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Methods of Processing Cylinder-Pressure Transducer Signals to Maximize Data Accuracy
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Abstract
Two disadvantages of using piezoelectic pressure transducers to measure cylinder pressure are the sensitivity of the transducer to temperature and the necessity to reference the output to absolute pressure (pegging). Transducer drift driven by the combustion event, often referred to as thermal shock, enhances measured cyclic variability by exaggerating the effects of actual cyclic variations in combustion temperature. Any artificial variability that persists until the portion of the cycle used for pegging offsets all of the referenced measurements of that cycle by the magnitude of the variability. This study reviews several methods of pegging, and examines the extent to which the four most viable methods propagate thermally-induced intracycle and intercycle measurement variability.
It is preferable to peg when artificial variability is minimized, which occurs when the transducer output is least affected by the thermally transient nature of the engine cycle. Unfortunately, the majority of thermally-induced measurement variability persists throughout the engine cycle and is thus inherent in all pegging procedures. However, this study shows that the pegging procedure selected does have a secondary influence. For the engine used in this study, referencing the transducer output at inlet bottom dead center (IBDC) to intake manifold pressure (MAP) performed best. Equating the average measured pressure during the exhaust stroke to the exhaust backpressure or forcing a fixed polytropic compression coefficient were slightly worse, while forcing a variable polytropic compression coefficient was considerably worse.
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Authors
Citation
Randolph, A., "Methods of Processing Cylinder-Pressure Transducer Signals to Maximize Data Accuracy," SAE Technical Paper 900170, 1990, https://doi.org/10.4271/900170.Also In
References
- Amann, C. A. “Classical Combustion Diagnostics for Engine Research,” SAE Transactions 94 1975 Paper 850395
- Randolph, A. L. “Cylinder-Pressure Transducer Mounting Techniques to Maximize Data Accuracy,” SAE International Congress 1990
- Brown, W. L. “Methods for Evaluating Requirements and Errors in Cylinder Pressure Measurement,” SAE Paper 670008
- Obert, E. F. Internal Combustion Engines and Air Pollution Intext Educational Publishers New York 1973
- Hohenberg, G. Killmann, I. “Basic Findings Obtained from Measurement of the Combustion Process,” AVL Publications 1984
- Van Hove, W. Sierens, R. “Possibilities of a Fast Data Acquisition System in Testing IC Engines,” State University of Gent Belgium 1986
- Lancaster, D. R. Krieger, R. B. Lienesch, J. H. “Measurement and Analysis of Engine Pressure Data,” SAE Transactions 84 1975 Paper 750026