Inside a rocket engine the propellant is sprayed, burned at enormous pressure and cooled so the metal survives. Follow fuel and oxidizer from two manifolds into the chamber and out of the nozzle, step by step.
The combustion chamber is the heart of a liquid rocket engine. It is a pressure vessel where fuel and oxidizer meet, ignite and burn, producing gas that is thousands of degrees hot at a pressure far higher than the tanks that feed it. At its top sits the injector plate; below it the gas accelerates through a throat and a nozzle.
From the outside the chamber is just a metal shell with pipes attached. Everything that matters â how the propellant is spread, sprayed, mixed, burned and cooled â happens inside, so cutting it open is the clearest way to see how the parts work together.
Fuel and oxidizer arrive from the turbopumps and wait in two separate manifolds just above the injector. They are kept apart because they would react on contact, so they only meet inside the chamber.
The injector plate is a thick disc drilled with many small orifices. It turns each stream into a spray of fine jets so that fuel and oxidizer mix as thoroughly as possible, which gives a clean and efficient burn.
The sprayed propellant ignites and burns, releasing heat and raising the pressure to a level far higher than the tanks. The chamber is built from heat-resistant metal to hold this gas.
Burning gas would melt ordinary metal, so cold propellant is routed through narrow channels along the chamber wall before it is burned. It absorbs heat and carries it away â this is regenerative cooling.
The gas squeezes through the narrow throat and reaches the speed of sound. Past it, the passage widens and the gas keeps expanding and accelerating to supersonic speed, leaving the engine as the fast exhaust that produces thrust.
It turns the two propellant streams into a spray of many fine jets. The finer and more even the spray, the better the fuel and oxidizer mix, and the cleaner and hotter the burn.
Because they react on contact. Keeping them apart until the injector is what lets the engine be stored and controlled safely, and it is only inside the chamber that they meet and burn.
By regenerative cooling. Cold propellant is routed through channels along the chamber wall before it is burned, carrying heat away so the metal stays below its melting point.
It is the minimum cross-section. Squeezing the gas through it brings the flow to the speed of sound, which is the condition that lets the widening nozzle accelerate it further to supersonic speed.
No. Past the throat a widening passage speeds the gas up rather than slowing it. That expansion is what turns hot, high-pressure gas into fast exhaust, and fast exhaust is thrust.