STUDY OF FUEL BEHAVIOUR UNDER PRESSURE AT THE EXTERNAL STIMULI

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1 202 Technical Sciences STUDY OF FUEL BEHAVIOUR UNDER PRESSURE AT THE EXTERNAL STIMULI Șerban Costin NICULAE * niculae.costin@yahoo.com Florin ILIE ** ilieflorinv@yahoo.com * Technical Military Academy, Bucharest, Romania ** Nicolae Bălcescu Land Forces Academy, Sibiu, Romania ABSTRACT The use of liquefied fuel (methane, propane, butane, etc.) as part of an improvised explosive device has not been studied in the literature, due to different requirements that must be met, among which we can mention: homogeneity of gaseous mixture, detonation limits of the gaseous mixture depending on the percentage of volumic participation of components etc. This document analyzes the possibility to release into the air the gaseous agent by shooting the containers of liquefied, under pressure fuels, with small caliber bullets (piercing and tracer) and study the initiation method of formed gaseous mixture. KEYWORDS: explosive atmosphere, combustion, explosion limits, tracer bullet 1. Introduction Many industrial operations or negligence in the use of pressurized containers containing flammable substances may give rise to unintended and inadvertent formation of explosive mixtures when a gas or fuel vapor is mixed with air. The purpose of this article is to explore the possibility of dissemination of fuel air under pressure and able to initiate their rapid heating. Have been tested 26 liter gas cylinders and LPG tanks produced by S.C. AEROSTAR S.A. from Bacău. According to SR 66:2007 LPG contains less than 9 % propane and 90 % butane minimum [1]. 2. Testing the Behavior of Pressured Fuel on Impact with S mall- Caliber Bullets Cylinders and pressurized fuel tanks were impacted by small-caliber bullets. Workload of cylinders and containers was between 10 % and 100 % of the maximum permissible mass. Combustible gas containers can be subject to the impact of high speed fragments or high speed bullets, which can generate gaseous agent release. For reasons of risk knowledge it is necessary to evaluate the response of the containers with liquid or gaseous fuel when these are impacted with bullets/projectiles.

2 Technical Sciences 203 Bullet impact test can only be a set of special conditions, because it is not possible to investigate a wide range of threats, using various attack weapons, using fragments of different sizes, with impact speeds and different angles from the cases that might be encountered in a real situation. For firing it was used a Beretta pistol caliber 9 mm and a H.K. assault rifle caliber 5.56 mm. The initial velocities of the bullets were 390 ± 12 m/s for 9 mm caliber and 890 ± 15 m/s for 5.56 mm caliber. The tests were carried out at a temperature of 26 C and a pressure of 996 mbar. Experiments have been made respecting the safety distances and they were recorded photo and video (Figure no. 1). Bullet Catche Support (Metallic boxes filled with sand) Cyllinder/Tank used for test Marked target Φ 10 cm Min 30 m Weapon installed on a support table Video camera Shelter (Protection screen) Fig. no. 1 Means Arrangement for the Execution of Tests On the impact with a tracer bullet LPG cylinder/container was perforated, without igniting the fuel. Using of small caliber bullets for piercing LPG cylinders/containers allows the dissemination of gaseous mixture

3 204 Technical Sciences without it s initiation. After dissemination of gaseous fuel into the air, it is possible to detonate the new formed mixture if this is found between the detonation limits. Fig. no. 2 Effect of Firing a Tracer Bullet on Butane Cylinder Fig. no. 3 Effect of Firing a Tracer Bullet on LPG Container Given the density of propane in the liquid phase (511 kg/m 3 ) [2, 3] and butane (581 kg/m 3 ) [4], at 18 C, as a result of the calculations, one liter of LPG in liquid state can be disseminated in more then 6 m 3 of gaseous atmosphere that can be within the explosion limits. LPG can be found bottled in pressured containers, which can exceed 80 liters, so the disseminated gas volumes can be significant. For components of liquified petroleum gas, in the literature we find the following parameters (Table no. 1) [5]: Table no. 1 Explosion limits for propane and butane [5] Fuel type The lower limit The upper limit of of explosivility (% v/v) explosivility (% v/v) Propan 2,2 9,5 Butan 1,9 8,5 3. Testing Fuel Behavior under Pressure from Rapid Heating It was evaluated the reaction and the occurrence time of reaction for a 26 liters stove gas cylinder and for a car LPG tank, on the action of an intense fire. Gas cylinders and car LPG tanks were tested in their usual configuration, as shipped by the manufacturer. In Figure no. 4 are presented the butane cylinder and the car LPG tank which have been tested and the device used to set them on fire.

4 Technical Sciences 205 Fig. no. 4 Photos of Test Configuration The test was performed in the fast heating device, which is a tank in which is disposed a layer of liquid fuel, above which it has been set the container (cylinder or car tank). The rapid heating device and the arrangement of the container is shown in Figure no. 5. Heating the bottle or container it will be performed on the entire surface located above the fast heating device. Fuel initiation is achieved by using electropyrotechnic primers. Test container Support Liquid Gas Water 30 ~ φ Electropyrotechnic primers Basin ~ 600 mm Support Electropyrotechnic primers ~ 600 mm Fig. no. 5 Fast Heating Device Diagram (Liquid Fuel Fire)

5 206 Technical Sciences In Figures no. 6 and 7 are shown the effects of heating the tested containers. Flames of violent combustion were measured about 4 m in most directions, and they were more pronounced in areas where cylinders/tanks succumbed to pressure. Fig. no. 6 Pictures Taken after 5 min 30 s, 5 min 31 s after the Onset of Fire (Butane Cylinder) Fig. no. 7 Picture Taken after 12 min 17 s after the Onset of Fire (LPG Container) After 5 min 30 sec and 12 min 17 sec since the ignition of the fuel located under the LPG tank it was achieved the ignition of butane/lpg as a powerful combustion. The formed mixture has not detonated because it was not within the appropriate limits of volume participation corresponding to explosivity (Table no.1). 4. Conclusions Firing small caliber bullets can disseminate a gaseous atmosphere, without achieving its initiation, even if the used cartridges got tracer or piercing bullet. To form an explosive aerosol, gas atmosphere should be disseminated in a confined space, in order to maintain the homogeneity of the mixture and the explosion limits. In open space these properties are lost in a very short time. Initiation by heating pressured fuels is achieved after long time (5-12 min) and takes the form of a powerful combustion. When heated, the pressure in pressurized containers rise until they brake and release the fuels mixture into the air. Mixed with air they enter in combustion. If the gaseous mixture would have detonated, inside the explosive aerosol would had been recorded overpressures of about bar [6], values which are comparable to those obtained by detonation of classic explosives, these values being also 100 % lethal [7]. REFERENCES 1. Dan Victor Cavaropol, Elemente de dinamica gazelor. Instalaţii de GPL şi GNL, (Bucharest: Publishing House of The Ministry of Interior, 2008), C.F. Beaton and G.F. Hewitt, Physical Property Data for the Design Engineer, (New York: Hemisphere Publishing Corp, 1989), 124.

6 Technical Sciences David R. Lide, CRC Handbook of Chemistry and Physics, (New York, 2003), Daniel A. Crowl, Understanding Explosions, (USA, 2003), Ibidem, D.A. Goga, Legi de similitudine la explozie, (Bucharest: Technical Military Academy Publishing House, 2000), 58. BIBLIOGRAPHY Beaton, C.F., and Hewitt, G.F. Physical Property Data for the Design Engineer. New York: Hemisphere Publishing Corp, Cavaropol, Dan Victor. Elemente de dinamica gazelor. Instalaţii de GPL şi GNL. Bucharest: Publishing House of The Ministry of Interior, Crowl, Daniel A. Understanding Explosions. USA, Goga, D.A. Legi de similitudine la explozie. Bucharest: Military Technical Academy Publishing House, Lee, E.L., H.C. Hornig, and J.W. Kury. Adiabatic Expansion of High Explosive Detonation Products. California: University of California, Lide, David R. CRC Handbook of Chemistry and Physics. New York, Orban, Octavian, and Doru-Adrian Goga. Fizica exploziei Culegere de probleme. Bucharest: Technical Military Academy Publishing House,