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Engine Performance
Geometric Properties
Piston Velocity vs Crank Angle
Piston Acceleration
Piston Inertia Force
The inertia force is simply the piston mass multiplied by the acceleration
• The maximum force occurs at TC, q = wt = 0 à F ~ amw2
• The primary term varies at the same speed as the crankshaft
and the secondary term varies at twice the crank shaft speed
• For a very long connecting rod (a/l) << 1 secondary term vanishes
and the force is harmonic
• Complete cancellation of the forces is possible for in-line 6 and 8
as well as for V-12 and V-16
Torque and Power
Torque is measured off the output shaft using a dynamometer
Brake Power
Torque is a measure of an engine’s ability to do work and power is
the rate at which work is done
Note torque is independent of crank speed.
The term brake power, , is used to specify that the power is measured at the output shaft, this is the usable power delivered by the engine to the load.
The brake power is less than the power generated by the gas in the cylinders due to mechanical friction and parasitic loads (oil pump, air conditioner compressor, supercharger, etc…)
The power produced in the cylinder is termed the indicated power, .
Indicated Work per Cycle
Given the cylinder pressure data over the operating cycle of the engine one
can calculate the work done by the gas on the piston. This data is
typically given as P vs V