Research On Fuel Injection Mode Of Diesel Engine Start-up Process Based On Demand Torque

The starting and idling condition of a vehicle engine is a typical transitional condition,which has a greater impact on vehicle emissions.Especially in the cold start,due to the low speed,low fuel injection pressure,and low coolant temperature,the fuel economy and emission performance of the starting process are poor.In order to improve the engine cold start performance and quickly increase the coolant temperature to shorten the heating time and improve the transient combustion process in the cylinder during the starting process,this paper proposes a fast idle speed control scheme and develops a fast idle speed cold start control strategy based on target torque,And established a corresponding model.This paper uses the AVL-FIRE first-cycle combustion model built in the previous stage to simulate and calculate the influence of different starting speeds(range 180～260r/min)on the first-cycle combustion characteristics at different starting temperatures(such as 20℃,5℃,-10℃),And use the cylinder pressure curve,combustion heat release rate curve and CO emissions as indicators to determine the corresponding optimal injection speed,and fit the optimal injection speed at different temperatures through the starting temperature and its corresponding optimal injection speed.Starting spray speed curve.In order to realize the precise control of the change law of the engine speed during the fast idling start process,the target speed curve during the cold start process is designed.In order to realize the cold start and fast idle speed control strategy,a working condition state machine module is built.This module can judge the engine operating condition according to parameters such as speed,cooling water temperature,and ambient temperature,and call the corresponding control module to realize the control of the engine.In order to achieve precise control of the fuel injection volume,a control model based on the target torque to start the injection mode is established.Finally,based on the technical parameters of the experimental prototype,the GT integration model of the prototype is established,and it is combined with the built control model.Finally,through the joint simulation model,the start injection mode of the engine at low temperature and medium temperature was optimized.Based on the comprehensive evaluation of the cumulative start time,cumulative fuel consumption,cumulative NOx emissions and other performance indicators,the engine cold start and The best injection method when starting at medium temperature: during cold start,three injections are used,the injection ratio is 2:3:5,the main injection timing is 3 ℃A BTDC,the near pre-injection timing is 7 ℃A BTDC,and the far pre-injection timing is 11 ℃A BTDC;When starting at medium temperature and normal temperature,three injections are used,the injection ratio is 1:2:7,the main injection timing is 4 ℃A BTDC,the near pre-injection timing is 7 ℃A BTDC,and the far pre-injection timing is 10.5 ℃A BTDC.