Testing the Rotating Liner Engine: Over 30% Reduction in Diesel Engine Fuel Consumption at Idle Conditions

The Rotating Liner Engine (RLE) is a design concept for internal combustion engines, where the cylinder liner rotates at a surface speed of 2-4 m/s in order to assist piston ring lubrication. The metal-to-metal contact/boundary friction that exists close to the piston reversal area becomes a significant source of energy loss when the gas pressure that loads the piston rings and skirts is high. Reduction in mechanical friction has a direct impact on brake thermal efficiency. This paper describes fuel consumption measurements of our prototype single cylinder engine, compared to a baseline at idle. The reduction in fuel flow is of the order of 40% when extrapolated to a complete engine. The margin in friction reduction is expected to grow at increasing load, but reduce at increasing speeds. Our earlier models estimated idle fuel consumption reduction to about 25%, at full load about 3.5%, for a Heavy-Duty FTP 6.8 %, and may have been conservative. The literature is inconsistent on the contribution of the piston assembly boundary friction to the engine brake thermal efficiency. Detailed theoretical simulations, while capturing the overall trends in engine friction, often rely on arbitrary assumptions to determine the transition between hydrodynamic and mixed lubrication, leading to large errors. Experimental efforts face the difficulty in isolating the relatively low friction forces from the very high-pressure forces that act on the piston during both the negative and positive work parts of the cycle. This prototype engine, in addition to offering a practical method for improving brake thermal efficiency, also offers insight as to the magnitude of piston assembly friction energy loss under high pressure diesel combustion. Our results indicate that well over 30% of the fuel energy at idle is wasted on piston assembly boundary friction on a diesel engine. The RLE could eliminate this wastage.