A MATHEMATICAL MODEL OF RECIPROCATING COMBUSTION ENGINE DYNAMICS FOR THE DIAGNOSIS OF DEFICIENT ENERGY CONVERSION

The dynamics of reciprocating combustion engines depends on the thermodynamic cycle that includes the efficiency of utilization of fuel energy. A mathematical model is introduced to describe the relationship between engine dynamics and the cycle thermodynamics. The computer simulation includes: (1) Modeling of the instantaneous friction in engines. (2) Modeling of the inertia forces in engines. (3) Modeling of the effect of torsional vibrations on the crankshaft. (4) Modeling of the instantaneous angular velocity of the flywheel.; The scope of this work is limited to deficiencies (such as misfiring) that result in measurable effects on the angular velocity of the crankshaft.; Experiments were conducted on different engines to determine the coefficients of the friction correlations. The mathematical model was verified with experimental instantaneous angular velocity data which were collected and processed by an Intel 8086 microcomputer. The average error was found to be 3%.; The results of the present study are: (1) Correlations that describe engine friction in terms of engine geometry and operating conditions. (2) Effects of gas pressure on the crankshaft angular velocity. (3) The following parameters can be used for the diagnosis of the misfiring cylinder(s): (a) Mean cyclic acceleration. (b) The range of variation of crankshaft angular velocity. (c) Periods of cyclic acceleration. (4) Compared to the available diagnostic techniques, such as variation in TDC's angular velocity, autocorrelation and Fourier transforms, the suggested diagnostic parameters have the advantage of identifying the position of the misfired cylinder(s) with less elaborate computations.