ABSTRACT

The chemical rocket propulsion system is a type which employs the use of chemical combustion for energy to attain enough thrust for launching artifact into space. Propulsion technologies can be categorized into various categories like deep space propulsion, space propulsion, and escape propulsion. Currently, the launch vehicle used is to escape.  This report will analyze how the chemical reaction can produce thrust for launching the artifacts into space. In chemical rocket propulsion, the hot exhaust gas is generated through chemical combustion. The propellant or chemical is always of two types oxidizer and fuel, which always corresponds to oxygen and gasoline in an automobile engine. Both are needed for combustion, and they can either be solids or liquid chemicals. After the combustion, a thrust given as the product of the reaction is given, usually after oxidizing or burning fuel.  Therefore, this paper will analyze some types of chemical propulsion, their working mechanism, and some of the mathematical equations that correspond to the thrust.

INTRODUCTION

Chemical rocket propulsion uses chemical propellants, which are different forms, but all have analogous basic components. There is a combustion chamber in such a propulsion system where a propellant of the condensed phase is converted to a very hot gaseous reaction.  There is also a nozzle that helps in accelerating the formed gaseous materials into a high exhaust velocity. The nozzle is very significant for attaining a higher thrust required in this system.  There is also a propellant container and also a means of feeding the propellants into the combustion chamber. This propulsion system is grouped into two general types, which is done according to whether the burning propellant is stored as a liquid or as solid. In this category, the solid is known as the motors, while the liquid system is known as the engines. These two types of propulsion are illustrated in the following diagram;

Figure 1: Showing types of chemical rocket propulsion ( https://www.britannica.com/technology/rocket-jet-propulsion-device-and-vehicle/Chemical-rockets)

A hybrid type combines both the solid and liquid types of the chemical rocket propulsion system.  The use of chemical rocket propulsions aids in a faster launch of spacecraft like satellites into space.  Such actions of launching a spacecraft can be illustrated in the following diagram,

Figure 2: Showing Titan II rocket, lifting off from an underground silo using chemical rocket propulsion system ( https://www.britannica.com/technology/rocket-jet-propulsion-device-and-vehicle/Liquid-propellant-rocket-engines)

DISCUSSION

Solid propellant rocket (Motor)

Here the fuel and the oxidizer are already mixed together and are given as a solid inside the combustion chamber; this type is also called a propellant grain.  The rate of chemical reaction in this type depends on the type of fuel selected and the propellant grain’s surface area. Inside the length is usually a hollow section, which helps to increase the amount of grain exposed thus available for reaction. A star-shaped section is always employed to maintain a steady burn with a uniform thrust.  This type of chemical rocket propellant is illustrated using the following diagram;

Figure 3: Showing a solid propellant ( https://www.sciencelearn.org.nz/resources/393-types-of-chemical-rocket-engines)

The standard requirement of nozzle used in this propulsion system should be able to generate a supersonic exhaust flow from the combustion chamber pressure to an exterior pressure; this is accompanied by a proper sizing and contouring of the conduct. The contour is originally convergent to the throat section.  The gas’s velocity at this point will be the same as the local sound velocity, and the throat cross-sectional area controls the rate of mass discharge.  The level of thrust in solid rocket is obtained through the burning rate of the propellent charges as in equation 1 below

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The designer may select a charge geometry, which will vary with time during the combustion process in a way required for a specific mission, and then select a propellant formulation that gives the required rate of burning.  This means that the thrust’s function is not amenable to any intentional modification after the manufacturing process.  The absence of real time control in the thrust is compensated through the ability to obtain an extraordinarily high rate of mass flow without any propellant pump, which is used in the liquid propellant rocket.  The level of thrust occurring in practice depends on the operating pressure of the motor. And this is illustrated in internal ballistic theory to depend on the property of propellent in according to below equations;

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Where At is the nozzle throat area, Þp is the density of the solid propellant, n and C are constants in the equation, which gives an estimated dependence of the propellant combustion rate under pressure. Cd is the coefficient that depends on the propellant’s thermochemical properties.

The thrust in this type given by the following equation

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The overall concept of the working of this is on newtons third law of motion where the action force is equal and opposite of the reaction force. Thus,

Forward force = backward force.

Liquid propellant

In this type, a fuel like kerosene or hydrogen or hydrogen and liquid oxidizer like liquid hydrogen is used. These fuels are stored in a separate tank and then get pumped to a combustion chamber when needed. While they get sprayed to the combustion chamber via an injection nozzle, these fuels quickly get mixed together and react before they get ejected.  This system can be illustrated in the following diagram;

Figure 4: Showing a liquid propellant type of chemical rocket ( https://www.sciencelearn.org.nz/resources/393-types-of-chemical-rocket-engines)

In this type, thrust can be obtained as below.

Thrust = force

F= m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4

The basic parameters of the liquid rock propulsion system include vehicle structure, fuel tans, and engines. The oxidizer and fuel tanks always of very lightweight construction since they operate at low pressure. The liquid propellant engine has the main chamber that is used for mixing and burning the oxidizer and fuel with the fore end, which is occupied by the oxidizer and fuel injectors and manifolds.   Integral to the main chamber is a coolant jacket where the liquid propellant is always circulated at a higher rate, which is sufficient to enable the engine to work continuously without any extra temperature increase in the chamber.

CONCLUSION

In summary, a chemical rocket propulsion system uses chemicals for combustion in order to generate a thrust. The thrust attained is due to the sufficient energy which enough to launch an artifact into space, the thrust is very significant since it helps escalating the speed of the spacecraft while it is being launched into the space. The propulsion makes it easier for the space craft to be easily launched into the space.  The chemical rocket propulsion system has two types which includes the liquid rocket propulsion and the solid rocket propulsion.  In solid rocket propulsion system, the fuel and the oxidizer are already mixed together and are given as a solid inside the combustion chamber. While in liquid a fuel like kerosene or hydrogen or hydrogen and liquid oxidizer like liquid hydrogen is used.

REFERENCES