propellant

1. Propellants

2. • In ballistics and pyrotechnics, a propellant is a
generic name for chemicals used for
propelling projectiles from guns and other
firearms.

3. • Propellants are usually made from low
explosive materials, but may include high
explosive chemical ingredients that are diluted
and burned in a controlled way (deflagration)
rather than detonation.
• The controlled burning of the propellant
composition usually produces thrust by gas
pressure and can accelerate a projectile,
rocket, or other vehicle.

4. Gun propellants, such as:
• Gunpowder (black powder)
• Nitrocellulose-based powders
• Cordite: a smokeless explosive made from
nitrocellulose, nitroglycerine, and petroleum jelly,
used in ammunition.
• Ballistite: a smokeless propellant made from two
high explosives, nitrocellulose and nitroglycerine. It
was developed and patented by Alfred Nobel in the
late 19th century
• Smokeless powders

5. • Grain: Propellants are used in forms called grains.
A grain is any individual particle of propellant
regardless of the size or shape. The shape and
size of a propellant grain determines the burn
time, amount of gas and rate produced from the
burning propellant and consequently thrust vs
time profile.

6. • There are three types of burns that can be
achieved with different grains.
• Progressive Burn Usually a grain with multiple
perforations or a star cut in the center providing
a lot of surface area.
• Digressive Burn Usually a solid grain in the shape
of a cylinder or sphere.
• Neutral Burn Usually a single perforation; as
outside surface decreases the inside surface
increases at the same rate.

7. Composition
• There are four different types of solid propellant
compositions:
• Single Based Propellant: A single based propellant has
nitrocellulose as its chief explosives ingredient.
Stabilizers and other additives are used to control the
chemical stability and enhance the propellant’s
properties.
• Double Based Propellant: Double based propellants
consist of nitrocellulose with nitroglycerin or other
liquid organic nitrate explosives added. Stabilizers and
other additives are used also. Nitroglycerin reduces
smoke and increases the energy output. Double based
propellants are used in small arms, cannons, mortars
and rockets.

8. • Triple Based Propellant Triple based propellants
consist of nitrocellulose, nitroquanidine,
nitroglycerin or other liquid organic nitrate
explosives. Triple based propellants are used in
cannons.
• Composite Composites contain no nitrocellulose,
nitroglycerin, nitroquanidine or any other organic
nitrate. Composites usually consist of a fuel such
as metallic aluminum, a binder such as synthetic
rubber, and an oxidizer such as ammonium
perchlorate. Composite propellants are used in
large rocket motors.

9. Liquid propellant
Common propellant combinations used for liquid
propellant rockets include:
• Red fuming nitric acid (RFNA) and kerosene or RP-1
• RFNA and Unsymmetrical dimethyl hydrazine (UDMH)
• Dinitrogen tetroxide and UDMH, MMH and/or
hydrazine
• Liquid oxygen and kerosene or RP-1
• Liquid oxygen and liquid hydrogen
• Liquid oxygen and ethanol
• Hydrogen peroxide and alcohol or RP-1
• Chlorine pentafluoride and hydrazine

10. Common monopropellant used for liquid rocket
engines include:
• Hydrogen peroxide
• Hydrazine
• Red fuming nitric acid (RFNA)

11. • When a projectile weapon is launched from the
gun barrel, it is accelerated to a high velocity by
the burning of propellant.
• The propellant may travel with the projectile or
be stationary in the barrel. The gasses produced
by the burning propellant are trapped in the
volume behind the projectile.
• The introduction of more heat into the product
gasses causes the pressure to rise which in turn
will accelerate the projectile.
• On the other hand, the movement of the
projectile increases the volume which tends to
drop the pressure.

12. Figure1. How projectiles are launched from a gun.

13. • Initially, the pressure will rise, dominated by the
introduction of heat.
• As the projectile gains speed, the expansion
effect will get larger until a maximum pressure is
reached.
• Afterwards, the pressure will drop rapidly.
• The maximum or peak pressure determines how
much stress the barrel must be designed to
withstand.
• Very large peak pressures require thick barrels.

14. Figure 2. Degressive burn rate

15. Figure3 Neutral burn rate
• On the other hand, if the propellant is burned
from the inside as well as the outside, the net
surface will stay the same, creating a neutral
propellant.

16. • Lastly, the burn may proceed from many
smaller interior positions, in which case the
propellant will be progressive:
Figure4.Progressiveburnrate

17. • Most propellant is not solid, but it comprised
of many small pellets. The shape of the
individual pellets will determine the type of
burn rate. For cylindrical pellets the three
types might look like this:
Figure 5.Pellet type propellant shapes.

18. • The type of propellant will alter the shape of the
pressure vs. position curve.
• Progressive pellets raise the pressure more slowly
than degressive propellants.
• For this reason, the peak pressure is often less.
• On the other hand, degressive propellants
accelerate the projectile more rapidly in the initial
portion of the barrel, while progressive
propellants can reach higher exit velocities.
• A comparison of the two types is shown below:

19. Figure 6.Progressive Vs digressive propellants

20. • Which type of propellant to use depends on the
application.
• If the barrel cannot be made very long, it is better
to use a degressive propellant to achieve the
maximum exit velocity in a limited distance.
• An example might be cannon on an aircraft. As a
consequence, however the barrel must be thicker
to withstand the increased peak pressure.
• If length is not restricted, a progressive propellant
can be used to minimize stress and achieve the
maximum exit velocity.
• An example might be a gun on a ship or tank.

21. Shapes of Propellant

22. Propellant Geometry Type
• Smokeless propellant has three basic chemistry
types; single base, double base, and triple base.
• Single base propellant uses only nitrocellulose as
the primary energetic.
• Double base propellant uses nitrocellulose and
nitroglycerine,
• while triple base uses the double base
formulation, and adds an additional energetic,
typically nitroguanidine.

23. • A propellant characteristic known as
“progressivity” is important because it causes
increasing gas generation as the propellant burns.
• Progressivity can be achieved either by chemical
means (via a deterrent coating on the exterior
grain) or by geometry (shapes selected because
their surface area increases as the grain burns).
• Figure 1 shows the relative surface area as a
fraction of propellant depth burned for typical
propellant geometries.

25. • Since the sphere, cord, and flake geometries have
decidedly digressive area vs. depth burnt
characteristics, those propellants have to use
surface deterrent coatings to enable any
“progressivity” to be exhibited.
• The tubular (single perforation) grain is ever-so-
slightly digressive in geometry; the inside surface
increases in area as the outside surface decreases
in area, the end faces can only lose area during
propellant burn.

26. • Application of deterrent coatings (sometimes
called combustion moderators) mean that when
simulating the interior ballistic behaviour of such
propellants, the initial burn rate coefficient will
be smaller than the final burn rate coefficient.
• When no deterrent coatings are applied, the
initial and final burn rate coefficients are equal to
one another.

27. • Ammunition engineers should be aware that,
best efforts of the propellant manufacturer to
the contrary, there will be minor variations in
propellants lot-to-lot.
• Thus, powder makers are usually relegated to
some sort of lot “blending” of fast and slow burn
stocks to achieve the desired pressure-velocity
performance for a particular application.

28. Flake:
• Flake propellant is commonly used in applications where
rapid and complete combustion is of primary importance.
• In these applications, the peak pressure is usually much
lower than other high performance ammunition, and
projectile mass/diameter ratio is usually low, meaning the
volume in which the propellant expands will grow very
quickly by projectile movement.
• This would otherwise cause rapid pressure fall-off unless
the powder is consumed rapidly. This propellant geometry
typically uses no exterior combustion inhibitors (e.g.
deterrents) to further enhance the ability of the powder to
burn rapidly.
• Chemically, flake powders are usually double base
formulations.
• Typical applications for this powder geometry include:
Pistol and shotgun cartridges, blanks and Mortar Charge
increments.

29. • Flake propellants are made by shaving
extruded propellant cords into thin flakes.
• The thickness of the shaving controls the
powder “web”, the minimum dimension which
must be burned for the propellant to be
completely consumed.
• Figure 2 shows a close-up of flake propellant
geometry.

31. Ball:
• “Ball” powder is a Trademark of the St. Marks
Powder Company for its brand of spherical double
base (e.g. nitrocellulose and nitroglycerine)
propellant.
• While the propellant grains start roughly spherical,
they are commonly “rolled” to change (flatten) their
shape to an oblate spheroid to enhance loading
density and ignitability.
• Depending on the exterior deterrent applied to the
propellant, it is commonly tailored for applications
from pistol cartridges up to 25x137mm direct fire
ammunition and mortar propelling charges.
• Figure 3 shows two Ball powder variants; W748 is on
the left and W231 is on the right.

33. • The W748 has a significant amount of deterrent
coating (~5%) applied to its exterior and is only
slightly “rolled”; it is intended for use at high
pressures in rifles.
• The W231 is a ball propellant with no deterrent
coating on its exterior and significantly rolled to
control the propellant web. This powder is
typically used in pistol cartridges.

34. Cord:
• Cord propellant is in the shape of a right circular
cylinder; it is formed by pressing plasticized
propellant through an extrusion die.
• The cords are cut to a length close to the grain
diameter to facilitate desirably dense loading.
• Cord propellant can be made with either single
base or double base chemistries.
• Applications range from rifle to 25x137mm.

36. Single Perf (Tubular):
• Single perf (oration) propellant is in the shape of a right circular
cylinder.
• It differs from cord propellant in that it has a hole along the
grain axis to allow the interior to burn from the inside out, as
the exterior burns from the outside in.
• Single perf, tubular powders are made with a variety of
deterrent levels depending on the application.
• For example, Blackhorn 209 is a black powder substitute
intended for use in muzzle loading firearms and as a result, this
powder uses no deterrent to help with ignitibility.
• The IMR powder series manufactured by GD-OTS in Valleyfield,
Québec has significant deterrent coating applied to its exterior
to allow for use at high pressures in rifle applications.
• Single perforation propellant grain geometry is used all the way
up to 155mm propulsion charges; with combination of web size
and deterrent coatings specifically tailored for the required
task.

38. • The geometry of Blackhorn 209 is chosen
specifically to limit the loading density of the
extruded grains, and enhance the permeability of
the propellant bed to the ignition flame front.
• Like the cord propellant, it is formed by pressing
plasticized propellant through an extrusion die,
but this die has a pin suspended in the center of
its axis by a thin metal sheet called a “spider”.
• The red circle on the right-hand side of Figure 5
indicates a propellant grain that shows signs of
the “spider” used to support the pin in the
center of the forming die used to shape the
propellant grain.

39. 7-Perf:
• The 7-perf propellant is in the shape of a right circular
cylinder, and it expands on the single perf grain by
adding 6 more perforations in a hexagonal
arrangement surrounding the center perforation.
• These grains are made typically in double base or triple
base chemical formulations and with few exceptions,
these grains typically do not have deterrent coatings
applied to their exterior.
• Usage extends from 25x137mm to 155mm artillery
applications; these powders typically launch projectiles
that are on the low end of the bullet mass/diameter
spectrum for the smaller calibers in which it’s used.
• Figure 6 shows the perforation arrangement of a 7-perf
propellant grain.

41. 19-Perf:
• The 19-perf propellant grain is also in the shape
of a right circular cylinder, and it expands on the
7-perf grain by adding 12 more perforations in an
evenly spaced arrangement surrounding the
center 7 perforations.
• Figure 7 shows a 19-perf grain intended for use
in an artillery application (203mm) in original
state (left) where the perfs are barely visible, and
a partially burned state (right) where the perfs
are clearly visible.
• This propellant geometry can be made with any
previously mentioned chemical composition.