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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 10.1520/D2699-11
- ASTM D2700-11 Standard Test Method for Motor Octane Number of Spark-Ignition Engine Fuel ASTM International 2011 10.1520/D2700-11
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- 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 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 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 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 http://dx.doi.org/10.1016/j.combustflame.2004.11.003