JP5283950B2 - Low temperature, premixed compression ignition engine fuel oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel oil composition for a low-temperature, premixed charge compression ignition engine that attains low-temperature, premixed charge compression ignition combustion even when operated under a condition such that an oxygen concentration in intake air is lowered down to 17 vol% or lower by employment of EGR, and can suppress deterioration in fuel volume consumption and decrease the discharge amount of CO<SB>2</SB>. <P>SOLUTION: The fuel oil composition is one for a low-temperature, premixed charge compression ignition engine which is equipped with an exhaust gas recirculation apparatus for recirculating at least a part of exhaust gas into intake air and is operated under a condition such that the oxygen concentration in a mixed gas of the intake air with the recirculated exhaust gas is 17 vol% or lower, where the fuel composition has a sulfur content of at most 10 mass ppm, a 90 vol% distillation temperature of 360&deg;C or lower, a cetane value (CN) of at least 55, an aromatic content of at most 10 mass%, a CO<SB>2</SB>emission unit of at most 0.069 g/kJ and a density at 15&deg;C of at least 0.820 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2010,JPO&amp;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 17% by volume or less, it is possible to reduce harmful exhaust gas components derived from low temperature, premixed compression ignition combustion, suppress fuel consumption reduction, and reduce CO ₂ emissions The present invention relates to an 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. Furthermore, in order to prevent global warming, it is necessary to reduce CO ₂ emitted by the combustion of fossil fuels, and reduction of CO ₂ emission from automobiles is required. On the other hand, the capacity fuel consumption efficiency (fuel consumption) of an automobile is a performance that leads to the cruising distance of an automobile in addition to the satisfaction of consumers, and its improvement is required. Thus, in automobiles, it is necessary to simultaneously achieve emission reduction of harmful exhaust gas components, CO ₂ emission reduction, and fuel efficiency improvement. Recently, as a countermeasure technology, low temperature, premixed compression ignition engine and the engine The quality of fuel used for

  Low-temperature, premixed compression ignition engines rely on self-ignition of fuel for the start of combustion (ignition), so it is necessary to improve ignitability when the temperature in the combustion chamber is low or when the load is low It is. On the other hand, under high-load conditions where the temperature in the combustion chamber is high, fuel with good ignitability causes rapid combustion due to multi-point simultaneous ignition in the combustion chamber, so combustion control is necessary to achieve slow combustion. is there. On the other hand, in order to realize slow combustion, exhaust gas recirculation (EGR) is used as a useful means in addition to optimization of fuel injection timing and compression ratio. EGR is effective in suppressing ignition and combustion, so a large amount of EGR can be introduced. However, an increase in the EGR amount reduces NOx but leads to an increase in PM, HC, CO, and an increase in combustion fluctuations. . Therefore, there is a limit in increasing the amount of EGR.

On the other hand, clean fuel that contributes to reducing emissions of various harmful gas components has been proposed for conventional diesel engines, but clean fuel that is optimal for combustion in low-temperature, premixed compression ignition engines that have introduced a large amount of EGR has been proposed. Not developed. Further, existing clean fuels are light fuels with a reduced aromatic content or a mixture of oxygen-containing compounds. Since the capacity fuel consumption is reduced due to a decrease in the calorific value, improvement is required. Furthermore, in order to directly reduce CO ₂ by fuel, it is necessary to reduce the CO ₂ emission intensity, low temperature with less harmful exhaust gas, establishment of premixed compression ignition combustion, improvement of capacity fuel consumption, CO ₂ The development of a fuel that simultaneously achieves the three of the reductions in emission intensity is desired.

Japanese Unexamined Patent Application Publication No. 2004-075901 JP 2007-270102 A

Under such circumstances, the object of the present invention is to achieve low-temperature, premixed compression ignition combustion even when the external cooled EGR is employed and the oxygen concentration in the intake air is 17% by volume or less. Furthermore, another object of the present invention is to provide a fuel oil composition for a low temperature, premixed compression ignition engine that can simultaneously suppress fuel consumption reduction and reduce CO ₂ emissions.

As a result of intensive studies to achieve the above object, the present inventors have a specific distillation property, a sulfur content, a cetane number (CN), an aromatic content and a density within a specific range, and CO ₂ emission. When a fuel oil composition with a small basic unit is used in a low-temperature, premixed compression ignition engine equipped with an exhaust gas recirculation device, the engine is used under the condition that the oxygen concentration in the intake air is 17% by volume or less. It has been found that even when the vehicle is operated, emission of harmful gas components can be reduced, fuel consumption can be suppressed and CO ₂ emission 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 360 ℃ or less,
・ Cetane number (CN) is 55 or more,
・ Aromatic content is 10% by mass or less,
-The CO ₂ emission intensity is 0.069 g / kJ or less, and the density at 15 ° C is 0.820 g / cm ³ or more.

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, and the aromatic content is determined by the Petroleum Institute of Japan Measured according to test related standard JPI-5S-49-97, density at 15 ° C. measured according to JIS K2249, CO ₂ emission intensity is Fujio Nagao, “Internal combustion engine lecture” (published by Yokendo) (1991) Is calculated by the following formula.
CO ₂ emission intensity = {(15.9994 × 2 + 12.011) /12.011} × {(carbon, mass%) / 100} / (true calorific value, kJ / kg × 1000)
(True calorific value, kJ / kg) = 4.186 × [{8100 × (carbon, mass%) / 100} + 29000 × {(hydrogen, mass%) / 100− (oxygen, mass%) / (8 × 100)} +2200 x (sulfur, mass%) / 100-600 x (moisture, mass%)]
Here, the moisture was a constant value of 0.01% by mass.

According to the present invention, a fuel oil composition having specific distillation properties and having sulfur content, cetane number (CN), aromatic content, CO ₂ emission basic unit and density within a specific range is converted into exhaust gas recirculation. Use in a low-temperature, premixed compression ignition engine equipped with a device to reduce emissions of harmful gas components even when the engine is operated under conditions where the oxygen concentration in the intake air is 17% by volume or less. It is also possible to reduce fuel consumption and contribute to CO ₂ reduction.

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 lower condition, having a sulfur content of 10 mass ppm or less, a 90 volume% distillation temperature of 360 ° C. or less, and cetane Characteristic (CN) is 55 or more, aromatic content is 10% by mass or less, CO ₂ emission unit is 0.069 g / kJ or less, and density at 15 ° C. is 0.820 g / cm ³ or more. To do. As described above, when a PCCI engine is operated with a conventional fuel at a high EGR rate, particularly when the oxygen concentration in the intake air is 17% by volume or less, PM, HC, and CO increase. Although there was a problem, the fuel oil composition of the present invention has a sufficiently high cetane number, a low 90 volume% distillation temperature, and a sufficiently low sulfur content and aromatic content. Even if is operated, an increase in harmful exhaust gas components such as PM, HC, and CO can be suppressed. Further, since the sulfur content is low, an oxidation catalyst having a strong oxidizing power can be used. Furthermore, since the fuel oil composition of the present invention has a sufficiently high density, the calorific value is large, the reduction in capacity fuel consumption can be suppressed, and since the CO ₂ emission basic unit is small, it can also contribute to CO ₂ emission reduction.

<Sulfur content>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention has a sulfur content of 10 ppm by mass or less, preferably 1 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 1 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% by volume distillation temperature (T90) of 360 ° C. or lower, preferably 340 ° C. or lower. If the 90 vol% distillation temperature (T90) exceeds 360 ° C, the amount of particulate matter (PM) discharged increases, and the environmental load cannot be reduced sufficiently. In addition, the volatility of the trailing portion of the fuel oil composition affects the formation of air-fuel mixture and combustibility of the fuel oil composition and air, and when the 90 vol% distillation temperature (T90) exceeds 360 ° 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 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. However, a fuel composition having a 90% by volume distillation temperature (T90) of 360 ° C. or less is easily vaporized and sufficiently vaporizes before the piston descends, and therefore does not cause dilution of engine oil. Therefore, as a property of the low temperature, premixed compression ignition engine fuel, the 90 vol% distillation temperature (T90) needs to be 360 ° C. or less. And in order to cope with said problem, since 90 volume% distillation temperature (T90) is so preferable that it is low, as for the fuel oil composition of this invention, 90 volume% distillation temperature (T90) is 330 degrees C or less. It is preferable. Although not particularly limited, the density decreases as the 90% by volume distillation temperature (T90) decreases, so the fuel oil composition of the present invention is subject to restrictions from density.

<Cetane number (CN)>
The fuel oil composition for a low temperature, premixed compression ignition engine of the present invention has a cetane number (CN) of 55 or more from the viewpoint of ensuring low temperature, premixed compression ignition combustion under low load conditions. If the cetane number (CN) is too low, ignition / combustion is insufficient and combustion fluctuations increase, so the fuel oil composition of the present invention has a cetane number (CN) of 55 or more. 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, 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 10% by mass or less. As 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 10% by mass or less, preferably 5%. It is below mass%.

<Density>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention has a density at 15 ° C. of 0.820 g / cm ³ or more, preferably 0.830 g / cm ³ or more in order to maintain capacity fuel consumption. Since the volume fuel consumption depends on the density of the fuel, the fuel oil composition of the present invention needs to have a density of 0.820 g / cm ³ or more.

<CO ₂ emission intensity>
The low temperature, premixed compression ignition engine fuel oil composition of the present invention has a CO ₂ emission basic unit of 0.069 g / kJ or less. The FT synthetic fuel GTL, which is a paraffinic fuel, has a small CO ₂ emission unit, but the density at 15 ° C is 0.79 g / cm ³ , which cannot comply with the above density regulations. By increasing the naphthene content, the regulations on density and CO ₂ emission intensity can be observed. Although the naphthene content in the low aromatic fuel is not specified, the density and the CO ₂ emission intensity are specified, and as a result, the paraffin content and the naphthene content are controlled.

<Preparation of fuel oil composition>
The fuel oil composition for a low-temperature, premixed compression ignition engine of the present invention is made of, for example, a light oil base material that satisfies the requirements of 90% by volume distillation temperature (T90), cobalt, nickel, molybdenum, so as to satisfy the above properties. And saturated hydrogenation in the presence of phosphorus-supported catalyst and hydrogen pressure 2.5-7.0 MPa, space velocity 0.9-6.0 h ^-1 , hydrogen / oil ratio 130-500 Nm3 / kL Is done. The fuel oil composition of the present invention can also be prepared by blending a hydrocarbon oil rich in naphthene such as a naphthene solvent into a low aromatic light oil base.

<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, 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.

<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 low-temperature, premixed compression ignition engine includes an exhaust gas recirculation device, and can suppress slow ignition and combustion by exhaust gas recirculation (EGR) to realize slow combustion even under high load conditions. NOx emissions can be reduced. However, when the amount of EGR is increased using a conventional fuel, there are problems that particulate matter (PM), carbon monoxide (CO), and hydrocarbon (HC) increase and combustion fluctuations increase. In response to this problem, when a clean fuel that is light and has a reduced aromatic content or a clean fuel mixed with an oxygen-containing compound is used, the calorific value of the fuel is low, leading to a decrease in capacity fuel consumption. On the other hand, by using the fuel oil composition of the present invention having a specific distillation property and having a sulfur content, cetane number (CN), aromatic content and density in a specific range, combustion fluctuation is reduced. However, emission of harmful gas components such as PM, HC, and CO can be suppressed, and fuel consumption can also be reduced. 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, noxious gas can be obtained even if low-temperature premixed compression ignition combustion operation is performed under the condition that the oxygen concentration in the intake air is 17% by volume or less. The emission of components can be reduced, and a reduction in fuel consumption can be suppressed. Furthermore, the use of the fuel oil composition of CO ₂ emission intensity is small invention, the reduction of CO ₂ is 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 to smoke, nitrogen oxide (NOx), hydrocarbon (HC) in the exhaust gas. Each concentration of carbon monoxide (CO) and carbon dioxide (CO ₂ ), indicated mean effective pressure, ignition delay, maximum value of dP / dt, and capacity fuel consumption were measured and evaluated by the following methods. In the fuel performance evaluation, the EGR rate was changed from 0 to 70% (oxygen concentration from 22 vol% to 8 vol%). The results are shown in Table 1. Based on the current JIS No. 2 diesel oil, the evaluation results are expressed as (◯) for excellent fuel, (Δ) for equivalent, and (×) for worsened fuel.

<Preparation of test fuel>
-Light oil: Commercially available light oil (JIS No. 2) was prepared.
-Fuel-1: Prepared by deep desulfurization of a light oil base (hydrocracked light oil).
-Fuel-2: Commercially available naphthenic solvent Exol D80 was mixed with 60 vol% of fuel-1 (hydrocracked light oil) by 40 vol%.
Fuel-3: paraffinic light oil (GTL) synthesized by FT.
-Fuel-4: T90 of commercially available light oil was set to 300 ° C. or less (light oil).
Fuel-5: prepared by mixing a commercially available light oil with a cracked light oil base material (LCO) (cracked oil).

<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)
・ Aromatic content: JPI-5S-49-97 “Petroleum products-hydrocarbon type test method-high-speed liquid ・ CO ₂ emission intensity: Fujio Nagao,“ Internal combustion engine lecture ”(published by Yokendo) (1991)

<Specifications of the test engine>
・ Number of cylinders: 1
-Bore, stroke (mm): 110, 106
・ Displacement (cm ³ ): 1007
・ Compression ratio: 16
・ Fuel supply method: In-cylinder injection (common rail)

<Operating conditions>
・ Rotation speed (rpm): 1320
-Fuel injection amount (mm ³ ): variable (covers the PCCI combustion range)
・ Fuel injection pressure (MPa): 40-120
・ Ignition timing: Top dead center (TDC) (Adjust injection timing)
-EGR rate (%): 0-70

<Performance evaluation method>
(1) Exhaust gas measurement Using the Horiba exhaust gas analysis system, the concentrations of carbon dioxide (CO ₂ ), nitrogen oxides (NOx), hydrocarbons (HC), and carbon monoxide (CO) in the exhaust gas are measured. It was measured. The smoke was measured using a smoke meter (transmitted light type) manufactured by Ono Sokki.

(2) Combustion analysis The indicated mean effective pressure, ignition delay, and maximum value of dP / dt were measured using a combustion analysis device manufactured by Ono Sokki.

(3) Capacity fuel consumption It calculated from the measured value of the indicated mean effective pressure and fuel consumption.

As is apparent from Table 1, when the fuel oil composition satisfying the properties defined in the present invention is used, the PCCI engine is operated under the condition that the oxygen concentration in the intake air is 17% by volume or less by adopting EGR. However, it is possible to reduce emission of harmful gas components such as PM, HC, and CO, suppress fuel consumption reduction, and reduce CO ₂ emission.

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 360 ° C or less, cetane number (CN) is 55 or more, aromatic content is 10 mass% or less, CO ₂ emission unit is 0.069 g / A fuel oil composition having a kJ or less and a density at 15 ° C. of 0.820 g / cm ³ or more.