The controlling fluid dynamic and chemical mechanisms of a pulsating combustion engine are being investigated to develop the necessary elemental understanding to determine the scalability of these engines. The behavior of liquid fuels is being investigated with a valved (convential) pulsejet design while gaseous fuels are being studied in both valved designs as well as valveless variants. A coupled dependence of acoustic and chemical processes is suspected, and thus pressure data has been collected using transducers at five ports located along the longitudinal axis of the jet. Acoustic experiments were performed and the engine was found to resonate at the natural frequency of the tube length. Chemiluminescence detection of CH* emission has been utilized to determine combustion time and frequency of combustion events. In addition, much interest has been placed on the nature of the exhaust velocity of the conventional pulsejet. In order to verify a time-resolved exhaust velocity, LDV has been used in conjunction with fuel mass flow rates to determine the nature of the pulsejet's thrust. Scalability experiments were conducted by varying tube lengths as well as inlet geometries. The fundamental operating frequency of the pulsejet is shown to have a strong dependence on the length of the exhaust tube—the longer the tube the lower the frequency. Similar experimentation was performed on a valveless variant with gaseous fuel. Ultimately, pressure fluctuation due to combustion and acoustic events will be separated for a clear understanding of the controlling factors of resonance. A Navier-Stokes 3-D compressible model is being developed along side experimentation to predict engine scalability. Scalable wall functions are implemented for boundary layer calculation, as well as, a k-ε turbulence model. For combustion processes, a Westbrook and Dryer two-step chemistry model is utilized for propane.