This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Phenomena that Determine Knock Onset in Spark-Ignition Engines
Technical Paper
2007-01-0007
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Language:
English
Abstract
Experiments were carried out to collect in-cylinder pressure data and microphone signals from a single-cylinder test engine using spark timingsbefore, at, and after knock onset for toluene reference fuels. The objective was to gain insight into the phenomena that determine knock onset, detected by an external microphone. In particular, the study examines how the end-gas autoignition process changes as the engine's spark timing is advanced through the borderline knock limit into the engine's knocking regime.
Fast Fourier transforms (FFT) and bandpass filtering techniques were used to process the recorded cylinder pressure data to determine knock intensities for each cycle. Two characteristic pressure oscillation frequencies were detected: a peak just above 6 kHz and a range of peaks in the 15-22 kHz range. The microphone data shows that the audible knock signal has the same 6 kHz peak. At audible knock onset, cycles begin to have knock intensities (based on the maximum peak to peak amplitude of the bandpass filtered pressure signal) greater than about 2 bar at this 6 kHz frequency band. This behavior occurs in a larger fraction of cycles as the spark timing is advanced through the borderline knock limit. The peak to peak amplitudes of the pressure oscillations in the 15-22 kHz frequency band are significantly larger than those in the 6 kHz frequency band. Thus a larger fraction of cycles (the majority) show knock intensities above the 2 bar level in the higher frequency band at the audible knock detection point. At knock onset and with more intense knock, the cylinder pressure and microphone knock intensities correlate well.
Our results show that prior to knock onset, autoignition occurs in a substantial fraction of the engine's cycles, producing higher amplitude pressure oscillations at frequencies above the audible threshold, but much smaller amplitude pressure oscillations in only a small percentage of cycles at the audible 6 kHz frequency. At knock onset conditions, cycles with significantly higher knock intensities (above about 2 bar, peak to peak) at the 6 kHz frequency start to occur. These cycles directly excite engine block vibrations and produce the audible knock signal. At more intense knocking conditions, as the spark is advanced, the fraction of cycles rapidly autoigniting, their knock intensity, and the audible knock signal amplitude, all increase.
Recommended Content
Authors
Topic
Citation
Mittal, V., Revier, B., and Heywood, J., "Phenomena that Determine Knock Onset in Spark-Ignition Engines," SAE Technical Paper 2007-01-0007, 2007, https://doi.org/10.4271/2007-01-0007.Also In
References
- Heywood, J.B. Internal Combustion Engine Fundamentals McGraw-Hill 1988
- Konig, G. Sheppard, C.G.W. “End Gas Autoignition and Knock in a Spark Ignition Engine,” SAE Paper 902135 International Fuels and Lubricants Meeting and Exposition Tulsa Oklahoma October 22-25 1990
- Naber, J.D. Blough, J.R. Frankowski, D. Goble, M. Szpytman, J.E. “Analysis of Combustion Knock Metrics in Spark-Ignition Engines,” 2006 SAE World Congress Detroit, MI April 3-6 2006
- Chun, K.M. Heywood, J.B. “Characterization of Knock in a Spark-Ignition Engine,” SAE paper 890156 , SAE International Congress & Exposition Detroit, MI February 27 March 3 1989
- Cheng, W.K. Hamrin, D. Heywood, J.B. Hochgreb, S. Min, K. Norris, M. “An Overview of Hydrocarbon Emissions Mechanisms in Spark-Ignition Engines,” SAE paper 932708 SAE Fuels and Lubricants Meeting and Exposition Philadelphia, PA October 18-21 SAE Trans. 102 1993
- Kleeman, A.P. Menegazzi, P. Henriot, S. Marchal, A. “Numerical Study on Knock for an SI Engine by Thermally Coupling Combustion Chamber and Cooling Circuit Simulation,” SAE 2003-01-0563 SAE World Congress Detroit, MI March 3-6 2003
- Castagne, J.P. Dumas, J.P. Henroit, S. Lafossas, F.A. “New Knock Localization Methodology for SI Engines,” SAE paper 2003-01-1118 2003 SAE World Congress Detroit, MI March 3-6 2003
- Syrimis, M. Assanis, D.N. “Knocking Cylinder Pressure Data Characteristics in a Spark-Ignition Engine,” Trans. of the ASME 125 April 2003
- Draper, C.S. “Pressure Waves Accompanying Detonation in the Internal Combustion Engine,” Journal of the Aeronautical Sciences 5 1938
- Scholl, D. Davis, C. Russ, S. Barash, T. “The Volume Acoustic Modes of Spark-Ignited Internal Combustion Chambers,” SAE paper 980893 International Congress & Exposition Detroit, MI February 23-26 1998
- Eng., J.A. “Characterization of Pressure Waves in HCCI Combustion,” SAE paper 2002-01-2859 Powertrain & Fluid Systems Conference & Exhibition San Diego, CA October 21-24 2002
- Brunt, M.F.J. Pond, C.R. Biundo, J. “Gasoline Engine Knock Analysis using Cylinder Pressure Data,” SAE Paper 980896 International Congress & Exposition Detroit, MI February 23-26 1998
- Gerty, M.D. Heywood, J.B. “An Investigation of Gasoline Engine Knock Limited Performance and the Effects of Hydrogen Enhancement,” SAE paper 2006-0228 2006 SAE World Congress Detroit, MI April 3-6 2006 April 2004
- Douaud, A.M. Eyzat, P. “Four-Octane-Number Method for Predicting the Anti-Knock Behavior of Fuels and Engines,” SAE paper 780080 , SAE Trans. 87 1978