. The system of the applicant can achieve the required cooling from sufficiently available waste engine heat.

The cooling system is positioned or located such that fuel cooled through the cooling system can be directed into the compression ignition engine without returning to the pre- cooled temperature of the fuel. It is noted that there may be some unavoidable increase in the fuel temperature after cooling. The temperature increase after cooling is desirably kept to a minimum through insulation of the fuel passage way or fuel line. Whilst fuel re-heating is desirably avoided, it is noted that a fuel temperature increase may occur at a point close to injection into the engine, where the temperature conditions are much higher. Thus, it is noted that the period during which the fuel temperature is to be maintained at the cooled temperature need only persist until the fuel reaches engine (such as the fuel injector component of the engine).

The cooling system may be positioned at any suitable location in advance of the compression ignition engine. The compression ignition engine will generally comprise or be associated with a fuel pump, which pumps fuel as required into the engine. The engine also typically comprises fuel injector(s). The cooling system may be positioned before the fuel pump or after the fuel pump, in the fluid pathway leading to the compression ignition engine (or fuel injector(s) thereof). Cooling or temperature control is suitably applied prior to injection via the injectors into the engine.

It is desired that, from the point (i.e. location) of temperature control (such as the point of cooling), leading to the fuel introduction into the engine, the passageways and equipment through which the fuel flows are insulated. Insulation is desired to minimise any subsequent heat change after any temperature control, such as cooling, applied to the fuel. As an example, if the fuel is cooled prior to being pumped through a fuel pump to the engine, then the fuel pump may be insulated to avoid excessive fuel heat gain prior to the fuel being introduced into the engine. In another example, if the fuel temperature is controlled (cooled), following pumping and prior to injection into the engine, then the fuel passage between the control stage (e.g. cooling stage) and the fuel injectors may be insulated. The fuel injector components, up to the fuel injector tip, may be insulated for this purpose. It will be appreciated that at the fuel injector tip, which is closely associated with the engine combustion chamber, heating of the fuel will be effected as it enters the engine, so insulation will be of little effect in that region, and is not required.

In some embodiments, the viscosity of the methanol water fuel, at a temperature of between -15°C and +15°C, is within a typical diesel fuel range, as measured at between 20°C and 80°C. The viscosity is affected by the prevailing pressure conditions.

At atmospheric pressure, the viscosity range for the methanokwater fuel, at a temperature of less than 15°C, (preferably at a temperature 10°C or less, 0°C or less, or - 10°C or less), may be between about 1.0 mPas and 6.0 mPas (which corresponds to a typical diesel range at this pressure across a temperature range of about 20°C and 80°C), suitably between 1 .0 and 5.0 mPas, 1.0 and 4.0 mPas, or 1.0 and 3.0 mPas. At 1000 bar, the viscosity range for the methanokwater fuel, at a temperature of less than 15°C,

(preferably at a temperature 10°C or less, 0°C or less, or -10°C or less), is between about 2.9 mPas and 12 mPas (which corresponds to a typical diesel range at this pressure across a temperature range of about 25°C and 80°C). At pressures between atmospheric pressure and 1000 bar pressure, the viscosity of the methanokwater fuel is suitably within these ranges. Overall, accounting for a wide range of pressure conditions extending to greater than 1000 bar pressure, the viscosity is suitably between 1 .0 and 18 mPas. The viscosity may be a minimum of 1.2, 1 ,4 or 1.6 mPas. The maximum viscosity of the range is suitably 18, 16, 14, 12, 10, 8.0, 7.0, 6.5, 6.0, 5,5, 5.0, 4.8, 4.6, 4.4, 4.2, 4.0, 3.8, 3.6 or 3.4. Each lower value and upper value can be combined independently, without limitation. The viscosity is kinematic viscosity.

It will be appreciated that, when cooling is effected following passage of the fuel through the fuel pump, the fuel will be at a pressure above atmospheric pressure, and it is at the point following cooling, or at the point of entry into the fuel injector(s), that the viscosity is considered. Where cooling is effected prior to passage through the fuel pump, lower (around atmospheric) pressure conditions may apply.

In some embodiments, the process comprises controlling the fuel viscosity through temperature control and/or compositional control, to achieve a viscosity performance up to the injectors similar to a traditional diesel fuel. Compositional control refers to control of the water content of the methanol-water fuel. Performance up to the injectors refers to the passage of the fuel just prior to fuel injection, and up to fuel injection. This may extend back to include the passage of the fuel through the fuel pump. Otherwise, this may extend through a part of the fluid line leading up to the fuel injector(s). Accordingly, expressed another way, the process may comprise controlling the fuel viscosity through temperature control and/or water composition control, to achieve a viscosity performance at fuel injection similar to a traditional diesel fuel. In some embodiments, this viscosity is the viscosity that prevails at the point of introduction of the fuel into the fuel injector(s). In some embodiments, this viscosity is the viscosity that prevails through passage through the fuel pump. In some embodiments, this viscosity is the viscosity that prevails through the passage through at least a portion of the fluid passageway between the fuel storage and unit and the compression ignition engine. In some embodiments, the viscosity is controlled through temperature control.

Compression ignition engine

The compression ignition engine, or diesel engine, may be of any construction or configuration known or used in the art. The fuel and process described herein is suitable for powering compression ignition (CI) engines. In particular the fuel and process is most suitable, but not limited to, CI engines operating at medium to low speeds such as 1000rpm or less. The speed of the engine may even be 800rpm or less, for instance 500rpm or less. The speed of the engine may even be 300rpm or less, for instance 150rpm or less.

The compression ignition engine is preferably a large diesel engine such as a ship diesel engine, train diesel engine or an electrical power generating diesel engine. The slower speeds in larger CI engines allows sufficient time for combustion of the selected fuel composition to be completed and for a sufficiently high percentage of the fuel to be vaporized to achieve efficient operation.

It is however understood that the CI engine could be a smaller CI engine operating at high speed. Examples of such engines are those operating at about 2000rpm and 1000rpm.

According to some embodiments, there is provided a ship, train or electrical power generation facility comprising: a fuel storage unit; a compression ignition engine; and a cooling system positioned to cool fuel from the fuel storage unit prior to its introduction into the compression ignition engine.

Methanol Water Fuel

The fuel composition, which may be referred to as a methanol water fuel, or "the main fuel composition", comprises methanol and water. The fuel is a compression ignition engine fuel, that is, a diesel engine fuel. The fuel may comprise further components as described below, and may as one example contain from 0% to 20% by weight dimethyl ether. It is noted that the methanol water fuel may also be referred to as a "traditional diesel replacement fuel", in that it is charged into the engine in place of traditional diesel fuel. (This distinguishes the methanol water fuel from "secondary fuels" that may be directed into the intake air stream into the diesel engine, as a supplement for a traditional diesel fuel driven engine.)

To date, methanol has not found commercial application in compression ignition engines. The disadvantages with using methanol as an engine fuel, either neat or blended, is highlighted by its low cetane index, which is in the range of 3 to 5. This low cetane index makes methanol difficult to ignite in a CI engine. Blending water with methanol further reduces the cetane index of the fuel making combustion of the methanol/water blend fuel even more difficult, and thus it would have been considered counter-intuitive to combine water with methanol for use in CI engines. The effect of water following fuel injection is one of cooling as the water heats up and evaporates, further lowering the effective cetane.

However, it has been found that a methanol-water fuel combination can be used in a compression ignition engine in an efficient manner and with cleaner exhaust emissions, provided that the engine is fumigated with a fumigant comprising an ignition enhancer. Methanol has been described for use in fuels compositions previously, but as a heating or cooking fuel, where the fuel is burned to generate heat. The principles that apply to diesel engine fuels are very different, since the fuel must ignite under compression in the compression ignition engine. Very little, if anything, can be gleaned from references to the use of methanol and other components in cooking/heating fuels. The main fuel may be a homogeneous fuel, or a single phase fuel. The fuel is typically not an emulsion fuel comprising separate organic and aqueous phases emulsified together. The fuel may therefore be emulsifier free. The accommodation of additive components in the fuel is assisted by the dual solvency properties of both methanol and water, which will enable dissolution of a wider range of materials across the various watenmethanol ratios and concentrations which can be utilised. The pre-fuel is also a homogeneous fuel, or a single-phase fuel.

All amounts referred to in this document are by reference to weight, unless specified otherwise. Where a percentage amount of a component in the main fuel composition is described, this is a reference to the percentage of that component by weight of the entire main fuel composition. In broad terms, the relative amount of water to methanol in the main fuel composition may be above 0.0:100.0 watenmethanol. In some embodiments, the relative amount of water to methanol is in the range of 0.5:99.5 to 80:20 by weight. According to some embodiments, the minimum water level (relative to methanol) is 2:98, such as a minimum ratio of, 3:97, 5:95, 7:93, 10:90, 15:95, 19:81 ; 21 :79. The upper limit of water (relative to methanol) in the composition according to some embodiments is 80:20, such as 75:25, 70:30, 60:40, 50:50 or 40:60. The relative amount of water in the composition may be considered to be in the "low to medium water" level range, or a "medium to high water" level range. The "low to medium water" level range covers the range from any of the minimum levels indicated above to a maximum of either 18:82, 20:80, 25:75, 30:70, 40:60, 50:50 or 60:40. The "medium to high water" level range covers the range from either 20:80, 21 :79, 25:75, 30:70, 40:60, 50:50, 56:44 or 60:40 to a maximum of one of the upper limits indicated above. A typical low/medium water level range is 4:96 to 50:50, and a typical medium/high water level range is from 50:50 to 80:20. A typical low water level range is from 5:95 to 35:65. A typical medium level water range is 35:65 to 55:45. A typical high water level range is 55:45 to 80:20.

Considered in terms of the percentage of water in the entire main fuel composition by weight, the relative amount of water in the main fuel composition may be above 2%, such as above 2.5% or a minimum of 3.0%, or 4.0%, or 5%, 10%, 12,%, 15%, 20% or 22% by weight. The maximum amount of water in the entire main fuel composition may be 68%, 60%, 55%, 50%, 40%, 35%, 32%, 30%, 25%, 23%, 20%, 15% or 10% by weight. Any of the minimum levels may be combined with a maximum level without limitation, save for the requirement that the minimum level be below the maximum water level. To obtain the maximum benefit of viscosity increase through the process as described herein, the relative amount of water to methanol in the fuel is suitably from 5:95 to 60:40. Preferably the water to methanol in the fuel is a minimum of 8:92, 10:90, 12:88, and a maximum of 50:50, 40:60, 30:70, 28:72, 26:74, 25:75, 24:76, 23:77, 22:78, 21 :79, 20:80. Suitable ranges are around 12-23% water based the combined weight of water and methanol, or between 15-20% based on the same measurement. This watenmethanol range takes into account a balance between viscosity improvement effects, as well as desirable BTE (brake thermal efficiency) and NOx emission reduction.

For a desirable BTE alone, the amount of water in the fuel composition in some embodiments is between 3% and 32% by weight. The optimal zone for a peak in brake thermal efficiency for a methanol-water compression ignition engine fuel is between 12% and 23% water in the main fuel composition, by weight. The range may be incrementally narrowed from the broader to the narrower of these two ranges. In some embodiments, this is combined with an amount of ignition enhancer in the main fuel composition that is not more than 20% by weight of the main fuel composition. Details of ignition enhancers are set out below.

For a maximum reduction in NOx emissions (excluding allowances for other desired outcomes), the amount of water in the fuel composition in some embodiments is between 22% and 68% by weight. The optimal zone for a maximum reduction in NOx emissions is between 30% and 60% water by weight of the main fuel composition. The range may be incrementally narrowed from the broader to the narrower of these two ranges. Since NO is the main NOx emission component, reference may be made to NO emissions as being the greater proportion of, or indicative of, the overall extent of NOx emissions.

In some embodiments, for a desirable balance of fuel properties, viscosity improvement and emissions, the main fuel composition comprises between 5% and 60% water by weight of the main fuel composition, such as between 8% and 50% water, between 8% and 40% water, 10% and 30% water, 10% and 25% water, 10% and 20% water, or between 12% to 20% water.

It is shown in the experimental results below that increasing amounts of water are associated with an increase in the viscosity in the methanol water fuel, for fuels of greater than 50% wt methanol. This viscosity increase is further driven by a temperature reduction in the fuel. As is shown below, by combining the concepts of water inclusion in the methanol-based fuel, with temperature reduction (or temperature control to a suitably low level) of the fuel, viscosity improvements can be achieved that bring the viscosity into the range provided by diesel fuel operating in engines at typical engine operation temperatures.

It is noted that since viscosity control can be achieved through temperature control and/or compositional control (i.e. water composition control), it becomes possible to minimise or eliminate the need for viscosity additives, lubricity additives, or both. The amounts of such additives that may be required in the fuel composition may be as low as 2000 ppm or less, 1500 ppm or less, 1000 ppm or less, 800ppm or less, 600ppm or less, or 500ppm or less. References to ppm are by weight.

For the operation of the compression ignition engine with the methanol/water main fuel composition and fumigation, but without other ignition enhancement techniques such as air inlet preheating or blowing (techniques described in the co-pending applications referred to previously), the water content in the fuel may be at the low to medium level, preferably at the low water level. Where the water level is at the higher end, the process generally benefits from inlet air preheating, to overcome the increased cooling effect of the increased water level in the main fuel composition. Preheating techniques are as described in our copending application, referred to above.

The amount of methanol in the total main fuel composition is preferably at least 20% by weight of the main fuel composition. According to some embodiments, the amount of methanol in the fuel composition is at least 30%, at least 40%, at least 50%, at least 60% or at least 70% of the fuel composition. The amount of water in the total main fuel composition may be at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at least 10%, at least 1 1 %, at least 12%, at least 13%, at least 14%, at least 15%, at least 16%, at least 17%, at least 18%, at least 19%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65% and at least 70%. As the weight of water in the main fuel composition increases it is increasingly more surprising that fumigation of the inlet air with a fumigant overcomes the penalty of water in the fuel in terms of igniting, with smooth operation in terms of COV of IMEP and producing net power out. Increasing water levels up to 50:50 watermethanol also provides the benefit of greater improvements (increases) in the viscosity level of the methanol water fuel.

The combined amount of methanol and water in the total main fuel composition may be at least 75%, such as at least 80%, at least 85%, or at least 90% by weight of the fuel composition. The main fuel composition may comprise one or more additives, in a combined amount of up to 25%, or up to 20% or up to 15% or up to 10% by weight of the main fuel composition. In some embodiments, the total or combined level of additives is not more than 5% of the main fuel composition. In relation to viscosity additives and lubricity additives, as indicated above, the amounts of these additives may be minimised, and may constitute only a small fraction of the total additives in the fuel composition. The amount of such additives may, in some embodiments, be set to a level of not more than l OOOppm, or not more than 800 ppm, not more than 600ppm or not more than 500ppm of the fuel composition. Additives outside this class may have the effect of reducing the viscosity of the methanokwater fuel (compared to the same fuel without such additives), so further temperature control and/or compositional control (water compositional control) may be used to counteract the effect of the additive content in the fuel.

The methanol for use in the production of the fuel composition may come from any source. As one example, the methanol may be a manufactured or waste methanol, or a coarse or semi-refined methanol, or an unrefined methanol. Such methanol sources are referred to herein collectively as "crude methanols", and this term refers to methanol sourced from sources with a methanol content of less than 95% The crude methanol could typically contain mainly methanol, with the balance being water and amounts of higher alcohols, aldehydes, ketones or other carbon hydrogen and oxygen molecules arising during the normal course of methanol manufacture. Waste methanol may or may not be suitable depending on the degrees and types of contamination. The references in the above sections to ratios of methanol and water, or amounts of methanol in the fuel composition by weight, refer to the amount of methanol itself in the methanol source. Thus, where the methanol source is a crude methanol containing 90% methanol and other components, and the amount of this crude methanol in the fuel composition is 50%, then the actual amount of methanol is considered to be 45% methanol. The water component in the methanol source is taken into account when determining the amount of water in the fuel composition, and the other impurities are treated as additives when assessing the relative amounts of the components in the products, unless otherwise specified. The higher alcohols, aldehydes and ketones which may be present in the crude methanol may function as soluble fuel extender additives.

According to some embodiments, the fuel composition comprises crude methanol. The term "crude methanol" encompasses low purity methanol sources, such as methanol sources containing methanol, water and up to 35% non-water impurities. The methanol content of crude methanol may be 95% or less. The crude methanol may be used directly in the fuel without further refining. Typical non-water impurities include higher alcohols, aldehydes, ketones. The term "crude methanol" includes waste methanol, coarse methanol and semi-refined methanol. It is a particular advantage of this embodiment that crude methanol containing impurities at higher levels can be used directly in the fuel for a CI engine without expensive refining. In this case, the additive (ie crude methanol impurities and other fuel composition additives excluding water) levels may be up to 60% of the fuel composition (including impurities in the crude methanol). For fuel compositions using a higher purity methanol (such as 98% or higher % pure methanol) as the source, the total additive level may be lower, such as not more than 25%, not more than 20%, not more than 15% or not more than 10%.

According to some embodiments, the methanol source for the fuel is a high purity methanol. This refers to a methanol containing more than 95% methanol, preferably at least 96%, 97% or 98% methanol.

Any water of a suitable quality can be used as the source of water for the fuel composition. The source of water may be water included as part of un-distilled coarse methanol, or recycled water, or a crude or contaminated water (for example, sea water containing salts) purified by reverse osmosis ("RO water"), purified by activated substances such as activated carbon, or further chemical treatment, deionisation, distillation or evaporative techniques. The water may come from a combination of these sources.

According to one embodiment, the water added in the process of the present application is water recovered from the exhaust of the compression ignition engine. This water may be recovered via heat exchangers and spray chambers or other similar operations. This recovery and reuse technique enables cleanup of exhaust emissions. The water in this case is recycled back to the engine with or without any captured unburnt fuel, hydrocarbons or particulates or other combustion products being returned to the engine and recycled to extinction via looping combustion steps, or treated by known means of purification. The water may in some embodiments be salt water, such as sea water, which has been purified to remove the salt therefrom. This embodiment is suited to marine applications, such as in marine CI engines, or for the operation of CI engines in remote island locations. The water quality will impact corrosion through the supply chain up to the point of injection into the engine and engine deposition characteristics, and suitable treatment of main fuel with anti-corrosion additives or other methods may in these circumstances be required. Additives in the methanol water fuel composition.

Additives which may be present in the pre-fuel composition and/or the main fuel composition may be selected from one or more of the following categories, but not exclusively so:

1 . Ignition improver additives. These may also be referred to as ignition enhancers. An ignition improver is a component that promotes the onset of combustion. Molecules of this type are inherently unstable, and this instability leads to "self start" reaction leading to combustion of the main fuel component (for example, methanol). The ignition improver may be selected from materials known in the art to have ignition enhancing properties, such as, ethers (including C1 -C6 ethers such as dimethyl ether), alkyl nitrates, alkyl peroxides, volatile hydrocarbons, oxygenated hydrocarbons, and mixtures thereof.

In addition to the typical ignition enhancers, finely dispersed carbohydrate particles present in the combustion zone following evaporation of the liquid fuel components prior to ignition may or may not have a role as ignition enhancer, however such species present may contribute to more complete and rapid combustion of the total air/fuel mixture.

While additional ignition improvers can be incorporated into the main fuel, the techniques described herein facilitate ignition throughout the engine operating range without such additions. Thus according to some embodiments the main fuel is free of ignition improver additives. In other embodiments, the main fuel is free of DME (although it may contain other ignition improvers). In the case of dimethyl ether as an ignition improver, according to some embodiments, less than 20%, less than 15%, less than 10%, less than 5%, less than 3%, less than 1 %, or no dimethyl ether is present in the fuel composition. In some embodiments, the amount of ether (of any type, such as dimethyl or diethyl ether) in the main fuel composition is less than 20%, less than 15%, less than 10%, less than 5%.

In some embodiments, at least 80% of the ignition enhancer present in the main fuel composition is provided by one or at most two specific chemicals, examples being dimethyl ether and diethyl ether. In one embodiment, an ignition enhancer of a single chemical identity is present in the main fuel composition. In one embodiment, at least 80% of the ignition enhancer in the main fuel composition is constituted by an ignition enhancer of a single chemical identity. In each case, the single ignition enhancer that constitutes the ignition enhancer, or the >80% ignition enhancer component may be dimethyl ether. In other embodiments, the ignition enhancer comprises a mixture of three or more ignition enhancers.

The amount of ignition enhancer in the main fuel composition in some embodiments is not more than 20%, such as not more than 10% or not more than 5% of the fuel composition.

Fuel Extender. A fuel extender is a material that provides heat energy to drive the engine. Materials used as fuel extenders may have this purpose as the main purpose for its inclusion in the fuel composition, or an additive material may provide this function and another function.

Examples of such Fuel Extenders are:

a) Carbohydrates. Carbohydrates include sugars and starch. The carbohydrate may be included for fuel extender purposes, although it may also function as an ignition improver, and/or a combustion improver. The carbohydrate is preferably water/methanol soluble, with higher water levels accommodating greater dissolution of sugar, for example, in the main fuel. An enriched water (single phase) main fuel composition enables dissolution of the carbohydrate, such as sugar, however as the liquid solvent (water/methanol) in the fuel composition evaporates in the engine, the carbohydrate solute can form micro-fine high surface area suspended particles of low LEL (lower explosive limit) composition which will decompose/react under engine conditions, improving the ignitability of the main fuel mixture. To achieve improvement in combustibility of the mixture, an amount of at least 1 %, preferably at least 1 .5% and more preferably at least 5% of this carbohydrate additive is preferred.

b) Soluble Fuel Extender additives. Fuel extender additives are combustible

materials. These additives may be added as separate components or may be part of an undistilled methanol used to produce the main fuel composition. Such additives include C2-C8 alcohols, ethers, ketones, aldehydes, fatty acid esters and mixtures thereof. Fatty acid esters such as fatty acid methyl esters may have a biofuel origin. These may be sourced through any biofuel sources or processes. Typical processes for their production involve transesterification of plant-derived oils, such as rapeseed, palm or soybean oil, amongst others. There may be opportunity to economically increase the level of fuel extender in the main fuel composition itself for particular markets where such additive can be produced or grown and consumed locally, reducing the need for importation of base fuel and/or additives. Under such conditions an amount, or treat rate, of up to 30%, or up to 40%, or up to 50% of the main fuel composition is preferred, though

concentrations of up to 60% total additives including such fuel extender additives can be considered particularly where the methanol source is crude methanol.

Combustion enhancers. These may also be referred to as combustion improvers. An example of a combustion enhancer is a nitrated ammonium compound, for example ammonium nitrate. At 200°C ammonium nitrate breaks down to nitrous oxide according to the following reaction:

NH ₄ N0 ₃ =N ₂ 0+2H ₂ 0

The nitrous oxide formed reacts with fuel in the presence of water in a similar way to oxygen, eg

H ₂ +N ₂ 0=H ₂ 0+N ₂

CH ₃ OH+3N ₂ 0=3N ₂ +C0 ₂ +2H ₂ 0

Other nitrated ammonium compounds that can be used include

ethylammonium nitrate and triethylammonium nitrate as examples, though these nitrates may also be regarded as ignition enhancers (cetane) rather than combustion enhancers as their main function in the fuel is ignition enhancement.

Other combustion improvers can include metallic or ionic species, the latter forming by dissociation under pre or post combustion environments.

Oxygen absorbing oil. The oxygen absorbing oil is preferably one that is soluble in water methanol mixtures. Oxygen absorbing oils have low auto-ignition point and also have the ability to directly absorb oxygen prior to combustion, in amounts of, for example, 30% by weight of the oil. This rapid condensation of oxygen from a hot gaseous phase into the oil/solid phase after evaporation of the surrounding water will more rapidly heat the oil particle causing ignition of the surrounding evaporated and superheated methanol. An oil ideally suited to this role is linseed oil, in a

concentration of about 1-5% in the main fuel mixture. If this additive is utilised in the main fuel composition, the fuel mixture should be stored under an inert gas blanket to minimise decomposition of the oil by oxygen. Linseed oil is a fatty acid-containing oil. Other fatty acid-containing oils can be used instead of or in addition to linseed oil. Preferred oils are those that dissolve in the methanol phase or are miscible in methanol, to produce a homogeneous, single phase composition. However, in some embodiments oils that are not water/methanol miscible may be used, particularly if an emulsification additive is also present in the fuel composition.

Lubricity additives. Examples of lubricity additives include diethanolamine derivatives, fluorosurfactants, and fatty acid esters, such as biofuels which are soluble to some extent in water/methanol mixtures, on which the main fuel composition is based.

Product colouration additives. Coloration additives assist to ensure that the fuel composition could not be mistaken for a liquid beverage such as water. Any water soluble colourant may be used, such as a yellow, red, blue colourant or a combination of these colourants. The colourant may be a standard accepted industry liquid colourants.

Flame colour additives. Non-limiting examples include carbonates or acetates of sodium, lithium, calcium or strontium. The flame colour additives may be selected to achieve the preferred product colour and stability in the final product pH. Engine deposition considerations, if any, may be taken into account in selecting the additive to be used.

Anti Corrosion additives. Non-limiting examples of anti-corrosion additives include amines and ammonium derivatives.

Biocides. While biocides could be added, these are generally not required because the high alcohol (methanol) content in the main fuel prevents biological growth or biological contamination. Thus according to some embodiments the main fuel is free of biocide.

Freeze Point depressant. While freeze point depressants can be incorporated into the fuel, the methanol (and optional additives such as sugar, added for other purposes) depresses the freezing point of water. Thus according to some embodiments the main fuel is free of an additional dedicated freeze point depressant.

Deposit reductant. Non-limiting examples include polyolether and triethanolamine. Denaturant if required. 13. pH controlling agent. An agent that raises or lowers the pH to a suitable pH can be used, which is compatible with the fuel.

14. Viscosity increasing additives. Such additives are available commercially.

The additives, and particularly those identified under items 1 and 2 above may be added to the fuel either as standard industry traded product (i.e. in a refined form) or as semi processed aqueous solution (i.e. in a non-refined form, semi-refined form, or a crude form). The latter option potentially reduces the cost of the additive. A condition of the use of such crude additive sources is that the impurities in the crude forms of such additives, such as crude sugar solution, or sugar syrup, as one example, do not adversely affect the fuel injectors or engine performance.

According to some embodiments, the fuel comprises at least one additive. According to some embodiments, the main fuel comprises at least two different additives.

Ethers are noted above as being examples of ignition improvers and soluble fuel extender additives. Irrespective of the intended function, in some embodiments, the ether may be present in total at a level of less than 20%, less than 15%, less than 10%, less than 5%, less than 3%, or less than 1 % of the fuel composition. The amount may be greater than 0.2%, 0.5%, 1 %, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%. The lower and upper limits can be combined without limitation, provided the lower limit is below the upper limit selected. The amount of dimethyl ether in the methanol water fuel, as a specific example, is preferably not more than 20%, suitably less than 20%. Other upper limits are as per the ether limits indicated above. The minimum amount may be as indicated earlier in this paragraph.

The fuel composition may comprise ethers other than dimethyl ether, but according to preferred embodiments, the fuel comprises dimethyl ether as the only ether component. In other embodiments, additional ether is included in the fuel composition in addition to dimethyl ether.

In some embodiments, the fuel used in the process, system and uses of the present application comprises methanol, water, and not more than 20% by weight dimethyl ether. It is to be noted that references to the fuel composition comprising methanol and water, and not more than 20% by weight dimethyl ether, should be interpreted as encompassing fuel compositions containing no dimethyl ether. However, according to some embodiments, dimethyl ether is present in the main fuel composition, in an amount greater than 0.2%, or one of the other minimum percentage amounts indicated above. In some embodiments, the main fuel composition comprises an ether in an amount of between 0.2% and 10% by weight of the main fuel composition. The ether is preferably a single ether or a combination of two ethers. The ether is preferably dimethyl ether.

Fumigant comprising dimethyl ether

According to some embodiments, the process of the present application comprises a step of fumigating the inlet air stream with an ignition enhancer, otherwise referred to as a fumigant.

Ignition enhancers are described above in the context of their use as a component of the fuel composition, and that discussion of suitable ignition enhancers applies equally to the use of ignition enhancers as fumigants.

Suitable ignition enhancers for use as fumigant may have a cetane of above 40. The cetane number is a measure of a materials ignition delay, being the time period between the start of injection and start of combustion, i.e. ignition, of that material. DME has a cetane of 55-57. The cetane number(s) of additional the ignition enhancer(s) that may be present in the fumigant should be taken into account when determining the relative amounts of ignition enhancers to other components in the fumigant, and also the amount of fumigant compared to the main fuel composition, load and engine speed. The overall cetane of the fumigant will be based on a combination of the proportional contribution of, and the cetane property of each component, the relationship not necessarily being linear.

Some non limiting examples of additional ignition enhancers include: ethers, such as the lower alkyl (being the C1-C6 ethers), notably dimethyl ether and diethyl ether, alkyl nitrates, alkyl peroxides, and mixtures thereof.

Dimethyl ether suitably comprises a minimum of 5% of the fumigant or a minimum of 10% of the fumigant, such as a minimum 15%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 82%, 84%, 86%, 88% or 90% of the fumigant. There is generally a preference for the dimethyl ether content of the fumigant to be at the upper end of the range, so in some embodiments the ignition enhancer content is above 70% or more. The dimethyl ether may comprise up to 100% of the fumigant.

The relative amounts of each component in the fumigant may be kept constant, or may be varied over the time period of operation of the engine. Factors that impact on the relative amounts of components in the fumigant include engine speed (rpm), level and variability of load, engine configuration, and the specific properties of the individual components of the fumigant. In other embodiments, the fumigant composition may be kept relatively constant, and instead the relative amount of fumigant (grams per second fumigated into the engine) compared to the main fuel composition injected into the engine (grams per second) is adjusted during the different stages of operation of the engine.

When it is desired to operate the CI engine with different fumigant compositions for different engine operation conditions (speed, load, configuration), the fumigant composition can be varied to suit by computer control of the fumigant composition, or by any other form of control. The adjustments may be sliding adjustments based on an algorithm that calculates the desired fumigant composition to match the prevailing engine operation conditions, or may be step-wise adjustments. For example, a higher overall cetane index fumigant (such as 100% DME) could be fumigated into the engine at a high weight % with respect to the fuel for operation in some conditions, and then the fumigant could be diluted with a lower cetane index component in other engine operation conditions. In another embodiment the composition may be stable and the air/fumigant ratio varied in changing conditions.

Examples of components that may be present in the fumigant in addition to the ignition enhancer include the additives outlined above and alkane gases (typically straight- chained alkanes, including lower alkanes such as the C1-C6 alkanes, notably methane, ethane, propane or butane, and longer chain alkanes (C6 and above).

Engine operation aspects and power generation

The amount of ignition enhancer(s) may be controlled relative to the mix of methanol to water contained in the main fuel in order to produce conditions within the combustion chamber where ignition of the main fuel is achieved in a timely manner, and thereby deliver the best possible thermal efficiency from the engine. Where the ratio of ignition enhancer to fuel mix is not controlled combustion could initiate significantly before top dead centre (TDC), such as 25-30° before TDC, and as such the use of an ignition enhancer could have a neutral effect and make a minimal or no contribution to the thermal efficiency of the engine. In a preferred operation of the engine ignition of the fumigant/air mixture is timed to delay the combustion of this fuel as late as possible (to avoid unnecessarily working against the power stroke of the engine) and to be consistent with good combustion of the main fuel after injection. This means that the fumigant (dimethyl ether) should ignite before the main fuel injection commences, but not so much before that the energy contained in the secondary fuel makes a minimal or nil contribution to the thermal efficiency of the engine.

Although the relative amounts of fumigant to main fuel introduced into the engine (either through the air intake, or into the combustion chamber, respectively), will vary depending on the engine operation conditions that apply, it is generally desired for the amount of dimethyl ether ignition enhancer in the fumigant during steady state operation at mid or high load to be a relatively low percentage by weight of the main fuel composition. For a fumigant comprising 100% DME, the relative amounts of fumigant to main fuel by weight is desirably up to 20% by weight, up to 18%, up to 15%, up to 13%, up to 10%, up to 8%, up to 7%, up to 6%, up to 5%. The fumigant level is preferably at least 0.2%, at least 0.5%, at least 1 % or at least 2% by weight of the main fuel composition. These figures are based on weight, assuming the fumigant comprises 100% ignition enhancer, and can be adjusted proportionally for a reduced ignition enhancer content in the fumigant by weight. These may be measured by reference to the amount introduced into the engine in grams per second, or any other suitable corresponding measure for the engine size. An upper limit of around 10% or less (such as 8% or 7%) is additionally advantageous, as a pre-fuel composition containing up to the required amount of dimethyl ether (such as 10%, 8% or 7% dimethyl ether, respectively) can be delivered to the compression ignition engine location, and a portion (or all) of the dimethyl ether driven off through water addition and recovered in a quantity corresponding to the needs of the engine operating with fumigation at the same target level. In other embodiments, there can be top-up of the fumigant level to a higher level at the engine location (for example, through top-up from separate storage of dimethyl ether).

Engine operation details

Figure 1 illustrates a flow chart outlining the components of the system for cooling of a methanol water fuel 1 1 to produce a cooled fuel 12, prior to introduction of the cooled fuel 12 into a CI engine 3. The system comprises a fuel storage tank 1 , a cooling system in the form of a chiller 2 and a CI engine. The process may optionally include pre-heating an intake air stream 13 and then introducing the pre-heated air into the combustion chamber of the engine 3 before introducing the cooled fuel 12 into the combustion chamber of the engine 3 and igniting the fuel/pre-heated air mixture in order to drive the engine. The process may optionally additionally, or alternatively, involve fumigation of a fumigant 14 comprising an ignition enhancer into the intake air stream.

The fuel is cooled by any suitable fluid cooling technique known in the art, such as through the use of a chiller, such as a vapour compression chiller or an absorption chiller, or other similar equipment. In the embodiment shown by Figure 1 , the methanol water fuel 1 1 may be cooled by a chiller 2 powered by the engine 3,

The intake air 13, which may optionally be pre-heated by a variety of techniques, is injected into the combustion chamber before or during the initial stage of the compression stroke of the engine so as to compress the air before the fuel is injected into the combustion chamber. Compression of the air raises the temperature in the combustion chamber to provide favourable ignition conditions for the fuel when it is sprayed into the chamber during the last stage of compression. The techniques for pre-heating the intake air are described in the earlier applications referred to previously.

Where inlet air preheating is performed, suitable pre-heat intake air temperatures are at least 50°C, or at least 100°C, such as about 100°C-150°C, for example about 130°C, or at least about 150°C, such as 150°C-300°C or higher.

Exhaust gases (22) from the engine may be subjected to an exhaust treatment (34) and components (28) collected from the exhaust may be recycled back into the fuel. In particular the treatment includes the recovery and integration of water, unburnt fuel, hydrocarbons, carbon dioxide and other small amounts of emissions.

The water rich exhaust components (28) collected from the engine can be a source of water for use in producing the fuel (and thus recycled to either fuel storage (1 ), channelled into the stream of fuel that is chilled in the chiller (2), or combined with the fuel (1 1 ) in the chiller (2) as the fuel is chilled). The small levels of exhaust pollutants can be captured and returned to the engine in this manner. Water recovery from exhaust material in the treatment stage (34) involves cooling and condensing the exhaust material and collecting the condensed water. The condensed water collected or recovered from the exhaust can additionally, or alternatively, be redirected to use in potable water supply, irrigation, or otherwise.

The exhaust material can be cooled through heat exchange with intake air in a heat exchanger, and then the cooled exhaust can be passed through a condenser through which water can be collected and returned as a recycled fuel component to the engine, as described above.

A second heat exchanger can be used in the final phase of the treatment process that assists condensation and additionally includes a spray chamber arrangement using water which may have been purified and may contain additives to capture and purify any unburnt methanol or other hydrocarbons in the fuel, soot and other particulates. These particulates are returned to the engine for elimination via a 'recycle to extinction' process with recycled fuel, while the purified clean exhaust can be released to atmosphere containing close to no pollutants. The water used in the spray chamber may be from a range of alternative sources, and may be purified or deionised. The water may contain optional additives. The optional additives should be consistent with the combustion process.

Additional exhaust treatment steps utilising condensate or other means can be also be taken to reduce targeted pollutants to low levels in the exhaust gas to atmosphere. In another embodiment, components such as any unburnt fuel can be adsorbed onto an active surface and later desorbed using standard techniques, and included as fuel or fumigant component to further reduce pollution. Alternatively a catalyst can be employed to catalytically react any oxidisable species such as unburnt fuel, increasing the exhaust temperature and providing an additional source of heat which may be utilized.

Additionally, if multiple engines are operating, for example to produce electricity (power), the aggregated exhaust gas can be treated as a single stream to be

treated/condensed with the recycle fuel from the exhaust being directed to one or more of such engines.

The final exhaust gas from the treatment and recycling process that is exhausted to atmosphere contains close to no fuel, hydrocarbon, particulate, sulphur oxides and nitrogen oxides emissions.

Any nitrogen oxides or sulphur oxides emissions formed in the combustion phase and/or the absorption of carbon dioxide in the water, may result in pH imbalances of water returning to mix with the fuel. To prevent build up of such components a chemical treatment may be added to the fuel to neutralise any imbalances or remove them.

A catalytic reactor (4) may be provided in the process for powering the CI engine, in which the catalytic dehydration of methanol (taken from a diverted portion of the fuel) to DME is effected. The DME produced is used as an ignition enhancer in fumigant (14) for fumigating the intake air. Other embodiments described herein utilize other techniques for generating the dimethyl ether, when used as the ignition enhancer of the fumigant. In some such embodiments, the DME may be generated at the location of methanol generation, and delivered as a part of a pre-fuel composition to the engine site. In other embodiments, the fumigant composition is supplied as a separate component, and fumigated into the engine as required.

The process of some embodiments comprises a control system (not shown) for measuring the temperature of the fuel (1 1 ) prior to its introduction into the compression ignition engine and adjusting the temperature of the fuel following measurement and prior to introduction of the fuel into the compression ignition engine. The location of the temperature monitoring is selected to provide meaningful information on the prevailing fuel temperature. It may be measured in the fuel storage tank (1 , when present), or in a fuel transmission line in advance of the engine (3). The engine (3) is generally associated with a fuel pump (not shown), which pumps fuel as required into the engine (3). The fuel is injected into the engine via fuel injectors (not shown). The temperature may be measured prior to the fuel pump, following the fuel pump or otherwise, and prior to injection via the injectors into the engine.

The process or system of embodiments of the present application may comprise a control system for measuring and controlling the temperature of the fuel. The control system may be a dedicated fuel temperature control system, or the fuel temperature may be one aspect controlled by a general engine operation control system. The control system may include any components and circuitry required to effectively control the fuel temperature and therefore viscosity. The techniques embodied on the control system may be of any type known generally in the fields of electronics and electronic operation of engines. The control system may comprise a computer and computer software for the operation of the computer. The control system may comprise a monitor for providing a visual display of information relating to the temperature of the fuel, and/or viscosity of the fuel. The computer and associated equipment may control many aspects of the engine operation, and such aspects may also be presented on a visual display. The control system, or computer, may additionally allow for user input to enable a user to set the temperature or temperature range within which the fuel temperature is to be controlled. This could be set manually by the user to achieve the desired viscosity. Alternatively, this may be pre-established by reference to a desired viscosity range.

Controlling of the temperature of the fuel, such as the cooling of the fuel, may be performed prior to the introduction of the fuel into the engine via the fuel injector(s).

It is desired that, from the point of temperature control (such as the point of cooling), leading to the fuel introduction into the engine, the passageways and equipment through which the fuel flows are insulated. Insulation is desired to minimise any subsequent heat change after any temperature control, such as cooling, applied to the fuel. As an example, if the fuel is cooled prior to being pumped through a fuel pump to the engine, then the fuel pump may be insulated to avoid excessive heat gain prior to the fuel being introduced into the engine. In another example, if the fuel temperature is controlled (cooled), following pumping and prior to injection into the engine, then the fuel passage between the control stage (e.g. cooling stage) and the fuel injectors may be insulated. The fuel injector components, up to the fuel injector tip, may be insulated for this purpose. It will be appreciated that at the fuel injector tip, which is closely associated with the engine combustion chamber, heating of the fuel will be effected as it enters the engine, so insulation will be of little effect in that region.

Further aspects and description of the mode of operation of the engine are provided in our co-pending applications, referred to above.

Examples Introduction

A series of experiments were performed to assess the viscosity of methanol-water mixtures over the temperature range of -30 to 30°C. Experiments were also performed to examine tribology measurements for methanol and methanol-water mixtures between stainless steel ball and disk in a rolling/sliding contact at 0 to 30°C. The results were extrapolated to demonstrate performance under sub-zero temperature conditions. The tribology properties examined here are classically represented in the form of a Stribeck curve, where the coefficient of friction is given either as a function of entrainment speed or film thickness, as shown in Figure 2. The frictional behaviour is usually divided into several regimes. The boundary lubrication regime (or boundary regime, indicated by "BL" in Figure 2) occurs at slow speeds when there is negligible fluid entrainment into the contact, In the boundary lubrication regime, the load is carried by the contacting asperities (high points) and is dependent on the surface and interfacial film properties at the molecular scale. In the hydrodynamic or elastohydrodynamic lubrication (EHL) regimes, a film of lubricant, whose thickness depends on the viscosity and entrainment speed, is entrained to fully separate the solid surfaces. The friction now depends on the viscosity of the lubricant film in the contact. In the mixed lubrication regime ("mixed"), which lies between boundary lubrication and EHL, both the boundary film and bulk lubricant play a role in determining friction.

Experimental Sample preparation

Methanol/water mixtures were prepared using reagent grade methanol (ACI

Labscan, 99.9% pure) and RO water (reverse osmosis purified water) at ratios of

watenmethanol of 50:50, 30:70, 20:80, 10:90 and 0:100 by weight.

Rheology

Tests were performed using a strain controlled Rheometrics Advanced Rheometric Expansion System (ARES) using parallel plates of diameter 50mm and a gap of 0.1 mm. In accordance with the procedure outlined in Davies G.A., J.R. Stokes, 'On the gap error in parallel plate rheometry that arises from the presence of air when zeroing the gap' Journal of Rheology 49 (4), 919-922 (2005) and Kravchuk O, Stokes JR, 'Review of algorithms for estimating the gap error correction in narrow gap parallel plate rheology' Journal of

Rheology, 57, 365 - 375 (2012), the raw measurements were adjusted for a gap error of 25±10 microns; this involves multiplying the values generated by the rheometer by 1 .25. Temperature was controlled by a thermal chamber surrounding the test pieces cooled using nitrogen boiled off a supply of liquid N ₂ . Temperature accuracy was ±1 °C. Steady shear tests were performed. Initial sweeps for pure Methanol over shear rates of 1 to 10000 s ^"1 showed that the sample was Newtonian, but that at low shear rates the torque generated was below the minimum recommended by the rheometer for accurate measurements. A single shear rate of 1000 s ^"1 was therefore selected for further

experiments.

Each sample was tested at -30°C, -15°C, 0°C, 15°C and 30°C in triplicate. Error in viscosity measurements is of the order of ±10%.

Tribology The tribological properties of selected methanol-water systems were characterised using a ball-on-disc tribometer (MTM2, PCS Instruments, London) fitted with stainless steel contacts (see Figure 2b). The friction force F _f was measured as a function of the entrainment speed, U, defined as the average surface speed of the ball and disc, over the range of 1 to 3000 mm/s in logarithmic intervals. Measurements were carried out for six repetitions of alternately descending and ascending entrainment speed. For all tests, a normal load (W) of 1 N was applied on the ball and a slide-to-roll ratio (SRR) of 50% was used to impart both sliding and rolling motion, where The friction coefficient (μ) is calculated as the friction force divided by applied load ^=F _f /W). Friction and wear are related; both are product of solid contact between moving surfaces. As it is the same solid material in all tests, friction coefficient in the boundary-mixed regimes is considered here to be an indicator of 'wear'; i.e. low friction coefficient typically corresponds to lower rate of wear (See: Pearson SR, Shipway PH, Abere JO, Hewitt RAA, The effect of temperature on wear and friction of a high strength steel in fretting', Wear, 303, 622-31 (2013).) The lubricants were maintained at the desired test temperature using a silicone oil temperature bath (DC30-K20, Haake) with a minimum stable lubricant temperature of 4°C. Tribological data was generated for samples at 4°C, 15°C and 30°C in duplicate.

Prior to testing, the stainless steel contacts were cleaned by ultra-sonication in iso- octane to remove the protective coating, followed by ultra-sonication in isopropanol. The surfaces were then dried and loaded onto the tribometer for testing. Results

Rheology

Table 1 provides the averaged measured viscosities in mPas. The standard deviation between the replicates was of the order of 5%. Table 1 shows that the measured viscosities at 30°C are similar to literature values (Literature values can be found in S Z Mikhail and W R Kimel, Journal of Chemical Engineering data, 6, 533 (1961 ) and H Kubota et al, The review of physical chemistry of Japan, 49, 59 (1979)). The variation of viscosity with temperature and with methanol content is shown in the Figure 3. The lines are empirical fits; (a) the viscosity scales linearly with concentration of water (and conversely, methanol) at each temperature, and (b) the viscosity scales exponentially with temperature for each water (and conversely, methanol) concentration. It is noted that wile "methanol %" is indicated in the tables, the balance is water, thus indicating the impact of increasing the water content (and decreasing the methanol content) on the viscosity measurements.

Tribology

Table 2 provides the measured friction coefficients at several conditions for selected methanol-water systems. The tribological properties of selected methanol-water systems are shown in Figure 4 in the classic form of Stribeck curves; i.e. friction coefficient is shown as a function of speed or the product of speed and viscosity. (See: Bongaerts J.H.H., K. Fourtouni, J.R. Stokes, 'Soft-Tribology: lubrication in a compliant PDMS-PDMS contact', Tribology International, 40 (10-12), 1531-1542 (2007).) The raw data, friction coefficient as a function of entrainment speed, is shown in the top graph.

All measurements we obtained are in the boundary and mixed regime (see introduction above), and full-film hydrodynamic lubrication is not observed under the conditions tested due to the low viscosity of the fluids. As hydrodynamics plays a role in the mixed and full film lubrication regimes, entrainment speed is multiplied by the viscosity to formulate the Stribeck curve, as shown in Figure 4. When this is performed, several Stribeck curves overlap when differences between curves are due to the viscosity.

It was observed that 100% methanol provides superior boundary lubricating films, and the friction coefficient decreases with increasing temperature. It also does not alter significantly when subsequent tests are performed on the same surfaces, indicating that the film is stable and the wear track is unlikely to be altering with testing.

An equally low boundary friction is observed at 4°C for 50% and 70% methanol (i.e. 50% water and 30% water, respectively), and lubrication is enhanced in the mixed regime due to their higher viscosity (lower friction for speeds > 100 mm/s compared to 100% methanol).

Friction at sub-zero temperatures was not measured directly. Therefore, to estimate the response, it was assumed that the Stribeck curve at sub-zero temperatures for the methanol-water mixtures is the same as that at 4°C. Figure 5 shows just the Stribeck curves at 4°C for each methanol solution - they closely overlap and fit to a single empirical relationship, detailed below:

μ _ύ = constant

MHL = ^K H ( ¹ leff ^U T

The fitted curve is given by: μ _b = 0.15; B = 400 μΝ/m; n = 1 .73. Values used for the hydrodynamic regime are m = 0.55 and 5.8 x 10 ^"6 , but these do not completely fit due to a lack of data in hydrodynamic regime.

Therefore, given that the viscosity at -15°C and -30°C of 70% methanol is 5.2 and 8.0 mPas respectively, this empirical model was used to estimate that at 500 mm/s, the viscosity x speed = 2600 and 4000 μΝ/m respectively. From the graph, the friction coefficient is estimated to be 0.006 and 0.003 respectively. Further increases in viscosity, for example by using a lower methanol concentration, would lower the friction coefficient further until a minimum value that signifies where the hydrodynamic regime is entered. It is estimated that the hydrodynamic regime is entered at (viscosity x speeds) of about 10,000 μΝ/ιη, where μ~0.001. Table 1 - Measured viscosities (adjusted for gap error) of methanol-water mixtures as a function of temperature and methanol concentration.

Table 2 - Values for the friction coefficients in the boundary and mixed regimes as a function of temperature and methanol concentration. The boundary friction coefficient values is taken at a value of 11η = 10 μΝ/m (it is relatively independent of ΙΙη). The friction in the mixed regime is dependent on entrainment speed; the friction coefficient at 500 mm/s is listed.

Friction Friction

coefficient Coefficient

Temperature wt% Methanol at Un = ^N/m at 500 mm/s

(boundary (mixed regime)

regime)

100 0.11 0.07

30 °C

70 0.26 0.15

100 0.13 0.05

15 °C

70 0.25 0.08

100 0.15 0.06

4 °C 70 0.15 0.02

50 0.15 0.01 In relation to Table 2, it is noted that for 100% methanol, the friction coefficient (mixed regime) remained relatively stable over decreasing temperature conditions (at 30°C it was 0.07, and remained at about this level (0.05 and 0.06) as the temperature decreased). In contrast, the inclusion of 30% water (70% methanol) in the methanol fuel composition, combined with temperature reduction, resulted in a decrease in the friction coefficient from 0.15, down to 0.08 (at 15°C) and then to 0.02 at 4°C. (See also Figure 6) Increasing the water content in the methanol-based fuel, combined with reducing the temperature, results in a decrease in friction co-efficient. Further decrease in temperatures are expected, based on the results indicated in Figure 5, to produced further decreases in the friction co-efficient (in line with an increased viscosity of the fuel).

Figure 6 provides a different presentation of the data shown in Figure 5. In this graph, a number of principles are demonstrated. Firstly, it is noted that, while the friction coefficient for a 70:30 mixture of methanokwater is higher than for 100% methanol at a temperature above 12°C, as the methanokwater mixture is cooled below +15°C, the friction coefficient drops quite significantly. The gradient of the line for 100% methanol is quite flat, In contrast, the gradient of the line for the 70:30 methanokwater mixture changes between about 15°C and -15°C. Once the temperature drops below 12°C, this drop in gradient provides a significant benefit in terms of controlling the friction coefficient of the fuel mixture. The gradients of the two lines then fall back into line with each other at temperatures below - 20°C, although the methanokwater mixture still maintains a lower friction coefficient than 100% methanol.

Traditional diesel fuel is reported to have a viscosity in the range of 1.6 to 3.4 mPas at 40°C. At the temperature at which diesel is channeled into the engine, and particularly through the passage through the fuel injector, the viscosity of the diesel is important to ensure no leakage, and to avoid in particular leakage from the fuel injector tip outside the time of fuel injection. By cooling a methanol fuel, which contains water, the viscosity is reduced and brought into a viscosity range required for performance similar to tradition diesel fuel.

Stribeck curves for traditional diesel fuel are presented in Maru, M.M. et al, Energy 69 (2014) 673 - 681 , for 20 and 60°C, respectively. The conditions are different to those applied here, in that a load of 4N was applied in place of the 1 N load applied herein, however the information nevertheless provides a useful comparison between diesel at higher temperatures, compared to methanol-water fuel at reduced (e.g. cooled) temperatures. The friction coefficient in the boundary regimes were around 0.15 at a load of 4N. Viscosity for the diesel fuel at 20°C and 60°C was 3.33 and 1 .47 mPas, respectively. Based on Figure 7a of this paper, for a speed of 500 mm/s, the (viscosity x speed) was about 1500 at 20°C, resulting in a friction coefficient of about 0.1.

Comments

Viscosities of methanol-water mixtures were measured across the temperature range of -30 to 30°C. It was found that the viscosity increased linearly with increasing water concentration in a methanol-water mixture (increase water, or decrease methanol, results in an increase in viscosity), and increases exponentially with decreasing temperature.

The friction coefficients were evaluated under low load conditions. Low fiction coefficients in the boundary regime are obtained for 50 and 70% methanol at 4°C on fresh steel surfaces, indicating the potential of these mixtures to provide boundary films at low temperatures. In the mixed lubrication regime (speeds > 100 mm/s), we observe that the more viscous mixtures have a lower friction coefficient.

As all concentrations of methanol collapse onto a single Stribeck curve when viscosity is taken into account, a "master curve" has been used to estimate the friction coefficient at sub-zero temperatures. For a speed of 500 mm/s, it is estimate that the friction coefficient is of order 0.003 and 0.006 at -15 °C and -30°C respectively for 70% methanol. This indicates that the mixtures of methanol-water will be capable of providing effective lubrication at sub-zero temperatures. The higher viscosity of the mixtures compared with 100% methanol indicates that lower friction will be achieved in the mixed regime and there will be greater potential to operate near the junction between the mixed and full film regimes where friction is a minimum.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention. ITEMS:

1 . A process for operating a compression ignition engine, the process comprising: measuring the temperature of a fuel comprising methanol and water prior to introduction into the combustion chamber of the compression ignition engine; and - controlling the temperature of the fuel to control the viscosity of the fuel prior to

introduction into the combustion chamber of the compression ignition engine.

2. The process of item 1 , comprising introducing the fuel into the combustion chamber of the compression ignition engine, introducing intake air into the combustion chamber of the compression ignition engine, and igniting the fuel/air mixture to thereby drive the engine.

3. The process of item 1 or item 2, wherein the controlling step comprises changing the temperature of the fuel prior to its introduction into the combustion chamber of the compression ignition engine.

4. The process of any one of items 1 to 3, wherein the controlling step comprises changing the temperature of the fuel to bring the temperature of the fuel into target temperature range, if the measured temperature is not within a target range for the fuel.

5. The process of any one of items 1 to 3, wherein the step of controlling the temperature comprises cooling the fuel prior to its introduction into the combustion chamber of the compression ignition engine.

6. A process for operating a compression ignition engine, the process comprising: - cooling a fuel comprising methanol and water, introducing an intake air into the combustion chamber of the engine, introducing the cooled fuel into the combustion chamber of the engine, and igniting the fuel/air mixture to thereby drive the engine.

7 The process of any one of items 1 to 6, comprising controlling the fuel viscosity through temperature control and/or water composition control, to achieve a viscosity performance at fuel injection similar to a traditional diesel fuel.

8. The process of any one of items 1 to 7, comprising controlling the viscosity of the fuel to be within the range of 1 .0 to 18 mPas at a temperature of between +15°C and -15°C.

9. The process of any one of items 1 to 8, comprising controlling the temperature of the fuel, or cooling the fuel, to a temperature of 15°C or less, prior to introduction into the engine, preferably to a temperature of 8 ^° C or less, 6 ^° C or less, 4 ^° C or less, 2 ^° C or less, 0 ^° C or less, -2 ^° C or less, -4 ^° C or less, -6 ^° C or less, -8 ^° C or less, -10 ^° C or less, -12 ^° C or less, - 14 ^° C or less, -16 ^° C or less, -18 ^° C or less, or -20 ^° C or less.

10. The process of any one of items 1 to 9, comprising cooling the fuel, by at least 2°C, prior to introduction into the engine, preferably by at least 3 ^° C, at least 4 ^° C, at least 5 ^° C, at least 6 ^° C, at least 7 ^° C, at least 8 ^° C, at least 9 ^° C, at least 10 ^° C, at least 1 1 ^° C, at least 12 ^° C, at least 13 ^° C, at least 14 ^° C, at least 15 ^° C, at least 20 ^° C, at least 25 ^° C, at least 30 ^° C, at least 40°C, at least 50°C, or at least 60°C, or more.

1 1. The process of any one of items 1 to 10, further comprising: fumigating the intake air with a fumigant comprising an ignition enhancer, and/or preheating the intake air.

12. The process of item 1 1 , wherein the intake air is fumigated with a fumigant comprising dimethyl ether as the ignition enhancer. 13. The process of any one of the preceding items, further comprising: treating engine exhaust to recover exhaust heat and/or water from the engine, and redirecting the heat and/or water for further use.

14. The process of item 13, wherein heat from the engine exhaust is used in the cooling of the fuel.

15. The process of item 13 or item 14, wherein heat from the engine exhaust is used in heating a hot water loop.

16. A system comprising: a compression ignition engine; and a control system for measuring the temperature of a fuel prior to its introduction into the compression ignition engine and adjusting the temperature of the fuel following measurement and prior to introduction of the fuel into the compression ignition engine.

17. The system of item 16, comprising a cooling system.

18. The system of item 16 or item 17, comprising a fuel storage unit.

19. The system of item 16, wherein the control system operates to cool the fuel if the fuel temperature is outside a pre-set range that corresponds to a target viscosity range for the fuel. 20. A system comprising: a fuel storage unit; a compression ignition engine; and a cooling system positioned to cool fuel from the fuel storage unit prior to its introduction into the compression ignition engine.

21. The system of item 20, wherein the cooling system is positioned in a fluid pathway between the fuel storage unit and the compression ignition engine, such that in operation, the cooling system cools the fuel from the fuel tank prior to the fuel being introduced into the compression ignition engine.

22. The system of item 20 or item 21 , comprising: a heat exchanger for transferring heat from exhaust gas that exits the compression ignition engine for a secondary use; and - a water condenser for recovering water from the exhaust gas.

23. The system of item 22, wherein the secondary use is in the operation of the cooling system to cool the fuel.

24. The system of item 22, wherein the secondary use is heating water in a hot water loop.

25. The system of any one of items 20 to 24, comprising a water recycling system for recycling water recovered in the water condenser for use as a component of the fuel introduced into the compression ignition engine, in irrigation, in potable water supply, or for a combination of the preceding uses. 26. Use of temperature adjustment to modify the viscosity of a fuel comprising methanol and water prior to introduction of the fuel into a compression ignition engine.

27. Use according to item 26, wherein the temperature adjustment is cooling.

28. A power generation process comprising: cooling a fuel comprising methanol and water, igniting the cooled fuel in a compression ignition engine and running the compression ignition engine to generate power; treating engine exhaust to recover exhaust heat and/or water from the engine, and; redirecting the heat and/or water for further use.

29 The power generation process of item 24, comprising: preheating an inlet air stream of the compression ignition engine, and/or fumigating the inlet air stream with an ignition enhancer.