[Gasification] ideal wood gas engine

Sun Feb 20 20:47:46 CST 2011

Dear Kelvin and members.

This may be my first post to this site, I trust you will all not hope it is my last.

Engine power output is a complex issue,  factors such as the energy density of the fuel, the air/fuel ratio that enters the engine, the volume of air/fuel which is able to enter the engine during the induction stroke, and the compression pressure reached prior to ignition and the mean pressure reached during the combustion stroke are just some of the most important factors.  Besides the detailed design of intake manifold and exhaust pipes which influence how well an engine can breathe.

Where an engine is to be run on wood gas alone, it would be better to do away with as many obstructions in the intake manifolds as possible.  The key point being to get as much of the gas/air mixture into the engine. This is one reason why Diesel engines are good as they only have suck in air, as fuel is added internally.  Fuel injected petrol engines come close behind, carburetor models are generally more restricted as air passes through the carburetor.

Getting the Air/fuel ratio correct is also vital.  Using a "colortune" sparkplug is the best way to really know when you have the correct mixture as you can see the flame color within the combustion chamber.

A turbocharger can be used to increase the volume of mixture which is drawn into engine but whether or not they are practical given the possibility of contaminated gas is something I cannot comment on.

The Mean effective pressure within the engine during the combustion stroke, is largely dependent on the length of stroke of the engine, the compression ratio and the ignition timing.
The stroke cannot easily be altered but the compression ratio can be changed on some engines by machining the cylinder head.
Altering the intake air pressure, using a turbo or other methods. Such as cooling the intake air/fuel temperature.
And by changing the ignition timing.
If a petrol (spark ignited) engine is run on wood gas or any other gas, the Ignition timing has to be altered.  In general the ignition timing will be advanced by several degrees, in order to ensure as high a mean pressure as possible is reached during the combustion stroke.
The benefit of using a computer controlled ignition system is that most if not all computer controlled systems have a "knock" sensor.  The purpose of this device is to sense when the ignition of the fuel has caused the pressure within the cylinder to rise so high that the remaining un burnt fuel spontaneously explodes.  This results in engine knock, the resulting noise is commonly known as "pinking"   Diesel engines knock a lot of the time because the very design of the engine is to raise the fuel temperature to point when it spontaneously burns.
Older engines that use a Distributor lack the anti-knock feature. Commonly distributors have a simple mechanical advise mechanism, to advance the ignition as the engine revs faster, and a Vacuum Retard mechanism which aids acceleration.  Engines which are subject to varying loads, can benefit from the retard mechanism if there is any kind of control valve /butterfly on the intake, which would alter the manifold vacuum.

Anyone setting the timing on an engine with a fixed load-speed, needs to be sure the advance/retard mechanisms are either working correctly or have been locked up. As fixed speed engines can "hunt" if there is any faults in or if there is any small changes in the loading or fuel supply.

Tony Batchelor, ex, road transport engineer, now teaching physics. Wellington, New Zealand.

-----Original Message-----
From: gasification-bounces at lists.bioenergylists.org [mailto:gasification-bounces at lists.bioenergylists.org] On Behalf Of Kevin
Sent: Monday, 21 February 2011 1:06 p.m.
To: Discussion of biomass pyrolysis and gasification
Subject: Re: [Gasification] ideal wood gas engine

Dear Charles

Your stated need is for "about 20 HP" at 1,800 RPM

You should be able to get about 21.4 HP with an engine of 2500 CC (153 Cubic
Inches), burning about 19 kG/Hr (42 Lbs/Hr)

It would be very helpful if others could comment on the other aspects of an
engine.... in particular, the Ignition system, whether Distributor or
"Computer Controlled", and the implications of using a Fuel Injected engine,
rather than a carburetor engine.

Best wishes,

Kevin

----- Original Message -----
From: <bayent at ns.sympatico.ca>
To: <gasification at lists.bioenergylists.org>
Sent: Sunday, February 20, 2011 11:32 AM
Subject: [Gasification] ideal wood gas engine

>
> Content analysis details:   (0.0 points)
>
>  pts rule name              description
> ---- ---------------------- --------------------------------------------------
> _SUMMARY_
>
> Hi All,
>
> I have several engines to chose from here for my next wood gas project.
> Going to go ahead with it and just hope the stink has settled form my
> insurance company ripping hair out of their heads. ( hope they are not on
> here.. bugger )
> Besides this is not a heating device so should not count.
> What out of the junk yard specials would be considered ideal for wood gas
> give I Only need this time to come up with 20 hp at 1,800 rpm?
> I have everything in the shop for a Mike clone.
> Spending a few bucks for the right engine is going to be real cheep just
> now.
> I am not keen on stuck valves through pistons. ( it that ever happens...
> never mind )
>
> Regards all,
> Charles
>
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