Performance Improvement Of High-power Natural Gas Engine Based On Air Intake System Optimization

In recent years,Energy and environment have always been important issues for the sustainable development of human society.China is rich in natural gas reserves,and the internal combustion engine using natural gas as fuel has less environmental pollution.Although the key technology of natural gas engine in China has reached the level of developed countries.However,there are relatively few developments on 200-300mm large-bore natural gas engines,and there is also a certain gap in the key performance parameters of the engine.This subject takes 3500GF high-power natural gas engine as the research object.In order to meet market demand,combining the structural characteristics of the engine and the technical parameters of similar engines in the world,the goal of performance optimization of the 3500GF natural gas engine is determined:when the rated speed is 1000r/min,the engine power is increased to 4200kW,the engine thermal efficiency is 42%,the exhaust gas temperature before the turbine is less than 560℃;and the emissions of NOx and HC are as low as possible on the basis of meeting emission regulations.The main tasks as follows:(1)Use AVL-BOOST software to simulate the performance of the engine,and calibrate the model based on the existing test data,so as to perform the thermodynamic calculation and turbocharing matching calculation of the engine after the power is increased;(2)The combination of lean combustion and Miller cycle can improve engine economy and reduce NOx emissions.On gas engines,different degrees of Miller cycle can be realized by changing the intake timing.Compare thethermal efficiency,in-cylinder explosion pressure,combustion pollutants and the engine performance between the weak Miller cycle when the intake valve closes at 543℃A and the strong Miller cycle when the intake valve closes at 530℃A under 50%load and 100%load,respectively;(3)After the engine performance is optimized,it is necessary to re-match the turbocharger,introduce the characteristics of the variable geometry turbocharing system,the intake bypass system and the exhaust bypass system respectively,and analyze the influence of the intake bypass turbocharing system on the engine performance.And verify the performance and efficiency of the newly selected turbocharger through tests;(4)According to the requirements of product development process,the load characteristic test,speed regulation characteristic test,cylinder uniformity test and emission test are carried out for the engine after performance optimization.The test results show that the performance indexes of 3500GF natural gas engine,such as thermal efficiency,maximum explosion pressure,exhaust temperature and emission,meet or exceed the design requirements,and the engine runs stably.In this paper,the performance optimization of 3500GF natural gas engine is studied.The influence of the strong Miller cycle and the turbocharged intake bypass system on the engine performance is calculated and analyzed.At the same time,the performance index of the engine is verified by the combination of simulation calculation and experimental verification.It can be used as a reference for the optimization and upgrading of spark ignition natural gas engine.