Bridging Fundamental Combustion Analysis and Engine Knock Behavior -1st Report, CFR Engine Test for Various RON Fuels

A collaborative study was conducted to bridge the gap between fundamental combustion research and engine-scale observations of knock in spark-ignition (SI) engines. Using Primary Reference Fuels (PRFs) with Research Octane Numbers (RON) of 80, 90, and 100, experiments were carried out with a Cooperative Fuel Research (CFR) engine at air-fuel ratio, λ = 1.0, focusing on knock onset conditions in terms of unburned gas pressure and temperature. In the engine tests, pressure traces under knocking conditions were analyzed to identify knock onset and to estimate the corresponding unburned gas temperature history. Results showed that the pressure at knock onset varies clearly with PRF value: higher RON fuels exhibited knock onset at higher pressures, likely due to changes in compression ratio applied to match standard RON test procedures. In contrast, the unburned gas temperature conditions showed partial overlap across different PRFs, but with a tendency for higher RON fuels to experience knock onset at slightly higher temperatures. These findings provide a coherent dataset linking engine-based knock behavior with fundamental combustion characteristics, forming the foundation for the reaction-kinetics-based analysis presented in the second report. Additionally, the CFR engine experiments were also conducted at λ = 0.88 to support the comparison with standard RON measurement conditions.