Static test of the “Snark” Variable-Thrust Bi-Propellant Liquid Rocket Engine by Airborne Engineering Limited.
This montage shows the engine operating at three different thrust levels (lowest at top of picture, highest at bottom). Notice how the mach-diamonds move apart as the thrust is increased.
The black wire hanging down near the flame is from the ignition system, the end of which is spat out from the nozzle at start-up. The bracket it is wrapped around is one of the mounts for the linear actuators which are used to steer the engine when it is attached to a rocket.
The spark trails visible near the flame are caused by the ablative combustion chamber liner.
The propellants are nitrous oxide and isopropyl alcohol. The maximum thrust level is 300N. Throttle ratios of up to 5:1 have been demonstrated without the engine showing any signs of instability. In this test, the throttle valves were digitally controlled using an Arduino microcontroller.
The Snark engine is of a modular design which can be configured for different thrust ranges. The example shown here is at the low end of the thrust spectrum. Thrust levels up to 2KN are possible in this form-factor (3 inch diameter chamber) by using a larger nozzle and injector.