Establishment And Application Of Natural Gas Engine Model Reduction Theory And Quantitative Relationship

Driven by the national "dual carbon" policy,all industries will develop in the direction of reducing carbon emissions and achieving carbon neutrality.The automotive industry is also accelerating its transformation.Of all vehicle types,heavyduty trucks,historically the biggest emitters and energy consumers,will be the most difficult to electrify.As a widely used clean energy,natural gas can be introduced into the fuel of heavy trucks,which can effectively reduce the pollutant emissions of vehicles,and at the same time,reduce the proportion of oil used and improve the national energy security.However,natural gas engines still face the challenges of insufficient power and poor economy,which greatly hinder the further development of natural gas engines.Therefore,it is urgent to improve the adaptability of natural gas in heavy truck engines and improve the use efficiency of natural gas in heavy trucks.However,due to the increasing requirements and constraints of modern vehicles on engine design parameters and control variables,the development is more and more difficult and the cycle period is longer.In this paper,the dimension reduction theory of engine model reduction theory is proposed,established and the performance quantification relationship is established by deciphering the internal relationship between performance and design and operating parameters.The performance parameters of the engine are decomposed into design,operation and control parameters Aand the relationship is verified by experiments,which greatly improves the speed of engine performance prediction.On this basis,in view of the challenges faced by natural gas engines,this paper proposes intake air supplementation technology and high compression ratio technology to improve the transient response and in-cylinder thermal power conversion performance of natural gas engines,respectively.The main research work and results of this paper are as follows:(1)Based on the three-point test method for gas exchange process proposed by the research group,through theoretical research,a more universally applicable test method is proposed: from three dynamic pressure sensors to one dynamic pressure sensor,which greatly reduces the test cost without reducing the accuracy too much,and the reduction rate is not more than 2%.At the same time,an improved calculation method of in-cylinder combustion heat release rate is proposed,which improves the accuracy of test data and provides data support for the establishment of quantitative relationship between engine parameters.(2)A theoretical system of engine model degradation is established,including simplified prediction models of gas exchange process and combustion process.In addition,a simplified calculation method of variable volume combustion cycle is proposed.By introducing the concept of average exponent,on the one hand,the calculation time and complexity of the cycle are greatly shortened,and on the other hand,it provides a theoretical basis and direction for the accurate calculation of this method.Correctly choose the average exponent so that the error between the simulated value and the experimental value does not exceed 1%.(3)Construct the quantitative relationship of natural gas engine performance.The quantitative relationship between the economy and dynamic performance of natural gas engine is proposed and verified.The relative error between the calculated results and the measured values is within 5%.Based on the quantitative relationship,the main control factors of the economical and dynamic performance of the natural gas engine are analyzed.(4)Based on the quantitative relationship of natural gas engine power performance,it is proposed that increasing the intake pressure is the most direct means to improve the transient response,and the quantitative impact of the increase in intake pressure on the engine power performance is obtained.On this basis,a technical scheme to improve the transient response of the engine is proposed: intake air supplement.Then,by building the experimental bench and analyzing the model,the influence of the intake air supplement on the transient performance and flow characteristics of the engine was studied,and the supplementary air surge boundary prediction model was built and verified.Finally,the air intake and air supplementation technology is applied to the real vehicle,and the results show that the air supplementation technology can greatly shorten the acceleration time of the whole vehicle and improve the climbing ability.(5)Based on the economic quantification relationship of natural gas engines,the relationship between in-cylinder thermal power conversion efficiency and effective expansion ratio is proposed.Combined with the high octane number of natural gas,a technical scheme to improve in-cylinder thermal power conversion performance is proposed: increase the compression ratio.Then,the effect of the compression ratio on the in-cylinder thermal power conversion process and the in-cylinder energy distribution was studied through experiments.When the compression ratio was increased from 11.6 to 16,the maximum effective fuel consumption rate of the engine was reduced by 7%.The results of this paper will provide a theoretical basis for reducing the number of parameter scans and development costs in the engine development process,and forming a core design technology with independent intellectual property rights.In addition,it can solve the challenging problems of insufficient power and poor economy faced by natural gas engines,provide theoretical guidance for the next step of applying this technology to heavy-duty natural gas vehicles,and is conducive to popularizing popularize the application of natural gas in heavy-duty trucks.