Thermodynamic Study Of Waste Heat Recovery System For Internal Combustion Engine Exhaust Based On Kalina Cycle

The internal combustion engine?ICE?is an important energy conversion device commonly used in automobiles,trucks,buses and ships.Though engine manufacturers have used all kinds of techniques or methods to improve thermal efficiency,the thermal efficiency of ICE is just 35-45%,and approximately 55–65%of the fuel energy is taken away through coolant or exhaust.Kalina cycle?KC?is a feasible method to recover waste heat.The combined ICE-Kalina cycle can reduce fuel consumption and pollutant emissions.Three ICE-Kalina systems,such as ICE-KC,ICE-KCS,ICE-KCF,composed of a topping ICE and three bottoming KCs,are proposed in this paper to recover waste heat from ICE.The thermodynamic and economic analyses are conducted for bottoming KCS.The effects of several important parameters on thermodynamic and economic performance,such as ICE percentage load and ammonia mass fraction,are investigated.The results show that the net power output,thermal efficiency and exergy efficiency increase with the increasing evaporator outlet temperature,turbine inlet temperature and ammonia mass fraction.How the turbine inlet pressure influences the thermal performance depends on the evaporator outlet temperature.There is a critical evaporator outlet temperature,which makes the thermodynamic performance present different trends with the turbine inlet pressure.When the evaporator out temperature is lower than this critical temperature,the net power output,the thermal efficiency and the exergy efficiency reduce with the turbine inlet pressure.When the evaporator out temperature is greater than this critical temperature,there is an optimal turbine inlet pressure(p_2,opt)which makes the KC system achieve the maximum net power output,the thermal efficiency and the exergy efficiency.The higher evaporator outlet temperature,the higher basic ammonia mass fraction and the lower turbine inlet pressure lead to the better economic performance.The thermodynamic and economic performance of KC system with a flash tank relies on the ratio of the pressure in the flash tank to the pressure in the evaporator?p₆/p₂?.When the value of p₆/p₂ is 0.32,KCF system achieves the best thermodynamic performance.And KCF system achieves the best economic performance with the value of p₆/p₂ of 0.3.ICE-KC,ICE-KCS,and ICE-KCF can recover the waste heat from ICE,and improve the thermodynamic performance.Under the load range of ICE?20%-100%?,the improvement of thermal efficiency of ICE-KC and ICE-KCF is about 12%,and the improvement of thermal efficiency of ICE-KCS is 6.4%-15.7%.When the ICE load is lower than 30%,KC and KCF have the better thermodynamic performance.When the ICE load is greater than 60%,KCS shows the better thermodynamic performance.KCS has the best economic performance.