How much cold does a converter generate?

[Valvebounce]

Why I ask is this,
I plan to fit an Impco gas carb to a 4.3ltr inline 6. LPG ticks a lot of the boxes for me.
I've read somewhere that if I boost reference one of the ports in the impco, it'll work in a turbo blowthrough application. Being high octane, and gas at room temperature make it quite ideal for this too.
Anyway, if I'm going to run boost, then an intercooler would be a mandatory accessory. Since I have quite a bit of room under the bonnet, I'm going to get a mate to build me a nice long custom water to air intercooler. And I have plenty of space behind the grill for a heat exchanger to unload the heat.
Now with the converter being water heated, how about plumbing this into the water to air intercooler? If the pump was moving fast enough, the coolant would circulate quickly. And the front exchanger would expose the coolant to the heat of ambient temperature. So it might prevent the converter from freezing?
The gain being getting say ten psi of boost, but at a very low temperature. Thus increasing intake charge density. Which is going to have a big impact on performance.
So how much cold does a converter generate? With the butane freezing at 0*C, if it gets too cold things come to a grinding halt. I suppose the same coolant feed could run through the turbo too, before going back into the converter? (But I'd still like to keep this circuit separate from the engine coolant.

[classicswede]

LPG boils at -40c

Now how much cold it generated will depend on how much flow you have. The more flow the more heat it needs to pull to vapourise.

Your idea of using the intercooler to heat the gas is not going to work as the vapouriser will not reach a high enough temprature and you would also need a seprate pump to pump the water around.

I'm assuming your inline 6 is a carb engine? If it was fuel injected then fitting a injection LPG system is the way to go with forced induction.

It is possible to make a carb system work with boost refernace but it will never run totaly right and usualy takes a lot of messing with to make drivable. If you were running a supercharger rather than turbo then a suck through system could be run and would avaoid a lot of complication in setup

[rossko]

Personally I think the intercooler might work in limited circumstances, but not for proper road use. I worked out some while back a vaporiser passing ~150kW of gas soaks up around 1kW of heat. You can re-work the numbers to be sure, buts its a ballpark for now.

I think the problem area is actually exchanging the heat ; how many kW you can exchange depends on temperature differences. I would guess that mostly the 'output' from the intercooler is at more or less ambient outside drag racing? Its gonna take really high coolant flows to maintain the vap temp. There's no real way to enlarge the vap's exchange area, short of multiple vaps - and you're going to have enough problems setting up an induction LPG system without that serious complication.

As the gas pressure increases, the minumum temperature that needs to maintained to ensure vaporisation goes up - so the turbo works against you. Lets say a sensible vaporiser minimum might be 0C - this thing's not gonna work well on a real winters morn - to give gas out at -10C or summat.

[stype3]

butane melts at -140C, so that wont be a problem. It does boil at -1 C, which might make things tricky if LPG was pure butane. but it isnt it has propane as well, which boils at -44C

[Tubbs]

Or alternatively introduce the gas pre intercooler so the gas gets cooled as well as the air. Best to fit an ok start though
You can just use a normal water cooling set up. I had a saab like that. Went mental when you pressed the pedal. You could break traction really easy in most of the gears.

[Gilbertd]

butane melts at -140C, so that wont be a problem. It does boil at -1 C, which might make things tricky if LPG was pure butane. but it isnt it has propane as well, which boils at -44C

Autogas in the UK is mostly 100% Propane, with maybe a little Butane added in the summer. In Europe it varies between 90/10 and 50/50 Propane to Butane.

[Valvebounce]

Oh yeah, I'm in NZ.
Our gas is a healthy mix of propane and butane. (And a miniscule amount of methane so as to make leaks detectable to the nose before there is a fire)
I've seen set ups like what I'd like to do on the www in Aussie. Most of the bigger HP set ups run two converters to keep the gas supply up to the carb.
Water to air is the best way to go. (They're like four times more efficent than air to air)
And it's not uncommon to see fill canisters/resivours packed full of ice to keep the temps down. So with all that cooling going to waste in the converter, there surely must be a way of utilising that wasted cold.
Like on a 30*c summers day, surely the ambeint air temp passing over the front exchanger would be able to keep up?
You can see what I'm getting at aye? Cold temps make forced engines fly.

[rossko]

Methane is odourless, the smell is another deliberately introduced compound.

I think you're taking the wrong view; the inherent difficulty with a vaporiser is keeping it from freezing, by inputting heat into it. While thats the same as looking at it as a 'free chiller' I think that approach is overlooking that you actually want the darn thing to do its job properly.

All the commercial vap designs assume a significant temperature difference between the water flow and the minimum desirable temperture of the vap, making for good heat transfer in a reasonable size. You might expect trouble trying to run these designs at ambient temperatures, and have to de-rate the power handling significantly.
You could cheat a bit and look into pre-heating that the aircooled LPG boys use - but then youd be losing the overall "chiller" effect and the whole exercise becomes pointless.

You can get away with e.g. cold starts in a conventional setup because of the inherent thermal mass of a large amount of water in an engine system, that also starts to warm itself up before the vap can cool it down significantly. I'd worry about the smaller mass of water in your intercooler system?

Have you worked out what heat you can get out of an intercooler? You can estimate what heat the vap absorbs, from the engine output.

Bear in mind what happens if heat exchange can't keep up; when the core vap temperature gets too low, liquid sprays through into the gas space. As it travels out of the vap into warmer hoses, mixer etc it gets the heat it needed to vaporise - so now you've a couple of hundred times more gas than liquid and a sharp pressure increase. The manifold - and in your case hot turbo etc. - is flooded with practically neat gas and kills the engine. Now you got an air system full of fuel, a stalled engine, the gas is even coming back out the air intake. It's actually usually uneventful, apart from stinking and being a pig to restart, but there is of course some risk which is best avoided.

[classicswede]

If you are wanting to use LPG to cool the intake charge then the only way I can see that working is to use the liquid LPG pre vapouriser.

I would keep the vaouriser plumbed in to the water hoses as usual.

What you would have to build is a intercooler that has the LPG flowing around it to give you kind of heat exchange before the gas reaches the vapouriser. How you would get that to work is going to take some thinging about and I'm not sure it would ever even offer that much cooling.

On the other had fitting a stand alone fuel injection system and opting for a liquid LPG injection system rather than vapour could well offer a good means of cooling the intake charge and if maximum power is what you are looking for this is the road to be going down.

[Valvebounce]

Thanks for your input team.

[SimonHobson]

Actually, I can see a way to make this work.

Fit a pressure reducing valve upstream of the reducer - not sure what pressure it would need to be, but look at the saturated pressure/temperature curves for propane. So say we dropped the pressure to a value where the boiling point of the propane is (say) 0˚C - and then pipe it round one side of a heat exchanger of some sort.

With no heat input, the gas will get cold due to a small amount of it boiling off - but once it's cold enough, you'll get a mixed phase going into the reducer at low temperature. If you add heat, then more gas will boil off so making the mixture more vapour and less liquid. Add enough heat and you'll get all vapour.
My experience is that some reducers (Romano and OMVL R90 are one's I've experience with) will pass enough vapour-only to keep my 3.5 V8 fed in a Land Rover. In fact, the OMVL actually passes liquid through a short loop of pipe immersed in the water jacket before it goes through the metering valve of the first stage.

For the 110, I estimated that I could get up to about 1kW of cooling while "making progress" on the motorway. If I didn't have so many other (more important) things to do, I'd be looking at making a small ice-box compartment (to keep the gas out of the passenger compartment) so I could freeze ice-packs to put in the cool box ... or just make the chocolate very much not meleted
I suppose another option would be a glycol loop and pump to cool an internal fridge.

But back to the OP ...
You could make a small intercooler and put the gas directly through it. But, the gas side needs to be rated for AT LEAST 20 bar - the tanks are rated for 25 bar and tested to higher still. Ditto all the pipework, and you'll need to use a reasonable size of pipe to avoid fuel starvation.
You'll need to do some development work to see what tradeoff of pressure/temperature gives best results. Lower pressure will give lower temperatures and more charge cooling, but will reduce flow rate into the reducer/through the pipework.

Also consider that if you get surfaces of the intercooler below freezing then you risk icing up.

And finally, non of this will meet standards/regulations !

[stype3]

Theory only, but if you compress the input charge to say 14.7psi boost, and then cool it back down to ambient, you will generate 0.42kW per litre (engine size) per 1000 RPM. The compression process is not 100 % efficient so it generates more heat, but you will not be looking to take too much heat out of it.

The way I see it you are looking to use the heat required to vapourise the LPG to cool the compressed intake air, the best way will be to use a liquid/air intercooler to cool the compressed air, and then circulate that around a vapouriser of the correct size for the engines performance. Going that route I don't think you fall foul of any of the lpg regulations. If you run with pure antifreeze then you will run less risk of it boiling and freezing, that way you won't need such a big reservoir. But you will need to have an air/liquid heat exchanger with thermostat to keep the antifreeze cold enough, and perhaps also a bleed of the cars cooling system to a liquid/liquid heat exchanger to keep it warm enough when required. To me that looks like a pump, some piping, two thermostats, and two different oil coolers as well as the vapouriser. Do you have enough room under the bonnet for all this?

[e301988325i]

if you've got loads of space, what's the issue with using a pace chargecooler for your boost and running your vap as normal??