ROCKET ENGINE: HEART OF A ROCKET

 

THE HEART OF THE ROCKET

The most complex piece of engineering. 

Raptor Engine - Starship (SpaceX)

If anyone can understand this, he's surely a genius. Designing a rocket engine is briefly how fast can you eject out a ton of high-speed propulsive jet of fluid, usually at high temperatures. Necessarily you should keep in mind that you also need to prevent it from blowing up. 

As it is evident from the picture if you try to figure out the piping in the upper half of the engine you would surely end up banging your phone on the ground. So we will discuss all of that peacefully. We'll list down a few important aspects regarding the functioning of this giant jerk and go deep into it. 

• Propellant 
• Injection 
• Nozzle
• Combustion Chamber 
• Specific Impulse 
• Net Thrust 
• Throttling
• Energy efficiency 
• Thrust to Weight Ratio 

A rocket engine is made up of thousands of different parts. Listing them down would surely bore you so let's look at what the above terms mean. 

PROPELLANT

Mighty one-word statement. 

The propellant is what makes up 80% mass of the rocket. It includes Fuel and the Oxidizer. To understand the need for an Oxidizer, an experiment needs to be conducted. 

In this experiment, when a burning candle is covered with a bell jar, the flame goes off. In the second case, where a green plant, is kept inside along with the candle, the candle doesn't go off until and unless the plant is alive and carry's out photosynthesis and produces oxygen. This concluded that oxygen is essential to ignite the fuel. Since we all know that the level of oxygen depletes as we go up. Therefore, to cope up with the requirements for fuel to burn in outer space, the rocket has to carry a ton of oxygen along with it. 
Another question that you may raise is, Which fuel do we use? 

The answer is not as simple as the question. There are different fuels for different engines. Since a rocket engine is specifically designed according to the choice of fuel, a different set of fuel cannot be used for the same engine. For example, we cannot use methane or hydrogen fuel in one engine. A hydrogen-powered engine has a completely different set of challenges than a methane-powered engine. 

One more question? How does this process of expelling propellant produce lift? 

Well, for the history behind this, watch my first blog, Here That explained the chronology of how the events occurred in the past. To provide a better explanation for that, Sir Isaac Newton comes into the picture. His famous third law of motion goes something like this: 

So, the higher the velocity of the gas that leaves the rocket, the higher the acceleration and therefore higher the lift force opposite to the direction of flow of gas and thus the rocket propels upwards. 

INJECTION

Kinda showerhead. 

F1 Engine Injector

Injectors are one of the most important parts of the rocket engine. The image has made it evident that it's like a normal showerhead. It's a thick metal plate with a bunch of tiny holes all over the area of the plate. Now, what is their role? Let's learn. 

Imagine a tank of water four times longer than your house. Make a hole at the bottom of it and just feel how nimble that speed would be. It would literally chop anything that obstructs its way. Now imagine, there are two of these tanks simultaneously pouring at brisk. In a rocket, one is a fuel tank and one is an oxidizer tank. The issue here is that the tanks are getting empty at a random rate. What if you need a specific ratio in which the ratios merge. Like for example, 10L of fuel shall mix with 1L of oxidizer. Now that's TROUBLE. Well, Injectors solve the problem. As mentioned earlier, they are a layer of tiny holes. Therefore the specific portions of the plates can be accordingly assigned to the fuel and oxidizer in different ratios respectively as per the requirements of the situation. While designing the first rockets, many different patterns for injectors were proposed not all passed the tests. The image above was the injector used in the F1 engines of the rocket Saturn V. (Click here). Indeed! The Apollo Mission contributed a lot to the space race. 

NOZZLE

Structure i.e similar to the dome of a temple

This massive dome-like structure, at the very end of the rocket, is the exit door for the hot gas. All the pressurized gas that is heated in the combustion chamber is exhaled out from the nozzle. Uniform acceleration in the increase in the surface area aids to the massive acceleration of the hot exhaust to produce thrust as described by Newton's third law of motion. These nozzles can be gimbaled (change the direction of flow) using hydraulic pistons. They are highly accurate in their measurements. 

Now, the second most important things in nozzles are the rings on the outer side of them. Any good rocket nozzle would have many rings running across its surface. These are pipes that are helical in the path and they run across the whole of the nozzle's surface. Why are they needed? 

Since the hot gas blowing out of the nozzle may take temperatures up to 3000 degrees. That's insane! No known materials to humans can withstand such temperatures. Therefore metals of choice for this part of the engine are Steel Niobium alloys. Materials with higher melting points are usually extremely heavy or simply don't match the other properties. Therefore this may lead to the melting of the nozzle mid-flight and therefore a BOOM! There's where these pipes come into the picture. These are the pipes through which excess super-chilled fuel (about -50 to -100 degrees Celsius) is passed which prevents the nozzle from melting. This fuel-rich mixture is then left out unburnt into the atmosphere which pollutes the environment and contributes to smogs. (Just like the vehicles on the road.) 

Rocket Science is a massive dimension to be studied. All at once can lead to constipation so we decide to end our article here. The second part of Rocket Engine would be uploaded in a couple of days. Till then, stay tuned. Comment for fruitful discussions. Thanks for reading. GOODBYE.