A thermodynamics-based turbocharger matching method for large-displacement methanol engines considering in-cylinder air state and exhaust composition

Methanol has attracted increasing attention for internal combustion engines due to its clean combustion characteristics and carbon-neutral potential. Most existing methanol engines are converted from natural gas or diesel engines. However, their performance is constrained by methanol's low heating value and lean-burn characteristics, which demand a larger intake air mass under high-power conditions. This challenge is further complicated by the high water content and relatively low temperature of the exhaust gas, which hinder efficient exhaust energy recovery. Consequently, turbochargers originally matched for fossil-fuel engines often fall short in meeting the needs of methanol engines, making dedicated re-matching of the turbocharging system necessary. In this study, a thermodynamics-based turbocharger matching method is proposed to improve engine performance by accounting for the in-cylinder air state and the effects of exhaust composition, thereby achieving thermodynamic synergistic matching among the engine, compressor, and turbine. The method was validated experimentally across a range of engine speeds and throttle openings, with the deviation between the measured and calculated values remaining within 5%. Finally, a well-matched turbocharger for a 14.5 L methanol engine is selected according to the method, achieving a maximum power of 481.82 kW and a maximum torque of 2880.17 N·m, representing improvements of 23.52% and 9.20%, respectively, compared with the original turbocharger. The proposed method directly determines key turbocharger performance parameters for given engine targets, enabling rapid turbocharger–engine matching and accelerating methanol engine development.