JP4458405B2 - Fuel for premixed compression self-ignition engines - Google Patents

Description

  In the premixed compression self-ignition engine, the engine output and the rotation range are widened by fuel to facilitate engine control and prevent engine knocking, and the NOx emission level is 10 ppm or less with no catalyst installed. The present invention relates to a fuel for a premixed compression self-ignition engine that can be easily suppressed.

Today, two types of internal combustion engines for automobiles are widely used: a spark ignition gasoline engine and a compression self-ignition diesel engine.
A spark-ignition gasoline engine is a system in which fuel is injected into an intake port or combustion chamber to form a premixed mixture of fuel and air, and is forcibly ignited and burned by electric discharge by a spark plug. It is required that it is easy to evaporate, difficult to self-ignite, and that the flame propagates smoothly after ignition. Spark-ignition gasoline engines emit nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO), and therefore, three-way catalysts are widely used for purification of these. However, since the exhaust gas purification system using a three-way catalyst can only be applied to a range where the ratio of fuel to air is close to the theoretical air-fuel ratio, there is a disadvantage that the thermal efficiency and fuel consumption are significantly inferior compared with a compression self-ignition diesel engine. is there.
On the other hand, the compression self-ignition type diesel engine is a system in which the air in the combustion chamber is compressed by the piston rise in the compression process, the temperature rises, and fuel is sprayed and self-ignited and combusted when it reaches the critical temperature of light oil or higher. In addition, fuel characteristics are required to be easily ignited. Although the compression self-ignition diesel engine is excellent in fuel efficiency and thermal efficiency, since fuel spray is performed from 30 crank angle before compression top dead center to around 10 crank angle after compression top dead center, the temperature distribution during combustion is shaded, The disadvantage is that NOx and soot emissions are significantly higher. Further, in a compression self-ignition diesel engine, a catalyst for purifying exhaust gas is not so popular, and NOx is sometimes released into the atmosphere at a very high level of 100 to 1200 ppm.
In this way, the conventional spark ignition gasoline engine can purify the exhaust gas to some extent, but there are problems in terms of fuel consumption and thermal efficiency, while the compression self-ignition diesel engine has low fuel consumption and high thermal efficiency. There is a problem in terms of exhaust gas such as NOx. For this reason, premixed compression self-ignition engines are currently being studied to solve the problem of simultaneously achieving low NOx emission, low fuel consumption and high thermal efficiency.
The premixed compression self-ignition engine injects fuel into the intake port or the combustion chamber at a fuel injection pressure that is significantly lower than the injection pressure level of the compression self-ignition diesel engine, with a fuel injection pressure level of 20 MPa or less. This is a system that terminates fuel injection combusted at 60 crank angle before compression top dead center and burns premixed fuel and air by self-ignition rather than forced ignition by a spark plug. A premixed compression self-ignition engine has a longer time from fuel injection to the start of combustion than a conventional compression self-ignition diesel engine, and the fuel is uniformly mixed in the fuel chamber. The high temperature range is not possible, the NOx emission level can be suppressed to 10 ppm or less with no catalyst installed, and the fuel efficiency and thermal efficiency can be reduced to the same level as the compression self-ignition diesel engine. Is possible.
Therefore, development of a fuel suitable for such a premixed compression self-ignition engine is desired.

  It is an object of the present invention to increase engine output and rotation range with fuel in a premixed compression self-ignition engine, thereby facilitating engine control and preventing engine knocking, and reducing the NOx emission level with no catalyst installed. It is an object of the present invention to provide a premixed compression self-ignition engine fuel that can be easily suppressed to 10 ppm or less.

As a result of intensive studies to solve the above problems, the present inventors have found that a fuel containing a specific amount of nitromethane, having a specific distillation property, and having specific requirements is a premixed compression self-ignition type. It has been found that the fuel is suitable for an engine fuel, and the present invention has been completed.
That is, according to the present invention, the composition contains 3% by volume to 15% by volume of nitromethane, has a distillation property of the following (1), and has the requirements shown by the following (2). A fuel for a mixed compression self-ignition engine is provided.
(1) Initial boiling point: less than 45 ° C, 50% distillation temperature: 60 ° C to 105 ° C, end point: 120 ° C to 210 ° C.
(2) C4 + C5 + C6 + C7 ≥ 50% by volume (where C4, C5, C6 and C7 represent the content of hydrocarbon compounds with 4, 5, 6 and 7 carbon atoms, and volume% is based on the total amount of fuel) .

  Since the fuel of the present invention contains a specific amount of nitromethane, has a specific distillation property, and has specific requirements, the characteristics of the premixed compression self-ignition engine can be sufficiently exerted, The engine output is improved and the rotation range is widened to facilitate engine control, and at the same time, low NOx exhaust gas can be achieved. The fuel of the present invention can also be used as a fuel for a hybrid engine using a premixed compression self-ignition engine and a spark ignition gasoline engine, an electric motor, or the like.

The present invention is described in detail below.
In the present invention, the premixed compression self-ignition engine refers to an engine that injects fuel under the following conditions (A), (B), and (C) and burns by self-ignition.
(A) Fuel injection pressure: 20 MPa or less, (B) Fuel injection position: inside intake port and / or combustion chamber, (C) Fuel injection end time: Before 60 crank angle before compression top dead center.
Compared to conventional compression self-ignition type diesel engines, the premixed compression self-ignition type engine has a significantly lower fuel injection pressure (A) and combusts after the fuel injection end time (C), that is, after the fuel is injected. It takes a long time to start. Therefore, in the premixed compression self-ignition engine, the fuel is uniformly mixed in the combustion chamber, so that a locally high temperature region cannot be formed in the combustion chamber, and the amount of nitrogen oxide emission is reduced with no catalyst installed. It can be 10 ppm or less.
The premixed compression self-ignition engine includes HCCI engine (Homogeneous Charge Compression Ignition Engine), PCCI engine (Premixed Charge Compression Ignition Engine), PCI engine (Premixed Compression Ignition Engine), CAI engine (Controlled Auto-Ignition Engine), Sometimes called AR engine (Active Radical (Combustion) Engine).
The fuel of the present invention is a fuel suitable for a premixed compression self-ignition engine, but for a hybrid engine using the premixed compression self-ignition engine in combination with a spark ignition gasoline engine, an electric motor, or the like. Can also be applied.

The fuel of the present invention contains nitromethane in a specific ratio. Nitromethane can improve ignitability in a premixed compression self-ignition engine and facilitate optimal combustion control in the engine.
In the fuel of the present invention, the lower limit of the content ratio of nitromethane is 3% by volume or more, more preferably 5% by volume or more, further preferably 8% by volume or more, and most preferably 10% by volume or more with respect to the total amount of fuel. . When the lower limit is less than 3% by volume, the self-ignition of the fuel is delayed, and the ignition control becomes difficult. On the other hand, the upper limit value is 15% by volume or less with respect to the total amount of fuel. If the upper limit exceeds 15% by volume, self-ignition is too early, ignition control becomes difficult, and it tends to cause knocking.

The fuel of the present invention has (1) initial boiling point: less than 45 ° C, 50% distillation temperature: 60 ° C to 105 ° C, preferably 65 ° C to 95 ° C, end point: 120 ° C to 210 ° C, preferably Has distillation properties of 120 ° C or higher and 200 ° C or lower.
When the initial boiling point is 45 ° C. or higher, the fuel evaporation characteristic in the premixed compression self-ignition engine is deteriorated, and it is difficult to obtain desired thermal efficiency and fuel consumption.
When the 50% distillation temperature exceeds 105 ° C., the balance with the light fraction is lost, and the thermal efficiency in the premixed compression self-ignition engine is deteriorated. On the other hand, if the 50% distillation temperature is less than 60 ° C., the air filling efficiency caused by the evaporation of the fuel may deteriorate.
When the end point exceeds 210 ° C., ignition is not stable, and the control becomes difficult, and the maximum output, thermal efficiency, and exhaust gas amount deteriorate. On the other hand, if the end point is less than 120 ° C., the maximum output may be reduced.
Here, the initial boiling point, 50% distillation temperature, and end point are values measured by JIS K2254 “Petroleum Product One Distillation Test Method”.

The fuel of the present invention has the requirement of (2) C4 + C5 + C6 + C7 ≧ 50% by volume. Here, C4, C5, C6 and C7 represent the content ratio of hydrocarbon compounds having 4, 5, 6 and 7 carbon atoms, and the volume% is based on the total amount of fuel.
The total content of the hydrocarbon compounds having 4 to 7 carbon atoms is preferably 60% by volume or more, more preferably 70% by volume or more in order to facilitate control based on fuel evaporation characteristics in a premixed compression self-ignition engine. .
In the fuel of the present invention, each content ratio of the hydrocarbon compound having 4 to 7 carbon atoms and the hydrocarbon compound having 8 or 9 carbon atoms is not particularly limited, and satisfies the requirement (2). What is necessary is just mentioned and the content rate mentioned later is mentioned preferably. The content ratio of the hydrocarbon compound having 4 to 7 carbon atoms is usually C4> 0% by volume, C5> 0% by volume, C6> 0% by volume, and C7> 0% by volume.

In the fuel of the present invention, the content ratio (C4) of the hydrocarbon compound having 4 carbon atoms can keep the amount of evaporative gas (evaporation) low, the handling property such as the flash point is good, and paper lock and icing are performed. From the viewpoint of suppression, it is usually 25% by volume or less, preferably 20% by volume or less, particularly preferably 15% by volume or less, based on the total amount of fuel.
The lower limit of the content (C5) of the hydrocarbon compound having 5 carbon atoms is preferably 10% by volume or more and more preferably 15% by volume or more with respect to the total amount of fuel from the viewpoint of flammability, in particular, prevention of knocking. On the other hand, the upper limit is preferably 60% by volume or less, and more preferably 50% by volume or less.
The lower limit of the content (C6) of the hydrocarbon compound having 6 carbon atoms is preferably 5% by volume or more and more preferably 10% by volume or more with respect to the total amount of fuel from the viewpoint of flammability, in particular, prevention of knocking. On the other hand, the upper limit is preferably 50% by volume or less, and more preferably 45% by volume or less.
The content ratio of the hydrocarbon compound having 7 carbon atoms (C7) is preferably 30% by volume or less, more preferably 20% by volume or less, based on the balance between thermal efficiency and output in the premixed compression auto-ignition combustion, 10% by volume or less is most preferable.
The content ratio (C8) of the hydrocarbon compound having 8 carbon atoms is preferably 30% by volume or less, more preferably 20% by volume or less, based on the balance between thermal efficiency and output in premixed compression auto-ignition combustion, It is more preferably 15% by volume or less, and most preferably 10% by volume or less.
The content ratio of hydrocarbon compounds having 9 or more carbon atoms (C9 or more) is preferably 25% by volume or less, more preferably 20% by volume or less, based on the balance between thermal efficiency and output in premixed compression auto-ignition combustion. Preferably, 15% by volume or less is more preferable, and 10% by volume or less is most preferable.
Here, the content ratio of hydrocarbon compounds of C4, C5, C6, C7, C8, and C9 or higher is a value measured using a gas chromatograph in accordance with JIS K2536 “Petroleum product one-component test method”.

Without any limitation density at 15 ℃ fuel of the present investigation, from the viewpoint of the accelerator response becomes dull, is preferably less than 0.80 g / cm ^3, more preferably less than 0.78 g / cm ^3, also paper lock etc. from problems, preferably 0.65 g / cm ³ or more, more preferably 0.68 g / cm ³ or more.
Here, the density at 15 ° C. is a value measured by JIS K2249 “Density test method and density / mass / capacity conversion table for crude oil and petroleum products”.

In the fuel of the present invention, the sulfur content is not particularly limited, but is preferably 30 ppm by mass or less. If it exceeds 30 ppm by mass, the exhaust gas purifying catalyst mounted on the engine is poisoned by sulfur, which causes a problem that the exhaust gas purifying ability is lowered, which is not preferable. The sulfur content in the fuel is more preferably 10 mass ppm or less, more preferably 5 mass ppm or less, and most preferably 1 mass ppm or less from the viewpoint of maintaining the performance of the catalyst.
Here, the sulfur content is a value measured by JIS K2541 “Crude oil and petroleum product one sulfur content test method”.

The fuel of the present invention contains the hydrocarbon compound as a main component, but may further contain an oxygen-containing compound such as ether, alcohol, ketone, ester and glycol.
Examples of oxygen-containing compounds include methanol, ethanol, normal propyl alcohol, isopropyl alcohol, normal butyl alcohol, isobutyl alcohol, dimethyl ether, diisopropyl ether, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), and tertiary amyl. Examples include methyl ether (TAME) and tertiary amyl ethyl ether.
When the fuel of the present invention contains the oxygen-containing compound, the amount of HC in the exhaust gas can be reduced, but the amount of NOx increases. Therefore, the content ratio of the oxygen-containing compound is preferably 20% by mass or less, more preferably 10% by mass or less, and most preferably 3% by mass or less with respect to the total amount of fuel in terms of oxygen element (oxygen content).

  The fuel of the present invention includes, for example, a straight-run propane fraction centered on propane obtained from a crude oil distillation apparatus, a naphtha reformer, an alkylation apparatus, etc. Desulfurized straight desulfurized propane fraction, straight desulfurized butane fraction, cracked propane fraction centered on propane / propylene obtained from catalytic cracker, etc., cracked butane fraction centered on butane / butene Naphtha fraction (full range naphtha) obtained by atmospheric distillation of crude oil, light fraction of naphtha (light naphtha), heavy fraction of naphtha (heavy naphtha), desulfurized full range naphtha, light range naphtha Desulfurized light naphtha desulfurized naphtha, desulfurized heavy naphtha desulfurized heavy naphtha, isomerized gasoline, isobutane, etc. obtained by converting light naphtha into isoparaffin using an isomerizer Alkylate obtained by adding (alkylating) a lower olefin to a hydrocarbon compound, reformed gasoline obtained by catalytic reforming method, raffinate that is a residue obtained by extracting aromatics from reformed gasoline, reformed gasoline Light fractions, reformed gasoline medium heavy fraction, reformed gasoline heavy fraction, cracked gasoline obtained by catalytic cracking, hydrocracking, etc., cracked gasoline light fraction, cracked gasoline heavy One or more base materials such as light fractions of GTL (Gas to liquids) obtained by FT (Fischer-Tropsch) synthesis after decomposing mass fractions and natural gas into carbon monoxide and hydrogen It can be prepared by mixing.

In the fuel of the present invention, if necessary, an appropriate amount of a cetane number improver can be blended to improve the cetane number of the resulting fuel.
As the cetane number improver, various compounds known as light oil cetane number improvers can be arbitrarily used, and examples thereof include nitrate esters and organic peroxides. One of these cetane number improvers may be used alone, or two or more thereof may be used in combination.
Nitric acid esters include 2-chloroethyl nitrate, 2-ethoxyethyl nitrate, isopropyl nitrate, butyl nitrate, primary amyl nitrate, secondary amyl nitrate, isoamyl nitrate, primary hexyl nitrate, Various nitrates such as dihexyl nitrate, n-heptyl nitrate, n-octyl nitrate, 2-ethylhexyl nitrate, cyclohexyl nitrate, and ethylene glycol dinitrate are included. The use of ˜8 alkyl nitrates is preferred.

In the fuel of the present invention, if necessary, an appropriate amount of a wear modifier can be blended to improve the lubricity of the resulting fuel. Examples of main wear control agents include higher alcohols; alcohol compounds having 1 to 4 hydroxyl groups and 1 to 30 carbon atoms; higher carboxylic acids; reaction products of higher monocarboxylic acids and glycols or trihydric alcohols. A hydroxyl group-containing ester; an ester of a higher polycarboxylic acid and a polyhydric alcohol;> NR (wherein R is a hydrocarbon group having 5 to 40 carbon atoms), and having at least one substituent. Examples include esters of polyhydric alcohols combined with one nitrogen compound; amide compounds of higher carboxylic acids and alcohol amines, and the like. These can be used alone or as a mixture.
Among these, a hydroxyl group-containing ester which is a reaction product of a higher monocarboxylic acid having 10 to 25 carbon atoms and glycol or a trihydric alcohol and / or an amide of a higher carboxylic acid having 5 to 25 carbon atoms and an alcohol amine. Compounds are preferred, and amide compounds of higher monocarboxylic acids having 10 to 25 carbon atoms and glycerin esters and / or higher monocarboxylic acids having 5 to 25 carbon atoms and diethanolamine are most preferred.
The amount of addition of the wear modifier is not particularly limited, but it is usually per liter of fuel of the present invention from the viewpoint that sufficient fuel efficiency and output improvement effect can be exhibited, while improvement of the effect cannot be expected even if more is added. It is preferable to add so that it may become a content rate of 10-300 mg, Preferably 30-250 mg.

  The fuel of the present invention may contain other fuel oil additives other than the cetane number improver, friction modifier and the like as necessary. Examples of other fuel oil additives include detergent dispersants such as succinimide, polyalkylamine, and polyetheramine, N, N'-diisopropyl-p-phenylenediamine, N, N'-diisobutyl-p-phenylene Antioxidants such as diamines, 2,6-di-t-butyl-4-methylphenol and hindered phenols; non-metals such as amine carbonyl condensation compounds such as N, N'-disalicylidene-1,2-diaminopropane Activators, surface ignition inhibitors such as organic phosphorus compounds, antifreezing agents such as polyhydric alcohols and ethers thereof, alkali metal or alkaline earth metal salts of organic acids, auxiliary alcohols such as higher alcohol sulfates, anions Anti-static agents such as ionic surfactants, cationic surfactants, amphoteric surfactants, coloring agents such as azo dyes, organic carboxylic acids and their derivatives, alkenyl succinic acid esters, etc. Agents, draining agents such as sorbitan esters, quinizarin, identifying agents such as coumarin, odorants such as natural essential oils synthetic perfumes, and the like. These additives can be added singly or as a mixture, and it is preferable to add them in such a ratio that the total amount of these additives is 0.1% by mass or less based on the total amount of fuel.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

Examples 1 to 5, Comparative Examples 1 and 2
According to the composition shown in Table 1, fuels of the present invention (Examples 1 to 5) and comparative fuels (Comparative Examples 1 and 2) were prepared by a conventional method. Table 2 shows the measurement results of the hydrocarbon compound and nitromethane content of each fuel and the distillation properties, density, and sulfur content.
The obtained fuel was evaluated by performing the following tests using the following premixed compression self-ignition engine. The results are shown in Table 2.

(Engine specifications)
Engine type: Inline 6-cylinder premixed compression self-ignition engine, displacement: 2000cc, compression ratio: 16, fuel injection pressure: 8MPa.
(Engine test)
The engine was operated according to the following procedure to create a rotation-output curve (map), and the maximum operable speed, maximum output, knocking level, nitrogen oxide amount, and engine start time were determined.
(1) A dynamometer (DC95 220kW DC dynamometer manufactured by Meidensha) is set to rotation-intake pressure control, and the engine is motored at a predetermined rotational speed.
(2) Inject fuel and gradually increase the injection amount.
(3) After starting self-ignition combustion, measure the output corresponding to the fuel injection amount, fuel consumption, exhaust gas, and knocking level.
(4) Increase the fuel injection amount until it can no longer operate, and continue the operation in (3).
(5) Repeat steps (2) to (4) while changing the rotation speed.
The output was calculated from the shaft torque and rotation speed obtained from the dynamometer.
As for the knocking level, knocking was analyzed with a combustion analyzer (DS9110, manufactured by Ono Sokki Co., Ltd.), and the results were evaluated in five levels of levels 1-5. At this time, the fuel of level 1 represents that it is difficult to knock in all the rotational speed regions up to the maximum rotational region, and represents that knocking is likely to occur as the level increases.
Nitrogen oxide emissions were measured with an exhaust gas analyzer (MEXA9100, manufactured by Horiba, Ltd.) by sampling combustion exhaust gas from the engine exhaust pipe.
(Engine start time)
Allow the engine to cool sufficiently by leaving it at -15 ° C for 48 hours, then start the starter and then start the first cylinder (the premixed gas in the cylinder is ignited for the first time after starting the starter) I measured the time required to do that. The longer this time, the worse the engine startability.

  From the results of Table 2, when the fuel of the present invention (Examples 1 to 5) is used, the maximum output is higher and the nitrogen oxide emission amount is less than that of Comparative Examples 1 and 2, enabling operation. It can be seen that the maximum engine speed can be increased, the knocking level can be decreased, and the engine start time can be shortened.

  It can be used as a fuel for a premixed compression self-ignition engine or a hybrid engine using a premixed compression self-ignition engine and a spark ignition gasoline engine, an electric motor or the like.

Claims (2)

A fuel for a premixed compression self-ignition engine characterized by containing 3% to 15% by volume of nitromethane, having the distillation properties of (1) below, and satisfying the requirements shown in (2) below: .
(1) Initial boiling point: less than 45 ° C, 50% distillation temperature: 60 ° C to 105 ° C, end point: 120 ° C to 210 ° C.
(2) C4 + C5 + C6 + C7 ≧ 50% by volume (where C4, C5, C6 and C7 represent the content of hydrocarbon compounds with 4, 5, 6 and 7 carbon atoms, and volume% is based on the total amount of fuel) . 2. The premixed compression self-ignition engine fuel according to claim 1, having a density at 15 ° C. of 0.65 g / cm ³ or more and less than 0.8 g / cm ³ and a sulfur content of 30 mass ppm or less.