Fuel-rich pyrolant

When a fuel-rich pyrolant burns in the atmosphere, oxygen molecules from the atmosphere diffuse into the initial combustion products of the pyrolant. The combustion products burn further and generate heat, light, and/or smoke in the atmosphere. A typical example is the combustion process in ducted rockets fuel-rich products generated in a gas generator are burnt completely in a combustion chamber after mixing with air pressurized by a shock wave that is taken in from the atmosphere. 

Similar to liquid ramjets, ducted rockets take in air from the atmosphere through an air-intake attached to the front end of the combustor. However, in contrast to liquid ramjets, the fuel components used for ducted rockets are fuel-rich pyrolants composed of fuel and oxidizer components. The products of incomplete combustion generated by a pyrolant in a gas generator burn with the air introduced from the atmosphere in the combustor.Ii- As in the case of liquid ramjets, the thrust of ducted rockets is generated by the momentum difference between the exhaust gas from the combustor and the air taken in from the atmosphere. 

Nitropolymers composed of -O-NO2 functions and hydrocarbon structures are pyrolants that produce fuel-rich products accompanied by exothermic reaction. Typical nitropolymers are mixtures of nitrocellulose, nitroglycerin, trimethylolethane trinitrate, or triethylene glycol dinitrate, similar to the double-base propellants used in rockets and guns. Mixtures of these nitropolymers are formulated as fuel-rich pyrolants used in ducted rockets. This class of pyrolants is termed NP pyrolants. 

Figures 6.10 and 6.11 show that the thermal equilibrium of fuel-rich pyrolants is less affected by pressure than that of fuel-lean grains, which explains the lower pressure exponents of fuel-rich grains as we will discuss later.

The selechon of fuel components to be mixed with oxidizer components is also an important issue in the development of pyrolants for various applications. Metal particles are used as fuel components to develop small-scale pyrolant charges as deployed in igniters, flares, and fireworks. Non-metal particles such as boron and carbon are used to formulate energetic pyrolants. Polymeric materials are commonly used as fuel components to develop relatively large-scale pyrolant charges, such as gas generators and fuel-rich propellants. 

The AN particles incorporated into GAP-AN pyrolants form a molten layer on the burning surface and decompose to form oxidizer fragments. The fuel-rich gas produced by the decomposition of GAP interdiffuses with these oxidizer fragments on and above the burning surface and produces a premixed flame. A luminous flameis formed above the burning surface. 

When AP particles are added to GAP-AN pyrolants, a number of luminous flame-lets are formed above the burning surface. These flamelets are produced as a result of diffusional mixing between the oxidizer-rich gaseous decomposition products of the AP particles and the fuel-rich gaseous decomposition products of the GAP-AN pyrolants. Thus, the temperature profile in the gas phase increases irregularly due to the formation of non-homogeneous diffusional flamelets. 

Since nitramine pyrolants are fuel-rich materials, the flame temperature decreases with increasing hydrocarbon polymer content The polymers act as coolants and generate thermally decomposed fragments as a result of the exothermic heat of the nitramine particles. The major decomposition products of the polymers are H2, HCHO, CH4, and When AP particles are incorporated into nitramine pyrolants, AP-nitramine composite pyrolants are formed. AP particles produce excess oxidizer fragments that oxidize the fuel fragments of the polymers that surround them. Thus, the addition of AP particles to nitramine pyrolants forms stoichiometricaUy balanced products and the combustion temperature increases. 

Though the pyrolants used in gas-hybrid rockets burn in a similar manner as rocket propellants, their chemical compositions are fuel-rich. The pyrolants burn incompletely and the combustion temperature is below about 1000 K. When an atomized oxidizer is mixed with the fuel-rich gas in the secondary combustor, the mixture reacts to generate high-temperature combustion products. The combushon performance designated by specific impulse, is dependent on the combinahon of pyrolant and oxidizer. 

The projectile acquires a specified supersonic flight speed after burn-out of the booster propellant. The booster nozzle is then ejected to the outside and the port cover is opened. The compressed air resulting from the aforemenhoned shock wave is then introduced through the air-intake. The booster chamber becomes a ramburner and the gas-generating pyrolant is ignited to produce fuel-rich combushon products. 

Tq, of gas-generating pyrolants such as fuel-rich AP-HTPB and fuel-rich nitropoly-mer pyrolants are lower than those of rocket propellants such as AP-HTPB and nitropolymer propellants. The gas-phase temperature is low and hence the heat flux feedback through the wires is low for the gas-generating pyrolants as compared with propellants. However, r /ro appears to be approximately the same for both pyrolants and propellants. The obtained burning-rate augmentations are of the order of 2-5. 

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