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Comparison of Liąuid Propellant Rocket Engine Feed Systems - 1 - 15

The turbinę inlet gases are to a very similar pressure to the one inside the gas generator. To make and optimistic estimation. it will be neglected any pressure fali that can occur in the heat exchanger and in the piping sections between the turbinę and the gas generator. In such a

way:

The ratio between the inlet and outlet turbinę gas pressure affects its efficiency. A higher value of this ratio is desirable but, however, very high values can causc pressure distribution problems in other parts of the engine [2],

It will be assumed that the rocket engine is vacuum operated, because this assumption was adopted for the other two feed Systems, and identical operation conditions are reąuired in order to make valid comparisons between the three systems. In conseąuence, an optimistic value of 20 is adopted for such ratio, taking into account that this is an open cycle engine, and thereby, the turbinę discharge pressure is defined as:

An optimistic value is taken for the turbinę efficiency according to the recommended values in the references [1 ] and [2] for an impulse turbinę

K =0.7|

Finally, the turbinę power density is estimated from [14] as:

3.6. Gas generator

With the objective of maximizing the efficiency, a chamber pressure as higher as possible is preferable. As the gas generator is fed from the propellants pumps, the same pressure than the one at the main combustion chamber will be adopted (which implies that the injector pressure fali in both combustion chambers will be the same), that is:

\P*=Pc\

In this case, the gas generator will work with the same propellants as the main engine. A strongly fuel rich mixture is reąuired to ensure a Iow combustion temperaturę, thus eliminating the use of some type of cooling system and, at the same time, limiting the turbinę blade erosion [1], So, it is adopted:

|0/F_g =0.01

From the above parameters, the gas generator molar mass, the specific heat ratio and the gas density can be estimated.

Finally, the stay time, for a gas generator like the one considered in this analysis, is established, according to [5]:

|/_s =1 Oms I