Welcome to MyElectricEngine.Com! I've created this page to present the work and research I've done on electrical aerospace propulsion systems such as magnetoplasmadynamic (MPD) and arcjet thrusters. This work is both my hobby and the focus of my recently completed Masters thesis paper which I completed as a requirement of my Master's program. I received my Bachelor's degree in Electrical Engineering with high distinction from the Electrical and Computer Engineering Department at Worcester Polytechnic Institute in 2006, and followed that up with a Masters degree in Electrical and Computer Engineering from Worcester Polytechnic Institute in 2007. If you'd like to read the complete text of my Masters thesis, you can find it here.
My original involvement in electrical propulsion began as a bit of a dining hall joke, and demonstrates the dangers of keeping too many engineers in one place. One of my mechanical engineering buddies remarked over a particularly uninspiring dinner that he had always wanted to see a magnetoplasmadynamic thruster fire and proceeded to explain how these devices work. The basic construction is simple enough, involving only a power supply, some capacitors, and a suitable spark gap. The first design was soundly within the category of "kludge", but adequately demonstrated this simple device which at the time amounted to a large spark machine. More advanced designs quickly appeared and were built, culminating in an independent study and finally a Masters thesis project. 
I'm currently employed in research and development at Boeing Research and Technology, which is pretty excellent, so I'm not looking for a job, but you can still feel free to e-mail me at MyElectricEngine@gmail.com and take a look at my resume here or view it as a word document here.

Anyway, on to the good stuff.
Here is a list of all of the projects that I've documented. Watch for updates and improved designs.

  Magnetoplasmadynamic (MPD, Arc) Thruster  
This is the project that started it all, and attempts to find a reasonable thruster package that can provide high levels of thrust at high specific impulse levels on a budget. It uses electromagnetic forces to accelerate an electrically conductive, or ionized,  propellant gas out of a nozzle, and attempts to sidestep the limitations of chemical rockets by eliminating the dependency on thermal expansion of the propellant.. This description also includes brief introductions to the various subsystems that were built to support this design. The other components used in this project are more thoroughly described in the sections below.
   Capacitor Bank   
If high energy experiments are to be performed on a reasonable budget then chances are you're going to need to operate your device in a pulsed mode - i.e. at very high power levels for very short periods of time. This approach strongly suggests using a carefully designed capacitor bank. Both the electrical and mechanical design issues are explored, including the reduction of parasitic inductances and the mechanical requirements of high current conductors. Here's my design for a 28kJ electrolytic capacitor bank capable of delivering 200 Megawatts or more.
   Ignition Circuit  
How do you accurately and reliably trigger a high current discharge across a spark gap, such as the nozzle of a MPD or arcjet thruster? This problem is deceptively difficult, especially on a student's budget. We can take some advice from the design of Tesla Coils and arc welding equipment and develop a relatively robust solution using common components to create a high voltage, high frequency ignition circuit.
   Improved Ignition Circuit (Coming Eventually!)   
The previously described ignition circuit works very nicely, but is very heavy and generates a huge amount of EMI that persistently fouled up sensors, interfered with data collection, and even crashed computers within several tens of feet. This design uses the same concepts but replaces the bulky and heavy line frequency neon transformer with a more compact high high frequency transformer. Similarly, the spark gap is replaced with solid state switches that can operate at high frequency without the EMI associated with a spark gap.
   Gas Injection System   
The delivery of a propellant gas into a thruster nozzle is another critical aspect of the design, as the propellant gas not only provides thrust, but can also provides cooling to the nozzle, charge carriers to the plasma stream, and prevents the discharge from consuming the electrodes.

   Capacitor Bank Charger (Coming Eventually!)
One of the more difficult aspects of this project was precisely charging the capacitor stack to its full voltage of 700V, if both stacks are connected in series. This project aims to remove any guess work from charging by using a switching DC to DC converter to precisely charge the capacitor stacks.
  Arcjet Thruster (Kinda-Sorta Here!) 
The arcjet thruster has more in common with chemical rockets than the MPD thruster in that it heats a propellant gas to a high temperature and then expands that gas through a nozzle to convert the thermal energy into thrust. The big difference here is that the propellant gas is heated by an arc discharge, allowing for much higher temperatures and specific thrusts. This project was selected as a follow-up to the MPD thruster as it is easily implemented without the use of a vacuum chamber.
   Arc Supply   
This device operates continuously at a power level of about 11 kW, and therefore replaces the capacitor bank from the pulsed MPD thruster with a switching power supply operating from AC mains. This has the advantage of being much more controllable, and the lower power level increases the useful life of the electrodes enormously. A detailed switching power supply design is presented along with design documentation, simulations, spreadsheets, and manufacturing files.
   Ignition Circuit   
The ignition circuit presented here is very compact with relatively little radiated EMI, and is based on a resonant converter that is transformer coupled to the power circuit. A noteable deviation from previous circuits is the inclusion of a ferrite core in the coupling transformer which is allowed to saturate after arc ignition.

   Gas Supply   
Higher operating pressures required the design and manufacture of several custom components, particularly the high pressure valve based on a simple ball valve and an electric motor.

Collected Information

I spend a lot of time researching and collecting information on a wide range of subjects, much of which is dispersed widely and often of an obscure nature. I've collected those bits of information that I find useful here, in hopes that other people may find it useful as well.

 Arc Discharge Properties / Plasma Physics 1 
A large portion of the projects on this site involve plasmas and arc discharges. This page presents some of the basic features of an arc discharge, some of the basic equations that govern plasmas, and some helpful tips I've picked up along the way. 

  Arc Discharge Properties / Plasma Physics 2
A discussion of some of the more practicle issues related to plasmas and arc discharges, especially regarding the electrical terminal properties and V-I characteristics of arcs, as well as the physical phenomena from which they rise. Load and source line matching for ignition circuits and power supplies are also discussed. 

  Compressible Flow Basics  
Gasses under high pressure or at high velocities behave in ways that seem counter-intuitive to our everyday experience, but can greatly influence how certain flows behave. This page explains some of the basic differences between incompressible flows and compressible flows, and how they differ from how we might otherwise expect them to behave.
  Cv and Flow Calculations  
If you're ever looking to purchase a valve or gas solenoid, you're probably going to come across this funny parameter called cv. As an electrical engineer, no one every explained this to me, so I had to figure it out myself. Here's the important stuff you need to work with this parameter laid out for you so you can find the flow of a fluid through a valve.

Everything Else

For the time being, everything that doesn't neatly fit into the other categories will go here. That'll consist of smaller projects, circuit examples, and other bits of information.

Magnetic materials are crucial to the design of transformers, inductors, chokes, and other components. The basics properties of magnetic materials will be discussed along with information on designing magnetic components.

   Litz Wire, Parallel Conductors and Winding   
The simple low frequency models of basic items like conductors break down and simply can't adequately explain the high frequency behavior of these components. Particular difficulty arises in the design of magnetic components like transformers and inductors, where high frequency signals make the task of reducing losses surprisingly involved. Using thicker wire or using many parallel strands may make losses worse, or have no effect at all, at high frequencies. This article covers some of the issues and solutions when getting high efficiency out of magnetic components is important 

   Ignition Coils   
Since most of the projects and information on this site pertain to making big sparks, ignition coils are a good topic to cover. Ignition coils are magnetic devices found in older automobiles and are used to generate high voltages. Topics such as operating principles, measuring characteristics, electrical modeling, and driver circuits are covered.

   eBay is a Wonderful Thing  
Anyone interested in building interesting and crazy contraptions should get very familiar with eBay. Components and equipment worth hundreds or thousands of dollars can be purchased for pennies on the dollar, making available to everyone the kind of materials usually only available to businesses with large budgets. As if you needed convincing, I've collected information on some of my purchases here.
There are plenty of ways to cause serious injury to yourself when working on the kinds of projects shown here. I have a few bits of information that might be helpful, from dealing with equipment with asbestos wiring to dealing with industrial chemicals.

visitors since September 2007

Questions? Comments? Suggestions? E-Mail me at MyElectricEngine@gmail.com
Copyright 2007-2010 by Matthew Krolak - All Rights Reserved.
Don't copy my stuff without asking first.