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Control of NOx and PM from diesel engines is a key for enlarging its application in transportation field. To achieve this, many improvements have been done, for instance, the introduction of highly flexible common-rail injection system and cooled EGR system with advanced control strategy. In order to meet more stringent emission regulations in near future, research and development activities have been carried out energetically in the world. In this paper, a low emission combustion strategy is realized by combination of common-rail and cooled EGR. First of all, low soot combustion is approached by optimizing pilot and main injection, in which pilot is controlled to eliminate hot flame. Then, once low soot combustion achieved, higher EGR can be used to reduce NOx.

The filtration efficiency of a DPF drops when it suffers a failure such as melting and cracks during regeneration. And then, on-board diagnostics (OBD) device has become needed worldwide to detect a DPF failure. In the development of an OBD soot sensor, evaluation of the sensor demands a portable instrument which can measure the soot concentration for on-board and in-field use. Some of the emission regulations require the in-field emission measurements under normal in-use operation of a vehicle. This study is intended to develop a high sensitivity and high response portable smoke meter for on-board soot measurements and a reference to OBD soot sensors under development. The smoke meter accommodates a 650 nm laser diode, and its principle is based on light extinction in high soot concentration range and backward light scattering for low soot concentration measurement.