Abstract: During quickly accelerating and sharply increasing load, the mass rate of air to engine doesn’t consist with the variation of fuel flow, which results in air-fuel ratio decrease and makes the quality of mixture bad. As a result, the combustion of engine becomes worse and the smoke emission increases. To solve this problem, the air intake is modified by installing an electric supercharger (ES) in parallel with the original intake manifold, which makes the intake air be boosted to engine by the ES during the transient opera- tions. Test results showed that ES injecting air to engine under transient operating conditions of increasing speed or torque improves the combustion quality of engine and reduces the smoke emission, as well as boost power output. The improvement is more remarkable especially under the low speed and high torque transient conditions.

Key words: Diesel engine, Electric supercharger, Emission smoke, Transient state