The "Rotating Liner Engine" project is a new concept that is focused on the reduction of piston friction in an internal combustion engine. Piston friction is the single biggest source of total engine friction, which limits engine efficiency. The piston reciprocates in the cylinder and the piston rings seal the combustion chamber. The wall of the cylinder is called the liner, which is stationary in current engines. For the RLE, the cylinder liners are rotated in order to substantially improve the lubrication of the piston and piston rings, especially during the high-friction and high-wear portions of the cycle around the piston reversals. The reduced piston friction and ring/liner wear from a rotating liner was well established by 200 million horsepower of WWII British Sleeve Valve aircraft engines. In those engines, the "sleeve" (cylinder liner) moved in an elliptical motion in order to expose intake and exhaust ports and thus replace the conventional poppet valves for the gas exchange processes. The sleeve valve deliberately introduced relatively high parasitic losses due to sleeve design and motion-of much higher order than the valvetrain friction it replaced. Despite these parasitic losses, the instantaneous rotation of the sleeve during piston reversal provided a significant and unexpected overall friction reduction and thus efficiency improvement, which more than compensated for the sleeve viscous drag. Naturally aspirated industrial diesel sleeve valve engines built in the 1930s achieved impressive fuel economy2