Engine fuel based on a mixture of alcohol and water and containing a combustion-enhancing additive.

Abstract

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

Description

Title of the invention: Engine fuel based on a mixture of alcohol and water and containing a combustion-improving additive. Field of invention

[0001] 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 major 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.. State of the art

[0002] Methanol of the "e-fuels" type represents a credible low environmental impact alternative to replace fossil fuels and biofuels for combustion engines in the near future. The combustion of this methanol thus produced leads to a neutral CO2 balance. Methanol as a fuel has an energy density usable 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 means for improving the ignition of methanol in a compression ignition engine have been described.

[0003] The first method is the co-injection into the engine of a pilot fuel or an additive with the 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 essentially of methanol in the gaseous state. During combustion in a specific RCCI mode (from the English “Reactivity Compression Controlled Ignition”, in French “Allumage In "controlled reactivity partial compression", a well - mixed low - reactivity fuel and an oxidizer (usually air) are compressed in the 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 fuels. A mass fraction of 7% of NEH co - injected in the presence of gaseous methanol is likely to lead to an acceptable combustion efficiency compared to a reference fuel consisting of a mixture of isooctane and n - heptane. This type of process has the major drawback of requiring control of the co - injection according to the engine operating conditions, structural modifications such as reservoirs and separate injection systems. Also, the use of a fuel as a pilot fuel generates CO2 emissions with a negative environmental balance.

[0004] The second method is a mixture of fuels with methanol. It is known to mix alcohols, such as methanol or ethanol, in a minority or majority proportion with fossil or synthetic diesel fuels of the dimethyl ether (DME) type or with gasolines. In this case again the CO2 emission balance has a negative impact on the environment.

[0005] The third means is the incorporation of an ignition-enhancing additive mixed with methanol, possibly also mixed with a 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 a 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.

[0006] It is also known to mix diesel, biodiesel and / or alcohol type 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 IL Methanol Fueled Engine” (Combustion Science and Technology Volume 18, 1978 - Issue 5-6) describe these effects of adding water to fuels.

[0007] On another level, in the field of diesel or biodiesel hydrocarbon fuels, 2-ethylhexyl nitrate (NEH) has been known for a long time as a cetane improver additive 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 diesel hydrocarbon 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 diesel fuel cetane improvement effect is still poorly understood and its use is based on empirical laws. For this reason, its effectiveness on fuels other than diesel fuels cannot be presumed. This additive is produced industrially and widely used in commercial diesel fuels. Since the 1980s, more than fifty thousand tons of NEH have been produced annually in Europe. Other alkyl nitrates can also be used as additives to improve the cetane number of diesel fuel..

[0008] The present invention provides a solution for improving the ignition of a fuel consisting essentially of a mixture of alcohol and water (also called in the remainder of the document an alcohol / water mixture) in combustion engines. This improvement is obtained by adding in a small mass proportion the NEH additive alone with the alcohol / water mixture. More broadly, other alkyl nitrates, whose power to improve the cetane index is known in a similar way to NEH for a diesel fuel, are also recommended in the context of the present invention to improve 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. Summary of the invention

[0009] The invention relates to a liquid fuel for a combustion engine, by self-ignition by compression or by spark ignition comprising approximately 95.0% to 99.9% by mass of a mixture of alcohol and water and approximately 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 approximately 1% to 15% by mass of water and approximately 85% to 99% by mass of alcohol.

[0010] Said compound for improving the ignition delay of the fuel is a nitrate alkyl, which is liquid at room temperature, low flammability, non-toxic and produced industrially.

[0011] Said compound, at these low levels in the presence of the alcohol / water mixture, is therefore conventionally considered to be a fuel additive.

[0012] 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.

[0013] 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 for improving the ignition of alcohol mixed with water. Brief description of the figures

[0014] [Fig-1] shows the effect of NEH on the ignition delay of a methanol / water mixture, water representing 5% 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.

[0015] [Fig.2] shows the effect of NEH on the ignition delay of a methanol / water mixture, 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

[0016] For the purposes of the present disclosure, alcohol is understood to mean an alcohol comprising from 1 to 4 carbon atoms. According to one embodiment, the alcohol is methanol or ethanol, advantageously methanol.

[0017] The present disclosure relates to a combustion engine fuel, whether compression-ignited or spark-ignited, which comprises about 95.0% to 99.9% by weight of a mixture of alcohol and water, the water comprising from 1% to 15% by weight of the mixture, and about 0.01% to about 5.0% by weight of an alkyl nitrate.

[0018] In one embodiment, the fuel comprises about 0.1% to about 3% by weight of alkyl nitrate.

[0019] 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).

[0020] 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 complete the fuel 100%, such as additives with preservative, anti-corrosion or detergent functions.

[0021] Said 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 admixture with one or more other alkyl nitrates as defined above, advantageously the alkyl nitrate is 2-ethylhexyl nitrate.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 of a ship (such such as oil tanker, container ship, etc.) containing a fuel as defined above. This disclosure also relates to a vehicle or vessel comprising an engine as defined above.

[0028] The present disclosure is illustrated by the following examples, given for information purposes. Examples

[0029] 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 in order 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 ​​recovered previously, the following quantities characterizing the combustion of the fuel and the operation of the engine are extracted:

[0030] - dAI Auto-Ignition delay (ms),

[0031] - the Indicated Mean Pressure (PMI)

[0032] - the Covariance of the PMI (COVPMI),

[0033] -the angle CAI,

[0034] - angle CA50,

[0035] - the combustion duration,

[0036] - pollutants (NOx, CO, H2O, HC),

[0037] - the heat release rate.

[0038] The addition of said compound with the methanol / water mixture improves all of 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 then a main injection.

[0039] The ignition delay as a function of the fuel intake temperature is the resulting value of the tests which is presented below to illustrate in the following examples the advantages of the invention.

[0040] The ignition delay dAI is defined according to the following formula in which Pc is the pressure applied to the injected fuel: Example 1

[0041] This example relates to the improvement by addition of the NEH compound of the combustion performance in an engine of a mixture consisting of 95% by mass of methanol and 5% by mass of water.

[0042] 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 [Fig.l] 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.

[0043] Under multiple injection conditions comprising 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. On the other hand, the fuel comprising 1% by mass of NEH ignites for temperatures as low as 313 K with an ignition delay of approximately 1.2 ms. Example 2

[0044] This example relates to 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.

[0045] 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 [Fig. 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 intake 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.

[0046] Under these multiple injection conditions comprising 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.

[0047] The results of Examples 1 and 2 are summarized in Table 1.

[0048] [Tables 1] Methanol / water % by mass % by mass of NEH Single injection Micro-injection followed by a main injection Minimum ignition temperature (K) Ignition time (ms) 95% / 5% 0 X 403 4 1% X 373 2 0 X 373 1.75 1% X 313 1.25 90% / 10% 0 X 413 3.5 1% X 403 4 2% X 403 2.2 0 X 393 3.5 1% X 383 1.5 2% X 333 1.75

[0049] These examples show that the use of alkyl nitrate in a low mass percentage makes it possible to significantly improve the ignition delay of a fuel based on alcohol and water. More generally, the addition of an alkyl nitrate type compound in an alcohol / water mixture improves the overall performance of the fuel in a combustion engine, while maintaining limited emissions of nitrogen oxides, up to intake temperatures close to ambient temperature. Nothing could suggest that additives known to increase the cetane number of a diesel or biodiesel hydrocarbon could be used as effectively, in very small quantities, to improve the ignition of an alcohol mixed with water.

Claims

Claims

1. A fuel for a combustion engine comprising 95.0% to 99.9% by mass of a liquid mixture of alcohol and water, the water representing 1% to 15% by mass of the mixture, and 0.01% to 5.0% by mass of an alkyl nitrate in the liquid state.

2. A 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. The fuel of claim 1 or 2, wherein the alkyl nitrate is a linear alkyl nitrate having 4 to 36 carbon atoms, a branched alkyl nitrate having 4 to 36 carbon atoms, a cyclic alkyl nitrate having 5 to 18 carbon atoms, or a mixture of these nitrates.

4. A fuel according to any one of claims 1 to 3, 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.

5. The fuel of claim 4, wherein the alkyl nitrate is 2-ethylhexyl nitrate.

6. A fuel according to any one of claims 1 to 5, wherein the alcohol is methanol or ethanol.

7.

8. A fuel according to claim 6, wherein the alcohol is methanol. A process for obtaining a fuel according to any one of claims 1 to 7, which comprises mixing in the liquid state the alkyl nitrate with a liquid mixture of alcohol and water.

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

10. 0 A method according to claim 8, wherein the mixture of alcohol and water and the alkyl nitrate are mixed in an injector.

11. 1 A method according to claim 8, wherein the mixture of alcohol and water and the alkyl nitrate are mixed in a premixing chamber of an engine.

12. 2 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.

13. 3 Use according to claim 12, wherein the alcohol is methanol or ethanol, preferably methanol.

14. 14. Use according to claims 12 or 13, wherein the alkyl nitrate is as defined in any one of claims 3 to 14.

15. J. 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.

16. 6 A method according to claim 15, wherein the alkyl nitrate is as defined in any one of claims 3 to 5.

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

18. A combustion engine comprising a fuel as defined in any one of claims 1 to 7.