[Gasification] Engine knock

[jim mason]

On 2/5/07, doug.williams <Doug.Williams at orcon.net.nz> wrote:
>
> Hi Fredrik, and Colleagues,
>
> You are correct.
>
> > A compression ratio of 1:25 sounds very high. Can someone come up with
> > more
> > information about this?
>
> Duel fuel diesels will only work reliably with compression ratios of 16:1,
> as the spontaneous ignition temperature of producer gas is about the same as
> for diesel. You cannot control the engine over this ratio, as spontaneous
> ignition takes over. Engines with higher ratios, have a separate
> pre-combustion chamber, and these are well proven to be unsuitable for
> producer gas.
>

nearly every diesel i know of is over 16:1.  especially if they are
non turbo, they are usually going to be 18:1 or more.  the lowest ones
i know of are the cummins 5.9 and dt466, both of which are about 16:1
i think.   but i of course could be very wrong.  i've yet to dual fuel
a diesel, but everyone here seems to not have problems.  even the
listers, which are relatively low compression, are over 16:1.  i think
they are 18:1, and indirect injection/precombustion usually.

so can you give us some of your experience with woodgas detonation in
diesels in dual fuel mode?  especially in indirect
injection/precombustion chamber engines.  all the diesel engines i
have lined up to wood gas dual fuel are of this type.  my heart might
break if i learn they are no go.



> If you are setting up a spark ignition engine, the compression ratio has
> little merit over 12.5:1 as the increase in frictional forces consume any
> extra power that a high ratio might provide. this has been well researched
> and proven, my papers go back to before WW2.

i'm confused by this doug.  as you know, thermodynamic efficiency has
a direct relationship to compression ratio.  we gain efficiency the
higher we can compress before combustion.  this was the main "a ha"
that led away from early atmospheric pressure internal combustion
engines.  mechanical friction becomes a smaller fraction of total
cycle energy the higher compression goes.  and more importantly, the
delta T we can mine goes higher the higher pressure under which the
original combustion happens.

if we had a fuel that could run at 100:1, and a motor that would stay
together, that would be a very high efficiency motor.

you of course know all this doug, so maybe i'm misreading what you mean.

j


> Hope this clarifies the issue of compression ratios.
> Regards,
> Doug Williams.
> Fluidyne Gasification.
>
>
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