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Three Japanese automobile manufacturers-Mitsubishi Motors Corp., Nissan Motor Co., Ltd., and Toyo Kogyo Co., Ltd.-have been making efforts over the past three years to design and develop effective thermal reactor-exhaust gas recirculation and catalytic converter systems suitable for small engines. The work is being done by members participating in the IIEC (Inter-Industry Emission Control) Program, and the exhaust emission levels of the concept vehicles developed by these companies have met the goal established by the IIEC Program at low mileage. Each system, however, has a characteristic relationship between exhaust emission level and loss of fuel economy. Much investigation is required, particularly with respect to durability, before any system that will fully satisfy all service requirements can be completed. This paper reports the progress of research and development of the individual concept vehicles.

Suppression of NH3 formation over NOx catalysts has been the subject of several reports in recent years. However, there are very few reports relating to the effects of modifications of both feed gas conditions and catalyst usage. Therefore, NH3 formation was investigated as a function of such feed gas boundary conditions as CO concentration, CO/O2 ratio, space velocity, linear velocity and catalyst bed temperature. Both fresh and aged NOx catalysts were used. Longitudinal patterns of NH3 formation in monolithic NOx catalyst were also determined. Based on these results, several ideas were tested to reduce NH3 formation in the NOx catalyst through control of feed H2, O2, CO and HC concentrations. Finally, the possibility of extending the optimum A/F range of a NOx catalyst toward leaner A/F ratios by the introduction of methane ahead of the NOx catalyst is discussed.