With increasingly stringent emission regulations and demand for fuel economy by the public,the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues.In this study,combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions(constant speed and increasing torque).Optimization of the transient combustion process was performed by adjusting the fuel injection parameters.The results indicated that the notable combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine,and took the form of combustion phasing delay,resulting in rapidly increasing smoke emission and fuel consumption.However,the delay in combustion phasing can be controlled by advancing the fuel injection timing,effectively increasing thermal efficiency.Unfortunately,smoke and NO x emissions increased at the same time.The deterioration in combustion phasing can also be improved by increasing injection pressure,resulting in decreased smoke emission while NO x emission increased.It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation. Withtens stringent emission regulations and demand for fuel economy by the public, the combustion and emission problems of automotive diesel engines during transient operation have become vital and urgent issues. In this study, combustion deterioration has been experimentally analyzed using a heavy-duty turbocharged diesel engine running under transient conditions (constant speed and increasing torque). Optimizing of the transient combustion process was performed by adjusting the fuel injection parameters. The results indicated that the not combustion combustion deterioration relative to steady state operation while transient was a function of the delay in the air-supply to the turbocharged engine, and took the form of combustion phasing delay, resulting in rapidly increasing smoke emission and fuel consumption. Even though the delay in combustion phasing can be controlled by advancing the fuel injection timing, effectively increasing thermal efficiency. Unfortunately, smoke and NOx emissions inc reased at the same time. The deterioration in combustion phasing can also be improved by increasing injection pressure, resulting in decreased smoke emission while NOx emission increased. It is worth noting that the effective thermal efficiency first increased and then decreased as fuel injection pressure increased during transient operation.