Rapid Compression Machine Measurements of Ignition Delays for Primary Reference Fuels

A rapid compression machine for chemical kinetic studies has been developed. The design objectives of the machine were to obtain: 1)uniform well-defined core gas; 2) laminar flow condition; 3) maximum ratio of cooling to compression time; 4) side wall vortex containment; and, 5) minimum mechanical vibration. A piston crevice volume was incorporated to achieve the side wall vortex containment. Tests with inert gases showed the post-compression pressure matched with the calculated laminar pressure indicating that the machine achieved these design objectives.

Measurements of ignition delays for homogeneous PRF/O₂/N₂/Ar mixture in the rapid compression machine have been made with five primary reference fuels (ON 100, 90, 75, 50, and 0) at an equivalence ratio of 1, a diluent (s)/oxygen ratio of 3.77, and two initial pressures of 500 Torr and 1000 Torr. Post-compression temperatures were varied by blending Ar and N₂ in different ratios. It was found that the ignition delays were not a linear function of the ON of the fuel. Within the experimental range covered, the first-stage ignition delays decreased rapidly as the temperature increased, whereas the second-stage ignition delays stayed unchanged as the temperature increased. Comparison with existing data showed that the ignition delay measurements made in other RCM's should be carefully reevaluated partially due to their high heat transfer characteristics and partially due to their improper mixture preparation procedures.