A correctly sized engine may be exactly where you should be heading first.
A smaller engine running at near full load when needed will be more efficient than a larger one running at say 1/2 load.
Absolutely correct there - and if I had my time again, I'd certainly use a smaller engine. I used the one I did for a plethora of reasons, including:
* readily available
* modest price from the car wreckers
* very common motor, spare parts should be available for a loooong time
* a "tried and true" engine that I was familiar with
* plenty of power even at the relatively low RPM I'm running it
That said, several of the problems I DID/DO have are:
* commercial automotive gas mixers didn't like such a small engine with such relatively low airflow
* such a large engine relative to the power I draw from it, is very "twitchy" when unloaded
Rossw's setup is a thing of beauty, but I could make out the total plumbing of the vapor based fuel either.
Sorry, I'll go see if I've got some more detailed or relevant pics. In short, I have a 2.75 ton vapour-takeoff pressure vessel outside, that sits around 200 PSI, that feeds a pre-regulator to take it to about 15 PSI that feeds the engine. That comes to a tap and connection point on the wall near the genset, with a flexible hose to the engine itself. At the "front" of the engine mounted on top is the safety valve and it's electronics (that monitors spark and turns off gas if the spark stops), that feeds the "gas converter" (in a car it would take liquid propane, and be plumbed in to the hot water to prevent it icing). Out of the converter to the servo-controlled fuel valve and then to the mixer by the throttle body.
RossW: I looked at all those great pictures of your system and couldn't quite make the total setup, but it sure looked like the high quality kits that were sold here in the USA by IMP. After reading your last post it is clearer/easier to understand.
It's likely the same bits, just sourced one component at a time.
IF I may ask RossW and bob g : are you found that allowing for back pressure to help recirculate some of the un-burned fuel? or since running at optimum speed range your not needing to?
Well, the length of my exhaust is a little longer than it would have been in the car - but it's also twice the diameter it would have been, so that helps keep the back pressure to "about nominal".
Because I have an oxygen sensor mounted in the exhaust manifold, and use that to control the air/fuel ratio, the exhaust is pretty clean. Running constant RPM but variable load and adjusting AFR seems to keep the engine pretty happy.
Like I said before, oil change after the equivalent of 50,000 miles and it's still in pretty good nick, I change the spark plugs after what is probably the equivalent of 500,000 miles - but I wonder why I bother - they come out looking much like the new ones go in
(only a slight exaggeration).