Accurate measurement of dynamic top dead center is essential for correct evaluation of IMEP in internal combustion engines. For the purpose of this measurements, microwave system and gap sensor were installed on the combustion chamber and cylinder wall of SI engines to find dynamic TDC.
In the tests using microwave system, dynamic TDC was determined by averaging symmetric points in 45-65 degree crank angle from TDC within 0.05 degree standard deviation. By this method, dynamic TDC was found to be nearly invariant with engine speed (1000-2500 RPM).
There was a difference of 0.1-0.2 degree in dynamic TDC determined by either microwave or gap sensor system. It is seen that the result from the microwave is more accurate than that from gap sensor whose inaccuracy is believed to be originating from piston tilting and gap sensor.
Thermodynamic loss angle was measured using spark plug type pressure transducer in motoring and its values were found to be in the range of 0.4-1.3 degree BTDC depending on brand of engine and operating conditions.