AN IMPROVED AMMONIA BASED FUEL FOR ENGINES

Abstract

A fuel formulation comprising a sugar and ammonia solution, wherein the sugar and ammonia are present in a combined amount of greater than 70 percent by weight of the fuel formulation, and wherein the sugar comprises fructose, glucose, sucrose or a combination thereof.

Claims

1. A fuel formulation comprising a solution of a sugar component and liquid anhydrous ammonia, wherein the sugar component and liquid anhydrous ammonia are present in a combined amount of greater than 70 percent by weight of the fuel formulation, and wherein the sugar component comprises fructose, glucose, sucrose or a combination thereof.

2. A fuel formulation according to claim 1, wherein the ratio of sugar to liquid anhydrous ammonia is in the range 0.01:1 to 2:1 w/w.

3. A fuel formulation according to claim 1, wherein the ratio of sugar to liquid anhydrous ammonia is in the range 0.1:1 to 1.5:1 w/w, preferably 0.1:1 to 1:1, and yet more preferably 0.2:1 to 0.8:1 w/w.

4. A fuel formulation according to claim 1, wherein the solution comprises the sugar component dissolved in liquid anhydrous ammonia.

5. A fuel formulation according to claim 1, further comprising one or more additives selected from at least one of: water, ammonium nitrate, an alcohol, a lubricant, a picrate, a permanganate, or a peroxide.

6. A fuel formulation according to claim 5, wherein the one or more additives comprise water, ammonium nitrate, potassium permanganate, iron picrate, hydrogen peroxide, ethanol, methanol, or a paraffinic oil.

7. A compression ignition engine fuel comprising the fuel formulation according to claim 1.

8. A method of operating a compression ignition engine or an Otto type engine using a fuel formulation according to claim 1, comprising injecting the fuel formulation into the engine for combustion.

9. A method according to claim 8, wherein the fuel formulation is injected into a combustion chamber of the engine as an atomised jet.

10. A method according to claim 9, wherein the droplets of the atomised fuel jet is injected at a selected pressure that prevents deposition of sugar residue on heated engine surfaces.

11. A method according to claim 10, wherein the fuel formulation is injected at a pressure of at least 25 bar.

12. A method according to claim 8, wherein the fuel formulation is port injected into the engine.

13. A method of operating a compression ignition engine according to claim 8, in which the engine includes at least two cylinders, each cylinder including a piston that moves reciprocally within that cylinder, each cylinder having a head location at one end located opposite to a compression end of the piston and defining a combustion chamber therebetween, the cylinder including at least one inlet valve through which combustion gases are fed into the combustion chamber and at least one exhaust valve through which spent combustion gases egress the combustion chamber, the piston moving the cylinder in a cycle between top dead center where the piston is located closest to the head location and bottom dead center where the piston is located furthest from the head location, and including at least one fuel injector, and wherein the method comprises: injecting the ammonia fuel into the combustion chamber of each cylinder using the at least one fuel injector as at least one fuel jet with a timing of: after the at least one exhaust valve of the respective cylinder is substantially closed; after the least one inlet valve is closed; and before the respective piston moves to at most 35 degrees prior to top dead centre.

14. A method of claim 13, wherein the ammonia fuel is injected into the combustion chamber of each cylinder during compression stroke of the engine cycle.

15. A method of claim 13, wherein the ammonia fuel is injected into the combustion chamber of each cylinder with a timing of: after the at least one exhaust valve is substantially closed; after the least one inlet valve is closed; and and before the piston moves to 35 degrees prior to top dead centre.

16. A method according to claim 8, further comprising: flowing the fuel formulation from a fuel tank for injection into the engine, and introducing at least one additive into the fuel formulation between the fuel tank and the injection of the ammonia fuel into the combustion chamber.

17. A method according to claim 16, wherein the at least one additive is introduced into the fuel formulation using an additive dosing system configured to adaptively dose the amount of the additive depending on an operating condition of the engine.

18. A method according to claim 8, wherein the compression injection engine comprises a diesel type engine.

19. A method according to claim 13, wherein the compression injection engine comprises a diesel type engine.

20. A method according to claim 15, wherein the compression injection engine comprises a diesel type engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0064] FIG. 1 is a schematic cross-sectional view of one cylinder of a trunk uniflow 2-stroke engine with an injector providing an example of an engine that operates using a fuel formulation according to an embodiment of the present invention.

[0065] FIG. 2 shows a modified stock jerk pump used to feed a fuel composition according to an embodiment of the present invention into a diesel engine for an experimental run.

DETAILED DESCRIPTION

[0066] The present invention comprises an improved ammonia-based fuel for reciprocating engines, gas turbines, and other combustion devices.

[0067] The inventor has discovered that an improved ammonia-based fuel can be formed by mixing a sugar content within ammonia. The present invention provides a fuel formulation comprising a solution of sugar and ammonia, wherein the sugar and ammonia are present in a combined amount of greater than 70 percent by weight of the fuel formulation. This new fuel formulation/composition is a solution, with the sugar content (solute) being dissolved within the ammonia (solvent). The sugar content may be dissolved within ammonia at ambient temperatures at up to around 60 wt %, although the actual amount depends on the amounts of the above-mentioned additional additives in the ammonia. It should be appreciated that the sugar content can be mixed directly into the ammonia in pure form, or in many cases, mixed as an aqueous solution, for example a 60 to 80% w/w sugar solution.

[0068] As explained previously, this new fuel formulation may also contain a smaller amount (less than 30 wt %) of other components such as one or more of water, ammonium nitrate and other ignition promoters such as potassium permanganate, iron picrate, peroxides and fuels such as ethanol, methanol, or a lubricant (for example a paraffinic oil) to reduce the wear of the fuel injection system and engine.

[0069] The present invention improves on previous ammonia-based fuel mixtures through the addition of a sugar content. Whilst not wishing to be limited to any one theory, it is believed that the sugar content both oxygenates the fuel and forms finely divided combustible aerosols and vapours during rapid heating within the engine, which improves ignition, flame speed, overall combustibility, engine thermal efficiency and reduces nitrogen oxide emissions.

[0070] Although the phenomena involved are complex and again not wishing to be limited to any one theory, the inventor proposes a combustion mechanism using the new fuel formulation can be summarised as follows: [0071] 1) the injected fuel is atomised by a combination of flashing and turbulence (in the case of pressure atomisation) to produce a 3-phase mixture of volatile ammonia, liquid fuel droplets, and finely distributed sugar-derived solids/aerosol;

[0072] 2) further heating of the mixture causes the “sugar” aerosol to decompose/melt and spontaneously combust; [0073] 3) the fine dispersion and high flame speed of the non-ammonia fuel components thereby increase the effective flame speed of the ammonia mixture.

[0074] Overall, this enhanced combustibility allows ammonia to be used in higher speed engines and gas turbines where the time for combustion is shorter than that required for ammonia only combustion.

[0075] The blending of sugar also reduces the heat of vaporisation of the fuel, which further assists combustibility by increasing the temperature of the mixture at the time of initiation of combustion.

[0076] The presence of sugar also reduces the vapor pressure of ammonia, allowing it to be stored in tanks at pressures closer to atmospheric pressure which reduces the cost of storage equipment and reduces the environmental and safety implications of leaks.

[0077] The preferred application for the fuel in the present invention is compression-ignition or diesel engines where the start of fuel injection is late in the compression stroke just prior to the required start of ignition. However, it should be appreciated that the fuel could also be used advantageously in Otto (spark, plasma or other ignitors) and homogeneous charge compression ignition (HCCI) reciprocating engines, and also in gas turbines and other continuous combustion devices such as furnaces and boilers.

[0078] As detailed above, the invention provides a method of operating a compression ignition engine (preferably a diesel engine) or Otto engine, comprising injecting the fuel formulation of the present invention disclosed herein into the engine for combustion. The fuel formulation may be injected under high-intensity atomisation conditions such that the fuel is sufficiently atomised to prevent deposition of sugar residue on heated engine surfaces. In some embodiments, the fuel formulation is injected at a pressure of at least 25 bar.

[0079] It has been discovered that the negative effects of the lower vapour pressure of the sugar-ammonia mixtures can be readily overcome by correct choice of atomiser and fuel pressure. Normally ammonia is injected at relatively low pressures due to the high vapour pressure of the fuel, for example, port injection of liquid ammonia is handled in a similar fashion to liquified petroleum gas or DME (dimethyl ether) occurs around 20 bar which is sufficient to ensure liquid at the injector nozzle. For these fuels this results in rapid flashing of the fuel jet(s) to give predominantly a gaseous fuel mixture. Port injection of the sugar-ammonia based fuel of the present invention requires more intense atomisation to produce the advantageous sugar aerosol, to ensure efficient combustion and to reduce the formation of sugar-based decomposition residues on the back of the inlet valve(s). This can be achieved, for example, by using higher injection pressure and finer nozzles than are normally required for port injection to ensure fine dispersal of the sugar-derived components of the fuel. Overall, the choice of fuel injection method and the intensity of atomisation should be matched to the sugar-ammonia blend used and engine type. For example, port injection of an Otto engine will likely require lower sugar:ammonia ratio and high injection pressure than for ammonia only. Direct injection will require optimisation of the injectors nozzle/delivery rate to account for the higher viscosity of higher sugar:ammonia ratios.

[0080] Where the fuel is used in a compression ignition engine, the method of operating that compression ignition engine preferably comprises injecting the fuel formulation of the present invention via fuel jets into the combustion chamber of a cylinder of the engine after substantial closure of the exhaust valve(s) of that cylinder, after the inlet valve/ports of that cylinder are closed, and before 35° before the piston in that cylinder reaches top dead centre. The fuel formulation is injected after closure of the exhaust valves and inlet valve/ports to limit or prevent loss of unburnt ammonia to the exhaust, and before 35° before top dead centre to allow fuel vaporisation and preparation for ignition.

[0081] FIG. 1 shows a cross-sectional view of one cylinder 100 and piston 105 combination for a trunk piston uniflow 2-stroke engine that can be fuelled using the fuel formulation of the present invention. The cylinder 100 includes a cylinder head 108 having a radial nozzle fuel injector 110 located near the centre of the cylinder 100 and cylinder head 108 which directs fuel jets 115 outwardly therefrom towards the cylinder walls 112. The cylinder head 108 includes exhaust outlet valves 130. As illustrated, the piston 105 includes a connecting rod 122 which is connected at the other end to a crankshaft (not shown). The cylinder 100 also includes a scavenger belt 160 which include inlet ports 115 that are uncovered by the piston 105 towards the bottom of the piston stroke (when the piston 105 is close to bottom dead center). In this schematic, the fuel is injected through injector 110 such that the centreline Y of fuel jets 115 form an angle A relative to baseline X. Suitable angles A are of −30° and +5° or −90° and −35°. The injectors 110 would typically include 1 to 16 orifices in the nozzle. Ammonia injection is timed to occur after the exhaust valve(s) 130 close and before 35 crank degrees of top dead centre. The exhaust valves 130 are closed and after the inlet valve/ports 115 are closed during ammonia injection so to limit/control ammonia slip to the exhaust.

[0082] As a further embodiment of the invention, the base sugar-ammonia fuel could be adaptively doped with trace additives between the fuel tank and the engines high-pressure injection system, including with additives such as a lubricant, or other liquids to promote ignition and combustion, and to reduce emissions. One such suitable device is a small high-pressure additive dosing system controlled by the engine's CPU. In this embodiment, the additive rate would be adjusted according to engine operating conditions to optimise the performance of the sugar-ammonia fuel for the particular engine and operating conditions (for example coolant temperature, engine load), thus avoid the requirement for bulk fuel treatment.

[0083] Therefore, in some embodiments, the fuel formulation can be flowed from a fuel tank for injection into the engine, and one or more additives are introduced into the fuel formulation between the fuel tank and fuel injection of the fuel into the combustion chamber. The one or more additives may be introduced into the fuel formulation using an additive dosing system configured to adaptively dose the amount of the additive depending on an operating condition of the engine. Advantageously, this may reduce or avoid the need for bulk pre-blending of fuel additives while allowing the engine to operate over a wider range of operating conditions.

[0084] The present invention has a sound economic and environmental basis. Ammonia has a heat of combustion of 18.8 GJ/t lower heating value, at a cost of around A$1,000/t from renewable electricity, giving a specific energy cost of A$44/GJ. In comparison, sugar has a heat of combustion of around 16 GJ/t, at a cost of around A$400/t or A$24.0/GJ. As Australia exports around 4 Mtpa of sugar, and has excess production capacity, there is considerable scope for exploiting sugar as sugar-ammonia fuel blends. On a life cycle basis, the energy efficiency of using sugar as an ammonia blended fuel is substantially higher than converting it to ethanol for similar applications.

[0085] EXAMPLE

[0086] A four litre single cylinder diesel laboratory engine (adapted from a single cylinder engine, Satyjeet SL22). The ammonia fuel was injected into the engine using a modified stock jerk pump 10 (shown in FIG. 2) and a standard fuel injection pump (not illustrated). The jerk pump 10 was modified by removing the delivery valve on top of the pump and replacing this with a shuttle pump 20 (i.e. a media separator, shown sectioned in FIG. 2) to enable the standard injection pump to pump ammonia using the diesel fuel pulses from the standard injection pump. Anhydrous ammonia was supplied from the ammonia bottle to the shuttle pump via a booster pump (a small air actuated pump) at 25 bar to avoid vapour formation in the low pressure supply line to the engine. Immediately after the booster pump, a concentrated sugar solution was injected into the ammonia from a laboratory high pressure syringe pump. The rate of dosing of sugar solution was adjusted to match the average flowrate of ammonia as measured by a Coriolis flowmeter. To assist mixing with this setup, a 200 mm length of 20 mm Swagelok tubing (filled with Swagelok ferrules to act as packing) was fitted to the line downstream of the dosing point and upstream of the shuttle injection pump. The sugar solution was 75% by weight domestic grade raw sugar in hot water. The sugar solution was dosed into the ammonia stream at approximately 25 to 30° C. At this temperature the sugar solution showed no apparent recrystallisation.

[0087] A control fuel comprising 100% anhydrous ammonia was also used as a fuel as a comparison.

[0088] Engine testing found that the inventive sugar-ammonia solution fuel gave excellent ignition and combustion at up to 700 rpm.

[0089] For this setup 5 to 10% sugar solution was required to provide acceptable engine performance at 400 rpm, using the standard fuel injection timing as for diesel fuel. 15% sugar (0.15:1 sugar:ammonia, or 20% by weight of sugar solution) was required to provide acceptable engine performance at 700 rpm giving an exhaust temperature of 480° C., using the standard fuel injection timing as for diesel fuel.

[0090] The effect of sugar in improving both ignition and combustion rate was evident by the faster heat release rate in the engine after the start of injection, and particularly by the exhaust gas temperature which decreased from over 650° C. without sugar, to 420 to 480° C. with 5 to 10% by weight sugar solution, respectively—all at a constant 15 kW engine output at 400 rpm.

[0091] The comparative runs using ammonia as fuel alone found that that fuel combusted only slightly in the engine giving very high exhaust temperatures and low power.

[0092] While this simple setup has served to demonstrate the method, in practice several improvements in the apparatus would be used to optimise the benefits of the invention. These include the use of a continuous flow dosing pump such as a speed controlled positive displacement multi-cylinder oil-backed diaphragm pump for the sugar solution, and an electronically controlled injection system which can vary the injection timing to account for engine temperature, load, and sugar dosing rate. These effects will vary according to the engine used. The ammonia-sugar mixer could also be improved, for example by the use of a static mixing tube comprising interrupted spiral vanes as are used for mixing various fluids.

[0093] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0094] Where the terms “comprise”, “comprises”, “comprised” or “comprising” are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.