Elon Musk enthusiasts will be rejoice on knowing SpaceX's newest technological success, which is
firing the first full-scale Raptor engine. Even though, it’s scary to witness a rocket
lift-off in an explosive manner, combustion is essential to create
a great force to keep the engine running. Engineers at SpaceX have improved their craft,
by discovering a method that will allow the raptor engine work at full capacity without problems,
even though it burns at a high temperature. And one thing that should tickle our interest
is how SpaceX engineers cool down superheated stainless steel used to
build the raptor engine when it burns at high temperatures without melting.
Stick around to discover the insane engineering miracle behind the cooling
system of the SpaceX Raptor engine. Let's do some assessments; we already
know that water boils to the stem at 100oC, which is hot enough to burn human skin, but human skin
is completely burned and destroyed at 162oC. We cannot compare human skin to metals, but we
need to include the human sense of touch to obtain a good understanding of rate temperature change,
which occurs in rocket engines. However, this is not the case with the stainless steel utilized
in the production of SpaceX Raptor engine. Stainless steel melts around 1530oC on average.
However, when SpaceX tested the raptor engine, the temperature was over 3,200oC, more than
double the melting point of the stainless-steel metal used in the engine's construction.
Coming back to the original topic, how does the engine not get red hot, melts and finally blast
off when heated to 3,200oC? To explain this, we must first explore the raptor engine's
operating mechanisms and stages of operation. We'll begin with a basic physics lesson.
Then we'll delve in and learn about a lot of nitty-gritty details, leaving no stone unturned,
and at the end, we hope you'll have a solid understanding of how rocket engines work, the
many varieties of liquid-fueled rocket engines, and why methane is a viable fuel source.
Rockets are propellants with skin over them to keep them in place
and a mechanism on the rear that can discharge propellant quickly. To look at it another way,
the faster the fuel is evacuated, the better. The simplest method is to store all of the fuel
in extremely high-pressure tanks, then install a valve at one end of the tank,
and a propelling nozzle that accelerates the fuel into usable thrust. There are no crazy pumps or
intricate systems; simply open a valve and let the fuel run out at high speed.
A pressure-fed rocket engine is what this is called, and there are three types:
cold gas, mono prop, and bipropellant pressure-fed engines. Because they are simple,
dependable, and fast, they are frequently utilized in reactive control systems.
However, there is one significant limitation to pressure-fed engines.
Because pressure continuously flows from high to low, the engine can never be pressurized
higher than the propellant tanks. The tanks must be robust to hold fuel
at high pressure, which means thicker and heavier. Consider composite overwrapped pressure vessels,
often known as COPVs. They can store gases at pressures of nearly 10,000 psi or 700 bar.
Despite this, they can only hold a certain quantity of fuel and pressure.
This does not scale well when attempting to deliver a payload to orbit.
So smart rocket engineers immediately recognized that there was only one thing they could do to
make the rocket as light as possible. And that solution is to raise the enthalpy.
Let us now look at the cooling engineering phenomena used in rocket engines.
The first topic is regenerative cooling, the most systematic approach to keeping a
liquid-fueled rocket engine from melting. This approach involves passing part or all of
the fuel through the combustion chamber walls and nozzle before
entering the chamber via the injectors. While the walls and nozzle of rocket engines
appear thin, there are tiny channels in the walls through which fuel may flow to keep them cool.
The discovery of this technology was a great development, as it permitted rocket
engines to run endlessly. Early regeneratively cooled engines included the main chamber and a
liner on the engine's exterior through which coolant or fuel could flow. It was common to
see pipes employed as the combustion chamber's walls. The RL-10 engine, which still employs
brazed tube construction, is an example. Nowadays, a more usual approach is to carve
a cooling channel in the nozzle's wall and then seal it with a copper or nickel alloy,
which serves as the chamber's inner wall. Because of their excellent thermal conductivity,
copper and nickel alloys are utilized here to transmit heat from the wall into the coolant.
This approach allows the fuel to boil before entering the chamber.
This process may also be utilized to spin the turbine and power the engine's pumps,
known as the expander cycle. The cycle uses the thermal expansion of the fuel as it transitions
from liquid to gas, and to power the pumps. The majority of engines utilize gasoline as a
coolant, although an oxidizer is also an option. When cryogenic fuel is employed, the exterior of
the rocket nozzle becomes extremely cold, while the wall's interior becomes extremely hot.
One of the most difficult aspects of regenerative cooling is that
the pressure within the walls must be greater than the pressure in the combustion chamber.
This is because the walls are just tubes that feed the injectors, and because pressure always
flows from high to low, the injectors require more pressure than the combustion chamber.
It's simple to picture a leak happening with such high pressure inside little walls. Fortunately,
because the pressure within the wall is higher than the chamber's, a leak would simply give
additional cooling owing to film cooling. Film Cooling is the second kind of cooling
employed in rocket systems. In this case, a fluid is injected
between the combustion chamber and nozzle surface and the hot combustion gases. Because
fluids are either gaseous or liquid, this may be accomplished using liquid or gaseous fuels.
The goal is to build a barrier between the wall and the hot combustion gas, operating as thermal
insulation with cooler fluid in between. The simplest technique to achieve
liquid film cooling is to have a larger concentration of fuel or oxidizer injectors
on the outside perimeter's injector face. Fuel is normally preferred because the primary
combustion chamber is rich in fuel. There will be a ring of additional fuel flowing around
the outside perimeter that will lack the necessary quantity of oxidizer to react with. This implies
that a ring of fuel-rich combustion will be present to prevent heat from passing from the
primary combustion gases to the walls. The bulk of the fuel adjacent to the
wall that will not react owing to a lack of sufficient oxidizer flows as a film
along the chamber walls, between the combustion gases and the chamber walls.
However, it will most likely phase transition from liquid to gas, forming a vapor boundary
layer that will continue to absorb heat as changing phases absorb some heat.
And finally, the last method of cooling is radiative cooling;
When fueled, both SpaceX's vacuum Merlin engine and Rocket Lab's vacuum Rutherford
engine flash bright red because the metal gets extremely hot and releases the heat into space.
Because space has no atmosphere, there is no air to pick up and transfer or convent heat
away. Instead, engines may radiate heat away from their nozzles because radiation does not require
matter to transmit heat - similar to how the Sun conducts heat across space via radiation.
The nozzle extensions of vacuum-optimized Merlin and Rutherford engines are constructed of very
thin metal, generally an alloy such as niobium alloy, that can endure severe heat loads.
However, the disadvantage of these nozzle extensions is that they are very thin
and rather weak. Furthermore, niobium is particularly reactive to oxygen,
which implies that this engine can only run in a vacuum and is more complicated to manufacture.
Is the Raptor engine the undisputed king of rocket engines? Rocket science, like everything else,
is a complicated series of tradeoffs. No, it is not the most efficient engine. No,
that is not the most powerful engine. But Is it the most affordable engine? Probably not.
Maybe it's the most reusable engine. But does it truly do everything well? Yes.
It is a goldilocks engine, capable of doing all of its duties admirably. It's
ideal for our intergalactic Starship. Despite its complexity, SpaceX is moving
quickly to create this engine. Given how much work SpaceX has put into their Merlin engine
over the last decade, the Raptor engine is still in its infancy. It will only get better from
here on out, which is incredible! Overall, the Raptor engine is the
undisputed king in this application. It's a terrific engine that will help SpaceX
achieve its ambitions for its Starship. So, what are your thoughts? Is it worth
going through several challenges to develop a strange and sophisticated raptor engine?
And talking about this let’s check How Realistic Is SpaceX's Idea of Catching
the Largest Rocket Ever Built with Chopsticks, just click on the video.