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Electrothermal Chemical Technology and Why it's Awesome

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Been delayed with stuff but I've wanted to post this.  Actually I'm surprised I've never seen anything in detail about this before, because it's an interesting topic.  (IF there IS a topic on this I apologize and it can be merged there.)  


ETC tech is something you probably hear about if you hang out on tank, military or gun forums.  Especially if Railguns or coilguns are mentioned.  Or 'next step' in gun design like 140-152mm guns.  There's lots of information out there if you look and you discover just how diverse it can be.


I'm sure most people are aware that Wikipedia has a article on ETC tech and as far as Wiki articles go it's decent.  But the person who worked on it in the past also wrote an article on ETC for the Nationstates draft room.  It's old but still good.  So despite the origins it's still useful (the writer was also a member on Tanknet IIRC.  Take that as you will.) 


In Jane's Technology of Tanks, Ogorkiewicz also commented about ETC:



3.10 Electrothermal Guns

Work on electromagnetic guns has led since the mid-1980s to the development of another category of guns which combine some of their features with those of solid or liquid propellant guns. These are electrothermal guns, which resemble solid or liquid propellant guns in that gases are generated in them to push projectiles through the barrels. In this respect they differ radically from the electromagnetic guns. But they also differ from solid and liquid propellant guns on account of the method by which the propulsion gases are created in them, this being by the interaction of an electrically generated plasma with a working fluid.


Because their projectiles are propelled by gases, electrothermal guns are not subject to the erosion which occurs with electromagnetic guns and their barrels can be much the same as those of conventional guns. At the same time, their working fluids can be selected so that the gases generated from them have a lower mass and. therefore, absorb less energy than the gases of solid propellant guns. But, whatever the working fluid, some energy is still absorbed in accelerating the propulsion gases and to this extent electrothermal guns are less suitable than electromagnetic guns for achieving very high projectile velocities. In fact, they are generally considered most suitable for velocities of up to about 2500 m/s.


Like electromagnetic guns, electrothermal guns require a source of pulses of electrical power, but the amount of electrical energy they need to propel projectiles can be reduced by generating a part of the propulsion energy by the chemical reaction of the working fluid. In consequence, there are two types of electrothermal guns. One might be described as a 'pure' electrothermal gun and derives all of its propulsion energy from the electrical power source. The other type derives some, or even most, of the propulsion energy from the working

The first type of electrothermal gun uses an inert working fluid such as water. This is heated endothermically by the plasma and vaporises to produce propulsion gases which have a lower molecular weight than those produced by the combustion of solid propellants. However, in this type of gun all the energy required to propel projectiles has to come from the electrical power source, with all the problems that this entails, as it does with electromagnetic guns.


The second type of electrothermal gun uses a reactive working fluid. This can be of a mildly exothermic nature, an example being a slurry consisting of aluminium,  titanium hydride and water. When such a slurry is heated by the plasma, chemical reaction between its ingredients produces heat as well as low molecular weight products. As a result, an electrothermal gun using this kind of working fluid not only has the internal ballistic advantage of low molecular weight propellant gases but also requires considerably less electrical energy to propel projectiles than the 'pure" electrothermal guns. In fact, only 30 to 40 per cent of the energy required to propel projectiles may need to come from the electrical power source, the rest being generated by the chemical reaction of the working fluid.


The working fluid can also be of a highly exothermic nature, an example being a mixture of a fuel, such as octane or kerosene, and of hydrogen peroxide. In this case plasma energy is used to vaporise the fuel and mix it with the peroxide to produce a chemical reaction which results in moderate molecular weight products and generates most of the energy for projectile propulsion. The percentage of energy generated by the reaction of the fuel-oxidizer mixture may actually be as high as 80 per cent and this obviously reduces considerably the size of the electrical power plant required with a gun using this kind of working fluid. Guns using such a high energy working fluid have been developed in the United States since 1986 by FMC Corporation, which has called them 'combustion augmented plasma', or CAP, guns. However, because most of their propulsion energy comes from the fuel-oxidizer mixture, they can also be regarded as bulk-loaded liquid bipropellant guns in which the instabilities associated with bulk-loaded liquid propellants have been suppressed by the flow of the electrically generated plasma.

The plasma which introduces electrical energy into electrothermal guns is generated in a cartridge with a capillary tube containing a wire connected to a blocking electrode at one end and an annular, nozzle electrode at the other end. The wire explodes when a large surge of current is made to pass through it and this establishes the plasma which flows rapidly out of the capillary into the chamber containing the working fluid.


As in the case of electromagnetic guns, the pulses of electrical power required to generate the plasma can come from a number of sources but they involve only two basically different methods of intermediate energy storage. In one, energy supplied by an engine is stored in the form of the rotational kinetic energy of a homopolar generator or of a compulsator. In the other, electrical energy supplied by an engine-driven alternator is stored in a bank of capacitors, either by charging them directly, or indirectly, through an intermediate battery storage subsystem. With either form of energy storage the pulses of power which are drawn from it have to be suitably shaped in a pulse forming network.


Ogorkiewicz also discusses the concept in Tanks: 100 years of evolution:



In contrast, the prospects of arming tanks with another type of electric gun, the electro thermal-chemical or ETC gun, were brighter from the start because only part of the energy it used to launch projectiles was electrical, the rest coming from the chemical reaction of a solid or liquid propellant. In consequence, the ETC guns did not require electrical equipment as large and as heavy as the EM guns.



Development of ETC guns was pioneered by GT Devices, a small US company that started firing 20mm ETC guns in 1985 and was subsequently taken over by General Dynamics Land Systems (GDLS). In 1985 FMC Corporation also started work on what it called Combustion Augmented Plasma Guns, in which originally most of the projectile propulsion energy was expected to be electrical but which were in effect ETC guns. The early work on ETC guns was so promising that by the end of 1989 a competitive trial was arranged between 120mm tank guns converted by GDLS and FMC into ETC guns, which were intended to demonstrate that an ETC gun could arm the next version of the US M1 tank. The trial was clearly premature, and proved so disappointing that it led to an equally rash view that ETC guns were less promising than EM guns. This view was reached, among others, by the US Army Science Board, which recommended in 1990 that development funds be diverted from ETC to EM guns. 23 Similar views were held in Britain, where RARDE had already shown little enthusiasm for ETC guns.

However, the US Army continued to support research into ETC guns and ordered a 9 MJ 120mm ETC laboratory gun from FMC, which was installed in 1991 and from which projectiles were fired at up to 2,500m/s. Work on ETC guns was also pursued in Germany, where it started in 1987, and resulted in the construction by Rheinmetall of a 105mm ETC gun thatby 1995 fired projectiles at up to 2,400m/s. This was followed by the design of a 120mm ETC gun that began to be used for firing trials in 1999, and by collaboration with France, where another 120mm ETC gun was built by GIAT and started firing trials in 2003.

Since 1986, work on ETC guns has also been pursued in Israel at the Soreq Nuclear Research Centre, which pioneered the use of solid propellants as the source of the chemical part of the projectile propulsion energy instead of the liquid or slurry propellants used originally by FMC and GDLS. Soreq’s lead was followed by others, and since the early 1990s the development of ETC guns has concentrated on the solid propellant form of them, becoming focused during the 1990s on guns of 120mm calibre.

The object of the development of the solid propellant 120mm ETC guns that was pursued in the United States, Germany and elsewhere became that of making them a potential alternative to 140mm solid propellant guns that were being developed for the defeat of future enemy tanks. In the course of this development, the use of a 120mm ETC gun was considered in the early stages of the US Future Combat Systems programme and in 2004 United Defense LP (originally FMC and now BAE Systems) successfully fired a 120mm ETC gun from a light tank developed from a much modified M8 Armored Gun System. An ETC gun was also included in the plans for a new family of armoured vehicles that were drawn up in Germany in the late 1990s, and by 2002 Rheinmetall demonstrated
a 120mm ETC capable of generating 30 per cent more muzzle energy than the 120mm solid propellant gun on which it was based. 24

However, even though 120mm ETC guns were considered capable of firing projectiles with a muzzle energy of 15 MJ, their performance still fell short of that of 140mm solid
propellant guns, which could fire projectiles with an energy of 18 to 23 MJ and at the same time enjoyed the advantages of being based on well proven technology.




One realization from this is ET/ETC technology is quite diverse and can be confusing.  One of the better sources covering that concerned Rheinmetall research into a German 120-140mm (courtesy of Wayback because the original source fell to link rot):


Link to image of Rheinmetall ETC classifcations



On the amateur experime which discusses ET/ETC stuff in detail too.   If you prefer the more 'hype' side of things, ETC was also tied to the Future Combat Systems - a link some people may recognize:




Encouraging results have been obtained with   Electro-Thermal-Chemical   (ETC) experimental  guns.   In  principle,  an  ETC gun utilizes a chemically energetic (reactive)  working  liquid  instead  of  conventional solid propellant. It requires considerably  less  electrical  energy  to  achieve adequate  projectile  propulsion  than  its predecessor,  the  Electro-Thermal  experimental   (ET)   gun.   It   needs   relatively smaller  and  lighter  auxiliary  equipment to   produce   and   store   electricity.   This equipment  could  ultimately  be  reduced to  a  suitable  size  to  warrant  its  installation   in   an   armored   vehicle.   Energetic working  liquid  is  naturally  prone  to  be problematic  in  operation,  handling,  storage,  and  supply,  such  that  its  utilization will  pose  a  potential  safety  concern  and a  logistic  burden,  much  similar  to  LP guns.  As  in  LP,  ETC  implementation  requires  new  industrial  and  military  infrastructures   for   production,   deployment, and logistics.


Current  developments  are  aimed  at  a medium caliber (60-80mm), antitank gun with  a  firing  rate  of  10-15  rounds/min. At  this  caliber  range,  various  types  of rounds  could  be  comprised  of  KE  projectiles  and  CE  rounds,  as  well  as  future ‘smart’  sensor-fuzed  munitions.  The  ultimate  objective  is  aimed  at  an  ETC  automatic  gun  with  a  muzzle  energy  of  20+ MJ  (corresponding  to  2500-3000  m/sec for  medium  calibers)  which  is  comparable to that of the conventional, solid propellant  140mm  gun.  Much  like  LP  guns,  ETC  technology  allows  better  control  of the  pressure  (propulsion)  generated,  so that it is maintained relatively close to its maximum  while  the  projectile  is  moving down  the  barrel,  resulting  in  more  energy conveyed to the projectile.


This  is  quite  contrary  to  conventional SP    technology,    where    the    pressure quickly  diminishes  as  the  projectile  departs   from   the   combustion   chamber. ETC  technology  is  recognized  by  many to  show  promise  of  “infinite”  or  multistage   variable   lethality   and   improved propulsion controllability. It also requires significantly   less   electrical   energy   in comparison   to   Electro-Magnetic   (EM) guns  that  use  only  electricity  for  projectile  propulsion.  Nevertheless,  ETC  technology,  as  promising  as  it  may  seem,  requires  further  fundamental  research  beyond the laboratory stage. Much detailed research and testing has yet to be accomplished  in  the  field  and  at  weapon  system  level.  It  must  achieve  maturation  to warrant  its  applicability  as  a  stand-alone solution,  or  in  conjunction  with  other mature   technologies,   or   with   existing 120/140mm guns.


As  an  additional  practical  alternative, ETC technology could be combined with existing  conventional  SP  120mm  and/or future   140mm   guns   and   ammunition, though   a   new   cartridge   and   modified gun chamber are required. It represents a near-term  upgrade  application  of  already leveraged  and  proven  technology.  The size  of  the  electrical  equipment  is  much smaller  than  that  of  current  EM  research guns  and  present  ETC  as  a  viable  upgrade  proposition.  Research  has  shown that  specially  designed  ammunition  and ETC  gun  technology  could  be  combined with  existing  conventional  SP  guns  to further  enhance  the  performance  of  the latter  up  to  30%  and  beyond.  Augmenting  the  energy  of  solid  propellant  is  possible  by  implementing  a  plasma  regenerative  injector  and  combustion  control to  the  conventional  pressure  chamber.  In the  event  that  ETC  technology  will  become   practical,   existing   conventional 120mm  and  future  140mm  guns  could be  economically  converted  into  ETC/SP guns  as  one  more  step  in  the  evolution of  SP  guns.  There  are  still  various  predominating   problems   to   be   addressed and  resolved  before  ETC  guns  can  become  a  practical  proposition  in  conjunction  with  conventional  solid  propulsion.  The  combination  of  controllable,  repeatable  inner  ballistics  with  a  compatible solid  propellant,  and  the  significant  increase  in  performance  (e.g.  muzzle  velocity)  in  large  caliber  guns,  has  yet  to be demonstrated.


Regardless  of  whether  ETC  technology will become a viable proposition, the use of  large  consumable  ammunition  in  addition  to  ‘energetic’  liquid  propellant  is contradictory  to  the  requirement  of  reduced    dependency    on    logistics    and weight.   The   combined   implementation of  SP  with  ETC,  will  probably  not  justify  the  enormous  investment  in  design, development  and  deployment  associated with  the  fielding  of  an  entirely  new  tank fleet.  Though  new  and  promising  technology,  it  will  not  change  the  nature  of armored warfare.



As you can see, ETC is evolutionary  not revolutionary like EM guns.  It takes existing technology and builds on it:  You can settle for improving propellant ignition (minimizing electrical cost) or add electricity to boost performance (up to the 'pure' ETC idea)   You can also utilize the technology on Liquid propellant and possibly even Light Gas guns - it stacks quite nicely with other ideas.  You can even use it with a bigger caliber.  This is part of the ETC charm.


Further information on ETC stuff can be found here:




Electro-Thermal Chemical Gun  Technology  Study


Both of these are articles I like, but there's more stuff:


Electrothermal-Chemical (ETC) Technology Weaponization Issues


Electrothermal-Chemical Gun Systems  Utilizing Novel Electric Solid Propellants


And of course DTIC is a wealth of ETC stuff:


(direct pdf links):

Overview on the  German R&D Programs on ETC  Gun Technologies for Main Battletank  Weaponization




And some dtic links to ETC stuff that requires download:


Electrothermal-Chemical (ETC) Propulsion with High Loading Density Charges.


Ballistic Analysis of Electrothermal-Chemical (ETC) Propellant.


Trade-Offs in Performance Enhancement of Solid-Propellant (SP) Electrothermal-Chemical Guns.


Sturgeon's House user sevich also posted a link to a useful ETC document off ditc  here


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