Burning Rate Curves Research Articles

Realization of quasi-steady-state piled smouldering using sequential operation chambers for industrial treatment of biomass wastes.

Piled smouldering has great potential for treatment and utilization of biomass wastes. However, its unsteady-state nature limits its industrial utilization, as well as treatment of smoke. This article addresses this issue by proposing the sequential operation of numerous smouldering chambers to realize steady- or quasi-steady-state piled smouldering. The superposition characteristics of sequential unsteady-state curves were analysed theoretically, and a code was developed to determine an appropriate number of piled chambers at an allowance oscillation percentage. Smouldering experiments were performed on a single mini chamber (length × width × height: 340 × 140 × 140 mm3) containing piled wood pellets mixed with wood powder. The superposition of sequential burning rate curves was demonstrated using the code based on the mass loss data of experiments. Analysis shows that the perfect-steady state is possible given the superposition value of the burning rate curve is a constant in this proposed system. Experiments show that the molar ratio of CO/CO2 in smoke is almost a constant around 0.5 during densely piled smouldering, showing the great potential for self-sustained burning out the smoke. Based on the experimental results, the calculation results show that the relative oscillation range of burning rate (OSC) decreases from 75% to 3% while increasing the number of chambers from 2 to 7. This work provides a novel technology to enable quasi-steady-state smouldering for industrial utilization.

Closed vessel burning rate measurements of composite propellants using microwave interferometry

AbstractBurning rate as a function of pressure is one of the primary evaluation metrics of solid propellants. Most solid propellant burning rate measurements are made at a nearly constant pressure using a variety of measurement approaches. This type of burning rate data is highly discretized and requires many tests to accurately determine the burning rate response to pressure. It would be more efficient to measure burning rate dynamically as pressures are varied. Techniques used to make transient burning rate measurements are reviewed briefly and initial results using a microwave interferometry (MI) technique are presented. The MI method used in tandem with a closed bomb enables nearly continuous measurement of burning rates for self‐pressurizing burns, capturing burning rate data over a wide range of pressures. This approach is especially useful for characterization of propellants with complex burning behaviors (e. g., slope breaks or mesa burning). The burning rates of three research propellants were characterized over a pressure range of 0.101–24.14 MPa (14–3500 psi). One research propellant exhibited a slope break at a pressure of 6.63 MPa (960 psi). Using MI in a closed pressure vessel, 14 propellant strand burns resulted in a nearly continuous burning rate curve over a pressure range of 0.41–24.13 MPa (60–3500 psi) that reasonably matched conventional burning rate measurements. The development of this technique provides an opportunity to quickly characterize the burning rate curve of solid propellants with greater fidelity and efficiency than traditional quasi‐static pressure testing techniques.

Burning Rate Characterization of Ammonium Perchlorate Pellets Containing Micro- and Nano-Catalytic Additives

Ammonium perchlorate (AP) is a common oxidizer in composite propellants, and its combustion behavior can be tailored by micro- and nano-metal oxide catalysts. Ammonium perchlorate pellets were manufactured with micro- and nano-titanium oxide () and iron oxide () at several mass loadings (0–3%) to isolate their effects on AP. The samples were burned from 3.45 to 34.5 MPa (500–5000 psi) in a constant-volume strand bomb. Microscopy characterization was completed for both additives and representative pellets. The incorporation of 1% micro- yielded the highest burning rate within the investigated pressure range. All micro-additive formulations increased the burning rate at pressures ranging from roughly 13.45 to 17.24 MPa (1950–2500 psi) and from 4.50 to 8.60 MPa (650–1250 psi) for micro- and micro-, respectively, and these effects were dependent on catalyst mass loading. The burning rates were increased at pressures greater than 11.27 (1620 psi) and 8.27 MPa (1200 psi) for nano- and nano-, respectively. Both nano-additives yielded burning rates that were independent of mass loading within the range of evaluated concentrations (0.25–1%). In all cases, the presence of the catalytic additives removed the negative slope generally observed in the burning rate curve of plain AP. Higher low-pressure deflagration limits were observed for nano-additive formulations, potentially due to radiative heat losses.

Isolating the effects of oxidizer characteristics and catalytic additives on the high-pressure exponent break of AP/HTPB-Composite propellants

AP/HTPB-composite propellants are widely used in the field of energetics due to their burning rate controllability using a variety of formulation variables. At higher pressures, the burning rate becomes less controllable as it experiences a transition regime often referred to as an “exponent break” typically between 20.7 and 34.5 MPa. The pressure exponent drastically increases to values greater than 1, making the burning rate extremely sensitive to pressure fluctuations. This study systematically evaluated the effects of catalysts on the exponent break and high-pressure burning rates of AP/HTPB-composite propellants containing a variety of AP particle sizes, distributions, and concentrations. The burning rates of seven formulations with varying AP characteristics and either Mach I iron oxide or titania nanoparticles or in-situ titania as a catalyst were evaluated between pressures of 6.89 MPa and 68.9 MPa. All formulations with the exception of two, 46.0-µm AP with Mach I titania and 138.9-µm AP with 0.50% in-situ titania, showed an exponent break. For the others, the characteristic pressure where the exponent break occurred changed with the inclusion of the catalysts, increasing it to 34.5 MPa and higher. The characteristic pressure was found to be dependent on the corresponding baseline burning rates, occurring where the additive burning rate curve intersected with its respective baseline burning rate curve. Additionally, all the burning rates fell above the AP deflagration rate curve, corroborating the existence of an AP barrier and the general theory in the literature that AP decomposition dominates in the very-high-pressure regime. This study adds new data to the severely limited database for very-high-pressure, AP-based, composite propellant burning rates in the open literature and provides one of the first fundamental studies on the exponent break feature with emphasis on the role of mixture variables and catalytic additives on the characteristic break pressure and the post-break pressure exponent.

Effects of nano-scale additives on the linear burning rate of nitromethane

This paper examines the effects of various nanoparticle additives on the combustion behavior of nitromethane, using a pressure-based method recently demonstrated by the authors to measure the linear burning rates of liquid monopropellants and heterogeneous mixtures with high precision. The linear burning rates of these mixtures were measured in a constant-volume system at chamber pressures ranging from 3 to 14 MPa, all without direct observation of the burning front. Nano-scale aluminum was used to increase the overall energy density of the mixture, fumed silica powder was used to increase the mixture thickness and encourage aluminum suspension, and nano-scale titania was also included based on its previous use as a burning rate modifier in solid propellants. The silica loading was varied from 1% to 3% by weight, aluminum was varied from 5% to 13.5% by weight, and titania was added at 1% by weight. The use of fumed silica yielded increased burning rates compared to those of neat nitromethane, and the pressure exponent of the burning rate curve shifted from lower to higher than the nitromethane baseline as more silica was added. This increased pressure sensitivity for mixtures containing 3% silica by weight was previously unobserved in similar studies by other groups and may be an effect of the higher specific surface area of the currently used silica. The subsequent addition of aluminum led to even faster burning rates and higher pressure exponents for all but one mixture. The addition of titania also led to elevated burning rates, with dramatically increased pressure sensitivity and rate inconsistency for chamber pressures above approximately 8 MPa but a decreased pressure sensitivity for the same mixture below 8 MPa. These changes in combustion behavior that accompanied titania were diminished by the presence of aluminum and completely negated in mixtures also containing fumed silica.

Multi‐Parameter Study of Nanoscale TiO2 and CeO2 Additives in Composite AP/HTPB Solid Propellants

AbstractA statistical Taguchi L8 matrix was used to conduct a multi‐parameter study of the use of nanoscale additives in composite solid propellants. The additives studied were TiO2 (titania) and CeO2 (ceria). The other parameters involved in the experiment were the oxidizer loading and distribution, additive percentage and size, additive size (nano‐scale or μm‐scale), and the mixing method. Four baseline propellants without additives were also produced for comparison. The propellants were tested from 3.45 to 13.78 MPa in a strand bomb, and burning rate curves were determined for all formulas. By analyzing the Taguchi matrix, the sensitivity of each parameter according to the pressure sensitivity and burning rate of the propellant was calculated. The dominant factors depend on whether the additive is needed for modifying the pressure index or the absolute value of the burning rate. In general, the effectiveness of the additives was most influenced by oxidizer percentage, oxidizer size distribution, and additive type. The amount of additive, mixing method, and additive size all had relatively minor impacts on the effectiveness of the additives.

Nano Additives and Plateau Burning Rates of Ammonium-Perchlorate-Based Composite Solid Propellants

Plateau propellants exhibit burning rate curves that do not follow the typical linear relationship between burning rateandpressurewhenplottedonalog–logscale,andbecauseofthisdeviation,theirburningbehaviorisclassifiedas anomalous burning. This paper contains a literature review chronicling the last half-century of research to better understand the mechanisms that govern anomalous burning and to shed light on current research into plateau and related propellants. In addition to the review, a series of experiments investigating the use of nanoscale TiO2-based additivesinammonium-perchloratehydroxyl-terminatedpolybutadienecompositepropellantswasperformed.The baseline propellant consisted of either 70 or 80% monomodal ammonium perchlorate (223 � m) and 30 or 20% binder composed of isophorone-diisocyanate-cured hydroxyl-terminated polybutadiene with Tepanol. Propellants were tested using a strand bomb between 3.45 and 17.24 MPa (34.0–170.1 atm). Analysis of the burning rate data shows that the crystal phase and synthesis method of the TiO2 additive are influential to plateau tailoring and to the apparent effectiveness of the additive in altering the burning rate of the composite propellant. Some of the discrepancy in the literature regarding the effectiveness of TiO2 as a tailoring additive may be due to differences in how the additive was produced. Doping the TiO2 with small amounts of metallic elements (Al, Fe, or Gd) showed additional effects on the burning rate that depend on the doping material and the amount of the dopant. This work providesthe firstpublishedpropellantmixturesandburningrateresultsforcompositepropellantsemployingmetaldoped nanoparticle additives.

Pressure and temperature effects on burning rate of the silicon - red lead system

The effects of ambient pressure ranging from 101 up to 3040 kPa and temperature from 233 up to 353 K on burning rate of both high and low fuel content Si-Pb3O4 mixtures have been investigated. Also tests have been made to further reduce pressure effects using additions of metal fluorides. Sodium and calcium fluorides applied diminished the pressure dependency of burning rate for the low fuel content mixture, while for that containing high amount of silicon they left it almost unaffected. This different behavior of the mixtures could be probably attributed to the difference in their combustion mechanism. Ambient temperature influenced the rate of burning in dependence on fuel content too. Temperature coefficients determined consist well with the assumption on prevailing solid state reaction mechanism of Si-Pb3O4 system, which is on the other hand complemented for silicon poor mixes with convective transport of heat. Pressure coefficients have not been calculated because of rather irregular shape of pressure - burning rate curves but the dependency is clearly recognizable for both the mixtures although the pressure influence on rate of burning was not very heavy, which is to be expected for this typical delay composition.

An improved model for the combustion of AP composite propellants

This paper presents several improvements in the Beckstead-Derr-Price model of steady-state burning of AP composite solid propellants. The Price-Boggs-Derr model of AP monopropellant burning is incorporated to represent the AP. A separate energy equation is written for the binder to permit a different surface temperature from the AP. The discussion includes an analysis of the sharing of primary diffusion flame energy and a correction in treating the binder regression rate. A method for assembling component contributions to calculate the burning rates of multimodal propellants is also presented. Results are shown in the form of representativ e burning rate curves, comparisons with data, and calculated internal details of interest. Ideas for future work are discussed in an Appendix.

The measurement of the burning rate of an individual dowel in a uniform fuel matrix

The weight of an individual dowel was measured as a fire swept through a matrix fuel bed. The burning rate curve was determined for a number of centre to centre distances, fuel bed widths, dowel lengths and dowel diameters in both still air and a uniform wind. The burning rate curve was found to be approximtely Gaussian for the 2.5 mm diameter dowels. As the dowel diameter increased the burning rate curve deviated from a Gaussian distribution with the largest deviation occurring for the largest diameter dowels studied, 12.7mm. The burning time, defined as the time between 80% and 20% initial weight was found to be independent of wind velocity and proportional to the diameter of the fuel to the 3/2 power.