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The U.S. Environmental Protection Agency (EPA) issued new emissions regulations, which came into effect in January, 2010. These EPA 2010 regulations are the most stringent emissions standards in the world, reducing both particulate matter (PM) and nitrogen oxides (NOx) to nearly zero levels. Hino Motors improved upon its previous EPA 2007-compliant engine, developing a new exhaust after-treatment system in which a Diesel Particulate active Reduction System (DPR), a Urea-Selective Catalytic Reduction (SCR) System and a Burner System are employed to meet EPA 2010 emissions regulations for medium duty commercial vehicles. DPR was already developed and utilized to reduce PM to meet EPA 2007 standards, but the Urea-SCR System is newly developed technology used to reduce NOx emissions to comply with EPA2010 emissions regulations. In addition, a Burner System is used to elevate exhaust gas temperatures in order to improve both SCR performance and DPR active Regeneration.

To investigate the future direction of diesel emission control technologies and fuel technologies, exhaust emissions tests of diesel vehicles/engines with advanced after-treatments such as NSR catalyst, CR-DPF, and Urea-SCR or a combination of these, were conducted using various fuels, and fuel sulfur effect on performance of the after-treatments after mileage accumulation was also evaluated in step II study of JCAP Diesel WG. Overall results shows that the after-treatments have significant effects on reducing emission and reducing fuel sulfur have significant effects on function of the after-treatments in term of decrease of sulfate and SOF, and less deterioration of function of after-treatments after mileage accumulation.

A new concept for diesel combustion has been investigated by means of engine experiments and combustion observations in order to realize a simultaneous reduction of NOx and particulate emissions. The concept is based on pre-mixed compression ignition combustion combined with multiple injection. In this method, some part of fuel is injected at an early stage of the process to form a homogeneous lean pre-mixture, then the remaining fuel is injected at around the TDC in the same manner as a conventional diesel injection. The emissions, ROHR (rate of heat release), and combustion pictures of conventional combustion, pilot injection combustion, and this new combustion concept were compared and analyzed. Engine tests were carried out using a single cylinder research engine equipped with a common rail injection system.

Historically the high speed diesel engine for commercial vehicles has been developed along with its combustion system in compliance with political and economical changes. After the 1970's, stricter exhaust emission regulations and fuel economy requirements induced combustion developments and application of turbocharged and inter cooled engines. From the late 1980's, high pressure fuel injection has been investigated and recognized as an essential tool for lowering emissions especially of particulate matter. Although turbulence effects on both in-cylinder air motion and during the combustion process are quite effective, they show different phenomena in conventional and advanced high pressure fuel injection systems. In the 1990's, multiple injection with high pressure has been attempted for further reduction of NOx and particulate matter.

A new concept for diesel combustion was investigated by means of numerical simulation, engine experiment, and combustion observation in order to realize a simultaneous reduction of NOx and particulate emission. This concept (HiMICS: Homogeneous charge intelligent Multiple Injection Combustion System) is based on pre-mixed compression ignition combustion combined with multiple injection. Combustion characteristics of HiMICS concept was investigated by comparing with both a standard single injection and a pilot injection. In HiMICS concept, the pre-mixture is formed by a preliminary injection performed during a period from the early stage of the induction stroke to the middle stage of the compression stroke. Modified KIVA-II code was used to predict engine performances and emissions of each injection method. The simulation results show a capability of considerable improvement in the trade-off relation between NOx emissions and fuel consumption of HiMICS.