Researchers work to create new rocket exhaust design

A rocket nozzle that provides thrust more efficiently than existing designs is to be tested early next year at the University of Bristol, UK.

The shape of the nozzle is a major factor in the ability of an engine to convert its hot combustion gases into directed thrust efficiently. The exhaust gas pressure at the exit of the nozzle relative to the ambient atmosphere indicates the nozzle's efficiency.

If the exhaust pressure at the nozzle exit is far greater than the surrounding atmosphere, then the chamber and nozzle are not working efficiently.

To be efficient, the nozzle geometry should ensure that the exhaust gas pressure at its exit reduces to match the ambient atmospheric pressure throughout a rocket's flight.

Existing cone and bell exhaust designs do not facilitate this, but one that can is known as an expansion deflection nozzle. However, the concept has not been tested to date because of the unpredictable shockwaves that it can generate.

Now Bristol University researchers believe they have solved the problem.

Their nozzle works using a central plug on a pintle that shapes the exhaust gas from the combustion chamber, directing it down the walls of the nozzle at lift off in "open wake mode" (see diagram).

As the rocket travels upwards and atmospheric pressure diminishes, the exhaust gases will further expand within the nozzle.

Filling the nozzle's volume in "closed wake mode", the gas maintains equal pressure with the surrounding atmosphere throughout the flight.


Source: Flight International