Based on the engine dynamics and the relationship between the harmonic angular vibration at arbitrary crankshaft measuring points of a multi-cylinder engine and the harmonic torque of each cylinder

the correlation between the angular vibration response at the crankshaft measuring point and the engine power was derived

and an on-line measurement of engine power was developed based on the harmonic amplitude of crankshaft angular vibration. Moreover

according to the principle of linear superposition

the influence of the gas exciting moment and reciprocating inertia moment of a heavy duty engine on the characteristic order amplitude of angular vibration at the crankshaft measuring point was compared under different working media. The correctness of the proposed theory is proved by the characteristic order amplitude curve through the experimental study and simulation of a gas engine and a diesel engine

respectively. When using the characteristic order amplitude of the torsional angular displacement at the crankshaft

measuring point to calculate the actual operating power of the engine

the maximum deviation is 3.5%.