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This study investigated the odorous components in the exhaust of DI diesel engines. The complete products of combustion are H2O and CO2, which have no odor. Therefore, other products of incomplete combustion like unburned fuel components, partially burned components, cracked products from thermal cracking and others are thought to be responsible for exhaust odor. The THC in the exhaust is the result of incomplete combustion. This study measured THC in the exhaust, and a good correlation was found between THC and exhaust odor at different engine conditions. The low boiling point hydrocarbon components, especially CH4 in diesel exhaust were found to show a good correlation with exhaust odor. Aldehydes in exhaust gases correlate with exhaust odor very well and among the aldehydes, formaldehyde is found to be the most important component in causing irritating odor. The other part of this study is devoted to the improvement in the odor assessment used for DI diesel engines.

This study investigated the effect of ignition delay and exhaust gas speed on exhaust odor in DI diesel engines. From the investigation of many engine parameters like injection timing and injection pressure, it has been found that the optimum ignition start position is more important than the shorter ignition delay, but the optimum ignition start position along with the shorter ignition delay is the best scenario for minimum odor. Further, it has been found that good mixture formation is more important than shorter ignition delay in reducing odor, but the optimum mixture formation together with shorter ignition delay results in the lowest odorous emissions. From the investigation of various fuels in the diesel engine, it seems that the combustion pattern and the raw odor of fuel are more important than ignition delay. A fuel with low raw odor and high cetane number with optimum boiling point significantly improves the exhaust odor.

This study proposes a new combustion chamber concept for small DI diesel engines. Reduction of fuel adhering to the cavity wall, improvements in mixture formation, and an optimum distribution of mixture inside and outside the cavity are the main characteristics of the combustion chamber. The spray formation and it's distribution inside and outside the combustion chamber was investigated photographically in a small DI diesel engine with transparent cylinder and piston. Optimization of the fuel spray distribution inside and outside the cavity was attempted by changing the shape of the cavity entrance and the location where spray impinges on the lip. In addition improvements in the mixture formation of the impinging spray and reductions in the fuel adhering to the cavity wall were attempted by introducing a small step on the cavity side wall. The results were confirmed by analyzing the combustion and emission in an actual DI diesel engine.

Since there is a trade-off relationship between NOx and particulates in exhaust gas emitted from a diesel engine, simultaneous reduction of the amounts of NOx and particulates in a combustion chamber is difficult. However, the amount of particulates produced in the combustion process could be reduced in a state of almost complete combustion, and the amount of NOx produced during the combustion process could be reduced by the use of a catalyst and reducing agent in the exhaust process. It has been demonstrated that the use of ethanol as a reducing agent on a silver-base catalyst in the presence of oxygen is an effective means for reducing NOx, although the mechanism of the reduction has not been elucidated. Therefore, in the present study, an NOx-reduction apparatus was conducted, and model experiments on NOx reduction were carried out in an atmosphere simulating exhaust gas emitted from a diesel engine and at the same catalyst temperature as that in a combustion chamber.

Small two stroke SI engines supplied with natural gas in the intake port are advantageous for low maintenance and low cost when used in co-generation systems for residential use. However in the engines with port injection systems, the unburned HC emissions are higher and thermal efficiency is lower than with 4 stroke engines. To overcome these disadvantages, an in-cylinder injection with a special low pressure injection nozzle system was attempted. The results showed that improvements in unburned HC emissions and thermal efficiency are possible due to the remarkable reduction in scavenging loss and the lean combustion.

Modern small DI diesel engines are operated at high loads and high speeds. In these engines the spray spreading on the cavity walls during the main combustion is kept approximately constant at all engine speeds to optimize the air utilization. However, spray spreading on the wall during the early and late part of combustion changes with engine speed due to the changes in air motion. At the end of impingement much of the spray moves outside the cavity due to a strong reverse squish when the injection timing is set near TDC. This causes incomplete combustion of fuel and increase emissions of HC and soot. Therefore, the study of the behavior of spray affected by the reverse squish is very important. In this study the fuel spray development under high injection pressure and high gas charging pressure was investigated photographically in a small direct injection diesel engine with a common rail injection system.

This study investigated the influence of aldehyde and hydrocarbon components (HC components) on exhaust odor in DI diesel engines. Aldehyde is an important odorous group in exhaust, and it correlates well with exhaust odor at any engine condition. Formaldehyde (HCHO) in the exhaust has been identified as an important component causing irritating odor. Water-washing of exhaust gases does not trap HC components, while most of the odorous components are trapped with remarkable odor reductions. This indicates that the HC components in the exhaust have no direct effect on exhaust odor. However, the exhaust odor increases with increases in the concentration of the low boiling point HC components. This maybe due to the increase in intermediate odorous compounds like aldehydes, organic acids, or other oxygenated compounds in the combustion condition where the low boiling point HC components increase.

Direct injection diesel engines emit a far more disagreeable exhaust odor at idling than gasoline engines, and with increasing numbers of DI diesel engines in passenger cars, it is important to promote the odor reduction research. High pressure injection in DI diesel engines promotes combustion and decreases particulate matter (PM) emissions, but injection pressures at idling and warm up are limited to 30∼40 MPa considering engine noise and vibration. In this pressure range, a part of the fuel adheres on the relatively cool combustion chamber walls and causes incomplete combustion, producing higher concentration of unburned HC and intermediate combustion components (aldehydes, other oxygenated compounds, etc.) with objectionable exhaust odors. To reduce the exhaust odor, oxidation catalysts are effective, but catalyst activity is poor at idling, when the exhaust gas temperature is low (about 100°C).

This study investigated the effect of high pressure injection and an oxidation catalyst on the exhaust odor of DI diesel engines. At idling an injection pressure of 60∼80 MPa resulted in the minimum exhaust odor, with the least aldehyde and minimum total hydrocarbon (THC). This is because of decreases in fuel adhering to the combustion chamber walls due to the shortest ignition delay at this pressure range. However, above 60 MPa there is no further shortening of the ignition delay and overleaning of the local mixture dominates at injection pressures above 100 MPa, where the exhaust odor increases again. The odor reduction at the optimum injection pressure and injection timing is not significant, and further experiments with an oxidation catalyst were performed. The oxidation catalyst was found less effective to reduce exhaust odor at long idling where the maximum catalyst temperature is only about 120°C.

Lean-burn engines now being developed employ in-cylinder injection which requires high pressures and so necessitates expensive injection equipment. The injection system proposed here is an air assisted in-cylinder injection system which is injecting a mixture of air and fuel in the cylinder during the intake stroke and allowing atomization at lower injection pressures than those necessary in compressing fuel with a usual solid injection. This time, the experiments used a testing engine of a 4 stroke gasoline OHV type replacing the Side Valve type. Performance with a small depression in the main combustion chamber was investigated with a spark plug and reed valve installed in the depression. The engine was operated then following the same method as last year (SAE 982698). As a result, the lean burn method employed here was possible over a wide range of engine speeds and loads. Moreover, it was also shown that this operation was possible with a fully opened throttle valve.

Exhaust odor of DI diesel engines is worse than that of gasoline engines, especially at low temperatures and at idling. As the number of passenger cars with DI diesel engines is increasing worldwide because of their low CO2 emissions, odor reduction research of DI diesel engines is important. Incomplete combustion is a major cause of exhaust odor. Generally, odor worsens due to overleaning of the mixture in the cylinder and due to fuel adhering on the combustion chamber walls. To confirm this, the influences of different engine running conditions and fuel properties were investigated. The reason for the changes in exhaust odor with injection timing is evaluated by considerations of optimum positions of the maximum heat release. With n-heptane, a low boiling point fuel, odorous emissions increase because of overleaning of the mixture.

Early stage combustion systems, with lean homogeneous charge compression ignition (HCCI), have been studied, with the intent to decrease the pollutant emission characteristics of DI diesel engines. Early stage combustion enables drastic reductions in both nitrogen oxides (NOx) and smoke emission, but the operating load range is restricted, due to combustion phenomena, such as unsteady combustion and knocking. In this study, we explored the possibility of broadening the operating load range in HCCI and reducing pollutant emissions using Dimethyl Ether (DME) fumigated through the intake pipe. However, the improvements in load range were found to be less than 0.1 MPa in brake mean effective pressure (BMEP), even when compression ratios were reduced and Methane with high octane number was mixed. Therefore, a DME premixed charge could be used only at light loads. At heavier loads a hybrid fuel system with a DME premixed charge and diesel fuel injection is necessary.

Lean burn engines now being developed employ in-cylinder injection which requires high pressures and so necessitates expensive injection equipment. The experiments reported here used air assisted in-cylinder injection, and injected a mixture of air and fuel during the intake stroke, so allowing atomization at lower injection pressures than those necessary in compressing fuel with solid injection. The experiments confirmed that operation in this manner resulted in similar output and fuel consumption as with a carburetor. Next, a divided combustion chamber was installed and connected to the main combustion chamber and air assisted in-cylinder injection from a reed type injection nozzle was attempted. With this arrangement, stable idling operation was possible to air-fuel ratios (A/F) of 70. Lean burn at A/F = 22 to 35 was also achieved at maximum rated outputs (3.7 kW at 4200 min-l) of 6 - 18 %.

A critical factor in improving performance of crankcase-scavenged two-stroke gasoline engines is to reduce the short-circuiting of the fresh charge to the exhaust in the scavenging process. To achieve this, the authors developed a reciprocating exhaust control valve mechanism and direct air-fuel injection system. This paper investigates the effects of exhaust control valve and direct air-fuel injection in the all aspect of engine performance and exhaust emissions over a wide range of loads and engine speeds. The experimental results indicate that the exhaust control valve and direct air-fuel injection system can improve specific fuel consumption, and that HC emissions can be significantly reduced by the reduction in fresh charge losses. The pressure variation also decreased by the improved combustion process. CRANKCASE SCAVENGED two-stroke gasoline engines suffer from fresh charge losses leading to poor fuel economy and it is a reason for large increases of HC in the exhaust.

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.

Blue smoke and HC emissions from a direct injection diesel engine increase gradually during long idling operation (for a few hours). The extent of this increase depends on the injection nozzle specification and engine operating conditions. The accumulation of carbon deposits on the nozzle tip and combustion chamber wall will depend on these factors. Since the carbon absorbs fuel well, low volatility components can not evaporate during the combustion period and the unburned fuel emissions increase over time. This tendency changes according to fluctuations of spray shape and cylinder to cylinder fuel quantity variations.

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.