Optimization of Methanol Cracking Gas Blending Ratios and Diesel Injection Timing for Combustion and Emissions Control in Marine Engines

Abstract To improve the thermal efficiency of marine engines and reduce NOX emission, the heat of waste gas is recycled to heat cracking methanol and the diesel micro-injection ignition method. The effects of methanol cracking gas and diesel injection timing on the performance of a compression-ignition diesel engine (cylinder diameter—137.2 mm, cylinder stroke—165.1 mm, and rated speed—910 rpm) are studied by converge simulation. The results show that the NOX emission and the indicated mean effective pressure (IMEP) increase with the increase of the blending ratios of methanol cracking gas. With delayed fuel injection timing, combustion becomes more concentrated, leading to increase in the IMEP and the indicated thermal efficiency. However, NOX emission also rises. As the injection timing is further delayed, NOX emission decreases. When the methanol substitution ratio is 94%, the methanol cracking gas blending ratio is 20%, and the injection timing is −4 °CA ATDC. This also causes NOX emission to reach 3.63 g/kW h with a 46.04% indicated thermal efficiency. These values are 22.64% lower and 4.44% higher, respectively, compared to the original diesel engine, while hydrocarbon and carbon monoxide emissions are nearly completely burned. The influence of the methanol cracking gas blending ratio and fuel injection timing parameter optimizations on the engine combustion and emission performance provides a theoretical basis for the study of methanol cracking gas blending marine engines.