Ethan A. Barbour

Hydrogen Peroxide Decomposition Rate: A Shock Tube Study Using Tunable Laser Absorption of H2O near 2.5 μm

The thermal decomposition of hydrogen peroxide was measured behind reflected shock waves in hydrogen peroxide/inert gas mixtures using a sensitive laser diagnostic for water vapor. In these mixtures, the formation rate of water is predominantly controlled by the decomposition rate of hydrogen peroxide. Rate determinations were made over a temperature range of 1000-1200 K and a pressure range of 0.9-3.2 atm for both argon and nitrogen carrier gases. Good detection sensitivity for water was achieved using tunable diode laser absorption of water at 2550.96 nm within its v(3) fundamental band. Hydrogen peroxide decomposition rates were found to be independent of pressure at 0.9 and 1.7 atm and showed only slight influence of pressure at 3.2 atm. The best fit of the current data to the low-pressure-limit rate for H(2)O(2) dissociation in argon bath gas is k(1,0) = 10(15.97+/-0.10) exp(-21 220 +/- 250 K/T) [cm(3) mol(-1) s(-1)] (1000-1200 K). Experiments conducted in a nitrogen bath gas show a relative collision efficiency of argon to nitrogen of 0.67.

Analytic Model for Single-Cycle Detonation Tube with Diverging Nozzles

An analytic model for quantifying the specific impulse of a single-cycle detonation tube fitted with a diverging nozzle is developed. The model takes advantage of the fact that the detonation tube is choked, thus enabling the straight-tube and nozzle impulses to be dealt with separately. No assumptions of steady flow are needed, and the model can be applied even for nozzles that are not pressure-matched to the environment. The model is validated against ballistic-pendulum measurements. Application of the model is demonstrated by identifying optimized area ratios over a wide range of pressures. The optimized area ratio is shown to be mainly a function of the ambient/ plateau pressure ratio P1=P3.

THE IMPACT OF A CONVERGING-DIVERGING NOZZLE ON PDE PERFORMANCE AND ITS ASSOCIATED FLOWFIELD

Performance impact of a converging-diverging nozzle on a pulsed detonation engine (PDE) is studied experimentally. Thrust and specific impulse are determined from integrated pressure measurements. Burned gas velocity is obtained from optical measurements of seeded cesium atom. Comparison of measured quantities with prediction from finite-rate chemistry computational fluid dynamics (CFD) models indicate heat transfer plays a significant role at late times during blowdown.

A Pulsed Detonation Tube with a Converging-Diverging Nozzle Operating at Different Pressure Ratios

A pulsed detonation tube (PDT) is operated at initial pressures equal to and greater than 1 atm in order to evaluate the effect of these pressures on the relative gains achieved by a converging-diverging nozzle, while the ambient pressure is maintained at 1 atm. Local heat flux is measured and is determined to play a significant role in overall energy release during blowdown, especially when a converging -diverging nozzle in implemented. With the addition of the nozzle, a decrease in Isp is observed at low initial pressures (near 1 atm) , whereas the nozzle becomes beneficial at higher initial pressures (above 2 atm) .

Chemical Nonequilibrium, Heat Transfer, and Friction in a Detonation Tube with Nozzles

Performance losses in the form of chemical nonequilibrium, heat transfer, and friction are investigated in the context of a detonation tube with nozzles using quasi-one-dimensional computational fluid dynamics. Finite-rate chemistry losses incur up to 10% penalty in overall cycle impulse for mixtures containing fuel and oxygen. These same losses are greatly reduced when oxygen is replaced by air because of reduced energy available through chemical recombination. Heat transfer and friction are less important, both for diverging and converging nozzles (∼5% overall cycle impulse). The exception is for H 2 /air where losses can be up to 15%. Finally, a method of predicting losses assuming steady flow nozzles, thereby greatly reducing computational cost, is explored.

Real-Time Measurements of C2H4 Concentration with Application to PDEs Operating on Oxygen and Air

An existing C2H4 sensor is enhanced by extending its range to low concentrations of C2H4 as well as by increasing its temporal resolution. The spectral absorption coefficient of C2H4 near 1626 nm is measured at various temperatures and mole fractions. The dependence of absorption coefficient on mole fraction is described in terms of broadening parameters. This database is used for fast (10 kHz) measurements of fuel concentration in a PDE which burns C2H4 with air. Two techniques of determining mole fraction are compared. Non-uniform distribution of fuel across the PDE diameter is quantified using a known difference in path length. The minimum measurable fuel mole fraction is determined and compared with practical limits on C2H4/air detonation.

UV Optical Diagnostics for PDE Applications

The time-resolved OH concentration and gas temperature are measured in the Stanford University pulse detonation tube facility using UV absorption spectroscopy. OH is monitored by direct absorption of the R21(5) and S21(1) transitions in the 0, 0 band of the A-X system near 306.5 nm using a CW ring dye laser source. A new technique based on a kinetic spectrograph is used to measure burned gas temperature from broadband UV CO2 absorption. Results from these diagnostics are useful in verifying computational simulations and in advancing PDE design and development.

The role of water in transient plasma ignition for combustion

Pulse detonation engines offer the potential for a single, air-breathing, propulsion system that can operate from subsonic speeds (including take-off) to high Mach number flight. Critical to this technology is rapid repetition rate operation. Plasma-based ignition systems based on short pulse, high voltage pulsed power have been shown to decrease the ignition time in experimental system. The presence of water in the fuel-air mixture, however, has been shown to adversely affect the performance of these ignition systems. Herein, we report on simulations of the plasma chemistry from the application of the pulsed power (10s of ns) through the ignition time (100s of microsecond). These simulations suggest a long-lived neutral species created by the transient plasma ignition process that are strongly affected by water, and can play a role in both combustion processes. Comparison with experimental results, potential mitigation schemes for the water effects, and implications for internal combustion engines will be discussed.

Mid-Infrared Gas Sensing For Combustion Applications

Progress is reported in the use of room-temperature, wavelength-tunable, solid-state mid-infrared (mid-IR) laser sensors for combustion and propulsion applications. Two such laser technologies have recently become commercially available: DFB tunable diode lasers near 2.7 μm and difference frequency generation (DFG) lasers near 3.3 μm. These lasers access the strong transitions in the fundamental O-H and C-H stretching vibrations as well as the ν1+ν3 and 2ν2+ν3 combination bands of CO2. These new laser sources provide the potential for sensitive detection of hydrocarbon fuels and combustion products H2O and CO2 in a wide variety of environments. Recent results in pulse detonation engines, laboratory flames, and shock-heated ignition experiments illustrate the potential of these tunable mid-IR laser sources for a wide variety of practical combustion applications.