David Michael Chapin

PULSED DETONATION ENGINE PROCESSES: EXPERIMENTS AND SIMULATIONS

Computational and experimental investigations of a pulsed detonation engine (PDE) operating in a cycle using ethylene/air mixtures are reported. Simulations are performed for two geometry configurations, namely, an ideal tube PDE with a smooth wall fueled with premixed C2H4/O2 and a benchmark tube PDE with internal geometry and a valveless air supply fueled with C2H4. Performance estimates of fuel-specific impulse (Ispf) of an ideal tube PDE, obtained using a two-step reduced mechanism for a C2H4/O2 mixture, are in good agreement with existing test measurements from the literature. Realistic simulations of all processes of the PDE cycle (fill, deflagration-to-detonation transition (DDT), detonation propagation, blowdown, and purge) of a benchmark tube PDE yielded important insights into continuous cycle operation. Experimental measurements include DDT visualizations and dynamic pressure measurements. Comparisons of experimental and computational visualizations show good agreement in cycle process timescales. However, run-up distance is underpredicted, indicating a need to improve the flame propagation mechanism. The predicted decrease in the fuel-specific impulse (Ispf) for the benchmark tube when compared to the I spf of an ideal tube may be attributed to nonuniformities in the mixture composition, the pressure drop resulting from internal geometry, and backflow in the benchmark tube due to a compression wave propagating into the upstream geometry.

IGNITION AND DETONATION INITIATION OF MOVING HYDROGEN-AIR MIXTURES AT ELEVATED TEMPERATURE AND PRESSURE

Experimental and computational studies of detonation initiation, using Deflagration-to-Detonation Tran sition (DDT) processes, were performed to investigate the effect of varying inlet parameters at elevated temp eratures and pressures on the run-up to detonation in hydrogen-air mixtures for a repeating detonation rig. It is found that the gasdynamic and chemical processes which effect the initial flame acceleration are the rate-li miting processes in determining the time scale of run-up t o detonation. A parametric study was performed in which the independent parameters of temperature, T (290 ‐ 615 K), pressure, P (1.0 ‐ 4.0 atm) and inlet fill velocity, Vb (10 ‐ 40 m/s) were systematically varied, and thei r effect on location, L DDT , and time of detonation, t DDT , initiation was quantified. A Pareto of effects in this parametric study shows variation in fill veloc ity and rig pressure have the largest effect on t DDT , while it shows variation in fill velocity and rig pressure followed by initial gas temperature have the largest effect on L DDT . Dimensionalized best-fit correlations were obtai ned from the test measurements for t DDT and L DDT as functions of P, T, and V. A nondimensional be st-fit correlations was obtained from the test measurements for t DDT as a function of key nondimensionalized independent variables, namely density expansion ratio α, a nondimensional length scale l/l F (where l is the integral length scale and l F is the laminar flame thickness) and a nondimensional velocity scale M (flow Mach number in the reactants) which govern the flow and chemical processes that occur during the DDT process.

An Experimental and Computational Study of Jet-A Fueled Pulse Detonation Engine Operation

An experimental and computational study regarding the operation of a Jet-A-fueled pulse detonation engine has been performed. In the experiments, liquid Jet-A fuel is injected into the head end of the engine in the form of atomized droplets. Preheated air serves to entrain and evaporate the fuel droplets, which are then spark ignited after traversing a finite length of pre-vaporizer section. The operation of the engine was investigated over a range of initial temperatures and pressures characteristic of high Mach-number operation or conventional gas turbine compressor discharge conditions. Pressure transducers and ionization probes were utilized to measure the absolute pressure rise and propagation speed of the combustion wave in order to verify detonation. Consistent and repeatable detonations have been observed in Jet-A / air mixtures at initial temperatures and pressures ranging from 225 - 312 F and 1.0 2.4 atm at frequencies up to 25 Hz. In addition, computational simulations of detonation propagation in an ideal-tube PDE fueled with Jet-A/air mixtures are presented.