Experimental and numerical studies on performance investigation of a diesel engine converted to run on LPG

With the growing environmental concerns and depletion of energy resources, considerable efforts are focused on developing ecofriendly and sustainable transportation systems. This includes the conversion of outdated diesel engines into ecofriendly liquefied petroleum gas (LPG) engines. In this study, a Euro-6 diesel engine mounted on a commercial vehicle (mega truck) was converted into a propane LPG engine. The combustion chamber was modified by changing the piston shapes (PSs), compression ratios (CRs), ignition system, throttle body, and injector design to enable operation using propane. The performance of the modified engines with two different PSs, PS1 and PS2, were experimentally investigated. In terms of the power, the engine designed using PS2 demonstrated better performance than PS1 under all operating speeds, except 2600 rpm. Particularly, PS2 outperformed PS1 by more than 10 Nm in the low-speed range of 1000-1600 rpm. Under full load, the PS2equipped LPG engine achieved the maximum torque and power of 834 Nm at 1600 rpm and 170 kW at 2600 rpm, achieving 106 % and 86 % of the target torque and power, respectively. Additional exhaust gas emission tests were performed using the PS2-equipped LPG engine. The engine performance varied with the application of exhaust-gas recirculation. Moreover, the results of the world-harmonized stationary cycle mode tests confirmed the conformance of the modified LPG engine to all Euro-6 emission standards. Furthermore, simulation-based performance optimization was conducted considering two PSs and four CRs. Based on the simulations, PS1 achieved higher engine performance and lower CO2 and soot emissions, whereas PS2 had lower NO emissions. Additionally, increasing the CR improved the performance and reduced the CO2 and soot emissions for both PSs. These results indicate the possibility of developing LPG engines with performance comparable to diesel engines. In particular, the modified LPG engine proposed in this work may be installed on buses and trucks in the future and is anticipated to replace outdated medium-generator and marine engines.