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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).

The blue and white smoke (cold smoke) emitted from diesel engines during warm up at low temperatures and idling conditions contains pollutant gases which irritate eyes and nose, and reductions in this irritating, odorous gas have become important with the increasing numbers of DI diesel engine vehicles. To assess the blue and white smoke a qualitative assessment method is necessary, though, there are no simple and exact measuring methods. In this study a new assessment method using a digital camera and photo analysis system with a computer is introduced. With this method the luminance of the cold smoke is displayed as 8 bit data, and a quantitative evaluation is simple, when the influence of sunshine is corrected for the smoke luminance. This paper describes the correction method for the sunshine illumination and the technique for taking the photographs.

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.