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Determination of Octane Index and K in a 2L, 4-cylinder turbocharged SI engine using the PRF method
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
Research Octane Number (RON) and Motor Octane Number (MON) have traditionally been used to describe fuel anti-knock quality. The test conditions for MON are harsher than those for RON, causing the RON for a particular fuel to be higher than the MON. Researchers have proposed the anti-knock performance can be described using the Octane Index (OI), defined as OI=RON-K(RON-MON), where ‘K’ is a weighing factor between RON and MON. The K-factor indicates that at a particular operating condition, knock tolerance is better described by RON as K approaches a value of 1, and MON as K approaches a value of 0. Previous studies claim that K-factor is dependent only on the engine combustion system and the speed-load point, and that it is independent of fuel chemistry. In these studies, K was determined experimentally using linear regression. In this particular study, K was determined using the PRF method for two test fuels; EPA certification tier 2 and tier 3 fuel. K was calculated for these fuels at multiple test points and the results showed that the K was different for the two fuels and that it did depend on fuel chemistry. For a majority of the test points, the fuel with the lower RON and MON values (tier 3 cert fuel) had a lower K-Factor as compared to the tier 2 cert fuel. A parameter was developed to relate engine speed, combustion phasing and cylinder trapped mass to K-factor, independent of the fuel. The dependence of K-factor on intake air temperature and engine speed was also studied as a part of this project.