Smoke-formation

As with secondary flame, the addition of potassium salts to the powder prevents the development of backflash. In modern guns of heavy calibre the development of backflash is prevented by blowing either air, or a stream of water through the barrel, immediately after each shot. 

Nitrocellulose and nitroglycerine powders should properly be called slightly smoky the name smokeless is inexact. The smoke from nitrocellulose and nitroglycerine powders is composed chiefly of water vapour. Shots from small arms or cannons of small calibre are slightly smoky or almost smokeless. Conversely guns of heavy calibre often give a considerable amount of smoke. The presence of metal torn off from inside the barrel and from the driving band in the products of combustion of the propellant is a partial cause of smoke. 

It has been observed that the majority of remedies for preventing the development of flash lead to an increase of smoke (e.g. potassium salts give white smoke, aromatic nitro compounds give black-grey smoke due to the presence of unburnt carbon). Nitroguanidine is the only additive that does not appreciably increase smokiness. The burning of blackpowder in the primer produces an insignificant amount of smoke. 

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Moreover, a limit to maximum density is set in order to avoid smoke formation at full load, due to an increase in average equivalence ratio in the combustion chamber. 

The smoke point corresponds to the maximum possible flame height (without smoke formation) from a standardized lamp (NF M 07-028). The values commonly obtained are between 10 and 40 mm and the specifications for TRO fix a minimum threshold of 25 mm. The smoke point is directly linked to the chemical structure of the fuel it is high, therefore satisfactory, for the linear paraffins, lower for branched paraffins and much lower still for naphthenes and aromatics. 

The vapor cloud of evaporated droplets bums like a diffusion flame in the turbulent state rather than as individual droplets. In the core of the spray, where droplets are evaporating, a rich mixture exists and soot formation occurs. Surrounding this core is a rich mixture zone where CO production is high and a flame front exists. Air entrainment completes the combustion, oxidizing CO to CO2 and burning the soot. Soot bumup releases radiant energy and controls flame emissivity. The relatively slow rate of soot burning compared with the rate of oxidation of CO and unbumed hydrocarbons leads to smoke formation. This model of a diffusion-controlled primary flame zone makes it possible to relate fuel chemistry to the behavior of fuels in combustors (7). 

Unlike the aircraft turbiae, the ground-based gas turbiae operates continuously at the same power setting, usually 60—80% of maximum power output except when starting. Air and fuel flow patterns are constant and the combustor can be tuned to minimise smoke formation and high metal temperatures. 

The burning pit is of simple constmction, with low capital and operating costs, and it can handle liquid as well as vapor hydrocarbons. Its use is usually limited by spacing requirements and smoke formation, and it is applied only in remote locations where there are essentially no pollution restrictions. 

Pollution Limitations - (i.e., smoke formation, malodorous or toxic combustion products, noise) which may be based on statutory and/or public relations requirements. 

A flare performance chart for the hydrocarbon being flared, should be consulted for additional guidelines on flare tip design. Figure 3 provides a provisional performance chart for propane. The chart defines the design envelop of exit velocities and steam ratios necessary to avoide smoke formation, excessive noise, flame boilover and flame lift-off. 

Normally an overcapacity line to an elevated flare is provided to handle the excess flow when the flaring rate exceeds the capacity of the multijet flare. The overcapacity flare is usually not equipped with steam injection, and smoke formation is accepted during infrequent operations. The overcapacity line and flare is designed to handle the entire maximum flow so that it can spare the multijet flare when the latter is shut down for maintenance. 

An important principle is that the coal becomes ignited from the fuel which is on top of it and further down the grate. This reduces carry-over of smalTunburned particles, as the burning coal on top filters them out. Volatiles released from the fresh coal are also ignited and consumed in the burning layer. This minimizes smoke formation which is caused by incomplete combustion of the volatiles. 

Trimerization to isocyanurates (Scheme 4.14) is commonly used as a method for modifying the physical properties of both raw materials and polymeric products. For example, trimerization of aliphatic isocyanates is used to increase monomer functionality and reduce volatility (Section 4.2.2). This is especially important in raw materials for coatings applications where higher functionality is needed for crosslinking and decreased volatility is essential to reduce VOCs. Another application is rigid isocyanurate foams for insulation and structural support (Section 4.1.1) where trimerization is utilized to increase thermal stability and reduce combustibility and smoke formation. Effective trimer catalysts include potassium salts of carboxylic acids and quaternary ammonium salts for aliphatic isocyanates and Mannich bases for aromatic isocyanates. 

The high-surface-area TUD-1 can serve as an anchor for many catalysts. Si- or Al-Si-TUD-1 (24,25) can be used as a support for various noble metals (Pt, PtPd, Ir, etc.). This will provide catalysts suitable for the hydrogenation of olefins and aromatics. In the refining industry, one use is the hydrogenation of polynuclear aromatics ( PNAs ) in diesel fuel, which can lower the fuel s toxic properties. Also, jet fuel has an aromatics constraint, designed to lessen smoke formation. Cracked stocks (e.g., coker or visbreaker liquids) generally have undesirable olefins (especially a-olefins) that also need to be saturated prior to final processing. 

Change the nature of the polymer combustion process to reduce smoke formation. 

E.B. Sanders, A.I. Goldsmith and J.I. Seeman, A model that distinguishes the pyrolysis of D glucose, D fructose, and sucrose from that of cellulose. Application to the understanding of cigarette smoke formation, J. Anal. Appl. Pyrol., 66, 29 50 (2003). 

In general, for NBS Smoke Chamber data, coated samples have a tendency to show an increase in smoke formation under non-flaming conditions. Smoke results under flaming conditions are unremarkable and specific coating dependent. 

An initial experiment involved determination of Arapahoe Smoke Chamber results for samples with and without the zinc coating present. Data are presented in Table II. Depending upon orientation of the sample, an increase in char occurred for some samples with zinc present, while no change in smoke formation was seen. Initial pyrolysis GC/mass spectroscopy results at 90CPC in helium showed no difference in volatiles formed with or without zinc. These results suggested enhanced char formation as the origin of the Radiant Panel results for zinc on modified-polyphenylene oxide (m-PPO). Zinc oxide is a known, effective thermal stabilizer in the alloy. The next work then focused on DSC/TGA studies. 

Smoke formation during combustion can be reduced if the aromatic content of the fuel is reduced. 

Low-temperature, low-speed, high-load operation can enhance smoke formation in diesel engine... 

The most important point is that this reaction does not contribute to smoke formation. However, smoke is formed due to the presence of ZnCl2 which is formed during the secondary reactions, as shown in Equation 5.14 ... 

COMBUSTOR INLET-AIR PRESSURE. Increased pressure accelerates smoke formation in both laboratory flames and combustors. Coke deposits are, in general, affected similarly. A leveling-off in deposit rate has been found once the pressure is increased to 2 to 3 atmospheres. This is attributed to increased rate of erosion with increased air density. Coke deposition would be expected to increase with pressure because smoke forms more readily at the higher pressures and because the evaporation of fuels is retarded. 

COMBUSTOR INLET-AIR TEMPERATURE. Inlet-air temperature has little or no effect on smoke formation. The influence of inlet-air temperature on coke deposition is a complex process depending on design, fuel used, and operating conditions. Different investigators have reported decreases, increases, maxima, and minima. The different basic processes resulting on coke deposition are important at different temperature levels. If the inlet-air temperature is above the temperature at which coke will bum, coke will not deposit on the hot metal surfaces. 

COMBUSTOR OVER-ALL FUEL-AIR RATIO. In general, coke and smoke both increase with increasing fuel-air ratio, although some investigations have shown that smoke can attain a peak point beyond which it decreases. However, the location of this peak value was variable and dependent on other factors. These fuel-air ratio effects can be attributed to more fuel wash on surfaces, richer local fuel-air ratios, and increased thermal cracking of the fuel. Increased burning and erosion might lower coke and smoke formation, however. 

Coke and smoke formation was found to increase up to an equilibrium level with increasing pressure, fuel-air ratio, and time of test. Variation in velocity and temperature produced conflicting results, with smoke and deposits increasing or decreasing, depending on operating conditions and design of the combustor. 

Smoke formation and coke deposition General reviews Theory of formation Effect of engine operating conditions... 

Vanadyl acetylacetonate (6) and vanadium pentoxide have been found to inhibit smoke formation in combustion tests on poly(vinyl chloride). The former is more active.5... 

When smoke formation accompanies traces of noxious vapors, it may be called a fume—for example, a metallic oxide developing with sulfur in a melting or smelting process. The term fume is also used in a more general way to describe a particle cloud resulting from mixing and chemical reactions of vapors diffusing from the surface of a pool of liquid. 

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