Determination of Octane Index and K-Factor in a 2.0L, Four-Cylinder Turbocharged SI Engine Using the Primary Reference Fuel Method—Part II

This is the second part of a two-phase study revolving around the determination of fuel K-factor for different fuels in a 2.0L, 4-cylinder, direct-injected, turbocharged spark-ignition (SI) engine for different engine speeds and loads. Prior studies relating to K-factor claim that K depends only on the engine’s combustion system and operating condition, but Phase 1 of this study detected contrary results. Experimental determination of K at multiple test points showed the K value was different for the Environmental Protection Agency (EPA) certification Tier 2 and Tier 3 regular fuels. That study also found strong correlations of the K value with macroscopic parameters (e.g., speed, load, and combustion phasing) and end gas conditions, irrespective of the fuel. This second phase of the study showed that the effect of variation in day-to-day conditions on the K-factor is negligible and that K-factor stays the same with changes in intake air temperature (IAT) for a specific speed-load condition.