Relaxation relationship
In rocket engines, the expansion ratio is the ratio of combustion chamber to nozzle outlet pressure . Since these depend on the area or the diameter of the nozzle neck (narrowest point after the combustion chamber) and the maximum nozzle diameter, it can also be calculated as a ratio of these values.
The expansion ratio is an important parameter for the utilization of the kinetic energy (and thus the efficiency or energy yield) of the fuel mixture to generate thrust and also affects the specific momentum of the engines. In the case of engines that are used on the ground for take-off, the nozzle orifice pressure cannot or should not be below the air pressure on the ground. A high degree of efficiency can only be achieved here by using a high combustion chamber pressure, which increases the complexity of the engine. For engines that work in space , a high expansion ratio (due to the practically non-existent external pressure) can be achieved relatively easily by using correspondingly long (or large) nozzles. The expansion ratio of today's upper stage engines is around 50-100, with the highest values being achieved by Russian upper stage engines such as the RD-119 .
Individual evidence
- ↑ Peter Stache, Russian rockets, ISBN 3-327-00302-5
- ↑ Chemical rocket fuels (Bernd Leitenberger)