A simple gasdynamic model, called CHEMSHOCK, has been developed to predict the temporal evolution of combustion gas temperature and species concentrations behind reflected shock waves with significant energy release. CHEMSHOCK provides a convenient simulation method to study various sized combustion mechanisms over a wide range of conditions. The model consists of two successive suboperations that are performed on a control mass during each infinitesimal time step: (1) first the gas mixture is allowed to combust at constant internal energy and volume; (2) then the gas is isentropically expanded (or compressed) at frozen composition to the measured pressure. The CHEMSHOCK model is first validated against results from a one-dimensional reacting computational fluid dynamics (CFD) code for a representative case of heptane/O 2 /Ar mixture using a reduced mechanism. CHEMSHOCK is found to accurately reproduce the results of the CFD calculation with significantly reduced computational time. The CHEMSHOCK simulation results are then compared to experimental results, for gas temperature and water vapor concentration, obtained using a novel laser sensor based on fixed-wavelength absorption of two H 2 O rovibrational transitions near 1.4 µm. Excellent agreement is found between CHEMSHOCK simulations and measurements in a progression of shock wave tests: (1) in H 2 O/Ar, with no energy release; (2) in H 2 /O 2 /Ar, with relatively small energy release; and (3) in heptane/O 2 /Ar, with large energy release.
A quasi-one-dimensional, Euler model with detailed finite-rate chemistry is used to conduct a parametric assessment of nozzle area ratio effects on the single-cycle performance of a pulse detonation engine. Using results from the parametric study, design criteria are suggested for evaluating optimal contraction and expansion nozzle area ratios. In particular, the optimal expansion area ratio is shown to be well-predicted by using isentropic theory and the time-averaged, head wall pressure as the stagnation condition. To validate the parametric analysis, three nozzle sections are fabricated and tested in a single-cycle pulse detonation engine facility. Time-resolved thrust and specific impulse (I sp ) measurements are made for each nozzle and compared to simulated results. Additionally, schlieren imaging is used to investigate the blowdown gasdynamics in each of the three nozzles. Comparisons between simulated and measured impulse data are addressed using insights gathered from the flow visualization. Resulting analysis indicates that multidimensional wave phenomena are important in nozzles with converging sections. Overprediction of I sp by the model is attributed to deficiencies in accurately capturing the plateau pressure (P 3 ), as well as the inability to model the experimentally observed deflagration-to-detonation transition process. The relative contribution of each of these effects is quantified. Experimental measurements validate trends observed in the parametric study and reveal that an appropriately optimized diverging nozzle produces the largest single-cycle I sp .Nomenclature A exit =A throat = expansion area ratio A throat =A tube = contraction area ratio A i = species i A i = concentration of species i E = energy per unit volume F = convective flux vector F x = thrust g = gravitational acceleration h = enthalpy per unit mass I sp = specific impulse k b = backward rate coefficient k f = forward rate coefficient M = molecular weight m = mass nr = number of reaction equations ns = number of species p = pressure P amb = ambient pressure P fill = reactant fill pressure P head = head wall pressure P i = partial pressure of species i P o;avg = time-averaged P head P spark = spark region pressure P wall = internal gauge wall pressure P 3 = plateau pressure Q = area-variation source term vector R i = specific gas constant for species i S = flux surface t = time t cycle = time from ignition until P wall P amb U = state vector u = axial velocity v 0 i = stoichiometric coefficient of reactant v 00 i = stoichiometric coefficient of product W = species production rate vector Y i = mass fraction of species i = mass density
An experimental fire was conducted in 2016, in the Pinelands National Reserve of New Jersey, to assess the reliability of the fire pattern indicators used in wildland fire investigation. Objects were planted in the burn area to support the creation of the indicators. Fuel properties and environmental data were recorded. Video and infrared cameras were used to document the general fire behavior. This work represents the first step in the analysis by developing an experimental protocol suitable for field studies and describing how different fire indicators appeared in relation to fire behavior. Most of the micro- and macroscale indicators were assessed. The results show that some indicators are highly dependent on local fire conditions and may contradict the general fire spread. Overall, this study demonstrates that fire pattern indicators are a useful tool for fire investigators but that they must be interpreted through a general analysis of the fire behavior with a good understanding of fire dynamics.
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