Date of Award


Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Scott A. Miers

Advisor 2

Christopher P. Kolodziej

Committee Member 1

Wolfram Gottschalk

Committee Member 2

Rebecca G. Ong


Octane numbers (ONs) are used worldwide to rate the knock propensity of gasoline-like fuels for spark-ignition engines, making ONs the leading indicator of fuel quality for commercial distribution. The ONs were established 90 years ago and have only received minor changes compared to significant advancements in modern engine operation and fuel composition. This has resulted in discrepancies between knock-limited modern engine operation and standard ON ratings. This dissertation used a standard CFR octane rating engine at Argonne National Laboratory that was instrumented with modern combustion research tools to investigate key differences between the Research Octane Number (RON) rating conditions and modern knock-limited engine operation. The D1 Detonation Pickup as part of the standardized knockmeter system was able to quantify high-frequency pressure oscillations associated with knocking combustion. On the contrary, the subsequent signal conditioner attenuated all high-frequency signal content rendering the standard knockmeter system for octane ratings blind to knocking cylinder pressure oscillations. Instead, the knockmeter system was found to rate the knock area above the cylinder pressure of knockpoint, which is associated with knocking combustion but does not quantify high-frequency pressure amplitudes. The high-frequency pressure amplitudes can be used to differentiate between highly aromatic and highly paraffinic fuels, and furthermore indicate the fuel RON-MON sensitivity. A shift to stoichiometric operation and oscillations amplitude-based knock threshold better represents modern knock-limited engine operation but only resulted in mediocre correlations to RON. A modified RON rating was developed to compensate for the increased heat of vaporization (HoV) and subsequent shift in volumetric efficiency of alcoholic blends, which showed a much-reduced effective RON rating without their HoV advantage. A toluene standardization fuel-based bracketing procedure was developed for octane ratings exceeding 100 to replace toxic tetraethyl lead and rate fuels within the reproducibility limits of the standard RON method. A novel Supercharged Octane Number (SON) was developed to better replicate cylinder pressure-temperature conditions of modern boosted SI engines, which improved the correlation over standard RON. Further improvements were found when incorporating the novel SON and RON as interpolation boundaries for an updated Supercharged Octane Index, which enhanced the correlation over the conventional Octane Index.

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Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.