(copied from the wiki here: http://gekgasifier.p...onversion-rules)
Here's some approximations and rules of thumb for understanding the relationships between common liquid fuels and woodgas, and the HP, KWe or MPG that results from each. There are more complicated ways to derive these numbers, but these rules of thumb are more than close enough to average the many variables of a gasifier-engine system. These rules of thumb will get you within 10% or so of the "correct" answer.
Relating Gasoline/Diesel to Woodgas to HP to KWe in your vehicle or genset
1 gal of gasoline or diesel will make about 15HP of shaft power for one hour. If driving a genset, this will produce about 10KWe.
1 gal of gasoline or diesel is equivalent to about 20lbs of biomass through a gasifier.
1 ton of biomass to power through a gasifier-engine system is equal to about 100gal of liquid fuel in a genset, or 1MW of electricity.
Thus, the main rule of thumb to remember:
1 kg of biomass ~ 2lbs biomass ~ 2m3/h woodgas ~ 1HP ~ 0.75KWe
2 lbs ~ 2 m3/hr ~ 1 HP
How much HP is your vehicle using at cruise?
60MPG = 1gal/hr or 15HP for one hour
30MPG = 2gal/hr or 30HP for one hour
15MPG = 4gal/hr or 60HP for one hour
How much woodgas do I need to make x amount of HP?
1HP = 2 cubic meters of woodgas per hour
5HP = 10 m3/h
10HP = 20 m3/h
50HP = 100 m3/h
100HP = 200 m3/h
You can use the above to size a gasifier for your engine and use situation. We find it more accurate to size a gasifier by actual HP needed and used during typical run conditions, not by swept volume and max rpm. Seldom is an engine running at wide open throttle, as such calculations suggest. Thus we suggest you use the equivalencies and rules of thumb to determine how much HP you need, convert this to the related woodgas flow rate in m3/hr, then find the dimensions that relate to this in the standard Imbert Hearth Sizing Chart.
The more complicated and "accurate" way to do this is by starting with the heating value of the fuel, swept volume of the engine, volumetric efficiency and rpm, all of which calculate a specific gas flow rate needed. We've found this to be way too many decimal points for what is really a compromise between many competiting interactions. You can see the details of the other method in the Fluidyne engine tables at http://www.fluidynenz.250x.com
Doug Williams of Fluidyne has also provides the most accurate conversion specifics for Woodgas to BTU to HP to KW. We've used Doug's numbers and other historic literature to derive the rules of thumb above. A big thank you to Doug Williams for authoring the main numbers and relationships.
1kg of wood 15% moisture content produces 2.185 cubic metres of gas
or 3.165kW heat from burning gas direct
or 0.837kW of shaft power (i.e engine)
or 1.12HP of shaft power (i.e. engine)
or 0.754kW of electric power generated
1lb of wood at 15% moisture content produces 35 cubic feet of gas
or 4,900 BTU heat from burning the gas direct
or 0.51 HP of shaft power (i.e engine)
or 0.342kW of electric power generated
Thus, the main rule of thumb to remember for thermal equivalencies:
1 kg of biomass ~ 2lbs biomass ~ 2m3/hr gas ~ 10,000BTU
Gasifier Sizing: Gasoline- Woodgas- BTU- HP- KWe
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