Evaluation of Cylinder Pressure Transducer Performance Including the Influence of Mounting Location and Thermal Protection

The piezoelectric cylinder pressure transducer is one of the most critical tools for internal combustion (IC) engine research and development. However, not all cylinder pressure transducers perform equally in every application, and the fidelity of transducers can vary across different models and manufacturers. Even slightly dissimilar models from the same manufacturer can have significantly different performance in areas such as sensitivity and resistance to intra-cycle thermal shock. These performance differences can lead to errors and inconsistencies in the calculation of combustion metrics like mean effective pressure (MEP), the polytropic compression and expansion exponents (PolyC and PolyE), and mass fraction burn (MFB) calculations. The variations can lead to suboptimal hardware and calibration choices during the engine development phase. The use of flame arrestors to prevent the flame front from impinging on the face of the piezoelectric cylinder pressure transducer can have an effect on thermal shock (short-term error in transducer output caused by heat flux into the transducer face causing physical distortion and changing of the loading on the crystal) as well, and that effect is not always as intuitive as it may seem. This project does a methodical evaluation of four discrete piezoelectric transducers over a range of engine speeds, loads, and combustion phasings for two different mounting locations—one in the center of the cylinder closer to the flame initiation location and one in the end-gas location—with and without the use of flame arrestors. The results showed extensive differences in performance of the four separate cylinder pressure transducer models, as well as differences owing to the location of the transducer and the presence of a flame arrestor.