Investigation of Waste Heat Recovery Systems for Improving Energy Efficiency in Internal Combustion Engines

Abstract

Internal combustion engines convert only part of the fuel chemical energy into useful brake work, while a substantial fraction is rejected through exhaust gases, coolant and other thermal pathways. This paper develops a compact methodology for investigating waste heat recovery (WHR) systems intended to improve engine energy efficiency. The approach combines a first-law engine energy balance, exhaust heat availability estimation, screening of Organic Rankine Cycle (ORC), thermoelectric generator (TEG) and turbocompounding options, and a detailed ORC performance model. A generic 45 kW compression-ignition engine operating at 25-100% load is used as the methodological case. Exhaust heat is calculated from mass flow rate, specific heat and exhaust-to-ambient temperature difference; recoverable heat is then corrected for heat-exchanger effectiveness and conversion efficiency. The model predicts that net ORC power increases from about 0.53 kW at 25% load to 4.48 kW at full load, raising brake thermal efficiency from 37.5% to about 41.2% at the rated point. The comparison shows that ORC offers the strongest efficiency potential for sustained medium-to-high loads, TEG provides compact solid-state recovery at lower conversion efficiency, and turbocompounding can be attractive where exhaust pressure energy is high. The methodology is suitable for preliminary design, sensitivity analysis and subsequent experimental validation.