[Gasification] Regarding Combustion Quality of Producer gas

[doug.williams]

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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