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Some Insights on the Stochastic Nature of Knock and the Evolution of Hot Spots in the End-Gas During the Engine Cycle from Experimental Measurements of Knock Onset and Knock Intensity
ISSN: 0148-7191, e-ISSN: 2688-3627
Published October 08, 2017 by SAE International in United States
This content contains downloadable datasetsAnnotation ability available
Knock in spark ignition engines is stochastic in nature. It is caused by autoignition in hot spots in the unburned end-gas ahead of the expanding flame front. Knock onset in an engine cycle can be predicted using the Livengood-Wu integral if the variation of ignition delay with pressure and temperature as well as the pressure and temperature variation with crank angle are known. However, knock intensity (KI) is determined by the evolution of the pressure wave following knock onset. In an earlier paper (SAE 2017-01-0689) we showed that KI can be approximated by KI = Z (∂T/∂x)-2 at a fixed operating condition, where Z is a function of Pko, the pressure, and (∂T/∂x) is the temperature gradient in the hot spot at knock onset. Then, from experimental measurements of KI and Pko, using five different fuels, with the engine operating at boosted conditions, a probability density function for (∂T/∂x) was established. In this paper the knock data for two other non-boosted operating conditions for the same fuels at the same engine speed in the same engine are analyzed. The crank angle at knock onset for a given fuel is more advanced at these two new conditions because of the more advanced spark timing needed to obtain knock, and this enables some insights to be gained on how the hot spots evolve during an engine cycle. With increasing crank angle, the mean absolute value of (∂T/∂x) decreases and its distribution narrows. This is consistent with a simple picture that at the start of compression in the engine cycle there is a wide distribution of scales in the turbulent temperature field and the mean temperature gradient is large but conditions become more homogenized with time (crank angle). The paper presents distributions in terms of normalized counts in histograms for other parameters related to knock onset as well as knock intensity which might be of use in modeling knock stochastically.
|Technical Paper||A New Diagnostic Method of Knocking in a Spark-Ignition Engine Using the Wavelet Transform|
|Technical Paper||Influence of direct electric field on the knock intensity in a spark-igntion engine|
CitationKalghatgi, G., Morganti, K., and Algunaibet, I., "Some Insights on the Stochastic Nature of Knock and the Evolution of Hot Spots in the End-Gas During the Engine Cycle from Experimental Measurements of Knock Onset and Knock Intensity," SAE Technical Paper 2017-01-2233, 2017, https://doi.org/10.4271/2017-01-2233.
Data Sets - Support Documents
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- Kalghatgi , G. , Babiker , H. , and Badra , J. A Simple Method to Predict Knock Using Toluene, N-Heptane and Iso-Octane Blends (TPRF) as Gasoline Surrogates SAE Int. J. Engines 8 2 505 519 2015 10.4271/2015-01-0757
- Kalghatgi , G. , Morganti , K. , Algunaibet , I. , Sarathy , M. et al. Knock Prediction Using a Simple Model for Ignition Delay SAE Technical Paper 2016-01-0702 2016 10.4271/2016-01-0702
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- Kalghatgi , G. , Algunaibet , I. , and Morganti , K. On Knock Intensity and Superknock in SI Engines SAE Int. J. Engines 10 3 2017 10.4271/2017-01-0689
- Bradley , D. and Kalghatgi , G.T. Influence of autoignition delay time characteristics on pressure fluctuations and knock in reciprocating engines Combustion and Flame 156 2307 2318 2009
- Westbrook , C.K. 2000 Chemical kinetics of hydrocarbon ignition in practical combustion systems Proceedings of the Combustion Institute 28 1563 1577
- Ghandhi , J. and Kim , K. A Statistical Description of Knock Intensity and Its Prediction SAE Technical Paper 2017-01-0659 2017 10.4271/2017-01-0659
- Chun , K. and Heywood , J. Characterization of Knock in a Spark-Ignition Engine SAE Technical Paper 890156 1989 10.4271/890156
- McKenzie , J. and Cheng , W. The Anatomy of Knock SAE Technical Paper 2016-01-0704 2016 10.4271/2016-01-0704
- Kalghatgi , G.T. and Bradley , D. 2012 Pre-ignition and super-knock in turbo-charged spark ignition (SI) engines International Journal of Engine Research 13 4 399 414