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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.

Spray model of KIVA-II code was modified by comparing with experimentally measured spray liquid phase penetration and spray image in a transparent engine. The KIVA-II code with modified spray model was applied to a HSDI engine with different combustion chamber shapes, nozzle specifications and injection pressures. The results were compared with experimental emissions and it was found that the modified KIVA-II code was relatively able to predict the effects of engine design factors such as combustion chamber shape and injector on NOx and soot emissions.

This paper introduced a very simple method to measure the liquid phase of spray in an optically accessible DI diesel engine. Particular attention was paid to easy usage and maintaining the compression ratio of the real engine. As a result, a less-expensive 4 W argon laser was used as the beam source and an E-10 high-speed camera was used for continuously observing the elastic-scatter liquid phase image. Meanwhile, the compression ratio can be kept as the real engines by this method. Through this method, the effects such as injection pressure, nozzle specification, intake air boost and temperature on liquid phase penetration before ignition were investigated. Reducing nozzle hole diameter decreased the length of the liquid phase. Increasing injection pressure hastened the evolution of liquid phase, while the liquid phase length varied complexly. Increasing intake air boost considerably shortened the liquid phase penetration and ignition delay.

Effects of pilot injection on diesel combustion have been studied on a turbocharged direct-injection diesel engine. Under various engine operating injection conditions, emissions were measured while the pilot quantity and timing were varied. The result showed that the pilot injection at low engine load could reduce NOx and THC and, also, improve fuel consumption in some degree. To grasp the phenomena, diesel combustion was analyzed and combustion process observed with an endoscope. It was found that the pilot injection reduced average combustion gas temperature due to a restriction on pre-mixed combustion and a slower combustion during diffusion. The photographs of the entrainment of the burned gas, generated from the pilot combustion, by the main fuel spray injected into the pilot flame and of the resulting slow down of the diesel combustion were taken.

To analyze the combustion phenomena of DI diesel engines in detail, the “cross-correlation method” and the “two-color method” have been applied to measure the combustion flame motion and the flame temperature, respectively by processing the high speed photographs. The purpose of this investigation is to study the effects of engine parameters such as pumping rate, injector nozzle hole size, and injection timing on combustion processes; particularly on flame motion and flame temperature. The results showed that the flame motion was more active during the injection period; and after the end of injection, the motion of flame was largely governed by the air swirl. Increasing fuel pumping rate and using a small hole area injector nozzle, caused the flame motion to become more active, especially during the injection period. The flame temperature was higher with both increased pumping rate and advanced injection timing.

In the case of an inline six cylinder diesel engine, first bending mode, second bending mode, bulge mode and panel modes of the cylinder block are related closely to the engine noise. The analysis of the bulge mode is carried out and the results are reported. The behavior of the engine block with the engine ignited and run, was measured using double pulsed laser holography with particular attention to the characteristics of exciting force and engine structure. In addition, oil pressure was applied to the combustion chamber of the engine with the crankshaft locked to compare the deflection characteristics with that of a running engine.