How does the Merlin engine work? How does it's working compare to the working of SuperDraco engine?
To be more specific,
What features of Merlin make it unique and more efficient than other rocket engines?
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The Merlin Engine is a gas generator cycle engine which uses liquid Oxygen(LOX) and refined Kerosene(RP1) as its propellants.
The SuperDraco engine is a pressure fed cycle engine which uses mono-methyl hydrazine (MMH) and dinitrogen tetroxide (N2O4) as their propellants.
The key differences of the engine are the size of the engine, the way the propellants are driven into the thrust chamber (the cycle), and the propellants themselves.
Engine Size: The Merlin 1D has a thrust of around 900kN, while the Superdraco has a thrust of around 70kN. Meaning the Merlin 1D engine is much more powerful than the SuperDraco engine.
Engine Cycle: The Merlin engine uses a gas generator cycle which in short uses a smaller combustion chamber to burn propellants which drive more propellant into the thrust chamber. It’s more complex than that but just know that the propellants are driven into the chamber by the combustion of the propellants in a smaller preburner. The Superdraco is a pressure fed cycle. The tanks are pressurized to a high pressure, and this pressure feeds the propellants into the thrust chamber. This is useful as it is very simple and reliable, but the pressure tanks add significant weight to the overall mass.
The Propellants: The engines also differ in the propellants they use. The Merlin utilizes refined kerosene and liquid oxygen as their propellants which give a modest efficiency. While the Superdraco uses MMH and N2O4, which give a slightly lower efficiency than the RP-1/LOX combination. It should also be noted that the MMH/N2O4 is hypergolic, so the propellants ignite once exposed to one another, further simplifying the combustion process as no igniter is needed.