Effects of EGR on combustion and emissions in a heavy-duty CI engine retrofitted to methanol SI operation

This study explores the impact of exhaust gas recirculation (EGR) as a dilution strategy, on performance and emissions of a heavy-duty diesel engine retrofitted for spark-ignited (SI) methanol operation. A 6-cylinder, 7.15L compression ignition (CI) engine was retrofitted by integrating methanol port injection and replacing diesel injectors with spark plugs, while retaining the original compression ratio of 17.6:1 and turbocharging setup. Tests were conducted at different EGR rates to evaluate the influence on combustion stability, knock tolerance, thermal efficiency, and emissions. Despite methanol’s high octane rating, the elevated compression ratio made knock a limiting factor, particularly at high loads. The results show that EGR dilution improves efficiency by enabling more advanced spark timing and reduces NO emissions. However, excessive dilution increased cycle-to-cycle variation while increasing CO emissions. EGR demonstrated knock suppression and extended the stable operating range, making it more effective under high-load conditions. EGR operation also allows the use of a three-way catalyst, providing a practical path for emission reduction. Overall, the study identifies EGR as a suitable dilution strategy for optimising methanol SI performance in high compression ratio heavy-duty engines.