The response of a valved pulse combustor to changes in the relative timing between the resonant pressure wave and the instantaneous energy release rate has been examined. Experiments were designed to examine the pulse combustor's response to independent changes in the experimental conditions that resulted in nearly independent changes in the fluid dynamic species mixing time, the fluid dynamic mixing time of cold reactants with hot products, the characteristic chemical kinetics time, and the characteristic resonance time. The time scales considered in this study were adjusted independently to modify the coupling between the instantaneous energy release rate and the resonant pressure wave, thereby modifying the magnitude of the pressure oscillations and altering the frequency of operation. All of these experimental observations of the pulse combnstor response to variations in characteristic time scales are interpreted in terms of Rayleigh's criterion.

Measurements of the total ignition delay time in a pulse combustor have been made for several chemical kinetic ignition delay times and several fluid dynamic mixing times. These measured total ignition delay times are compared with calculated values of the characteristic time for mixing and with calculated values for the homogeneous ignition delay time. A chemical kinetic model was used to calculate the homogeneous chemical kinetic ignition delay time for conditions typical of an operating pulse combustor. Similarly, a fluid dynamic mixing model was used to estimate characteristic times for a transient jet of cold reactants to mix with an ambient environment of hot products to an ignition temperature. These calculated time scales compared well with measured values in both trend and magnitude. It has also been shown that a simple sum of the characteristic mixing times and chemical kinetics times provides a good first-order approximation to the total ignition delay time.

A numerical model has been developed to study the sensitivity of a pulse combustor's performance to changes in the relative timing between several of the dominant physical processes. The model is used to demonstrate the importance of the characteristic times associated with acoustics, fluid mixing, and chemical kinetics, which have been identified from both theoretical and experimental evidence. The combination of submodels for acoustics, injection, and combustion produces a pulse combustor model that is dynamic in that it fully couples the injection and mixing processes to the acoustic waves. Comparisons of simulations with experimental results show good agreement, verifying the model over a wide range of operating conditions. Because the model provides more control of the dominant processes than can be obtained in experiments, the parametric study establishes the cause-effect relation between the characteristic times and the resulting combustor performance.

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