A Telemetry Linkage System for Piston Temperature Measurements in a Diesel Engine

A telemetry linkage system has been developed for piston temperature measurements in a direct-injection diesel engine. In parallel with the development of the telemetry linkage system, fast response thermocouples were installed at three piston locations - two on the bowl surface and one on the crown surface. A novel design was used to achieve electrical continuity between the piston and the connecting rod by means of a flexible steel strap pivoted on the piston skirt. The telemetry linkage system was then used to transport the electrical wires from the thermocouples to the external data acquisition system. A series of tests was run to determine the effects of location and load on piston surface temperatures. Surface temperature profiles varied substantially among the three locations, reflecting the differences in the combustion and heat flow characteristics of their surrounding regions. Mean piston surface temperatures and cyclic swings increased with increasing load at constant speed for all three locations. Three tests were also conducted under the same speed and load to examine the effect of soot deposits on surface temperatures after the engine had accumulated 1, 5, and 10 total running hours, respectively. It was determined that deposit formation on a surface over the first five running hours causes the most significant reductions in the mean temperature and the cyclic swings of that surface. Overall, it was demonstrated that the telemetry linkage system can provide a reliable and effective means for measuring instantaneous properties of reciprocating diesel engine components.