Combustion-modifying additive

Ferrocene is a combustion-modifying additive especially for -+ Composite Propellants. 

Lead acetylsalicylate is a combustion-modifying additive, especially so in rocket propellants based on double base powder -> Double Base Propellants. 

Stone, H., Basics of Polyurethane Eoam and the Use of Combustion Modifying Additives, Polyurethane Eoam Association, presentation at San Erancisco meeting, April 29, 2003, http // www.pfa.org//EFC9 Handout.html. 

Other Additives. The addition of alcohols was found to give finecell foams. Flame retardants may also be added if combustion-modified foams are required. 

One of the additives being used in combustion-modified flexible polyurethane foams is melamine. Small-scale tests conducted at NIST indicated that a melamine-treated flexible polyurethane foam generated six times more HCN than an equal amount of foam that did not contain melamine. The presence of CuiO reduced the HCN from the melamine foam by 90%. Melamine-treated flexible polyurethane foam is one of two flexible polyurethane foams currently allowed in Great Britain. 

The application of NN in product design concentrates on a few classes of materials. The fuel additives have been used as combustion modifiers, antioxidants, inhibitors of corrosion, deposit controllers, etc. The authors have proposed a hybrid approach combining modeling and NN. The results obtained from modeling have been introduced into the net and compared with the experimental results. Such an approach enabled the tuning of the model allowing for the prediction of the build-up of the deposit as a function of the composition of the additives. 

The combustibility tests demonstrate that introducing PEDA into the compositions based on PVC resin promotes formation of a large coke layer the coating film does not bum, because the presence of nitrogen in the modifying additive enables an enhancement of the fire and heat resisting effect. 

Some technologies have identified other groups of additives. For example, for tobacco products combustion modifiers (activated carbon and ammonium chloride), substances for direct printing on cigarette paper, additives for chewing and snuff tobacco and others are used. 

The Octane Requirement Increase, ORI, is a phenomenon manifested by the appearance of knocking and is due to the increase in engine octane demand with time. This phenomenon is correlated with the increase of solid deposits in the combustion chamber. Although the causes have not been determined with certainty, some companies have patented additives which modify the deposits. The effect is to limit the increase in octane demand (Bert et al., 1983 Chevron, 1988 Nelson et al., 1989). 

In order for a soHd to bum it must be volatilized, because combustion is almost exclusively a gas-phase phenomenon. In the case of a polymer, this means that decomposition must occur. The decomposition begins in the soHd phase and may continue in the Hquid (melt) and gas phases. Decomposition produces low molecular weight chemical compounds that eventually enter the gas phase. Heat from combustion causes further decomposition and volatilization and, therefore, further combustion. Thus the burning of a soHd is like a chain reaction. For a compound to function as a flame retardant it must intermpt this cycle in some way. There are several mechanistic descriptions by which flame retardants modify flammabiUty. Each flame retardant actually functions by a combination of mechanisms. For example, metal hydroxides such as Al(OH)2 decompose endothermically (thermal quenching) to give water (inert gas dilution). In addition, in cases where up to 60 wt % of Al(OH)2 may be used, such as in polyolefins, the physical dilution effect cannot be ignored. 

Prior to shut down, switching to higher grade fuels for a week or so and increasing the use of soot blowers helps remove deposits from fireside surfaces. Additionally, fuel treatments such as combustion additives, slag modifiers, and anticaking agents may prove very useful. 

Because there seldom is only one specific problem associated with the fuel being used, most fuel treatments are blends of active agents, such as combustion improvers and slag modifiers. In addition, fireside problems tend to be interrelated, so that, for example, inefficient fuel combustion leads to heavy sooting in the combustion area and dry smutting from the exit gases. 

SNCR programs typically employing liquid additive formulations based on urea (carbamide, NH2CONH2), together with stabilizers and modifiers, are particularly useful. The additive is sprayed into the combustion area, after the burner. The use of such additives reduces the NOx level by between 50 and 90% by converting NOx into harmless nitrogen and water. 

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