JP5019802B2 - Fuel for premixed compression self-ignition engines - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a fuel for a premixed compression self-ignition engine, and more particularly, has excellent ignitability in premixed compression self-ignition combustion, and widens the engine output and the engine rotation range as much as possible to achieve improvement in engine thermal efficiency. The present invention relates to a premixed compression self-ignition engine fuel that can be used.

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. In spark-ignition gasoline engines, nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) are exhausted, and three-way catalysts and the like 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 due to 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 type diesel engine is excellent in fuel efficiency and thermal efficiency, the fuel spray is performed from 30 crank angle before compression top dead center to around 10 crank angle after compression top dead center, so the temperature distribution during combustion is shaded, There is a drawback that the amount of NOx and soot emissions is significantly increased. Further, in a compression self-ignition diesel engine, a catalyst for purifying exhaust gas is not so popular, and there is a case where NOx is released into the atmosphere at a very high level of 100 to 1200 mass 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.
A premixed compression self-ignition engine injects fuel into the intake port or the combustion chamber at a fuel injection pressure level of 20 MPa or less, which is significantly lower than the injection pressure in a compression self-ignition diesel engine. 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 when no catalyst is installed, and the fuel efficiency and thermal efficiency are as low as those of a compression self-ignition diesel engine. It is possible.

As fuels for such premixed compression self-ignition engines, fuels have been proposed that focus on fuel volatility indices, existing gasoline engines such as cetane number and octane number, and diesel engine ignitability indices (for example, , See Patent Document 1).
In addition, the present inventors have already developed and filed patent applications for fuels that can efficiently perform premixed compression self-ignition combustion and exhibit good performance (see, for example, Patent Documents 2 to 13). .
However, there is a demand for the development of a fuel that is superior in terms of thermal efficiency and fuel efficiency in premixed compression self-ignition combustion.
JP 2004-315604 A JP 2004-91657 A JP 2004-91658 A JP 2004-91659 A JP 2004-91660 A JP 2004-91661 A JP 2004-91662 A JP 2004-91663 A JP 2004-91664 A JP 2004-91665 A JP 2004-91666 A JP 2004-91667 A JP 2004-91668 A

  An object of the present invention is to provide a fuel for a premixed compression self-ignition engine that has excellent ignitability in premixed compression self-ignition combustion, can widen the engine output and the engine rotation range as much as possible, and can improve the engine thermal efficiency. Is to provide.

In order to solve the above-mentioned problems, the present inventors have conducted extensive research and found that a fuel having a specific composition and having specific requirements is suitable as a fuel for a premixed compression self-ignition engine. As a result, the present invention has been completed.
That is, the present invention relates to a premixed compression self-ignition engine fuel characterized by satisfying the following (a), (b), (c) and (d).
(A) Total content of hydrocarbons having a content of 5% by volume or less is 30% by volume or more (b) Research method octane number is 60 or more and less than 90 (c) HCCI Index represented by the following formula (1) is 20.68 54.24 or less
HCCI Index = MON−0.424 × A−0.377 × B−0.202 × C−0.205 × D (1)
(In formula (1), MON is a measured value based on the motor method octane number, A is normal paraffin content (volume%), B is isoparaffin content (volume%), C is olefin content (volume%), and D is aromatic. Represents the group content (volume%).)
(D) The content of naphthene is 1.3% by volume or more and 20% by volume or less.

  The present invention also relates to the premixed compression self-ignition engine fuel described above, wherein the initial boiling point is 45 ° C. or lower and the end point is 210 ° C. or lower.

The present invention also relates to the premixed compression self-ignition engine fuel described above, wherein the NDI represented by the formula (2) is 115 or more and 225 or less .
NDI = 4 × E1 + 3 × E2 + 2 × E3-1 × E4-4 × E5 (2)
(In the formula (2), E1 is a fraction having a boiling point of less than 70 ° C. (volume%), E2 is a fraction having a boiling point of 70 ° C. or more and less than 100 ° C. (volume%), and E3 is a fraction having a boiling point of 100 ° C. or more and less than 130 ° C. (Volume%), E4 represents a fraction having a boiling point of 130 ° C. or more and less than 160 ° C. (volume%), and E5 represents a fraction having a boiling point of 160 ° C. or more (volume%).)

The present invention relates to a homogeneous charge compression ignition engine fuel of the wherein the density at 15 ℃ is less than 0.60 g / cm ³ or more 0.78 g / cm ^3.

  The present invention also relates to the fuel for a premixed compression self-ignition engine as described above, wherein the sulfur content is 50 ppm by mass or less.

  The fuel of the present invention has excellent ignitability in the premixed compression self-ignition combustion, and can increase the engine output and the engine rotation region during premixed compression self-ignition combustion as much as possible, thereby achieving improvement in engine thermal efficiency.

The present invention is described in detail below.
The fuel in the present invention is a fuel suitable for a premixed compression self-ignition engine. Here, the premixed compression self-ignition system refers to a combustion mode in which fuel is injected under the following conditions (A), (B), and (C), and combustion is performed by self-ignition.
(A) Fuel injection pressure: 20 MPa or less (B) Fuel injection position: intake port and / or inside combustion chamber (C) Fuel injection end time: 60 crank angle before compression top dead center

In the premixed compression self-ignition method, compared with the compression self-ignition method found in conventional diesel engines, the fuel injection pressure in (A) is remarkably low, and the fuel injection end time in (C), that is, fuel is injected. It takes a long time to start burning. Therefore, in the premixed compression self-ignition method, the fuel is uniformly mixed in the combustion chamber, so that a region having a high temperature locally cannot be formed in the combustion chamber, and the amount of nitrogen oxide emitted is 10 in a state where no catalyst is mounted. It can be made into mass ppm or less.
The premixed compression self-ignition method includes HCCI (Homogeneous Charge Compression Ignition), PCCI (Premixed Charge Compression Ignition), PCI (Premixed Compression Ignition), CAI (Controlled Auto-Ignition), and AR (Active Radical (Combustion)). Sometimes called.

The premixed compression self-ignition engine fuel of the present invention (hereinafter also referred to as the fuel of the present invention) is important in terms of the balance of distillation properties and ignitability, and is a fuel based on a multicomponent fuel. Desired. For this reason, the total content of 5% by volume or less of hydrocarbons contained in the fuel needs to be 30% by volume or more, preferably 35% by volume or more, and more preferably 40% by volume or more.
The isomers are counted as separate hydrocarbons.

The research octane number (RON) of the fuel of the present invention needs to be 60 or more and less than 90, preferably 60 or more and 88 or less, more preferably 60 or more and 86 or less. When the octane number of the research method is less than 60, the thermal efficiency of the engine is reduced by knocking, and when it is 90 or more, various devices are required to establish premixed compression self-ignition combustion by narrowing the operation range. This is not preferable.
Here, the research method octane number (RON) is the value of the research method octane number measured by JIS K2280 “Petroleum products-fuel oil-octane number test method, cetane number test method and cetane index calculation method”.

The fuel of the present invention is required to be HCCI Index represented by the following formula (1) is 20.68 or more 54.24 or less, preferably 5 0 or less.
HCCI Index = MON−0.424 × A−0.377 × B−0.202 × C−0.205 × D (1)
(In formula (1), MON is a measured value based on the motor method octane number, A is normal paraffin content (volume%), B is isoparaffin content (volume%), C is olefin content (volume%), and D is aromatic. Represents the group content (volume%).)
The content of isoparaffin, normal paraffin, olefin, and aromatic as used herein is a value measured using a gas chromatograph in accordance with JIS K2536 “Petroleum products-component test method”. is there.

  Conventionally, the ignitability of fuel has been expressed only by the research method octane number and the motor method octane number, but in the case of premixed compression self-ignition combustion, an index that takes the step further and considers the composition is required. The HCCI Index represented by the formula (1) is obtained from research conducted by the present inventors, and is a combination of the motor octane number and the fuel composition. In the premixed compression self-ignition combustion, an example in which the motor method octane number is the same and the ignitability is different can be expressed by the equation (1).

In the fuel of the present invention, the content of naphthene contained in the fuel needs to be 1.3 % by volume or more and 20% by volume or less, and preferably 1.3 % by volume or more and 10% by volume or less. If the naphthene content exceeds 20% by volume, the low-temperature oxidation reaction during premixed compression self-ignition combustion becomes small, which is not preferable.

The initial boiling point of the fuel of the present invention is preferably 45 ° C. or lower. If the initial boiling point exceeds 45 ° C., startability deteriorates, which is not preferable.
The 50 volume% distillation temperature (T50) of the fuel of the present invention is preferably 50 ° C. or higher and 130 ° C. or lower, more preferably 50 ° C. or higher and 120 ° C. or lower. When T50 is less than 50 ° C., it leads to poor operability and output due to excessive fuel evaporation, and when it exceeds 130 ° C., it leads to poor operability and low output due to poor fuel evaporation. It is not preferable.
The end point of the fuel of the present invention is preferably 210 ° C. or lower. When the end point exceeds 210 ° C., the evaporation characteristics deteriorate, soot and unburned hydrocarbons are excessively discharged, which is not preferable.
Here, the initial boiling point, T50, and end point are values measured by JIS K2254 “Petroleum products—distillation test method—atmospheric pressure distillation test method”.

In the fuel of the present invention, the NDI represented by the following formula (2) is preferably 115 or more and 225 or less , and more preferably 120 or more. An NDI of less than 115 is not preferable because it causes poor engine startability, or the balance between air and fuel is lost during acceleration and the drivability is remarkably deteriorated.
NDI = 4 × E1 + 3 × E2 + 2 × E3-1 × E4-4 × E5 (2)
(In the formula (2), E1 is a fraction having a boiling point of less than 70 ° C. (volume%), E2 is a fraction having a boiling point of 70 ° C. or more and less than 100 ° C. (volume%), and E3 is a fraction having a boiling point of 100 ° C. or more and less than 130 ° C. (Volume%), E4 represents a fraction having a boiling point of 130 ° C. or more and less than 160 ° C. (volume%), and E5 represents a fraction having a boiling point of 160 ° C. or more (volume%).)

Density at 15 ℃ fuel of the present invention is preferably not more than 0.60 g / cm ³ or more 0.78 g / cm ^3, more preferably at 0.65 g / cm ³ or more 0.78 g / cm ³ or less . When the density is less than 0.60 g / cm ^3, vapor lock is a problem, which is not preferable. On the other hand, if it exceeds 0.78 g / cm ³ , the accelerator response becomes dull, which is not preferable.
In addition, the density here 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 in the fuel is preferably 50 ppm by mass or less, more preferably 10 ppm by mass or less, and further preferably 5 ppm by mass or less. If the sulfur content exceeds 50 ppm by mass, the exhaust gas purification catalyst mounted on the engine is poisoned by sulfur, which causes a problem that the exhaust gas purification capacity is lowered, which is not preferable.
In addition, the sulfur content here is a value measured by JIS K2541 “Crude oil and petroleum product one sulfur content test method”.

  The base material of the fuel of the present invention is not particularly limited as long as a fuel having a predetermined property can be obtained as described above. For example, a crude oil distillation device, a naphtha reforming device, an alkylation device, etc. From propane, mainly from propane, straight butane from butane, straight desulfurized propane, desulfurized butane, and catalytic cracking equipment Cracked propane fractions mainly from propane / propylene, cracked butane fractions centered on butane / butene, naphtha fractions obtained by atmospheric distillation of crude oil (full-range naphtha), light naphtha Distillate (light naphtha), heavy fraction of naphtha (heavy naphtha), desulfurized full range naphtha desulfurized full range naphtha, desulfurized light naphtha desulfurized light naphtha, dehydrated heavy naphtha Desulfurized heavy naphtha, light naphtha converted to isoparaffins by isomerization equipment, alkylates obtained by adding (alkylating) lower olefins to hydrocarbon compounds such as isomerized gasoline and isobutane, catalytic reforming Reformed gasoline obtained by the method, raffinate, which is a residue of aromatics extracted from reformed gasoline, light fraction of reformed gasoline, medium heavy fraction of reformed gasoline, heavy fraction of reformed gasoline , Cracked gasoline obtained by catalytic cracking method, hydrocracking method, etc., light fraction of cracked gasoline, heavy fraction of cracked gasoline, straight-run gas oil and straight-run kerosene obtained from atmospheric distillation equipment of crude oil, normal pressure Contact oil obtained by catalytic cracking or hydrocracking vacuum gas oil, vacuum gas fuel oil or desulfurized fuel oil obtained by treating straight-run heavy oil or residual oil obtained from a distillation unit with a vacuum distillation unit. Cracked gas oil, catalytic cracked kerosene, hydrocracked gas oil or hydrocracked kerosene, hydrorefined gas oil obtained by hydrorefining these petroleum hydrocarbons, hydrodesulfurized gas oil, hydrorefined kerosene, and natural 1 type of base material such as naphtha fraction, kerosene fraction, light oil fraction of GTL (Gas to liquids) obtained by FT (Fischer-Tropsch) synthesis after cracking gas etc. into carbon monoxide and hydrogen Or it can prepare by mixing 2 or more types.

  You may add a well-known fuel additive to the fuel of this invention as needed. For example, fuel additives include friction modifiers such as amide compounds of higher carboxylic acids and alcohol amines, detergent dispersants such as succinimides, polyalkylamines and polyetheramines, N, N′-diisopropyl-p- Antioxidants such as phenylenediamine, N, N'-diisobutyl-p-phenylenediamine, 2,6-di-t-butyl-4-methylphenol, hindered phenols, N, N'-disalicylidene-1, -Metal deactivators such as amine carbonyl condensation compounds such as diaminopropane, surface ignition inhibitors such as organophosphorus compounds, anti-icing agents such as polyhydric alcohols and ethers thereof, alkali metal salts or alkaline earths of organic acids Auxiliary surfactant such as metal salt, higher alcohol sulfate, anionic surfactant, cationic surfactant, amphoteric surfactant Such as antistatic agents such as azo dyes, organic carboxylic acids and derivatives thereof, rust preventives such as alkenyl succinic acid esters, draining agents such as sorbitan esters, nitrate esters and organic peroxides, etc. Low-temperature fluidity improvers such as cetane improvers, carboxylic acid-based, ester-based, alcohol-based and phenol-based lubricity improvers, silicon-based antifoaming agents, ethylene-vinyl acetate copolymers, alkenyl succinic acid amides, etc. And discriminating agents such as quinizarin and coumarin, and odorants. These additives can be added singly or as a mixture, and the total amount of these additives is added at a ratio such that the total amount of fuel is 0.5% by mass or less, more preferably 0.2% by mass or less. It is preferable. Here, the total amount of additive means the amount added as an active ingredient of the additive.

The fuel of the present invention contains hydrocarbon as a main component, but may contain oxygen-containing compounds such as ether, alcohol, ketone, ester, glycol and the like.
Examples of the oxygen-containing compound 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), tertiary amyl ethyl ether, fatty acid methyl ester, and fatty acid ethyl ester.

  By containing the oxygen-containing compound, the fuel of the present invention can reduce unburned hydrocarbons (HC), fine particulate matter, and the like in the exhaust gas. In addition, when an oxygen-containing compound derived from biomass is used, it contributes to carbon dioxide reduction and the like. However, in some cases, an increase in nitrogen compounds may be caused. Therefore, the content ratio of oxygen-containing compounds is preferably 20% by mass or less, more preferably 10% by mass or less, based on the total amount of fuel in terms of oxygen element (oxygen content). Preferably, 3 mass% or less is the most preferable.

  The fuel of the present invention is a fuel suitable for a premixed compression self-ignition engine, a premixed compression self-ignition engine, a spark ignition engine, a diesel engine, an electric motor engine, a spark ignition engine, or a diesel engine. The present invention can also be applied to an engine that uses a hybrid engine combined with an electric motor engine.

  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 1-6 and Comparative Examples 1-6]
According to the composition shown in Table 1, fuels of the present invention (Examples 1 to 6) and comparative fuels (Comparative Examples 1 to 6) were prepared by a conventional method. Table shows the hydrocarbon compound content, octane number (research method octane number, motor method octane number) of each fuel obtained, initial distillation point and end point of distillation properties, measurement results of sulfur content, HCCI Index value, and NDI value calculation results This is also shown in 1.
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: 14
Fuel injection pressure: 8MPa

(Engine test)
Combustion analysis apparatus manufactured by Ono Sokki Co., Ltd. for combustion pressure data (resolution: 0.25 CAdeg) for 2400 cycles (400 cycles × 6 times) at an engine speed of 1500 rpm and a torque of 65 Nm for the fuels of Examples and Comparative Examples (Model No. DS2100) was used to obtain the following values.
(1) Fluctuation value of average effective pressure (average effective pressure fluctuation range / average effective pressure)
(2) Maximum pressure increase rate (3) Fuel consumption improvement rate relative to Example 6 (4) Rotation speed upper limit

  As is clear from the results in Table 2, all of the fuels of the examples show the maximum pressure increase rate appropriate for the premixed compression self-ignition combustion, and the average effective pressure is within the allowable range. On the other hand, the fuels of Comparative Example 1 and Comparative Example 2 having an HCCI Index value of less than 20 have a large maximum pressure increase rate, cause severe knocking, and are not at all suitable as a fuel for a premixed compression self-ignition engine. The fuels of Comparative Example 3 and Comparative Example 4 having an HCCI Index value exceeding 55 are at a problematic level due to large fluctuations between combustion cycles. The fuel of Comparative Example 5 is a normal standard fuel having an octane number of 93 consisting of two components of 93% by volume of normal heptane and 7% by volume of isooctane, and Comparative Example 6 is a case in which 30% by volume or more of naphthene is contained. The fuels of Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6 are all inferior to the fuels of all Examples in terms of fuel consumption, and the upper limit of the possible engine rotation range is low. The fuels of Example 4, Comparative Example 5, and Comparative Example 6 are fuels that are completely unsuitable as fuels for premixed compression self-ignition engines.

Claims (5)

A premixed compression self-ignition engine fuel characterized by satisfying the following (a), (b), (c) and (d):
(A) Total content of hydrocarbons having a content of 5% by volume or less is 30% by volume or more (b) Research method octane number is 60 or more and less than 90 (c) HCCI Index represented by the following formula (1) is 20.68 54.24 or less
HCCI Index = MON−0.424 × A−0.377 × B−0.202 × C−0.205 × D (1)
(In formula (1), MON is a measured value based on the motor method octane number, A is normal paraffin content (volume%), B is isoparaffin content (volume%), C is olefin content (volume%), and D is aromatic. Represents the group content (volume%).)
(D) The content of naphthene is 1.3% by volume or more and 20% by volume or less.   2. The fuel for a premixed compression self-ignition engine according to claim 1, wherein an initial boiling point is 45 ° C. or lower and an end point is 210 ° C. or lower. The fuel for a premixed compression self-ignition engine according to claim 1 or 2, wherein the NDI represented by the formula (2) is 115 or more and 225 or less .
NDI = 4 × E1 + 3 × E2 + 2 × E3-1 × E4-4 × E5 (2)
(In the formula (2), E1 is a fraction having a boiling point of less than 70 ° C. (volume%), E2 is a fraction having a boiling point of 70 ° C. or more and less than 100 ° C. (volume%), and E3 is a fraction having a boiling point of 100 ° C. or more and less than 130 ° C. (Volume%), E4 represents a fraction having a boiling point of 130 ° C. or more and less than 160 ° C. (volume%), and E5 represents a fraction having a boiling point of 160 ° C. or more (volume%).) 15 Density at ℃ is 0.60 g / cm ³ or more 0.78 g / cm ³ or less homogeneous charge compression ignition engine fuel as claimed in any one of claims 1 to 3, characterized in that.   The fuel for a premixed compression self-ignition engine according to any one of claims 1 to 4, wherein the sulfur content is 50 ppm by mass or less.