Research On Exhaust Heat Recovery System Of Internal-Combustion Engine Based On Two Thermodynamic Cycle Modes

China is a big country of production and consumption of internal combustion engine(ICE),The ICE consumes about 60% of the total petroleum in our country.Energy saving in ICE has great significance to national energy security economy.The exhaust energy is about 35% of the total heat released by the fuel when the internal combustion engine is running.Therefore,recovery of exhaust heat of an automotive engine has attracted attention on numerous occasions to date.Recovery of exhaust energy using Stirling cycle is in the primary research and there is not sufficient theory to predict performance.Some experimental results showed the recycle power by stirling cycle is relatively small.The Rankine recycle system on the other hand,numerous theoretical research had been done on working fluid selection and working performance.But the structure of system is complex and too large.The research of exhaust heat recovery in the paper was based on a 2.0DCVVT gasoline engine.First,for the Stirling recycle system,take the exhaust gas as heater,a Stirling engine model was established,and performance parameters were studied according to the experiments It established the base of further optimizing design for the system,by simulation study on the characters of the system.Second,for the Rankine system with water as working fluid,there are some weakness like complex structure and less steam production,which will limit the system output power.This paper studied the structure of expander and gave some changes with expander to build a smaller size system with high efficiency.Finally evaluated the effects of energy recovery through the two recycle system experiments data.Then the theoretical and experimental research on waste heat recovery system using Stirling cycle was carried out according to the characteristics of exhaust heat capacity.Using the exhaust of the gasoline engine as heat source,the mathematical model of Stirling engine was established in use of the two order simplified analysis method based on classical ideal adiabatic analysis method and combined with all kinds of heat losses.And then the performances of the Stirling recycle system were simulated and analyzed under the specific working conditions of gasoline engine.The main performance parameters of Stirling engine were indicated based on the simulation.The simulation provided a theoretical basis for the next experimental study.A Stirling heat recovery test system was established and tested at 3000r/min,three different loads conditions of gasoline engine.The experimental results showed that the gasoline engine power output and exhaust back pressure didn't change obviously,the Stirling system can recovery 0.156-0.545 kW of shaft power,which were equivalent to 0.86%-2.94% improvement of gasoline engine power.The thermal efficiency of the system was between 0.75% and 2.61%.The distribution of wall temperature and cylinder pressure tested in laboratory showed that improper design in heater structure and heat losses are the possible reasons of differences between the test result and theoretical analysis.On the research of exhaust heat recovery by using Rankine cycle,a type of reciprocating expander with single inlet valve and exhaust port was put forward and used in the research in order to obtain simple and reliable structure.The simulation model of this expander was founded.Based on the simulation,the expander working process was analyzed;the influences of inlet and outlet structure parameters on expander output and adiabatic efficiency are obtained.All these simulations are helpful for in the design of the intake and exhaust structure.The effects of expander speed and inlet parameters on exhaust system were finally analyzed and the running conditions were determined.A waste heat recovery test system of the Rankine cycle with plunger type high pressure pumps and the tubular evaporator was adopted successfully in the Rankine system,the system can be satisfied the requirement of high temperature,high pressure and low mass flow of water.And the system volume is only 0.95×0.57×0.50m3.The parameters of affecting system performances such as temperature,pressure,speed and mass flow of water were analyzed,and a new plan for control and survey was presented based on the analysis.The experimental researches on system performances were carried out under different working conditions of the gasoline engine.The test results showed that when the gasoline engine output was 39.8—77kW,the expander maximum shaft power was 1.61 —2.78 kW,which was equivalent to 3.6—4.72% improvement of gasoline engine power.The total efficiency of the recovery system is 3.91—5.8%,The maximum use efficiency of exhaust energy was 7.7—10.93%.The tests results indicated that the single-valve expansion machine has small volume,simple structure and high speed,which is appropriate for the occasion of small mass flow and low power.It has great potential in energy recovery of gasoline engine exhaust and means a good prospect of engineering application.The Rankine cycle recovery system has more advantages in the proportion of recycle power increase and system volume from the comparisons results of the two thermodynamic cycles.