Fuel for compression engine

Abstract

A fuel for a combustion engine comprises from 95.00% to 99.75% by weight of ammonia and from 0.25% to 5.00% by weight of a pilot fuel comprising hydrocarbons having a cetane number greater than 60 and containing from 0.02% to 30.0% by weight of an alkyl nitrate or alkyl nitrate mixture. The invention also relates to a method for obtaining such a fuel.

Description

TECHNICAL FIELD

[0001] The field of the invention is fuel for compression ignition engines, more specifically for engines used in marine applications. The fuel of the invention is one of the new generation of fuels with less environmental impact, such as one of the fuels commonly known as "e-fuels", produced with low-carbon electricity, low-carbon hydrogen and / or CO2. They are considered a solution for carbon emission reduction in heavy long-distance transport. Thus, the fuel of the invention, mainly composed of ammonia, is one of the environmentally friendly alternatives to diesel and heavy fuel oil. The invention relates to an ammonia-type fuel for use with a pilot fuel, which ensures better ignition of the fuel in the engine and makes it burn faster and more energetically. BACKGROUND

[0002] Ammonia (NH3) is an environmentally friendly alternative and a reliable renewable fuel that can soon replace diesel and heavy fuel oil in marine transport. The combustion of NH3 produces only water and nitrogen, without carbon molecules (CO2, CO) or soot particles. Ammonia is a compound with a proven and common manufacturing process, which means that its use, transport and storage are well known. It is also a product whose cost remains reasonable enough to be used as fuel. Ammonia has an energy density that can be used in compression ignition engines, but its cetane number is low. 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 is injected into the engine in liquid or gaseous form.

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

[0004] US patent application 2010 / 288211 describes a method of preparing a mixture of ammonia and heavy fuel oil for use in an internal combustion engine, comprising: (i) supplying ammonia to a metering mixing module; (ii) providing a supply of heavy fuel to the metering mixing module; (iii) mixing the heavy fuel and ammonia supply in predetermined proportions in the metering mixing module.

[0005] The scientific article "Ignition and combustion study of premixed ammonia using GDI pilot injection in CI engine", published in Fuel, vol. 331, part 1, 1 January 2023, 125768, describes the benefits of n-heptane as a pilot fuel in the case of ammonia. N-heptane was chosen because of its low viscosity (facilitating injection) and because its cetane number (53 to 56) is close to that of commercial diesel fuel.

[0006] U.S. Patent Application 2011 / 0259290 describes a combustion engine operated with a mixture of ammonia and a highly combustible substance that is more easily combustible than ammonia. U.S. Patent Application 2022 / 056856 describes a propulsion system comprising a piston engine capable of operating with ammonia (NH3) as the primary fuel and a pilot system configured to ignite a pilot fuel to ignite a mixture of air and ammonia, the pilot fuel comprising hydrogen, biofuel, and / or fossil fuel.

[0007] Patent applications US2011 / 0259290 and US2022 / 056856 do not specify the weight ratio between ammonia and the additional fuel used.

[0008] On another level, in the field of diesel or biodiesel hydrocarbon fuels with low natural cetane number, typically close to 42 to 55, 2-ethylhexyl nitrate (EHN) has been used for a long time as a cetane number improver additive in diesel fuel. Higher cetane number ensures lower fuel consumption, reduces particulate and NOx emissions, makes cold engine start-up faster, reduces engine knock and noise, and reduces engine wear. For example, in the scientific publication “The Autoignition Behaviour of Surrogate Diesel Fuel Mixtures and the Chemical Effects of 2-Ethylhexyl Nitrate (2-EHN) Cetane Improver” (Vol. 108, No. 4: Journal of fuels and lubricants (1999), pp. 1029-1045), the reaction mechanism of EHN in the presence of hydrocarbon diesel fuel has been studied. This additive can be industrially produced and is widely used in commercial diesel fuel. Over 50,000 metric tons of EHN have been produced in Europe every year since the 1980s. Other alkyl nitrates can also be used as additives to improve the cetane number of diesel fuel. When alkyl nitrates are added to diesel fuel at a concentration of about 0.03% by weight, a cetane number improvement effect can be obtained.

[0009] When the fuel already has a naturally high cetane number, typically over 60, fuel cetane number improvers such as alkyl nitrates are useless. It should also be noted that cetane numbers with values over 67 are still difficult to measure according to the standard measurement method using EN 16715. SUMMARY

[0010] This invention provides a solution to improve the ignition and combustion of ammonia in a standard engine by using an ignition fuel containing highly reactive hydrocarbons (high cetane number, greater than 60) and alkyl nitrate additives (e.g., 2-ethylhexyl nitrate (2-EHN or NEH)) in a very small proportion relative to the fuel. The ignition fuel energy fraction (PEF) added to the primary ammonia fuel is 0.1% to 5% of the total fuel (ammonia + ignition fuel).

[0011] The PEF of the ignition fuel is calculated using the following formula:

[0012]

[0013] PCI: Low heating value

[0014] m carb The weight of the ignition fuel.

[0015] m NH3 : Weight of the main fuel (ammonia).

[0016] The low calorific value of ignition fuel depends on its properties; therefore, the weight percentage of ignition fuel relative to ammonia corresponding to a PEF varies depending on the properties of the fuel with the same PEF. For example, for 1% PEF, if the ignition fuel is HVO (an abbreviation for "hydrogenated vegetable oil"), the weight percentage of HVO relative to ammonia is approximately 0.52%. Surprisingly, very small amounts of ignition fuel can very effectively improve or even enable the ignition and combustion of fuels primarily composed of ammonia, both hot and cold. The low proportion of ignition fuel added helps limit greenhouse gas combustion product emissions. Thus, the high cetane number hydrocarbons and alkyl nitrate additives constituting the ignition fuel work synergistically to improve ammonia combustion. Attached Figure Description

[0017] Figure 1 The pressure measured in the combustion chamber relative to the crankshaft angle (CA) is shown, where, for CA = -10°, an ignition fuel consisting of dodecane and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0018] Figure 2 The temperature measured in the combustion chamber relative to the crankshaft angle (CA) is shown, where for CA = -10°, an ignition fuel consisting of dodecane and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0019] Figure 3 The heat release in the combustion chamber is shown as measured relative to the crankshaft angle (CA), where, for CA = -10°, an ignition fuel consisting of dodecane and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0020] Figure 4 The pressure measured in the combustion chamber relative to the crankshaft angle (CA) under cold (30°C) and hot (80°C) start conditions is shown, where at CA = -10°, an ignition fuel consisting of dodecane and containing 10% by weight of EHN is injected.

[0021] Figure 5 The display shows the temperature in the combustion chamber relative to the crankshaft angle (CA) under cold (30°C) and hot (80°C) start-ups, where for CA = -10°, an ignition fuel consisting of dodecane and containing 10% by weight of EHN is injected.

[0022] Figure 6 The pressure measured in the combustion chamber relative to the crankshaft angle (CA) is shown, where for CA = -10°, an ignition fuel consisting of HVO and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0023] Figure 7 The temperature measured in the combustion chamber relative to the crankshaft angle (CA) is shown, where for CA = -10°, an ignition fuel consisting of HVO and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0024] Figure 8 The heat release in the combustion chamber is shown as measured relative to the crankshaft angle (CA), where, for CA = -10°, an ignition fuel consisting of HVO and containing 0 wt%, 1 wt%, and 10 wt% EHN is injected.

[0025] Figure 9 The pressure measured in the combustion chamber relative to the crankshaft angle (CA) under cold (30°C) and hot (80°C) start conditions is shown, where for CA = -10°, an ignition fuel consisting of HVO and containing 30% by weight of EHN is injected. Detailed Implementation

[0026] This invention relates to a fuel for combustion engines, particularly compression-ignition engines, which uses ammonia as the primary fuel and adds an ignition fuel comprising a hydrocarbon with a cetane number greater than 60 and containing about 0.02 wt% to about 30.0 wt% of an additive composed of alkyl nitrates or mixtures thereof. In some embodiments, the hydrocarbon with a cetane number greater than 60 contains about 0.5 wt% to about 30.0 wt%, or about 1.0 wt% to about 30.0 wt%, or about 1.0 wt% to about 20.0 wt%, or about 1.0 wt% to about 10.0 wt% of an additive composed of alkyl nitrates or mixtures thereof.

[0027] As described above, the combustion engine fuel according to the present invention contains ammonia as the main fuel, and the amount of ammonia is from about 95.00% by weight to about 99.75% by weight.

[0028] As described below, ignition fuel is injected into the combustion chamber of a spark-ignition engine before or after the supply of ammonia. In some embodiments, the resulting fuel (ammonia + ignition fuel) comprises approximately 0.25% to approximately 5.0% by weight of ignition fuel relative to the total weight of the fuel (ammonia + ignition fuel). In some embodiments, when the sum of the amounts of ammonia and ignition fuel is not equal to 100% by weight, the remaining 100% is the addition of one or more other additives (e.g., additives with lubricating, anti-corrosion, or cleaning functions) to the fuel. Such additives or these additives may be included in the ignition fuel or may be introduced into the combustion chamber separately.

[0029] The hydrocarbons in ignition fuels are obtained through petroleum distillation or synthesis from renewable feedstocks. Ignition fuels can also be pure substances from the family of linear or branched alkanes.

[0030] In some embodiments, the hydrocarbon with a high cetane number (>60) in the ignition fuel is selected from at least one of the following compounds:

[0031] - Diesel fuel with low aromatic compound content (<10%) and low oligomeric aromatic compound content (<10%).

[0032] - Hydrogenated vegetable oil HVO (or renewable diesel from waste oil or animal fat), such as the HVO 100 fuel model sold by TotalEnergies.

[0033] -Isoalkanes, such as the Isane Biolife model of isoalkanes sold by TotalEnergies.

[0034] - n-Alkanes, such as dodecane,

[0035] - Sustainable aviation fuel (SAF – based on standards established as part of the International Aviation Carbon Offset and Reduction Programme as part of ICAO / UN).

[0036] In some implementations, the hydrocarbons in the ignition fuel are selected from hydrogenated vegetable oils, n-alkanes (especially dodecane), and mixtures thereof.

[0037] The additives contained in the ignition fuel at a content of about 0.02% to about 30.0% constitute about 0.0002% to about 1.5% of the total weight of the fuel.

[0038] The additive added to the ignition fuel consists of alkyl nitrate esters or mixtures of alkyl nitrate esters, selected from linear, branched, or cyclic alkyl nitrate esters. In some embodiments, the alkyl nitrate ester is selected from linear alkyl nitrate esters containing 4 to 36 (advantageously 4 to 24) carbon atoms, branched alkyl nitrate esters containing 4 to 36 (advantageously 4 to 24) carbon atoms, cyclic alkyl nitrate esters (or cyclic alkyl nitrate esters) containing 5 to 18 carbon atoms, and mixtures thereof. In some embodiments, the alkyl nitrate ester is selected from 2-ethylhexyl nitrate, cyclohexyl nitrate, dodecyl nitrate, n-nonyl nitrate, 2-tetradecyl-1-octadecyl nitrate, isononyl nitrate, hexyl nitrate, 2-octyl nitrate, isononyl nitrate, 2-propylheptyl nitrate, and C9-C nitrate. 13 Mixtures of alkyl esters, and mixtures thereof. In some embodiments, the alkyl nitrate ester is 2-ethylhexyl nitrate alone or a mixture of 2-ethylhexyl nitrate and one or more other alkyl nitrate esters as defined above; advantageously, the alkyl nitrate ester is 2-ethylhexyl nitrate alone.

[0039] Nitric acid C9-C 13 Mixtures of branched alkyl esters can be derived from the corresponding C9-C... 13 Mixtures of branched alcohols (e.g., available from Exxon under the trade name Exxal) TM The alcohol is obtained by means of the C9 branched alcohol. For example, alcohols selected from C9 branched alcohols, ... 10 Branched alcohol, C 11 Branched alcohol, C 12 Branched alcohols and C 13 At least two branched alcohols are mixed, and then a mixture of the corresponding alkyl nitrate esters is synthesized.

[0040] Fuels consisting of ammonia, ignition fuel, and optional additives can be used in engines (particularly combustion engines), such as vehicle engines (e.g., cars, trucks, tractors, etc.) or marine engines (e.g., tankers, container ships, etc.). Therefore, one aspect of the invention relates to a vehicle or marine engine comprising the fuel as defined herein. The invention also relates to a vehicle or vessel comprising an engine as defined herein.

[0041] Ammonia is typically injected into the engine's combustion chamber in liquid form or enters the combustion chamber in gaseous form, where it may or may not be premixed with air at the intake port.

[0042] Ignition fuel and ammonia (in liquefied form) are stored separately. Ignition fuel is injected into the combustion chamber before or after the addition of ammonia (more specifically, after the addition of ammonia in a gaseous form premixed with air, as shown in Examples 1 and 2 below), or co-injected with ammonia via a dual injection system.

[0043] Therefore, according to one aspect, the present invention relates to a method for obtaining a fuel as defined herein, the method comprising mixing, in the combustion chamber of an engine, an ignition fuel (as defined herein) and liquefied or gaseous ammonia premixed with or not premixed with intake air. In some embodiments, the ignition fuel and ammonia are co-injected into the combustion chamber via a dual-injection system. In some embodiments, the ignition fuel is injected into the combustion chamber before the ammonia is introduced or injected. In some embodiments, the ignition fuel is injected into the combustion chamber after the ammonia is introduced or injected.

[0044] Injection of ignition fuel helps to ignite ammonia, which may be difficult or even impossible to do under certain engine conditions (such as enrichment, temperature, or load).

[0045] The use of ignition fuels as defined herein provides improved ignition and combustion performance compared to ammonia alone, and helps ensure cold ignition.

[0046] Therefore, in one aspect, the present invention relates to the use of an ignition fuel as defined herein as a fuel ignition improver, said ignition fuel being present in an amount of 0.25% to 5.0% by weight in said fuel comprising about 95.00% to about 99.75% by weight of ammonia. The invention also relates to a method for improving the ignition of a fuel comprising about 95.00% to about 99.75% by weight of ammonia in an engine, the method comprising adding an ignition fuel as defined herein to the ammonia, said ignition fuel being present in an amount of 0.25% to 5.0% by weight.

[0047] According to one aspect, the present invention relates to a vehicle or marine engine containing (operating with) the fuel as defined above.

[0048] According to one aspect, the present invention relates to a vehicle or vessel comprising an engine as defined above.

[0049] The present invention will be illustrated by the following embodiments, which are provided for illustrative purposes only.

[0050] Example

[0051] Fuel performance tests according to the invention were conducted using a reaction-controlled compression ignition engine (“RCCI” type). Engine operation in RCCI mode involves igniting a low-reactivity fuel through an energy input of a high-reactivity fuel. The low-reactivity fuel is indirectly injected or introduced into the engine during the intake phase. High-reactivity fuel, present in small amounts in the entire mixture, is injected directly into the cylinder in one or more injections, as in a compression ignition engine. This involves premixing the low-reactivity fuel with air at the intake (thus knowing its enrichment), and then igniting it by one or more direct injections of small amounts of high-reactivity fuel. Therefore, each point can be controlled independently: the premix enrichment, the conditions of the low-reactivity mixture (temperature, pressure), and the injection of the high-reactivity fuel (pressure, duration, staged injection).

[0052] Research using RCCI engines allows for appropriate limitation of fuel load responsiveness, and its relative amount, timing, and combustion can be adjusted for optimal operation.

[0053] Experimental data collected for each embodiment are presented with respect to the applied indicated mean pressure (IMP) and the applied air / NH3 mixing ratio.

[0054] Indicated mean pressure (IMP) corresponds to the average pressure in the cylinder caused by fuel combustion. It represents the work done by this combustion in relation to engine displacement.

[0055] The experimental data measured in the combustion chamber are as follows:

[0056] -P: Pressure in the combustion chamber

[0057] -T: Temperature in the combustion chamber,

[0058] -Q: Heat generated through combustion.

[0059] These experimental data are related to crankshaft angle. The changes are reported.

[0060] For Examples 1 and 2, after ammonia is introduced in a gaseous phase premixed with air, ignition fuel is injected at a CA angle of -10°.

[0061] Example 1

[0062] In this embodiment, the ignition fuel is dodecane alone (hexadecane number > 67) (0% 2-ethylhexyl nitrate) or dodecane (hexadecane number > 67) containing 1% or 10% 2-ethylhexyl nitrate (EHN). The primary fuel is ammonia.

[0063] The amount of ignition fuel injected corresponds to a PEF of 2% of the total energy input relative to the ammonia + ignition fuel mixture. The ignition fuel accounts for 0.9% by weight of the total fuel (ammonia + ignition fuel).

[0064] Steady-state operation under hot conditions (inlet air temperature = 80℃)

[0065] For an air / NH3 ratio of Φ = 0.7 and an intake air temperature of 80°C, the engine operating point corresponds to an IMP of 3 bar. Experimental data were collected after at least 200 engine operating cycles.

[0066] Under these operating conditions, ammonia used alone without ignition fuel did not ignite.

[0067] refer to Figure 1 , Figure 2 and Figure 3 We observed that:

[0068] - When the ignition fuel consists of dodecane and does not contain EHN, the first pressure peak appears almost at TDC (mixture compression, CA = 0°), the second pressure peak appears at around 20°, and the peaks of heat release and temperature rise due to the start of combustion are observed at an angle of approximately CA = 5°.

[0069] - When the ignition fuel consists of dodecane and contains 1% by weight of EHN, the pressure continues to increase after an angle of approximately CA = 0°. A very slight plateau is observed, but the pressure continues to increase until an angle of approximately CA = 20°. Combustion is initiated at an angle of approximately CA = 0°, generating heat and causing the temperature to rise.

[0070] - When the ignition fuel consisted of dodecane and contained 10% by weight of EHN, a sustained increase in pressure was observed after the pressure peak caused by compression, reaching a level higher than that observed for ignition fuel containing 1% EHN. Therefore, combustion initiated at a CA angle of approximately -2.5°. This improvement in heat generation initiation can also be seen in the temperature and heat release curves based on CA.

[0071] In summary, injecting highly reactive alkane ignition fuel (high cetane number) containing up to 10% EHN (dodecane in this example) can significantly improve ignition delay, combustion, and heat generation.

[0072] No significant difference was observed in the same type of test conducted with dodecane-ignited fuel containing 30% EHN compared to tests conducted with dodecane-ignited fuel containing 10% EHN by weight.

[0073] Cold start and warm start

[0074] The advantages of ignition fuel, as described in this article, are also confirmed in terms of cold ignition. For an air / NH3 enrichment of Φ = 1 and intake air temperatures of 80°C (hot) and 30°C (cold), the engine operating point corresponds to approximately 8.5 bar IMP. The fuel PEF is 2%.

[0075] Under these operating conditions, and in a cold environment with an intake air temperature of 30°C, the following fuels did not ignite combustion:

[0076] -Ammonia alone,

[0077] -Ammonia + Ignition fuel consisting only of dodecane (excluding EHN),

[0078] -Ammonia+ is an ignition fuel consisting of dodecane and containing 1% by weight of EHN.

[0079] refer to Figure 4 and Figure 5 Combustion initiation was observed in both hot and cold conditions when fuel was ignited with dodecane containing 10% by weight of EHN.

[0080] Compare Figure 4 and Figure 5 During cold and hot operation, the following observations were made:

[0081] - IMP is higher in cold conditions because the combustion duration is longer, recovering more energy throughout the cycle, even if the peak of thermal release is lower.

[0082] Combustion begins later at low temperatures than at high temperatures. At low temperatures, combustion begins at a CA angle of approximately 5°, while at high temperatures, combustion begins at a CA angle of approximately 0°.

[0083] - Combustion pressure and temperature are lower when the air is cold.

[0084] The same type of test conducted with dodecane-ignited fuel containing 30% by weight of EHN showed no significant difference from the test conducted with dodecane-ignited fuel containing 10% by weight of EHN.

[0085] In summary, for Example 1, the ignition fuel consisting of dodecane and containing 10% by weight EHN (which is present in all fuels at a low PEF of 2% (corresponding to 110 ppm to 1200 ppm by weight of total fuel (ammonia + ignition fuel)) significantly improves engine performance at both high and low temperatures.

[0086] In this embodiment, increasing the EHN content to more than 10% by weight did not result in any significant performance improvement.

[0087] Tables 1 and 2 summarize the results of Example 1.

[0088] Table 1

[0089]

[0090]

[0091] * Combustion stability index after 200 cycles.

[0092] Table 2

[0093]

[0094] Example 2

[0095] In this embodiment, the ignition fuel is hydrogenated vegetable oil HVO100 (cetane number > 60) sold by TotalEnergies, which is either alone (0% 2-ethylhexyl nitrate) or contains 1% or 10% by weight of 2-ethylhexyl nitrate (EHN). The primary fuel is ammonia.

[0096] The amount of ignition fuel injected corresponds to a PEF of 2% relative to the total energy input of the mixture (ammonia + ignition fuel) in terms of energy input. The ignition fuel accounts for 1.1% by weight of the total fuel (ammonia + ignition fuel).

[0097] Steady-state operation (intake air temperature = 80℃)

[0098] For an air / NH3 enrichment ratio of Φ = 0.7 and an intake air temperature of 80°C, the engine operating point corresponds to an IMP of 3 bar. Experimental data were collected after at least 200 engine operating cycles.

[0099] refer to Figure 6 , Figure 7 and Figure 8 We observed that:

[0100] - When the ignition fuel consists of HVO and does not contain EHN, the first pressure peak appears at approximately CA = 0° TDC, the second peak appears at approximately CA = 20°, and the peak for heat release and temperature rise due to the start of combustion appears at approximately CA = 5°.

[0101] - When the ignition fuel consists of HVO and contains 1% EHN by weight, the combustion profile is similar to that obtained with ignition fuel consisting of HVO and containing no EHN. The ignition fuel consisting of HVO and containing 1% EHN by weight provides a small but significant improvement in ignition advance, heat, pressure, and temperature peaks.

[0102] - When the ignition fuel consisted of HVO and contained 10% EHN by weight, a sustained increase in pressure was observed after the pressure peak caused by compression, reaching a level higher than that observed for ignition fuel containing 1% EHN. Combustion initiation began at an angle CA of approximately -2.5°. This improvement in heat generation initiation can also be seen in the temperature and heat release curves based on CA.

[0103] In summary, injecting an ignition fuel consisting of HVO (cetane number > 67) and containing 10% EHN significantly reduces combustion initiation delay and generates heat.

[0104] No significant difference was observed in the same type of test conducted with an ignition fuel consisting of HVO and containing 10% EHN by weight compared to the test conducted with an ignition fuel consisting of HVO and containing 30% EHN by weight.

[0105] Cold start and warm start

[0106] The advantages of the ignition fuel described in this article are also confirmed in terms of cold ignition. For an air / NH3 enrichment ratio of Φ = 1 and intake air temperatures of 80°C (hot) and 30°C (cold), the engine operating point corresponds to approximately 8.5 bar IMP. The fuel PEF is 2%.

[0107] Under these operating conditions, and in a cold environment with an intake air temperature of 30°C, the following fuels did not ignite combustion:

[0108] -Ammonia alone,

[0109] -Ammonia + Ignition fuel consisting only of HVO (excluding EHN),

[0110] -Ammonia + an ignition fuel composed of HVO and containing 1% by weight of EHN

[0111] -Ammonia + an ignition fuel consisting of HVO and containing 10% by weight of EHN.

[0112] refer to Figure 9 As shown in Figure 10, ignition combustion was observed under both hot and cold conditions using an ignition fuel composed of HVO and containing 30% by weight of EHN.

[0113] Compare Figure 9 And in the cold and hot operation shown in Figure 10, we observed:

[0114] Under cold conditions, combustion begins later than under hot conditions, and for simultaneous injections, it lasts for a shorter time. Under cold conditions, combustion begins at an angle CA of approximately 5°, while under hot conditions, combustion begins at an angle CA of approximately 0°.

[0115] In summary, for Example 2, the ignition fuel, which consists of HVO and contains at least 10% EHN (which is present in the total fuel at a low PEF of 2% (corresponding to 0.14% by weight of the total fuel (ammonia + ignition fuel)), significantly improved engine performance.

[0116] Tables 3 and 4 summarize the results of Example 2.

[0117] Table 3

[0118]

[0119] *CA 50 °: The average angle determined to achieve 50% combustion energy.

[0120] Table 4

[0121]

Claims

1. A combustion engine fuel comprising 95.00% to 99.75% by weight of ammonia and 0.25% to 5.00% by weight of an ignition fuel, said ignition fuel comprising a hydrocarbon with a cetane number greater than 60 and containing 0.02% to 30.0% by weight of an alkyl nitrate or a mixture of alkyl nitrates.

2. The fuel according to claim 1, wherein, The ignition fuel contains 0.5% to 30.0% by weight, preferably 1.0% to 30% by weight, more preferably 1.0% to 20.0% by weight, and most preferably 1.0% to 10.0% by weight of alkyl nitrate or a mixture of alkyl nitrates.

3. The fuel according to claim 1 or 2, wherein, The hydrocarbons are selected from at least one of the following compounds: diesel fuel with low aromatic content (<10%) and low polyaromatic content (<10%), hydrogenated vegetable oil (HVO), isoalkanes, n-alkanes and sustainable aviation fuels.

4. The fuel according to any one of claims 1 to 3, wherein, Alkyl nitrate esters are linear alkyl nitrate esters having 4 to 36 carbon atoms, branched alkyl nitrate esters having 4 to 36 carbon atoms, cyclic alkyl nitrate esters having 5 to 18 carbon atoms, or mixtures thereof.

5. The fuel according to any one of claims 1 to 4, wherein, Alkyl nitrates are 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, and C9-C nitrate. 13 Mixtures of branched alkyl esters, and mixtures thereof.

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

7. A method for obtaining fuel according to any one of claims 1 to 6, comprising mixing an ignition fuel and liquefied or gaseous ammonia premixed with or not premixed with intake air in the combustion chamber of an engine.

8. The method according to claim 7, wherein, The ignition fuel and ammonia are injected together into the combustion chamber through a dual injection system.

9. The method according to claim 7, wherein, Ignition fuel is injected into the combustion chamber before ammonia is introduced or injected.

10. The method according to claim 7, wherein, After ammonia enters or is injected, ignition fuel is injected into the combustion chamber.

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

12. A vehicle or vessel comprising an engine as defined in claim 11.

13. Use of an ignition improver for an ammonia-based fuel, wherein the ammonia-based fuel comprises 95.00% to 99.75% by weight of ammonia, the amount of the ignition improver in the ammonia-based fuel is 0.25% to 5.0% by weight, the ignition improver comprises a hydrocarbon with a cetane number greater than 60 and contains 0.02% to 30.0% by weight of alkyl nitrates or mixtures of alkyl nitrates.

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