Reduced-smoke propellant

AP composite propellants without aluminum particles are termed reduced-smoke propellants and are employed in tactical missiles to conceal their launch site and flight trajectory. No visible smoke is formed when the relative humidity of the atmosphere is less than about 40%. However, since high-frequency combustion oscillation tends to occur in the combustion chamber in the absence of solid particles that serve to absorb the oscillatory energy, a mass fraction of 0.01-0.05 of metallic particles is still required for the reduced-smoke propellants. These particles and/or their oxide particles generate thin smoke trails. The white smoke trail includes the white fog generated by the HCl molecules and the condensed water vapor of the humid atmosphere. 

Thus, AP is a valuable oxidizer for formulating smokeless propellants or smokeless gas generators. However, since the combustion products of AP composite propellants contain a relatively high concentration of hydrogen chloride (HCI), white smoke is generated when they are expelled from an exhaust nozzle into a humid atmosphere. When the HCI molecules diffuse into the air and collide with H2O molecules therein, an acid mist is formed which gives rise to visible white smoke. Typical examples are AP composite propellants used in rocket motors. Based on experimental observations, white smoke is formed when the relative humidity exceeds about 40 %. Thus, AP composite propellants without any metal particles are termed reduced-smoke propellants. On the other hand, a white smoke trail is always seen from the exhaust of a rocket projectile assisted by an aluminized AP composite propellant under any atmospheric conditions. Thus, aluminized AP composite propellants are termed smoke propellants. 

Flynn, S., Fossey, D.R., Catton, D.G., and Wagstaff, D. (1998) Evaluation of poly(NiMMO) in reduced smoke propellants. Proc. 29th Inti Ann. Conf. ICT, Karlsruhe, Germany, June 30-July 03,1998, Paper 42. 

Reduced Smoke. Propellants without metals or primary smoke, but containing oxidizers such as AP which gives HC1 gas as a principal combustion product, are called reduced smoke propellants. If HC1 is exhausted in atmospheres of high or moderate humidity, water droplets will coalesce about the HC1 molecules, resulting in a visible exhaust trail of what is called secondary smoke. In atmospheres of low humidity, the exhaust plume of reduced smoke propellants is not visible. 

The addition of AP particles within AN-PU propellants increases the burning rate and reduces the pressure exponent without catalysts. The specific impulse is also increased from 225 s to 235 s at 10 MPa by the replacement of 30% AN by the same amount of AP. However, the smokeless nature is eliminated because of the production of HC1, and these propellants are classified as reduced smoke propellants. 

The proplnts described above are in the realm of prior art and depict those NC proplnts with low smoke potential that are used primarily as gun proplnts. Recent research and development work has been concentrated on creating both gun proplnts and rocket proplnts with reduced smoke output in order to foil countermeasures. Lavitt (Ref 76) found that the concurrent use of optimum proportions of lead stearate and sodium barbiturate in double-base proplnts resulted in a marked reduction in smoke output. This was attributed to the synergistic interaction of the two salts to produce more complete oxidation of the exhaust products. The importance of using the optimum ratio of the two catalysts is demonstrated by the higher smoke values shown in Table 4 for Propellants 105, 106 and 107, when compared to other... 

Eiselle, S., and Menke, K. (2001) About the burning behaviour and other properties of smoke reduced composite propellants based on AP/CL-20/GAP. Proc. 32nd Inti. Ann. Conf. of ICT, Karlsruhe, Germany, July 03-06, pp. 149/1-149/18. 

Addnl Reports on the Use of DNT Not Used in this Article A) C.S. Davis, Develop Improved Caliber. 50 Propellant of Modified Composition to Reduce Smoke , PATR 343 (1933)... 

Classification of Propellents Based on Exhaust Properties. Based on the exhaust properties, solid propellants can be classified as smoky, reduced smoke, minimum smoke, or minimum signature propellants. The description of these categories are listed as follows ... 

Powell J (2005) Reduced vulnerability minimum smoke propellants for taetieal roeket motors. In 41st AIAA/ASME/SAE/ASEE joint propulsion conference and exhibit, Tueson... 

Secondary smoke is produced mosdy by the condensation of water in humid or cold air. The presence of hydrogen chloride or hydrogen fluoride in the combustion products increases the extent and rate of condensation. Composition modifications to reduce primary smoke may reduce secondary smoke to some extent, but complete elimination is unlikely. The relatively small amount of smoke produced in gun firings by modem nitrocellulose propellants, although undesirable, is acceptable (102—109). 

In propellants (see Propellants, Solid in this Vol), some of the work reported by Dunkle (Ref 6) examined the addn of flash reducing agents versus smoke evolved in propint compns for the cal. 50 rifle. The oxides examined included aluminum oxide, stannic oxide, silicon dioxide, ferric oxide and, after proplnt ignition, nickel... 

For instance, Hale Audrieth(Ref 9) claimed that incorporation of up to 25% of 5-ATZ in smokeless propellants reduced the amt of flash and smoke without changing the ballistic potential or sensitivity to mechanical action... 

DIANP is a colorless liquid, which is soluble in acetone, methanol, dimethylformamide, DMSO, ethyl acetate, and benzene. It is not very soluble in water, ethanol, or butanol. DIANP is used in gun propellants and rocket propellants to reduce flame temperatures, toxic combustion products, smoke, and to increase performance without sacrificing bum rate. DIANP is an excellent substitute for nitroglycerine for gun propellants and rocket propellants. ... 

HMX is a very powerful explosive, which is more powerful then RDX. It has exceptional physical properties, and it demonstrates excellent shock and percussion resistance. The use of HMX in explosive compositions and munitions for military purposes is growing, and it is likely it will over take RDX in the future HMX exists in two primary modifications beta-HMX, and alpha HMX. Beta-HMX is useful in hollow charges, but alpha-HMX is more useful in explosives compositions, munitions, high performance rocket propellants, and gun propellants—HMX is a great smoke and flash-reducing agent for propellant formulations. 

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