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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.

It is well known that two representative methods satisfy the EURO4 emission regulation. The one is the EGR system that reduces NOx by using EGR (Exhaust Gas Recirculation) and eliminates PM (Particulate Matter) by DPF (Diesel Particulate Filter). But this system has disadvantages of fuel efficiency and requirement for larger engine cooling capacity. The other is SCR (Selective Catalyst Reduction) system that reduces NOx by dosing reagent into exhaust gas. The SCR system also needs to decrease PM by optimization of combustion. The SCR system has advantages of fuel economy and good engine durability. As the price of oil goes up, the commercial vehicle drivers are more concerned about the fuel economy lately, so the European major manufacturer of commercial vehicle adopted the SCR system because of above mentioned advantages. This paper focused on the development of EURO4 engine and commercial vehicle equipped with SCR system.