JP2009203459A - Fuel oil composition for low-temperature, pre-mixed compression ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel oil composition for a low-temperature, pre-mixed compression ignition engine establishing stable ignition/combustion, and contributing to a decrease in noxious exhaust gas components, even if operated by low-temperature, pre-mixed combustion under conditions of not higher than 17 vol% oxygen in intake-air adopting EGR (exhaust gas recirculation). <P>SOLUTION: This fuel oil composition is for low-temperature, pre-mixed compression ignition engine equipped with an exhaust gas recirculation unit which recirculates at least a part of the exhaust gas to intake-air and operated under conditions in which the oxygen concentration in the mixed gas of the intake-air and the recirculated exhaust gas is not higher than 17 vol%, and its sulfur content is not higher than 10 mass ppm, the 90 vol% distilling temperature is not higher than 300°C, the cetane number (CN) is not lower than 50, the aromatics content is not higher than 25 vol%, and the content of the aromatics having three or more rings is not higher than 0.6 vol%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a fuel oil composition for a low temperature, premixed compression ignition engine that includes an exhaust gas recirculation device and uses a large amount of EGR, and in particular, recirculates exhaust gas and oxygen concentration in intake air. Even when operated under the condition of less than 17% by volume, stable low temperature and premixed combustion can be established, emission of harmful gas components can be reduced, and it can also be applied to conventional diesel engines The present invention relates to a fuel oil 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. Thus, diesel vehicles with low CO ₂ emissions have attracted attention, but diesel vehicles are inferior to gasoline vehicles in terms of exhaust gas, and there is a strong demand for improved exhaust gas. In addition, although it is necessary to install an aftertreatment device to purify the exhaust gas, clean diesel combustion is required to reduce the load on the device that is used for a long time and to maintain the performance. Low temperature, premixed combustion has been developed that employs large amounts of exhaust gas recirculation (EGR). The operating range of the engine capable of low temperature and premixed combustion is limited, so it will be used in combination with conventional diesel combustion, but development for expanding the low temperature and premixed combustion range is progressing .

  Under engine conditions where a large amount of EGR is used to achieve low temperature and premixed combustion, NOx is reduced by increasing the amount of EGR, but increases in PM, HC, CO, and ignition / combustion become unstable, resulting in fluctuations in combustion Will increase. Therefore, there is a limit to the increase in the amount of EGR, and the ignitability of fuel and the exhaust gas characteristics play an important role. In addition, since an engine employing low temperature and premixed combustion uses conventional diesel combustion, the fuel for the engine needs to be applicable to both low temperature, premixed combustion and conventional diesel combustion.

  On the other hand, in conventional diesel engines, the use of petroleum-based light oil as a clean fuel that contributes to the reduction of emissions of various harmful gas components has been proposed. However, harmful effects from low-temperature, premixed combustion using a large amount of EGR are proposed. No clean fuel has been developed that can reduce emissions. Therefore, it is desired to develop a clean fuel with low harmful emissions from both low temperature, premixed combustion and conventional diesel combustion.

JP 2000-144155 A Watanabe, “Development of light diesel oil to reduce particulate matter emitted from existing diesel vehicles”, Petrotech Vol.27, No.1, Page.74-81 (2004.01.01)

  Under such circumstances, the object of the present invention is to provide a condition in which the conventional diesel combustion is effective in purifying the exhaust gas, and the oxygen concentration in the intake air is 17% by volume or less by employing a large amount of external cooled EGR. Light clean fuel oil for low temperature, premixed compression ignition engines that can achieve stable ignition / combustion and contribute to the reduction of harmful exhaust gas components even under low temperature, premixed combustion operation It is to provide a composition.

  As a result of intensive studies to achieve the above object, the present inventors have a specific distillation property, a low sulfur content, a total amount of aromatic components, and a small amount of aromatic components of three or more rings, and a high cetane number. When the fuel oil composition is used in a low temperature, premixed compression ignition engine having an exhaust gas recirculation device, the engine may be operated under conditions where the oxygen concentration in the intake air is 17% by volume or less. The inventors have found that low-temperature, premixed combustion can be established, and that emission of harmful gas components can be reduced, and the present invention has been completed.

That is, the fuel oil composition of the present invention is
・ Equipped with an exhaust gas recirculation device that recirculates at least part of the exhaust gas into the intake air, and operates under conditions where the oxygen concentration in the mixed gas of the intake air and the recirculated exhaust gas is 17% by volume or less. A low temperature, premixed compression ignition engine fuel oil composition comprising:
・ Sulfur content is 10 mass ppm or less,
・ 90 vol% distillation temperature is below 300 ℃,
・ Cetane number (CN) is 50 or more,
-Aromatic content is 25 volume% or less, and-3 or more ring aromatic content is 0.6 volume% or less.

  In the present invention, the sulfur content is measured according to JIS K2541-6, the 90% by volume distillation temperature is measured according to JIS K2254, the cetane number (CN) is measured according to JIS K2280, the total amount of aromatics and three rings. The above aromatic content is measured according to the Petroleum Institute Petroleum Testing Related Standard JPI-5S-49-97.

  According to the present invention, a fuel oil composition having a specific distillation property and having a sulfur content, a cetane number (CN), a total amount of aromatic components, and an aromatic content of three or more rings within a specific range is provided as an exhaust gas. By using it in a low-temperature, premixed compression ignition engine equipped with a recirculation device, low-temperature, premixed combustion can be performed even if the engine is operated under conditions where the oxygen concentration in the intake air is 17% by volume or less. It can be established stably, and emission of harmful gas components can be reduced.

  The present invention is described in detail below. The fuel oil composition of the present invention comprises an exhaust gas recirculation device that recirculates at least part of the exhaust gas into the intake air, and the oxygen concentration in the mixed gas of the intake air and the recirculated exhaust gas is 17%. A fuel oil composition for a low-temperature, premixed compression ignition engine operated at a volume% or less condition, having a sulfur content of 10 ppm by mass or less, a 90% by volume distillation temperature of 300 ° C. or less, and cetane The valence (CN) is 50 or more, the aromatic content is 25% by volume or less, and the aromatic content of 3 or more rings is 0.6% by volume or less. Since the fuel oil composition of the present invention has a sufficiently low 90% by volume distillation temperature, it does not hinder the formation of air-fuel mixture and combustibility of the fuel oil composition and air, and has a cetane number (CN). Therefore, even if the low temperature premixed compression ignition engine is operated under the condition that the oxygen concentration in the intake air is 17% by volume or less, the low temperature premixed combustion is established. In addition, as described above, when a low temperature, premixed compression ignition engine is operated at a high EGR rate using a conventional fuel, there is a problem that PM, HC, and CO increase. Since the 90% by volume distillation temperature is sufficiently low, the sulfur content, the total aromatic content, and the aromatic content of three or more rings are also sufficiently low, so a low-temperature, premixed compression ignition engine is operated at a high EGR rate. However, the increase in PM, HC, and CO can be suppressed. In addition, the fuel oil composition of the present invention is effective in reducing harmful exhaust gas even in conventional diesel combustion.

<Sulfur content>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention has a sulfur content of 10 mass ppm or less, 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. 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.

<90% volume distillation temperature (T90)>
The low-temperature, premixed compression ignition engine fuel oil composition of the present invention has a 90 vol% distillation temperature (T90) of 300 ° C or lower, preferably 290 ° C or lower, more preferably 285 ° C or lower. If the 90% by volume distillation temperature (T90) exceeds 300 ° C., the amount of particulate matter (PM) discharged increases and the environmental load cannot be reduced sufficiently. In addition, the volatility of the rear distillation portion of the fuel oil composition affects the formation of air-fuel mixture and the combustibility of the fuel oil composition and air, and when the 90 vol% distillation temperature (T90) exceeds 300 ° C, This may hinder the formation of an air-fuel mixture of the fuel oil composition and air, or the combustibility of the air-fuel mixture may be reduced. Furthermore, in a low-temperature, premixed compression ignition engine that injects fuel earlier than a diesel engine, part of the fuel reaches the cylinder liner, is scraped off when the piston descends, and flows into the oil pan. However, a fuel composition with a 90% by volume distillation temperature (T90) of 300 ° C or less is easily vaporized and sufficiently vaporizes and burns before the piston descends, causing dilution of the engine oil. There are few things. Therefore, as a property of the low temperature, premixed compression ignition engine fuel, the 90 vol% distillation temperature (T90) needs to be 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 290 ° C. or lower. The temperature is preferably 285 ° C. or lower. Although not particularly limited, the fuel oil composition of the present invention preferably has a 90% by volume distillation temperature (T90) of 230 ° C. or higher in order to suppress a decrease in the production amount of light oil. .

<Cetane number (CN)>
The low temperature, premixed compression ignition engine fuel oil composition of the present invention has a cetane number (CN) of 50 or more from the viewpoint of ensuring low temperature and premixed combustion under low load conditions. If the cetane number (CN) is too low, ignition / combustion is insufficient, combustion fluctuation is large, and exhaust gas is deteriorated. Therefore, the fuel oil composition of the present invention has a cetane number (CN) of 50 or more, preferably 51 Above, more preferably 52 or more, still more preferably 55 or more, particularly 57 or more. The conventional engine exhibits sufficient performance when the cetane number (CN) is 45 or more, but the low-temperature, premixed compression ignition engine has a high cetane number (CN) and a low 90 vol% distillation temperature (T90). The combination with is essential. In order to adjust the cetane number, a cetane number improver may be added to the fuel oil composition of the present invention.

<Cetane number improver>
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.

<Aromatic content>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention has an aromatic content of 25% by volume or less. When the aromatic content increases, carbon monoxide (CO) and particulate matter (PM) in the exhaust gas increase. Therefore, the fuel oil composition of the present invention has an aromatic content of 25% by volume or less, preferably 21 It is not more than volume%, more preferably not more than 15 volume%, particularly not more than 12 volume%.

<Aromatic content of 3 or more rings>
The fuel oil composition for a low temperature, premixed compression ignition engine of the present invention has an aromatic content of 3 or more rings of 0.6% by volume or less, preferably 0.4% by volume or less. When polycyclic aromatics increase, particulate matter (PM) in the exhaust gas increases, so the fuel oil composition of the present invention requires that the aromatic content of three or more rings is 0.6% by volume or less. , Preferably 0.4% by volume or less.

<Preparation of fuel oil composition>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention has a distillation property so as to satisfy the above properties, for example, to have a distillation property that meets the requirements of 90% by volume distillation temperature (T90). The obtained light oil base is subjected to deep desulfurization and aromatic saturated hydrogenation to reduce sulfur and aromatics, and if necessary, paraffinic light oil base (for example, GTL which is FT synthetic light oil) is used. It can be produced by mixing and adjusting the cetane number. The cetane number can also be adjusted by adding the above cetane number improver.

<Other additives>
The low-temperature, premixed compression ignition engine fuel oil composition of the present invention has an antioxidant other than the cetane number improver, an antioxidant for ensuring the stability of the fuel oil composition, and low-temperature fluidity. A low temperature fluidity improver for ensuring, a lubricity improver for ensuring lubricity, a detergent for ensuring engine cleanliness, and the like can be appropriately added.

  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. 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, a long chain (for example, having 12 to 24 carbon atoms) fatty acid or a fatty acid ester thereof is 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.

<Low-temperature, premixed compression ignition engine>
The fuel oil composition of the present invention described above is used in a low temperature, premixed compression ignition engine. The engines include PCCI (Premixed Charge Compression Ignition) and HCCI (Homogeneous Charge Compression Ignition) engines, which are premixed compression ignition engines, and achieve premixed combustion mainly by a large amount of EGR. Low-temperature, premixed combustion is compression ignition, similar to conventional diesel engines, but fuel and air achieved by optimizing fuel injection timing, fuel injection pressure, injection pattern, compression ratio, combustion chamber structure, etc. It is a combustion method that completes combustion only with a premixed flame formed by the combustion of a well-mixed premixed gas, and the low temperature, premixed combustion has a long ignition delay necessary for the formation of the premixed gas. This is achieved with a large amount of EGR, and a large amount of EGR is a premixed combustion that is essential. In the conventional diesel engine, a diffusion flame in which a flame is formed in the boundary layer between fuel and air is observed in addition to the premixed flame, but this diffusion flame is not observed in the low temperature premixed compression ignition engine. That is, in the low temperature, premixed combustion, when the heat generation rate curve is observed, the heat generation peak due to the main combustion following the weak heat generation associated with the cool flame is combustion of only one peak corresponding to the premixed flame. Yes, NOx and PM are suppressed. On the other hand, in the actual heat generation curve, the latter half of the heat generation may tail, so a low-temperature, premixed compression ignition engine generates 90% or more of the heat generated by premixed combustion (premixed combustion or diffusion combustion) It is defined as an engine whose combustion in the latter half is less than 10%). In addition, the premixed compression ignition engine can be operated at a high compression ratio, and therefore has a characteristic that it is more efficient than a gasoline engine (spark ignition engine).

  In addition, the premixed compression ignition engine has an exhaust gas recirculation device, which suppresses the ignition timing by a large amount of exhaust gas recirculation (EGR), and under conventional engine conditions for lowering the temperature and premixing. When fuel is used, there are problems that particulate matter (PM), carbon monoxide (CO), and hydrocarbon (HC) increase and combustion fluctuations increase. On the other hand, the fuel oil composition of the present invention having specific distillation properties and having a sulfur content, a cetane number (CN), a total amount of aromatic components, and an aromatic content of three or more rings within a specific range is used. As a result, combustion fluctuations are reduced while suppressing emission of harmful gas components such as PM, HC, and CO. This effect is achieved, for example, by setting the exhaust gas recirculation (EGR) rate to 35% by volume or more, and further to 45% by volume or more, and the oxygen concentration in the mixed gas of the intake air and the recirculated exhaust gas is 17%. This becomes conspicuous when operated under the condition of volume% or less. More specifically, by using the fuel oil composition of the present invention, stable combustion even at low temperature and premixed compression ignition combustion operation under conditions where the oxygen concentration in the intake air is 17% by volume or less It is also possible to reduce emissions of harmful gas components.

  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 particulate matter (PM), nitrogen oxide (NOx) in exhaust gas, Measure and evaluate the maximum values of hydrocarbon (HC) and carbon monoxide (CO) concentrations, combustion fluctuations, ignition delay, and heat release rate by the following methods. (○) when performance is improved, (×) when it is deteriorated, (△) when there is almost no change, (△ / ○) when it is slightly improved, and (△ /) when it is slightly improved X) relative evaluation. The fuel performance was evaluated by changing the EGR rate from 0 to 70% (the oxygen concentration in the intake air was from 22 vol% to 8 vol%), and the engine performance under high EGR conditions was evaluated. The results are shown in Table 1.

<Preparation of test fuel>
-Light oil: Commercially available light oil (JIS No. 2) was prepared.
Light diesel oil: A diesel fuel base material having sulfur and aromatic content reduced by deep desulfurization was prepared by fractional distillation so that the 90% by volume distillation temperature (T90) was 300 ° C. or lower. Further, in order to increase the cetane number, 0.5% by mass of a commercially available cetane number improver (alkyl nitrate) was added.
-Ultralight oil: A light oil base with sulfur and aromatics reduced by deep desulfurization is fractionally distilled so that 90% by volume distillation temperature (T90) is 235 ° C or less, and a cetane number improver (alkyl nitrate) ) Was added at 0.5% by mass.
Highly aromatic oil: prepared by mixing 80% by volume of a commercially available light oil base material with 20% by volume of catalytically cracked oil (LCO) obtained from a catalytic cracking apparatus.
-Heavy oil: A heavy fraction of a commercially available light oil base was prepared.
Low aromatic oil: A cetane number improver (alkyl knight) is added to light low aromatic oil obtained by hydrocracking a straight-run gas oil base material and fractionally distilling so that 90 vol% distillation temperature (T90) is 300 ° C or lower. 0.5% by mass) was added.
-GTL mixed oil 1: 80 volumes of light gas oil base material prepared by fractionating a light oil base material with reduced sulfur and aromatic content by deep desulfurization so that 90% by volume distillation temperature (T90) is 300 ° C or less. % And 20% by volume of GTL were mixed.
-GTL mixed oil 2: 60 volumes of light diesel fuel base material prepared by fractionating a 90% by volume distillation temperature (T90) of a diesel fuel base material with sulfur and aromatics reduced by deep desulfurization % GTL was mixed with 40% by volume of light GTL prepared by fractional distillation so that the 90% by volume distillation temperature (T90) was 300 ° C. or less.
-GTL: A moss gas product [GTL with a cetane number of 82] was purchased through JOMO Sun Energy Co., Ltd.
・ Alkyl nitrate: HITEC-4105K manufactured by Afton Chemical Japan Co., Ltd.

<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)
-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"

<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 amount (mm ³ ): variable (covers the PCCI combustion range)
・ Fuel injection pressure (MPa): 40-120
-EGR rate (%): 0-70 variable

<Performance evaluation method>
(1) Measurement of exhaust gas Using a Horiba exhaust gas analyzer, the concentrations of nitrogen oxide (NOx), hydrocarbon (HC), and carbon monoxide (CO) in the exhaust gas were measured. Black smoke was measured with a smoke meter manufactured by Ono Sokki.

(2) Combustion analysis Using a combustion analysis device manufactured by Ono Sokki, the maximum values of combustion fluctuation, ignition delay, and heat generation rate were measured.

  As is apparent from Table 1, when a fuel oil composition satisfying the properties defined in the present invention is used, the use of a large amount of EGR causes the oxygen concentration in the intake air to be 17% by volume or less under low temperature and pre- Even when the mixed compression ignition engine is operated, low temperature, premixed combustion is established, and emission of harmful gas components such as PM, HC, and CO can be reduced.

Claims (1)

It is equipped with an exhaust gas recirculation device that recirculates at least part of the exhaust gas into the intake air, and is operated under the condition that the oxygen concentration in the mixed gas of the intake air and the recirculated exhaust gas is 17% by volume or less. A low temperature, premixed compression ignition engine fuel oil composition comprising:
Sulfur content is 10 mass ppm or less, 90 vol% distillation temperature is 300 ° C or less, cetane number (CN) is 50 or more, aromatic content is 25 vol% or less, and aromatic content of 3 or more rings. A fuel oil composition characterized by being 0.6% by volume or less.