Micro-discharge in porous ceramics for exhaust gas cleaning

Abstract

This chapter presents a novel NOx removal method using micro-discharge in porous ceramics for exhaust-gas cleaning. Micro-discharge consists of many discharges in narrow channels inside porous ceramics, and transition to flashover can be suppressed because of narrow channel. The micro-discharge is generated by 60Hz AC high voltage using 29 mm diameter ceramics plate with 10 W electrical inputs, and is applied for the cleaning of exhaust gas from diesel engine. Nitrogen oxides (NOx) in exhaust gas from internal combustion engines, especially from diesel engines, cause air pollution and health problems. Conventional NOx removal process for automobile engines is a catalytic process. Such a catalytic process, however, requires high temperature and low oxygen concentration. Recently, nonthermal discharge plasma or combination of nonthermal discharge plasma and catalysts has been extensively investigated for NOx removal because nonthermal discharge plasma can induce chemical reactions under moderate temperatures. The packed-bed type is a NOx removal reactor that can be used in combination with pellet type catalysts. In this reactor, an intense plasma is generated in limited area around many contact points among the pellets. The packed-bed reactors achieved good performance in spite of the small plasma volume. If an effective combination of plasma and honey-comb catalyst is developed, the performance will be improved. For this purpose, the NOx removal using the micro-discharge is examined. Porous ceramics are used to generate the micro-discharge due to electrical breakdown in micro channels. This micro-discharge can possibly be used to generate discharge plasma in honey-comb catalyst having porous structure with micro channels.