| With the rapid development of society today,the demand for energy is increasing day by day.Corresponding to the emergence of various energy problems.To promote energy conservation and environmental protection is the requirement of the times.In view of this development requirement,combined with the fact that the waste heat of the internal combustion engine occupies a large proportion of the total energy input,and there is less research on waste heat utilization of the combine harvester engine.This article mainly studies how to reasonably and efficiently recover the waste heat of the internal combustion engine of the combine harvester.To achieve the effective use of energy,the collected waste heat can be used for immediate drying,pretreatment of new harvested food,etc.The results of the study are as follows:(1)In order to study the waste heat collection problem of the combine harvester,this article first carried out the experiment of the waste heat characteristics of the internal combustion engine.The waste heat characteristic experiment was carried out on the tractor l G1504.The experiment was divided into two groups: full-load speed change test and variable load six-state test.The test obtained the residual heat characteristic parameters such as circulating water temperature,flow rate,exhaust gas temperature,and flow rate of the internal combustion engine cylinder liner.Based on this analysis,the changes in available heat of the internal combustion engine under different operating conditions are obtained.Under the full-load speed test,the available residual heat of the circulating water in the cylinder liner and the available residual heat of the exhaust gas decreased with the decrease of the engine speed,among which the highest was at 2 200 r/min,which was 76.23 k W and 31.29 k W respectively.Under the experimental conditions of variable load six conditions,with the reduction of the load,the residual heat available for circulating water in the cylinder liner and the available heat in the exhaust gas are also reduced,with the maximum at full load,which is 75.12 k W and 28.16 k W,respectively.(2)According to the obtained parameters of waste heat characteristics experiment,two models of collecting the two grade waste heat were built using the single working fluid and two kinds of working fluids.The selected four working conditions for analysis were: The two working conditions of 2 200 r/min and 1 700 r/min at full-load speed change,and 100% and 50% of two working conditions under variable load six conditions.When using a single working fluid to collect two types of waste heat,five kinds of working fluids,R152 a,R600,R245 fa,R123,and water,were selected and analyzed for thermodynamic performance.It was concluded that when using a single working medium to collect two types of waste heat,under the same conditions,R152 a,R600 and water absorb the maximum amount of waste heat.Using R123 get the highest temperature after heat exchange which is 97 °C and 101.9 °C,89.43 °C and 101.1 °C,respectively,in the selected four operating conditions;for the three kinds of heat exchange medium R152 a,R600 and water with the largest heat exchange under the same conditions,the maximum temperature change is R152 a,in the selected four conditions,the heat transfer temperature is 76.4 °C and 82.57 °C,75.99 °C and 81.85 °C,respectively.And when the working medium R245 fa is used,the unit mass heat transfer produces the smallest exergy loss,which are 0.122 k W and 0.129 k W,0.107 k W and 0.127 k W,respectively.When using two different working fluids to recover two kinds of waste heat respectively,the thermodynamic performance analysis was performed using six combinations,which are R152 a and R123,R152 a and R245 fa,R600 and R123,R600 and R245 fa,water and R123,water and R245 fa.When the combined mediums R152 a and R123 were used to collect the waste heat of the circulating water of the internal combustion engine liner and the residual heat of the exhaust gas of the internal combustion engine,the exergy loss generated when recovering the same waste heat were the least.Under the selected four working conditions,they were 14.42 k W and 16.43 k W,11.48 k W,and 16.05 k W,respectively.And the highest temperature rise occurs when collecting the same amount of residual heat.And the lowest exergy loss per unit of heat absorbed during heat exchange are 0.156 k W and 0.154 k W,0.126 k W and 0.153 k W,respectively.(3)Mathematical expectation was used to analyze the irreversible heat loss in the heat exchange process between the heat transfer medium and the heat source.An analysis model was established to collect the waste heat of the heat exchange working fluid and the heat transfer working fluid of the single heat transfer medium,and the corresponding mathematical analysis was performed.It is concluded that under the premise of ensuring the maximum amount of heat exchange when collecting the residual heat of cylinder liner circulating water,R152 a produces the least irreversible heat loss in the process of heat exchange,and the temperature variation and heat source of R245 fa in the selected working medium.The average temperature difference is the smallest,indicating that R245 fa is selected as the heat transfer medium and the irreversible heat loss in the heat exchange process can be minimized.When collecting the waste heat of the exhaust gas,when the heat exchange medium R123 is used for heat exchange,the irreversible heat loss in the heat exchange process can be minimized.When a single type of working fluid is used to collect two different grades of waste heat,the use of the heat exchange medium R152 a for heat exchange can minimize the irreversible heat loss in the heat exchange process.The results of irreversible heat loss in the heat transfer process obtained by the mathematical expectation method are consistent with the results obtained by the analysis of exergy loss.(4)Based on the obtained residual thermal characteristic parameters and the corresponding mathematical model theoretical analysis,a test bench for the waste heat recovery of the internal combustion engine was designed,and a test based on the residual heat characteristic parameters was performed on the waste heat recovery device of the internal combustion engine using water as the heat transfer medium.It can be concluded that under the four conditions selected,the amount of waste heat obtained by the experiment accounts for about 60% of the theoretical value.The theoretical analysis and the data obtained from the experiment show that the trends of the data are basically the same,indicating that the theoretical analysis results can represent the relevant changes in the experiment process to some extent.The expected value of collecting a single type of waste heat should be higher than the expected value of collecting two types of waste heat under all operating conditions.Therefore,the irreversible heat loss caused by the direct collection of two grades of waste heat from a single working fluid can be less than that of using a single working fluid to separately collect the corresponding grades of waste heat.This result is consistent with the theoretical analysis results,indicating that the theoretical analysis data can provide the basis for the actual experiment.Therefore,in order to reduce the irreversible heat loss in the heat exchange process,it is preferable to use a single type of working fluid to collect the waste heat of two different grades. |
PDF Full Text Request