Impact of natural gas injection timing on the combustion and emissions performance of a dual-direct-injection diesel/natural gas engine

Under the background of carbon neutrality, the natural gas (NG) is deemed as a competitive alternative fuel for the internal combustion engine (ICE) industry to respond increasingly stringent emission and fuel consumption regulations. To better understand the effect of the NG injection timing (SOING) on the combustion and emissions performance of a dual-direct-injection diesel/NG engine, a detailed investigation concerned with the SOING is carried out. The testing work was operated on a self-developed single-cylinder engine under a constant speed of 1200 r/min, and the SOING was changed from - 120 degrees CA ATDC to - 60 degrees CA ATDC. During the testing, the mass flow rate of NG was changed from 0.337 to 0.807 kg/h and the mass flow rate of diesel was changed from 0.48 to 1.22 kg/h, and the engine cylinder pressure, pressure rise rate, NOx, UHC, CO2, CO emissions were investigated. The results show that the engine performance was strongly affected by the NG injection timing. When the mass flow rate of diesel was kept at 0.82 kg/h, the mass flow rate of NG was kept at 0.467 kg/h, with the SOING was changed from - 60 degrees CA ATDC to - 120 degrees CA ATDC, the brake thermal efficiency increased from 25.09% to 28.75%, the CO2 emissions increase from 6.00 to 6.42%. Overall, higher thermal efficiency can be achieved by advancing NG injection timing.