Effect of Two-Stage Fuel Injection Parameters on NO<em>_x</em> Reduction Characteristics in a DI Diesel Engine

The aim of this study was to confirm the effects of two-stage combustion on the combustion and NO<em>_x</em> reduction characteristics of a four cylinder direct injection diesel engine. In order to analyze the combustion and emission characteristics, various injection parameters, such as injection quantity, injection timing and injection pressure were used under constant engine speed and engine load. In addition, the experimental results of two-stage combustion are compared to the single injection when injection timing is 5° BTDC. The experimental results showed that NO<em>_x</em> emissions were significantly reduced when applying two-stage combustion. In particular, an injection strategy when the first and second injections have a same quantity, the results showed the maximum reduction of NO<em>_x</em> emissions in this experiment. The NO<em>_x</em> emissions were also reduced when the timing of the first injection was advanced. However, NO<em>_x</em> emissions indicated almost similar concentration regardless of first injection timings when the first injection timing was earlier than 50° BTDC. In the case of soot emissions were slightly increased compare to the single injection cases at tested conditions.