Thermodynamic analysis on the effect of altitude on the exhaust energy recovery of electric turbocompound engines

The deterioration of fuel economy for turbocharged engines with altitude is an urgent problem. Turbocompounding is a promising technology to fully recover exhaust energy and reduce engine fuel consumption at off-design altitudes, but it is affected by the environmental boundary caused by altitude. In this study, the effect and mechanism of altitude on the exhaust energy recovery of turbocompound engines were revealed via thermodynamic analysis. The results show that the total system power output of the turbocompound engine is higher than that of the base engine at different altitudes, the maximum improvement percentage of which reaches up to 4.3%; and the total power output deteriorates less with increasing altitude. When the altitude increases to 4 km, the exhaust energy utilization coefficient of turbocompound engine decreases by only about 2%. Based on energy and exergy analysis, full recovery and utilization of exhaust energy contribute to improving the altitude adaptability of turbocharged engines. The maximum altitude while maintaining the engine power constant for the turbocompound engine is 4.66 km under an engine speed of 1800 r/min. Thus, the altitude range over which turbocompound diesel engines can operate efficiently is widened.