Club 80-90 Forums

Can anyone help with some ideas I have for using LPG to cool the inlet charge.
My 2.1 runs on LPG at the moment I intend to supercharge it.
Because the liguid LPG converts to gas in the regulator I will get no cooling effect. How can I use the cooling affect.

Idea 1. Inject Liquid LPG into the air stream after the Supercharger this could be controlled under boost as you would with Nitrous

Idea 2. Connect the regulator water supply via an electric pump to a water to air intercooler So the heat from the intercooler is transfered by water to heat the regulator. The cool water returning from the regulator cools the charge in the water to air intercooler.
Alot more complicated than just squirting liguid in.

Anyone any ideas

The first thing you need to know is the evaporative cooling effect of the LPG liquid to gaseous phase. You need to know the fuelling mass flow rate and subsequently estimate how much this cooling effect is worth.

Then you should also look at the efficiency of the supercharger at the pressure ratio and flow rates you're after. This will indicate how much heat you need to remove to make a worthwhile difference and whether the cooling effect of the LPG evaporation is even of the same order of magnitude. If it's not then forget it and maybe look at water injection (when under boost) or an intercooler working at say 50% effeiciency (typical).

If it is (of the order of magnitude you need to cool the charge), then any effort to engineer this will be worthwhile, or you'll know how worthwhile.

If the supercharger is a Rootes type, then its efficiency will be poor, around 45%, whereas a centrifugal compressor often runs at 65~70% in the PR= 2 to 3 range. Compressor efficiency determines how much additional heat is added to the charge during compression, over and above that expected due to the ideal gas laws.

Choosing and sizing a compressor for the design Pressure Ratio and flow rates could make more difference than working off-design or with a poor compressor and then trying to cool the charge afterwards.

You can now get an electric supercharger that gives a guaranteed boost pressure of 1 psi for about $300. 1 psi may not sound a lot, but for a petrol engine running a high compression ratio, in hot weather, this would definitely be noticeable when switched on at high throttle settings. With LPG, detonation would not be a problem. If its a 2.1 DJ, then this might be a route worth looking at, as it's an easy install and the shipping of a such a lightweight item shouldn't be too much if you can avoid Import Duty somehow.

the eaton chargers used on merc's and mini's are quite suited to the flat engines shape..
plus they can be found cheap.. loads of mini eaton ones on ebay..

Gave my thoughts the other week..
we should sit down over a beer or three!!!

A level physics, anyone!!!

When my daughter struggles with her homework, I will get her to poston here!!!

Emma

TTT - will three beers help me understand any of the above??