Emission reduction using a close post injection strategy with a modified Nozzle and piston bowl geometry for a heavy EGR rate

As EURO-6 regulations will be enforced in 2014, the reduction of NOx emission while maintaining low PM emission levels becomes an important topic in current diesel engine research. EGR is the most effective way to reduce the NOx emission because EGR has a dilution and thermal effect as a means to reduce the oxygen concentration and combustion temperature. Although EGR is useful in reducing the NOx emission, it suffers from a higher level of CO and THC emissions, which indicates a low combustion efficiency and poor fuel consumption. Therefore, in this research, a close post injection strategy, which is implemented using main injection and post injection, is introduced to improve combustion efficiency and to reduce PM emission under a high EGR rate. In addition, a modified hardware configuration using a double-row nozzle and a two-staged piston bowl geometry is adapted to improve the effect of the close post injection. As a result, the CO, THC and PM emissions were reduced up to half of what is seen in conventional cases, while holding the NOx emission level low due to a synergistic effect of the hardware combination and the close post injection strategy for diesel combustion with a large EGR rate.