Optimization of In-Cylinder Pressure Filter for Engine Research

Report No. ARL-TR-8034
Authors: Kenneth S Kim; Michael T Szedlmayer; Kurt M Kruger; Chol-Bum M Kweon
Date/Pages: June 2017; 38 pages
Abstract: Proper filtering of an engine's in-cylinder pressure is very important for analyzing combustion events. The objective of this study was to investigate and determine the optimal filter and its parameters for removing signal noise while retaining in-cylinder pressure characteristics of interest, for both normal and abnormal combustion events. A 4-cylinder direct-injection aviation diesel engine was instrumented to acquire in-cylinder pressure with a range of combustion events. Simple smoothing filters showed limited performance for an abnormal combustion event, resulting in biased in-cylinder pressure near start-of-combustion. The Savitzky-Golay filter, one of the simple smoothing filters, determined filtered in-cylinder pressure with high accuracy near start-of-combustion but underperformed in removing signal noise after start-of-combustion. Various linear continuous-time filters with frequency stop-band have advantages over simple smoothing filters in removing signal noise with magnitude response as a function of frequency. A number of linear continuous-time filters with different phase-response characteristics were investigated, and the optimal filter response and parameters were determined to effectively filter in-cylinder pressure of an aviation diesel engine. The Chebyshev filter with 5th-order polynomial and 0.001%-allowed ripples showed the best results in matching the raw signal near start-of-combustion and minimizing oscillations after start-of-combustion.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2017