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This paper shows development challenges for 6 liter heavy duty off-road diesel engines to meet the Tier4 final emission regulations with a base diesel engine compliant with Tier4 interim emission regulations. Even if an after-treatment system helps to reduce emissions, quite amount of particulate matters (PM) reduction is still necessary since a diesel particulate filter (DPF) system is supposed to be excluded in Tier4 final diesel engine. The objective of this research is to see if the base engine has a feasibility to meet Tier4 final emission regulations by a change of piston bowl geometry without DPF. Quite amount of PM can be reduced by piston bowl geometry because piston bowl geometry is a very important part that enhances air and fuel mixing process that help the combustion process.

As presented in the previous study [1], 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.