An Analysis Of Cigarette Ignition Environmental Sciences Essay

An Analysis Of Cig bette Ignition Environmental Sciences auditionHydrogen or deuterium botch up when mixed humorh air or oxygen forms a exceedingly flammable mixture over a round-eyed fly the coop of proportions they also form flammable mixtures with chlorine and the oxides of nitrogen, shape up, they impart also react spontaneously with fluorine and chlorine trifluoride.Because it is impossible to take on that any system al impression for be completely leak loosen every effort should be made to exclude all line of descents of redness. The origin and the user should give cargonful consideration to the risk from a wide variety of fervor sources e.g. smoking, flames, tempestuous draw nears, electrical and opposite sparking, static electricity, shock, impact, catalytic and chemical action.,Thus flatulency drying up mixed with air has a lower flammability strangle of just over 1% and an upper limit of 6% by raft petrol vapour in air, at normally encountered temperat ures. Concentrations below the lower limit are said to be lean mixtures and those above the upper limit rich mixturesFlammabilityFor flammable liquids with flaunt point temperatures above normal ambient, e.g., kerosene, white spirit and diesel oil, an fervour source has to ignite non scarce the flammable mixture of terminate vapour scarce to generate this mixture in the first dwelling house by heating the bulk liquid.Ignition agreeA further factor in the mechanism of kindling of gaseous statees and blue devils is the ignition delay time or induction period, that is the time period between bring a potentially flammable mixture to a condition w here it go away ignite,Ignition delay times are dependent on temperature and are reduced with an increase in temperature.Cigarette composition and combustion piece of writingThe most commonly encountered, patch upd can consists of a cylindrical jam-packed bed of 1 g of shredded tobacco plant enclosed in paper and is generally 8 mm in diameter and 65 mm to 85 mm massive. The strands of tobacco are non-uniformly packed and the volume of the scarcelyt consists of well-nigh 75 percent free space. Often a smoke filter is attached and this is typically 20 mm long and contains cellulose acetate, paper fibres and sometimes char burn.The Virginia tobacco typically used in the manufacture of British cigarettes contains less(prenominal) than 0.1 % of nitrates.One obvious difference in their anxious characteristics is that hand-rolled cigarettes tend to go out unless puffed by the smoker, whereas a cigarette with tightly packed tobacco will smoulder for about xx delicates with no assistance from the smoker. The experimental work reported here and the discussion relates to manufactured cigarettes.The smoke itself consists of mainstream smoke, from the supreme gas chassis temperature (850C) was at the centre butt end of the cigarette during suction by a smoker, and. sidestream smoke during the smoking cycle. Th e term used here for the suction or drawing process during smoking is puffing of the cigarette. One puff of a cigarette is, there- the fore, ane suction or draw by the smoker. there are two main regions at the tip on the coal, videlicet the combustion z hotshot A and the pyrolysis and distillation zone B. Combustible vapours are produced in zone B prior to ignition in zone AIn the interval between puffs, the natural convection issue of air around the combustion coal in an upwards focussing sustains have a fiting, and forms the sidestrearn smoke.Baker 33 employed two different methods of measurement, one for the solid build and one for the gas point, and his results are generally accepted as creation representative of the temperatures encountered inside a earnest cigarette tip.smoking machine, victorious a 35 cm3 volume of 2 sec duration, once per minuteof both the gas and solid phases, were determined. These temperatures can, therefore, be regarded as approaching the max imum attained during the drawing of a cigarettesurprisingly, the maximum solid phase temperature in the area region of 900C-950C was attained at the points of maximum air flow, i.e., 0.2 mm to 1 mm forward of the paper burn line. This is the area of the cigarette where a distinct pale red luster can be seen when a cigarette is puffed. The maximum gas phase temperature (850C) was at the centre of the cigarette coal.Ignition of gases and vapours by het up surfacesAlthough the tip of a cigarette cannot be treated simply as a hot surface in a discussion about its potential to ignite pumps, it is useful to consider such an ignition source and the combustion parameters touch on. Powell has reviewed much detailed experimental work on hot surface ignition 42, and the results provide an insight into some of the reasons for ignition or otherwise of flammable gas and vapour mixtures by a lighten up cigarette.Some of the factors involved in the ignition of flammable mixtures of vapour or g as by hot surfaces are temperature of heated surface sense of touch time of gas and surface movement of gas composition of surface shape and size of surface chemical nature of substance ignition delay time.Ignition of gases and vapours by lighted cigarettesExperiments carried out at the US Bureau of Mines found that a smoked (puffed) cigarette would only ignite methane air mixture if the latter were caused to flow across the enthusiastic cigarette at 1000 ft per min. Attempts were made to ignite propane, petrol and butane with lighted cigarettes without success and similar results were obtained with white spiritLaboratory studies of ignition by a lighted cigarette were carried out by Yockers and Segal scrutiny the liquids blow disulphide, ethyl ethoxyethane, benzene, toluene, xylene, acetone,methylethylketone, amylacetate, ethylacetate, ethyl benzene, ethanol, methanol, petroleum ether, petrol and Stoddard solvent (white spirit) 50. They suggested that it superpower be though t that a cigarette would ignite these substances as their ignition temperatures were lower than those encountered in the burning tip of a cigarette. Carbon disulphide was pronto burn and ignition also occurred during one of the tests with toluene. Ignition of toluene could not be achieved, however, in several subsequent tests under the conditions which prevailed during the one ignition. It was speculated that this one ignition was perhaps owing to a hot spot when a solid chunk of tobacco seems to spit or sizzle. (It was later suggested that as some tobaccos in the USA contain nitrates, a concentration of this substance could give rise to a hot spot as describe in Yockers and Segals paper.) They also tried without success to ignite natural gas (mostly methane), butane and acetylene.Carbon disulphide, acetylene, ethylene oxide, hydrogen sulphide and hydrogen phosphide were readily light.Diethyl ether was ignited but only in a closed vas and after a long delay. Included in the subst ances which were not ignited were methane, butane, benzene, hexane and cyclohexane.In 1989 scientists at the Research and Technology Division of British splash studied the effects of lighted cigarettes on methane and ethylene. Six tests were carried out wit smoked cigarettes in natural gas-air mixtures over a concentration range of 5.6% (v/v) to 9.6% (v/v) natural gas in air tests were also carried out with ethylene-air mixturesFlammability limitsThe low values of the upper flammable limits of methane, gasoline and propane suggest that in the burning tip of the cigarette or indeed at the surface, oxygen is not present in a sufficient concentration to allow ignition. At the temperatures encountered (700C to 950C), the upper limit would be much higher than those quoted for ambient temperatures but insufficient oxygen molecules are present. Some regions of the cigarette coal are virtually depleted of oxygen and in other areas less than 10% oxygen by volume was measured.In addition to this, nose candy dioxide is produced during the combustion of the tobacco and it has been shown by Jones et a1 54 that gasoline vapour-air-carbon dioxide mixtures are non-flammable when the concentration of carbon dioxide in the mixture exceeds 28.9% by volume. Although some combustible gases such as carbon monoxide and hydrogen are produced, inside the cigarette coal there is a reducing atmosphere depleted in oxygen.A cigarette tip does not, therefore, have sufficient heat energy both to cartoon strip off vapour from the liquid surface and to ignite the air vapour mixture produced.Auto-ignition temperatureFor a burning cigarette, a given parameter involved in the combustion process cannot be discussed in isolation from the others but for ignition by hot surfaces the number of these factors is reduced. It has been found that at the temperatures encountered in a cigarette where the smoulder is stable (ca 700C to 775C) ignition of methane and gasoline by a hot surface in this temper ature range is highly unlikely. For methane, temperatures in excess of 1,000C are needed for ignition. Temperatures in the region of 900C to 950C are generated when a cigarette is puffed, so even at this elevated temperature methane would not be expected to be ignited.During the puff of a cigarette in a flammable atmosphere there will be a continuous flow of fuel and air wasted into the combustion zone. Only substances with short ignition delay times, of around 1 millisec or less, at the temperatures encountered in the cigarette, will be expected to be ignited. For substances with long ignition delay times cooler reactants would be sweep into the path of reacting fuel and oxygen molecules, before a flame could diffuse through the mixture.Namely that methane and gasoline constituents are not ignited, diethyl ether is but after a long delay and hydrogen and carbon disulphide are ignited.Quenching distanceThe ignition of flammable gases and vapours will believably take place in the airlgas space between the glowing tobacco fibres. It is possible that some substances are ignited in this region but the flame does not propagate to the flammable gas outside the cigarette. invitee 44 found that some surfaces, which formed a layer of scale or ash, e.g., iron or impure carbon, did not ignite natural gas mixtures with ease, and that surfaces which were strongly catalytic or possessed an interstitial structure requisite higher temperatures. This latter effect could be similar to the flame stunning property of a fine-mesh wire gauze (e.g., as in the DavyLamp). passion is conducted away by the gauze from the reacting gaslair mixture, lowering the temperature of the reactants and preventing the progression of flame to unburned fuellair mixture. This phenomenon is think to the quench distance of the fuel and these distances for stoichiometric mixtures of fuels (at 20C and one atmosphere) tested by cigarettes are given in Table 2 57 and 58. The substances which are ig nited by a cigarette have the shortest extermination distances. These are the substances where, because of their reactivity, the loss of heat or destruction of reacting molecules at a boundary is not significant until the dimensions of the boundary are small. As with the other parameters discussed, this alone cannot provide an explanation why some substances are ignited and others are not. For example diethyl ether, which is ignited by cigarettes, has a greater quenching distance than hexane, which is not ignited.