Optimization Research Of Heavy Trucks Thermal Management Systems Coupled With Waste Heat Recovery System

About 2/3 of the combustion energy of internal combustion engine（ICE）is lost through exhaust and cooling system during its operation.Besides,the air conditioning system as an automobile accessory will also consume additional power.Improving vehicle energy efficiency is vital to national energy security and CO₂ emission reduction.To improve the ICE efficiency and the vehicle driving efficiency,this paper focuses on some coupling thermal management systems with different structures for vehicles using a typical six-cylinder four-stroke diesel engine（Yuchai YC6L330-42）.These thermal management systems include the air conditioning subsystem,the waste heat recovery subsystem,engine subsystems and coolant system.CO₂ is chosen as the working fluid for both the air conditioning subsystem and the waste heat recovery susystem,which also forms a strong bond between these two subsystems.After conducting experimental study and performance analysis for the subsystems,the coupled thermal management system is evaluated at different ambient temperatures and engine operating conditions to choose the optimal structure.Besides,themoeconomic analysis is performed to investigate the effects of additional weight caused by the extra components on the system performance.Both steady conditions and driving cycle conditions are considered.For the waste heat recovery system,the system pressure will be affected by the size of the structure under the actual operating conditions,there is an optimal pressure and the optimal pump speed to make the system achieve the maximum value of net output power.The optimal pump speed increases with the increase of ambient temperature and the decrease of engine load.After coupling with the coolant system of ICE,accessory power consumption could be reduced by adjusting the power of radiator and condenser and therefore the net power of vehicle is improved.The rate of optimal coolant utilization rate decrease with the increase of engine load and ambient temperature.The system has the maximum net power when the utilization rate is between 38%and 52%.Due to the mutual influence between the components of the vehicle thermal management system,multi-stage compression would not be adopted and the structure should not be too complicated.However,the dynamic performance is poor when the system structure is too simple,which should be considered comprehensively in the design process.This research proposes a thermal management system,which not only has a relatively simple structure but also uses recompression and shared condensers to adjust the system conditions,showing advantages in power,weight and cost.The equivalent net power of the system is 10.8 k W which could improve the fuel economy by 3.1%if the energy consumption of components in the original vehicle is not taken into account.While considering the energy consumption of the original engine and all accessories of the thermal management system,the net power will be reduced to 4.2k W,improving the fuel economy by 1.2%.When the vehicle runs at a constant speed of 72 km/h,the thermal management system could generate a net power of 2.45 k W and improve the fuel economy by 0.7%.These values are calculated by taking several factors into consideration,including:1)effect of different environmental temperature and road conditions from real driving;2)vehicle accessories and thermal management system power consumption;and 3)the power consumption caused by additional weight system.Considering the cost and weight of the system,the optimal thermal management system proposed in this paper can save 14.3 tons of diesel oil during its life cycle and generate an economic benefit of 29.8 thousand Yuan.