Aerospace & Defense Technology - October 2024 - 8

Weapons & Armament
The initial study highlighted in this article will occur at the Texas Tech University Combustion Lab. Pictured
here is the lab's High Velocity Impact Ignition Testing System (HITS). (Image: Texas Tech University)
force and stress in the gun chamber and
barrel. Safe designs must restrain this pressure
without yield and fatigue of the metal
components to keep soldiers safe. Pressure
over time also directly correlates to acceleration
and velocity of the projectile. As
next-generation weapon systems aim to
push traditional performance boundaries,
an aggregate macroscopic view of the interior
ballistic cycle is no longer adequate. In
addition, advances in manufacturing
technology have opened the design space
for control of geometry and spatial distribution
of chemical species, even within a
single propellant grain, for optimal performance.
Therefore, further improvements
to projectile velocity and range, without
exceeding a gun chamber's material allowable
stress level require detailed knowledge
and fine-tuning of several parameters such
as grain geometry, chemistry/burn rate
and ignition propagation through the
porous propellant bed. However, it all
starts with the ignition event and flame
propagation throughout the propellant
bed. Without a more thorough understanding
of the early time initiation mechanisms,
weapon system performance
improvements from modification of other
system parameters will be limited.
A team of scientists and engineers led
Rounds feed into the chamber of an M2HB .50-caliber machine gun on the fantail aboard Nimitz-class aircraft
carrier USS Carl Vinson (CVN 70) during a live fire exercise as a part of Annual Exercise (ANNUALEX)
2023. (Image: U.S. Navy)
Weapon designers often simplify the
ignition and combustion process by
assuming it behaves in a quasi-static
manner, and therefore the thermodynamic
state across the entire combustion
chamber at any point in time is
modeled by single, uniform state variables
such as temperature or pressure.
Unfortunately, experience has shown
that this assumption is not always accurate,
sometimes with dramatic safety
and performance consequences. In
8
many cases, deviations from ideal quasi-static
conditions in the combustion
chamber can be attributed to variations
in the ignition of the propellant bed and
are therefore a direct consequence of
inadequate ignition train design and a
fundamental lack of understanding of
the ignition mechanisms.
After the ignition event, gun chamber
pressure is generated by the propellant
combustion creating heat and gaseous
products. Pressure is directly linked to
mobilityengineeringtech.com
by Texas Tech University, Department of
Mechanical Engineering Combustion
Lab with support from Element U.S.
Space and Defense and the U.S. Army
Combat Capabilities Development Command
- Armaments Center (DEVCOMAC)
at Picatinny Arsenal are in initial
phases of an experimental program to
measure and better understand these
gun propellant ignition phenomena.
Typically, the ignition event starts with
either a mechanical device such as a
spring-accelerated pin striking a percussion
primer, or an electric current passing
through the primer. This stimulates the
first chemical reaction in the ignition
train, with a small primary explosive generating
heat and products that further
ignite the main primer charge. Finally, the
thermal energy, pressure and products
from the primer charge vent into the main
propellant chamber as a two-phase flow.
The main propellant chamber is loaded
with propellant grains which can be characterized
as a porous bed of solid particles.
The two-phase primer exhaust flows in
Aerospace & Defense Technology, October 2024

https://mobilityengineeringtech.com

Aerospace & Defense Technology - October 2024

Table of Contents for the Digital Edition of Aerospace & Defense Technology - October 2024