The efficiency of thermal protection of ICE pistons with the micro-arc oxidation

Abstract

BACKGROUND: Ceramic coatings formed on the piston crown of ICE by micro-arc oxidation are increasingly used to protect pistons from burnout and increase their durability. Many scientific papers have been devoted to the study of the effectiveness of these coatings. However, most of these studies were carried out on laboratory installations simulating the operation of the engine, and do not take into account the real thermophysical parameters of the coating. Therefore, the thermal protection effectiveness of these coatings is very difficult to assess.
 AIMS: investigation by numerical simulation of the thermal protection efficiency of pistons using a coating formed by microarc oxidation on the piston crown.
 MATERIALS AND METHODS: The study was conducted in the SolidWorks Simulation program. Two piston aluminum alloys were used as the piston material: AK12d (with a silicon content of 12%) and AK4-1 (with a silicon content of 0.35%). Temperature loads corresponding to the operation of a real engine were applied to the surfaces of the model piston. The thermal state of pistons made of different uncoated alloys was modeled at the first stage of research. The coating was formed on the piston crown. The effect of the coating thickness on the piston thermal state was modeled at the second and third stages of the study. The piston material of the second research stage was AK4-1 alloy. The piston material of the third research stage was the alloy AK12d. Ceramics were used as the coating material. The properties of ceramics corresponded to the coatings properties formed by the microarc oxidation method on these alloys. The coating thickness varied in the range from 50 to 350 mm in increments of 100 mm. The probing method was used to determine the temperature in various areas of the piston. 
 RESULTS: The simulation results showed:
 
 The micro-arc coating of the piston crown reduces the thermal tension of the piston regardless of the aluminum alloy chemical composition.
 The efficiency of the piston's thermal protection increases with an increase in the ceramic coating thickness and a decrease in its thermal conductivity coefficient.
 The greatest heat-shielding effect is achieved in the piston made of the eutectic alloy Ak12d.
 
 CONCLUSIONS: It is established that the MAO coating on the piston crown is an effective way to reduce the thermal tension of the internal combustion engine pistons. Increasing the ceramic coating thickness and a decrease in its thermal conductivity coefficient increases the efficiency of the pistons thermal protection. Reducing the thermal conductivity and increasing the coating thickness increases the temperature on the coating surface.