Atmospheric environment has been improved in Japan, but compliance rate with the environmental quality standards for nitrogen dioxides has remained at insufficient level. Diesel-powered automobiles are identified as primary emission source of nitrogen dioxides. It is desired that emission standards for diesel-powered automobiles are reinforced.
In this paper, present technical levels and problems were described for NOx control, particularly concerning with engine modification (EM) and exhaust gas recirculation (EGR) techniques, which have been mainly adopted by automobile manufacturers. So far the manufacturers have applied fuel injection timing retard out of EM techniques, but further remarkable improvement of this technique is not expected, so that the application of EGR technique is being studied. Because the durability of many parts in the engine are deteriorated by means of EGR application, the improvement of lubricating oil grade and reduction of sulfur content in gas oil are desired in addition to the improvement of the quality of material in the engine.
