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Hi! My name is Salvatore Aiello, I live in London and this site is a
personal record of my ongoing project for the designing and construction of
a DIY home built turbocharger based jet engine/gas turbine/turbojet and
using this engine in a motorcycle type vehicle. I'm a motorcyclist so
this type of vehicle was a natural choice for me! ;o) There are many
personal websites ( see links below ) and a few groups devoted to building
these engines where the theory and practice of how these fiery beasts
work is well documented. I've always been interested in engines and things
mechanical and like many others have dreamed of building my own jet engine
but always thought it to be an impossibly difficult task. It was only when I
heard that someone had built a jet engine based on an automotive
turbocharger that set me off on an internet search for more information...
I belong to ( and moderate ) a Yahoo Group ( see
below ) whose
members are devoted to the building and often mounting of these home
built jet engines into moving vehicles and who have been an invaluable
source of information and support. I've been working on and off my
project for a good few years now and the design has gone through many changes.
there are many off the shelf options in the form of model jet engines that
you can buy that are light, efficient and with high thrust to weight ratios
or there are even plans to build these yourself, but these ready-to-run engines are
relatively expensive and building them yourself more technically
challenging ( Here's an unusual use for a few of these engines!
). With a turbocharger based engine most of the hard work is done,
the only other major item is the addition of a suitable combustion chamber (
plus a few other bits and pieces..! ). Most of these items can be found in a
scrap yard and can be picked up for next to nothing. Ebay is also a very
good source for parts, in fact I've managed to find at least 95% of my parts
this way! If you can use a welder, have access to basic tools and
don't mind getting your hands dirty then you too can own one of these
There is no one definitive design of
turbocharger based engine that you can follow, there are as many different
designs as there are engines that people have built. Having said that, there
are general design guidelines that you will need to consider in order to get
one of these engines to run.
How Do Jet
A jet engine works
on the principle of
Sir Isaac Newton's third law of
physics, i.e. for every action there is an equal and opposite re-action.
The action of forcing gases out from the rear of the jet engine results
in a re-active force in the opposite direction, and is commonly referred
to as 'thrust'.
This thrust is measured in pounds force (lbf ), kilograms force (kgf ),
or Newtons (N).
Engines of this type are often referred to as 'Reaction Engines', a
rocket engine being another example. Newton's third law and the action
of a jet can be demonstrated in simple terms by inflating a balloon and
releasing it, the escaping air propels the balloon in the opposite
Creating thrust takes energy. The energy required is obtained from
burning fuels, whether it be in gas or liquid form such as propane,
kerosine, diesel or even vegetable oils! This fuel is normally combined
with pressurised air to increase the efficiency and power output for a
given engine size. This fuel/air mixture is burned in some form of combustion
chamber where the resulting hot gases expand creating an increase in
pressure inside the combustion chamber. The expanding gases are then
used to do useful work. One example of this process is what happens
inside the cylinder of a car engine. Air and fuel are drawn into the
cylinder by the downward movement of the piston, the piston then moves
up and squeezes this mixture which is then ignited. The fuel burns
creating a sudden sharp rise in pressure inside the cylinder. This
pressure then forces the piston back down producing mechanical work. The
piston then moves back up the cylinder to eject the burnt fuel ready for
another cycle. This process is commonly referred to as the 'Suck,
Squeeze, Bang, Blow' cycle! (SSBB).
of the Operation
of a Typical Jet Engine
and a Four
Stroke Internal Combustion Engine
The way a basic
Turbojet engine burns it's fuel is exactly the same as
in a car engine, but instead of burning the fuel in discrete packets, the
jet engine continuously sucks, squeezes, bangs and blows all at the same time! Also,
instead of using the expanding gases to push on a piston, they are
released through the turbine blades which takes some of the energy to
drive the compressor, the rest being released to the atmosphere which results in 'Newtons' thrust
described above. In a basic turbo jet, the air enters the front intake
(suck) and is compressed by the compressor (squeeze), then forced into
combustion chambers where fuel is sprayed into them and the mixture is
ignited (bang). The gases which form expand rapidly, and are exhausted
through the rear of the combustion chambers and out through the nozzle
(blow) providing the forward thrust. Just before the gases enter the
engine nozzle, they pass through a fan-like set of turbine blades
which rotates the engine shaft. This shaft, in turn, rotates the
compressor, thereby bringing in a fresh supply of air through the
intake. All of these processes are happening at the same time. Engine
thrust may be increased by the addition of an afterburner section into
which extra fuel is sprayed into the exhausting gases ( which contains
surplus hot oxygen ) to give the added thrust.
this point you may be asking yourself, "what actually makes it work?".
When we effectively create a continuous explosion in our combustion
chambers, what's to stop that explosion exiting the wrong way out of the
compressor as opposed to out of the turbine? What is the physical
explanation involved that will drive our engine ( and for that matter
ANY jet engine ) the right way? The short answer to this is turbine to
For a slightly longer answer, I shall endeavour to explain below what it
is and how it's used in a jet engine.
Lets start with an experiment. Imagine we have a typical jet engine like
the one in the diagram above, that isn't running. We inject a quantity
of fuel in to the combustion chamber, ignite it and create a single
explosion. If we haven't over egged the pudding and the engine is still
in one piece, some of the gases from the explosion will have exited out
of the compressor intake ( not what we want ), but most of the gases
will have exited out of the exhaust. As a result we find that our single
explosion has given us a small kick of forward thrust, but additionally
and crucially, has given the engine's compressor/shaft/turbine assembly
a small rotational 'kick' in the direction it would have in normal
operation. If our intention was to design and build a one-shot 'pulse'
jet then we have succeeded, the compressor/shaft/turbine assembly's
rotational 'kick' being a bit redundant from a design point of view and
actually detrimental from an efficiency point of view, but comes in
handy later on as we shall see! ;o)
The reason the gases exit mostly out of the exhaust which is what we
want for forward thrust and also gives us our small rotational 'kick',
is exhaust turbine to intake compressor mechanical advantage. How it
works is this: following our explosion, the gases try to go equally in
opposite directions through the compressor and turbine wheels, and due
to the specific orientation of their blades, also tries to rotate them
in opposite directions. If the compressor and turbine wheels were
exactly the same size and shape, then we would have the situation where
the exhaust gases would exit from both ends equally, generating equal forces in
opposite directions resulting in no net thrust. Also, because the
rotational forces acting on the compressor and turbine wheels
would be equal and opposite, and because they are both connected to the
same shaft, the whole compressor/shaft/turbine assembly would remain
stationary. But the compressor and turbine wheels are not the same. The
turbine blades are generally at a 'steeper' angle than the compressor
blades, i.e. their 'pitch' is greater, and the area through which the
gases flow through the turbine is generally larger than the compressor.
The result of this is that the whole assembly is 'unbalanced' in
terms of resistance to the explosion. What this means is that the gases
will pass through the turbine more easily giving us our resultant net
thrust in one direction, but equally importantly, because of the steeper
blade angles of the turbine, the exiting gases give the turbine wheel
more torque or 'turning force' in one direction than the compressor
wheel's turning force in the opposite direction. The net result of these
unbalanced torque's or turning forces is that the whole
compressor/shaft/turbine assembly is given a rotational 'kick' in the
direction that favours the turbine. This is the turbine to compressor
mechanical advantage mentioned earlier that is employed in jet engines
and is key
to making them work! ;o)
OK, so we made one explosion, got a short pulse of thrust and spun our
compressor/shaft/turbine assembly a bit in the right direction. But hey,
why not do this again, immediately following our first explosion with
another explosion and then another, etc, in rapid succession, making the
engine spin faster and faster? Well, we can do this but we have to wait
a bit before we can create another explosion. Our first explosion used
up the available oxygen in the combustion chamber and it needs to be
refreshed. This is where our now free-wheeling/spinning ( as a result of
our mechanical advantage ) compressor comes into play. As it spins, it
pulls in fresh air from the outside and eventually replenishes the
combustion chamber with a charge of fresh air/oxygen. We can now inject
more fuel, create our second explosion and get a second 'kick' of
thrust. If we time things right, we can get our second explosion to add
to the already spinning compressor/shaft/turbine and make it spin faster
than before. We can repeat this process, creating our explosions more
frequently as the compressor spins faster and faster, recharging the
combustion chamber ever more quickly. Additionally, because of the ever
increasing in-rush of air from the compressor, we find there is less and less tendency for
our explosions to exit out of the compressor because of the ever
increasing pressure barrier coming from that direction. Note also that
so far our jet engine is still working discretely, i.e. it is still
operating on the SSBB cycle as used in a car engine. Eventually though,
there will come a point when our compressor is spinning so fast that it
recharges the combustion chamber almost instantaneously, the pressure
barrier it creates as a result of the in-rush of air means that our
explosions exit fully out through the turbine only, and finally, our
explosions are so close together that we have left the discrete SSBB
cycle behind and are now experiencing the
continuous roar of a typical jet engine! ;o)
Although it is possible in theory to start a jet engine with discrete
explosions, it would not be a very practical way to do it but more
importantly would more than likely be a very destructive process!
Normally the compressor/shaft/turbine is spun up either electrically, or
pneumatically to a speed that sees enough in-flow of air from the
compressor to make a decent pressure barrier, at which point enough fuel
is introduced and burned so that it can take over from the 'starter
motor'. This is the point at which the engine can be said to be
'self-sustaining' or 'idling'.
A bit of a long winded explanation but I hope this helps to give a
clearer understanding of how things work! ;o) A slightly different and
more mathematical approach ( although still employing the mechanical
advantage principle ) can be found
Turbocharger for a Jet Engine
A turbocharger is used on internal combustion engines to increase the
amount of air and consequently the amount of fuel that can be introduced
into the engines cylinders and as a result increases the amount of power
that can be produced for a given engine size.
Cross-Section Through a Typical
The turbocharger's compressor provides the pressurised air for the
engines cylinders. The compressor wheel is driven by a turbine wheel via
an interconnecting shaft. The turbine wheel is driven by the exhaust
gases produced by the engine. The whole compressor/shaft/turbine
rotating assembly is exactly the same setup as in a typical turbojet.
Flow Diagram for a
in Normal Use
So, fortunately for us, a turbocharger already has two of the three
major the elements that we need to build a turbojet, i.e. a compressor
section and turbine section. The only difference between the
turbocharger and a real commercial turbojet are the designs of the compressor
and turbine wheels. In a commercial turbojet the wheels are designed to
work 'axially' which means that the gases flow through the wheels
along their axes of rotation.
with Axial Wheels and Gas Flow
In a turbocharger, the wheels are designed to work 'radially' that is,
the gases exit the compressor and enter the turbine in a radial
direction, i.e. at right angles to their axis of rotation, which is the
reason for the 'snail shell'-like shape to the housings. The
reason for this is efficiency, radial compressors and turbines work more
efficiently below a certain size, above this size axial compressors and
turbines are used, but this is not an issue for us apart from one of
Radial Wheels and Gas Flow
The third element that we need to build our jet engine, requires us to build some form of suitable combustion
chamber. A turbocharger, when bolted to an engine is almost
behaving like a jet engine already, it provides compressed air to the
engine's combustion chamber where fuel is burned, the resulting
gases then being forced out of the chamber by the piston which spins the
turbine wheel and hence driving the compressor. When we introduce a jet
engine style combustion chamber we effectively replace the engine and
it's cylinders for the burning of our fuel, turning the discrete 'suck,
squeeze, bang, blow' cycle into a continuous one as in a real turbojet.
The combustion chamber will essentially be a large can into which
the fuel is sprayed and burned. The air from the turbocharger's
compressor is fed in, fuel is added, burned and the resulting hot
exit the combustion chamber through a pipe connected to the inlet
of the turbochargers turbine thereby completing the loop. Combustion
chambers have been constructed using a variety of basic materials, built
up from tubular steel or from modified fire extinguishers using mild or
sometimes stainless steel for durability.
Because of the inherent design of the turbocharger ( radial inflow
wheels as opposed to the more normal axial flow wheels ) and the fact
that on most DIY jet engines we are using
it 'as is', the combustion chamber needs to be constructed 'outside' of
the turbocharger as a separate unit. This leads to the construction of a
jet engine that is bulkier, heavier and far less efficient, thrust for
thrust, than their more streamlined commercial brethren ( both full-size
and model jets ) but is the price we have to pay in order to reduce
complexity and cost to achieve a real working jet.
Ok, so we know that we can use a turbocharger to build a jet engine, but
how do we go about choosing the right turbo? What sort of thrust levels
can we expect? How do I go about designing my combustion chamber? What
other bits and pieces do we need to make it work such oil and fuel
systems? Because of the numerous types of turbocharger out there and the
varying levels of access to parts and materials that builders
encounter, but moreover the fact that 'There Is More Than One Way To Do
It..', there is no one definitive set of plans to go by. Instead,
what is presented below are links to a set of guidelines ( 'Rules of
Thumb' ) in Adobe Acrobat Reader format (.pdf) that have been an invaluable aid to myself and others to help
get to grips with these problems and come up with working solutions.
They were originally drawn up by Australian John Wallis a veteran DIY
gas turbine builder and long time member of the DIYGasturbines
Yahoo group. The 'Rules of Thumb' are reproduced here with his
permission. You can see examples of John's (Racketmotorman) projects on
the DIYGasturbines group
and on Nick Haddocks website ( see
The diagram below
shows a typical layout of a DIY gas turbine and gives the names of the various
parts ( click on diagram for a more detailed version ).
Adobe Acrobat Reader for
your particular operating system can be downloaded
The two main
design decisions that need to be made are what shape the engine is going
to take and the type of fuel that is to be used. The shape of the engine
is mainly determined by how the combustion chamber is attached to
the turbo. The most efficient ( and common ) way is to have the
combustion chamber attached radially to the turbocharger's axis, i.e.
the output of the combustion chamber is attached directly to the input
of the turbine scroll so that it feeds the turbine without any
intervening pipe work. This results in the engine taking on an 'L' form
( without the jetpipe ) which is the most efficient, but not necessarily
the most compact. Other arrangements that people have used are axially
pointing forwards ( as in the diagram above ) or axially pointing
backwards, transversely in an 'X' shape, as well as others. These latter
forms need extra pipe work giving slightly reduced efficiency. Whichever
shape you choose depends on what best suits the mounting of the engine
and of course aesthetics! ;o) My original engine design ( see 'Jet
Single' below ) has the combustion chamber arranged axially with a 90 degree transfer pipe from the combustor
to the turbine inlet. The reason I chose this form is because of an idea
I had when I first started out on this project.
Apart from the design's relative compactness, I wondered about the
possibility of adding a second turbocharger at a later stage in the
manner show in the pictures below ( Twin Jet ). As time went on
and I came to understand a bit better about how a jet likes this works I
could think of less reasons as to why it wouldn't work in theory. I
imagined this sort of design a bit like the inverse of
first engine ( see images below ), where instead there were multiple
combustion chambers centred around a single compressor/turbine. The
layout lends itself well to the addition of a second turbocharger with
minimal extra work with a view to adding more thrust with a small
increase in weight. I could simply replace the original small turbo with
a larger unit, but larger turbo's are harder to come by, are more
expensive and would have different operating characteristics which may
require a combustion chamber redesign. Using one type of turbo means you
can get to know it's operating characteristics and build on that
knowledge. The idea is that the second turbocharger will share the
combustion chamber with the first turbo.
My reasoning behind the twin ( or multiple ) turbo jet is that from the
combustion chamber's point of view it doesn't care where it's air comes
from or where it's combustion products go to, it's job is to burn fuel
as efficiently as possible and heat excess air. It is the turbo's job to
deliver the required air, making use of the exhaust gases as efficiently
as possible such that it can sustain it's function in providing
compressed air, as well as leaving enough energy in the exhaust gases to
do useful work. Having said that, there are obvious technical
difficulties that will need to be addressed with a twin or multiple
turbo setup such as starting, balancing gas flows, etc...
For fuel I decided to go liquid and use Diesel. Propane gas is the first
choice for many because it is clean burning, easy to ignite and doesn't
require any auxiliary pump to deliver the fuel. The downside is that it
is stored in heavy containers that have to be carted around which is
more problematic if the engine is to be used in a vehicle, the propane
is quickly used up resulting in short run times and is relatively
expensive and more trouble to refill ( at least where I live! ). There
is also the personal aspect in that, for me, working with gas I feel is
inherently more risky and requires greater care. Using a liquid fuel
requires the use of a pump and driving motor so is more complicated to
set up initially, but the great advantage is that you can use almost any
liquid fuel ( NOT petrol, very volatile! ). I decided to use Diesel
because it is relatively safe to use ( you can put a blowtorch to a pool
of diesel and it won't ignite, you have to atomise and/or heat it before
it will light off ) and is readily available at the local fuel
station ( half the cost if 'Red' Diesel can be obtained that is used for
off road vehicles and generators ).
My original engine
Two variations of my dream machine! If the twin turbo jet goes to plan then
I'll be on the hunt for more turbo's... Whittles original engine is shown
below, the radial six is like an inverted form of this design.
This is an improved
version of the original design above. The turbo's are angled
backwards at 45 degrees to improve gas flow to and from the turbine
sections. The exhausts combine in to a single jet pipe/afterburner.
There have been a number of phases in the development process so far. I
chose to document progress in terms of general build phases as opposed
to dating things in a diary like fashion which would have been
considering the rapidity with which changes have occurred.
With all these design changes, at least one thing has remained constant, and that is the juxtaposition of the turbo(s) and combustion chamber
as shown in the engine designs above.
Below are links to progress in roughly chronological order.
Phase 1 documents my first faltering steps, blind alleys, false
starts, crude designs, naive assumptions and a rush to get things
going spurred on by turbine fever...
Phase 2 followed a period of rest, a step back and a more measured
approach to things. I wanted to build something that worked first
time and looked right. I still had a way to go and the design was constantly changing,
resulting in new parts to find and re-making old parts, so was a
constant two steps forward and a one step back process!
Phase 3 - New
Having partially documented Phase 2, I've since changed my
designs to incorporate a better oil/fuel system without the need for
heavy batteries using a model aero engine, an idea for oil cooling
using the fuel itself, an on-board starting device and my own design
for an adjustable
jet nozzle for easing the process of fine tuning for maximum thrust!
Phase 4 - Jet
Having already done
a fair bit of work on the Jet Single design, I have decided to go
straight for the Twin Jet. One of the reasons for this was that in
starting to make up the combustor to turbine transfer pipe for the
single, I realised that it would be better to invest time in making
the pipe(s) ready for the twin jet, as well as the other parts that
were needed. The other reason was that I had an idea that would
allow me to run just one of the turbo's leaving the second idle.
This means I could have the benefits of learning to run a single and
when I was ready to bring the second online, all the necessary
components were in place to allow me to do so. It would take a bit
longer to get something up and running but shorter in realising a
Phase 5 - Freepower!
Moving a vehicle using pure thrust is fine, but for faster
acceleration and making more efficient use of the exhaust gases from
a gas turbine requires the use of a freepower setup...
Phase 6 - Jet Cycle, a.k.a. ...
My original idea was to put a jet engine in a bicycle frame for
lightness, but found that space would be too limited especially
considering the space needed for a large enough fuel tank that would
allow reasonably long runs without the need to re-fuel. Instead, I
decided to build something more robust and stable using parts
from a variety of motorcycles, Mini Moto's and bicycles. Every project needs a name, but up until this
point I hadn't really decided on one. On seeing the partially
completed cycle with it's large bulging fuel tank a friend remarked
that it looked something like a contraption from one of the 'Wallace and
Any vehicle needs devices to monitor the operating conditions of the
various systems . A DIY jet powered vehicle is no exception. Sensors
are needed to measure and display temperatures, pressures, speed,
RPM, etc. These measurements can also be used to control other
systems, e.g. switching on cooling fans, controlling start
up procedures or shutting down the engine if critical conditions
occur. At the very least temperature measurement of the hot exhaust
gases impinging on the turbine wheel is essential to avoid meltdown
and some form of RPM sensor for indicating the speed of the turbo
without which over-speed can easily lead to a destructive scenario!
The ideal solution would be to have some form of complete process
control system. All of the desired measurements would be fed in to
a microcontroller type processing device or PC/laptop where display,
logging and monitoring can be performed, start-up sequences can be
programmed and decisions taken to avoid disastrous situations.
This is a huge project in itself so I am starting with the minimum
requirements, an RPM sensor(s) and exhaust gas temperature
DIY Jet Engine Links
Large library of images
and video by people who have built jet engines
and mounted them in a
variety of moving vehicles, many of whom can be
seen testing their
vehicles at the former testing ground of the Yahoo!
UK branch. Check out Nick's MK3 twin
and John Wallis's many and
varied gas turbine
If you're into
experimental gas turbine engineering of quality
and a prolific nature then Don
Giandomenico's site is a must see!
Russ W. Moore
showing that this man has fingers in lots of pies!
Check out the progress of
Russ' jet powered mini sportbike.
Mark Nye of Nye
Thermodynamics. Lots of gas turbine related stuff,
commercial gas turbines, and educational resources.
Gary Packham and 'Turbitrac'
his turbocharged afterburning tractor!
Check out Larry
Berg's website. A veritable smorgasbord of links
to DIY gas turbine
builder's sites, as well as his own turbine tricks of course...!
DIY Gas Turbines Group
Mailing list for DIY jet enthusiasts.
Lots of information on hand and
help from expert members.
( If you'd like a
link to your own DIY gas turbine related site then just contact me
Below is a collection of links to completely free resources
( no trials, cripple free
other rubbish strings attached! ) that I use everyday
in my project and in the maintenance of this site.
All 3D graphics on
this site were created
for all platforms.
DraftSight ( AutoCAD
clone) is a professional-grade, open 2D CAD product for users who
want a better way to
create, edit and view DWG files. DraftSight is easy to use and is available
professional CAD users, students and educators to download and activate for
ExpressPCB Circuit Design
Great couple of
programs to help you design and build those electronic circuits.
alternative to the severely limited calculator provided by Windows.
Very useful program
to help you convert between lots of different units.
program that I use to update this site. Simple, easy to use
and free from the
usual bells and whistles..! ;o)
Very useful utility
for grabbing whole screens, windows or parts thereof.
Microsoft Office suite of programs. Reads all Microsoft Office files and
useful facility for
converting Microsoft Word documents (.doc ) to Adobe Reader format (.pdf)
OpenOffice.org project is primarily sponsored by Sun Microsystems, which is
contributor of code
to the Project. Other major corporate contributors include Novell,
CH2000, IBM, and Google.
Adobe Acrobat Reader
Reader for your particular operating system.
Wolfram|Alpha is the
first step in an ambitious, long-term project to make all systematic
knowledge immediately computable by anyone. Enter your question or
calculation in the text box below and Wolfram|Alpha uses its built-in
algorithms and a growing collection of data to compute the answer ( Press
return or click on the '=' sign to compute ).
If you believe what the doomsayers are spouting about 2012,
do yourself a
favour and check this website out by clicking the logo.