The Research On Destruction Experiment Of Detonation Wave To Piston

The internal combustion engine is affected by the operating factors and its own structural factors in the work.Unusual knocking combustion often occurs.When the combustion is not evaded in time,it will often be transformed into a destructive and powerful knock.Severe knock is very dangerous and often causes damage to components such as pistons.The mechanism of severe knock is still unclear.In order to understand the mechanism of the destruction of pistons and other components after the occurrence of severe knock,the research group proposed the hypothesis that the detonation wave converges in the closed space in the preliminary work.The mathematical model is used to calculate and simulate the convergence phenomenon of the detonation wave.This hypothesis can well explain the formation mechanism of over-temperature and overpressure in the closed space of the combustion chamber.In order to verify the results of this calculation and to clarify the destructive effects of detonation wave convergence on the components of the combustion chamber,this thesis conducts two aspects of experimental research on the detonation bomb: On the one hand,the influence of initial back pressure,clearance and equivalence ratio on the pressure fluctuation of detonation wave is experimented on the DBD,and the pressure data collected are analyzed,and the pressure fluctuation characteristics of detonation wave under intense detonation are summarized.On the other hand,the effects of the intensity and number of detonation,the structure and material of the piston on the shape variables of the piston specimens were carried out on the DBD,and the data of the shape variables were analyzed,and the macroscopic image analysis was used.The method describes the crack growth process of the piston specimen under the action of detonation.The main conclusions of this thesis are as follows:The initial conditions determine the detonation wave pressure fluctuation characteristics.When the equivalence ratio and the clearance are kept constant,with the increase of the initial back pressure,the maximum peak pressure at the cylinder head,the center of the piston top surface,1/4 of the piston top surface and the edge of the piston top surface will increase significantly.When the initial back pressure and the equivalence ratio are kept constant,with the increase of clearance,axial oscillation frequency of detonation wave decreases,and the initial peak pressure increases.The experiment found that the equivalence ratio has no linear relationship with the detonation pressure,and the too small or too large equivalence ratio cannot be successfully detonated.In addition,under the same initial conditions,the maximum peak pressure at the center is greater than 1/4 of the top surface of the piston and the 1/4 of the top surface of the piston is larger than the edge of the top surface of the piston,and the edge of the top surface of the piston is larger than the cylinder head.The piston structure and material play a decisive role in the piston’s ability to resist detonation.The intensity of the detonation wave also has an important influence on the anti-detonation capability of the piston.It is found that under the action of the initial detonation wave,the larger the thickness of the test piece,the smaller the deformation variable is,the stronger the ability to resist deformation.At the same time,the experiment also found that the ZL108 aluminum alloy material has better resistance to detonation than the 2A12 aluminum alloy.As the initial back pressure increases,the central shape variable of the piston test piece increases significantly.When the equivalence ratio is less than 1,the increase of the equivalence ratio can significantly increase the deformation amount of the piston specimen.When the equivalent ratio is greater than 1,the equivalent ratio is continuously increased,and the amount of deformation of the specimen is not significantly increased.The detonation wave destroys the piston specimen in multiple stages.The destruction of the piston specimen has gone through four stages: expansion of micro-damage,dissociation of the interface,delamination of the layer,and rupture of the aluminum film.By comparison,it can be seen that the damage of the simulated piston specimen caused by the detonation wave generated in the designed fixed-capacity bomb with detonation wave is basically consistent with the damage of the real internal combustion engine piston under the severe knock.This proves the correctness of the hypothesis that the internal combustion engine piston is destroyed by the detonation wave transformed by the severe knock.The designed detonation capacity can meet the demand of the detonation wave to the piston destruction experiment under the severe knock.