Simulation Study On The Engine Auxiliary Brake

The working principles and progresses of engine brake,exhaust brake and bleeding brake are analyzed and studied.The power of these auxiliary brakes is evaluated through both experimental and simulation methods to discuss the factors which can improve the brake power without disturbing normal working progress of the engine.A single engine is chosen as the researching and experimental object.Using electronic dynamometer to drive the engine and high speed data acquisition system to record the cylinder pressure of the engine working under the auxiliary brake condition.The performances of the engine auxiliary brake are evaluated through the parameters,given by the previous,such as "mean average brake pressure","brake ratio" and "brake coefficient".Mathematical model is established,on the base of reference materials,according to the working progress of the engine working at auxiliary conditions,by the MATLAB software.Then the p-V diagrams at different speeds are got.The cylinder pressures of all these auxiliary increase with speed and the peak pressure phase is more near the TDC under the high speed conditions.The brake power is made of losses such as heat release,pump loss,friction loss.So the brake power of these brakes is low and primarily depends on the engine speed. The power of exhaust brake is improved through the increased exhaust pressure.The brake power depends on both engine speed and exhaust pressure.The higher the speed and the exhaust pressure is,the more the brake power is.The secondary opening of the exhaust valve is studied based on the previous results.The de-compressure brake opens the bleeding valve before TDC at the compression stroke.The high temperature and pressure gas is exhausted so the cylinder pressure is low at the beginning of the power stroke.There is less power returned to the piston at the power stroke so the brake ability is improved.The power of de-compressure brake depends on both engine speed and parameters of bleeding valve(including the maximum bleeding valve opening and the bleeding valve angle).There is one optical bleeding valve angle with the speed which has the maximum brake power.