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A Comparison of Four Methods for Determining the Octane Index and K on a Modern Engine with Upstream, Port or Direct Injection
ISSN: 0148-7191, e-ISSN: 2688-3627
Published March 28, 2017 by SAE International in United States
This content contains downloadable datasetsAnnotation ability available
Combustion in modern spark-ignition (SI) engines is increasingly knock-limited with the wide adoption of downsizing and turbocharging technologies. Fuel autoignition conditions are different in these engines compared to the standard Research Octane Number (RON) and Motor Octane Numbers (MON) tests. The Octane Index, OI = RON - K(RON-MON), has been proposed as a means to characterize the actual fuel anti-knock performance in modern engines. The K-factor, by definition equal to 0 and 1 for the RON and MON tests respectively, is intended to characterize the deviation of modern engine operation from these standard octane tests. Accurate knowledge of K is of central importance to the OI model; however, a single method for determining K has not been well accepted in the literature.
This paper first examines four different methods for determining K, using literature results from a modern SI engine operating with direct injection (DI), port fuel injection (PFI) and homogeneous, upstream fuel injection (UFI). The test fuels were ethanol-gasoline blends spanning a wide range of RON and MON, together with isooctane as a reference. The quality of the K results from some of these methods is particularly dependent on the design of the test fuel matrix, with unreliable K values resulting in some cases.
One of the more reliable methods is then used to examine how K varies with the intake pressure, fueling strategy, engine speed and compression ratio, with throttled conditions considered in detail. Several of the observed trends are consistent with prior studies, including K being consistently negative at higher loads for DI. In contrast to other studies, however, K is also observed to approach 0.5 at part load, throttled conditions, irrespective of whether the engine is fuelled by DI, PFI or UFI. Preliminary analysis of the autoignition chemistry for different fuelling methods then suggests plausible reasons for these results.
CitationZhou, Z., Yang, Y., Brear, M., Lacey, J. et al., "A Comparison of Four Methods for Determining the Octane Index and K on a Modern Engine with Upstream, Port or Direct Injection," SAE Technical Paper 2017-01-0666, 2017, https://doi.org/10.4271/2017-01-0666.
Data Sets - Support Documents
|[Unnamed Dataset 1]|
- ASTM D2699-11, "Standard Test Method for Research Octane Number of Spark-Ignition Engine Fuel", ASTM International, 2011. doi:10.1520/D2699-11.
- ASTM D2700-11, "Standard Test Method for Motor Octane Number of Spark-Ignition Engine Fuel", ASTM International, 2011. doi:DOI: 10.1520/D2700-11.
- Kalghatgi, G., "Fuel Anti-Knock Quality - Part I. Engine Studies," SAE Technical Paper 2001-01-3584, 2001, doi:10.4271/2001-01-3584.
- Kalghatgi, G., "Fuel Anti-Knock Quality- Part II. Vehicle Studies - How Relevant is Motor Octane Number (MON) in Modern Engines?," SAE Technical Paper 2001-01-3585, 2001, doi:10.4271/2001-01-3585.
- Mittal, V. and Heywood, J., "The Relevance of Fuel RON and MON to Knock Onset in Modern SI Engines," SAE Technical Paper 2008-01-2414, 2008, doi:10.4271/2008-01-2414.
- Davies, T., Cracknell, R., Lovett, G., Cruff, L. et al., "Fuel Effects in a Boosted DISI Engine," SAE Technical Paper 2011-01-1985, 2011, doi:10.4271/2011-01-1985.
- Remmert, S., Campbell, S., Cracknell, R., Schuetze, A. et al., "Octane Appetite: The Relevance of a Lower Limit to the MON Specification in a Downsized, Highly Boosted DISI Engine," SAE Int. J. Fuels Lubr. 7(3):743-755, 2014, doi:10.4271/2014-01-2718.
- Kalghatgi, G., Nakata, K., and Mogi, K., "Octane Appetite Studies in Direct Injection Spark Ignition (DISI) Engines," SAE Technical Paper 2005-01-0244, 2005, doi:10.4271/2005-01-0244.
- Mittal, V. and Heywood, J., "The Shift in Relevance of Fuel RON and MON to Knock Onset in Modern SI Engines Over the Last 70 Years," SAE Int. J. Engines 2(2):1-10, 2010, doi:10.4271/2009-01-2622.
- Stein, R., Polovina, D., Roth, K., Foster, M. et al., "Effect of Heat of Vaporization, Chemical Octane, and Sensitivity on Knock Limit for Ethanol - Gasoline Blends," SAE Int. J. Fuels Lubr. 5(2):823-843, 2012, doi:10.4271/2012-01-1277.
- Jung, H., Leone, T., Shelby, M., Anderson, J. et al., "Fuel Economy and CO2 Emissions of Ethanol-Gasoline Blends in a Turbocharged DI Engine," SAE Int. J. Engines 6(1):422-434, 2013, doi:10.4271/2013-01-1321.
- Leone, T., Olin, E., Anderson, J., Jung, H. et al., "Effects of Fuel Octane Rating and Ethanol Content on Knock, Fuel Economy, and CO2 for a Turbocharged DI Engine," SAE Int. J. Fuels Lubr. 7(1):9-28, 2014, doi:10.4271/2014-01-1228.
- Anderson, J., Leone, T., Shelby, M., Wallington, T. et al., "Octane Numbers of Ethanol-Gasoline Blends: Measurements and Novel Estimation Method from Molar Composition," SAE Technical Paper 2012-01-1274, 2012, doi:10.4271/2012-01-1274.
- Kalghatgi, G., "Auto-Ignition Quality of Practical Fuels and Implications for Fuel Requirements of Future SI and HCCI Engines," SAE Technical Paper 2005-01-0239, 2005, doi:10.4271/2005-01-0239.
- Yuan, H., Foong, T., Chen, Z., Yang, Y. et al., "Modeling of Trace Knock in a Modern SI Engine Fuelled by Ethanol/Gasoline Blends," SAE Technical Paper 2015-01-1242, 2015, doi:10.4271/2015-01-1242.
- Mehl, M., Pitz, W.J., Westbrook, C.K., and Curran, H.J., "Kinetic modeling of gasoline surrogate components and mixtures under engine conditions," Proceedings of the Combustion Institute (33):193-200, 2011, doi:http://dx.doi.org/10.1016/j.proci.2010.05.027.
- Dagaut, P., and Nicolle, A., "Experimental study and detailed kinetic modeling of the effect of exhaust gas on fuel combustion: mutual sensitization of the oxidation of nitric oxide and methane over extended temperature and pressure ranges," Combustion and Flame (140):161-171, 2005, doi:http://dx.doi.org/10.1016/j.combustflame.2004.11.003.