An experimental investigation was conducted to correlate thermal characteristics with primary reference fuel (PRF) using an “isothermal” flow reactor. Objective of the investigation was to assess whether or not thermal characteristics measured in a radiant-heated flow reactor could serve as an indicator of fuel octane number. The experimental set-up consisted of a radiant furnace and a pyrex-tube test section inside. The pyrex tube was fitted with thermocouples alongside the tube wall. Four PRF compositions of iso-octane and n-heptane were considered: 0, 65, 85 and 100% of iso-octane by volume; noted as PRF0, 65, 85 and 100, respectively. The test conditions reported in the paper set the fuel-air mixture temperature to 180 °C at the inlet of the test section and the radian furnace temperature to 345 °C. The equivalence ratio was set in the range 0.93 to 2.0. For a pre-set PRF and equivalence-ratio condition, the experiments were run with fixed mixture velocities over the range 0.019 m/s to 0.400 m/s. Over the conditions tested, the thermocouples recorded two temperature oscillations along the flow reactor for each of PRF0, 65 and 85 mixtures. Both oscillation locations moved downstream when PRF number was increased and the two oscillation locations merged when PRF was set to 85. No temperature oscillations were recorded for experiments with PRF100 mixture. The results suggest that the temperature oscillation locations from the experiments using isothermal flow-reactors can be used to correlate fuel octane number.

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