JP5334557B2 - Fuel oil composition for premixed compression ignition engines - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a fuel oil composition for a premixed compression ignition type engine, and in particular, a fuel oil for a premixed compression ignition type engine capable of improving the operability when the premixed compression ignition type engine is cold. It relates to a composition.

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. Therefore, as a fuel for PCCI engines, a fuel having a high cetane number (CN), which is an index of ignitability under low load conditions, and a high research octane number (RON) capable of expecting slow combustion under high load conditions is desirable.

  On the other hand, when the temperature inside the combustion chamber is low before the PCCI engine is warmed, the fuel injected into the combustion chamber is a disadvantageous condition for vaporizing to form a homogeneous premixed gas. When cold, the volatility of the fuel is important.

JP 2004-91657 A

  However, in general, a highly volatile component among hydrocarbons has a low cetane number (CN), so it is necessary to develop a fuel for PCCI engines with controlled volatility and ignitability in consideration of operability during cold operation. There is.

  Therefore, an object of the present invention is to provide a fuel oil composition for a premixed compression ignition type engine capable of improving the operability when the premixed compression ignition type engine is cold.

  As a result of intensive studies to achieve the above object, the present inventors have a specific distillation property, a flash point and a research octane number (RON) within a specific range, and a cetane number ( CN) and a fuel oil composition having a cetane number (ΔCN) of a fraction from the initial boiling point to 240 ° C. in a specific range is used for a premixed compression ignition engine, thereby improving the operability when the engine is cold. The present inventors have found that it can be improved 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,
・ The flash point is 40 ℃ or higher.
・ The initial boiling point is 130-180 ℃,
・ 90 vol% distillation temperature is below 300 ℃,
-The cetane number (CN) of all fractions is 40-50 ,
・ The cetane number (ΔCN) of the fraction from the initial boiling point to 240 ° C. is 40 or more, and the research octane number (RON) is 20 or more.

  In the present invention, the sulfur content is measured in accordance with JIS K2541-6, the flash point is measured by the Penstig Rutens closed type specified in JIS K2265-3, and the 10 vol% distillation temperature and the 90 vol% distillation temperature are The cetane number (CN) and research octane number (RON) are measured according to JIS K2280.

  According to the present invention, it has a specific distillation property, has a flash point and a research octane number (RON) within a specific range, and also has a cetane number (CN) of all fractions and a distillation temperature from the initial boiling point to 240 ° C. By using a fuel oil composition having a minute cetane number (ΔCN) in a specific range for a PCCI engine, it becomes possible to improve the operability when the engine is cold.

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 flash point of 40 ° C. or more, an initial boiling point of 130 to 180 ° C., and a 90 vol% distillation temperature. The cetane number (CN) of all fractions is 40-50 at 300 ° C or lower, the cetane number (ΔCN) of fractions from the initial boiling point to 240 ° C is 40 or more, and the research octane number (RON) is 20 It is the above. Since the fuel oil composition of the present invention has a high cetane number (ΔCN) of the fraction from the initial boiling point to 240 ° C. (previous fraction), the ignitability is high even when the PCCI engine is cold. The operability when the PCCI engine is cold can be improved.

<Sulfur content>
The fuel oil composition for PCCI engines of the present invention has a sulfur content of 10 ppm by mass or less, preferably 3 ppm by mass 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. And since these effects become so remarkable that a sulfur content is low, it is preferable that the sulfur content in the fuel oil composition of this invention is 3 mass ppm or less.

<Flash point>
The fuel oil composition for PCCI engines of the present invention has a flash point of 40 ° C or higher, preferably 50 ° C or higher, from the viewpoint of ensuring safety during handling. The fuel oil composition of the present invention is also flammable from the viewpoint of preventing a very volatile fraction from being mixed into the fuel oil composition and suppressing volatility fluctuation of the fuel oil composition. The point needs to be 40 ° C or higher, and is preferably 50 ° C or higher.

<First stop point (IBP)>
The fuel oil composition for PCCI engines of the present invention has an initial boiling point (IBP) of 130 to 180 ° C, preferably 140 to 170 ° C. If the volatility of the previous fraction of the fuel oil composition is low, vaporization of the fuel oil composition during cold operation becomes insufficient, so the fuel oil composition of the present invention has an initial boiling point (IBP) of 180 ° C. or lower. It is preferable that it is 170 degrees C or less. Further, if the volatility is too high, the fuel oil composition of the present invention has an initial boiling point (IBP) because the fuel is vaporized in the fuel system and a sufficient fuel flow rate cannot be secured under an environment where the temperature condition is high. It is 130 degreeC or more, and it is preferable that it is 140 degreeC or more.

<90% volume distillation temperature (T90)>
The fuel oil composition for PCCI engines of the present invention has a 90 vol% distillation temperature (T90) of 300 ° 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. 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 the fuel oil composition with a 90 vol% distillation temperature (T90) of 300 ° C or less Things are easy to evaporate and evaporate well before the piston descends, so that it does not cause dilution of the engine oil. Therefore, as a property of the fuel for the PCCI engine, it is necessary that the 90 vol% distillation temperature (T90) is 300 ° 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. Further, although not particularly limited, since the production amount of light oil is reduced when the 90 volume% distillation temperature (T90) is too low, the fuel oil composition of the present invention has a 90 volume% distillation temperature (T90). ) Is preferably 220 ° C. or higher.

<Cetane number (CN) of all fractions>
For PCCI engine fuel oil composition of the present invention is a cetane number (CN) is 40-50 of the total fraction affects the lower limit value of the load condition which can ensure PCCI combustion, preferably 43 to 50. In order to ensure reliable ignition and combustion stability of the fuel oil composition when cold, the cetane number (CN) of the fuel oil composition itself needs to be 40 or more, and 43 or more. It is preferable. If the cetane number (CN) of the fuel oil is too high, the time from the fuel oil injection to ignition, that is, the ignition delay is shortened under conditions where the engine is warmed and the load is large. The cetane number (CN) of the total fraction of the fuel oil composition is 50 or less because the time allowed for the formation of the fuel is reduced or the engine performance is deteriorated due to the advance of the ignition timing due to the early ignition.

<Cetane number (ΔCN) of the fraction from the initial boiling point to 240 ° C>
The fuel oil composition for PCCI engines of the present invention has a cetane number (ΔCN) of a fraction from the initial boiling point (IBP) to 240 ° C. of 40 or more, preferably 41 or more, more preferably 42 or more. Since the highly volatile component in the fuel oil composition is vaporized and contributes to ignition when cold, the cetane number (ΔCN) of the previous fraction (the fraction from the initial boiling point to 240 ° C.) is important. And since the cetane number ((DELTA) CN) of the fraction from an initial boiling point to 240 degreeC is as high as 40 or more sufficiently, the fuel oil composition of this invention is excellent in ignitability also at the time of the cool-down of a PCCI engine.

<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 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 is set to 20 or more .

<Preparation of fuel oil composition>
The fuel oil composition for a PCCI engine of the present invention is a low sulfur light oil base material in which sulfur is reduced by deep desulfurization or the like, for example, a petroleum light gas oil base material (T90 is 300 ° C. or lower) so as to satisfy the above properties. It can be prepared by mixing a paraffinic light oil base (for example, a light fraction such as GTL produced by FT synthesis).

<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.

  When the above-described fuel oil composition of the present invention is used in such a premixed compression ignition engine, the cetane number (ΔCN) of the fraction from the initial boiling point of the fuel composition to 240 ° C. is high, and the engine is cold Since the ignitability is high, the operability when the engine is cold can be improved.

  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 fuels were subjected to property analysis by the following method. Further, the following engine was operated under the following conditions, and the fuel startability was measured and evaluated by the following method. The results are shown in Table 1.

<Preparation of test fuel>
-Light oil: Commercially available light oil (JIS No. 2) was prepared.
Light oil 1: Prepared by mixing 80% by volume of a light gas oil base material that was deeply desulfurized with 20% by volume of a paraffinic base material (SHNP).
Light oil 2: Prepared by mixing 90% by volume of commercially available kerosene with 10% by volume of butylbenzene.
-Heavy oil: prepared by mixing 50% by volume of commercially available light oil and 50% by volume of heavy light oil base.
SHNP: A commercially available n-paraffin mixture mainly containing carbon numbers 14, 15, and 16 was purchased through JOMO Sun Energy Co., Ltd.

<Fuel property analysis method>
・ Density: JIS K2249 “Crude oil and petroleum product density test method”
-Flash point: JIS K2265-3 "How to find the flash point-Part 3: Penschrimtens sealing 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"

<Specifications of the test engine>
・ Number of cylinders: 1
・ Displacement (cc): 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

<Performance evaluation method>
The engine was set to a stable condition with a 1007 cc single-cylinder PCCI engine sufficiently warmed up, left for a day and night, then started cold, and the transition of combustion behavior was measured. For combustion analysis, the combustion analysis device manufactured by Ono Sokki was used to determine the transition from the start to the complete explosion and the indicated mean effective pressure (IMPE) from the start to the stabilization of combustion. The case where it was improved was indicated as (◯), the case where it deteriorated was indicated as (×), and the case where it was hardly changed was indicated as (Δ).

  As is apparent from Table 1, by using a fuel oil composition that satisfies the properties defined in the present invention, the startability of the PCCI engine is improved, and the operability during cold operation can be improved.

Claims (1)

Sulfur content is 10 ppm by mass or less, flash point is 40 ° C. or more, initial boiling point is 130 to 180 ° C., 90 vol% distillation temperature is 300 ° C. or less, and cetane number (CN) of all fractions is 40 A fuel for a premixed compression ignition type engine characterized by having a cetane number (ΔCN) of 40 or more and a research-method octane number (RON) of 20 or more at a fraction of from ~ 50 to 240 ° C Oil composition.