Abstract
Direct injection (DI) systems are increasingly being applied to gasoline engines in order to meet global demands for reduction of CO2 emissions. However, with existing DI-G systems, lean A/F ratio operation for improving fuel economy is used only a hot engine and catalyst condition on account of the need to stabilize combustion and reduce NOx emissions. It is difficult to lower the light-off temperature of current NOx traps further in order to reduce NOx at a lean A/F ratio and low exhaust gas temperature following a cold start. Therefore, in this study, it was examined that a new NOx reduction technology that uses different types of catalyst for exhaust gas after-treatment under cold-lean conditions.
For example, some types of zeolite are known to trap NOx in polluted air. A method of applying this technology to vehicle exhaust gas is examined. The following results were obtained in experiments conducted with exhaust model gases. A zeolite catalyst trapped nearly 100% of NOx in the exhaust gas under a low temperature condition (catalyst temperature of less than 100°C) following a cold start where the water vapor and oxygen concentrations in the gas were suitably controlled. The quantity of NOx trapped by the catalyst increased with a decreasing water vapor concentration in the exhaust gas. On the other hand, the onset of NOx desorption was delayed with the exhaust gas contained a certain level of water vapor. This paper also discusses about the examination result that used other catalyst ingredients.