Hi Vakrant,
Sorry for this slow response to offer comment on your questions. We rarely get
exchanges with those actually working for engine companies on this forum, but
privately I know of the frustration of engine manufacturers who have tried
working with producer gas. We all know engines run on PG, but with many
contradicting results, so we need to chip away at why you in an engine
laboratory would appear to be experiencing problems.
>Doug, I agree with you. We have engines on PG but more over we want to go for
>higher capacity engines. Currently engines running on PG have the CR 11 for NA
>>engines and For TC its 8.5 ..
As others have commented, these are very low ratios for a gas engine, and while
17: 1 CR is possible, this does require the best quality of clean PG possible,
and very stable operating temperatures of the cooling system.
But fpr same case in NG we can go higher.
Using NG is a trap for engine operating specifications. The gas quality depends
on how much condensate they remove before it goes into the pipeline. This was
discovered during the commissioning of a power station at Alice Springs in
Australia. It took four days for the gas to reach the engine, so every time it
was precisely set up, it changed and shut the engine down after a few days.
This detail can be giving you a lot of false information.
I am trying to think from combustion perspective to increase further to sqeeze
out more power and thermal eff. . So far i tried till 12.5 (though literature
mentioned about 17) and whatever thermodynamic state of mixture (PG + Air)
shows positive signs and CFD also support it..
My understanding of the Cummins range of gas engines, is that only the biggest
model PSV 91G has been optimized for PG. The fact that it can extract more from
PG than previously thought, is a very big advance, and with a TC and CR at
11:1 sounds like your difficulty is at another level. Remember that literature
only reports what has been done, and in some cases become more of a
Bibliography collection. If it was of any value to you in a engine laboratory,
then all the problems would be solved!
At a guess, I suggest the gasifier you are using is making less than tar free
gas, and you rely on a gas cleaning system to remove all condensable. If this
is the case, then you are probably experiencing how the differing gas mixtures
spontaneously ignite at various CR.
A huge amount of work was done in New Zealand on conversion of diesel engines
to gas and exported around the World for bus fleets. I had a lot of exchanges
of information with those guys, and their opinion of PG was that it would offer
the best performance at around 14:1 CR. This would appear to me to be a tad
low, but your engine has to be able to optimize the most common denominator of
the gas in the target market, which in the main, is contaminated PG. In this
instance, the difficulty is sometimes found in the tuning of the inlet
manifolds, where a pressure pulse can form which then affects the VE of each
cylinder. You won't see this with a single cylinder engine, so you may need to
review the engine used for compression experiments.
When I consider combustion issues, it sometimes helps to look in other
directions, and this I found a while ago which may offer a clue to PG engine
combustion. How one might relate shock wave ignition to the chemistry found in
PG, would probably fill a book, but purist answers to resolve the problems just
don't seem to work in practice, so we must be missing something important.
http://www.princeton.edu/mae/people/faculty/dryer/homepage/research/hydrogen-fire-safety/movies/Dryer_et_al_CST_179_2007.pdf
Hope this gives you a few ideas to consider.
Doug Williams,
Fluidyne...
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