LPG max total ignition advance

[countrymansouth]

My research suggests that 10.5 to 1CR is about the max given the variation in fuel quality petrol and LPG. The next Q is what is the optimum total ignition advance for LPG given that on petrol it is about 36degrees BTDC on my Rover 3.9 V8, should it be more on LPG? On my engine I can advance the tickover advance to 16 degrees BTDC without pinging under load on petrol. My dizzy will give 28.5 degrees of mechanical advance so 28 +16 = 44. In theory too much advance but on LPG no pinging and good performance. Comments much appreciated

 

[Tmoose]

Aluminum heads? Some used to say the greater heat conductivity/dissipation/?? of aluminum was worth about a point of compression ratio. I think Smokey may have said that he intentionally reduced aluminum heads' heat rejection with a coating of something in the water passages.

 

[MikeHalloran]

ISTR that a CR of 14:1 is usable with LPG.

If you are building to run on either fuel, you are limited by the swill that's sold for petrol these days.



Mike Halloran
Pembroke Pines, FL, USA

 

[Lou Scannon]

14:1 sounds pretty high to me for LPG. Any data or examples for that?

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[MikeHalloran]

Two conflicting discussions about LPG CR:

http://www.eng-tips.com/viewthread.cfm?qid=159998

http://www.f1technical.net/forum/viewtopic.php?f=4&t=8857

... I'm remembering from a much older discussion that I can't find right now.


Mike Halloran
Pembroke Pines, FL, USA

 

[winfieldblue]

The octane rating of the inducted lpg/air mix goes down with A. high intake swirl and B. high intake temps. Ignition lead should be reduced to 25* total centrifugal + whatever vacuum advance the engine can run with without encountering pre-ignition. There is a book available on tuning an engine for propane,here

http://www.amazon.com/Economy-Perfo...=UTF8&qid=1367471658&sr=1-10&keywords=propane

but if your buying propane that is cut with butane (as it is in some country's) then the octane rating will be much lower.

 

[Tmoose]

Wow. $130 for a used SA Design book that probably cost less than 30 bucks new just a couple of decades ago.

 

[franzh]

Wow, I have that book! It was written in the late 80's and references basic technology available at that time and has no real relevance today. This book is great material for basic level tinkering but doesnt contain any real engineering sciences.

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Lou Scannon]

I don't have that book, and what Franz posted is a large part of the reason why (not).

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[winfieldblue]

The book is a bit ancient, but lpg and propane haven't changed much as far as I know! If the O.P. were to specify the operational goals then more could be added to the above, from memory Franz has a bit of experience in this area....Probably the most exciting (for me) tech advance concerning lpg systems would have to be the liquid injection systems developed over the last 2 decades, especially when combined with computerized engines. I killed several engines (pre computerized)(remember points?) by using too much ignition advance, I couldn't hear any pinging but the end result was usually a shattered piston/fractured rings, usually on the cylinder that got a leaner mixture due to intake manifold design. Interestingly even though the engine was pinging (presumably intermittently) power still went up with the increased ignition advance.

 

[turbocohen]

I second what FranzH said.. That book aint worth a darn now.. The technology has matured.