Analysis of the performance and emissions generation mechanism of natural gas/diesel dual-fuel under different strategies by combining experiments and mechanisms

Abstract

In natural gas/diesel dual-fuel engines, natural gas (NG) still produces some emissions during combustion, especially at high NG substitution rates. In order to reduce the emissions and to clarify the emissions formation mechanism. In this work, the performance and emission characteristics of the dual-fuel engine under different diesel injection strategies, as well as the formation mechanism of emissions (NOx, CO, THC and soot) were analyzed by combining bench test and chemical mechanism. The results showed that compared with diesel single injection, the diesel pilot injection strategy (PIS) could effectively improve the engine BTE (22.6%), CO and THC emissions were reduced by 87.8% and 76.1%, respectively. By advancing the diesel pilot injection timing (PIT), the combustion efficiency and BTE increased by 5.1% and 10.9%, respectively; the soot, THC, and CO emissions reduced by 63.9%, 69.4% and 76.9%, respectively. Increasing the diesel pilot injection ratio (PIR) could improve the combustion efficiency and reduce CO and THC emissions. According to the path analysis, the CO consumption was mainly the reaction R120: HO2+COOH + CO2, the generation of THC were mainly affected by path 1: CH3→CH3O→CH2O→HCO→CO and path 2: CH3→C2H6→C2H5→C2H4, and the soot was mainly related to C2H2, but it was mainly affected by the synergistic effect of multi-step reaction. Therefore, through the analysis of different diesel injection strategies, advanced the MIT and PIT of diesel and the medium PIR of diesel, the pressure and temperature of the engine were within the appropriate range, and the reactivity was kept in a good state, which could achieve low NOx, soot and THC emissions, high BTE and low BSEC from the engine.