Method of purifying exhaust gases of an Otto-cycle engine

摘要

Exhaust gases are caused to flow back into the cylinders of an Otto-cycle engine through exhaust valves when the pistons stay at the bottom dead centers of the induction stroke. This enables the exhaust gases leaving the cylinder during the exhaust stroke to have a sufficiently high temperature to activate a catalyst for purifying the exhaust gases even when the engine still has a low temperature during the beginning of its operation at a low load.