Effect of post-injection on combustion and exhaust emissions in DI diesel engine

An experimental investigation was conducted in a direct-injection (DI) diesel engine to investigate the effect of different post-injection strategies on combustion and regulated/unregulated exhaust emissions. Various exhaust emissions at different post-injection timings and quantities were measured and analyzed by FTIR, including common regulated emissions and certain unregulated emissions, such as aromatic hydrocarbon (AHC), acetylene (C2H2), propane (C3H6), and n-octane (NC8). Experimental research showed that the addition of post-injection can significantly reduce NOx emissions compared to no post-injection condition, with a maximum reduction of 26.7%. Meanwhile, NOx emissions had obvious trade-off relation with soot particulate, CO and light hydrocarbons (HC) emissions under the post-injection condition. Further, the CO and light HCs emissions was slightly increased when the post-injection quantity was increased from 10 mg to 15 mg. A delay in the peak of higher emissions was observed form 60 degrees crank angle (CA) to 80 degrees CA between fuel cracked and uncracked components. In addition, under most operation conditions, post-injection could provide more light HCs and THC for the aftertreatment equipment, with the THC emissions up to 4911 ppm. However, soot emissions were not sensitive to post-injection timing compared to other emissions, except for the early post-injection timing at 20 degrees CA. Overall, an appropriate quantity and timing of post-injection could have a positive effect on pollutant emissions reduction from the perspective of the exhaust pollutants in this DI diesel engine.