Experiment Research And Performance Prediction Of Exhaust Energy Recovery System Based On Rankine Cycle For A Vehicle Gasoline Engine

Exhaust Energy Recovery （EER） technology based on Rankine cycle （RC） forInternal Combustion （IC） engines has been proved to not just bring measurableadvantages for improving fuel consumption but also increase engine power output,further reducing CO₂and other harmful exhaust emissions correspondingly. The keyfor applying EER technology on IC engine is to design a smart EER system, which isnot only effective and compact, but also has a good match with IC engine. In thispaper, the impact factors and the interaction between the EER system and the lightduty gasoline engine were investigated.The distribution of exhaust energy under the entire engine operating conditionswas analyzed based on the experiment data of gasoline engine. The results showedthat, the energy brought by exhaust gases account for25%-40%of the total fuelenergy among the main operating conditions, and the exhaust gases temperature rangefrom500℃to750℃while its flow rate vary between33kg/h and150kg/h. Thisinformation reveals that it is great potential to recover the exhaust energy of ICengine.An open EER system based on RC was built up on the gasoline engine test rig,and study for exploring the influence of EER system on engine performance wascarried out. It was shown that, by comparing the exhaust backpressures and brakespecific fuel consumptions （BSFC） between the engine with and without theevaporator under different loads, both of the backpressure and BSFC were increasedslightly as a whole, but the deterioration was so low that it almost could be ignored.The former rose by less than0.2kPa while the latter was increased by2%at most.However, this is a special case for this given gasoline engine and EER system,therefore, it is very necessary to take the influence of EER system on the engine fueleconomy into account.An EER system model was established by MATLAB based on the existingmulti-coil helical evaporator. The influence of working fluid flow rate andevaporating pressure on the system performance was investigated. The resultsdemonstrated that the allowable working fluid flow rate for the given EER systemwas rather low and the evaporating pressure could vary among a narrow range. The flow rate has significant influence on the heat exchanger efficiency, while the Rankinecycle efficiency was mainly determined by the evaporation pressure. Relatively lowevaporation pressure is desired in order to broaden the flow rate range as well asmaintain a stable operation for the EER system, while it is beneficial to operating athigh evaporation pressure for improving the system efficiency. According to thesimulation results, it is predicted that the EER system could increase the engine fuelconversion efficiency between3%and8%under general vehicle operating conditions.Study was also presented to explore the influence of evaporation pressure and theinlet temperature of turbine expander on several system performance index, such ascycle efficiency, specific work, UA number and system output power, using R141B、R123、R245FA、R245CA as working fluid, respectively. Results indicated that R141Bpresent the maximum cycle efficiency and specific work, and better adaptability to theengine operating conditions, however, it also brought the highest requirements on theheat transfer ability of heat exchanger due to its highest UA number.