Impacts of diesel injection timing and syngas fuel composition in a heavy-duty RCCI engine

This research aimed to assess the impacts of Diesel Direct Injection Timing (DDIT) [-6 to-16 Crank Angle (CA) After Top Dead Center (ATDC) with 2 CA steps], syngas to diesel energy ratio [0 (Pure Diesel Combustion (PDC)), 20% (DSC20), and 40% (DSC40) of total fuel energy per cycle], and syngas fuel composition [H2 to CO volumetric ratio of 75%-25% (R = 3), 50%-50% (R = 1), and 25%-75% (R = 0.33)] in a heavy-duty RCCI engine. The numerical findings revealed that increasing syngas energy ratio to 40% at DDIT of-10 CA ATDC and R of 1 is an effective strategy to reduce NOx, PM, HC, and CO2 emissions by about 12%, 88%. 82%, and 40.36% versus the baseline PDC case, respectively. Regarding engine performance, by advancing the DDIT from-6 to-16 CA ATDC under all engine operating conditions, Gross Indicated Efficiency (GIE) enhanced by about 2.76%, 1.93%, and 1.34%, respectively, in comparison to the baseline PDC, DSC20, and DSC40 cases. Besides, at DSC40 conditions, exhaust gas loss was improved by nearly 4.74% but combustion loss and heat transfer loss were increased by 2% and 3.4%, respectively, compared to the baseline PDC operating mode. Also, increasing syngas energy ratio to 40%, R to 3, and diesel injection at-16 CA ATDC led to about 15.9% and 41% reduction of HC and CO emissions, respectively, compared to the baseline DSC40 case. In addition, under diesel-syngas combustion conditions, regions near cylinder walls and the center of the piston bowl are the main sources of unburnt syngas emission.

Automated summary

This research shows that increasing syngas energy ratio and adjusting diesel injection timing can effectively reduce emissions and improve engine performance. However, increasing syngas ratio may also lead to higher combustion and heat transfer losses.