Ciclo Ramjet

A schematic of a ramjet is given in Figure 3.25.
|
Figure 3.25: Ideal ramjet [J. L. Kerrebrock, Aircraft Engines and Gas Turbines] |
In the ramjet there are ``no moving parts.'' The processesthat occur in this propulsion device are:
*  : Isentropic diffusion (slowing down) and compression, with a decrease in Mach number,  .
*  : Constant pressure combustion.
*  : Isentropicexpansion through the nozzle.
The ramjet thermodynamic cycle efficiency can be written in terms of flight Mach number,  , as follows:

and

so

See also Section 11.6.3 for other figures of merit.11.6.3 Ideal Ramjet
To get started with a simple example (no turbomachinery), we will reexamine the ideal ramjet, picking up where we left off in Section 3.7.3. (Note that we will continue to usestation 5 as the exit station, consistent with Figure 3.25.)
11.6.3.1 Thrust
The coordinate system and control volume are chosen to be fixed to the ramjet. The thrust,  , is given by:where  and  are the exit and inlet flow velocities, respectively. The thrust can be put in terms of nondimensional parameters as follows:
| |     |
  | |     |

Using  ,  in the expression for stagnationpressure,

The ratios of stagnation pressure to static pressure at inlet and exit of the ramjet are

The ratios of stagnation to static pressure at exit and at inlet are the same, with theconsequence that the inlet and exit Mach numbers are also the same.

To find the thrust we need to find the ratio of the temperature at exit and the temperature at inlet. This is given by

where  is thestagnation temperature ratio across the combustor (burner). The thrust is thus

11.6.3.2 Fuel Air Ratio
To find the Isp will will need to find the ramjet fuel-air ratio,  . Using a control volumearound the burner, as shown in Figure 11.13, we get:

From the steady flow energy equation:

The exit mass flow is not greatly different from the inlet mass flow,  , because the fuel-air ratio...