Space Propulsion
Quarantine Lectures
Ihtzaz Qamar
Abstract
• These lectures are for the quarantine period
• Please go through the material carefully. Use internet
for further reading
• The topics will not be repeated once the university
resumes
And please:
• Follow self quarantine strictly. Educate your family
too.
• Wash you hands frequently with soap
• Use hand sanitizer when appropriate
• Stay Safe
Chapter 1
Atomization and Injectors
1.1 Impinging Injectors
We have already covered these in the classroom.
1.2 Swirl injectors
In these injectors the fluid is imparted an angular momentum when it passes
through. When the swirling liquid stream enters the large volume of the
combustion chamber, a change of momentum cause large forces to act on the
liquid jet which consequently is broken into small particles.
There are several types of swirl injectors.
1.2.1 Mono propellant pressure swirl injectors
1. Elements of a typical mono propellant pressure swirl injector are shown
in Figure 1.1
2. The main part is the swirler (#2)
3. The grooves (#4) impart the angular momentum to the fluid. Usually
3-4 grooves are used. More then 4 will not have a significant effect.
4. Spray is ejected as a cone from the injector.
5. The cone angle depends upon the groove inclination angle ϑ. Higher
the inclination angle more is the spread of the resulting cone. The
cone angle could vary from 60◦ to 160◦ . Cone angle also increases
initially with pressure drop across the injector, but is insensitive at
higher pressure drops. See Figure 1.3
2
6. The central hole, axial orifice (#3)plays an important role.
(a) An absence of axial hole results in a hollow cone as shown in
Figure 1.2 a&c
(b) In the presence of axial hole, the resulting cone is solid (filled) as
shown in Figure 1.2 b&d
For rockets we prefer the swirler without an axial hole. However, if this
type of injector is used for film cooling we would prefer a filled cone.
Someone trying to paint would also use the filled version
7. When two or more such injectors are close by, the cones intersect caus-
ing mixing of the propellants which is a desired effect.
8. In Ghouri missile, we use hollow cone mono propellant pressure swirl
injectors.
1.2.2 Mono propellant tangential swirl injectors
Having a swirler is not the only way to impart angular momentum to the
fluid. Consider the design shown in Figure 1.4. The fluid enters a cylindrical
cavity (swirl chamber) from four input ports which are tangent to the swirl
chamber. The fluid hits the inner wall of the swirl chamber at a tangent and
swirls around the wall. This imparts angular momentum to the fluid. The
fluid leaves from the nozzle. Once out, it is atomized in the form of a spray
cone. The situation is depicted in Figure 1.5.
Usually 2,3 or 4 input ports are used in these type of injectors. They are
simpler in design and quide popular in modern rocket technology. We have
done FYPs on the design and implementation of tangential swirl injectors.
The spray cone properties such as angle are controlled by diameter ratios
and other dimensions of the injector. The droplet average diameter increases
with increasing nozzle diameter. The effect of pressure is typical, pronounced
initially while it levels off at high pressures. Figure 1.6 showns a typical
graph.
Design Procedure
The document (attached) DesignProcedure097.pdf is a research paper which
all of you are required to read. Section 2 Design Considerations and Spray
Predictions explains effect of different dimensional ratios on sparay charac-
teristic.
3
Figure 1.1: Elements of full cone pressure swirl atomizers (Bayvel and Orze-
chowski., 1993) 1, body; 2, inserted swirl; 3, axial orifice; 4, groove and 5,
discharge orifice.
4
Figure 1.2: Pressure swirl injectors (Schick, 1997). (a) Hollow cone injector,
(b) full cone injector, (c) projection of hollow cone spray and (d) projection
of full cone spray.
5
Figure 1.3: Variation of cone angle with pressure drop at different groove
angles.
6
Figure 1.4: Elements of a Tangential Swirl Injector
Figure 1.5: Flow pattern of a typical tangential swirl injector
7
Figure 1.6: Effect of pressure on mean droplet size for three nozzle sizes
1.3 SMD: Sauter Mean Diameter
Please note that the mean droplet diameter being referred to is call SMD,
Sauter Mean Diameter. The atomized spray does not consist of single sized
droplets. There is always a droplet size distribution. As distributions, such
as Normal, are represented by two parameters, mean and variance, it be-
comes difficult to compare two droplet size distributions. For combustion,
the surface area of the droplets and the volume of these droplets play a sig-
nificant role. Sauter defined a mean diameter known as SMD and is defined
as diameter of a sphere that has the same volume/surface are ratio as the
particle of interest. Wikipedia entery ’Sauter mean diameter’ is a good read.
