JP5355064B2 - Fuel for premixed compression self-ignition engines - Google Patents

Description

  The present invention relates to a fuel for a premixed compression self-ignition engine, and more particularly, to a premixed compression self-ignition engine capable of controlling combustion reaction in premixed compression self-ignition combustion and achieving improvement in engine thermal efficiency. Regarding fuel.

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 by the piston rise in the compression stroke, 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 efficiency and thermal efficiency, while the compression self-ignition diesel engine has fuel efficiency 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, fuel saving 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 mass 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. It is possible.

As fuels for such premixed compression self-ignition engines, fuels have been proposed that focus on fuel volatility indicators and existing gasoline engines such as cetane number and octane number, and diesel engine ignitability indicators ( See, for example, Patent Documents 1 to 13, and the mechanism of premixed compression self-ignition combustion (self-ignition characteristics of the fuel itself) does not necessarily indicate that the characteristics are sufficiently exhibited. The development of a fuel more suitable for an 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

In an internal combustion engine that performs premixed compression self-ignition combustion (hereinafter also referred to as HCCI combustion), an air-fuel mixture in which fuel is sufficiently premixed with air rises in temperature and pressure due to compression of the piston, resulting in ignition. Since the air-fuel mixture ignites almost at the same time, a sharp increase in pressure causes knocking of the engine, and the load cannot be increased.
An object of the present invention is to provide a fuel for a premixed compression self-ignition engine capable of controlling the combustion reaction in the premixed compression self-ignition combustion and achieving an improvement in engine thermal efficiency.

  The present inventors have developed a C5 to C10 paraffinic hydrocarbon mainly starting to decompose in a cold flame reaction (temperature of 750 K or more and less than 900 K) in HCCI combustion, and an aromatic that is opened by a hot flame reaction (1100 K or more). Combining C6 to C11 monocyclic aromatic hydrocarbons, which generate aromatic radicals and aromatic hydrocarbons, prolongs the combustion period and suppresses steep pressure rise during ignition The present invention has been completed by finding that it is possible to realize a high-load operation that avoids knocking.

That is, the present invention is a premixed compression self-ignition engine characterized by being a fuel that satisfies all the following properties (1) to (6) and satisfies the requirements (7) or (8): Related to fuel.
(1) The total content of normal paraffins from C5 to C10 is from 40.31 % by volume to 70% by volume.
(2) The content of aromatic hydrocarbons from C6 to C11 is 30% by volume or more and 59.69 % by volume or less.
(3) The content of olefinic hydrocarbon is 20% by volume or less.
(4) The content of oxygen-containing hydrocarbon is 5% by mass or less in terms of oxygen atom.
(5) The research octane number is 70 or more and less than 92.
(6) The initial boiling point of the distillation property is 30 ° C or higher and the end point is 220 ° C or lower.
(7) Same average effective pressure value and high temperature oxidation under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing) Compared with a positive reference fuel (Primary Reference Fuel: hereinafter abbreviated as PRF) indicating the reaction combustion center of gravity (HTHR CA50), the average value of the maximum continuous pressure increase rate of 400 cycles is 15% compared with PRF. Smaller fuel than that.
(8) Under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing), the maximum pressure increase rate is the same. Fuel whose average value of the measured mean effective pressure measured over 400 cycles increases by 20% or more compared to the PRF with the same research octane number.

  The fuel of the present invention can suppress the maximum pressure increase rate during premixed compression self-ignition combustion and can realize quiet engine combustion. Further, under the same maximum pressure increase rate condition, it is possible to improve the engine output by 20% or more compared with the conventional one.

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, a type that switches between the premixed compression self-ignition engine and a spark ignition engine or a diesel engine, and an electric motor and spark ignition. The present invention can also be applied to a hybrid engine in which a system engine or a diesel engine is combined.

  When the fuel self-ignites, a low temperature oxidation reaction (Low Temperature Heat Release: LTHR) occurs first, followed by a high temperature oxidation reaction (High Temperature Heat Release: HTHR). The premixed compression self-ignition engine fuel according to the present invention is characterized by combining a highly decomposable fuel (normal paraffin) and a low decomposable fuel (aromatic and olefin), as shown in FIG. First, a highly decomposable fuel (paraffinic hydrocarbon) is oxidatively decomposed during the period of Cool Flame and Blue Flame, and has an aromatic benzene ring structure during the period of Hot Flame. Two-stage combustion can be achieved by the oxidative decomposition of aromatic radicals and aromatic hydrocarbons.

The fuel of the present invention needs to satisfy all the following properties (1) to (6).
(1) C5 from the total content of normal paraffins to C10 is 40.31 volume% or more, or less 70% by volume, preferably 5 0% by volume or less. C4 or lower normal paraffin hydrocarbons cannot exhibit a sufficient low temperature oxidation reaction. Moreover, C11 or higher hydrocarbons have a high boiling point and are not suitable as fuel for HCCI engines.
(2) the content of aromatics from C6 to C11 is 30 volume% or more, or less 59.69 volume%, preferably 50 volume% or more. C12 or higher hydrocarbons have poor volatility and are not suitable as fuel for HCCI engines. Moreover, when the aromatics exceeding 75% by volume are contained in the fuel, the operable load rotation region is narrowed.
(3) The content of the olefinic hydrocarbon is 20% by volume or less, preferably 10% by volume or less.
(4) The content of oxygen-containing hydrocarbon is 5% by mass or less in terms of oxygen atom.
(5) The research octane number is 70 or more and less than 92, preferably 70 or more and 86 or less.
(6) The distillation property has an initial boiling point of 30 ° C or higher and an end point of 220 ° C or lower, preferably an initial boiling point of 30 ° C or higher and an end point of 150 ° C or lower.
The definition of the hydrocarbon content here means a value measured using a gas chromatograph in accordance with JIS K 2536 “Petroleum product-component test method”. Normal paraffin means a straight-chain hydrocarbon and does not contain naphthene (cyclic saturated hydrocarbon).

  In addition to the above, the fuel of the present invention needs to satisfy the following requirements (7) or (8).

(7) The fuel injection amount is changed (injector fuel) under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing). When operated with the injection time adjusted), it is compared with a positive reference fuel (Primary Reference Fuel: hereinafter abbreviated as PRF) showing the same average effective pressure value and high temperature oxidation reaction combustion gravity center value (HTHR CA50). The average value of the continuous maximum pressure increase rate for 400 cycles is a fuel that is 15% or less smaller than that of the PRF, preferably a fuel that is 20% or smaller.
Note that the same mean effective pressure value and high temperature oxidation reaction combustion gravity center value here are within the range of ± 20 kPa in the illustrated mean effective pressure and ± 0. It is defined as being within 8 deg crank angle. PRF means a primary reference fuel used when measuring octane number. For example, PRF80 is a fuel with a research octane number of 80 produced by mixing 80% by volume of isooctane and 20% by volume of normal heptane. Means. The measurement method of the mean effective pressure value and the definition of HTHR CA50 are based on the description in the paper SAE2006-01-0207.

(8) Under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing), the maximum pressure increase rate is the same. The average value of the measured mean effective pressure measured over 400 cycles is a fuel that is increased by 20% or more, preferably a fuel that is increased by 25% or more, more preferably 50% compared to a PRF having the same research octane number. This is an increasing fuel.
The error of the maximum pressure increase rate here is defined to be within ± 4 kPa / deg with respect to the PRF as the comparative fuel.

  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 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, since an increase in nitrogen compounds may be caused depending on circumstances, the content ratio of the oxygen-containing compound is preferably 5% 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 is not particularly limited as long as a fuel having a predetermined property can be obtained as described above. For example, a naphtha fraction obtained by atmospheric distillation of crude oil ( Full-range naphtha), naphtha light fraction (light naphtha), naphtha heavy fraction (heavy naphtha), desulfurized full-range naphtha desulfurized full-range naphtha, desulfurized light naphtha desulfurized light naphtha, desulfurized heavy naphtha Alkylate obtained by adding (alkylating) lower olefins to hydrocarbon compounds such as isomerized gasoline and isobutane obtained by converting desulfurized heavy naphtha and light naphtha into isoparaffin using an isomerizer, catalytic reforming method Reformed gasoline, raffinate, which is a residue obtained by extracting aromatics from reformed gasoline, light fraction of reformed gasoline, reformed gasoline Middle heavy fraction, heavy reformed gasoline fraction, cracked gasoline obtained by catalytic cracking, hydrocracking, etc., light fraction of cracked gasoline, heavy fraction of cracked gasoline, atmospheric distillation of crude oil Contact with straight-run gas oil and straight-run kerosene obtained from the equipment, straight-run heavy oil and residual oil obtained from the atmospheric distillation equipment with reduced-pressure light oil, reduced-pressure heavy light oil or desulfurized heavy oil obtained by processing with a vacuum distillation device Catalytic cracked diesel oil, catalytic cracked kerosene, hydrocracked diesel oil or hydrocracked kerosene obtained by cracking or hydrocracking, hydrorefined diesel oil, hydrodesulfurized diesel oil obtained by hydrorefining these petroleum hydrocarbons GTL (Gas to liquids) naphtha fraction, kerosene fraction obtained by FT (Fischer-Tropsch) synthesis after decomposing young hydrorefined kerosene and natural gas into carbon monoxide and hydrogen, Mixing one or more base materials such as light oil fractions Can be prepared.

  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 alone or as a mixture. The total amount of these additives is preferably 0.5% by mass or less, more preferably 0.2% by mass or less based on the total amount of fuel. It is desirable to add. 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.

  According to the composition shown in Table 1, fuels of the present invention (Examples 1 and 2) and comparative fuels (Comparative Examples 1 and 2) were prepared by a conventional method. Table 1 shows the hydrocarbon compound content and properties of the obtained fuels.

(Engine specifications)
Engine type: Inline 4-cylinder, premixed compression self-ignition engine with a compression ratio of 15 The specifications of the following literature were used for the engine specifications.
SAE 2006-01-0207 (April 2006 issue)

Example 1
<Engine operating conditions>
Engine speed control conditions such as engine speed 1000rpm, supercharging absolute pressure 155kPa, intake pipe temperature 58 ° C, engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate are The experiment was conducted by changing only the fuel injection amount (adjusting the fuel injection time of the injector) regardless of the fuel.

<Fuel>
FIG. 2 shows a list of the average values of 400 cycles of the high temperature oxidation reaction combustion center of gravity (HTHR CA50) and the indicated mean effective pressure (IMEP) when operated using various fuels. . From these conditions, point 1, point 2, and point 3, which are almost the same IMEP and almost the same HTHR CA50 conditions, were selected, and the change in the maximum pressure increase rate for 400 cycles at each point was measured. The details of this experiment are based on the description of the paper SAE2008-01-0007.

3 shows changes in the maximum pressure increase rate of 400 cycles at point 1, FIG. 4 shows changes in the maximum pressure increase rate of 400 cycles at point 2, and FIG. 5 shows changes in the maximum pressure increase rate of 400 cycles at point 3. The details are shown in Table 2, Table 3, and Table 4.
In any case, the NTL fuel (NTL70, NTL75) corresponding to the fuel of the present invention has a maximum pressure increase of 20% or more compared to the PRF fuel (PRF90, PRF85) operated under the same operating conditions (same IMEP, same HTHR CA50). It can be seen that the rate is reduced. Further, even when compared with the other fuels (NDB fuel, NMP fuel) in Comparative Example 1, there is no fuel that can reduce the maximum pressure increase rate like the NTL fuel. In the present invention, by utilizing the fact that the ignition temperature of the component mainly composed of paraffinic fuel and the fuel mainly composed of aromatic fuel is different, the HCCI that suppresses such a maximum pressure increase rate by preventing abrupt combustion. Driving is possible.

(Example 2)
<Fuel>
The following fuels were prepared as fuels with the same research method octane number (note that the research method octane number of PRF and NTL fuel here is the CFR engine (Cooperative Fuel Research) measured by the research method octane number defined by JISK2280) The error is within 3).
(1) Fuel with a research octane number of 75 (Comparative example) PRF75, NDB75, NMP75, NCP75
(Example) NTL75
<Engine operating conditions>
The engine control conditions such as engine speed 1000rpm, supercharging absolute pressure 155kPa, intake pipe temperature 58 ° C, engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, etc. Experimental data was collected under the following conditions with the same average maximum pressure increase rate for 400 cycles under the same conditions regardless of the fuel.

  Measured under the conditions of a maximum pressure increase rate of 800 kPa / deg for a fuel with a research octane number of 75 (measurement condition A).

<Result>
The measurement condition A, B, cylinder pressure and heat release rate of 400 cycles the average measured by C and that list is shown in FIGS. 6 and 7 and Table 5.

In any of the figures, the NTL fuel (NTL75) corresponding to the fuel of the present invention is higher than the comparative fuel (PRF fuel, NDB fuel, NMP fuel, NCP fuel) under the same maximum pressure increase rate. The improvement rate of 28.2% is shown in the indicated mean effective pressure. As shown in FIG. 7, in the present invention, it is possible to extend the combustion period and prevent sharp combustion by utilizing the fact that the ignition temperature of the component mainly composed of paraffinic fuel and the component mainly composed of aromatic fuel is different. This is because many fuels can be burned under the same maximum pressure increase rate, and the heat generation rate can be increased.

The way of occurrence of HCCI combustion (two-stage combustion) of the present invention will be described. The average value of 400 cycles of HTHR CA50 and IMEP in the engine operating condition of Example 1 is shown. The change in the maximum pressure increase rate of 400 cycles at point 1 is shown. The change in the maximum pressure increase rate of 400 cycles at point 2 is shown. The change in the maximum pressure increase rate of 400 cycles at point 3 is shown. The in-cylinder pressure in the measurement condition A is shown. The heat release rate under measurement condition A is shown.

Claims (1)

A fuel for a premixed compression self-ignition engine characterized by satisfying all the following properties (1) to (6) and satisfying the requirements (7) or (8).
(1) The total content of normal paraffins from C5 to C10 is from 40.31 % by volume to 70% by volume.
(2) The content of aromatic hydrocarbons from C6 to C11 is 30% by volume or more and 59.69 % by volume or less.
(3) The content of olefinic hydrocarbon is 20% by volume or less.
(4) The content of oxygen-containing hydrocarbon is 5% by mass or less in terms of oxygen atom.
(5) The research octane number is 70 or more and less than 92.
(6) The initial boiling point of the distillation property is 30 ° C or higher and the end point is 220 ° C or lower.
(7) Same average effective pressure value and high temperature oxidation under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing) Compared with a positive reference fuel (Primary Reference Fuel: hereinafter abbreviated as PRF) indicating the reaction combustion center of gravity (HTHR CA50), the average value of the maximum continuous pressure increase rate of 400 cycles is 15% compared with PRF. Smaller fuel than that.
(8) Under the same engine operating conditions (engine compression ratio, rotation speed, supercharging pressure, intake pipe temperature, air flow rate, valve timing, EGR rate, fuel injection start timing), the maximum pressure increase rate is the same. Fuel whose average value of the measured mean effective pressure measured over 400 cycles increases by 20% or more compared to the PRF with the same research octane number.

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