Continuous reduction of cyclic adsorbed and desorbed NO_x in diesel emission using nonthermal plasma

Highlights: • High-efficiency continuous diesel NO_x reduction method is proposed. • Characteristics of diesel NO_x adsorption and desorption on adsorbent is provided. • Efficiency of NO_x reduction with nonthermal plasma is evaluated. • Efficiency of NO_x reduction with exhaust gas component recirculation is evaluated. • High NO_x removal efficiency equal to only 1.0% penalty of engine power is achieved. - Abstract: Considering the recent stringent regulations governing diesel NO_x emission, an aftertreatment system for the reduction of NO_x in the exhaust gas has been proposed and studied. The proposed system is a hybrid method combining nonthermal plasma and NO_x adsorbent. The system does not require precious metal catalysts or harmful chemicals such as urea and ammonia. In the present system, NO_x in diesel emission is treated by adsorption and desorption by adsorbent as well as nonthermal plasma reduction. In addition, the remaining NO_x in the adsorbent is desorbed again in the supplied air by residual heat. The desorbed NO_x in air recirculates into the intake of the engine, and this process, i.e., exhaust gas components' recirculation (EGCR) achieves NO_x reduction. Alternate utilization of two adsorption chambers in the system can achieve high-efficiency NO_x removal continuously. An experiment with a stationary diesel engine for electric power generation demonstrates an energy efficiency of 154 g(NO₂)/kWh for NO_x removal and continuous NO_x reduction of 70.3%. Considering the regulation against diesel emission in Japan, i.e., the new regulation to be imposed on vehicles of 3.5–7.5 ton since 2016, the present aftertreatment system fulfills the requirement with only 1.0% of engine power.