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This project aimed to develop a compact and lightweight telemetry system that mechanically decouples measurements, enabling versatile applications across different measurement scenarios, particularly for pistons and other moving systems. Utilizing an ESP8266, a printed circuit board design was created from individually tested integrated circuits, which formed the foundation for measuring various physical variables. Given the challenging conditions inside a piston of an internal combustion engine, ensuring high robustness was paramount during the electrical engineering process to prevent failures due to high temperatures and acceleration levels. Alongside the installation process for thermocouples, software for energy-efficient measurement with customizable resolution and optional transmission via Wi-Fi or internal storing was developed. Demonstrating feasibility during full-load operation of a heavy-duty diesel engine, the telemetry system with a high-resolution surface thermocouple was integrated in one piston to establish a method for assigning crank angles, enabling measurement and transmission of surface temperatures with crank angle resolution. Further series of measurements, including the use of alternative fuels, were conducted with a third piston, expanding the findings. The outcome is an innovative telemetry measurement device capable of recording experimental data from moving components, potentially expediting market solutions by reducing development times.
An experimental study was conducted to investigate combustion and in-cylinder heat transfer characteristics under light and heavy knocking conditions in a spark ignition engine. A special, single cylinder, Mitsubishi R52 engine was used, in its extended piston configuration. Fast response heat flux probes on the piston and the cylinder head provided instantaneous surface temperature measurements at different locations, both inside and outside the end-gas region. The knocking combustion process was characterized by several knock indices, based on the net heat release analysis of cylinder pressure, as well as, the amplitude of the knock induced pressure fluctuations. Knock initiation and development were investigated by sampling cylinder pressure data at two different locations in the chamber. The cyclic variability associated with knocking combustion was investigated by studying the variation, as well as the interdependence of the knock indices, under different knock severity conditions. Finally, the effects of knock on heat transfer were explored by studying changes in ensemble-average heat flux with increasing knock intensity, and also by the magnitude of the correlation coefficients between peak heat flux and the developed knock indices. Evidence of multiple autoignition sites was found during the knock initiation process. Knock induced pressure waves were of acoustic nature, becoming weak shock waves in cases of violent autoignitions. Cyclic variability in knock intensity was found to be driven by variations in burn rate. The correlation between burn rate and knock intensity was higher for lower overall combustion rates. Under light knock, the ensemble-average peak heat flux at locations near the end-gas zone increased with spark advance, departing from its trend prior to the onset of knock. Under heavy knock, the ensemble-average peak heat flux increased over the entire piston crown. High statistical correlation (up to 0.80) was found between peak heat flux and certain of the autoignition indices within and near the end-gas zone. Knock was found to increase heat transfer by the 'scouring' action of the induced pressure waves on the wall thermal boundary layer. Apart from knock intensity, the location of autoignition initiation, and the characteristics of the flame and wave front patterns following autoignition were found to affect the magnitude of heat transfer changes.