Research On The Influence Of Variable Exhaust Valve On Low Speed Diesel Engine Performance

The valve timing of engine has an important impact on power,economy and emissions performance of diesel engine.There are different requirements for intake and exhaust when the speed and load of the low-speed two-stroke diesel engine change.The application of flexible exhaust valve technology adjusts the valve phase and the maximum lift of the exhaust valve according to different working conditions,which can fully exert the performance of the diesel engine and improve the power,economy and emission performance indicators.On this paper,based on GT-Power software and modeFRONTIER software,the exhaust parameters of the exhaust valve as the variables,and the multi-objective optimization of the exhaust parameters under different working conditions is carried out.The optimal exhaust valve lift parameters are obtained,so that the low-speed diesel engine can exert better performance under different working conditions.The influence of the phase,lift and opening and closing speed of the exhaust valve on the brake power,brake specific fuel consumption and NOx emission of the diesel engine was analyzed by using GT-Power software.The Miller cycle is achieved by the late opening and closing of the exhaust valve to improve the power and emissions of the diesel engine.The specific work is as follows:Firstly,the GT-Power one-dimensional working process was modeled in lowspeed diesel engine with multiple working conditions.The calibration of each working condition model was carried out.The simulation values of cylinder pressure,brake power,brake specific fuel consumption and NOx emissions were compared.The experimental values given are more consistent.The parametric design of the lift of the original exhaust valve was carried out,and the lift,phase,opening and closing speed of the exhaust valve were parameterized to optimize the subsequent exhaust parameters.The parameters provide the basis for the analysis of the impact of diesel engine performance.Then,combined with modeFRONTIER and GT-Power software,the multiobjective optimization simulation workflow was established.Using NSGA-II optimization algorithm,50 sets of exhaust valve initial parameter groups were selected by pseudo-random Sobol sequence,and 20 generations were moved according to genetic algorithm.Through the calculation,there are 1000 calculation points in each working condition,and the exhaust parameters under different working conditions are optimized by using the brake power and NOx emission as the priority optimization targets respectively,and the optimal exhaust parameter table on each working condition is obtained.Finally,using GT-Power software,the effects of exhaust valve phase,lift,opening and closing speed on diesel engine performance are studied under low working conditions,medium working conditions and high working conditions,respectively.The burst pressure and volumetric efficiency in the cylinder under the parameters are analyzed from the perspective of the total energy distribution of the fuel.The variation of NOx is analyzed according to the maximum temperature in the cylinder,which provides a reference for the optimal design of the low-speed diesel engine exhaust parameters.The Miller cycle of the low-speed diesel engine is realized by the late opening and the late closing of the exhaust valve.The brake power,brake specific fuel consumption and NOx emission of the diesel engine under the Miller cycle are studied.