In order to improve the performance of a new designed diesel engine, a simulation model of in-cylinder combustion was set up to study the effects of combustion chamber and injector nozzle parameters on combustion performance. Then a prototype of engine was built and tested according to the simulation results. The simulation results show that nozzle protrusion and spray include angle have a significantly greater impact on fuel consumption and soot emissions under the rated operating conditions than under the maximum thermal efficiency conditions. A 9.09% change in injector flow rate has a negligible effect on fuel consumption and soot emissions under the maximum thermal efficiency operating conditions, but increasing the flow rate is more effective in controlling the high-temperature thermal load on the cylinder block under the rated operating conditions. Among the three schemes of V01-V03, V01 scheme achieves the greatest reduction in high-pressure cycle indicated specific fuel consumption (HPISFC) with reaching 4.70% and soot emissions by 29.72% under the maximum thermal efficiency operating conditions, while the reductions in HPISFC and soot emissions under the rated operating conditions were the smallest. V02 scheme shows the smallest reduction by 4.23% in HPISFC under the maximum thermal efficiency operating conditions, but the largest reductions in HPISFC and soot emissions under the rated operating conditions. The test results of V01 scheme indicate that the effective specific fuel consumption reduces by 4.10% and the soot emissions reduce by 30.23% under the maximum thermal efficiency operating conditions, which is consistent with the simulation results regarding the expected reductions in HPISFC and soot emissions.