Yoshiyuki Kidoguchi

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.

Effect of Air Entrainment and Oxygen Concentration on Endothermic and Heat Recovery Process of Diesel Ignition

The mixture formation prior to the ignition process is a key element in the diesel combustion because it significantly influences throughout the combustion process and exhaust emissions. Purpose of this study is to clarify the effects of ambient temperature, oxygen concentration and air entrainment into the spray on the heat release process during ignition delay periods. This study investigated diesel combustion fundamentally using a rapid compression machine and high speed digital video camera. The detail behavior of spray evaporation, spray interference and mixture formation during ignition delay period was investigated using the schlieren photography system. Ignition process, flame development and images of the spray ignition with extremely dark flame were investigated by light sensitivity direct photography method. Heat release processes were analyzed by pressure measurement in the chamber. Results show that short endothermic process produces slow heat recovery, leading to gentle increase of initial heat release rate. Low oxygen concentration produces slow heat recovery process rather than long endothermic period, which suggests fuel-air mixing is required to promote chemical reaction for the case of low oxygen-concentration atmosphere. Initial heat release is activated to some extent by increase of air entrainment into spray during ignition delay period. However, excessive air entrainment increases initial heat release little and rather affects diffusion combustion.

A Multidimensional Model Prediction of Heat Transfer in Non-Fired Engines

An axisymmetric three-dimensional model for in-cylinder processes has been applied to the predictions of wall heat transfer in a non-fired engine cylinder. Computed heat fluxes are shown for combustion chambers with a flat piston and a deep-bowl piston for swirl and non-swirl cases. The predictions compare well with existing experimental heat fluxes at several different radii on a cylinder head except in a central part. It is also shown that the predictions of surface-averaged heat flux are consistent with those obtained from empirical correlations. The effect of compression-expansion work is indicated by predicted temperature profiles and typically demonstrated by phase difference between the heat flux and the bulk-mean gas temperature. Computational discussions are given on local heat fluxes in the deep-bowl-piston combustion chamber and suggest that local heat fluxes are greatly increased by squish motion, squish-induced vortex, and swirling motion spun-up in the bowl.

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.

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.

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.

Effect of Wall Configuration on Atomization of Rapeseed Oil Diesel Spray Impinging on the Wall

Fuel-air mixing is important process in diesel combustion. It has been well known that wall configuration of the piston affects spray atomization. Biomass fuel, that is viable alternative fuel for fossil one, needs great help of mixing to atomization because the fuel has high viscosity and high distillation temperature. This study investigates spray atomization characteristics of rapeseed oil (RO) when it impinges on the piston wall. Optical observation of RO spray was carried out using shadowgraph photography technique. The optical images and image analysis show that wall impingement effectively promotes RO spray atomization. Spray atomization is more sensitive to wall configuration for RO than diesel fuel. The wall that has flat floor at the bottom can improve atomization. It is necessary for RO spray to promote spray penetration followed by wall-impingement because long spray path offers wide spray boundary region to form droplets.

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.