The Effect of Gas Pressure on Piston Friction 360117
THE effect of gas pressure on piston friction was investigated, in the laboratory of the Massachusetts Institute of Technology, by driving with an electrical dynamometer a six-cylinder engine with the valves removed and the valve-stem bushings plugged. Air under pressure was admitted to the closed space made up of the cylinders, valve passages, and manifolds, and a constant air pressure was maintained on the pistons.
Under these conditions, it was found that the friction increased approximately as a linear function of the pressure and the running speed. The effect of jacket-water temperature on piston friction was marked, but it could not be directly connected with the absolute viscosity of the oil at the temperature of the jacket water. Tests run with gas pressure relieved from behind the piston rings indicated that about a fourth of the rate of increase in friction with pressure is due to gas pressure behind the rings.
Computations from the test results indicate that the increase in friction due to gas pressure on pistons, as compared with piston friction on the ordinary motoring friction test, is in the neighborhood of 2 to 3 lb. per sq. in. m.e.p., for this type of engine.