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A detailed comparison of cylinder pressure derived combustion performance and engine-out emissions is made between an all-metal single-cylinder light-duty diesel engine and a geometrically equivalent engine designed for optical accessibility. The metal and optically accessible single-cylinder engines have the same nominal geometry, including cylinder head, piston bowl shape and valve cutouts, bore, stroke, valve lift profiles, and fuel injection system. The bulk gas thermodynamic state near TDC and load of the two engines are closely matched by adjusting the optical engine intake mass flow and composition, intake temperature, and fueling rate for a highly dilute, low temperature combustion (LTC) operating condition with an intake O2 concentration of 9%. Subsequent start of injection (SOI) sweeps compare the emissions trends of UHC, CO, NOx, and soot, as well as ignition delay and fuel consumption.

A 2.4L commercial diesel engine was developed for light-duty commercial and off-road applications such as skid-loader, forklift and construction equipments. This engine complies with US Tier 4-final regulation, without PM after-treatment device by virtue of improved combustion strategy which is named as ULPC (Ultra-Low Particulate Combustion). This paper explains how ULPC works to reduce particulate matter (PM) based on the optimization of combustion system - piston bowl and nozzle specification. A baseline, re-entrant shape piston bowl, is useful to improve mixing of fuel and air in the main combustion chamber due to squish jet flow, especially in high-speed diesel engines. However, operating speed of commercial engines is almost half slower than that of passenger car engines and the merits by squish flow become deteriorated.

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.