The Research On The Exhaust Heat Recovery Of A Diesel Engine Under Different Conditions With The TEG-ORC Combined System

Basically approximately2/3of the engine energy is released through the lubricationsystem, the engine cooling system and the exhaust system into the atmosphere,resulting in the environment pollution and the waste of energy. In recent years, theresearch of waste heat recovery from engines has made rapid development. In thefield of waste heat recovery of low temperatures, the organic Rankine cycle (ORC) iswidely used. But it is not well applied in vehicle engines as the exhaust temperaturesare changing with the variable working conditions. In addition, the decomposedtemperatures of ORC working fluids are mostly lower than the exhaust temperatures.When the working fluids exchange heat directly with the exhaust, they will bedecomposed so that the ORC can’t normally run. In order to use the ORC in wasteheat recovery from a vehicle engine and avoid the working fluid from decomposition,this paper has designed the thermoelectric generator and the organic Rankine cyclecombined system, called "the TEG-ORC combined system" for short.In the paper, the model of a6L diesel engine has been established and the exhaustparameters under different working conditions have been caculated based on the AVLBoost. After that, the working mechanism of the TEG-ORC has been deeply studiedand the simulation program has been developed and simulated the performanceparameters based on the MATLAB. According to the results, we can find that theperformance of the TEG-ORC under different working conditions is in connectionwith the exhaust energy. The lowest exhaust energy value is about50kW. Under the1900r/min-90%working condition, the total output power and the thermal efficiencyreach their maximum values---the maximum output power is24.53kW and themaximum thermal efficiency is25.6%. Compared to a single ORC system, the outputpower is increased by21%and the thermal efficiency is increased by8.7%. Finally,the way to improve the performance of the TEG-ORC under the calibrated conditionhas been explored. We can improve the system’s performance under the calibrationworking condition from three aspects: change the ORC working fluid---theperformance of the RC318-TEG-ORC system is obviously improved. The total output power is16.8%higher than that of the original design and the thermal efficiency isincreased by4.2%; change the thermoelectric material---the performance of theCoSb3-TEG-ORC system is increased slightly; change the thermoelectric modulearray---the total output power of the10*7-TEG-ORC is2.2%higher than that of theoriginal design and the thermal efficiency is increased slightly.The research shows that the TEG-ORC combined system can realize the waste heatrecovery from the diesel engine and overcome the ORC’s defects including matchingwith the engine in temperatures and decomposition. In addition, the optimizationmethods on the performance of the TEG-ORC under the calibration workingcondition can be used and extended to the performance improvement of theTEG-ORC under operating working conditions in the vehicle engine experimentalresearch and engineering application in the future.