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Titles and Abstracts for Issue 22, Winter 2005

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Interior Pressure in the Mortar and Motion of a No. 3 Shell in a Fireworks Shot
Yuzo Ooki, Dayu Ding, Masamori Higaki and Tadao Yoshida Department of Mechanical Engineering, Ashikaga Institute of Technology, 268-Omae-cho, Ashikaga-shi, Tochigi 326-8558, Japan

Abstract: Interior pressure in a fireworks mortar and initial velocity for the shot of a no. 3 shell were measured and results were analyzed. The observed initial velocity was mainly explained by the action of the interior pressure during the shot. On the other hand, a delay in pressure propagation in the mortar, the effect of gas flow through the gap between the mortar and shell, and acceleration of the shell just after leaving the muzzle were suggested.

Keywords: fireworks, shot, interior ballistics, initial velocity

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A Prediction of Aerial Shell and Comet Trajectories Using SHELLCALC©
John Harradine and Tom Smith
Manly, Queensland, Australia; Davas Ltd, 8 Aragon Place, Kimbolton, UK

Abstract: This paper describes a model for predicting the path of aerial shells and Roman candle comets. This model, incorporated in a Microsoft® Excel-based freeware program, SHELLCALC©, predicts the trajectory of these fireworks using point mass equations for range and height. These equations are modified to take into consideration mortar/candle angle, launch altitude above sea level, wind speed and direction, comet consumption, air density and terrain, and incorporate an approximation of shell drift through tumbling motion and mortar balloting. The graphical output from the model also incorporates typical shell burst diameters.

Keywords: shells, comets, ballistics, trajectory, fall-out

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Reaction propagation between fireworks shells and compositions confined in steel pipes
E. Contestabile and B. von Rosen
Canadian Explosive Research Lab, 555 Booth St., Ottawa, Ontario K1A 0G1, Canada

Abstract: This study presents the experimental results on the ignition of linear arrays of fireworks articles and bulk stars and describes their propensity to mass explode. Star and report shells, roman candles, and bulk cylindrical and spherical stars were functioned in steel pipes through initiation with a small black powder charge or an explosives booster. Continuous velocity of detonation probes was used to monitor the rate of reaction among the pyrotechnic components and the resultant fragmentation of the steel pipe was used to rate the violence of the reaction. All pipes fragmented and the measured reaction rate ranged from 170 to 870 ms-1. Based on fragmentation, the violence of reaction increased from the star shells, to the roman candles, to the report shells, and then to the bulk stars.

Keywords: explosion, steel, mortars, fragments, reports

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Thermodynamic and Spectroscopic Analysis of a Simple Lilac Flame Composition
B. T. Sturman and K. L. Kosanke
6 Corowa Court, Mount Waverley, Victoria 31 49, Australia;
PyroLabs, Inc., Whitewater, CO, USA

Abstract: A simple lilac flame composition consisting of 80% potassium nitrate and 20% shellac was investigated by emission spectroscopy and thermodynamic modeling. The flame from the burning composition had a reddish-pink core with a brighter pale lilac outer envelope. The core of the flame is presumably close to the equilibrium conditions predicted by thermodynamic modeling. The calculated equilibrium flame temperature is 1526 K; seven gases (CO, H2O, N2, CO2, H2, KOH, K) and one liquid (K2CO3) account for 99.7% of the molecules in the core of the flame. Of these, liquid potassium carbonate (mole fraction 9.6%) is expected to emit a continuous spectrum while atomic potassium (mole fraction 2.5%) imparts a red colour from the resonance doublet (766.491 and 769.897 nm), which is considerably broadened by self-absorption. The outer flame envelope is presumably a diffusion flame in which flammable gases from the core burn in entrained air. The maximum adiabatic temperature of such a flame was calculated as 1723 K; seven gases (N2, CO2, H2O, KOH, K, Ar, K2O2H2) account for 99.8% of the molecules in the outer flame envelope. The emission spectrum of atomic potassium superimposed on a continuous spectrum arising from the combining of atomic potassium with OH radicals to form gaseous KOH is responsible for the lilac colour of laboratory flames containing potassium and is the likely cause of the lilac colour of the outer regions of this pyrotechnic flame. The article includes a brief tutorial outline of some relevant aspects of the atomic spectroscopy of potassium.

Keywords: lilac flame colour, potassium nitrate, shellac, thermodynamic modeling, visible spectrum

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A Thrust and Impulse Study of Guanidinium Azo-Tetrazolateas a Fuel Additive for Hybrid Rocket Motor
Ann Wrighta, Warfield Teaguea, M. Keith Hudsonb, Andrew Wrightb, Patrick Foleyb
a
Department of Physics and Department of Chemistry, Hendrix College, Conway, AR 72032, USA;
bDepartment of Applied Science and the Graduate Institute of TechnologyUniversity of Arkansas at Little Rock, Little Rock, AR 72204, USA
Abstract: Guanidinium azo-tetrazolate (GAT) is an organic salt with a high percentage of nitrogen. GAT was mixed with the standard hybrid rocket fuel, hydroxyl-terminated polybutadiene (HTPB), in concentrations of 15% and 25% by mass. The fuel grains with the GAT additive were fired for 4 seconds with oxygen flows of 0.04, 0.06, 0.08, and 0.10 lbm/sec. Physical characteristics of the rocket were measured while firing the GAT fuels. Thrust, internal pressure, fuel mass consumed, oxygen flow rate, nozzle throat diameter, and fuel port radius were measured. Fuel regression rate, specific impulse, total impulse, and average thrust were calculated from the data.

GAT was found to increase the thrust output when added to the standard hybrid rocket fuel, HTPB. 25% GAT fuel produced approximately the same thrust as the 15% GAT fuel. Specific impulse was slightly lower with both 15% and 25% GAT fuels than with plain HTPB fuel.Standard deviation of thrust was used as a crude measure of amplitude of oscillations during combustion. GAT-added fuels showed a very small decrease in thrust oscillation amplitude.

Keywords: GAT, rocket, additive, motor

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Pressure in a Mortar and Estimation of Muzzle Velocity of Expelled Stars
Dayu Ding, Morimasa Higaki, Yuzo Ooki, and Tadao Yoshida Ashikaga Institute of Technology268-1 Omae-cho, Ashikaga-shi, Tochigi 326-8558, Japan
Abstract: Firing firework star experiments have been carried out using 20 mm and 25 mm inner diameter steel mortars equipped with two or four pressure transducers, and the pressure profiles were recorded. The relative pressure profiles of the four positions in the mortar changed with the gap ratio between sectional areas of the star and the mortar wall, and with the mass of the lifting charge. The maximum pressure attained decreased and the scatter of observed data increased with an increase of the gap ratio. It was shown by experiment using four pressure transducers that, when the gap ratio is large, the pressures to the rear and front of a star should be corrected for the pressure distribution in the mortar.

In the first half of the experiment, using two pressure transducers the muzzle velocity of a star was estimated from the pressure profile of the bottom transducer. When the gap between star and mortar wall and the mass of lifting charge were small, the calculated and observed muzzle velocities agreed well. However, in the case of a large gap, the calculated value was larger than the observed one.

In the latter half of the experiment, four pressure transducers were used and it was found that in the case of a large gap the pressure profile from the bottom transducer did not give the real pressures to the rear and front of the star in the mortar. A correction for the difference was tried and the agreement between the observed and calculated values was improved.

Keywords: fireworks, interior ballistics, pressure profile, muzzle velocity

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Notes on chlorinated rubber and some other chlorine donors
Barry T. Sturman
6 Corowa Court, Mount Waverley, Victoria 31 49, Australia

Abstract: A brief review is given of the history and technology of chlorinated rubber. The empirical formula is approximately (C10H11C17)n, corresponding to 65.4% Cl. The structure is complex, and includes partially chlorinated cyclohexane rings. All the Cl is released as HCl on pyrolysis. The enthalpy of formation was estimated from the reported heat of combustion as -395 kJ/mol. For comparison, the enthalpy of formation of solid polyvinyl chloride (C2H3Cl)n was reported to be -94.6 kJ/mol and that of solid polyvinylidene chloride (C2H2Cl2)n was reported to be -100.4 kJ/mol.

Keywords: chlorinated rubber, Parlon, enthalpy of formation, chlorine donors, PVC, polyvinyl chloride, polyvinylidene chloride

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Communications :
  • An Introduction to the European CHAF Project by D. Chapman
  • Abstract: The CHAF project was instigated following a series of accidents in large-scale storage of fireworks, by far the most serious being that at Enschede in the Netherlands. The project aims to quantify and suggest means to control the hazards associated with large-scale fireworks storage by small-, medium- and large-scale investigations on a series of well-defined fireworks. Additionally, it is hoped that correlations will be found between the small- and/or medium-scale tests results and those obtained in large-scale trials, and that these will lead to better test methods to predict mass storage hazards. Reports from the individual activities undertaken in the workpackages are posted on a dedicated web site www.chaf.info as they are delivered.

  • Review by Tom Smith of: Review of Firework Art by Mark Flemming
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