Impact of post-injection strategies on combustion and unregulated emissions during different loads in an HSDI diesel engine

Abstract

This research was done to study combustion and emissions characteristics especially unregulated emissions from a heavy-duty diesel engine based on three engine loads (20%, 40%, 60%) with different post-injection (PI) strategies, at six start of injection timings (SOI) with a 20° crank angle (CA) interval (20–120 °CA) and three post-injection fuel masses (PIM) (5 mg, 10 mg and 15 mg) at constant speed of 1200 revolution per minute (rpm). Common regulated (NOx, soot, and THC) and un-regulated emissions including carbonyl compounds (acetaldehyde, formaldehyde), saturated (methane, ethane, propane) and unsaturated (ethylene, propylene, 1,3 butadiene) emissions were recorded with Fourier Transform Infrared analyzer (FTIR). An early post-injection can increase the engine power output and raise the temperature of the exhaust gases at all engine loads. Reduction in NOx up to 25% and THC up to 60% were recorded at 60°CA while up to 80% reduction in soot emissions was recorded at SOI 80-120°CA with PI strategies at medium to high loads. For all the P.I strategies results indicated that unregulated emissions increased with the increase in the PIM and mostly the peak values of unregulated emissions recorded at SOI 60–80 °CA with 15 mg PIM. Post-injection at 60-80 °CA found most suitable to produce light hydrocarbon (HC) at lower engine load. In general, the post-injection reduced regulated/unregulated emissions and generate light HC relative to the single main injection which is beneficial for after-treatment devices.