Abstract
Waste heats of an internal combustion engine (ICE) are recovered by a dual-loop organic Rankine cycle (DORC). Thermodynamic performance analyses and optimizations are conducted with 523.15–623.15 K exhaust gas temperature (Tg1). Cyclopentane, cyclohexane, benzene, and toluene are selected as working fluids for high-temperature loop (HTL), whereas R1234ze(E), R600a, R245fa, and R601a are selected as working fluids for low-temperature loop (LTL). The HTL evaporation temperature, condensation temperature, and superheat degree are optimized through a genetic algorithm, and net power output is selected as the objective function. Influences of Tg1 on system net power output, thermal efficiency, exergy efficiency, HTL evaporation temperature, HTL condensation temperature, HTL superheat degree, exhaust gas temperature at the exit of the HTL evaporator, heat utilization ratio, and exergy destruction rate of the components are analyzed. Results are presented as follows: the net power output is mainly influenced by HTL working fluid. The optimal LTL working fluid is R1234ze(E). The optimal HTL evaporator temperature increases with Tg1 until it reaches the upper limit. The optimal HTL condensation temperature increases initially and later remains unchanged for a cyclopentane system, thus keeping constant for other systems. Saturated cycle is suitable for cyclohexane, benzene, and toluene systems. Superheat cycle improves the net power output for a cyclopentane system when Tg1 is 568.15–623.15 K.
Highlights
Increased fossil fuel consumption causes environmental pollution, global warming, and energy crisis; waste heat recovery is considered a promising technology for solving these problems [1,2,3].The waste heat utilization of internal combustion engine (ICE) can effectively reduce the use of fossil fuels and is crucial for saving energy and reducing emission because oils consumed by ICE account forAppl
The point temperature difference (PPTD) of the high-temperature loop (HTL) evaporator is the largest [5,19] because the heat transfer performance of engine exhaust gas is low; the PPTD of the HTL evaporator is set to 20 K on the basis of Literature [18,43]; the PPTDs of the low-temperature loop (LTL) preheater and condenser/evaporator are set to 10 K on the basis of Literature [40,43]; and PPTD of 5 K is common for an LTL condenser [5,19,40,43]
When Tg1 is 523.15–553.15 K, ILpre is the fourth largest exergy destruction rate at higher than 5%; when Tg1 is 573.15–623.15 K, the heat absorption ratio of the jacket cooling water accounting for the total heat absorption decreases, and ILpre decreases and becomes the second smallest exergy destruction rate considering the increase in exhaust gas heat absorption
Summary
Increased fossil fuel consumption causes environmental pollution, global warming, and energy crisis; waste heat recovery is considered a promising technology for solving these problems [1,2,3].The waste heat utilization of internal combustion engine (ICE) can effectively reduce the use of fossil fuels and is crucial for saving energy and reducing emission because oils consumed by ICE account forAppl. Among all of the existing solutions for the waste heat utilization of ICE, organic Rankine cycle (ORC) is a promising technology. Shu et al [12] used ORC to recover waste heat of diesel engine using alkanes as working fluids. Vaja et al [13] performed a thermodynamic analysis of ICE waste heat recovery using ORC, benzene, R11, and R134a as working fluids and considered different cycle configurations. Their results indicated that the overall efficiency of ORC is better by 12% than when ORC is not applied. Song et al [17] designed an optimized
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