PowerLabs Electro-Thermal Research!

 Project Introduction:

 Electro-Thermal, or Electro-Thermal-Chemical guns (ET and ETC guns, respectively), along with Electro-Thermal Ignition (ETI) guns (these the subject of a later study) are not a novel idea, nor are they a particularly complex proposition. ET/ETC guns (from here on termed “ET” guns on this article) operate on the very same basic underlying principles of the simplest and oldest firearms; pressure is produced inside a sealed barrel, and this pressure is used to propel a projectile out of the barrel at high speeds. The modern twist employed here is that, by placing the energy source outside of the barrel, a much finer control of the propellant pressure achieved can be obtained. This opens up possibilities that were up until now unexplored, such as the ability to “dial in” to a very high degree of precision whatever muzzle velocity or energy is desired. Also, and more interestingly, by utilizing an external power supply to create propellant pressure, ET guns are not bound by the limitations of conventional propellants; energies and velocities can be as high as the structure of the gun will allow; as long as more power is introduced, the projectile will never outrun the propellant burn rate, as occurs with conventional propellant firearms at speeds of around 5000fps.

 My particular motivation for starting this research is my ongoing quest for more knowledge in what is currently my favorite research topic; electromagnetic propulsion. As with the railgun research, I am not looking at developing a weapon but rather trying to improve on this technology so that it may become more useful for all of the potential applications it has.

 Project Description and Goals:

1-     Produce a compact and reliable 50cal (1/2”, 11.22mm) caliber electro thermal gun also capable of operating in Electro Thermal Chemical regimen.

2-     Quantify gun performance in terms of muzzle velocity and kinetic energy for different types of projectiles in both ET and ETC regimen, calculate energy conversion efficiency from electrical power supply, and compare it with a similar conventional propellant gun.

      3- Optimize gun design with the ultimate goal of surpassing the conventional propellant gun in muzzle velocity achieved.

 Theory (a simplified overview):

Power Supply

Barrel Design:

Specifications: These barrels are made of Heat Trated Cromium Molybdenum steel (4140alloy). They are heat treated for maximum hardness. The barrels have a 1" outer diameter and are bored out to 50 calibre (1/2" inner diameter). The design operating pressure is 60 000PSI.

 The barrels are treated with a special bluing solution (a form of oxide coating to protect the metal) and then varnished on top of the bluing. Corrosion resistance is important since the ETC gun will be constantly exposed to electrolytes.

Here are the finished barrels (blued and varnished). I used the 1/2 dia. bolt below as a test for my bluing method. I read on numerous gunsmithing sites that DIY bluing was not worthwhile; I managed the results pictured here with a $4.00 bottle of bluing solution and about an hour's worth of cleaning and polishing. Not bad...

 Setup:

The current setup is embarrassingly primitive, but it works. Since I am not conducting this research at the University or with any external funding, everything is as simple and inexpensive as possible, while still being safe, of course.

 A 12kV 60MA Neon Sign Transformer is rectified by a 100kV X-Ray transformer full wave oil immersed rectifier and then used to charge a 20kV 10uF Aerovox oil filled pulse capacitor. The capacitor is then discharged into the gun through a solenoid actuated ball gap. 12 gauge 40kV high voltage silicone wiring is used for the charging connections and 8 and 4 gauge oxygen free copper cable is used for the gun connections. A high voltage probe is used to monitor charging.

 Electrode Design:

Currently automotive plugs are being employed. This greatly simplifies the design, even though it is non optimal. Automotive spark plugs are designed to withstand combustion temperatures of 1600F maximum at pressures of around 1000PSI. The ETC gun was designed to withstand pressures of up to 60 000PSI and it is estimated from other works that the plasma temperature is in the 30000 - 50000F range.
 In the future a proper electrode will be designed.
 Specs on the plugs are: Non resistive, copper cored, 14mm thread.

The center plug has been fired and has had its center section (pillar insulator) pulverized as a result. I am currently attempting to fill the gap with epoxy so as to avoid these problems in the future.

 Results:

At low energies the spark plugs stay together and produce a sharp crack and a jet of mist that will split thin wooden boards in half. At higher energies Bosch spark plugs explode in half. Champion plugs have stayed together so far.
 No attempts have been made yet to fire projectiles or to increase energy past 1kilojoule.

 Works Cited: