| As the main power equipment,the energy saving and emission reduction of internal combustion engine is of great significance to alleviate the problem of energy shortage and environmental protection.The waste heat recovery system of internal combustion engine based on organic Rankine cycle is a key technology to improve the total energy efficiency of internal combustion engine,which can effectively recover the waste heat energy of internal combustion engine and convert it into useful work.When applied in the field of heavy-duty trucks,how to meet the strong adaptability of waste heat recovery system to different working conditions of internal combustion engine and how to meet its own integration and miniaturization are the two major challenges faced by the application of this technology.In this paper,the heavy-duty truck internal combustion engine is taken as the research object,and the comprehensive design method to improve the adaptability of the waste heat recovery system in the whole situation is carried out.Guided by this method,the experimental prototype of the integrated waste heat recovery system is designed and built.Based on the design of waste heat recovery system of heavy duty truck internal combustion engine with complex and changeable waste heat characteristics,this paper presents a comprehensive design method of on-board waste heat recovery organic Rankine cycle system based on OFF-DESIGN.In order to select the best design condition and the best combination of heat exchanger,the method can be divided into three stages: system design and optimization stage,non design performance evaluation stage and overall comprehensive performance evaluation stage.In the system design stage,the influence of component structure,weight,pressure drop and non design performance of the system can be taken into account simultaneously,which is beneficial to the design of the system It can be used to realize the integrated lightweight design of waste heat recovery system and strong robustness to heat source fluctuation.For the case of applying the comprehensive design method to the specified target engine,this paper uses the global comprehensive performance evaluation model to evaluate the comprehensive performance of the waste heat recovery system under the global conditions of the target engine.Through the analysis of the selection of the best heat exchanger and the best design range,it can be concluded that the best heat exchanger of the waste heat recovery system can select PFS group for the target engine and the best design condition can be selected in the range of medium load condition and high probability of occurrence,which provides theoretical guidance for the design and construction of the follow-up experimental system.In addition,through the comparative analysis of the comprehensive design method and the rated condition design method,the results show that the comprehensive design method has stronger adaptability to the working conditions,and its adaptability to the working conditions is improved by 51.5% compared with the rated condition design method,at the same time,the comprehensive energy utilization rate of the system designed by the comprehensive design method is higher under feasible non design conditions,which is 13.7% higher than that of the design method under rated conditions.For the design and construction of integrated experimental prototype,guided by the comprehensive design method,this paper optimizes the best design conditions and heat exchanger forms of the experimental prototype,and makes a reasonable structural layout of the experimental prototype.Finally,the integrated experimental prototype is built.After the completion,the size of the overall experimental prototype is 80 cm ×75cm × 62 cm,and the weight is controlled at about 200 kg,which has certain advantages of miniaturization and application potential.Through the operation reliability test of the experimental prototype and the main components of the system,including working fluid pump,expander and heat exchanger,it is proved that due to its own structure,the heat transfer on the flue gas side is always greater than that on the working fluid side,the average difference is 6.5kw,and the average heat loss is about18%.In addition,the experimental prototype has good stability and reliability.Through the system performance test under different engine load conditions,it can be concluded that the actual shaft efficiency of the expander is not affected by the engine load conditions,and always maintains at a low level of about 36%,while the thermal efficiency of the system gradually increases with the increase of engine load,and finally maintains at about 6%.Through the system performance test of engine under fixed load condition,it can be concluded that the increase of system superheat has a positive effect on the improvement of actual shaft efficiency of expander,and has little effect on the improvement of system thermal efficiency.With the increase of superheat,the net output power of the system first increases and then decreases.For the net output power of the system,the best superheat is selected in the range of 10-25 ℃ The optimal speed of expander can be selected in the range of 1100-1500 rpm.The maximum output power of the system is 2.64 k W at 1350 rpm,650Nm,0.1716kg/s working fluid flow,1.32 MPa evaporation pressure and 1456 rpm.Under this condition,the relative thermal efficiency of the engine can be improved by 3.79%.The experimental results show that the error between the maximum output power and the designed maximum power is mainly due to the large heat loss of the evaporator and the low actual shaft efficiency of the expander.Therefore,the next step is to carry out the optimization research of the key components of the experimental prototype.On the one hand,the evaporator with large heat transfer loss should be further optimized with high enhancement and high integration.On the other hand,the small and efficient expander should be researched and developed.In addition,the layout of the experimental system based on the heavy truck body structure should be studied to further explore the feasibility of ORC waste heat recovery system. |
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