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
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
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
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
quickly appeared and were built, culminating in an independent study
and finally a Masters thesis project.
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
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.
is a list of all of the projects that I've documented. Watch for
updates and improved designs.
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.
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.
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
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.
ignition circuit works very nicely, but is very heavy and
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.
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.
of the more
difficult aspects of this project was precisely charging the capacitor
stack to its full voltage of 700V, if both stacks are
series. This project aims to remove any guess work from charging by
using a switching DC to DC converter to precisely charge the capacitor
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
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 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.
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.
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.
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,
some helpful tips I've picked up along the way.
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.
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.
If you're ever looking to purchase a valve or gas
solenoid, you're probably going to come across this funny parameter
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.
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.
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.
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
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.
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.
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.