When shuttle's engines are rev-ing up at liftoff, what are those little sparks that come out by main engines?

Answer 1

Those are called 'long throw igniters'. During the early startup phase, some hydrogen fuel leaks from the engines. If it was allowed to collect under them prior to ignition the resulting explosion could cause instability in the engines and lead to a shutdown or worse. The 'spark throwers' are there to burn off excess hydrogen prior to main engine start.

[Edited to add]

The sparks are not the igniters for the main engines. The SSMEs are highly complex pieces of engineering, and the ignition is within the engines near the throat where the fuel and oxidiser first meet. Liquid fuelled engines like the SSMEs are anything but simple. They do not just have the fuel and oxidiser fed into them but the fuel has to be pumped, the engine cooled, the ignition arranged. All of that is part of the design of the engine.

Answer 2

Any white smoke popping out of the engines in basic terms before ignition are tension valves that are liberating the oxygen and hydrogen vapor. the main important tremendous tank besides because of the fact the gas on board the holiday is often liquid hydrogen and oxygen. because of the fact that there is not any appropriate insulator the warmth from exterior motives the quite a few liquid to enhance right into a gas. If the holiday had no way of liberating this gas, then the tank could explode with the tension of the tension created in component.

Answer 3

I think they are from the igniters, which are spark making devices used to light the engines. How else to light the engines? Just letting the fuel and oxygen flow into the engine will not do it and I wouldn't want to the the man standing there holding the match to light those suckers!

Answer 4

They are little sparks.