The invention relates to air cylinders and pistons of a variable multi-cylinder aerodynamic engine. The pistons are arranged in the air cylinders, spiral grooves are arranged on outer surfaces of the pistons along the circumferential direction, piston friction rings are welded in the spiral grooves through laser welding, and the piston friction rings are coaxial with the pistons. The air cylinders and the pistons are characterized in that the piston friction rings are made of a Cu-Si alloy, the Cu-Si alloy includes, by weight, 3.5-4.5% of silicon element, not lower than 95% of Cu element and the balance impurity elements. The impurity elements comprise a C element and a Ti element. The mass fraction of the C element in the Cu-Si alloy is 0.015%-0.03%, and the mass fraction of the Ti element in the Cu-Si alloy is 0.015%-0.02%. A sealing lubricating coating is respectively coated on cylinder walls of cylinder bodies, and the coatings are carbon nano tube composite wear resistant coatings. The carbon nano tube composite wear resistant coatings are arranged on the surfaces of the piston friction rings.