Development of Advanced Emission-Control Technologies for Gasoline Direct-Injection Engines

An extensive effort has been made, at Mitsubishi Motors, in the technology field of new catalysts and of the catalyst reaction control for the purpose of further improvement of the emission control with the GDI engines [1-2]. A new NOx-trap catalyst has been developed to satisfy the required higher catalyst performance under high-temperature condition. The new catalyst contains potassium (K) of excellent NOx-storage capacity under high-temperature region in the catalytic atmosphere, and to retain K stability zeolite is mixed in the catalyst layer as well as the substrate is coated with silica (SiO₂). This new catalyst has been proven of the improved NOx conversion efficiency, and solved the long-pending problems particularly those experienced under high-temperature operation. In addition to the NOx-trap catalyst, a new dual-layer three-way catalyst (hereinafter referred to TWC), using platinum (Pt) effective for HC emissions control, has been developed with the aim of improving HC emissions reduction in lean-combustion region, which frequently occurs in the GDI engine.

In the field of the activation-control technology, several innovative technologies have also been created such as the controls of stratified slightly-lean combustion for faster catalyst light-off, of the purge-pulse injection and of oxygen (O₂)-storage control to improve the catalyst-activity efficiency, and of the assisted catalyst temperature-rise to extended the sulfur-poisoning resistivity of the catalyst.