Rankine cycle waste heat recovery for a heavy-duty natural gas engine meeting China VI emission standards

Abstract

The China VI natural gas engine is based on the theory of the air–fuel ratio method, leading to a high exhaust temperature, large heat load and difficult cooling. The paper carried out a thermal balance experiment of the China VI natural gas engine under different working conditions. A dual-loop organic Rankine cycle system is designed to reduce the difficulty of cooling system and improve the thermal efficiency. The high-temperature loop uses water as working fluid to recover the heat of engine exhaust gas and recirculation exhaust gas. The low-temperature loop recovers the heat from cooling water and waste heat of the high-temperature loop. The high-temperature and low-temperature loops are coupled through a shared heat exchanger. The results show that the China VI natural gas engine has a higher and more stable waste heat temperature than traditional engines and is more adaptable to waste heat recovery under variable operating conditions. For fixed evaporation temperature, with the increase of inlet temperature of the expander, the net output power of high-temperature loop increases first and then decreases, reaching the maximum value at about 800 K. In the low-temperature loop working fluids R601a, R601b, R600, R600a and R12333zd, The maximum net output power of the waste heat recovery system based on the combination of water and R12333zd is approximately 75.4 kW under the rated condition, which is 22.24% of the rated power of the engine.