Why do rocket engine produces green flame?
The Rocket Engines are the heart of the rockets which produces thrust to moves the rocket structure to outer space. The rocket engines work with the fuel and oxidizer mixture which are kept in the separate tanks inside stage 1 of the structure.
The three main elements of a rocket engine that work to raise its oxidizer and fuel pressure to an extent sufficient for generating one-way thrust are the inlet, the turbopump and the combustion chamber. The first two are responsible for diverting the fuel and oxidizer from the vehicle’s tanks to the rocket’s combustion chamber where the final, pre-thrust ignition takes place.
The turbopump assembly will have two different types .
- Oxidizer Rich Turbopump.
- Fuel Rich Turbopump.
For perfect combustion the mixing phenomenon of fuel and oxidizer should be uniform which is termed as Fuel -to-oxidizer Ratio. The weight ratio of oxidizer to fuel in the combustion chamber of a rocket engine. For example, the mixture ratio for the space shuttle’s main engine is 6:1, meaning six parts of oxidizer (liquid oxygen) to one part of fuel (liquid hydrogen).So back to turbopump assembly the impellers and blades in the turbopump assembly are designed and fabricated to certain threshold temperature which is the maximum temperature(positive or negative) where the material can withstand .
GREEN FLAME :
There are two possibilities that the engine can produce green flame in its exhaust plume
A. IGNITION FLUID:
If the ignition fluid of the rocket engine is TEA-TEB (Triethylaluminum + Triethylboron). During the ignition phase, we may see green flames in the rocket engines. For example, SpaceX’s Merlin 1D Engine uses TEA-TEB as its Ignition Fluid.
In the above picture ,the exhaust of engine section is green flame which is because of the TEA - TEB during the engine startup phase the flight computers are programmed to release this fluid from HPU-Hydralic Pressure Unit .
B.ENGINE RICH COMBUSTION:
The title engine rich combustion may seem weird to you, instead of fuel-rich or oxidizer rich the engine material itself reacts with combusted gases and it leads to RUD- Rapid Unscheduled Disassembly. For example, during the SN8 launch in the landing phase of the flight, the green flame appeared in the engine section and RUD.
Green flames emanating from the Raptor engine six minutes and forty seconds after liftoff were the second sign during yesterday’s test that perhaps SN8 wouldn’t come out of its test flight in a single piece.
Fuel Pressure Drop Caused Raptor Engine To Melt And Emit Green Flames
For the Raptor, it’s possible that the engine’s combustion chamber burned off as the fuel pressure from the vehicle’s secondary (header) tank dropped and the proportion of Oxygen in the chamber increased.
In a tweet, Elon Musk explained:“…Fuel header tank pressure was low during landing burn, causing touchdown velocity to be high & RUD, but we got all the data we needed!! Congrats SpaceX team hell yeah!!”
In header tanks, the landing phase propellants are stored. Since a rocket engine uses fuel and an oxidizer and as the former disappeared and the latter continued to burn, the engine itself started to melt and generated the green flame. On a side note, during the engine restart for landing, only two of the three Raptors restarted, and roughly eight seconds after this, one engine shut off — which might also have been due to SN8’s landing parameters. These are the possible ways where the engines can produce green flame.
