Results are reported of an experimental study of the behavior of a fuel droplet suspended in the plane of collision of two oppositely-facing shock waves, which bring the surrounding oxidizer gas instantaneously to a high-temperature stagnant state. For three kinds of liquid fuels, viz. decane, tetralin and cetane, strong emissions indicating ignition were observed to start from around the droplet with a certain delay time and to spread out later in all directions. Observations by Schlieren photography revealed that the droplet is not atomized prior to ignition as in the incident shock experiments. The distortion and breakup of the droplet take place after ignition, whereby the luminosity appears to spread with the fragments. The ignition lags were plotted against the temperatune attained in the collision plane for each fuel, and an Arrhenius-type dependence was obtained. The absolute value of the ignition delay was found to be definitely shorter than the available furnace (static-experiment) data. Some inferences are presented for anomalous aspects of the droplet behavior observed.
Molecular energy transfers in a CO2-N2-He mixture are discussed. A supersonic flow of the shock-heated CO2-N2-He mixture is computed in a conventional conical nozzle, With the most reliable results of relaxation times in molecular energy transfers, using the two different methods; the RKG method and Time-dependent method. Theoretical results and shock-tunnel results of vibrational relaxations of CO2 are compared.