JP5436849B2 - Fuel oil composition for premixed compression ignition engines - Google Patents

Description

  The present invention relates to a fuel oil composition for a premixed compression ignition type engine, and in particular, has an optimal ignitability as a fuel for a premixed compression ignition type engine, and causes less dilution of the engine oil, and The present invention relates to a fuel oil composition having a small amount of particulate matter (PM) in exhaust gas.

Nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) emitted from automobiles have a certain contribution to the concentration of these harmful components in the atmosphere. From the viewpoint of improvement, reduction of these harmful exhaust gas components is strongly demanded. On the other hand, in order to prevent global warming, it is necessary to reduce the CO ₂ emitted by the combustion of fossil fuels, which reduces CO ₂ emissions from automobiles, that is, improves the fuel consumption efficiency (fuel consumption) of automobiles. There is a strong demand. As described above, in automobiles, it is necessary to simultaneously achieve emission reduction of harmful gas components and CO ₂ emission reduction. Recently, as a corresponding technology, a premixed compression ignition (PCCI) engine is used. Attention has been paid.

  In the PCCI engine, since the start (ignition) of combustion depends on the self-ignition of fuel, a fuel with good ignitability is required when the temperature in the combustion chamber is low or the load is low. However, fuel with good ignitability causes rapid combustion due to multi-point simultaneous ignition in the combustion chamber under high load conditions where the temperature in the combustion chamber is high, resulting in increased combustion noise and engine damage. Therefore, under high load conditions where the temperature in the combustion chamber is high, a fuel with low ignitability, that is, a fuel exhibiting slow combustion behavior is required.

  In addition, in the PCCI engine, fuel is injected earlier than a diesel engine so that the fuel injected into the combustion chamber can be sufficiently mixed with air to form a uniform premixed gas. It tends to reach the cylinder liner and adhere easily. Since the fuel adhering to the cylinder liner is difficult to be consumed in the combustion process, it may dissolve in the engine oil and cause dilution of the engine oil. Therefore, in addition to the above ignition characteristics, the PCCI engine fuel is required to have appropriate volatility in order to prevent dilution of engine oil. Further, PCCI engine fuels are desired to further reduce harmful exhaust gases.

JP 2004-293394 A Automotive Technology, 2006, Vol.60, No.9, P83-88

  Accordingly, an object of the present invention is to provide a fuel oil composition that has optimum ignitability as a fuel for a premixed compression ignition type engine, causes little dilution of engine oil, and has less harmful exhaust gas. It is in.

  As a result of intensive studies to achieve the above object, the present inventors have specific distillation properties, cetane number (CN) and research octane number (RON) are in a specific range, and have an aromatic content. By using a fuel oil composition having a low total amount and aromatic content of three or more rings and exhibiting specific properties in high pressure differential scanning calorimetry (DSC) for a premixed compression ignition engine, it is possible to prevent dilution of engine oil. In addition, the inventors have found that harmful exhaust gas can be reduced and have completed the present invention.

That is, the fuel oil composition for the premixed compression ignition engine of the present invention is
・ Sulfur content is 10 mass ppm or less, 90 volume% distillation temperature is 281.0 ℃ or less, cetane number (CN) is 45 to 65, research octane number (RON) is 20 or more, aromatic content is 22.9 volumes %, And the aromatic content of 3 or more rings is 0.5% by volume or less,
The heat generation starting temperature in high-pressure differential scanning calorimetry (DSC) is 250 ° C. or lower, and the peak value of the heat generation peak is 25 W / g or higher.

  In the present invention, the sulfur content is measured in accordance with JIS K2541-6, the 90% by volume distillation temperature is measured in accordance with JIS K2254, the cetane number (CN) and the research octane number (RON) are measured in accordance with JIS K2280, and aroma. The total amount of aromatics and the aromatic content of 3 or more rings are measured according to JPI-5S-49-97 “Petroleum products—Hydrocarbon type test method—High performance liquid chromatograph method”

  According to the present invention, having a specific distillation property, the cetane number (CN) and the research octane number (RON) are in a specific range, the total amount of aromatics and the aromatic content of three or more rings are low, By using a fuel oil composition exhibiting specific properties in high pressure differential scanning calorimetry (DSC) for a PCCI engine, dilution of engine oil can be prevented and exhaust gas can be improved.

The present invention is described in detail below. The premixed compression ignition type engine fuel oil composition of the present invention has a sulfur content of 10 ppm by mass or less, a 90% by volume distillation temperature of 281.0 ° C. or less, a cetane number (CN) of 45 to 65, a research method The octane number (RON) is 20 or more, the aromatic content is 22.9 % by volume or less, the aromatic content of 3 or more rings is 0.5% by volume or less, and the heat generation starting temperature in high-pressure differential scanning calorimetry (DSC) is 250 ° C. The peak value of the exothermic peak is 25 W / g or more. The fuel oil composition of the present invention has a 90% by volume distillation temperature that is sufficiently low, has very little aromatic content of three or more rings, and has a sufficiently high combustibility as evaluated by DSC. The reached fuel is sufficiently vaporized and burned before the piston descends. As a result, the engine oil is less likely to be diluted and contributes to the improvement of exhaust gas.

<Sulfur content>
The fuel oil composition for PCCI engines of the present invention has a sulfur content of 10 mass ppm or less, preferably 5 mass ppm or less, more preferably 3 mass ppm or less. Since the fuel oil composition of the present invention has a sulfur content of 10 ppm by mass or less, there are few sulfur oxides as combustion products, which can contribute to a reduction in environmental burden. Further, since the sulfur content poisons the exhaust gas purification catalyst, the reduction of the sulfur content can contribute to the reduction of the environmental load through the maintenance of the performance of the exhaust gas purification catalyst. Furthermore, in a vehicle equipped with a NOx occlusion reduction catalyst, fuel is used for regeneration of sulfur poisoning of the catalyst. Therefore, reduction of the sulfur content also contributes to improvement of fuel consumption. Since these effects become more significant as the sulfur content is lower, the sulfur content in the fuel oil composition of the present invention is preferably 5 ppm by mass or less, more preferably 3 ppm by mass or less.

<90% volume distillation temperature (T90)>
The fuel oil composition for PCCI engines of the present invention has a 90% by volume distillation temperature (T90) of 281.0 ° C or lower, preferably 280 ° C or lower. The volatility of the trailing portion of the fuel oil composition affects the formation and combustion of the mixture of the fuel oil composition and air, and when the 90 vol% distillation temperature (T90) exceeds 300 ° C, the fuel oil composition This may hinder the formation of an air-fuel mixture of the composition and air, or the combustibility of the air-fuel mixture may be reduced, leading to deterioration of exhaust gas. In addition, in a PCCI engine that injects fuel earlier than a diesel engine, part of the fuel reaches the cylinder liner and is scraped off by the lowering of the piston and flows into the oil pan, causing dilution of the engine oil. Yes, especially under conditions where the engine is not warmed up sufficiently, vaporization and combustion of the fuel adhering to the cylinder liner will be insufficient, but a fuel oil composition with a 90 vol% distillation temperature (T90) of 281.0 ° C or less Things are easy to vaporize and are sufficiently vaporized and burned before the piston descends, so that it does not cause dilution of engine oil. Therefore, as a property of the fuel for the PCCI engine, the 90 vol% distillation temperature (T90) is 281.0 ° C. or less . In order to cope with the above problem, the lower the 90 volume% distillation temperature (T90), the better. Therefore, the fuel oil composition of the present invention has a 90 volume% distillation temperature (T90) of 280 ° C. or lower. It is preferable. Although not particularly limited, the fuel oil composition of the present invention preferably has a 90% by volume distillation temperature (T90) of 250 ° C. or higher so as not to reduce the production amount of light oil.

<Cetane number (CN)>
The fuel oil composition for PCCI engines of the present invention has a cetane number (CN) that affects the lower limit of the load condition that can ensure PCCI combustion is 45 to 65, preferably 45 to 60. In order to ensure reliable ignition and combustion stability of the fuel oil composition under low load conditions, the cetane number (CN) of the fuel oil composition itself needs to be 45 or more. If the cetane number (CN) of the fuel oil is too high, the time from fuel oil injection to ignition, that is, the ignition delay is shortened, so the time allowed for the formation of the air-fuel mixture is shortened, Since the engine performance is deteriorated due to excessive advance of the ignition timing due to the early ignition, the cetane number (CN) of the fuel oil composition needs to be 65 or less, and preferably 60 or less.

<Research Method Octane Number (RON)>
The fuel oil composition for PCCI engines of the present invention has a research octane number (RON) of 20 or more, preferably 21 or more, from the viewpoint of ensuring slow combustion under high load conditions. In order to avoid premature ignition and rapid combustion, measures such as the introduction of an exhaust gas recirculation system (EGR) are taken on the engine side, but noise and combustion pressure that are acceptable as PCCI combustion under high load conditions. In order to ensure the rate of increase, the research method octane number (RON) of the fuel oil composition needs to be 20 or more, preferably 21 or more.

<Aromatic content of 3 or more rings>
In the fuel oil composition for PCCI engines of the present invention, the aromatic content of three or more rings is 0.5% by volume or less, preferably 0.3% by volume or less. Aromatic components having 3 or more rings not only have a high boiling point but also have poor flammability, and therefore tend to remain as a component adhering to the wall surface of the cylinder liner. Therefore, the fuel oil composition of the present invention requires that the aromatic content of three or more rings is 0.5% by volume or less and preferably 0.3% by volume or less from the viewpoint of preventing dilution of engine oil.

<Aromatic content>
When the total amount of aromatic components including the aromatic components of 3 or more rings increases, the exhaust gas deteriorates. Therefore, the fuel oil composition for PCCI engines of the present invention has an aromatic content of 22.9 % by volume or less, preferably 21 The capacity is less than%. More specifically, the increase in the aromatic content expands the area of the PM generation map that is organized by the temperature and air-fuel ratio at which particulate matter (PM) is generated. The group content is 22.9 % by volume or less, preferably 21% by volume or less.

<High pressure differential scanning calorimetry (DSC)>
The fuel oil composition for a PCCI engine of the present invention has an exothermic start temperature in high pressure differential scanning calorimetry (DSC) of 250 ° C. or lower and a peak value of exothermic peak of 25 W / g or higher, preferably 30 W / g or higher. It is. The fuel-air mixture formation and combustibility in a PCCI engine are greatly affected by the ignitability and combustibility of the fuel evaluated by DSC. In particular, when the peak value of the exothermic peak is less than 25 W / g, the combustibility is deteriorated. Moreover, when the heat generation start temperature in DSC exceeds 250 ° C., the ignition characteristics are inferior. Furthermore, if the heat generation start temperature exceeds 250 ° C, the ignitability is insufficient in PCCI combustion under low load conditions where it is necessary to ignite under low temperature and lean air-fuel mixture as compared with conventional engines, and heat generation The starting temperature should be below 250 ° C. In addition, since the emission of black smoke accompanying combustion increases with a fuel whose heat generation start temperature is too high, the heat generation start temperature needs to be 250 ° C. or less. Furthermore, the exothermic peak is an indicator of the amount of heat generated under the conditions of the fuel, and when the peak value is low, the fuel causes incomplete combustion. In addition, when the peak value is low, the combustion period is long, and in extreme cases it becomes afterburning, deteriorating combustion efficiency and exhaust gas, so the peak value of the exothermic peak needs to be 25 W / g or more. . Therefore, in a PCCI engine under engine conditions where ignition and combustion conditions are relatively poor, it is important to define the DSC heat generation start temperature and the heat generation peak.

<Preparation of fuel oil composition>
The fuel oil composition for a PCCI engine of the present invention may be formed by, for example, deep desulfurization or aromatic saturated hydrogenation of a light oil base material having a 90% by volume distillation temperature (T90) of 300 ° C. or less so as to satisfy the above properties. To produce a specified diesel fuel base material, to increase the cetane number of the diesel fuel base material, paraffinic fuel (for example, GTL that can be manufactured by FT synthesis), to increase the octane number, isoparaffinic fuel base material Can be prepared by mixing.

<Additives>
The fuel oil composition for the PCCI engine of the present invention includes a cetane number improver for improving the cetane number (CN) of the fuel oil composition, an antioxidant for ensuring the stability of the fuel oil composition, a low temperature A low temperature fluidity improver for ensuring fluidity, a lubricity improver for ensuring lubricity, a detergent for ensuring engine cleanliness, and the like can be added as appropriate.

  Examples of the cetane improver include alkyl nitrate cetane improvers and organic peroxide cetane improvers. As said alkyl nitrate type | system | group cetane improver, a C6-C12 alkyl nitrate is preferable and 2-methylhexyl nitrate is especially preferable. Moreover, as said organic peroxide type | system | group cetane number improver, a C6-C12 dialkyl peroxide is preferable and di-t-butyl peroxide is especially preferable. The addition amount of these cetane number improvers is preferably in the range of 0.5% by mass or less, and more preferably in the range of 0.1% by mass or less.

  Examples of the antioxidant include 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,4-dimethyl-6-t-butylphenol, 2,4,6- Phenolic antioxidants such as tri-t-butylphenol, 2-t-butyl-4,6-dimethylphenol, 2-t-butylphenol, N, N'-diisopropyl-p-phenylenediamine, N, N'- Examples thereof include amine-based antioxidants such as di-sec-butyl-p-phenylenediamine, and mixtures thereof. The addition amount of these antioxidants is not particularly limited, and can be appropriately selected according to the purpose.

  As the low-temperature fluidity improver, known ethylene copolymers and the like can be used, and in particular, vinyl esters of saturated fatty acids such as vinyl acetate, vinyl propionate, and vinyl butyrate are preferably used. The addition amount of these low temperature fluidity improvers is not particularly limited, and can be appropriately selected according to the purpose.

  As the above-mentioned lubricity improver, for example, long chain (for example, C12-24) fatty acids or fatty acid esters thereof are preferably used. By adding the lubricity improver in the range of 10 to 500 ppm by mass, preferably in the range of 50 to 100 ppm by mass, the wear resistance can be sufficiently improved.

  Examples of the detergent include succinimide, polyalkylamine, and polyetheramine. The addition amount of these detergents is not particularly limited, and can be appropriately selected according to the purpose.

<Premixed compression ignition engine>
The fuel oil composition of the present invention described above is used in a premixed compression ignition (PCCI) engine. The PCCI engine is also called an HCCI (Homogeneous Charge Compression Ignition) engine, and is compression ignition like a conventional diesel engine, but fuel injection timing, fuel injection pressure and injection pattern, EGR, compression ratio, combustion chamber structure, etc. Is a combustion system that completes combustion only by a premixed flame formed by combustion of a premixed gas in which fuel and air are sufficiently mixed. Therefore, when the heat generation pattern is observed, one heat generation peak due to the premixed flame that is the main combustion is observed following the weak heat generation accompanying the cold flame (which may not be observed). Conventional diesel combustion is greatly different in that two peaks associated with premixed flame and diffusion flame are observed. It is also different from a gasoline engine where combustion is completed by propagation of a premixed flame. In an actual PCCI engine, tailing of the heat generation pattern may be observed, but the cause (whether premixed flame or diffusion flame) is not clear, so the main combustion in the PCCI engine is 90% or more (tailing). The heat generation associated with is less than 10%). Further, the PCCI engine has a feature that it is more efficient than a gasoline engine (spark ignition type engine) because it can be operated at a high compression ratio.

  And by using the fuel oil composition of the present invention described above for such a premixed compression ignition engine, it is possible to prevent dilution of engine oil and improve exhaust gas while ensuring sufficient fuel ignitability. It becomes possible.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

  The following test fuel is subjected to property analysis by the following method, and further, the following engine is operated under the following conditions, and the engine oil dilution ratio, black smoke, and PCCI engine combustion state by the test fuel are measured. Evaluation was made by comparison with commercial light oil. The results are shown in Table 1.

<Preparation of test fuel>
-Light oil: Commercially available light oil (JIS No. 2) was prepared.
Fuel-1: A fuel obtained by fractionating a deep desulfurized light oil base material so that a 90% by volume distillation temperature (T90) is 300 ° C. or less.
Fuel-2: Prepared by mixing 80% by volume of a commercially available light oil base material and 20% by volume of catalytic cracked light oil (LCO) obtained from a catalytic cracker.
Fuel-3: Prepared by mixing 5% by volume of heavy oil mainly composed of a bicyclic aromatic compound and a tricyclic aromatic compound with a commercially available light oil base.
Fuel-4: A commercially available light oil base was prepared by hydrocracking to reduce the aromatic content.
Fuel-5: Prepared by mixing 50% by volume of commercial kerosene with fuel-1.

<Fuel property analysis method>
・ Density: JIS K2249 “Crude oil and petroleum product density test method”
・ Distillation properties: JIS K2254 "Distillation test method"
・ Sulfur content: JIS K2541-6 “Sulfur content test method (ultraviolet fluorescence method)”
-Cetane number (CN): Measured method defined in JIS K2280 "Petroleum products-Fuel oil-Octane number and cetane number test method and cetane index calculation method" (index is not applicable)
-Research octane number (RON): JIS K2280 "Petroleum products-Fuel oil-Octane number and cetane number test method and cetane index calculation method"
-Total amount of aromatics and aromatic content of 3 or more rings: JPI-5S-49-97 "Petroleum products-Hydrocarbon type test method-High performance liquid chromatographic method"
High pressure differential scanning calorimetry (DSC): The temperature was raised from 30 ° C. to 500 ° C. at a rate of 2 ° C./min in an air atmosphere of 5 MPa, and the heat generation start temperature and the heat generation peak value were measured.

<Specifications of the test engine>
・ Number of cylinders: 1
・ Displacement (cm ³ ): 1007
・ Compression ratio: 14-18
・ Fuel supply method: In-cylinder injection (common rail)

<Operating conditions>
・ Rotation speed (rpm): 1200
・ Fuel injection pressure (MPa): 40-120
・ Injection time: Fixed

<Evaluation method of engine oil dilution ratio>
The PCCI engine is operated continuously for 8 hours. After 0 hours, 4 hours, and 8 hours, the engine oil is collected and analyzed, and the dilution rate of the engine oil with the test fuel is measured and evaluated by comparison with commercially available light oil. did.

<Black smoke evaluation method>
Black smoke in the exhaust gas was measured with a smoke meter manufactured by Ono Sokki and evaluated by comparison with commercially available light oil.

<PCCI engine combustion state evaluation method>
Using an Ono Sokki combustion analyzer, the stability of ignition (fluctuation in the indicated mean effective pressure), the intensity of combustion (maximum value of heat generation rate), etc. were observed to evaluate the PCCI combustion state. In addition, the determination was based on commercially available light oil, and the case where it was improved (O), the case where it deteriorated (X), and the case where it hardly changed were indicated as (Δ).

  As is apparent from Table 1, by using a fuel oil composition that satisfies the properties defined in the present invention, dilution of engine oil can be prevented and exhaust gas can be improved.

Claims (1)

Sulfur content 10 mass ppm or less, 90 vol% distillation temperature 281.0 ° C or less, cetane number (CN) 45-65, research octane number (RON) 20 or more, aromatic content 22.9 vol% And the aromatic content of 3 or more rings is 0.5% by volume or less,
A premixed compression ignition type engine fuel oil composition characterized in that an exothermic start temperature in high-pressure differential scanning calorimetry (DSC) is 250 ° C. or lower and a peak value of an exothermic peak is 25 W / g or higher.