Kei Miwa

Effects of fuel cetane number and aromatics on combustion process and emissions of a direct-injection diesel engine

This study investigated the effects of fuel properties on combustion characteristics and emissions such as NOx. THC, smoke and particulate in a direct-injection diesel engine. Cetane number and aromatic content of fuels were varied independently. The results showed that reducing cetane number resulted in the increase of NOx and the decrease of particulate at high load. The aromatic content had little effect on combustion characteristics. However, increasing aromatic content for high cetane number fuel resulted in high NOx and particulate emissions. For low cetane number fuel, increasing aromatic content produced high THC emission at retarded injection timing. In the case of high injection pressure, fuel properties showed little effect on particulate emissions.

A study of hydrogen fuelled compression ignition engines

Abstract The possibility of establishing a hydrogen fuelled compression ignition engine has been investigated experimentally using a conventional swirl chamber diesel engine. Two different attempts are included in this work; one dealing with the compression ignition on an air-aspirated engine system, and another with an engine operating with an argon-oxygen charge. In the former, the effect of preliminary fuelling was clarified in detail. It has been suggested that both pilot injection and fuel leakage from the injector can aid ignition of the hydrogen fuel, bringing about a smooth operation. A discussion is given of the mechanism of stabilizing ignition, from the viewpoint of thermal interactions between the engine cycles. In the latter attempt, a closed-cycle engine system is oriented and has been simulated by supplying a 21% oxygen containing mixture to the test engine. The result has indicated that ignition and engine operation are satisfactory without any ignition aid. A considerable gain has also been proved in thermal efficiency of using the argon mixture. Also, the practical feasibility of a closed-cycle compression ignition engine has been discussed.

A study on thermal decomposition of fuels and NOx formation in diesel combustion using a total gas sampling technique

Abstract The effects of aromatic components and distillation temperature of diesel fuel on the decomposition of hydrocarbons and NOx formation during diesel combustion were studied at different injection pressures using a rapid compression machine and a total gas sampling device. It was found that fuel injected into hot compressed air is quickly gasified and then thermally cracked, and a large amount of unsaturated light hydrocarbons, mainly C2H4, C2H2 and C3H6, are produced during the ignition delay period. It was also found that the level of the initial rate of heat release is approximately proportional to the amount of light unsaturated hydrocarbons observed. As the injection pressure is increased, both the amount of light hydrocarbons formed and the initial rate of heat release increase, which results in an NOx concentration higher than that at a lower injection pressure. As for the effects of fuel properties, it was revealed that aromatic components in the fuel enhance NOx formation over the combustion period through their higher adiabatic flame temperatures and that a high-distillation temperature of fuel yields a lower rate of heat release and lower NOx formation due to the slower rate of evaporation.

Effects of Aromatic Hydrocarbons on Fuel Decomposition and Oxidation Processes in Diesel Combustion

The chemical behaviors of diesel fuel and the effects of aromatic content on combustion characteristics and NO x histories were experimentally investigated using a rapid compression machine and a total-gas sampling device. The aromatic content was changed under constant cetane number. Composition of the individual hydrocarbons, inorganic gases and NO x under various ambient temperatures and fuel injection pressures were analyzed with aromatic-free and aromatic-containing fuels. The results indicate that injected fuel is rapidly decomposed and dehydrogenated during the ignition delay period. The decomposed low boiling-point hydrocarbons consist of mainly unsaturated hydrocarbons such as C 2 H 4 , C 2 H 2 and C 3 H 6 at the initial combustion phase. At the diffusion combustion phase, the low boiling-point hydrocarbons consist of mainly CH 4 . The aromatic-containing fuel is decomposed with difficulty because of the lower decomposition rate of not only aromatic component but also other heavy saturate hydrocarbons, resulting in higher concentration of low-boiling point hydrocarbons after the ignition than that in aromatic-free fuel. Aromatic-containing fuel gives long NO x formation duration and high final NO x concentration than those of aromatic-free fuel.

Combustion and Pollutant Formation in an Indirect Injection Diesel Engine

A traversed fast-sampling technique has been applied to explore the processes of combustion and pollutant formation in an indirect injection, swirl chamber type diesel combustion system. To permit traversed gas-sampling in each chamber, experiments were made on a double-scavenged two-stroke cycle engine with a simulated two-dimensional chamber configuration. Parameters of interest in the experiments include the extent of fuel rich zones and their decay with time, the action of swirling air motion, nitric oxide formation, the formation of hydrocarbons and soot, the state of gas outflow from the swirl chamber into the main chamber, and flame spread within the main chamber. The effect of certain operating conditions and design parameters, such as overall fuel-air ratio, injection timing, connecting passage dimension, and fuel spray direction on experimental parameters were investigated.

Experimental and Theoretical Optimization of Combustion Chamber and Fuel Distribution for the Low Emission Direct-Injection Diesel Engine

Effects of combustion chamber geometry and initial mixture distribution on the combustion process were investigated in a direct-injection diesel engine. In the engine experiment, a high squish combustion chamber with a squish lip could reduce both NO x and particulate emissions with retarded injection timing. According to the results of CFD computation and phenomenological modeling, the high squish combustion chamber with a central pip is effective to keep the combusting mixture under the squish lip until the end of combustion and the combustion region forms rich and highly turbulent atmosphere. This kind of mixture distribution tends to reduce initial burning, resulting in restraint of NO x emission while keeping low particulate emission.

A Study on Diesel Emission Reduction using a High-frequency Dielectric Barrier Discharge Plasma

The aim of this study is to develop a plasma-assisted after-treatment system for simultaneous reduction of NOx and PM in diesel exhaust, which is less sensitive to the fuel sulfur. The work presented focuses on development of a high-frequency dielectric barrier discharge reactor for oxidation of NO to NO 2 in diesel exhaust and low-temperature oxidation of diesel soot with NO 2 . The first part of this paper describes the combustion characteristics of carbonaceous matters with pure NO 2 and discusses the difference when oxygen Is used as oxidation agent. The second part focuses on the development of a high-frequency dielectric barrier plasma reactor and describes the effects of plasma reactor configuration, energy density and gas composition on the NO conversion into NO 2 , and last part describes the soot oxidation with the plasma gas. The results reveal that NO can be efficiently oxidized into NO 2 using the developed plasma reactor. NO 2 formation is greatly affected by the energy density, gas composition and temperature. Hydrocarbons show positive effects on NO conversion into NO 2 by increasing the conversion rate, lowering the required electrical energy and preventing the formation of byproducts. Diesel soot oxidation experiments reveal that oxidation of soot with NO 2 begins at temperature of about 270°C that is 200°C lower than that of O 2 . This result show that NO 2 , which is produced by the plasma assisted conversion of NO can be used for continuous regeneration of PM filter at low temperature range, which is usually available in diesel exhaust.

TREND AND ORIGINS OF PARTICULATE AND HYDROCARBON EMISSION FROM A DIRECT-INJECTION DIESEL ENGINE

A systematic study on particulate mass emission from a high-speed direct-injection diesel engine was conducted using a mini-dilution sampling method. Effects of fuel-air equivalence ratio, engine speed, injection timing, and swirl intensity are presented and discussed with special regard to soluble organic fraction (SOF) and hydrocarbons. Results show that these concentrations are greatly affected by ignition delay or by temperature level in the engine cylinder. As the sources of SOF and hydrocarbons, local and bulk quenching of the charge, interaction of the fuel spray with the combustion chamber walls, and slow thermal decomposition of fuel are considered and discussed. Among them, the significance of the fuel decomposition is pointed out, by separate experiments on a simulated engine by using an in-cylinder gas-sampling technique. The proposed mechanism is that at low air temperature, thermal cracking is too slow for the injected fuel to be fully decomposed, resulting in the accumulation of raw and partially cracked fuel.

Experimental Study on Combustion Characteristics and Emissions Reduction of Emulsified Fuels in Diesel Combustion Using a Rapid Compression Machine

Effects of water-emulsified fuel on diesel combustion and emission reduction process were investigated under various ambient temperatures, equivalence ratios and water addition ratios using a rapid compression machine and a total-gas sampling device. The results indicate that promoted diffusion combustion of emulsified fuels offers a shorter combustion duration and an increase in amount of heat release when compared with those of gas oil. NO x concentration decreases with increasing the water content in emulsion fuels. This reduction is due to low NO formation rate and short duration of NO formation. Laser extinction measurement of the inchamber KL factor shows that soot oxidation is promoted for emulsified fuels during the diffusion combustion stage.

DeNOx mechanism caused by thermal cracking hydrocarbons in the stratified rich zone during diesel combustion

Abstract This study concerns an experimental and theoretical investigation of the deNO x mechanism caused by thermal cracking hydrocarbons during diesel combustion. A total gas sampling experiment using a rapid compression machine showed that NO x can be reduced under fuel-rich and high-swirl conditions. It was found that under these conditions, a large amount of thermal cracking hydrocarbons, including unsaturated hydrocarbons such as C2H4, are produced during the ignition delay period, and that stratified fuel-rich combustion regions that contain these thermal cracking hydrocarbons are distributed widely throughout the combustion chamber. During the diffusion combustion phase, the CH4 concentration surpasses that of C2H4 and becomes the dominant hydrocarbon species. These thermal cracking hydrocarbons are supposed to be active in NO x reduction chemistry. To confirm the assumption, a flow reactor experiment was conducted focusing on the thermal cracking process of diesel fuel and the NO x reduction process. The experiment showed that when a solvent was used as fuel, light hydrocarbons similar to those observed in the rapid compression experiment are formed, and that about 60 per cent of NO x was reduced at equivalence ratios over 2.5 and a temperature of 1500 K. In addition to the above experiments, a chemical kinetic calculation using CHEMKIN III was carried out. The calculation revealed that C2H4 is easily decomposed during its oxidation process, forming HCCO or CHC2, which reacts promptly with NO and that in this reaction path, C2H22 formed through the thermal cracking process of C2H4 is an essential species to the formation of HCCO and CH2.