Ammonia-based fuel for compression engines containing combustion-enhancing additives

Abstract

A compression ignition engine fuel is provided which contains 95.0 to 99.9 wt % of ammonia and 0.01 to 5.0 wt % of alkyl nitrate.

Description

[Technical Field]

[0001] The field of the present invention relates to fuels for compression ignition engines, particularly marine engines. The fuels of the present invention are part of new fuels with reduced environmental impact, such as those commonly referred to as "e-fuels" when produced from low-carbon electricity, low-carbon footprint hydrogen, and / or CO2. These fuels are being considered as solutions for decarbonizing heavy goods transportation and long-distance travel. Thus, the ammonia-based fuels of the present invention are part of environmentally friendly alternative fuels to diesel and heavy fuel oil. The present invention relates to an additive that can be blended with ammonia to improve the ignition of the fuel in engines and increase its burning rate. [Background technology]

[0002] Ammonia (NH3) is a low-impact alternative and a promising renewable fuel for marine transportation, replacing diesel and heavy fuel oil in the near future. When NH3 is burned, only water and nitrogen are produced; no carbon molecules (CO2, CO) or soot are emitted. Because ammonia is a common chemical compound with a proven production process, its use, transportation, and storage methods are well-known. It also remains a reasonably priced product for use as a fuel. While ammonia as a fuel has usable energy density in compression-ignition engines, it has a low cetane number. Ignition of ammonia in diesel engines remains problematic, especially at low engine speeds. Ammonia is stored in liquid form in tanks under pressure (approximately 9 bar) and injected into the engine in either liquid or gas form.

[0003] Various means have been disclosed for improving the ignition of ammonia in compression ignition engines.

[0004] The first approach involves co-injecting a pilot fuel into the engine along with ammonia. Prior art, such as U.S. Patent Application Publication No. 2022 / 0056856, describes the co-injection of so-called "pilot fuels," or oxygen and / or hydrogen, with ammonia. This co-injection in the premixing chamber facilitates ignition of the ammonia. This approach has the major drawback of requiring control of the co-injection depending on the engine's operating conditions and the structural arrangement of the individual tanks and injection system. Furthermore, the use of fuel oil as a pilot fuel results in undesirable CO2 emissions and smoke.

[0005] The second approach is ammonia-based fuel blends. Fuels based on ammonia and dimethyl ether (DME) have been described in the prior art. DME is a synthetic fuel recommended as a diesel replacement. These fuels are described in two papers: "Ignition delay times of NH3 / DME blends at high pressure and low DME fraction: RCM experiments and simulations" (Combustion and Flame, Volume 227, May 2021, Pages 120-134) and "Ignition delay time and laminar flame speed measurements of ammonia blended with dimethyl ether: A promising low-carbon fuel blend" (Renewable Energy, Volume 181, January 2022, Pages 1353-1370). These papers demonstrate that ammonia-based fuel blends with dimethyl ether have better ignition delay than ammonia alone. The DME fraction in these ammonia / DME fuels is greater than 2%, ideally closer to 18%. This high concentration of hydrocarbon co-fuels in ammonia makes it incompatible with CO2 emission reduction targets, while DME is gaseous at atmospheric pressure, presenting drawbacks in storage and use.

[0006] A report by the R&D department of a U.S. oil company (Continental Aviation and Engineering Corporation, Detroit, US, vol. II, no. 1054, May 1, 1967, pages 1–251) concerns compounds that can be used in combination with ammonia fuel. This technical report presents a series of tests measuring the light-off temperature of ammonia alone and in the presence of additive compounds when slowly heated linearly in a furnace. The first series of tests identified gaseous acetylene as the only additive effective in improving ammonia combustion in compression-ignition engines. The second series of tests measured the light-off temperature of ammonia alone and in the presence of additives when slowly heated, and concluded that amyl nitrate was the second worst additive (after potassium azide) for lowering the light-off temperature of ammonia. Therefore, this report does not provide a strong indication of the effectiveness of fuels composed of ammonia and alkyl nitrates as combustion-enhancing additives in compression-ignition engines.

[0007] A third approach involves injecting an ignition accelerator into the engine compartment before injecting ammonia. U.S. Pat. No. 8,904,994 describes injecting a highly flammable compound, which autoignites when ammonia is injected, before the ammonia in order to improve the ignition of the ammonia. This compound may be GTL or DME diesel fuel (as mentioned above), cetane-modified sulfate, acetone, ethylene, hydrazine, or a nitro compound of acetylene, with hydrazine being the preferred compound. All of these compounds have obvious drawbacks: they may be highly toxic, unstable, and / or highly flammable or sulfurized.

[0008] On the other hand, in the field of hydrocarbon diesel fuels and biodiesel fuels, 2-ethylhexyl nitrate (EHN) has long been known to be used as a cetane improver in diesel fuels. Higher cetane numbers result in reduced fuel consumption, reduced particulate matter and NOx emissions, faster cold starts, reduced engine knock and noise, and reduced engine wear. The reaction mechanism of EHN in the presence of hydrocarbon diesel fuels has been studied in scientific literature, for example, in "The Autoignition Behavior of Surrogate Diesel Fuel Mixtures and the Chemical Effects of 2-Ethylhexyl Nitrate (2-EHN) Cetane Improver" (vol. 108, section 4: Journal of fuels and lubricants (1999), pp. 1029-1045). However, the reaction mechanism of its cetane improver effect has not yet been fully elucidated, and its use is based on empirical rules. Therefore, its effectiveness in fuels other than diesel cannot be assumed. This additive is produced industrially and is widely used in commercial diesel fuel. Over 50,000 tons of EHN have been produced annually in Europe since the 1980s. Other alkyl nitrates can also be used as cetane-improving additives in diesel fuel. Figure 1 shows that the cetane-improving effect of various alkyl nitrates on a standard diesel fuel (medium paraffinic (approximately 40%) with a low natural cetane number but a typical cetane-improving response) is similar to that of EHN. Cetane-improving effects are achieved when the alkyl nitrate is blended in the diesel fuel at a concentration close to 0.03 wt%.

[0009] This disclosure provides a solution for improving the ignition of ammonia in standard engines by adding alkyl nitrates such as EHN to ammonia fuel. It is unexpected that an additive known to increase the cetane number of hydrocarbons can be used to improve the ignition of a carbon-free fuel so effectively. Summary of the Invention [Means for solving the problem]

[0010] The present invention relates to a compression auto-ignition engine fuel containing about 95.0 to about 99.9 wt % ammonia and about 0.01 to about 5.0 wt % of a compound that significantly improves the ignition delay of ammonia.

[0011] The compound is an alkyl nitrate or a mixture of alkyl nitrates.

[0012] The compounds have the advantages of being liquid at room temperature, having low flammability, and being produced industrially.

[0013] Because these compounds are present in such low concentrations in the presence of ammonia fuel, they are conventionally incorporated into fuel additives.

[0014] The liquid compound is added by co-injection with liquid or gaseous ammonia in the premixing chamber of the engine, preferably by mixing with liquid ammonia before injection into the engine.

[0015] Thus, the alkyl nitrate type compounds previously used to improve the cetane number of hydrocarbon diesel fuels are surprisingly effectively used as additives to improve the ignition quality of ammonia. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows the effect of alkyl nitrates on the cetane number of standard diesel fuel. [Figure 2] Ignition delay of ammonia as a function of temperature at an enrichment (air / fuel) of 1 and a compression pressure Pc of 40 bar (left curve: fuel consisting of 100% ammonia, right curve: fuel consisting of 99.6% ammonia and 0.4% EHN). [Figure 3] The ignition delay of a fuel consisting of 99.8% ammonia and 0.2% EHN at an enrichment (air / fuel) of 1.5 and a compression pressure Pc of 30 bar is shown as a function of temperature. [Figure 4] Ignition delays of ammonia-based fuels containing various amounts of EHN at an enrichment ratio (air / fuel) of 0.35, a compression pressure Pc of 43.4 bar, and a temperature range of 1000K to 1100K are shown. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present disclosure relates to a compression ignition engine fuel comprising about 95.0 to about 99.9 wt.% ammonia and about 0.01 to about 5.0 wt.% of a fuel ignition enhancing compound comprising an alkyl nitrate. In one embodiment, the fuel comprises about 0.05 to about 2.0 wt.% of the compound. In another embodiment, the fuel comprises about 0.1 to about 0.8 wt.% of the compound.

[0018] In one embodiment, the fuel of the present invention consists of ammonia and the compound, in which case the amount of the compound in the fuel is at least 0.1% by weight.

[0019] In another embodiment, if the sum of the amount of ammonia and the amount of the above compounds does not equal 100% by weight, the fuel may include one or more other additives, such as additives with antiseptic, anticorrosion, or detergency functions, to bring the total to 100%.

[0020] The compound added to the ammonia is selected from one or more linear, branched, or cyclic alkyl nitrate esters.

[0021] More specifically, the compound is selected from linear alkyl nitrates having 4 to 36 carbon atoms, preferably 4 to 24 carbon atoms, branched alkyl nitrates having 4 to 36 carbon atoms, preferably 4 to 24 carbon atoms, cyclic alkyl nitrates (or cycloalkyl nitrates) having 5 to 18 carbon atoms, and mixtures thereof. In one embodiment, the compound is 2-ethylhexyl nitrate, cyclohexyl nitrate, dodecyl nitrate, n-nonyl nitrate, 2-tetradecyl-1-octadecyl nitrate, hexyl nitrate, 2-octyl nitrate, isononyl nitrate, 2-propylheptyl nitrate, C9 to C 13The alkyl nitrate is selected from the group consisting of 2-ethylhexyl nitrate alone or in a mixture with one or more other alkyl nitrates as defined above. Advantageously, the alkyl nitrate is 2-ethylhexyl nitrate alone.

[0022] C9~C 13 The mixture of branched alkyl nitrates is 13 Alcohols, such as Exxal® from Exxon TM It can be synthesized from a mixture of alcohols available under the trade names C9 branched chain alcohol, C 10 Branched chain alcohol, C 11 Branched chain alcohol, C 12 Branched chain alcohols, and C 13 A mixture of at least two branched chain alcohols selected from the branched chain alcohols can be prepared and then a corresponding mixture of alkyl nitrates can be synthesized.

[0023] In one embodiment, the fuel according to the invention is obtained by mixing a compound consisting of alkyl nitrates with liquefied ammonia (under pressure) in a tank that supplies the engine.

[0024] In one embodiment, the compound and liquefied ammonia are stored separately and placed in the presence of each other in an injector to form a fuel according to the invention, which is then delivered to the combustion chamber of the engine.

[0025] In one embodiment, the compounds are stored separately from ammonia and co-injected with liquefied or gaseous ammonia in the premix chamber of the engine to form the fuel of the present invention.

[0026] In some embodiments, the fuel does not include sugars such as fructose, glucose, or sucrose.

[0027] In some embodiments, the fuel is free of farnesene (alpha or beta), and generally speaking, free of isopenoids.

[0028] The present disclosure also relates to the use of an alkyl nitrate (as defined above) in the proportions defined above as an ignition enhancer for ammonia-based fuels.

[0029] The present disclosure also relates to a method for improving the ignition quality of an ammonia-based (or ammonia-based) fuel in an engine (particularly a combustion engine), the method comprising the step of adding an alkyl nitrate (as defined above) to ammonia in the ratio as defined above. In one embodiment, the alkyl nitrate and liquefied ammonia are mixed in an injector. In one embodiment, the alkyl nitrate and liquefied or gaseous ammonia are mixed in a premixing chamber of the engine.

[0030] The present disclosure also relates to an engine (particularly a combustion engine) of a vehicle (car, truck, tractor, etc.) or a vessel (tanker, container ship, etc.) containing a fuel as defined above. The present disclosure also relates to a vehicle or vessel having an engine as defined above.

[0031] The invention is illustrated by the following examples, which are provided for reference purposes. [Example]

[0032] The improvement in ignition delay of liquid ammonia was measured under test conditions equivalent to those described in the scientific paper "Ignition delay times of NH3 / DME blends at high pressure and low DME fraction: RCM experiments and simulations" (Combustion and Flame, Volume 227, May 2021, Pages 120-134). The laboratory engine is a high-speed compressor equivalent to that described in this scientific paper, designed to measure the auto-ignition time of the mixture. This machine allows the mixture to be compressed in a very short time to achieve the desired pressure and temperature conditions. The liquid is introduced into the tank through an orifice separate from the gas inlet. The amount of liquid is measured using a syringe and precision balance.

[0033] Ignition delay dAI is defined by the following formula:

number

[0034] Example 1 Ignition delay was measured as a function of injection temperature (950-1100 K) for a fuel consisting of 99.6 wt. % ammonia and 0.4 wt. % EHN at a pressure Pc = 40 bar and an air mixture enrichment of 1. The predetermined reference point for ignition delay with ammonia alone (Figure 2, left curve) was taken from the aforementioned paper. Figure 2 confirms a significant reduction of the ignition delay of the fuel by a factor of about 10 compared to ammonia alone (right curve). This reduction in ignition delay with the fuel of the present invention compared to ammonia alone is greater at lower temperatures.

[0035] Example 2 The ignition delay of a fuel consisting of 99.8 wt. % ammonia and 0.2 wt. % EHN was measured as a function of injection temperature (925–1000 K) at a pressure Pc of 30 bar and an enrichment factor of 1.5 with air. The ignition delay of the fuel was less than 800 ms (Fig. 3), but ammonia alone did not ignite under these test conditions.

[0036] Example 3 The ignition delays of fuels consisting of ammonia alone, 99.9 wt.% ammonia and 0.1 wt.% EHN, or 98.0 wt.% ammonia and 2.0 wt.% EHN were measured at three temperatures (1000 K, 1050 K, and 1100 K), a pressure Pc of 43.4 bar, and an air enrichment of 0.35. At all three temperatures, the ignition delays of the fuels were shorter than those of ammonia alone (Figure 4). The effect of EHN addition on ignition delay compared to ammonia alone (as confirmed in Example 1) increases at lower temperatures. By extrapolating the curves for these three temperature conditions, the optimal weight ratio of 0.25% EHN is essentially achieved.

[0037] These examples demonstrate that the use of very small weight percentages of alkyl nitrates can significantly improve the ignition delay of ammonia-based fuels. There was no reason to believe that such an effective improvement in ammonia ignition could be achieved using only small amounts of an additive known to increase the cetane number of diesel or biodiesel hydrocarbons.

Claims

1. A compression ignition engine fuel containing 95.0 to 99.9 wt % ammonia and 0.01 to 5.0 wt % alkyl nitrate.

2. 2. The fuel according to claim 1, comprising 0.05 to 2.0% by weight, in particular 0.1 to 0.8% by weight, of said alkyl nitrate.

3. 3. The fuel of claim 1, comprising ammonia and an alkyl nitrate.

4. 4. The fuel according to claim 1, wherein the alkyl nitrate is a linear alkyl nitrate ester having 4 to 36 carbon atoms, a branched alkyl nitrate ester having 4 to 36 carbon atoms, a cyclic alkyl nitrate ester having 5 to 18 carbon atoms, or a mixture of these nitrate esters.

5. The alkyl nitrate may be 2-ethylhexyl nitrate, cyclohexyl nitrate, dodecyl nitrate, n-nonyl nitrate, 2-tetradecyl-1-octadecyl nitrate, hexyl nitrate, 2-octyl nitrate, isononyl nitrate, 2-propylheptyl nitrate, C ９ ~C １３ A fuel according to any one of claims 1 to 4, selected from mixtures of branched alkyl nitrate esters, and mixtures thereof.

6. A fuel according to any one of claims 1 to 5, wherein the alkyl nitrate is 2-ethylhexyl nitrate.

7. A method for obtaining the fuel according to any one of claims 1 to 6, comprising the step of mixing the alkyl nitrate with liquefied ammonia or gaseous ammonia.

8. 8. The method of claim 7, wherein the liquefied ammonia and the alkyl nitrate are mixed in an engine tank.

9. 8. The method of claim 7, wherein the liquefied ammonia and the alkyl nitrate are mixed in an injector.

10. 8. The method of claim 7, wherein the liquefied or gaseous ammonia and the alkyl nitrate are mixed in a premix chamber of an engine.

11. 1. The use of 0.01 to 5.0 wt. % of an alkyl nitrate in an ammonia-based fuel as an ignition promoter for said fuel.

12. Use according to claim 11, wherein the alkyl nitrate is present in the fuel in an amount of 0.05 to 2.0% by weight, in particular 0.1 to 0.8% by weight.

13. The use according to claim 12, wherein the alkyl nitrate is as defined in any one of claims 4 to 6.

14. A method for improving the ignition ability of a fuel containing 95.0 to 99.9 wt % ammonia in an engine, the method comprising the step of adding 0.01 to 5.0 wt %, preferably 0.05 to 2.0 wt %, more preferably 0.1 to 0.8 wt %, of alkyl nitrate to liquefied ammonia or gaseous ammonia, based on the weight of the fuel.

15. 15. The method of claim 14, wherein the alkyl nitrate is as defined in any one of claims 4 to 6.

16. 16. The method of claim 14, wherein the alkyl nitrate and the liquefied ammonia are mixed in an engine tank.

17. 16. The method of claim 14, wherein the alkyl nitrate and the liquefied ammonia are mixed in an injector.

18. 16. The method of claim 14, wherein the alkyl nitrate and the liquefied or gaseous ammonia are mixed in a premix chamber of an engine.

19. A vehicle or marine engine containing a fuel as defined in any one of claims 1 to 6.

20. 20. A vehicle or watercraft having an engine as defined in claim 19.

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