5

I am designing a liquid fueled amateur rocket with my brother, and settled on a gas generator engine. We understand the concept and process, however we are still confused on how the engine is initially ignited. Does a battery/other means of energy kick-start the turbopumps? Thank you for the help

Raymond Bowman
  • 83
  • 4
  • 1
    One solution is the use of a solid fuel gas generator used to start the turbine and the turbo pumps. The solid fuel is only used for start, but the pressure and gas flow should continue when the solid fuel burns out and the liquid fuel takes over. – Uwe Aug 07 '17 at 10:16
  • 1
    I don't think the answer is in Scott Manley's Rocket Engine Plumbing but you may find it interesting or helpful if you haven't seen it already; https://youtu.be/4QXZ2RzN_Oo also possibly this answer. – uhoh Aug 07 '17 at 13:01

1 Answers1

10

One common solution is what is referred to as a "start bottle" (see the J-2 flow schematic diagram below -- look for the item labeled "start tank") -- a small tank of highly compressed gas (e.g., helium or hydrogen) with either a nozzle that impinges directly on the turbine of the turbopump or a line that pressurizes the gas generator exhaust lines to spin the turbopump up to pump the propellants into the gas generator. When you hear of an engine that cannot be restarted or can only be restarted once or twice, this is a likely reason why -- one start bottle per start. When it's used up, that's it.

J-2 engine flow schematic

Tristan
  • 17,263
  • 1
  • 63
  • 83
  • What engine is this diagram from? – Organic Marble Aug 07 '17 at 15:54
  • 1
    Edited post to clarify -- thought I had typed it in there already. It's the J-2. – Tristan Aug 07 '17 at 15:56
  • 1
    For first stage engines, this start tank may be on the launch pad, connected to the stage via an umbilical. – Hobbes Aug 07 '17 at 16:39
  • This is true. For the J-2, in fact, the start bottle was in the stage's hydrogen tank and not on the engine. – Tristan Aug 07 '17 at 17:31
  • Thank you so much! This diagram and your explanation definitely cleared things up. – Raymond Bowman Aug 07 '17 at 19:26
  • 2
    If you are happy with the answer, please accept it by clicking on the gray check-mark. – Organic Marble Aug 08 '17 at 11:32
  • The answer cover the turbopump starts and is initially pressurized but not how gases are ignited. Correct me if there is something I missed that explains the high temperature needed to start the combustion in the gas chamber. – Manu H Apr 17 '19 at 09:33
  • @ManuH That's the Augmented Spark Igniter, which is basically a spark-lit blowtorch that blows into the combustion chamber, fueled by a small amount of fuel and oxidizer that are tapped off the main flow. – Tristan Apr 17 '19 at 13:56