As presented in the previous study , a 2.4L ULPC(Ultra Low PM Combustion) diesel engine was achieved through optimal matching with piston bowl geometry and nozzle spray angle that significantly reduce the amount of engine out soot generated in the combustion. This engine complies with US Tier 4 Final regulation without DPF (only DOC) which was developed for off-road applications such as skid-loader, forklift and construction equipment. Improvement in fuel consumption of diesel engine for off-road applications and construction equipment which are operating continuously for a long time at high load conditions will be very important for reducing the operating costs. This paper explains a detailed review of improvement BSFC of 2.4L ULPC diesel engine by optimizing the combustion system with swirl ratio, nozzle flow rate and piston bowl geometry while maintaining non-DPF solution. In this study, three dimensional commercial CFD software (Diesel 3D) was used to compare with the various swirl ratio levels, nozzles with the different nozzle flow rate and piston bowl geometries. The robust optimal design method by DFSS (Design for Six Sigma) used to optimize the piston bowl geometry. In the results of 3-D combustion simulation which was evaluating the each parameter, It shows a higher potential to improve BSFC while maintaining the low level of soot emission. The results of engine bench tests can prove the effect of swirl ratio, nozzle, piston bowl geometry and the results match the simulation results well. Finally, over 6.0% improvement of fuel consumption at the rated power condition which is the main operating condition in the off-road applications has been achieved in the new 2.4L ULPC diesel engine which is applied the optimized combustion system with higher swirl ratio, higher nozzle flow rate and modified piston bowl geometry in compared with the base ULPC diesel engine.