Research On The Biodiesel Engine Performance Under High EGR Rate

Under traditional combustion mode, the diesel engine exist trade-off relationship between Soot and NOx emissions, which makes the combustion not ideal. Low temperature combustion achieved by high EGR rate can solve the problem effectively. Combining with alternative fuels, especially the oxygen fuel can further optimize the performance of diesel engine. Therefore, based on VMR425, this paper studied the engine performance when using biodiesel and the control method of transient conditions under high EGR rate.In order to achieve high EGR rate, this study first remould the engine bench. A throttle valve was installed after EGR valve to adiust EGR rate by using Venturi effect. Through the engine bench test, the influence of EGR and biodiesel on diesel engine was verified and summed up. On this basis, the simulation model of turbocharged diesel engine was built by using GT-POWER software. A throttle physical model was established by using Simulink software. After fuel characteristics analysis, four feature parameters(fuel mass flow rate, EGR rate, intake pressure, exhaust oxygen concentration) were extracted and used to establish the identification model based on the neural network.A co-simulation platform was established based on GT-POWER and Simulink software. The selection of EGR rate boundary and the control of transient loading process were researched on the paltform. Study shows that the air-fuel ratio and torque output rate are the main basis of the selection, and the boundary value is different for different blending ratio. In this, the transient loading process was studied using biodiesel and under high EGR rate. A throttle opening correction method was proposed based on the variation of the load, which improves the transient torque response.