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Complexity of the modern diesel engine has increased to meet the stringent future emission regulations especially for NO (nitrogen oxide) and PM (particulate matter). Air management system including exhaust gas recirculation (EGR), turbocharger and variable valve actuation (VVA) must be optimized of its design and control algorithm for combustion improvement coupled with precision control of fuel injection. As a matter of course, the optimization of aftertreatment system is extremely important for the exhaust emissions reduction. In addition, improvement of fuel consumption is very important from the standpoint of response to energy security and reduction of CO₂ (carbon dioxide) emission as the greenhouse gas. However an enormous amount of energy will be required to develop such kind of the complex engine system by conventional actual testing.

Further improvement in fuel consumption is needed for diesel engines to address regulatory requirement particularly for heavy duty diesel in Japan enforced in 2015, in addition to the compliance to the regulatory requirements for exhaust emission, which seems to be more stringent in future. The authors have participated in the project of “Comprehensive Technological Development of Innovative, Next-Generation, Low-Pollution Vehicles” organized by New Energy and Industrial Technology Development Organization (NEDO), and innovative devices such as multi stage boosting system, ultra high-pressure fuel injection system and variable valve actuation (camless) system had been developed in this project from a standpoint of simultaneous improvement of fuel consumption and exhaust emission. In camless system, intake and exhaust valves are driven by hydraulic pressure. So, fully flexible setting of opening and closure timings and lift of the intake and exhaust valves is possible.

An exhaust turbocharging system makes it possible to increase the brake mean effective pressure (BMEP) and lower emissions levels for a diesel engine while further improving the thermal efficiency. However, in order to meet future emission regulations, further reductions in NOx and particle matter (PM) emissions are necessary. In addition, the diesel engine should have further reductions in fuel consumption to reduce CO₂, which is one of the main greenhouse gases. Authors participated in a program for the comprehensive technological development of innovative, next-generation, low-pollution vehicles with the New Energy and Industrial Technology Development Organization (NEDO) from 2004 through 2008 in cooperation with the National Institute of Advanced Industrial Science and Technology (AIST). A low-emission and high-efficiency diesel engine system was developed to meet the target of NEDO project.

Aggravation of combustion efficiency cause by increase of un-burnt fuel is the major problem in case of premixed compression ignition combustion with early timing injection. In this study, formation of lean air-fuel mixture by near TDC injection timing was investigated. As a natural consequence of this approach, permissible mixing time fall short. Therefore ultra high pressure injection system combined with micro hole nozzle was used in this work for increase of turbulent mixing rate. In this study, commercial Diesel fuel of Japan (JIS#2) was used as the test fuel. Cetane number of this fuel is 62. Some of previous research work shows that required injection timing for lean mixture formation to reduce NOx emission with high cetane number fuel was -90 deg.ATDC or more advanced point. On the other hand, injection timing of indicating extremely low NOx emission level is -38 deg.ATDC in our test result.