JP2007091819A - Fuel for premixed compression autoignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel for a premixed compression autoignition engine, which has excellent ignition property in the combustion by the premixed compression autoignition, can improve the engine output and extend the engine rotational region as much as possible, and can attain improvement of the engine heat efficiency. <P>SOLUTION: The fuel for the premixed compression autoignition engine is the one which has a cyclopentane content of ≤7 vol%, a pentene content of ≤4 vol% and initiates the high temperature oxidation reaction under the condition that the temperature and the pressure satisfy the high temperature oxidation reaction formula (1) mentioned below. The formula (1) is -0.0105×T+14≤P≤-0.0105×T+16, wherein P and T are pressure (MPa) and a temperature (K), respectively, at the start of the high temperature oxidation reaction. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 the 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 efficiency 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. 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 fuel efficiency 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 that focus on the volatility index of fuel, the existing gasoline engines such as cetane number and octane number, and the ignitability index of diesel engines have been proposed ( For example, see Patent Documents 1 to 13), and from the viewpoint of the mechanism of premixed compression self-ignition combustion (self-ignition characteristics of the fuel itself), it cannot be said that the characteristics are sufficiently exhibited. Development of a fuel more suitable for an ignition engine is desired.
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 JP 2004-315604 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.

As a result of intensive studies to solve the above problems, the present inventors have determined that a fuel having a specific composition and starting a high-temperature oxidation reaction under a specific condition is used as a fuel for a premixed compression self-ignition engine. It has been found suitable, and the present invention has been completed.
That is, the present invention is a condition in which the content of cyclopentanes is 7% by volume or less, the content of pentenes is 4% by volume or less, and the temperature and the pressure satisfy the following high-temperature oxidation reaction formula (1). The present invention relates to a premixed compression self-ignition engine fuel characterized in that a high-temperature oxidation reaction starts.
(1) −0.0105 × T + 14 ≦ P ≦ −0.0105 × T + 16
(Here, P represents the pressure (MPa) at the start of the high temperature oxidation reaction, and T represents the temperature (K) at the start of the high temperature oxidation reaction).

  The fuel of the present invention can increase the engine output and the engine rotation region during premixed compression self-ignition combustion as much as possible, and achieve an improvement in engine thermal efficiency. The fuel of the present invention is a premixed compression self-ignition engine and a spark ignition engine, a diesel engine, an electric motor engine, a spark ignition engine, or a hybrid engine that combines a diesel engine and an electric motor. It can also be used as fuel.

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

When the fuel self-ignites, as shown in FIG. 1, a low temperature oxidation reaction occurs first, followed by a high temperature oxidation reaction. FIG. 1 shows a pre-mixed compression self-ignition engine modified from a 4-cycle in-line 6-cylinder gasoline engine with a displacement of 2000 cc and a compression ratio of 14, a fast response pressure sensor embedded in the cylinder (for example, 601A manufactured by Nippon Kisler Co., Ltd.). FIG. 6 is a graph showing changes in the heat generation rate obtained from (1) with the crank angle (CAdeg) on the horizontal axis and the heat generation rate (J / CAdeg) on the vertical axis. Here, when the activity of the low-temperature oxidation reaction is reduced, the temperature and pressure at the start of the subsequent high-temperature oxidation reaction are negatively affected, and the engine rotation area of the premixed compression self-ignition engine is significantly reduced. The present inventors made it clear by the examination results. The high-temperature oxidation reaction formula (1) shown below is based on the above-mentioned self-ignition characteristics, and the range in which stable self-ignition can be obtained in a premixed compression self-ignition engine is the temperature (T) and pressure at the start of the high-temperature oxidation reaction. The present inventors have found out from the relationship (P). The temperature (T) and pressure (P) at the start of the high-temperature oxidation reaction here are the temperature (K) in the engine cylinder at the crank angle at which the heat generation rate (J / CAdeg) turns from minus to plus in FIG. ) And pressure (MPa).
If this high temperature oxidation reaction formula (1) is a premixed compression self-ignition engine, the engine type and operating conditions (rotation speed, load, supercharging pressure, air amount, fuel consumption, intake air temperature, EGR rate, It is obtained from the pressure (P) and temperature (T) in the formula without being influenced by the valve timing.
(1) −0.0105 × T + 14 ≦ P ≦ −0.0105 × T + 16
The fuel of the present invention has a temperature (T) and a pressure (P) at the start of the high-temperature oxidation reaction from the viewpoint that stable combustion in a premixed compression self-ignition engine, improvement in engine output, and a wide engine rotation range are obtained. It is necessary to satisfy the condition of the high temperature oxidation reaction formula (1). If the temperature and pressure at the start of the high-temperature oxidation reaction deviate from the conditions of the high-temperature oxidation reaction formula (1), the high-temperature oxidation reaction is hindered and the premixed compression self-ignition combustion becomes unstable.

The fuel of the present invention needs to satisfy that the content of cyclopentanes is 7% by volume or less and the content of pentenes is 4% by volume or less. The content of cyclopentanes is preferably 5% by volume or less, and more preferably 3% by volume or less from the viewpoints of achieving stable combustion in a premixed compression self-ignition engine, improving engine output, and obtaining a wide engine rotation range. For the same reason, the content of pentenes is preferably 2% by volume or less.
When the content of cyclopentanes and the content of pentenes exceed the above-mentioned upper limit, the activity of the low-temperature oxidation reaction is lowered in the premixed compression auto-ignition combustion, and the subsequent high-temperature oxidation reaction is hindered.
Examples of cyclopentanes include those in which one or more side chains such as alkyl groups are attached to the cyclopentane skeleton, and typical examples include cyclopentane, methylcyclopentane, ethylcyclopentane, propylcyclopentane, and dimethyl. Examples thereof include cyclopentane, methylethylcyclopentane, trimethylcyclopentane, and isomers thereof.
Examples of pentenes include 1-pentene and 2-pentene.
In addition, content of cyclopentane here and content of pentene say the value measured using a gas chromatograph based on JISK2536 "petroleum product-component test method".

In the fuel of the present invention, the aromatic content and the naphthene content are not particularly limited, but these have a low temperature oxidation reaction during premixed compression self-ignition combustion and have an inhibitory action to suppress the low temperature oxidation reaction. In each of these fuels, it is preferable that the amount is 15% by volume or less. Further, in order to further expand the premixed compression self-ignition combustion region having high thermal efficiency with respect to the engine load and the rotational speed, it is more preferable that the amount is 10% by volume or less.
In addition, the content of each of aromatic content and naphthene content referred to here conforms to JIS K2536 “Petroleum product-component test method” when the end point by JIS K2536 “Atmospheric pressure distillation test method” is 250 ° C. or less. If the end point exceeds 250 ° C, the naphthene content (volume%) is ASTM D2786 “Standard Test Method for Hydrocarbon Types Analysis of Gas-Oil Saturates Fractions by High Ionizing Voltage. Measured according to “Mass Spectrometry” and the aromatic content (volume%) is JPI-5S-49-97 “Hydrocarbon Type Test Method—High Performance Liquid Chromatograph Method” published by the Japan Petroleum Institute. The value measured in accordance with "".

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

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 hydrocarbon (HC), fine particulate matter, etc. 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 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 Combustors such as metal salts and higher alcohol sulfates, anionic surfactants, cationic surfactants, amphoteric surfactants 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. Discriminating agents such as quinizarin and coumarin, and odorants. These additives can be added alone or as a mixture, and are added in such a ratio that the total amount of these additives is 0.5% by mass or less, more preferably 0.2% by mass or less based on the total amount of fuel. It is preferable. Here, the total amount of additive means the amount added as an active ingredient of the additive.

  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 1-9 and Comparative Examples 1-8)
According to the composition shown in Table 1, fuels of the present invention (Examples 1 to 9) and comparative fuels (Comparative Examples 1 to 8) were prepared by a conventional method. Table 1 shows the measurement results of the hydrocarbon compound content, sulfur content, temperature at the start of the high-temperature oxidation reaction, and pressure in each fuel obtained.
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)
<Case 1>
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 2000 rpm and a torque of 80 Nm for the fuels of the examples and comparative examples. (Model No. DS2100) was used to obtain the following values.
(1) Temperature T (K) and pressure P (MPa) at the start of the high-temperature oxidation reaction
(2) y-intercept A: calculated by substituting the temperature (T) and pressure (P) at the start of the high-temperature oxidation reaction into the equation of P = −0.0105 × T + A. (3) Maximum pressure increase rate (4) Average effective Pressure fluctuation value (average effective pressure fluctuation range / average effective pressure)
(result)
The fuels of the examples all showed a maximum pressure increase rate appropriate for premixed compression self-ignition, the fluctuation rate of the average effective pressure was small, and stable premixed compression self-ignition combustion was obtained. On the other hand, it can be seen that the fuel of the comparative example is not suitable for the premixed compression self-ignition engine because the maximum pressure increase rate is small and the fluctuation rate of the average effective pressure is large and unstable combustion occurs.
Further, when the temperature, pressure and y-intercept A at the start of the high-temperature oxidation reaction were obtained, all y-intercepts A of the fuels of the examples were within the range of 14 to 16 and satisfy the high-temperature oxidation reaction formula (1). The y intercept A of the fuel of the comparative example is less than 14 and does not satisfy the high temperature oxidation reaction formula (1).
<Case 2>
About the fuel of an Example and a comparative example, an engine is drive | operated by various load, the limit of the maximum and minimum rotation speed which can be drive | operated is calculated | required, and the comparison of the width of an engine operation area | region is implemented for every fuel.
(result)
Compared with the fuel of the example, the fuel of the comparative example has a remarkably narrow possible operation rotation range, and it can be seen that the fuel is not suitable for the premixed compression self-ignition engine.

It is the figure which showed the change of the heat release rate in a cylinder with the crank angle on the horizontal axis and the heat release rate on the vertical axis.

Claims (1)

The high-temperature oxidation reaction starts under the condition that the content of cyclopentanes is 7% by volume or less, the content of pentenes is 4% by volume or less, and the temperature and pressure satisfy the following high-temperature oxidation reaction formula (1). A fuel for a premixed compression self-ignition engine characterized by that.
(1) −0.0105 × T + 14 ≦ P ≦ −0.0105 × T + 16
(Here, P represents the pressure (MPa) at the start of the high temperature oxidation reaction, and T represents the temperature (K) at the start of the high temperature oxidation reaction).

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