Titanium hydride potassium perchlorate (THPP), which is one of the most commonly utilized pyrotechnic initiators, can fail or deviate from the desired performance when subjected to aging. The aging ...process is known to change its composition as well as its thermochemical kinetics; however, the variation in the performance of THPP in terms of its combustion behavior has not been addressed. This experimental paper reports new correlations between the ignition and combustion characteristics of THPP. A thermal analysis, along with morphological observations, conducted on aged samples revealed that aging caused progressive oxidation of the fuels and subsequent decomposition of the oxidants. The reaction kinetics extracted using the isoconversional method pointed to a decrease in the activation energy due to thermal aging while the opposite was noted in the case of hygrothermal aging. In particular, an increase in the activation energy limited the range of ignition temperature and decreased the reactivity, thereby increasing both the ignition delay time and burn time. Such altered characteristics due to aging could lead to an inconsistent performance of the pyrotechnic initiators.
In this study, instantaneous measurement of fuel concentration and flame diagnostics in both liquid and gas hydrocarbon fueled flame is presented using a simplified laser-induced breakdown ...spectroscopy (LIBS) approach. The newly developed device or hereinafter the “plug” receives specified lines from the plasma emission without resorting to the conventional LIBS system. Bandpass filters and photodiodes were mounted in the plug to capture hydrogen (656 nm) and oxygen (777 nm) atomic lines. Since H/O intensity ratio has a linear relationship with fuel concentration, the plug’s calibration curve between equivalence ratio and H/O intensity ratio is constructed. Single phase and two-phase hydrocarbon fuel fields were measured with the device using gasoline (liquid) and LPG (gas). With the advantage of simplicity of the plug, multiple plasma points and plugs were simultaneously applied in the fuel field and showed possibility of using a single laser device to construct multi-points concentration mapping. Also, flame diagnostics scheme was proposed based on the observed difference of intensity duration between reactive and non-reactive fuel fields.
•A LIBS plug for being installed in operating engines was produced.•Hydrocarbon fuel distribution was detected with multiple LIBS plugs.•Reactive regions were identified from the decay time of the LIBS plug signal.•Instantaneous in-situ fuel property analysis of ‘any’ phase reactive flow is demonstrated.
A two-dimensional measurement of fuel distribution in a gasoline spray flow was performed using multiple laser-induced plasma-forming regions. Multiple plasma-forming regions were generated by a ...laser sheet with a low breakdown threshold for a two-phase flow. To observe the formation of multiple laser-induced plasma-forming regions, shadowgraphs were imaged using a high-speed camera. Hydrogen and oxygen atomic emissions from the plasma-forming regions were obtained by attaching bandpass filters to the high-speed camera, and a two-dimensional visualization of the fuel distribution in the wide plasma-forming region was obtained by dividing the hydrogen line-filtered image with the oxygen line-filtered image. The result complements a novel method for two-dimensional measurement of instantaneous fuel concentration in the reacting flow by utilizing laser-induced breakdown spectroscopy (LIBS).
When a point source detonation occurs, high temperature and pressure gases are released and then propagate through the open atmosphere as a blast wave. This leads to an explosive sound in the form of ...environmental noise, which has been known to cause hearing damage to nearby residents surrounding the explosion area. In an effort to reduce such noise levels, explosion test sites are installed with sound barriers to mitigate and minimize the noise associated with the blasts. In this study, realistic explosion pressure was calculated at an initial detonation source inside a concrete sound barrier, and a numerical prediction was made to evaluate the environmental noise propagation in an actual terrain. In particular, we applied the concrete equation of state to the governing conservation equations for a spherical detonation in a confined geometry and compared the experimental data taken within 3 m from the test site and a few kilometers away from the sound source. Moreover, the amount of noise reduction was predicted by first considering the absorbed explosion pressure by the sound barrier, which later dissipated at a far distance at which the noise propagation in an actual terrain was compared with the measurements.
When a high explosive detonates, a large amount of energy is released within a short time, creating a high-temperature and high-pressure environment accompanied by a blast wave. When the blast wave ...interacts with field obstacles such as building structures and ground soil, it produces a reflected wave. The complexity of the pressure field created by blast waves depends on the spatial characteristics of the explosion domain. To understand the blast wave characteristics in various environmental constraints, this study develops a large-scale hydrodynamic solver of shock wave propagation in complex spatial domains of two kinds. First, the propagation of a blast wave in large open spaces (20 m × 10 m area) was simulated using an adaptive mesh refinement technique programmed to capture the details of moving blast waves and multiple reflections. Second, a point source explosion in a two-room concrete structure (5 m × 7 m × 3 m) was simulated which makes use of the optimal merging of two equations of state, while a spherical detonation wave is stabilized before spreading into multiple rooms. The experimental data in both tests are used to validate the computational results presented.
In recent times, there is a growing interest in the development of electrically controlled solid propellants (ECSPs) because they offer various advantages over conventional solid propellants. ...However, the fundamental understanding on the complex reaction mechanism of decomposition/combustion of these ECSPs is still limited. The present study attempts to expand the knowledge on thermal decomposition mechanisms of ECSPs based on lithium perchlorate (LP) oxidizer and poly vinyl alcohol (PVA) binder, and to further investigate the influence of tungsten (W) as a metal additive, using thermal analysis. The chemical kinetic parameters for different metallized samples are obtained and compared with the non-metallized baseline propellant. Decomposition of non-metallized sample occurs over three stages involving primary reactions between molten oxidizer and pyrolysis products of PVA, and secondary gas-phase reactions overlapping with pyrolysis of unreacted LP. However, metallized ECSPs exhibit only single step decomposition that incorporates metal oxidation as well. It is obtained that the initial decomposition temperature of non-metallized ECSP is 349 °C with a heat release from the overall decomposition reaction of 2043 J/g. Addition of W increases this overall heat release up to 43% for ECSP-M1 containing 5% W, whereas the decomposition temperature is reduced by ∼60 °C, when compared to the non-metallized case. This indicates that the thermal stability of ECSPs is lowered due to the inclusion of W particles. Further increase in W content diminishes the overall heat release by 10% and 13% with correspondingly more unreacted samples, and rises the effective activation energy by 36% and 60% for ECSP-M2 and ECSP-M3, respectively, relative to ECSP-M1. Based on the present findings, we propose the global reaction mechanism for both non-metallized and metallized ECSPs.
A degradation in performance parameters related to thermal decomposition and combustion behaviour of tungsten based pyrotechnic delay composition can occur when subjected to accelerated aging ...conditions in a controlled environment. The present study utilizes various methods to quantify the extent of degradation in thermo-kinetic and burning characteristics as well as to postulate a fundamental aging mechanism for traditional tungsten (W) pyrotechnic delay material, which has not been attempted in the past. The delay composition based on metallic fuel (W) and perchlorate oxidizer is subjected to aging at constant temperature of 71 °C and 95% relative humidity, for 2 and 12 weeks, respectively. Experiments including thermal analysis, combustion temperature profile and burning rate measurements are conducted together with numerical simulation of an actual pyrotechnic delay device. Moreover, the reaction mechanism, chemical kinetics, and combustion behaviour between pristine and aged cases are examined. Results illustrate that there exist two aging induced processes, which increases the presence of large agglomerated particles, high metal oxide content by thickening the outer oxide layer of metallic fuel, and more unreacted oxygen to instigate incomplete combustion in aged samples. This alters the reaction pathway of combustion process, lowers average thermal conductivity, and reduces diffusion of reactants in aged samples, thus causing significant decrement in the heat of reaction (31%), combustion zone temperature (10%), reactivity (12%), and burning rates (10%), such that the overall pyrotechnic delay device experiences misfiring during operation or a failure in accomplishing its actual intended task.
•Large eddy simulation of hydrogen-enriched partially-premixed combustor is performed.•Effects of hydrogen composition on combustion instability are examined.•Flame-vortex interaction is identified ...as the key element of stability characteristics.
Large eddy simulations (LES) of a hydrogen enriched partially premixed gas turbine combustor are performed for various operating conditions for examining the fuel condition effects. The LES turbulence model and multi-step chemical mechanism of hydrogen-methane combustion are applied for simulating the three-dimensional swirling flame in the combustor. To confirm the adequacy of the numerical simulation, a comparison with the existing experimental data is conducted which indicates that hydrogen-enriched methane fuel conditions trigger unstable pressure fluctuations in the combustor. The analysis on pressure spectra and harmonic mode on the unsteady flame is performed to investigate the driving source of combustion instability. In the unstable case, rigorous vortex burning appears as unburnt mixture is periodically supplied into the recirculation zone. By considering the fuel composition and flow rate modifications, it is shown that hydrogen content and fuel flow rate play a dominant role in determining the flame structure and its combustion instability. If hydrogen content is increased or fuel flow rate is decreased, the flame structure changes and the flow field is stabilized. Then, vortex burning does not appear as flame is formed in a narrow region near the dump plane. Thus, the present investigation has identified the change of flame structure and its interaction with vortex field as the key features for understanding the combustion instability.
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