Measurement of Dynamic TDC in SI Engines Using Microwave Sensor, Proximity Probe and Pressure Transducers

In order to find the dynamic TDC a microwave sensor was installed on the head and a proximity probe on the wall of 4-cyl SI engines. The dynamic TDC determined by the microwave system exhibited fairly consistent results having less than 0.05 degrees in standard deviation and remaining nearly constant throughout the speed range of 1,000-2,500 rpm. There was 0.1-0.2 degrees difference between the dynamic TDC measured by the microwave sensor and that measured by the proximity probe; the microwave result was believed to be more reliable. The difference seemed to originate from the built-in system errors on the part of proximity apparatus caused by insufficient sensitivity and availability of data points and piston tilting motion. Both flush mounted and spark plug type pressure transducers were used to measure the motoring peak pressure. Although there was a somewhat unexpected result on the coolant temperature effect the thermodynamic loss angle(TLA) showed an explainable trend increasing from 0.4 to 1.5 degrees as the motoring speed decreased from 2,500 to 1,000 rpm.