Ammonia fuel for compression engines comprising combustion additive

Abstract

A fuel for a compression ignition engine is provided that includes 95.0% to 99.9% by weight of ammonia and 0.01% to 5.0% by weight of an alkyl nitrate.

Description

Technical Field

[0001] The field of the invention is that of fuels for compression ignition engines, more specifically for engines for marine applications. The fuels of the invention are part of new fuels with reduced environmental impact, such as those commonly referred to as "e-fuels" when they are made from low-carbon electricity, low-carbon footprint hydrogen and / or CO2. They are considered a solution for decarbonizing transport for heavy and long-distance movements. The fuel of the invention, which is mainly composed of ammonia, is therefore part of an ecological alternative to diesel and heavy fuel oil. The invention relates to an additive which, when introduced into ammonia, ensures better ignition and faster combustion of the fuel in the engine. Background Art

[0002] Ammonia (NH3) is a reduced environmental impact alternative and a reliable renewable fuel that can replace diesel and heavy fuel oil for marine transport in the near future. The combustion of NH3 produces only water and nitrogen, without emitting carbon molecules (CO2, CO) or soot particles. Ammonia is a compound whose manufacture is proven and common, which makes its use, transportation and storage well known. It is also a product whose cost is still reasonable enough to be used as a fuel. Ammonia as a fuel has an energy density that can be used in compression ignition engines, but has a low cetane number. Its ignition in diesel engines is still problematic, especially at low engine speeds. Ammonia is stored in liquid form in tanks under pressure (about 9 bar) and injected into the engine in liquid or gaseous form.

[0003] Various approaches to improving the ignition of ammonia in compression ignition engines have been described.

[0004] The first method is to co-inject the pilot fuel with ammonia into the engine. Prior art, such as patent application US2022 / 0056856, describes a method of co-injecting so-called "pilot fuel" or oxygen and / or hydrogen with ammonia. This co-injection in the premixing chamber is conducive to the ignition of ammonia. The main disadvantage of this type of method is that the co-injection needs to be controlled according to the operating conditions and structural arrangement of the engine (such as a separate tank and injection system). Moreover, the use of fuel oil as a pilot fuel will produce undesirable CO2 emissions and soot.

[0005] The second method is a mixture of fuel and ammonia. Fuels consisting of a mixture mainly of ammonia and dimethyl ether (DME) have been described in the prior art. DME is a synthetic fuel recommended as a diesel substitute. These fuels are described in a document entitled "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 a document entitled "Ignition delay time and laminar flame speed measurements of ammonia blended with dimethylether: A promising low carbon fuel blend" (Renewable Energy, Volume 181, January 2022, Pages 1353-1370). These documents describe a fuel consisting of a mixture mainly of ammonia and dimethyl ether, which has a better ignition delay than ammonia alone. Ammonia / DME fuel contains more than 2%, ideally close to 18% of DME. Such high levels of hydrocarbon co-fuel in ammonia are therefore not in line with CO2 reduction targets. On the other hand, DME is gaseous at atmospheric pressure, which is a disadvantage for its storage and use.

[0006] A report from the research and development department of an American oil company (Continental Aviation and Engineering Corporation, Detroit, USA, Volume II, Issue 1054, 1967-05-01, Pages 1-251) relates to compounds that can be used in combination with ammonia fuel. The technical report describes a series of tests that measure the ignition temperature by slowly linearly heating ammonia alone in a furnace and in the presence of added compounds. The first series of tests determined that gaseous acetylene is the only additive that effectively improves the combustion of ammonia in compression engines. The second series of tests measured the ignition temperature by slowly heating ammonia alone or in the presence of additives, and concluded that amyl nitrate is the second worst additive (second only to potassium azide) to reduce the ignition temperature of ammonia. Therefore, the report does not bode well for the effectiveness of fuels composed of ammonia and alkyl nitrates (as combustion-promoting additives) in compression ignition engines.

[0007] The third method is to inject an ignition enhancer into the engine compartment before injecting ammonia. Patent US8904994 describes that in order to improve the ignition of ammonia, a highly flammable compound is injected before ammonia, and the compound spontaneously ignites when ammonia is injected. The compound can be GTL or DME diesel fuel (as mentioned above), hexadecane modified sulfate, nitro compounds of acetone, ethylene, hydrazine, acetylene, and hydrazine is a preferred compound. These compounds all have obvious disadvantages because some compounds are highly toxic and unstable and / or highly flammable or sulfided.

[0008] On the other hand, in the field of hydrocarbon diesel or biodiesel fuel, 2-ethylhexyl nitrate (EHN) has long been known to be used as a cetane enhancing additive in diesel fuel. Higher cetane number ensures lower fuel consumption, reduced particulate matter and NOx emissions, faster cold engine start, reduced engine knock and noise, and reduced engine wear. The reaction mechanism of EHN in the presence of hydrocarbon diesel fuel has been studied in, for example, the scientific publication "The Autoignition Behavior of Surrogate Diesel Fuel Mixtures and the Chemical Effects of 2-Ethylhexyl Nitrate (2-EHN) Cetane Improver" (Volume 108, Section 4: Journal of fuels and lubricants (1999), Pages 1029-1045). However, the reaction mechanism of its cetane improvement effect is still poorly understood, and its use is based on empirical rules. Therefore, it is impossible to assume its effectiveness for fuels other than diesel. This additive is industrially produced and widely used in commercial diesel fuels. More than 50,000 tonnes of EHN have been produced in Europe each year since the 1980s. Other alkyl nitrates are also used as cetane enhancement additives in diesel fuels. Figure 1 It was shown that the effect of different alkyl nitrates on cetane number when added to standard diesel fuel (medium paraffin content (about 40%), with low natural cetane number but standard cetane enhancement response) was similar to that of EHN. The cetane enhancement effect was obtained when the alkyl nitrate introduced into the diesel fuel was close to 0.03 wt%.

[0009] The present invention provides a solution to improve the ignition of ammonia in standard engines by adding alkyl nitrates (such as EHN) to the ammonia fuel. Surprisingly, additives known to increase the cetane number of hydrocarbons can be used so effectively to improve the ignition of carbon-free fuels. Summary of the invention

[0010] The present invention relates to a compression autoignition engine fuel comprising about 95.0 wt % to about 99.9 wt % ammonia and about 0.01 wt % 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 compound has the advantages of being liquid at room temperature, having low flammability, and being industrially producible.

[0013] Therefore, the compounds at these low levels in the presence of ammonia fuel are typically assimilated as fuel additives.

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

[0015] Said compounds of the alkyl nitrate type, which have previously been reserved for improving the cetane number of hydrocarbon diesel fuels, are therefore effectively and surprisingly used as additives for improving the ignition of ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The effect of alkyl nitrates on the cetane number of a standard diesel fuel is shown.

[0017] Figure 2 The ignition delay of ammonia as a function of temperature is shown, with a richness (air / fuel) of 1 and a compression pressure Pc of 40 bar; left curve = fuel composed of 100% ammonia; right curve = fuel composed of 99.6% ammonia and 0.4% EHN.

[0018] Figure 3 The ignition delay as a function of temperature is shown for a fuel consisting of 99.8% ammonia and 0.2% EHN, with a richness (air / fuel) of 1.5 and a compression pressure Pc of 30 bar.

[0019] Figure 4 The ignition delay of ammonia fuel containing different amounts of EHN is shown, where the richness (air / fuel) is 0.35, the compression pressure Pc is 43.4 bar, and the temperature range is 1000K to 1100K. DETAILED DESCRIPTION

[0020] The present invention relates to a compression ignition engine fuel comprising about 95.0% to about 99.9% by weight of ammonia and about 0.01% to about 5.0% by weight of a fuel ignition enhancing compound consisting of an alkyl nitrate. In one embodiment, the fuel comprises about 0.05% to about 2.0% by weight of the compound. In another embodiment, the fuel comprises about 0.1% to about 0.8% by weight of the compound.

[0021] In one embodiment, the fuel of the invention consists of ammonia and the compound (and in this case, the amount of compound in the fuel is at least 0.1% by weight).

[0022] In another embodiment, when the sum of the amount of ammonia and the amount of the compound is not equal to 100% by weight, the fuel may contain one or more other additives to bring the fuel to 100%, for example additives having an anti-corrosion, anti-corrosion or detergent function.

[0023] The compound added to ammonia is selected from one or more linear alkyl nitrates, branched alkyl nitrates or cyclic alkyl nitrates.

[0024] The compound is more particularly chosen from linear alkyl nitrates having 4 to 36 carbon atoms (advantageously having 4 to 24 carbon atoms), branched alkyl nitrates having 4 to 36 carbon atoms (advantageously having 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 chosen from 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 C18 nitrates. 13 Mixtures of branched alkyl esters, and mixtures thereof. In one embodiment, the alkyl nitrate is 2-ethylhexyl nitrate alone or in mixture with one or more other alkyl nitrates as defined above, advantageously, the alkyl nitrate is 2-ethylhexyl nitrate alone.

[0025] From the corresponding branch chain C9 to C 13 A mixture of alcohols (e.g., marketed by Exxon under the trade name Exxal TM Alcohol for sale) Synthetic nitric acid C9 to C 13 For example, a mixture of branched alkyl esters selected from C9 branched alcohols, C 10 Branched chain alcohol, C 11 Branched chain alcohol, C 12 Branched chain alcohols and C 13 A mixture of at least two of the branched alcohols can then be used to synthesize a mixture of the corresponding alkyl nitrates.

[0026] In one embodiment, the compound consisting of alkyl nitrates is mixed with liquefied ammonia (under pressure) in a tank supplied to the engine in order to obtain the fuel according to the invention.

[0027] In one embodiment, the compound and the liquefied ammonia are stored separately and are brought into contact with each other in an injector so as to form the fuel according to the invention before supplying it to the combustion chamber of the engine.

[0028] In one embodiment, the compound is stored separately from ammonia and co-injected with liquefied or gaseous ammonia to form the fuel according to the invention in a premixing chamber of an engine.

[0029] In some embodiments, the fuel does not comprise a sugar, such as fructose, glucose, or sucrose.

[0030] In some embodiments, the fuel does not contain farnesene (alpha or beta), and generally, does not contain isoprenoids.

[0031] The invention 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.

[0032] The invention also relates to a method for improving the ignition of a fuel based on (or consisting of) ammonia in an engine, in particular a combustion engine, the method comprising adding an alkyl nitrate (as defined above) to ammonia in the proportions 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.

[0033] The invention also relates to an engine (in particular a combustion engine) of a vehicle (e.g. a car, truck, tractor, etc.) or a vessel (e.g. a tanker, container ship, etc.) containing a fuel as defined above. The invention also relates to a vehicle or a vessel comprising an engine as defined above.

[0034] The invention is illustrated by the following examples which are given as guidance.

[0035] Example

[0036] The ignition delay improvement of liquid ammonia was measured under test conditions comparable to those described in the scientific literature "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 test laboratory engine is a fast compressor comparable to the engine described in this scientific literature. It is a fast compressor used to measure the autoignition time of a mixture. The machine can compress the mixture in a very short time to obtain preset pressure and temperature conditions. The liquid enters the tank through a different hole from the gas inlet. The amount of liquid is measured using a syringe and a precision balance.

[0037] The ignition delay dAI is defined according to the following formula, where Pc is the pressure applied to the injected fuel:

[0038]

[0039] Example 1

[0040] The ignition delay of a fuel consisting of 99.6 wt. % ammonia and 0.4 wt. % EHN was determined as a function of the injection temperature (between 950 K and 1100 K) at a pressure Pc of 40 bar and at a mixture enrichment with air of 1. The given reference point for the ignition delay of ammonia alone ( Figure 2 , the left curve) comes from the above literature. Figure 2 (right curve), a significant reduction of the fuel ignition delay compared to ammonia alone by a factor of about 10 is observed. The lower the temperature, the greater this reduction in the ignition delay of the fuel of the invention compared to ammonia alone.

[0041] Example 2

[0042] At a pressure Pc of 30 bar and at a mixture enrichment with air of 1.5, the ignition delay of a fuel consisting of 99.8% by weight of ammonia and 0.2% by weight of EHN was determined as a function of the injection temperature (between 925 K and 1000 K). The ignition delay of the fuel was less than 800 ms ( Figure 3 ), whereas ammonia alone will not ignite under these test conditions.

[0043] Example 3

[0044] The ignition delay of a fuel consisting of ammonia alone, 99.9 wt. % ammonia and 0.1 wt. % EHN, or 98.0 wt. % ammonia and 2.0 wt. % EHN was measured at three temperatures (1000 K, 1050 K and 1100 K), a pressure Pc of 43.4 bar, and a mixture enrichment with air of 0.35. For all three temperatures, the ignition delay of the fuel was lower than that of ammonia alone ( Figure 4 ). The lower the temperature, the greater the effectiveness of the addition of EHN on the ignition delay compared to ammonia alone (as already observed in Example 1). By extrapolating the curves for these three temperature conditions, the optimum weight ratio of 0.25% EHN is essentially achieved.

[0045] These examples show that the use of very low weight percent alkyl nitrates can significantly improve the ignition delay of ammonia fuels. There is no reason to believe that additives known to increase the cetane number of diesel or biodiesel hydrocarbons can be used so effectively in very small amounts to improve the ignition of ammonia.

Claims

1. A compression ignition engine fuel comprising 95.0 to 99.9 weight percent ammonia and 0.01 to 5.0 weight percent alkyl nitrate.

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 alkyl nitrate.

3. The fuel according to any one of claims 1 and 2, which consists of ammonia and alkyl nitrate.

4. The fuel according to any one of claims 1 to 3, wherein The alkyl nitrate is a nitrate having a linear alkyl group of 4 to 36 carbon atoms, a nitrate having a branched alkyl group of 4 to 36 carbon atoms, a nitrate having a cyclic alkyl group of 5 to 18 carbon atoms, or a mixture of these nitrates.

5. The fuel according to any one of claims 1 to 4, wherein The alkyl nitrate is selected from 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 13 Mixtures of branched chain alkyl esters, and mixtures thereof.

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

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

8. The method according to claim 7, wherein: The liquefied ammonia and the alkyl nitrate or the mixture of alkyl nitrates are mixed in a tank of the engine.

9. The method according to claim 7, wherein: The liquefied ammonia and the alkyl nitrate are mixed in an injector.

10. The method according to claim 7, wherein: The liquefied or gaseous ammonia and the alkyl nitrate are mixed in a premixing chamber of the engine.

11. Use of alkyl nitrate in ammonia fuel as an ignition enhancer of the fuel, wherein the amount of the alkyl nitrate is 0.01 wt% to 5.0 wt%.

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

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

16. The method according to any one of claims 14 and 15, wherein: The alkyl nitrate and liquefied ammonia are mixed in a tank of the engine.

17. The method according to any one of claims 14 and 15, wherein: The alkyl nitrate and liquefied ammonia are mixed in the injector.

18. The method according to any one of claims 14 and 15, wherein: The alkyl nitrate and liquefied or gaseous ammonia are mixed in a premixing chamber of the engine.

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

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

Images