Research Of Dual-loop Organic Rankine Cycle (DORC) Used For Large-temperature-difference Recovery Of Engine Exhaust Waste Heat

According to the energy distribution of internal combustion engine (ICE), it isfound that lots of the fuel combustion energy has been wasted by the engine coolantand exhaust, which accounts for60%~70%. It is significant to recover these parts ofwaste heat. Currently, Organic Rankine Cycle (ORC) is a high-effective method forwaste heat recovery. Therefore, recovering the high-temperature exhaust waste heatwith ORC is of promising future in waste heat recovery of internal combustionengine.The exhaust’s temperature of engine is very high and the temperature range ofthe available waste heat of the engine (about500~120℃) is large. If using traditionalORC to recover the high-temperature exhaust waste heat, there are two main issuessuch as that the organic working fluid is easy to compose and the waste heat is hardlyto be recovered completely. Based on this, a Dual-loop Organic Rankine Cycle(DORC) is established in this paper. The DORC system includes a high-temperatureloop and a low-temperature loop, in which the high-temperature loop adopts theworking fluid with high decomposition temperature to avoid it from decomposing andthe low-temperature loop adopts common organic fluid with high thermal efficiencyto respectively recover the waste heat of the engine coolant, the high-temperaturecycle and the exhaust. Based on the parameters of a6-cylinder4-stroke engine and thefirst law and second law of the thermodynamics, the simulation model of the DORCsystem is established and the calculation and analysis are carried out. In order tovalidate the thermodynamic model, the comparison between the model of this DORCsystem with the published model is carried out. Results show that this DORCthermodynamic model is of high accuracy. Through the optimization of this DORCsystem from cycle type, system configuration and working fluid, the optimal system isobtained.Results show that the system with two regenerators performs best when it adoptstoluene as the working fluid of the high-temperature loop and R143a as the workingfluid of the low-temperature loop and both loops adopt transcritical cycles. Themaximum net output power is42.71kW, thermal efficiency is12.84%and exergy efficiency is46.69%. The waste heat of the exhaust and engine coolant is utilizedcompletely. Through analyzing the influence of operation parameters on systemperformance, it is found that the system performs better when the condensationtemperature of the high-temperature loop is lower and the temperature increments bytwo regenerators are bigger. The influence of the turbine inlet temperature of thehigh-temperature loop is not consistent for different working fluids and cycle types. Insubcritical cycles, it should be higher for wet fluids and lower for dry fluids. Intranscritical cycles, it should be lower for dry fluids.In conclusion, a Dual-loop Organic Rankine Cycle (DORC) is established,analyzed and optimized to recover the high-temperature exhaust waste heat, whichprovides instruction for future study. Research shows that this DORC system is aneffective means to recover the high-temperature exhaust waste heat of engine.