Thermal Load Characteristic Research And Performance Optimization For V2 Air-cooled Gasoline Engine

Air-cooled gasoline engines are mainly used in the field of general machinery.Due to the large thermal load,a series of reliability problems are caused,which restricts the performance of the engine.However,the existing research lacks complete engineering solutions to evaluate and analyze the heat load problem.In this paper,the V2 air-cooled gasoline engine with displacement of 999 cc is taken as the research object.Firstly,its working condition is tested,including the reverse drag and external characteristic test,combustion analysis and component temperature test.The result shows that a higher thermal load resulted in the cylinder score.In order to solve this problem,the one-dimensional thermodynamic model,the in-cylinder combustion CFD model and the thermal load analysis model of the whole prototype were respectivelyestablished according to the test results,and all models were calibrated and validated.The thermal load simulation analysis shows that the maximum temperature of the cylinder head firedeck is up to 307 °C,which exceeds the safety limit of 300 °C.At the same time,the temperature in most parts of the upper part of liner exceeds 220 °C,which resulted in the cylinder scoring.Subsequently,based on the prototype thermal load analysis model(CHT model),the thermal load characteristic was studied.that is,the influence of the key design parameters such as fan air volume,ambient temperature and oil radiator temperature on the fan power consumption,maximum temperature of the inner and outer sides on the cylinder head and block,heat transfer loss and the oil heat dissipation were analysed,pointing the technical direction for subsequent optimization analysis.Finally,the combustion system and the heat dissipation structure were optimized according to the in-cylinder CFD analysis and the thermal load CHT analysis results.The comparative analysis results show that not only the the thermal efficiency of optimization scheme is improved slightly,but also the overall temperaturefalls by20～40 °C relative to the basic prototype scheme.The temperature linerabove the only one ring in 5mm height rangeof the cylinder exceeds 220 °C.The risk of the cylinder score iseliminated.The thermal load state andreliability of the whole machine is significantly enhanced.Through the above research content,the following main conclusions are obtained:1.The main factors that limit the further improvement of air-cooled gasoline engine performance and thermal efficiency include the thermal load and the reliability problems caused by it.2.By increasing air volume of the fan,the thermal condition can be improved to some extent.Simply increasing the air volume can not only continuously reduce the maximum temperature inside the cylinder head and the block,but also substantialy increase power consumption of the fan and heat transfer loss,therefore deteriorating thermal efficiency of the engine.3.The power and economy performance of the engine can be improved by means of reducing local vortex and dissipation to some extent,because it is beneficial to accelerate combustion rate and improve combustion efficiency to enhance the in-cylinder tumble intensity.4.It is effective to boost up the capacity of heat dissipation,reduce thermal load and improve reliability of the engine by optimizing the structure,including enlarging the fins of head and block near the combustion chamber,adopting longitudinal-flow channel of cylinder head,reducing the air leakage phenomenon of heat shield,removing the fan shroud and enlarging oil radiator.