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In this paper authors propose a new method for estimation of cylinder compression. Under motoring condition, when the transient rotational speed fluctuation of flywheel within a working cycle has been measured, the Max. compressive pressure of each cylinder were calculated based on the principle of inertia acceleration. The testing results of 4 and 6 cylinder engines show that, the measured errors were within ±3%, so it is a proper tool for fast estimation the compression of engine mounted on vehicles especially.

The unevenness between cylinder's operations for multi-cylinder engine Is one of the most important factors affecting an the engine performance. The authors presented a new approach to diagnose it, that is, deriving each cylinder's compression pressure, maximum combustion pressure and work from the transient crankshaft speed. The diagnostic principle and calculating method of pressures and work were described in detail, the experimental equipment and results were illustrated. The derived work, compression engine and combustion pressure were compared to their measured values. Figures and tables were given. The first phase of study indicated that the diagnostic method above is acceptable and simple, after enhanced it's accuracy futher, it will find good use.