Control Strategy for NO_x Emission of Lean Burn Gasoline Engine Using Three-Way Catalyst

The control strategy with three-way catalyst(TWC) was investigated to reduce NOx emission of lean-burn gasoline engine. By analyzing the causes of the NOx conversion efficiency reduction of TWC under lean conditions when air fuel ratio (APR) was a little greater than stoichiometric AFR, it is proposed that lean-bum NOx emission could be controlled with TWC under higher lean-burn AFR. Tests were carried out. On the basis of oxygen storage mechanism analysis, a new lean-burn gasoline engine emission control strategy was given using TWC. Through AFR lean/rich modulation and TWC control, the lean-burn NOx emission reduced dramatically. The number and ratio of lean/rich modulations were optimized through tests. The conversion efficiency of NOx under lean-burn conditions reached 45%. The NOx emission could be reduced to less than 200×10-6. The strategy was proved effective in the control of lean-burn NOx emission of gasoline engines.