CONTROL OF LEAN BURN ENGINE USING EXHAUST GAS RECIRCULATION

There is provided a method of controlling an internal combustion engine fuel with hydrogen. The method comprises supplying fuel and fresh air with substantially no re-circulated exhaust gas into a combustion chamber of the internal combustion engine, so that an air-fuel ratio in the combustion chamber is a first ratio leaner than the stoichiometric air-fuel ratio, during a first engine operating condition. The method further comprises supplying fuel, fresh air and re-circulated exhaust gas into the combustion chamber, so that an air-fuel ratio in the combustion chamber is a second ratio leaner than the stoichimetric air-fuel ratio, the second ratio being richer than the first ratio, during a second engine operating condition at which time the desired torque is greater than that during the first engine operating condition. During the second operating condition with the greater desired torque, by supplying the lean air-fuel mixture with the EGR into the combustion chamber, the EGR can decrease the NOx generation caused by the lean air-fuel ratio, while realizing the benefit of the lean burn operation such as fuel economy improvement. During the first operating condition with the less desired torque, by supplying the further lean air-fuel mixture with substantially no EGR into the combustion chamber, the EGR generation may be minimal because of the further lean air-fuel ratio and the combustion stability is maintained because of the substantially no EGR.