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To design diesel engines adapted to future exhaust gas regulation, it would be advantageous to have a driving mode simulation for vehicle performance and exhaust emissions, including after-treatment systems. The combustion model for this objective must be able to simulate the engine performance in very short time. We have tried to develop such diesel engine combustion model by adding the improvements to the Hiroyasu model. In this paper, we detail the improvements that were added to this model and comparisons the calculated results by the improved model with experimental result.

This paper investigates the effect of enhancing mixing of spray tip region on NOx reduction from diesel engines. The concept is based on the fact that dominant part of NOx formation is the flame tip region with weak mixing intensity. Two methods to realize our concept were attempted in a constant volume combustion bomb and in an actual diesel engine. One is the two-stage injection and another is the method with a jet created by combustion of premixed charge in a turbulence cell. The paper presents results of variety trials of experiment, and it discusses necessary means to achieve the concept.

The authors have previously reported significant reductions in particulate emissions by generating strong turbulence during the combustion process. Extending this, it was attempted to reduce NOx, particulate, and fuel consumption simultaneously by two-stage combustion: forming a fuel rich mixture at the initial combustion stage to prevent NOx formation, and inducing strong turbulence in the combustion chamber at the later stage of combustion to oxidize the particulate. The purpose of this study is to examine the effect of two-stage combustion in emission control. The paper gives an evaluation of the NO reaction-kinetics of the system and experimental results for a combustion chamber specially made for the two-stage combustion. With this combustion system, it was possible to reduce NOx levels to 1/3 of the base engine. Combination of EGR and the two-stage combustion was also examined.

Extensive experiments were conducted on a low emission DI diesel engine by using Dimethyl Carbonate (DMC) as an oxygenate fuel additive. The results indicated that smoke reduced almost linearly with fuel oxygen content. Accompanying noticeable reductions of HC and CO were attained, while a small increase in NOx was encountered. The effective reduction in smoke with DMC was maintained with intake charge CO2, which led to low NOx and smoke emissions by the combined use of oxygenated fuel and exhaust gas recirculation (EGR). Further experiments were conducted on an optically accessible combustion bomb and a thermal cracking set-up to study the mechanisms of DMC addition on smoke reduction.

This paper uses NO Reaction Kinetic to determine NO formation characteristics in diesel engines. The NO formation was calculated by Extended Zel'dovich Reaction Kinetics in a diffusion process. The results show that the NO formation rate is independent of the mixing of the combustion gas, and that internal EGR (combustion gas mixing in a cylinder) has no effect on NO reduction. The paper also shows the potential of two stage combustion, and its effect strongly depends on the time-scale of mixing. Additionally the paper investigates the mechanism of increased NOx emissions in high pressure fuel injection.

This paper presents a theory and its experimental validation for air entrainment changes into fuel sprays in DI diesel engines. The theory predicts air entrainment changes for a variety of swirl speeds, number of nozzle holes, nozzle diameters, engine speeds, injection speeds and fuel densities. The formulae of the theory are simple non-dimensional equations, which apply for different sized engines. Experiments were performed to compare theoretical predictions and experimental results in six different engines varying from 85 to 800mm bore. All results showed good agreement with the theoretical predictions for shallow-dish piston engines. However the agreement became poor in the case of deep cavity piston engines. With the theory, it is possible to interpret a variety of combustion phenomena in diesel engines, providing additional understanding of diesel combustion processes.

This paper presents experimental results of the reduction of both particulate and NOx emitted from direct injection diesel engines by a two stage combustion process. The primary combustion is made very rich to reduce NOx and then the particulate is oxidized by strong turbulence generated during the secondary combustion. The rich mixture is formed by low pressure fuel injection and a small cavity combustion chamber configuration. The strong turbulence is generated by a jet of burned gas from an auxiliary chamber installed at the cylinder head. The results showed that NOx was reduced significantly while maintaining fuel consumption and particulate emissions. An investigation was also carried out on the particulate reduction process in the combustion chamber with the turbulence by gas sampling and in-cylinder observation with an optical fiber scope and a high speed camera.

Dimethyl ether (DME) can be converted easily from methanol in a catalytic reactor, and it has very good compression ignition characteristics. This paper presents experimental results on a compression ignition methanol engine with DME as an ignition improver. The results show that engine operation is sufficiently smooth with high efficiency without spark or glow plugs. In the experiments, two methods for DME introduction were investigated: an aspiration and a torch ignition method. The aspiration method introduces DME into the intake manifold, and is structurally simple but suffers from poor emission characteristics at partial loads, and a large amount of DME is required for ignition. With the torch ignition method, DME is introduced into a torch ignition chamber during the intake stroke, and significant reductions in both the necessary DME quantity and emissions were obtained. Engine operation was also attempted with DME-dissolved methanol fuel without ignition aids.

This paper presents a theoretical and experimental study on the possibility of combustion similarity in differently sized diesel engines. Combustion similarity means that the flow pattern and flame distribution develop similarly in differently sized engines. The study contributes to an understanding and correlating of data which are presently limited to specific engine designs. The theoretical consideration shows the possibility of combustion similarity, and the similarity conditions were identified. To verify the theory, a comparison of experimental data from real engines was performed; and a comparison of results of a three dimensional computer simulation for different engine sizes was also attempted. The results showed good agreement with the theoretical predictions. THE PURPOSE of this research is to determine the possibility of the existence of combustion similarity in differently sized diesel engines, and to propose conditions for realizing model experiments.

This paper presents results of experiments to reduce smoke emitted from direct Injection diesel engines by strong turbulence generated during the combustion process. The turbulence was created by jets of burned gas from an auxiliary chamber installed in the cylinder head. Strong turbulence, which was induced late in the combustion period, enhanced the mixing of air with unburned fuel and soot, resulting in a remarkable reduction of smoke and particulate; NOx did not show any increase with this system, and thermal efficiency was improved at high loads. The paper also shows that the combination of EGR and water injection with this system effectively reduces the both smoke and NOx.

Copper ion-exchanged ZSM-5 zeolite catalyst, which reduces nitrogen oxides (NOx) in the presence of oxygen and hydrocarbons, was applied to actual diesel engine exhaust. Copper ion-exchanged ZSM-5 zeolite effectively reduced NOx by 25% in normal engine operation, and by 80% when hydrocarbons in the exhaust were increased. Water in the exhaust gas decreased the NOx reduction efficiency, but oxygen and sulfur appeared to have only a small effect. Maximum NOx reduction was observed at 400°C irrespective of hydrocarbon species, and did not decrease with space velocity up to values of 20,000 1/h. THE PURPOSE of this paper is to evaluate the possibilities and problems in catalytic reduction of NOx in actual diesel engine exhaust. Here, a copper ion-exchanged ZSM-5 zeolite (Cu-Z) catalyst was applied to diesel engine exhaust to examine the dependency of the NOx reduction efficiency on temperature and space velocity. The effects of oxygen, water and hydrocarbons were also examined.

This paper is a systematic investigation of the effects of combustion and injection systems on hydrocarbon(HC) and particulate emissions from a DI diesel engine. Piston cavity diameter, swirl ratio, number of injection nozzle openings, and injection direction are varied as the experimental parameters, and the constituents in the soluble organic fraction (SOF) of the particulate were analyzed. The results show that the emission characteristics of deep dish chambers greatly differ from those of shallow dish chambers varying with the number of nozzle openings, the injection direction, and swirl intensity. The HC analysis shows mainly low carbon number gaseous HC constituents, and there is a tendency towards increasing polynucleation of polynuclear aromatic hydrocarbon(PAH) in SOF with increasing soot formation.

This paper is concerned with the effects of temperature of heavy fuels on combustion and engine performance in a naturally aspirated DI diesel engine. Engine performance and exhaust gas emissions were measured for rapeseed oil, B-heavy oil, and diesel fuel at fuel temperatures from 40°C to 400°C. With increased fuel temperature, mainly from improved efficiency of combustion there were significant reductions in the specific energy consumption and smoke emissions. It was found that the improvements were mainly a function of the fuel viscosity, and it was independent of the kind of fuel. The optimum temperature of the fuels with regard to specific energy consumption and smoke emission is about 90°C for diesel fuel, 240°C for B-heavy oil, and 300°C for rapeseed oil. At these temperatures, the viscosities of the fuels show nearly identical value, 0.9 - 3 cst. The optimum viscosity tends to increase slightly with increases in the swirl ratio in the combustion chamber.

Two laboratory engines, one direct, injection and one indirect injection, were operated for a range of speeds, loads, injection timings, fuels, and steady and transient conditions. Rate of combustion data were derived and analyzed using a double Wiebe's function approximation. It is shown that three of the six function parameters are constant for a wide range of conditions and that the other three can be expressed as linear functions of the amount of fuel injected during ignition lag. Engine noise, smoke, and thermal efficiency correlate with the parameters describing the amount of premixed combustion and diffusive combustion duration. These characteristics may be optimized by reducing the quantity of premixed combustion while maintaining the duration of diffusive combustion to less than 60°CA.

The purpose of this investigation is to evaluate the feasibility of rapeseed oil and palm oil for diesel fuel substitution in a naturally aspirated D.I. diesel engine, and also to find means to reduce the carbon deposit buildup in vegetable oil combustion. In the experiments, the engine performance, exhaust gas emissions, and carbon deposits were measured for a number of fuels: rapeseed oil, palm oil, methylester of rapeseed oil, and these fuels blended with ethanol or diesel fuel with different fuel temperatures. It was found that both of the vegetable oil fuels generated an acceptable engine performance and exhaust gas emission levels for short term operation, but they caused carbon deposit buildups and sticking of piston rings after extended operation.

Spark-assisted diesel engines operated with alcohol fuels usually display misfiring or knocking problems. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a swirl chamber diesel engine with a multi-spark ignitor. In the experiments, cycle-to-cycle combustion variations and the degree of knocking were investigated by changing engine parameters over a wide operating range. The results of the investigations showed that stable ignition and smooth combustion is achieved when a flammable mixture is formed in the vicinity of the spark plug when only a small amount of the injected fuel has evaporated. By optimizing the design factors, operation with high efficiency and low exhaust emissions was achieved.

Many of the promissing alternative fuels have relatively low cetane numbers, and may-result in combustion variation problems. This paper presents the chracteristics of the cycle-to-cycle combustion variations in diesel engines, and analyzes and evaluates the mechanism. Combustion variations appear in various forms, such as variations in ignition lag, indicated mean effective pressure, maximum combustion pressure, or rate of heat release. These variations are clearly correlated, and it is possible to represent the combustion variations by the standard deviation in the combustion peak pressure. The combustion variations are random (non-periodic), and are affected by ethanol amount, intake air temperature, engine speed and other various operating conditions.

Forced ignition with glow plugs has great potential for the utilization of alcohol fuels in diesel engines. However, the installation of glow plugs may cause misfiring or knocking in parts of the operating range. This paper presents an analysis of the factors influencing the ignition characteristics of ethanol in a glow plug-assisted diesel engine; these factors may be classified into two categories: the factors related to the temperature history of the drop lets before contact with the glow plug, and those related to the probability of contact. By optimizing these factors, the combustion difficulties were successfully eliminated over the whole operating range, and engine performance comparable with conventional diesel operation was achieved.