Research On Performance Optimization Of An Engine Based On Adjustable Parameters

In the engine development process,the performance of the engine can be optimized from product development,optimization to the test phase.Engine calibration test is an extremely important link in the engine test phase,which plays a vital role in improving the engine power,economy and emission performance.It is a complicated and tedious task to comprehensively consider each performance parameter and seek an ideal solution with the best comprehensive effect during the calibration process.The requirements for calibration engineer’s theoretical and practical ability are very high.Therefore,in order to facilitate the calibration engineer to complete the calibration test efficiently,it is very important to study the main adjustable parameters in the calibration process.The main research content of this article is based on a gasoline engine under research by the team.The main adjustable parameters of the engine are analyzed for its power,economy,combustion process and emissions.By constructing the numerical model and adopting the multi-objective optimization method,the adjustable parameter MAP is obtained,which provides some reference and guidance for the calibration engineer in the engine calibration test.The main research contents are:(1)A simulation model of gasoline engine performance is built and the model is calibrated using test data to ensure that the model is in accordance with the actual state,so as to be used as an effective reference for guiding practice.Based on the built GT-POWER model,the effects of air-fuel ratio,ignition timing and valve phase on engine torque and fuel consumption rate(BSFC)are analyzed.The results show that: The air-fuel ratio has a significant influence on torque at a high speed and on the effective fuel consumption at a full speed.With the increase of air-fuel ratio,the torque increases gradually and then decreases,and BSFC decreases gradually.At the ignition time,the influence of low speed on torque and BSFC was obvious.With the advance of ignition time,the torque and BSFC increased first and then decreased,and the influence of ignition time on BSFC was less than that of air-fuel ratio.In addition,the late closing Angle of intake has a greater impact on torque,while other phase angles have a smaller impact on torque and BSFC.(2)The three-dimensional combustion numerical model of the gasoline engine was built and calibrated.Based on the combustion model built by AVL-FIRE,the effects of air-fuel ratio and ignition time on combustion process parameters such as cylinder pressure,cylinder temperature,instantaneous combustion heat release rate and cumulative combustion heat release rate are analyzed,and then analyzed the influence of NOx,HC and CO emissions.The results show that the air-fuel ratio has a significant effect on the maximum pressure in the cylinder and the maximum instantaneous heat release rate;when the air-fuel ratio is near the theoretical air-fuel ratio,the temperature in the cylinder is the highest;as the air-fuel ratio increases,NOx increases first and then decreases,and HC gradually increases,CO gradually decreases.The ignition time has a significant effect on the maximum pressure in the cylinder and the maximum instantaneous combustion heat release rate.With the advance of the ignition time,the maximum temperature in the cylinder gradually increases,NOx gradually decreases,HC and CO gradually increase.(3)Based on the performance requirements for different working conditions,using MODEFRONTIER optimization software and GT-POWER co-simulation,an approximate model between the air-fuel ratio and ignition timing to power,economy,and emissions was established,the MAP of air-fuel ratio and ignition time were obtained to meet the requirements of different working conditions.and the process and method for optimizing the air-fuel ratio and ignition timing using the approximate model are summarized.The results show that when the engine is started,the air-fuel ratio should be 14.2-14.5,the ignition advance angle should be 14°CA-20°CA,and the ignition advance angle should decrease as the load increases;under low load and medium high speed conditions,the air-fuel ratio is 14.5-15.1,the ignition advance angle is 25°CA-33°CA;under heavy load and high-speed operating conditions,the air-fuel ratio is 13.5-14.5,and the ignition advance angle is 21°CA-27°CA;in performance contour,the air-fuel ratio is controlled at 13.5-14.3,and the ignition advance angle is 14° CA-23°CA.(4)To quantify the air-fuel ratio and ignition advance Angle effect on the improvement of the engine performance before and after optimization,the optimization engine external characteristic were compared before and after the analysis,the results show that in 2000 r/min to 5500 r/min engine power performance has different degrees of improvement,which in 3500 r/min torque increase 4.64%,at 1500 r/min to 4500 r/min also have different degree to improve BSFC,which at 2500 r/min 1.8% lower fuel consumption.