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Abstract
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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.
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