Sameeha Bhende T.E EXTC
Engines have been evolving ever since the invention of automobiles. Along with it, man’s requisite to reach into space has fuelled the development of rocket engines. Although there have been experimentations on gunpowder engines, also known as explosion engines during the early 17th century, the first ever engine to be used was the liquid propellant rocket engine. It was developed by Germans during the second world war. Their V-2 missile launched in 1944 is an excellent example of the engine’s utilization.
A liquid-propellant rocket engine, as the name suggests uses liquid propellants like liquid fuels. In order to generate a sufficient thrust for the rocket, it is necessary for it to have a high mass flow rate. This means that a given mass of the propellant must flow in as less time as possible. Oxygen and low molecular weight hydrocarbons were used as fuels in this engine. Being in the gaseous state, they needed to be liquefied first which could be done by pressurising them. But, this led to an increase in the size of containers needed to store them, reducing the rocket efficiency.
Thus, cryogenics came into the picture. Cryogenics is a branch of physics that deals with the behaviour of various substances at extremely low temperatures, specifically much lesser than 273.15K(0ºC). A cryogenic technology is the process of involvement or including of usage of rocket propellants at a cryogenic temperature. It can be the combination of liquid fuels such as liquid oxygen (LOX), and liquid hydrogen (LH2) as an oxidizer and fuel in the different mixtures or proportions. The mixture of fuels offers the highest energy efficiency for the rocket engines that produces a very high amount of thrust. Here, the oxygen remains liquid only at the temperature below (–183 C) and hydrogen at below (–253 C). This is a type of rocket engine that is functionally designed to use the oxidizer which must be refrigerated in the liquid state. Sometimes, the liquid nitrogen (LN2) is sometimes used as a fuel because the exhaust is also nitrogen. Liquid oxygen is injected below critical temperature but above the critical pressure. In our atmosphere nitrogen is nearly about 78%. Nitrogen is a non-pollutant gas and during exhaust, no other harmful gases are produced. Hence its efficiency is very high than any other Jet engines. But why do thy say it is highly efficient? The answer lies behind Newton’s Third Law: Every action has an equal and opposite reaction. Rocket engine operates through force of its exhaust pushing it backwards. Thrust is in opposite direction and more efficient in lower atmosphere or vacuum (sometimes). It makes the use of liquid oxygen as an oxidizer and liquid hydrogen as fuel.
CRYOGENIC: THE EMERGING ROCKET ENGINE TECHNOLOGY