The Mechanism Of Eutectic Aluminum-silicon Piston Damaged In Engine Knocking

Engine knock is a key structure parameters to restrict their fuel economy increase,efforts to improve the compression ratio is the important way of energy saving and emission reduction of internal combustion engines.Therefore,clarify cylinder detonation mechanism of damage to components such as Pistons,identify factors influencing the structure of detonation to avoid damage to the piston,in order to further improve the engine's compression ratio to improve the efficiency of internal combustion engines to provide theoretical support.The research work is mainly focused on the following aspects.Firstly,the engines were fueled with pure experimental research on knock combustion of methanol fuel.Testing is conducted on a compression-ignition engine.Test method is to keep it running in speeding overload of intensive work,recording cylinder pressure for observing its detonation process.Pure methanol was observed in the test engine when the blast occurred,outbreaks of engine combustion chamber pressure increases rapidly,and variations in intensity,forming detonation pressure wave.When the pressure wave on the Pistons,its surface and internal rapid thermal oxidation and corrosion,until the surface is perforated.Proved the blast happened to strongly damaged engine parts.Secondly,after destroying the Pistons for metallographic analysis of macro-and micro-structures.Found Silicon aluminum alloy piston detonation on the surface under the influence of combustion chamber blast under the action of the macroscopic damage of Silicon aluminium alloy piston surface formed by a penetrating perforation and pits,mainly by penetrating perforation,back bulge with cracks and caving;Under the action of compression wave and reflection lashenbo,it showed delamination,and rockslide destroyed.Silicon aluminum alloy piston alloy extrusion deformation in a Shockwave,the formation of high-density dislocation as well as amorphous and microcrystalline.Away from the penetrating perforation site,alloy deformation decreases defects is dominated by micro-crack and micro-holes.Silicon aluminum alloy piston solid solution and aging microstructure in sheared parts of the adiabatic shear band formed by high density along the shear direction wrong width of 15~45nm on Earth Organization,shear Center wrong by a large number of low density 40~80nm in diameter composed of grains,recrystallization of the typical organization features,recrystallization grain machinery is fragmented and grain boundary migration.Asian grain coarsening combined results.Further analysis by scanning electronic microscope and found adiabatic shear failure of piston surface melt holes.By XRD components identified,observed failure surface of piston of Crystal form had changed.Based on an analysis of the results,can maintain purity methanol ignition engine detonation damage piston failure is in the form of thermal-mechanical coupling type.Thirdly,engine detonation occurs in the combustion chamber formed ultra mild numerical analysis of the overpressure.A two-dimensional numerical simulation based on development research in combustion chamber of a cone-shaped shock wave shock,be acting on pressure distribution of the piston in different places.Simulation results show that because of the uniqueness of the combustion chamber,caused shock waves in the particular area of the gathering,causing excess pressure in the region than other regions.Compare simulation results and actual damage failure of piston,found that shock waves converging areas often is where the piston is damaged.Numerical simulation results and actual damage results are a good match.Design combustion chamber shape for us to avoid the shock wave caused damage to piston provides a theoretical basis.Results obtained through this research,we can draw the detonation on piston failure mechanism is,detonation shock Burns,under the right conditions translate into destructive detonation,detonation wave in Combustors are brought together to produce effects on the surface of the part's more moderate overpressure conditions,resulting in destruction of the blast pressure wave on the surface of the piston.This study illustrates the result of blast damage to the internal structure of components such as Pistons feature gives a detonation in the combustion chamber formed ultra mild overpressure model,made a blast damaged the basic form of the piston,initially stated that the blast to damage mechanism of piston materials.For engine combustion control system design and operation factors raise important theoretical basis.