Torsional Response of Internal Combustion Engines

A digital simulation technique for determining the torsional response of internal combustion engines subject to constant and pulsating end item torques is described herein. A refined mathematical model of the engine and end item power shafts is utilized to determine their natural frequencies, mode shapes, torsional motions and stresses using a digital computer. The mathematical model is composed of a finite number of elements which simulate lengths of continuous, massive, elastic shaft with end attached lumped masses and springs. Forcing functions, obtained by Fourier series expansion of the engine pressure-crank angle curve, are applied at the lumped masses. The technique is applied to a small gasoline engine attached to a reciprocating compressor and to a large Diesel engine with a constant torque end item.