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<DIV><FONT face=Arial size=2><STRONG>Hi Tony and Colleagues<BR><BR></STRONG>>
This may be my first post to this site, I trust you will all not hope it is my
last.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><STRONG>As a fellow New Zealander, lets hear more
from you, we cover a lot of engine "stuff", and new voices are most
welcome.</STRONG></FONT><FONT face=Arial size=2><STRONG> </STRONG></DIV>
<DIV> <BR>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>Fluidyne bought a Colortune 500 kit back in 1974-5, and I used it
to teach how exhaust temperatures and engine sound changed across gas/air
mixtures, using a single cylinder Iron Horse engine. I sent both Kevin and
Arnt a copy of the colour guide out of our kit, seeing as they were interested
in this subject.</STRONG><BR> <BR>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>This is a problem for producer gas in most DIY systems. We do
better at the commercial level with more sophisticated filtration systems, but
it is better to use naturally aspirated engines of larger cylinder capacity of
lower RPM, than undersized turbocharged engines relying on high RPM for DIY
projects.</STRONG></DIV>
<DIV> </DIV>
<DIV>> 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.<BR>> The stroke cannot easily be
altered but the compression ratio can be changed on some engines by machining
the cylinder head.</DIV>
<DIV> </DIV>
<DIV><STRONG>Generally speaking, this would mainly be applied to very old
engines, probably pre-dating around 1949. The literature records a lot of work
in this area of compression ratios by Woods in the late 1930's early
40's (from memory), where it was established that around 11:1 was the
optimum for producer gas. At this point, the extra friction from compressive
forces consumed the "extra energy", and little was gained from higher
compression. </STRONG></DIV>
<DIV><BR>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>This is true, but remember that WW2 petrol was of lower
octane, and required ignition advancement. Modern engines have that advancement
already built in for the higher octane available today. Then, separate charcoal
gasifiers away from wood gasifiers, because the H2 content again changes
ignition behaviour. Most engines set up to operate on LPG or natural gas, are
from 10-12:1 compression ratio (of the smaller sizes), and run without
alteration on 110-120 octane producer gas perfectly. Having said that, you
can always tweak them if the situation demands that degree of perfection. The
engine is the least of your worries if the gas making is unstable
(:-)</STRONG></DIV>
<DIV><BR>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>Speaking "generally", producer gas has no problem in most standard
spark ignition engines, as the spontaneous ignition temperature for producer gas
in our experience, is around 600C. You find these compression temperatures in
diesels around 16:1 ratio, and again from experience, once you go over 17:1, the
spontaneous ignition temperature makes the engine very unstable. We worked with
Lister (NZ) to develop dual fuel conversion kits for the Pacific
region, converted to gas Ford diesels in the UK, Ford natural gas engines in
USA, and purpose built gas engines in Germany. </STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>In all cases, the operating temperatures around the engine can
affect the behaviour of the ignition temperatures, as will the actual CO,H2, and
CH4 content. Any uncracked hydrocarbons will also affect the timing behaviour,
so be careful how you tinker with the timing. Nothing is written in
stone!</STRONG></DIV>
<DIV> </DIV>
<DIV>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>My genset engine is a 1949 Hillman engine, one of the early
higher compression engines (8:1) out of the UK. The vacuum advance and
retard is disconnected, but we have not noticed any problems across a wide range
of outputs for 1,000's of hours. It is a moot point however, and I will
reconnect it next time I play to see if it makes any
difference.<BR></STRONG>> <BR>> 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.</DIV>
<DIV> </DIV>
<DIV><STRONG>Gensets have to operate at fixed speed, so use a governor on the
throttle butterfly, and as I said, our advance/retard control is disconnected,
so cannot in any way affect how the engine hunts on load or gas changes.
Producer gas has many surprises as an engine fuel, and we learn more by the
day.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Most of the above comments apply to fixed speed (RPM)
applications used for electrical power generation, both base and variable
loads, from our installation experiences 1978- 2010.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG>Doug Williams,</STRONG></DIV>
<DIV><STRONG>Fluidyne Gasification.</STRONG></DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG></STRONG> </DIV>
<DIV><STRONG></STRONG> </DIV>
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