coolant pump to use the cold.

The coolant temp has to be maintained at a high enough temp to prevent the vapouriser from freezing, from what I can remember the outlet temp of the coolant from the vap. has to be at least 15 deg C, requiring a considerable increase on this at the inlet under high demand situations.

Consider an auxilliary coolant pump from a BMW 3 or 5 series (E39 or E46) for the pumping part, dunno how you'd rig the control side though!

Other than the current consumed by the pump...... Good luck, Badger.

FWIW LPG is almost entirely propane, and propane is used in the refrigeration circuit of major gas plants where they chill the natural gas that comes in from the North Sea to condense out any impurities. Although I realise that this is not what you are thinking of, I just thought I would point out that you could 'in theory' use the same LPG as part of a refrigeration circuit. Of course the LPGA might not approve (and for good reasons) !

Steve

On or around Tue, 21 Aug 2007 13:36:25 -0700, Cheshire Steve enlightened us thusly:

effectively, I would be: the propane works as a refrigerant by evaporating, absorbing heat as it does so. In a closed circuit plant, you then compress it mechanically outside the cooled area (in a fridge, it's done at the back) and start again. In the vehicle, you're looking to burn a largeish amount so it'd be a single-use propane fridge :-)

Main issue is that the vehicle heater probably won't supply enough heat to the vapouriser.

Austin,

You seem clued up on this sort of stuff, so maybe I can bounce an idea off you. I have built a couple of V8s, and enjoyed tuning and running them - but I have a 3.5 V8 engine sitting in the garage and I was wondering about building a bespoke LPG engine. I understand that LPG has a very high octane ratio so I could use the old 10.25 to 1 pistons (and maybe go slightly higher if I can clear the valves), and as far as I can see there is no reason not to run LPG all the time. The only issue would be getting the initial heat for the vaporiser (which is how it links into this thread - in reverse). I was wondering about using an electric heater for the first few minutes of running - I haven't done the sums yet - but getting rid of the petrol tank could allow the conversion without loosing load space - and optimising an engine for LPG as regards compression ratio and timing might be interesting.

What do you think ? Apart from not being able to find an LPG garage - is there any reason to retain petrol ?

Steve

Dont worry about the initial vaporiser temp. There are plenty of us just running LPG only - both my car and my 101 start on LPG with no problems - I dont have a petrol tank on the car and the 101 has a petrol tank with a hole in the bottom! Never had a vaporiser freeze up on a cold start and ive driven the car daily year round for close to 2 years now.

I think petrol starting is more relevant with injection LPG setups. but im not sure why.

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The 101 Forward Control Club and Register

Wot he said. I used to have a 3.9vse on LPG, never used petrol at all, never had the vaporiser ice up, even on very cold mornings.

Thanks guys,

So no need for petrol - so next step is - if you were building the engine from scratch (which I do) what compression ratio can you go for with LPG ? Can you calculate it from the octane rating, or is there some other critical limit.

AFAIK the efficiency of an engine and the power goes up with higher compression ratios, so maybe an engine can both be high performance and a bit better on fuel if built specifically for LPG and running a high compression.

Steve

On or around Wed, 22 Aug 2007 13:48:55 -0700, Cheshire Steve enlightened us thusly:

Just go with the highest comp pistons you can get as standard. P6 ones are theoretically to be had in 10.5:1, but that's using tin gaskets; composite ones are better.

The other thing to do is to optimise the ignition - have a word with Badger about that, you can switch things around in the distributor.

You need, IIRC, more initial advance and less centrifugal advance.

The only other thing you MUST do is keep at least 25% antifreeze in it at all times. Otherwise, it really will freeze up...

Yes thermodynamic efficiency goes up in almost direct relation to compression ratio in the range common in petrol engines.

Theoretically yes but there are some variables to consider, the torque, and hence power curves will change, so gearing may need to change to make use of the better torque at higher rpm. Also consider that the flame speed of lpg is slower, which may limit rpm in a high revving engine plus I think the range of mixture strengths of lpg is less than petrol, making tuning for performance or economy a narrower option.

BTW although I run a 110 V8 almost solely on lpg it can be next to impossible to restart from hot on lpg, this is the only time I revert to petrol unless I'm out of lpg. This is to do with failings in the set up but I've not managed to sort it in over 5 years.

AJH

I have long given up on the tin gaskets, having been advised against them by RPi - who are also pretty clued up on propane fuelled engines.

I was mooching the web on this topic and found an interesting thread at

like 11:1 is safe, and 12:1 may be OK - but then the threaddiverged onto liquid phase propane injection. Now that soundsinteresting. I converted my V8 to programmable fuel injection andtiming using a Holley Commander 950 ECU, I wonder whether the samesystem could be adapted for liquid phase propane injection. Obviouslyit runs at a higher pressure, so the injectors and plumbing will needto change, but the fully programmable control system could stay. With liquid injection, the cooling benefit you were after for the aircon occurs in the inlet tract, so should increase the amount of air the engine swallows. I understand that Vialle in Holland make a LPFI system.

Steve

How much can you skim off of a stock v8 head?

10:1(ish) pistons are the highest that are easily available arnt they? so to get it higher you are skimming off the head.

The place here looked at me funny when i had 0.7mm skimmed of mine just (to fit composite rather than tin). If you want to run composite+increase the compression you are looking at having 1mm+ taken off the heads. Thats quite a bit isnt it?

I asked my local installers about a liquid injection kit.

They say that they eat pumps in this country due to the LPG quality (swarf in the tank). Due to how i have blocked my LPG filter in the past I believe them about the swarf. They said that the vialle system uses an intank pump - which is only available with the tank - so you are looking at £1000 or so for a tank+pump assembly each time - thus they have converted vehicles back to conventional LPG systems as it is cheaper than replacing the pump!

I still fancy doing it one day though :D

Also - as in that thread remember that uk LPG is a butane propane mix and that thread seems to refer to propane only for the higher compressions. I wasnt aware that butane wasnt that good but i do know that when i go to france their LPG makes my car go better due to it being a different mix - so there must be something in it!

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The 101 Forward Control Club and Register

On or around Thu, 23 Aug 2007 10:14:13 +0100, AJH enlightened us thusly:

what parts are on it?

sounds like a tuning issue. Never had problems on any of my V8 installs.

Landi Renzo

I think so but it's also to do with gas getting into the manifold in the small time between the ignition impulse stopping and the solenoid cutting the gas off. This suggests the gas regulator is over pressure. I've fiddled around in the past and only made it worse so I've given up. It's only a workhorse and not much of a problem to me but is the reason I always keep petrol in the tank.

AJH