Engine fuels based on a mixture of alcohol and water and containing additives to improve combustion.

Abstract

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

Description

Technical Field

[0001] This invention pertains to fuels for internal combustion engines. The fuels of this invention belong to a category of novel fuels with less environmental impact, such as those commonly referred to as "electronic fuels" when they are produced from low-carbon electricity, low-carbon hydrogen, and / or carbon dioxide. They are considered a solution for decarbonizing transportation. The fuels of this invention are essentially composed of a water / alcohol mixture, and are therefore one of the eco-friendly alternatives to fossil fuels. Water constitutes up to 15% by weight of the mixture. The role of water is to reduce the formation of nitrogen oxides in engine combustion products. Therefore, alcohol is the main component of the fuel. This invention relates to an additive that, when introduced into a water / alcohol mixture, ensures better ignition and faster combustion of the fuel in the engine. Background Technology

[0002] "Electronic fuel" methanol is a reliable, low-environmental-impact alternative that promises to replace fossil fuels and biofuels used in internal combustion engines in the near future. The combustion of the resulting methanol achieves a neutral CO2 balance. Methanol offers usable energy density as a fuel in internal combustion engines, but its cetane number is low. Ignition of methanol in compression-ignition engines (such as diesel engines) presents challenges, particularly at low engine speeds. Different methods for improving methanol ignition in compression-ignition engines have been described.

[0003] The first method involves co-injecting an ignition fuel or additive with methanol into the engine. For example, patent application CN 214944586 describes the co-injection of a diesel-type ignition fuel with methanol as the primary fuel. The scientific paper “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 (EHN) with a fuel primarily composed of gaseous methanol. During combustion in a specific RCCI (Reactive Compression Controlled Ignition) mode, a well-mixed fuel and a low-reactivity oxidant (usually with air) are compressed in the gaseous state but do not spontaneously combust. Subsequently, still in the compression cycle, a high-reactivity fuel (in this case, EHN) is injected to form a localized mixture of the low-reactivity and high-reactivity fuels. Co-injection of 7% EHN in the presence of gaseous methanol reportedly achieves acceptable combustion efficiency (compared to a reference fuel consisting of a mixture of isooctane and n-heptane). The main drawback of this process is the need to control co-injection based on engine operating conditions, such as the configuration of separate fuel tanks and the injection system. Furthermore, using fuel oil as the ignition fuel generates CO2 emissions, negatively impacting the environment.

[0004] The second method is a mixture of fuel and methanol. It is well known that alcohols (such as methanol or ethanol) can be mixed in small or large proportions with fossil fuels or synthetic diesel fuels (such as dimethyl ether (DME)) or with gasoline. In this case, the CO2 emission balance is also detrimental to the environment.

[0005] The third method involves introducing ignition-improving additives into the methanol mixture, and possibly into the diesel fuel mixture. Numerous patent applications, such as CN 103865592 and CN 104232180, describe the introduction of mixtures of multifunctional additives into methanol mixtures, and possibly into fuel oil mixtures. These additives possess functions such as corrosion prevention, anti-corrosion, improved combustion, and cleaning. These additives typically constitute at least 10% by weight of the fuel. The proportion of methanol in the fuel ranges from 30% to 90% by weight, depending on the additives present in the fuel and the weight percentage of diesel fuel. The combined effect of these additives can only be observed holistically, and the desired amount cannot be precisely controlled. Therefore, it is not a fuel composed primarily of methanol.

[0006] Furthermore, it is known to mix fuels such as diesel, biodiesel, and / or alcohols with water (typically up to 15% by weight) to reduce the production of nitrogen oxides in the combustion products of compression-ignition or spark-ignition engines. However, adding water lowers the combustion temperature and flammability of the fuel. These effects of adding water to fuel are described in U.S. Patent 7,216,607 and the scientific paper “Performance and NOx Emissions of Spark Ignited Combustion Engines Using Alternative Fuels-QuasiOne-Dimensional Modeling II. Methanol Fueled Engine” (Combustion Science and Technology, Vol. 18, 1978, Nos. 5-6).

[0007] On the other hand, in the field of diesel or biodiesel hydrocarbon fuels, 2-ethylhexyl nitrate (EHN) has long been known as a cetane number enhancer in diesel fuels. A higher cetane number ensures lower fuel consumption, reduced particulate matter and NOx emissions, faster cold engine starts, reduced engine knock and noise, and reduced engine wear. The reaction mechanism of EHN in the presence of diesel hydrocarbon fuels has been studied, for example, in scientific publications such as "The Autoignition Behavior of Surrogate Diesel Fuel Mixtures and the Chemical Effects of 2-EthylhexylNitrate (2-EHN) Cetane Improver" (Vol. 108, Section 4: Journal of fuels and lubricants (1999), pp. 1029-1045). However, the reaction mechanism by which it improves cetane numbers in diesel fuels remains poorly understood, and its use is based on empirical rules. Therefore, its effectiveness for fuels other than diesel cannot be assumed. This additive is industrially produced and widely used in commercial diesel fuels. Since the 1980s, Europe has produced more than 50,000 tons of EHN annually. Other alkyl nitrates can also be used as cetane number enhancers in diesel fuels.

[0008] Patent application EP 030429 describes a fuel comprising a mixture of the following (A) and (B): (A) at least one alcohol with an average molecular weight less than 160; (B) at least one other organic compound, or a mixture of organic compounds, wherein the overall auto-ignition temperature of these compounds or mixtures is below 450°C. Compound (B) can be, in a variety of possibilities, an organic compound selected from: azo compounds, tetrazine compounds, nitroso compounds, nitro compounds, nitrate esters, and hyponitrite esters. It should be understood that compound (B) is not entirely composed of C2-C8 alkyl esters of nitrate. It should be noted that the only fuel example containing water does not contain any alkyl esters of nitrate.

[0009] This invention provides a solution for improving the ignition of fuels in internal combustion engines that consist essentially of a mixture of alcohol and water (hereinafter also referred to as an alcohol / water mixture). This improvement is achieved by separately adding a small amount (by weight) of EHN additive to the alcohol / water mixture. More broadly, other alkyl nitrate esters known to have similar diesel fuel cetane number improving properties to EHN are also recommended in this invention for improving the ignition of alcohol / water mixtures. Surprisingly, additives known to improve the cetane number of diesel or biodiesel hydrocarbon fuels can be effectively used at very low weight percentages to improve the ignition of alcohols (e.g., methanol) mixed with water. Summary of the Invention

[0010] The present invention relates to a liquid fuel for compression-ignition or spark-ignition internal combustion engines, comprising a mixture of about 95.0% to about 99.9% by weight of an alcohol and water, and about 0.01% to about 5.0% by weight of a compound for improving fuel ignition delay, wherein the alcohol and water mixture consists of about 1% to about 15% by weight of water and about 85% to about 99% by weight of alcohol.

[0011] The compound used to improve fuel ignition delay is an alkyl nitrate ester, which is liquid at room temperature, has low flammability, is non-toxic, and can be industrially produced.

[0012] Therefore, the compound used in low amounts in the presence of an alcohol / water mixture is often compared to a fuel additive.

[0013] The addition of the liquid compound to the alcohol / water mixture is carried out in a liquid state, thereby forming the fuel according to the invention in the fuel tank. It can also be stored separately and mixed with the alcohol / water mixture before injection into the engine to form the fuel according to the invention; or it can be co-injected with the alcohol / water mixture in the engine's premixing chamber to form the fuel according to the invention.

[0014] The compound is an alkyl nitrate ester, previously used to increase the cetane number of fossil diesel or biodiesel hydrocarbon fuels, and thus it has been effectively and unexpectedly used as an additive to improve the ignition of alcohols mixed with water. Attached Figure Description

[0015] Figure 1 The effect of EHN on ignition delay of methanol / water mixture (water accounts for 5% by weight of the mixture) is shown, with the method of single main injection (dots in the figure) or micro-injection followed by main injection (squares in the figure) into the engine cylinder.

[0016] Figure 2 The effect of EHN on ignition delay of methanol / water mixture (water accounts for 10% by weight of the mixture) is shown, with the method of single main injection (dots in the figure) or micro-injection followed by main injection (squares in the figure) into the engine cylinder. Detailed Implementation

[0017] As defined herein, “alcohol” should be understood to mean an alcohol having 1 to 4 carbon atoms. In some embodiments, the alcohol is methanol or ethanol, advantageously methanol.

[0018] The present invention relates to a fuel for compression-ignition or spark-ignition internal combustion engines, comprising about 95.0% to about 99.9% by weight of a mixture of alcohol and water (water comprising 1.0% to 15.0% by weight of the mixture), and about 0.01% to about 5.0% by weight of alkyl nitrate.

[0019] In one embodiment, the fuel contains about 0.1% by weight to about 3.0% by weight of alkyl nitrate.

[0020] In one embodiment, the fuel of the present invention consists of an alcohol / water mixture and an alkyl nitrate (in this case, the amount of alkyl nitrate in the fuel is at least 0.1% by weight).

[0021] In another embodiment, when the sum of the amount of alcohol / water mixture and the amount of alkyl nitrate ester is not equal to 100% by weight, the fuel may contain one or more other additives to make the fuel 100% complete, such as additives with anti-corrosion, anti-corrosion or cleaning functions.

[0022] In one embodiment, the fuel according to the invention does not contain dimers of unsaturated fatty acids and / or esters of phosphorous acid. In another embodiment (which may be combined with the preceding embodiment), the fuel according to the invention does not contain C8-C... 20Aliphatic monocarboxylic acids. In another embodiment (which may be combined with the first two embodiments), the fuel according to the invention does not contain a mixture of C4 and / or C5 / C6 and / or C5-C7 hydrocarbons, nor a mixture of gasoline and at least one of said hydrocarbons.

[0023] The alkyl nitrate ester added to the water / alcohol mixture is more specifically selected from straight-chain alkyl nitrate esters having 4 to 36 (advantageously 4 to 24) carbon atoms, branched-chain alkyl nitrate esters having 4 to 36 (advantageously 4 to 24) carbon atoms, cyclic alkyl nitrate esters (or cycloalkyl nitrate esters) having 5 to 18 carbon atoms, and mixtures thereof. In one embodiment, the alkyl nitrate ester is selected from 2-ethylhexyl nitrate, hexyl nitrate, cyclohexyl nitrate, 2-octyl nitrate, nonyl nitrate, isononyl nitrate, dodecyl nitrate, 2-propylheptyl nitrate, 2-tetradecyl-1-octadecyl nitrate, and C9-C nitrate. 13 Mixtures of branched alkyl esters, and mixtures thereof. In one embodiment, the alkyl nitrate is either 2-ethylhexyl nitrate alone or a mixture with one or more other alkyl nitrates as defined above; advantageously, the alkyl nitrate is 2-ethylhexyl nitrate.

[0024] According to one embodiment, a fuel ignition improving compound (i.e., the alkyl nitrate) is mixed in liquid form with an alcohol / water mixture supplied to the engine's fuel tank to obtain fuel according to the invention.

[0025] According to one embodiment, the alkyl nitrate ester (on one hand) and the alcohol / water mixture (on the other hand) are stored separately and mixed in a liquid state in the injector to form the fuel according to the invention before being delivered to the engine combustion chamber.

[0026] According to one embodiment, the alkyl nitrate ester and the alcohol / water mixture are stored separately and co-injected with the alcohol / water mixture to form the liquid fuel according to the invention in the premixing chamber of the engine.

[0027] The present invention also relates to the use of alkyl nitrate esters in the amounts defined above as ignition modifiers for alcohol- and water-based fuels (consisting of alcohol and water).

[0028] The present invention also relates to a method for improving fuel ignition in an engine (particularly an internal combustion engine) of a mixture based on alcohol and water, the method comprising adding an alkyl nitrate ester (as defined above) to the mixture in an amount defined above. In one embodiment, the alkyl nitrate ester and the alcohol / water mixture are mixed in an injector. In another embodiment, the alkyl nitrate ester and the alcohol / water mixture are mixed in a premixing chamber of the engine.

[0029] The present invention also relates to engines (particularly internal combustion engines) for vehicles (e.g., automobiles, trucks, tractors, etc.) or ships (e.g., oil tankers, container ships, etc.) that use the fuels defined above. The present invention also relates to vehicles or ships that include engines as defined above.

[0030] The present invention is illustrated by the following embodiments provided for reference.

[0031] Example The performance of the fuel according to the invention was measured using laboratory compression ignition (single-cylinder, 0.499-liter direct injection engine with a target mean indicated pressure (MIP) of 3 bar at 1500 rpm) and compared with a fuel consisting only of methanol and water. Engine operating parameters were measured after 100 cycles (necessary to obtain consistent averages in subsequent calculations). Simultaneously, 20 pollutant measurement cycles were recorded at 5-second intervals to obtain representative averages of emissions from different cycles. Based on the values ​​obtained above, the following parameters characterizing fuel combustion and engine operation were extracted: - dAI automatic ignition delay (milliseconds) - Mean Indicated Pressure (MIP) - MIP covariance (COVMIP) - CA1 angle - CA50 angle - Burning time, - Pollutants (NOx, CO, H2O, HC). - Heat release rate.

[0032] Compared to fuels consisting solely of a methanol / water mixture, the addition of alkyl nitrates to the methanol / water mixture improves overall combustion and engine operating parameters. The performance of the fuel of this invention can be further improved by controlling fuel injection through multiple injections in each engine cycle, for example, by performing one or more so-called ignition micro-injections followed by the main injection.

[0033] The ignition delay, which varies with the fuel intake temperature, is a value obtained from testing, as shown below, to illustrate the advantages of the invention.

[0034] The ignition delay dAI is defined by the following formula, where Pc is the pressure applied to the injected fuel: Example 1 This embodiment relates to improving the combustion performance of a mixture of 95% by weight methanol and 5% by weight water in an engine by adding the compound EHN.

[0035] At a pressure Pc of 300 bar, the ignition delay of the fuel according to the invention, consisting of 99.0 wt% methanol / water mixture (water comprising 5.0 wt% of the mixture) and 1.0 wt% EHN, was determined as a function of intake air temperature (313 K to 473 K, i.e., 40 °C to 200 °C), wherein the air enrichment of the mixture was 0.25. The results are shown in Figure 1 The ignition delay was compared to that of a methanol / water mixture (95 wt% / 5 wt%). It can be seen that the ignition delay of the fuel containing EHN is significantly reduced compared to the methanol / water fuel. This reduction in ignition delay is particularly significant at low temperatures compared to the methanol / water mixture. Under single main injection and an intake air temperature of 403 K, the ignition delay of the fuel of the present invention according to this embodiment is approximately one-third that of the reference fuel containing methanol and water. The fuel of the present invention can ignite even at low intake air temperatures below 403 K (as low as 373 K) with an ignition delay of 2 milliseconds, while the methanol / water mixture cannot ignite at this temperature.

[0036] Under multiple injection conditions, including micro-injection (at a crankshaft angle of -25° for 400 microseconds) followed by main injection (at a crankshaft angle of -15° for 1500 microseconds), improved combustion characteristics of the methanol / water mixture were observed, with ignition at 373 K and an ignition delay of approximately 1.75 milliseconds. The combustion of the methanol / water mixture under these conditions and at this temperature was close to that of a methanol / water mixture containing 1.0 wt% EHN but only subjected to main injection. Below 373 K, the methanol / water mixture failed to ignite. In contrast, the methanol / water mixture containing 1.0 wt% EHN ignited at temperatures as low as 313 K with an ignition delay of approximately 1.2 milliseconds.

[0037] Example 2 This embodiment relates to improving the combustion performance of an engine mixture consisting of 90% by weight methanol and 10% by weight water by adding EHN.

[0038] At a pressure Pc of 300 bar, the ignition delay of the fuel according to the invention, consisting of 98.0 wt% methanol / water mixture (water comprising 10.0 wt% of the mixture) and 2.0 wt% EHN, as a function of intake air temperature (313 K to 463 K), was determined, wherein the air enrichment of the mixture was 0.25. The results are shown in... Figure 2The ignition delay of the methanol / water mixture alone was used as a reference point. With the addition of 1 wt% EHN, improved fuel combustion performance was observed at intake air temperatures below 433 K. At an intake air temperature of 413 K, the ignition delay of the fuel containing 1 wt% EHN was reduced by approximately one-third compared to the methanol / water reference fuel. At an intake air temperature of 413 K and an EHN content of 2 wt%, the ignition delay at this temperature was reduced by half compared to the methanol / water mixture. At an intake air temperature of 403 K, the methanol / water mixture failed to ignite, while the fuels containing 1 wt% EHN and 2 wt% EHN ignited with delays of approximately 4 ms and 2.2 ms, respectively.

[0039] Under multiple injection conditions, including micro-injection (at a crankshaft angle of -25° for 400 microseconds) followed by main injection (at a crankshaft angle of -15° for 1500 microseconds), improved combustion characteristics of the methanol / water mixture were observed. This mixture ignited at 393 K with an ignition delay of approximately 3.5 milliseconds. Below 393 K, the methanol / water mixture failed to ignite. In contrast, fuels containing 1 wt% EHN ignited at temperatures as low as 383 K with an ignition delay of approximately 1.5 milliseconds. Fuels containing 2 wt% EHN ignited at 333 K with an ignition delay of approximately 1.75 milliseconds.

[0040] The results of Examples 1 and 2 are summarized in Table 1.

[0041] Table 1 These examples demonstrate that using a low weight percentage of alkyl nitrates can significantly improve ignition delay in alcohol- and water-based fuels. More generally, the addition of alkyl nitrate compounds to alcohol / water mixtures improves the overall fuel performance of internal combustion engines while maintaining limited nitrogen oxide emissions at intake air temperatures close to ambient. There is no reason to believe that additives known to improve the cetane number of diesel or biodiesel hydrocarbon fuels can be effectively used in very small amounts to improve the ignition of alcohols mixed with water.

Claims

1. A fuel for an internal combustion engine, comprising 95.0% to 99.9% by weight of a liquid mixture of alcohol and water and 0.01% to 5.0% by weight of an alkyl nitrate, wherein, Water comprises 1% to 15% by weight of the mixture, and the alkyl nitrate is a nitrate of a straight-chain alkyl group having 4 to 36 carbon atoms, a nitrate of a branched-chain alkyl group having 4 to 36 carbon atoms, a nitrate of a cyclic alkyl group having 5 to 18 carbon atoms, or a mixture of these nitrates.

2. The fuel according to claim 1, comprising 95.0% to 99.9% by weight of an alcohol / water mixture and 0.1% to 3.0% by weight of an alkyl nitrate ester.

3. The fuel according to any one of claims 1 to 2, wherein, The alkyl nitrate ester 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 nitrate to isotriadecyl nitrate, and mixtures thereof.

4. The fuel according to claim 3, wherein, The alkyl nitrate ester is 2-ethylhexyl nitrate.

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

6. The fuel according to claim 5, wherein, The alcohol is methanol.

7. A method for obtaining a fuel as claimed in any one of claims 1 to 6, comprising mixing the alkyl nitrate with an alcohol / water mixture in a liquid state.

8. The method according to claim 7, wherein, Alcohol, water, and alkyl nitrate esters are mixed in the engine oil tank.

9. The method according to claim 7, wherein, A mixture of alcohol and water, along with alkyl nitrate esters, is mixed in the injector.

10. The method according to claim 7, wherein, A mixture of alcohol and water, along with alkyl nitrate esters, is mixed in the engine's premixing chamber.

11. The use of 0.01% to 5.0% by weight of liquid alkyl nitrates as a reagent to improve the ignition of alcohol- and water-based liquid fuels, wherein the alkyl nitrate is a nitrate of a straight-chain 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 5 to 18 carbon atoms, or a mixture of these nitrates.

12. The use according to claim 11, wherein, The alcohol is methanol or ethanol, preferably methanol.

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

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

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

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

17. An internal combustion engine comprising the fuel as claimed in any one of claims 1 to 6.

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