Innovative Piston Design Performance for High Efficiency Stoichiometric Heavy Duty Natural Gas Engine 2023-01-0288

Internal combustion engines will continue to be the leading power-train in the heavy-duty, on-highway sector as technologies like hydrogen, fuel cells, and electrification face challenges. Natural gas (NG) engines offer several advantages over diesel engines including near zero particle matter (PM) emissions, lower NOx emissions, lower capital and operating costs, availability of vast domestic NG resources, and lower CO2 emissions being the cleanest burning of all hydrocarbons (HC). The main limitation of this type of engine is the lower efficiency compared to diesel counterparts. Addressing the limitations (knock and misfire) for achieving diesel-like efficiencies is key to accomplishing widespread adoption, especially for the US market.

With the aim to achieve high brake thermal efficiency (BTE), three (3) computational fluid dynamics (CFD) optimized pistons with three different compression ratios (CR) have been tested. Tests were carried out using a Cummins ISX-based 2.5-liter single-cylinder heavy-duty engine. A custom exhaust gas recirculation (EGR) system that simulates a high-pressure EGR loop was used to achieve EGR rates from 0 to 35%. The measurements were performed with variable EGR rate, IMEP, and rate of combustion.

Limitations on combustion control and high knock tendency were found on the highest CR piston, as limited heat transfer led to overheating of the piston crown. Higher BTE was achieved for two of the pistons tested, with peak values above 44%, the baseline efficiency of the diesel engine platform used. Controlled end-gas autoignition was achieved, contributing to the increase in peak BTE and expanding the engine load range. The positive results obtained with the CFD-optimized piston designs encourage the continued development of heavy-duty NG engines as feasible alternatives to reduce CO2 and NOx emissions, PM, and diesel fuel dependency.