In order to reduce the smoke of a sequential-turbocharged diesel engine during the switching process

a real-time controlling and measuring system of compressed air assist was established for a TBD234 diesel engine. An experimental study was performed to investigate the reduction of smoke emissions during the switching process by air injection. The results show that an optimal strategy is to start the air injection at the opening of exhaust valve with injection duration of 3 s. Earlier air injection or longer injection duration is ineffective to reduce engine smoke. Delaying injection or shortening injection duration weakens the benefit of the air injection. Compared with the performance of the base engine

the air injection with the optimal strategy improves the air to fuel ratio and combustion process during the switching process

with smoke reduced by 50.5%.