Engine fuel based on a mixture of alcohol and water and containing an additive for improving combustion

Abstract

The invention relates to a fuel for a combustion engine, comprising: - 95.0% to 99.9% by weight of a mixture of alcohol and water, the water representing 1% to 15% by weight of the mixture; and - 0.01% to 5.0% by weight of an alkyl nitrate.

Description

[0001] Engine fuel based on a mixture of alcohol and water and containing a combustion-enhancing additive

[0002] Field of invention

[0003] The field of the invention is that of fuels for combustion engines. The fuel of the invention is one of the new fuels with reduced environmental impact, for example those commonly called "e-fuels" when they are produced from low-carbon electricity, low-carbon hydrogen, and / or from CO2. They are considered a solution for the decarbonization of transport. The fuel of the invention is essentially composed of a mixture of alcohol and water, and is thus one of the ecological alternatives for replacing fossil fuels. Water represents up to 15% by mass of said mixture. The function of water is to reduce the production of nitrogen oxides in the combustion products of the engine. Alcohol is therefore the majority component of the fuel. The invention relates to an additive which, incorporated into the mixture of alcohol and water, ensures better ignition and faster combustion of the fuel in the engine.

[0004] State of the art

[0005] Methanol, such as "e-fuels," represents a credible low-impact alternative to replace fossil fuels and biofuels in combustion engines in the near future. Combustion of the resulting methanol results in a CO2-neutral balance. Methanol as a fuel has a usable energy density in combustion engines but has a low cetane number. Its ignition in compression-ignition engines, such as diesel, is problematic, especially at low engine speeds. Various methods for improving the ignition of methanol in a compression-ignition engine have been described.

[0006] The first method is the co-injection of a pilot fuel or an additive into the engine with methanol. For example, patent application CN 214944586 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 composed primarily of gaseous methanol. During combustion in a specific RCCI (Reactivity Compression Controlled Ignition) mode, a well-mixed low-reactivity fuel and oxidant (usually air) are compressed to a gaseous state but do not reach auto-ignition.Later, still during the compression cycle, high reactivity fuel, here NEH, is injected to form a local mixture of low and high reactivity fuel. A mass rate of NEH of 7% co-injected in the presence of gaseous methanol is likely to lead to an acceptable combustion efficiency in comparison with a reference fuel consisting of a mixture of isooctane and n-heptane. This type of process has the major disadvantage of requiring co-injection control according to the engine operating conditions, structural arrangements such as separate tanks and injection systems. Also, the use of a fuel as a pilot fuel generates CO2 emissions with a negative impact on the environment.

[0007] The second method is a mixture of fuels with methanol. It is known to mix alcohols, such as methanol or ethanol, in minority or majority proportions with fossil or synthetic diesel fuels such as dimethyl ether (DME) or with gasoline. In this case, the CO2 emissions balance has a negative impact on the environment.

[0008] The third method is the incorporation of an ignition-enhancing additive mixed with methanol, possibly also mixed with diesel fuel. Many patent applications, such as patent applications CN 103865592 and CN 104232180, describe the incorporation of a cocktail of multifunctional additives mixed with methanol, possibly also mixed with fuel. These additives have, for example, preservation, anti-corrosion, combustion-improving, and detergency functions. These additives generally represent at least 10% of the mass of the fuel. The proportion of methanol in the fuel is between 30% and 90% by mass depending on the mass percentages of additives and diesel fuel present in the fuel. The combined effects of these additives are only observed globally without precisely measuring the necessary quantities. It is therefore not a fuel essentially composed of methanol.

[0009] It is also known to blend diesel, biodiesel and / or alcohol fuels with water (typically up to 15% by mass) to reduce the production of nitrogen oxides in the combustion products of compression or spark engines. On the other hand, the addition of water reduces the combustion temperature and the flammability of the fuel. US Patent 7,216,607 and the scientific article "Performance and NOx Emissions of Spark Ignited Combustion Engines Using Alternative Fuels—Quasi One-Dimensional Modeling II. Methanol Fueled Engine" (Combustion Science and Technology Volume 18, 1978 - Issue 5-6) describe these effects of adding water to fuels.

[0010] On another level, in the field of hydrocarbon diesel or biodiesel fuels, 2-ethylhexyl nitrate (NEH) has been known for a long time as a cetane improver for diesel fuel. A higher cetane value ensures lower fuel consumption, reduced particulate matter and NOx emissions, faster cold engine starting, reduced engine knocking and noise, and reduced engine wear. The reaction mechanism of NEH in the presence of a hydrocarbon diesel fuel has been studied, for example, in the scientific publication "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 effect on improving diesel fuel cetane remains poorly understood and its use is based on empirical laws. For this reason, its effectiveness on fuels other than diesel fuels cannot be assumed. This additive is produced industrially and widely used in commercial diesel fuels. More than fifty thousand tons of NEH have been produced annually in Europe since the 1980s. Other alkyl nitrates can also be used as additives to improve the cetane index of diesel fuel.

[0011] Patent application EP 030 429 describes a fuel comprising a mixture of (A) at least one alcohol having an average molecular weight of less than 160 and (B) at least one other organic compound or mixture of organic compounds which together have a spontaneous ignition temperature of less than 450°C. Compound (B) may be, among several possibilities, an organic compound selected from azo compounds, tetrazines, nitroso compounds, nitro compounds, nitrates and hyponitrites, it being understood that this compound (B) does not consist entirely of a C2-C8 alkyl nitrate. It should be noted that the only example of a fuel containing water does not contain an alkyl nitrate.

[0012] The present invention provides a solution for improving the ignition of a fuel consisting essentially of a mixture of alcohol and water (also referred to in the remainder of the document as an alcohol / water mixture) in combustion engines. This improvement is obtained by adding the NEH additive alone in a small mass proportion to the alcohol / water mixture. More broadly, other alkyl nitrates, whose cetane index improvement power is known in a similar manner to NEH for a diesel fuel, are also recommended in the context of the present invention for improving the ignition of the methanol / water mixture. It is unexpected that additives known to increase the cetane index of a diesel or biodiesel hydrocarbon can be used so effectively, at a very low mass percentage, to improve the ignition of an alcohol such as methanol in a mixture with water.

[0013] Summary of the invention

[0014] The invention relates to a liquid fuel for a combustion engine, by compression auto-ignition or by spark ignition comprising about 95.0% to 99.9% by mass of a mixture of alcohol and water and about 0.01% to 5.0% by mass of a compound for improving the ignition delay of the fuel, the mixture of alcohol and water consisting of about 1% to 15% by mass of water and about 85% to 99% by mass of alcohol.

[0015] The said compound to improve fuel ignition delay is an alkyl nitrate, which is liquid at room temperature, low flammability, non-toxic and industrially produced.

[0016] The said compound, at these low levels in the presence of the alcohol / water mixture, is therefore conventionally considered a fuel additive.

[0017] The addition of said liquid compound to the alcohol / water mixture is carried out in the liquid state to form the fuel according to the invention in a tank. It can also be stored separately and mixed with the alcohol / water mixture to form the fuel according to the invention prior to its injection into the engine, or co-injected to form the fuel according to the invention in a premixing chamber of the engine.

[0018] The said compound, of the alkyl nitrate type, previously reserved for improving the cetane index of fossil diesel or biodiesel hydrocarbon fuels, is therefore used effectively and surprisingly as additives to improve the ignition of alcohol mixed with water.

[0019] Brief description of the figures

[0020] Figure 1 shows the effect of NEH on the ignition delay of a methanol / water mixture, with water representing 5% by mass of the mixture, with a single main injection (circular dots in the figure) or a micro-injection followed by a main injection (square dots in the figure) in the engine cylinder.

[0021] Figure 2 shows the effect of NEH on the ignition delay of a methanol / water mixture, with water representing 10% by mass of the mixture, with a single main injection (circular points in the figure) or a micro-injection followed by a main injection (square points in the figure) in the engine cylinder. Description of the invention

[0022] For the purposes of the present disclosure, alcohol means an alcohol comprising from 1 to 4 carbon atoms. According to one embodiment, the alcohol is methanol or ethanol, advantageously methanol.

[0023] The present disclosure relates to a combustion engine fuel, whether compression-ignited or spark-ignited, which comprises about 95.0% to 99.9% by mass of a mixture of alcohol and water, the water comprising from 1% to 15% by mass of the mixture, and about 0.01% to about 5.0% by mass of an alkyl nitrate.

[0024] In one embodiment, the fuel comprises about 0.1% to about 3% by weight of alkyl nitrate.

[0025] In one embodiment, the fuel of the invention consists of the alcohol / water mixture and the alkyl nitrate (and in this case, the amount of alkyl nitrate in the fuel is at least 0.1% by mass).

[0026] In another embodiment, when the sum of the amount of the alcohol / water mixture and the amount of alkyl nitrate is not equal to 100% by mass, the fuel may contain one or more other additives to make the fuel 100%, such as additives with preservative, anti-corrosion or detergency functions.

[0027] In one embodiment, the fuel according to the invention does not comprise an unsaturated fatty acid dimer and / or a phosphorous acid ester. In another embodiment, which can be combined with the previous one, the fuel according to the invention does not comprise a C8-C2o aliphatic monocarboxylic acid. In another embodiment, which can be combined with the two previous ones, the fuel according to the invention does not comprise a mixture of C4 and / or C5 / C6 and / or C5-C7 hydrocarbons, nor a mixture of gasoline with at least one of said hydrocarbons.

[0028] The alkyl nitrate, added to the alcohol / water mixture, is more particularly chosen from linear alkyl nitrates comprising 4 to 36, advantageously 4 to 24 carbon atoms, branched alkyl nitrates comprising 4 to 36, advantageously 4 to 24 carbon atoms, cyclic alkyl nitrates (or cycloalkyl nitrate) comprising 5 to 18 carbon atoms, and mixtures thereof. In one embodiment, said alkyl nitrate is selected from 2-ethylhexyl nitrate, hexyl nitrate, cyclohexyl nitrate, 2-octyl nitrate, n-nonyl nitrate, isononyl nitrate, dodecyl nitrate, 2-propylheptyl nitrate, 2-tetradecyl-1-octadecyl nitrate, a mixture of C9-C13 branched alkyl nitrates, and mixtures thereof.In one embodiment, the alkyl nitrate is 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.

[0029] According to one embodiment, the compound for improving fuel ignition, i.e. the alkyl nitrate, is mixed in the liquid state with the alcohol / water mixture in the tank which supplies the engine, to obtain the fuel according to the invention.

[0030] According to one embodiment, said alkyl nitrate on the one hand, and the alcohol / water mixture on the other hand, are stored separately, and brought into contact with each other in the liquid state in an injector, thus forming the fuel according to the invention before it is conveyed into the combustion chamber of the engine.

[0031] According to one embodiment, said alkyl nitrate is stored separately from the alcohol / water mixture and is co-injected with the methanol / water mixture to form the liquid fuel according to the invention in a premixing chamber of the engine.

[0032] The present disclosure also relates to the use of an alkyl nitrate e, in the proportions defined above, as an agent for improving the ignition of a fuel based on (consisting of) alcohol and water.

[0033] The present disclosure also relates to a method for improving the ignition of a fuel based on (consisting of) a mixture of alcohol and water in an engine (in particular a combustion engine), the method comprising adding to said mixture an alkyl nitrate (as defined above), in the proportions defined above. In one embodiment, the alkyl nitrate and the alcohol / water mixture are mixed in an injector. In one embodiment, the alkyl nitrate and the alcohol / water mixture are mixed in a premixing chamber of the engine.

[0034] The present disclosure also relates to an engine (in particular a combustion engine) of a vehicle (such as a car, heavy goods vehicle, tractor, etc.) or a ship (such as an oil tanker, container ship, etc.) containing a fuel as defined above. The present disclosure also relates to a vehicle or ship comprising an engine as defined above.

[0035] This disclosure is illustrated by the following examples, given for information purposes.

[0036] Examples

[0037] The performance of the fuel according to the invention compared to a fuel composed solely of methanol and water was measured with an experimental laboratory engine with compression ignition, single cylinder with a volume of 0.499 L with direct injection, targeting an indicated mean pressure (IMP) of 3 Bars at 1500 rpm. After having passed 100 cycles (necessary for the calculations to come to have a consistent average of the values), the values ​​of the engine operating parameters are measured. At the same time, it is possible to record 20 pollutant measurement cycles, each spaced 5 seconds apart to have a representative average of the emissions of different cycles. From the values ​​previously recovered, the following quantities characterizing the combustion of the fuel and the operation of the engine are extracted:

[0038] - dAI Auto-Ignition delay (ms),

[0039] - the Indicated Mean Pressure (IMP)

[0040] - the Covariance of the PMI (COVPMI),

[0041] - the CAI angle,

[0042] - angle CA50,

[0043] - the combustion duration,

[0044] - pollutants (NOx, CO, H2O, HC),

[0045] - the heat release rate.

[0046] The addition of said compound with the methanol / water mixture improves all the combustion and operating parameters of the engine compared to a fuel consisting solely of a methanol / water mixture. The performance of the fuel of the invention can be further improved by controlling the injection of the fuel with multiple injections at each engine cycle, for example with one or more micro-injections called pilot injections followed by a main injection.

[0047] The ignition delay as a function of the fuel inlet temperature is the resulting value of the tests which is presented below to illustrate in the following examples the advantages of the invention.

[0048] The ignition delay dAI is defined according to the following formula in which Pc is the pressure applied to the injected fuel:

[0049] Example 1

[0050] This example concerns the improvement by addition of the NEH compound of the combustion performance in the engine of a mixture consisting of 95% by mass of methanol and 5% by mass of water.

[0051] The ignition delays were determined as a function of the intake temperature (from 313 K to 473 K), at a pressure Pc of 300 bars, of a fuel according to the invention consisting of 99% by mass of methanol / water mixture, the water representing 5% by mass of the mixture, and 1% by mass of NEH and for a richness of 0.25 of mixture with air. The results are shown in Figure 1 with the reference points of the ignition delay of the methanol / water mixture (in mass ratio 95% / 5%) alone. A significant reduction in the ignition delays of the fuel containing NEH is observed, compared to the methanol / water fuel. This reduction in the ignition delay compared to that of the methanol / water fuel alone is all the more significant as the temperature is low.For operation with a single main injection, at an intake temperature of 403 K, the ignition delay of the fuel of the invention according to the present example is approximately 3 times lower than that of the reference fuel comprising methanol and water. The fuel of the invention ignites even at low intake temperatures below 403 K, up to 373 K with an ignition delay of 2 ms, for which the methanol / water mixture does not ignite.

[0052] Under multiple injection conditions involving a micro-injection (lasting 400 ps at a crank angle of -25°) followed by a main injection (lasting 1500 ps at a crank angle of -15°), an improvement in the combustion characteristics of the methanol / water mixture is observed, which ignites at 373 K with an ignition delay of approximately 1.75 ms. The combustion of the methanol / water mixture under these conditions and at this temperature is therefore close to that of the methanol / water fuel with the addition of 1% by mass of NEH in operation with a single main injection. Below 373 K, the methanol / water mixture does not ignite. In contrast, the fuel comprising 1% by mass of NEH ignites at temperatures as low as 313 K with an ignition delay of approximately 1.2 ms.

[0053] Example 2

[0054] This example concerns the improvement of performance by adding NEH to the combustion in an engine of a mixture consisting of 90% by mass of methanol and 10% by mass of water.

[0055] The ignition delays were determined as a function of the intake temperature (between 313 K and 463 K), at a pressure Pc of 300 bars, of a fuel according to the invention consisting of 98% by mass of methanol / water mixture, the water representing 10% by mass of the mixture, and 2% by mass of NEH and for a richness of 0.25 of mixture with air. The results are shown in Figure 2 with the reference points of the ignition delay of the methanol / water mixture alone. For an addition of 1% by mass of NEH, an improvement in the combustion performance of the fuel is observed for intake temperatures below 433 K. For an intake temperature of 413 K, the fuel which contains 1% by mass of NEH has an ignition delay approximately 1.5 times lower than the reference fuel methanol / water. For an inlet temperature of 413 K with a mass rate of 2% NEH, the ignition delay at this temperature is 2 times lower than that of the methanol / water mixture.At an inlet temperature of 403 K, the methanol / water mixture does not ignite, whereas fuels containing 1% by mass NEH and 2% by mass NEH ignite with a delay of approximately 4 ms and 2.2 ms, respectively.

[0056] Under these multiple injection conditions involving a micro-injection (lasting 400 ps at a crank angle of -25°) followed by a main injection (lasting 1500 ps at a crank angle of -15°), an improvement in the combustion characteristics of the methanol / water mixture is observed, which ignites at 393 K with an ignition delay of approximately 3.5 ms. Below 393 K, the methanol / water mixture does not ignite. On the other hand, the fuel comprising 1% by mass of NEH ignites for temperatures as low as 383 K with an ignition delay of approximately 1.5 ms. The fuel comprising 2% by mass of NEH ignites up to 333 K with an ignition delay of approximately 1.75 ms. The results of Examples 1 and 2 are summarized in Table 1.

[0057] Table 1 These examples show that the use of alkyl nitrate in low mass percentages makes it possible to significantly improve the ignition delay of an alcohol and water-based fuel. More generally, the addition of an alkyl nitrate-type compound to an alcohol / water mixture improves the overall performance of the fuel in a combustion engine, while maintaining limited nitrogen oxide emissions, up to intake temperatures close to ambient temperature. Nothing could have suggested that additives known to increase the cetane number of a diesel or biodiesel hydrocarbon could be used so effectively, in very small quantities, to improve the ignition of an alcohol mixed with water.

Claims

Claims 1. Fuel for a combustion engine comprising 95.0% to 99.9% by mass of a mixture in the liquid state of alcohol and water, the water representing from 1% to 15% by mass of the mixture, and from 0.01% to 5.0% by mass of an alkyl nitrate in the liquid state, said alkyl nitrate being a linear alkyl nitrate having from 4 to 36 carbon atoms, a branched alkyl nitrate having from 4 to 36 carbon atoms, a cyclic alkyl nitrate having from 5 to 18 carbon atoms, or a mixture of these nitrates.

2. Fuel according to claim 1, comprising 95.0% to 99.9% by mass of alcohol and water mixture and 0.1% to 3% by mass of alkyl nitrate.

3. Fuel according to any one of claims 1 to 2, wherein the alkyl nitrate is selected from 2-ethylhexyl nitrate, hexyl nitrate, cyclohexyl nitrate, 2-octyl nitrate, n-nonyl nitrate, isononyl nitrate, dodecyl nitrate, 2-propylheptyl nitrate, 2-tetradecyl-1-octadecyl nitrate, isononyl to isotridecyl nitrate, and mixtures thereof.

4. Fuel according to claim 3, wherein the alkyl nitrate is 2-ethylhexyl nitrate.

5. Fuel according to any one of claims 1 to 4, wherein the alcohol is methanol or ethanol.

6. Fuel according to claim 5, wherein the alcohol is methanol.

7. A method of obtaining a fuel according to any one of claims 1 to 6, which comprises mixing in the liquid state the alkyl nitrate with a liquid mixture of alcohol and water.

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

9. The method of claim 7, wherein the mixture of alcohol and water and the alkyl nitrate are mixed in an injector.

10. The method of claim 7, wherein the alcohol and water mixture and the alkyl nitrate are mixed in a premixing chamber of an engine.

11. Use of an alkyl nitrate in the liquid state, in an amount of 0.01% to 5.0% by mass, in a liquid fuel based on alcohol and water, as an agent for improving the ignition of said fuel, said alkyl nitrate being a linear alkyl nitrate having from 4 to 36 carbon atoms, a branched alkyl nitrate having from 4 to 36 carbon atoms, a cyclic alkyl nitrate having from 5 to 18 carbon atoms, or a mixture of these nitrates.

12. Use according to claim 11, wherein the alcohol is methanol or ethanol, preferably methanol.

13. Use according to claim 11 or claim 12, wherein the alkyl nitrate is as defined in any one of claims 3 to 4.

14. A method for improving the ignition, in a combustion engine, of a fuel comprising from 95.0% to 99.9% by mass of a mixture of alcohol and water in the liquid state, comprising adding to said mixture an alkyl nitrate in the liquid state, in an amount of from 0.01% to 5.0% by mass, said alkyl nitrate being a linear alkyl nitrate having from 4 to 36 carbon atoms, a branched alkyl nitrate having from 4 to 36 carbon atoms, a cyclic alkyl nitrate having from 5 to 18 carbon atoms, or a mixture of these nitrates.

15. A method according to claim 14, wherein the alkyl nitrate is as defined in any one of claims 3 to 4.

16. A method according to claim 14 or claim 15, wherein the alcohol is methanol or ethanol, preferably methanol.

17. A combustion engine comprising a fuel as defined in any one of claims 1 to 6.

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