Experimental performance analysis of a heavy-duty marine diesel engine retrofitted to operate on LPG propane

Reducing exhaust gas emissions from heavy-duty diesel engines remains a critical challenge in the off-road transportation sector. To address this issue, extensive research has focused on retrofitting conventional diesel engines to operate on alternative gaseous fuels, such as natural gas and LPG. In this study, a heavy-duty marine diesel engine was modified into a spark-ignited LPG propane engine, and its performance was experimentally evaluated. The feasibility of the developed LPG engine was assessed through basic performance tests conducted under full-speed and full-load conditions, with particular emphasis on achieving the target power and complying with the IMO Tier III NOx and EU Stage V PM regulations. In addition, part-load performance tests were performed under various operating conditions by varying spark timing and air-fuel ratio, and dynamometer performance, combustion, and exhaust emissions characteristics were evaluated. In the feasibility test, the power and torque of the modified LPG engine achieved target levels and over 90% of the performance compared to diesel, while NOx and PM emissions also remained below their respective regulations limit. In the spark timing variation test, power output decreased and fuel consumption and exhaust gas temperature increased as spark timing was retarded. Additionally, as the combustion phasing increased, thermal and combustion efficiency decreased, while NOx emissions decreased and HC, CO, and CO 2 emissions increased. In the air–fuel ratio variation test (from enrichment to stoichiometric), power was maximum at λ = 0.95 (slightly rich condition) and subsequently decreased. Furthermore, combustion pressure was maximum at λ = 0.85 (rich condition), and IMEP–COV showed an upward trend after λ = 0.90. Finally, as λ approached 1.00, NOx and CO 2 emissions increased, while HC and CO emissions decreased.