PROPELLANTS

PROPELLANT A propellant is a mixture of a fuel and an oxidizer that reacts to form energy and gas products. Example hydrogenand oxygen is used as rocket fuel. A propellant can also be defined as a chemical which is used in the production of energy or pressurized gas that is subsequently used to create movement of a fluid or to generate propulsion of a vehicle, projectile or other object. Common propellants are energetic materials and consist of fuel; like gasoline, jet fuel, rocket fuel, and an oxidizer. Propellants are burned or decomposed to produce the propellant gas. Other propellants are liquid that can readily vaporize. Propellant is any gas, liquid, or solid the expansion of which can be used to impart motion to another substance or object. In aerosol dispensers, compressed gases such as nitrous oxide, carbon dioxide, and many halogenated hydrocarbons are used as propellants. The propellant may remain in gaseous form (nitrous oxide or carbon dioxide), or it may liquefy under pressure. Food products, such as artificial whipped cream, are propelled by nitrous oxide or carbon dioxide; non-food products, such as cosmetics, insecticides, paints, and pharmaceuticals, formerly were dispensed with the aid of fluorinated hydrocarbons. Because of the threat believed to be posed to the Earth’s ozone layer by halogenated propellants, they have been banned in many countries except for essential uses such as some drugs, pesticides, lubricants, and cleaners for electrical or electronic equipment. Solid and liquid propellants are substances that undergo rapid combustion, producing gaseous products. Black powder was used as a propellant in guns and rocket until the 20th century, when double-base gun powder (40 percentnitroglycerin, 60 percent nitrocellulose) came into use. Other modern solid propellants are castper chlorate (using perchlorate as oxidizer and various oils or rubbers as fuel) and composite propellants (using a plastic binder with ammonium picrate, potassium nitrate, or sodium nitrate). There are various liquid rocket propellants: monopropellants, such as nitromethane, which contain both oxidizer and fuel and are ignited by some external means; bipropellants, consisting of an oxidizer such as liquid oxygen and a fuel such as liquid hydrogen, which are injected into a combustion chamber from separate containers; and multipropellants, consisting of several oxidizers and fuels. Rocket propellant is a material used by a rocket as , or to produce in a chemical reaction, the reaction mass that is ejected, typically with very high speed, from a rocket engine to produce thrust, thus provide spacecraft propulsion. In a chemical rocket propellant undergo exothermic chemical reactions to produce hot gas. There may be a single propellant, or multiple propellants; in the latter case one can distinguish fuel and oxidizer. The gases produced expand and push on a nozzle, which accelerates them until they rush out of the back of the rocket at extremely high speed. In firearm ballistics, propellants fill the interior of an ammunition cartridge or the chamber of a gun or cannon, leading to the expulsion of a bullet or shell. Explosives can be placed in a sealed tube and act as a deflagrant low explosive charge in mining and demolition, to produce a low velocity heave effect (gas pressure blasting). Cold gas propellants may be used to fill an expansible bag or membrane, such as automobile or in pressurised dispensing systems, such as aerosol sprays, to force a material through a nozzle. Example of can propellants include nitrous oxide that is dissolved in canned whipped cream, and the dimethyl ether or low-boiling alkane used in hair spray. Rocket propellants may also be expelled through an expansion nozzle as a cold gas that is, without energetic mixing and combustion, to provide small changes in velocity to spacecraft use of cold gas thrusters. Liquid Propellant In rockets, three main liquid bipropellants combinations are used: • Cryogenic oxygen-hydrogen combination system- used in upper stages and sometimes in booster stages of space launch systems. This is a nontoxic combination. • Cryogenic oxygen-hydrocarbon propellant system – this combination of fuel/oxidizer has high density and hence allows for a more compact booster design. • Storage propellant combinations – used in almost all bipropellant low-thrust, auxiliary or reaction control rocket engines, as well as in some large rocket engines for first and second stages of ballistic missiles. They are instant starting and suitable for long-term storage. Solid Propellant Solid propellants are usually made from low explosive materials, butt may include high explosive chemical ingredients that are diluted and burned in a controlled way rather than detonation. The controlled burning of the propellant composition usually produces thrust by gas pressure and can accelerate a projectile, rocket, or other vehicle. Solid propellants are used in forms called grains. A grain is any individual particle of propellant regardless of the size or shape. The shape and size of a propellant grain determines the burn time, amount of gas, and rate produced from the burning propellant and, as a consequence, thrust versus time profile. There are three types of burns that can be achieved with different grains; Progressive burn: usually a grain with multiple perforations or a star cut in the centre providing a lot of surface area. Degressive burn: usually a solid grain in shape of a cylinder or sphere. Neutral burn: usually a single perforation; as outside surface decreases the inside surface increases at the same rate.

There are four different types of solid propellant compositions; they are single-based propellant, double-based propellant, triple-based propellant and composite. Single-base propellants contain only one explosive ingredient, Nitrocellulose. Double- base and Triple-base propellants contain, respectively, Nitroglycerine (NG) and Nitroguanidine (NQ) in addition to Nitrocellulose (NC). Composite propellants are compositions that contain mixtures of fuel and inorganic oxidants. There are combinations of composite and double-base propellants called composite double-base propellants.