Methanol-based engine fuel containing combustion additive

Abstract

The invention relates to a fuel for a compression ignition engine, comprising 98.0% to 99.9% by mass of methanol and 0.01% to 2.0% by mass of an alkyl nitrate or a mixture of alkyl nitrate.

Description

Technical Field

[0001] The field of the invention is that of fuels for combustion engines. The fuels of the invention belong to a new class of fuels with a lower environmental impact, such as those commonly called "electrofuels" made from low-carbon electricity, low-carbon hydrogen and / or CO2. They are considered a solution for the decarbonization of transport. The fuels of the invention consist essentially (at least 98%) of methanol and are therefore part of an ecological alternative to fossil fuels. The invention relates to an additive which, when mixed with methanol, ensures better ignition and faster combustion of the fuel in an engine. Background Art

[0002] In the near future, methanol of the "e-fuel" type represents a reliable low environmental impact alternative to fossil fuels and biofuels for combustion engines. The combustion of the methanol thus produced results in a neutral CO2 balance. Methanol has a usable energy density as a fuel in combustion engines, but has a low cetane number. The ignition of methanol in compression ignition engines (such as diesel engines) is problematic, especially at low engine speeds. Different methods for improving the ignition of methanol in compression ignition engines have been described.

[0003] The first method is to co-inject a pilot fuel or additive with methanol into the engine. For example, patent application CN214944586 describes the co-injection of a diesel-type pilot fuel with methanol as the main fuel. The scientific article "Effect of Cetane Improvers on Gasoline, Ethanol, and Methanol Reactivity and the Implications for RCCI Combustion" (SAE International Journal of Fuels and Lubricants Vol. 6 No. 1 (April 2013) pp. 170-187) describes the co-injection of 2-ethylhexyl nitrate (NEH) with a fuel consisting mainly of methanol. During combustion in a specific RCCI (Reactive Compression Controlled Ignition) mode, a well-mixed fuel is compressed with a low-reactivity oxidizer (usually with air), but autoignition is not achieved. Subsequently, still during the compression cycle, a high-reactivity fuel (NEH in this case) is injected to form a local mixture of low-reactivity fuel and high-reactivity fuel. The mass ratio of the co-injected NEH is about 6%. The main disadvantage of this method is that it requires co-injection control according to the engine's operating conditions, structural arrangements (such as separate tanks and injection systems). In addition, the use of fuel oil as a pilot fuel will produce CO2 emissions, which has a negative impact on the environment.

[0004] The second method is to mix fuel and methanol. It is known that alcohols (such as methanol or ethanol) can be mixed with fossil fuels or synthetic diesel fuels (such as dimethyl ether (DME)) or gasoline in a minority or majority ratio. In this case, the CO2 emission balance is also unfavorable to the environment.

[0005] The third method is to mix the ignition improvement additive into the blend with methanol, and also into the blend with diesel. Many patent applications, such as CN 103865592 and CN 104232180, describe the multifunctional additive mixture into the blend with methanol, and also into the blend with fuel oil. These additives have functions such as protection, corrosion protection, improved combustion and cleaning. These additives usually account for at least 10% of the fuel weight. The proportion of methanol in the fuel is between 30% by weight and 90% by weight, depending on the weight percentage of the additive and diesel present in the fuel. In the absence of the dosage accurate to the necessary amount, the combined effect of these additives can only be observed in general. Therefore, it is not a fuel that is basically composed of methanol.

[0006] On another level, in the field of hydrocarbon diesel fuels or biodiesel fuels, 2-ethylhexyl nitrate (NEH) has long been known to be used as a cetane enhancer in diesel fuels. A higher cetane number ensures lower fuel consumption, reduced particulate matter and NOx emissions, faster engine cold starts, reduced engine knock and noise, and reduced engine wear. For example, the reaction mechanism of NEH in the presence of hydrocarbon diesel fuels has been studied in the scientific publication "The Autoignition Behavior of Surrogate Diesel Fuel Mixtures and the Chemical Effects of 2-Ethylhexyl Nitrate (2-NEH) Cetane Improver" (Vol. 108, Section 4: Journal of fuels and lubricants (1999), pp. 1029-1045). However, the reaction mechanism of its diesel fuel cetane improver effect is still unclear and its use is still based on empirical laws. Therefore, it cannot be assumed that it is effective for fuels other than diesel. This additive has been produced industrially and is widely used in commercial diesel fuels. Over 50,000 tonnes of NEH have been produced in Europe each year since the 1980s. Other alkyl nitrates are also used as cetane enhancing additives in diesel fuel. Figure 1 The effects of different alkyl nitrates on cetane number are shown to be similar to NEH, except for standard diesel fuel (medium paraffin (~40%), low natural cetane number, but with standard cetane enhancement response). Cetane enhancement effect is obtained when the alkyl nitrate is incorporated into diesel fuel at a level close to 0.03 wt%.

[0007] The present invention provides a solution for improving the ignition of methanol in combustion engines. This improvement is obtained by adding NEH alone in a very small weight percentage in a mixture with methanol fuel. More generally, in the context of the present invention, other alkyl nitrates known to have cetane improving properties similar to NEH for diesel fuel are also advocated for improving the ignition of methanol. It is surprising that additives known to increase the cetane number of diesel hydrocarbons or biodiesel hydrocarbons can be so effectively used to improve the ignition of alcohols such as methanol at very low weight percentages. Summary of the invention

[0008] The present invention relates to a fuel comprising 98.0 to 99.9 wt % of methanol for a compression self-ignition engine or a spark ignition engine and 0.01 to 2.0 wt % of a compound for improving the ignition delay of methanol.

[0009] The compound is an alkyl nitrate.

[0010] The compound has the advantages of being liquid at room temperature, having low flammability, being non-toxic, and being industrially producible.

[0011] Therefore, at these low levels in the presence of fuel methanol, the compound is generally assimilated as a fuel additive.

[0012] The addition of the liquid compound is carried out in a mixture with liquid methanol to form the fuel according to the invention in the tank. It can also be stored separately and then mixed with methanol to form the fuel according to the invention before injecting it into the engine, or injected together into the engine premixing chamber to form the fuel according to the invention.

[0013] The alkyl nitrate type compounds described, which have previously been used to improve the cetane number of fossil diesel or biodiesel hydrocarbon fuels, are therefore effectively and unexpectedly used as additives for improving the ignition of methanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The effect of alkyl nitrates on the cetane number of a standard diesel fuel is shown.

[0015] Figure 2 The effect of NEH on the ignition delay of methanol at a compression pressure Pc of 30 bar and a richness (air / fuel) of 0.5 is shown: left curve = fuel composed of 100% methanol; right curve = fuel composed of 99.8% methanol and 0.2% NEH.

[0016] Figure 3The effect of NEH on the ignition delay of methanol at a compression pressure Pc of 30 bar and a richness (air / fuel) of 1 is shown: left curve = fuel made of 100% methanol; right curve = fuel made of 99.8% methanol and 0.2% NEH.

[0017] Figure 4 The effect of NEH on the ignition delay of methanol at a compression pressure Pc of 30 bar and a richness (air / fuel) of 1.5 is shown: left curve = fuel made of 100% methanol; right curve = fuel made of 99.8% methanol and 0.2% NEH.

[0018] Figure 5 The curves showing the ignition delay as a function of temperature for methanol-based fuels containing different amounts of NEH at a compression pressure Pc of 30 bar and a richness (air / fuel) of 1 are: curves from left to right = fuel consisting of 100% methanol; fuel consisting of 99.8% methanol and 0.2% NEH; fuel consisting of 99.5% methanol and 0.5% NEH; fuel consisting of 99.0% methanol and 1.0% NEH.

[0019] Figure 6 The ignition delay of methanol-based fuels containing different amounts of NEH in the temperature range of 850K to 1000K is shown at a compression pressure Pc of 30 bar and a richness (air / fuel) of 1.

[0020] Figure 7 for Figure 6 Expanded view over the 900K to 1000K temperature range. DETAILED DESCRIPTION

[0021] The present invention relates to a motor fuel (particularly for combustion engines) comprising about 98.0% to about 99.9% by weight of methanol and about 0.01% to about 2.0% by weight of a compound consisting of alkyl nitrates. In one embodiment, the fuel comprises about 0.05% to about 1.5% by weight of the compound. In another embodiment, the fuel comprises about 0.1% to about 1.0% by weight of the compound. In another embodiment, the fuel comprises about 0.1% to less than 1.0% by weight (<0.1%) of the compound.

[0022] In one embodiment, the fuel of the invention consists of methanol and the compound (in this case, the amount of the compound in the fuel is at least 0.1% by weight).

[0023] In another embodiment, when the sum of the amount of methanol and the amount of the compound is not equal to 100% by weight, the fuel may contain one or more other additives to complete the fuel to 100%, such as additives with protective, anti-corrosive or cleaning functions.

[0024] The compound added to the methanol is selected from one or more linear, branched or cyclic alkyl nitrates.

[0025] The compound is more particularly chosen from nitrates of linear alkyl groups having from 4 to 36 (advantageously from 4 to 24) carbon atoms, nitrates of branched alkyl groups having from 4 to 36 (advantageously from 4 to 24) carbon atoms, nitrates of cyclic alkyl groups having from 5 to 18 carbon atoms (or cyclic alkyl nitrates), 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 a mixture of 2-ethylhexyl nitrate and one or more other alkyl nitrates as defined above, advantageously the alkyl nitrate is 2-ethylhexyl nitrate.

[0026] Nitric acid C9 to C 13 The mixture of branched alkyl esters can be from C9 to C 13 Branched alcohols (e.g. from Exxon as Exxal TM As an example, a corresponding mixture of alcohols selected from C9 branched alcohols, C 10 Branched alcohol, C 11 Branched alcohol, C 12 Branched alcohol, C 13 A mixture of at least two branched alcohols of the branched alcohols can then give a corresponding mixture of alkyl nitrates.

[0027] According to one embodiment, the compound and methanol are stored separately and then brought together in an injector so as to form the fuel according to the invention before feeding it into the combustion chamber of the engine.

[0028] According to one embodiment, the compound is stored separately from the methanol and then co-injected with the methanol into the premixing chamber of the engine to form the fuel according to the invention.

[0029] The invention also relates to the use of an alkyl nitrate (as defined above) in the proportions defined above as an ignition improver for fuels based on (or consisting of) methanol.

[0030] The invention also relates to a method for improving the ignition of a fuel based on (or consisting of) methanol in an engine, in particular a combustion engine, said method comprising adding an alkyl nitrate (as defined above) to the methanol in the proportions defined above. In one embodiment, the alkyl nitrate and the methanol are mixed in an injector. In one embodiment, the alkyl nitrate and the methanol are mixed in a premixing chamber of the engine.

[0031] The invention also relates to a vehicle (e.g. car, truck, tractor, etc.) engine or a ship (e.g. tanker, container ship, etc.) engine (in particular a combustion engine) containing a fuel as defined above. The invention also relates to a vehicle or ship comprising an engine as defined above.

[0032] The present invention is illustrated by the following examples, which are provided for reference only.

[0033] Example

[0034] The ignition delay improvement of methanol was measured under test conditions equivalent to those described in the scientific article "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 equivalent to the engine described in this scientific article. This is a fast compressor used to measure the autoignition time of a mixture. The machine compresses the mixture in a very short time to reach preset pressure and temperature conditions. The liquid enters the tank through an orifice different from the gas inlet. The amount of liquid is measured with a syringe and a precision balance.

[0035] The ignition delay dAI is defined by the following formula, where Pc is the pressure applied to the injected fuel:

[0036]

[0037] Example 1

[0038] The ignition delay was determined as a function of the injection temperature (between 800 K and 1000 K) of the fuel according to the invention, which consisted of 99.8 mass % methanol and 0.2 mass % NEH, at a pressure Pc of 30 bar and a mixture with air of enrichments of 0.5, 1 and 1.5, respectively. The results are shown in Figure 2 , Figure 3 and Figure 4The ignition delay of methanol alone is used as the benchmark. When the fuel contains NEH, the fuel ignition delay is significantly reduced, about 5 to 10 times, compared to methanol alone. More importantly, this reduction in ignition delay is due to the low temperature compared to methanol alone.

[0039] Example 2

[0040] The ignition delay of different fuels containing methanol alone or a mixture of methanol with NEH (0.2 wt. %, 0.5 wt. % or 1 wt. %) was determined at different injection temperatures (temperature range 790 K to 1000 K) at a pressure Pc of 30 bar and a mixture with air enrichment of 1. Figures 5 to 7 As shown, adding NEH to methanol fuel can significantly reduce the ignition delay compared with methanol alone.

[0041] These examples show that the use of one or more alkyl nitrates at very low weight percents can significantly improve the ignition delay of methanol-based fuels. There is no reason to believe that additives known to increase the cetane number of diesel or biodiesel hydrocarbons can be so effectively used to improve the ignition of alcohols such as methanol in very small amounts.

Claims

1. A compression ignition engine fuel comprising 98.0 to 99.9 weight percent of liquid methanol and 0.01 to 2.0 weight percent of liquid alkyl nitrate.

2. The fuel according to claim 1, comprising 0.05 to 1.5 wt. %, in particular 0.1 to 1.0 wt. % of the alkyl nitrate.

3. The fuel according to any one of claims 1 to 2, wherein The alkyl nitrate is a nitrate of a linear alkyl group having 4 to 36 carbon atoms, a nitrate of a branched alkyl group having 4 to 36 carbon atoms, a nitrate of a cyclic alkyl group having 4 to 18 carbon atoms, or a mixture of these nitrates.

4. The fuel according to any one of claims 1 to 3, wherein The alkyl nitrate is selected from the group consisting of 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 alkyl esters, and mixtures thereof.

5. The fuel according to any one of claims 1 to 4, wherein The alkyl nitrate is 2-ethylhexyl nitrate.

6. The fuel according to any one of claims 1 to 5, which consists of 98.0% to 99.9% by weight of liquid methanol and 0.01% to 2.0% by weight of liquid alkyl nitrate.

7. A method for obtaining a fuel according to any one of claims 1 to 6, comprising mixing an alkyl nitrate with methanol in a liquid state.

8. The method according to claim 7, wherein: Mix methanol and alkyl nitrate in the engine oil tank.

9. The method according to claim 7, wherein: Methanol and alkyl nitrate were mixed in an injector.

10. The method according to claim 7, wherein: Methanol and alkyl nitrate are mixed in the engine's premix chamber.

11. Use of liquid alkyl nitrates in an amount of 0.01% to 2.0% by weight in a fuel based on liquid methanol as an ignition improver for said fuel.

12. The use according to claim 11, wherein The alkyl nitrate is as defined in any one of claims 3 to 5.

13. A method for improving the ignition of a fuel containing 98.0 to 99.9 wt. % liquid methanol in an engine, the method comprising adding liquid alkyl nitrate to the methanol in an amount of 0.01 to 2.0 wt. %, preferably 0.05 to 1.5 wt. %, more preferably 0.1 to 1.0 wt. %.

14. The method according to claim 13, wherein: The alkyl nitrate is as defined in any one of claims 3 to 5.

15. The method according to any one of claims 13 and 14, wherein: Alkyl nitrate and methanol were mixed in an injector.

16. The method according to any one of claims 13 and 14, wherein: The alkyl nitrate is mixed with methanol in the engine's premix chamber.

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

18. A vehicle or vessel comprising an engine as defined in claim 17.

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