ll of the friction measurement procedures except the difference between brake and gross indicated power or mep measured directly assume that motored engine friction and firing engine friction are closely comparable. This is not an accurate assumption for the pumping component. Summarize the differences between the gas exchange processes under motoring and firing conditions for a spark-ignition engine at a fixed part-load throttle setting that will result in the pumping work being significantly different under these two conditions.
Q70;
On separate accurately proportioned sketches of the piston, cylinder, connecting rod, and crank mechanism (similar to Fig. 2-I), during the intake stroke (at 120' ATC), compression stroke (at 60" BTC), expansion stroke (at 60' ATC), and exhaust stroke (at 120" BTC), draw an arrow for each of the forces acting on the piston (pressure forces, force from connecting rod, friction force, inertia force). Mark clearly the positive direction of each force. Express each force in terms of cylinder pressure p,, crankcase pressure p,, , friction force Ff, piston area Ap, effective piston (and part of connecting rod) mass m,, piston acceleration a, connecting rod force Fa.