An investigation into particulate emission and the formation mechanism of soot precursors in ammonia-diesel dual-fuel engines

The complex chemical reaction between ammonia and hydrocarbon molecules influences the formation of soot precursors like benzene, complicating the study of soot in ammonia-diesel fuels and limiting research on the particulate matter emission characteristics of these engines. It is found that as the ammonia energy ratio (AER) increases, the average particle size of soot decreases, and the particle morphology gradually transitions from an accumulation mode to a nuclear mode. The mass concentration of particulate matter also decreases. The reduction in particulate matter mass concentration is significantly greater than the increase in AER. When the fuel injection timing is set to-5 degrees CA ATDC, using the soot mass concentration at a 20 % AER as the baseline, the soot mass concentration decreases by 56.3 % as the AER rises to 40 % and by 90.4 % when it reaches 60 %. The ammonia-n-heptane chemical reaction mechanism model reveals that the introduction of ammonia effectively suppresses the formation of C2H2. Ammonia consumes a substantial amount of OH during its dehydrogenation process, and this reduction in OH significantly curtails the production of n-heptane oxidation products, including benzene, C3H3, and FULVENE. These compounds serve as crucial intermediate products in the formation of particulate matter. With the molar fraction of oxidation products at AER = 20 % as a reference point, when AER = 60 %, the reductions in benzene, C3H3, FULVENE, and C2H2 are 68.5 %, 68.7 %, 73.2 %, and 62.7 %, respectively. These findings provide important insights and directions for future control strategies targeting particulate matter emissions from ammonia-diesel dual-fuel engines.