The Study On The Performance Of Engine Auxiliary Braking Of A Model Of A Certain Type Of CNG Engine

When the vehicle is driving on the long slope,the driving brake is easy to overheat,resulting in reduced braking efficiency and even vehicle deviation.The brake power generated by the engine-assisted braking is relatively stable,engine assisted braking can prevent the engine from being overcooled,however,there is a problem of low braking power in engine assisted braking,this paper proposes a new engine-assisted braking method combining decompression braking with leakage braking.The GT-power was used to build a model of a certain type of CNG engine auxiliary braking mode,a method of combining simulation and experimental to study the influence of boundary conditions such as rotation speed,decompression valve opening time,valve lift in decompression section,and valve lift in leakage section on the braking performance of engine-assisted braking under both univariate conditions and multivariate conditions,the results show that the braking power of auxiliary braking power increases linearly with the increase of engine speed;Near the compression top dead center,the high-pressure gas in the cylinder will be instantaneously discharged,so the greater the valve lift in the decompression section is,the higher the braking power will be,however,the decompression valve lift is limited by the compression clearance.At the same time,the decompression valve opening time has a great influence on the braking power,if the valve open too early,the maximum pressure in the compression stroke cylinder drops,and the braking power decreases;also if the valve open too late,the remain gas in the cylinder cannot be discharged near the compression top dead center,the remain gas will do positive work on the piston during power stroke,resulting in the braking power decrease.When the rotation speed,valve opening time,decompression section lift,and exhaust back pressure are constant,there exist an optimal valve lift in decompression section that make the braking power maximum.It is verified by experiments that under the same boundary conditions,the error between the simulated value and the experimental value of the in-cylinder pressure and the braking power is within 5%.The braking power of the joint auxiliary brake is the highest among the three types of braking methods,the braking power of the united auxiliary braking is about 8%-12%higher than decompression braking,and with the increase of rotation speed,the braking power of the joint auxiliary brake increases fastest.Research shows that combined braking works best.