Partially Premixed Combustion (PPC) is a promising combustion concept with high thermodynamic efficiency and low emission level, and also with minimal modification of standard engine hardware. To use PPC in a production oriented engine, the optimal intake charge conditions for PPC should be included in the analysis. The experiments in this paper investigated and confirmed that the optimal intake conditions of net indicated efficiency for PPC are EGR between 50% and 55% as possible and the lambda close to 1.4. Heat-transfer energy and exhaust gas waste-energy contribute to the majority of the energy loss in the engine. The low EGR region has high heat-transfer and low exhaust gas enthalpy-waste, while the high EGR region has low heat-transfer and high exhaust gas waste-enthalpy. The optimal EGR condition is around 50% where the smallest energy loss is found as a trade-off between heat transfer and exhaust-gas enthalpy-waste. Lambda close to 1.4 results from the trade-off of high gas-exchange efficiency with low lambda and high thermodynamic efficiency with high lambda. The optimal inlet charge condition was also applied to a multi-cylinder engine from low load to high load. The results indicate that the highest net indicated efficiency of the experimental engine was 49.7% at 13.5 bar IMEPn (Net Indicated Mean Effective Pressure), the highest brake efficiency was 44.2% observed at 17.2 bar IMEPn.