as usual you are very practical and on the spot with your advice to “simulate” a woodgas motorcycle. And I guess no one will second your restriction estimate from your large amount of experience and IC Engine knowledge. Well appreciated!
But from what I understand, the question in Egypt right now is DOW or not driving at all…
Hello Mohamed,
as Brian stated and as you’ve probably looked up by now, pi is an irrational number, i.e. a fixed value with an infinite number of digits after the decimal point. And it is used for all calculations on circles and spheres and so on… (as Brian stated also).
For normal technical and engineering uses and applications 3.14 is precise enough; when you are going with 3.142, that is more than sufficient!
For those formulae:
In my opinion, that formula from Max Gasman, which Arvid cited, is the better one. Why? It is easier to calculate, you can do it mentally, don’t even need a calculator! And as you see, the difference (or error, if you will) between those results is about 4 %. I bet you, that ANY environmental factor BY ITSELF will cause a larger error: Air humidity, fuel humidity, shape of the fuel, size of the fuel, and so on… even ambient temperature will have an effect). And do you really know, if those estimated factors 0.78 and 0.42 are really precise for your application? If it was 0.44 instead, that’s an error of more than 4 % already…
Best regards,
Sam
PS: And please let go of those square brackets. 2 meters per second are 2 m/s. Normally, the usage is to define the unit of a dimension with a square bracket: [v] = m/s or [v] = ft/s or [v] = mph or [m] = lbs.
I know there are many books out there that have this all screwed up. These are not the better books, though…
Mohamed,
Arvid,
Nils,
Guys, As I read some of the posts I would like to add my 2 cents worth and comment on the “G” gas needed in liters per second. I think both formulas have errors in them or at least lack some detail. I cant get the Max gasman formula to work for me without a substantial difference. Neither formula account for absolute pressure, and on a four stroke engine there is one intake stroke in every other revolution. Thus, when calculating the gas needed you have to cut the volume required in half because not every stroke is an intake stroke. I will attempt to explain the absolute pressure component and hopefully its requirement in a formula will be obvious. At the end of the day you need to know the volume of gas needed not just to run an engine but also to size supporting components and equipment like pipes and filters being able to check velocities and pressure drops through various components, and the system as a whole. I will not address sizing a gasifier but stick to the “G” calculation. The formula I use doesn’t take into account air temp, or SG or RH. I will use my 4.7 dakota as an example. I’m old school CFM not liters. I prefer a 427cu/in over a 6.9 liter any day.
Think about it- You have a gas engine idling at 800 rpm. The motor is not running at atmospheric pressure but below atmospheric pressure. If you put a vacuum gauge on the intake manifold it would read somewhere in the vicinity of 18 inches of mercury gauge. If you where to place your hand over the exhaust pipe you would feel a certain amount of gas leaving the pipe. Now suppose you could impose a load on the motor so it could not exceed 800 rpm and open the throttle all the way. First you would see that you have zero vacuum and the gas coming out the tail pipe would be 2-3X, substantially more. What has happened? The density of air entering the cylinders has increased but the volumetric displacement is still the same. When we think about engine displacement it is easy to assume that the engine breathes at atmospheric pressure. The only time it comes close is when the peddle is to the metal. A motor placed in a vacuum chamber will displace nothing at any rpm. Not to be confused with the diesel which does breathe at atmospheric pressure. Atmospheric pressure at sea level is 14.7 psia. A gas engine operates below 14.7 psia. Keep in mind that 14.7 psia is a base line that is used in many calculations for air density just like water is used as a base line for specific gravity. A std cubic foot of air or a liter of air is assumed to be at sea level pressure as a base line. If you took an empty liter soda bottle to the sea shore and secured the cap and then went to the Rocky’s 10,000 ft you would find that the bottle has collapsed because of equalized pressure and now the volume in the bottle is no longer a liter. On an engine the displacement is the same but because it operates below atmospheric pressure the air entering the cylinder is thin or low density. The formula I use is in CFM therefore I have converted where applicable. This is the CFM at 800 rpm idle speed on my 4.7L
G in CFM= (displacement in cu/ft)rpm/2 (in Hg gauge converted to PSIA/ 14.7)/2
4.7 liter=286.8cu/in or .1659 cu/ft
.1659800/2= 66.36
18” Hg gauge is 5.85psia 5.85/14.7=.397
.39766.36=26.4
26.4/2=13.2 (26.4 is total CFM both air and gas and I have made the ratio 1:1
G=13.2 CFM
At 55mph my rpm is 1750 and vacuum 15” therefore-
.16591750/2(7.32/14.7)/2=36.13
G=36.13 CFM
It’s a good idea to chart your motor measuring Hg, rpm, speed and the type of terrain. This will help determine the nominal volume through the gasifier and know the extremes. With rpm and Hg you would always know the volume and/or velocity through the system. Respectfully submitted
Wes: Good info except one area… A soda bottle closed at sea-level pressure and then taken to 10,000ft would expand, not collapse, because the internal pressure remained the same but the external pressure is now much less from thinner air/less air above crushing down on you. If you equalized the pressure to 10,000ft (IE openned the bottle and then recapped it) and took the bottle back to sea-level, then it would collapse because the external pressure has gone up.
Doesn’t all the figuring become moot when using a Wayne Kieth type adjustable system? Maybe it gets tricky on a mini gasifier, but if i was a desperate to drive in Egypt I think I would do the simplest thing and build adjustable.
John
You can calculate super-precisely how much cold gas you need and how big a restriction you should have. But it is futile, since you don’t know all the circumstances of operation and environmental influences. The better you know them, the better you can do your calculations, of course, like Wes showed us.
In my opinion, it is best to start with a rough estimate (I looked up a typical german word for this first step in engineering, and it came back as “plunging”, which I’ve never heard before - would you say that is ok?). Then you should start with a restriction on the small side (basically what Steve and Arvid suggested). You expect low performance, but are safe w.r.t. tar formation. After that, when you feel comfortable, you gradually increase your restriction, as long, as you haven’t the power you want and - more important! - as long as you don’t make tar.
I have a new abbreviation for our list: Ask yourself:
Hello SamF.
Yes good summery and good advise. One correction though - the “maths” which were derived from much 1940’s, 50’s and 60’s larger vehicle and truck system post operation analyzed expereinces break down and will calculate out too small for practical woodfueled usable restictions as “off the charts of experience”. The maths do the same thing on over large systems as out of that direct expereienced data range also. This IS what DJ found. Why he recommend doubling the internal sizing of his project systems in acomment here on the DOW.
Arvid and I are actually recommending what math would derive as overlarge restictions. Hundreds of hours Expereinced now (11 engine types for me now) we know we can control the actual gases flow through rates with the fed in fuelwood sizing, species selection and grate forms & shaker rates.
Math derived; or expereinced based guesses; will only ever get you 70% close. The final found to be used dimensioning will aways have to be specific user actual expereinced dialed in acomodating all variables by actual operating experence results.
As has been said here now: too many unknown and unknowable variables to calculate for anything except for a starting point.
Here is a picture of two of my wood gasifier systems I have operated.
Mohamad the one on the right is a GEKII system one version later (newer) than the system you found pictured. The restiction cone pictured is cast iron and an actual 2 7/8" = 73mm restiction cone. Later verson GEK III and IV’s went to larger with often 4" = 100mm restictions even for the smallest 5 horsepower engines. Depends on the fuel type and form used.
System on the left is a Victory hearth system and highly insulated and has operated with the 4" = 100mm restiction plate show on as small as sub 300cc engines 3600 RPM at ~3 horsepower to electrically generate 1800 watts up through 3930cc, 1800RPM at ~30 shaft horsepower capable of 20 kW electrical genration.
Restiction plate is drop in and out for different ID and height desires. Air jets are machined, screw in and out for length and internal air jet diameter changes. Grate grid is one bolt changable for pattern, opening areas and height changes.
This is a minimin 10 to 1 turn down ratio unit. Add in an expereinced operator allowed fuel prepping control and it will half again increase this range with no internal changing. True measured min 15 to 1 turndown ratio.
With an angled poker ported riser between the 2 hour hopper and hearth I could operate on actual stick wood fuel if I so desired.
So the real question is do you want to build to operate? Then use DJ’s excellant site information. And grow and learn from this.
Or math calculate? Or internet poll for opinions?
You will still have to build to begin to operate to actually learn the real world realities of useable woodgasification.
You will still have to grow and learn from whatever you do build. You will still have to modifiy much whatever you start out with.
Read, talk, for a whole year as I did 2007-08 but the real learning and understanding only comes from actual operating.
Regards
Steve Unruh
Hey Sam SWAG I think is in the acronyms list I think. Scientific (said as a joke on the actual limitations to exploring possibilities repeatable standardized scientific method actually imposes) Wild Ass (not a joke - an actual difficult, almost impossible to control Donkey - able to bite you from the one end and kick you from the other! And always looking for your leat inattention to do this!) Guess (but based on a LOT of failed/succeeded experiences). S.U.
hello thank for all who help me I’m sorry to late in answer but i take time to translate what u writ and really i filling im coming better by ur information
now in i think the time is come to make gasification to run the motorcycle
so i need to help me to my Basic calculations or Specifically calculate Tubing diameters and size
any way i try to do it 4 my self but my be im wrong so if u find me wrong plz tell me
general information about my motorcycle
150 cc
3000 rbm
G = V x n x 0.5 x 0.48 x 0.72 [l/s]
60
G = .150 x 3000 x 0.5 x 0.48 x 0.72 = 1.29 [liter cold gas per second
60
d = square root from (4/pi x G/Vi)
d = square root from ((4/3,142) x (1.29/25)) = 0.24 [dm] = 24 (mm)
We recalculate this flow using a conversion in Kelvin. 0 degrees Celsius are 273 Kelvin. 350 degrees Celsius are 273 + 350 = 623 Kelvin. 1.29 [l/s] at 350 degrees becomes:
(623/273) x (1.29) = 2.9 [l/s]
In the tube after the generator, we want a turbulent gas stream, to avoid settling of dust particles in the tube. Take 10 [m/s] =100 [dm/s]
Diameter pipe D = gas flow/gas speed = 2.9/100 = 0.029 [dm2] = 290 [mm2]
Pipe diameter d = square root ((4 x 290) /pi) = 19.21 [mm]
I’d say yes your basic calculations are correct… I have a spread sheet that I plug numbers into to do the math for me, but don’t have it with me right now…
I still wouldn’t make anything with a restriction less than 50 mm. and i wouldn’t use less than 25 mm for your piping
Mohamed, Find some guys (in the military) with some steel and some welding.
Start with about 150 mm Diameter fire tube pipe, about 30 cm high, Adjustable jets(holes) near the top.
Fabricate adjustable restriction near bottom. (various holes in plates) (maybe as small as 19mm)
Provide for adjustable distance from jets to restriction. (raise and lower plates)
(not need to be air tight)
Install inside 30 cm diameter container. With fuel rezevoir on the top, Air tight.
Experiment with insulation.
Utilize tubing to Let air into jets.
Vacuum woodgas out the bottom.
Test and Repeat until successful.
You can do it.
Stop figuring.
Start welding.
hello Mr John Stout and Mr Arvid Olson and all I will do larger size of 150 cm and a height of 30 centimeters as advised me our friend John . But I want you, Mr. Arvid Olson tell me on details ur gasfication with u make u can look 4 ur pic
This is a Imbert style gasifier, according to the woodgas.nl website it is very smart to have oporotunities to regulate the main dimensions. The design has a screw arrangement to lift the grate, but it is apparantly smart to be able to adjust lenght of air nozzles and preferrably the distance from the nozzles to the constriction and the diameter of the constriction.
Mohamed,
150mm hearth diameter.
30cm hearth height
Grate on the bottom to support charcoal
Fuel magazine on the top
Movable restriction (up and down)
Changable restriction washers (to adjust restriction diameter)
! Everything must be made air tight except the movable parts inside the hearth!
Now, build this and you can make experiments.
This plan is not perfect.
You will learn very much by experiments.
Remember to see web site recommended by Arvid. http://oppozit.ru/article85319.html
Very many details.
Very big work.
You ride on wood.
