Discuss/Detail out THE PEGASUS UNIT

THE PEGASUS UNIT was a book written and published out by Niels A. Skov and Mark L. Papworth.

For all of the discussions here on the DOW about woodgasifier air jetting, pre-heating, “firetube”/hearths, restrictions, grating, hopper sizing, condnesing/non-consneding, woods dryness, engine grade-use filtering steps, cooling steps . . . .
90% of these are detailed answered out in this publication.
1st published out in 1974. Reprint published in 1975 and 1979/80. Then in ~2006 rights got by Dr tlug and offered as a pdf download.
AdminChris has put this up here on the DOW in the Library section → WWII designs & history → “Driving on Wood: The Lost Art of Driving Without Gasoline”
A 136 page pdf download following (almost except for the introduction page) exactly the original print publication books.

Again. 90% of your questions can be answered in this publication. For Charcoal, Peat fuel and Fossil Coals too.
Ask and I’ll point out the chapter, page, graph and chart.

The other 10%?
Adapting to electronic fuel injections and electronically controlled engine ignition timings. Skirting around emissions/safety inspections and some of the insurance requirements that did not exist back then.

Their page 125, Fig. 52 Wood Burning Pegasus unit if honestly built up would real-world use performance exceed any that I’ve seen so far.

So go ahead . . . . try and cut off this limb I’ve boldly walked out onto. At least try and shake me out of my tree.
Someone was complaining the DOW has gotten info-exchanging boring.
woods-for-power Steve unruh


To start. Why did they insist re-naming from “gasification” to PEGASAS? Page 9.
Thier personal WWII era slave-labor histories had them having to German learn “Wood-Coke-Air/Gas-Heater-Generators” and many other German jawbreakers.
PEGASAS was their chosen contraction for Petroleum/Gasoline Substitute Systems.
Let them use the historic winged flying horse logo. The new beginnings rising out of the ashes of the old.


Link to PDF: Library / Pegasus Gasifier | Drive On Wood!

BTW Steve the hard copy of the PEGASUS book just arrived in the mail, with your other goodies. Thanks much!


Steve and I have talked on a couple occasions about the proposed compact gasifier that’s shown in the book.

Apparently they never got around to building one, this was a prototype design. You can see how compact it is.

Some interesting stuff in here, including a horizontal cyclone, and extensive air preheat. Insulated hopper too.


Yes. Much relevant detail in that vehicle intended system if you look very carefully.
Coarse HOT gas/ash cleaning first. With a huge collector chamber with a large clean-out port.
Immediately then as much heat extraction from the gas to the incoming gasifier air as is possible in the U exchanger. And that with it’s own upper soots brushing out ports. The hand of much usage experiences shown in these.
Then the gas still hot enough to be above condensation point fine filtered through a large cartridge “glass wool” filter. That chamber again with a very large sloped bottom catch chamber with it own separate large clean-out port.

And all of this under a hinged up sheet metal housing. To retain heats for recovery. To keep the gas still warm enough for hot filtering. To keep users and observers hands from ever becoming heat damaged.
The PEGUSUS UNIT book’s unique Chapter 5 “The Heat Budget” shows that these former Danish resistance fighters had been watching, listening to their German masters and their own University physicists/engineers like Niels Boer very well. Stationary gas producers for Town gas had very well engineering evolved out to be 80% heat to conversion gas efficient 1860’s to the 1940’s… Read in the DOW Library Tylors 1907 Treatise summery to confirm this.
They saw the best WWII mobile system hit 50-70% efficient. They were going for 90% on this system as a more controlled stationary electrical generator/pumping unit. At least 70% as a mobile unit.

The gas once coarse, then fine hot filtered, going to a forward facing exposed vehicle tubed cooler/washer. Ha! Heat from that blowing back past warming the whole system!
Engine drawn upward flowing gas at last being cooled for a condensate rain drop out final washing. Lower part of that cooler/washer with a large horizontal condensate collection tank. With it’s own, large drain/clean-out.

Note the drop-in cast ceramic hearth core; the places insulated; the places not insulated; the very large lower inspection/cleaning out port that Imbertlike spans both below and above the grate; the forward lower flat side heavy system mounting plates.

What? No poke-Steve, make-him-prove questions?
Busy reading this relatively short 136 page pdf download I would hope.
tree-farmer Steve unruh


Interesting stuf indeed, but i am missing the "Pegasus Wayne Keith design " and the “Pegasus Gary Gilmore design” in this book :grin:

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Some day they will up date the book to show off Wayne’s, and Gary’s much improved designs, and yours too.


Steve and Chris,
thank you so much for presenting this. I am planing to do a very similar compact system for my Mercedes and this was most usefull. I will certainly use this horisontal cyclone, but a bit different preheat/cooling and filtration.


OK, I´m only half way through the pdf, but just a little poking won´t hurt.
I think I´ve read this before but it sticks a lot better ones you have a foundation of preunderstanding. Makes you turn pages nodding instead of rereading over and over again.

There are lot´s of nice features in this build, or should I say drawing. I sence a lack of crediblity since this thing was never built and tested. The pencil is a much easier tool to use than the ones used building. This is when Mr Wayne´s words come in handy “the devil is in the details”.

A few random things that comes to my mind:

Yes, large cleaning out ports are good for cleaning out. Personally I would not spend hours and hours (and money) fabricating and maintaining ports and seals to save a few minutes of trouble at cleanout. A threaded cap or simular is good enough to me.

Heat budget:
I was a little surprised by the low energy saving made by air preheat. 0.3% of the total energy content in the wood is nothing.
BUT, the proportion of heat added to the heart by incoming air at idle is what is important.
I least I now know I add preheat for turndown ratio reasons only, not wood saving.

Hopper condesation:
A big question mark to me. I wonder why there is no monorator features present here. Or am I missing something? An insulated hopper could easily be combined with WK-tubes or simular.

Are there two grates? One full diameter grate near the bottom is obvious, but is there a second one across the reduction tube bottom? It sure looks like it.


Hi Jo,

Read careful, its not one gasifier, but a lot of gasifiers ( Pegasus = Gasifier)
Many type’s are described with every advantage or disadvantage, each build has its own “heat balance” each build its own challenges ( depending fuel and power / gas production )

Hopper condensation: i did see a picture / drawing with slits in the hopper for steam/ vapor extraction :grin:

Yes, this Pdf has a lot of info, but no info is more important then your own build ( what feedback every single hurdle gives you )

My question to many builders would be: what did you build ? ( Fema, Imbert style, Wayne Keith, Gilmore ? )

My builds are based on Gary Gilmore’s pioneering / road paving…
My full wood gasifier preference would be near a WK gasifier… ( i am having dreams about buying “the Book” and just get started with it , but what would be the fun of it if i can’t make errors and learn ? )


I hawe downloaded but not read yet, but l must say l do have mixed thoads on hopper condensation.
On my chevy l had a similar insulated hoper. I cant complain about max power output so l suspect hopper condensation is allso a factor of turndown ratio (idle), like air preheat.

Wayne’s system recaptures a LOT more than 0.3%. I don’t have a solid number for you, but I’d venture 10-20%.


Oh, I’m sorry if I was unclear. I was commenting mostly on the gasifier drawing Chris posted. Downdraft wood gasifiers are my focus. I hope you can forgive me :hushed:

Good point. Steam cooling the heart is a disadvantage mostly at low demand, but it will also take up a lot of space until it’s condenced in the cooler.


I think we’re talking different numbers here.
0.3% is outof total energy content in the wood. The 10-20% you’re mentioning is probably outof heat in the outgoing gas. Still a good number since 1/3 of the heat in the outgoing gas is all the incoming air can carry, in theory.
I know, even more heat is blown into the WK nozzles. But that’s not heat that otherwise would be lost. More like a transfer within the gasifier. I’ll stop here :smile:

EDIT: Chapter 5, page 59. A very clarifying picture.

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O.K. All good questions. And all answered in the text reading of this book.
At least one of the two authors was a new citizen American (and one non-cited advisor - Harry Lafontiane). So with English as a second language their written English is very standard 1974 late 20th century usage. And two of these fellows DID go on to university teaching, in America, in English.
The sentence phrasing is very straightforward, plain. Is very dense, compact. Every sentence, half sentence has meaning.

Where is the Wayne Kieth Pegasus in this book?
page 108: “In order to improve the heat budget of the pegasus it is normal to preheat the air stream from the heat content of the gas or BY RADIATION FROM THE HEARTH ZONE.” The WK used extreme fire tube air pre-heating. " . . . the pegasus will be equipped with heat exchangers just beyond the gas exit. . . " The WK external heat exchanger/soot dropper. " . . . the air stream is led around the wall of the stack (fire-tube/hearth), cooling this in the process." Goota’ be careful highlighting this out as this IS a dedicated WK-book feature.
WK heat budget designing is told by Mr. Wayne saying to paint with low temp black paint. Look for heat changes in this paint. Redesign to stop losing that heat energy.

Actually much more on the WK big flexible volume ‘charcoal tub’ (my words) method in the page 56 beginning “Inertia in Processes” section. Very, very important vehicle in traffic considerations in just a few sentences pointed out there.
Where the true WK’s as Wayne makes then can exceed these authors experiences and design is in his incorporating the IC engine waste heats back into the wood-for-shaft-power balancing act.
Easy to do stationary.
Hard to do mobile. Why mobile, most all except Waynes own builds, and some shown up 1940 European Ag tractor systems just ignore engine heats. Throwing out the baby with the baby-bath water imho.

Why no condensation collecting wood drying hopper shown?
The authors are very aware of these. Chapter 10, Design of a Vehicle Pegasus System, page 95: " . . . but many endeavor by a double wall arrangement to use the heat of the raw gas to pre-heat and dry the fuel column by passing it through (a) space between xxx inner and outer (hopper) walls, see Fig 6. The inner wall should be CORROSION RESISTANT to withstand the effects of distillation products, particular acidic acid." Then two sentences describing the construction of a double wall with steaming slits and collector space. “This type never gained popularity, as only a modest fraction of distillates was exacted from the fuel, and the corrosive liquids caused frequent leakages.”
Their design for weight, space and maintenance concerns was based as they said clearly in the Fuels chapter, on pre-dryed down sub 15% moisture fuel wood.

Kudo’s to Wayne and others building for really wet woods and airs.
The price? Higher weight, space and maintenance’s.

As a PNW 9 months of the year wet-footer unable to air dry woods, well worth it in my opinion.
tree-farmer Steve unruh


Two grates?
Ahh. I see now. What looks like a must-be-perforated? floor holding up the ceramic hearth core. With the movable center post mounted grate with pins below.
I do not know.
Just an illustrators mistake. How else could the stand-up rotaing pins function?
I did search out and pay-well for an unearthed copy of their “includes WWII gasifier plan set”. Was NOT this sytem. A rolled sheet metal “tank” build of an 1940’s top flanged Imbert design. But w/o the patent Imbert high chromium/nickel cast steel hearth hourglass.
More usable full system building details in S.E. Werners site information’s.

They reviewed their young in-thier-twenties life experiences. And in the just post-no-gasoline 1974 embargo era was offering this up as 50’s year-olds matures as an for-individual solution to younger unawares. Sound too much like the DOW, eh?
Niels A. Skov DID actually make up a system. Install and mount it onto a Checker brand sedan car and drive it around promoting.
I think that their intent if they could get the investor money was to build up the Fig 52 system. Build, refine as a production item. Very legally possible back in the early 1970’s USofA.

A lot of needs-must, anger-shock no-gasoline systems did get tried 1974/75. Then 1970/80. Mercury out boards converted to steam and such.
Just like post WWII. Cheap gasoline became available again.

And this fellows is why I will insist that woodgas power is for die-hard independent minded/insistent do-it-yourselfers.
All others will give-up; and can be bought-out by Top-Down energy “suppliers”.
And these suppliers have the money and legislative muscle to illegalize “for safety”, “for the environment” our activities.

No reasoning with them.
Keep bootlegging along. Some day they will run out of gas, then money, then votes/power, for good. Then will be our day.
tree-farmer Steve unruh


Patience please on Pegasus Gary Gilmore responce.
I am having to read-back much to define Gary’s Simplifier? from his Gilmore? from his Kahle-clone works build-ups in my mind.


K.V.L. I think that i have failed my 90% relevancy test on any of GaryG’s designs in this pdf/book presentation.

Here are the few things that do predict Gary’s DOing-It (and yours) found results:
pages 106 and 107 The Air Stream has a lot to say about nozzles, arrangements and materials. “When high response fuel . . . is used . . . special nozzle cooling is superfluous. . . . Nozzles of cast iron or alloy steel will usually stand up well.”
That was from diagonal downdraft.
Your and his are single lower centered nozzle updrafts. Closest in this book is Fig 42 and 51.
Back to Gary’s discoveries. Water/steam or engine exhaust injection boosting:
pages 108 and 109 STEAM INJECTION. Last paragraph: “The problem of steam injection is solved mostly by using engine exhaust as shown in Fig 42. The exhaust constituents of steam and carbon dioxide are disassociated in the hearth zone, and the dilution of the air stream with exhaust causes a drop in oxygen content. All of these processes tend to lower the hearth temperature (by dissociation absorbing heat pull) and the (heat) strain on the hearth materials.”

The pitifully poor two paragraph “Charcoal” section does have relevant very hard found-out charcoaling experiences though. “The best charcoal is derived from hardwood, as it is less susceptible to powdering and fragmentation than softwood charcoal.” Softwood conifer wood only me; I could have saved myself a few months back in ~2008 having read and headed this advice.

Charcoal weight/volume comparison info on Table 5, page 67
Charcoal energy comparison info on Table 6, page 68
(useable) Charcoal moisture comparison info on Table 7, page 70

Different wood charcoaling “grain breakingdown” and “dusting” highlighted out on page 76:
When grain breakdown DOES occur as in charcoal produced in the gasification of wood fuel, it will NOT be bothersome if only large fragments are formed, as these will be participate in the gasification process.
This is the case of beechwood derived charcoal.
Pinewood will on the other hand swell and form more dust than beechwood."
Table 10 Summery of Required Qualities in Pegasus Fuels should be required reading for any asking about straw-grasses, car tires, plastics and municipal solid wastes!!

Koen I would think you would find the Fig 5c charts most helpful in your teaching.
Pages 126, 127 and 128 Conversion Factors and Units should be helpful to all.

Ha! Ha! You got me alright.
tree-farmer Steve unruh


I am not sure what happend here ?

Your Original post and your comments are real marbles, must have’s. Your knowledge base undisputed, whatsup ?

I feel the need to come over there and grab a beer with ya


Max is always talking about reheating gas and then paper filtering before sending it to the engine. The last paragraph on page 69 as follows

Does that mean that 105 degrees is the magic temp needed before paper filter?

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