A review of water-steam-assist technology in modern internal combustion engines

Abstract Internal combustion engines consuming fossil fuels produce roughly one-quarter of the world’s anthropogenically generated power. In automobiles, over 50% of the fuel’s energy is dissipated as waste heat. Exhaust heat and jacket water heat are good candidates for waste heat recovery applications. To recover reusable energy from exhaust gases and coolant, water-steam-assist technology has been proposed and established based on an in-cylinder steam-assisted cycle. In this paper, typical water-based waste heat recovery technologies are reviewed and analysed, including the Rankine, Kalina and trilateral cycles. Relevant studies on water-steam-assist implementation are reviewed, and a novel thermodynamic cycle named the in-cylinder steam-assisted cycle is proposed based on their common features. The main characteristics of this cycle are compared with those of previous techniques in terms of principles, parameters, merits and demerits, and development trends. The analysis shows that water-steam-assist technology has the potential to increase engine efficiency considerably. This work helps elaborate the utilization of this waste heat recovery technology in automobiles and provides a comprehensive overview of its mechanisms.