would LPG and Miller Cycle make a good combination? 1

[treetotreef]

I've recently started looking into LPG and from what i've learnt so far, because of its high RON (~110+) i'm thinking it would be very suitable to supercharging...but what about miller cycle? the engine i have in mind is the Mazda 2.25L KJ-ZEM V6 engine.

Could there be a danger of backfires in the inlet manifold(frontfires)?

any thoughts on this?

thanks

 

[TDIMeister]

Propane-fuelling of a Miller-cycle engine should not present any more danger of backfiring than a port-injected gasoline engine as your engine originally is.

Many SAE papers cover industrial engines operating on the Miller cycle running on natural gas, LPG and process gas (a mish-mash of light hydrocarbons with CO, CO2, N2, etc. as impurities.

Burning hydrogen is a different story when it comes to backfiring risk...

All else being equal, (boost pressure, etc.), expect lower full-load power, due to the volume displacing effect of the propane gas, and lack of charge cooling that has been widely posted already.

 

[treetotreef]

I have read some posts on the lack of charge cooling that LPG offers, so could the lack of charge cooling be compensitated by running a larger intercooler?

 

[patprimmer]

A larger intercooler and/or water/alcohol injection will help.

Regards

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.

 

[TDIMeister]

There are some systems that inject propane in liquid form into the intake ports. This is the best way to approach if you can find such a systems as it take advantages of the charge cooling effect of evaporating liquid fuel.

Failing that, I assume this Miller cycle engine is supercharged. Injecting the propane just before the compressor will reduce compressor work (because the specific heat ratio will be reduced).

Lotus exploits this thermodynamic phenomenon and injects E85 pre-compressor in the not-for-production Exige 265E. It cools the charge and reduces the compressor work simultaneously, and quite substantially at that.

 

[TDIMeister]

Man, that was shameful grammar on my part but I can't edit my post. This is not typical of me. Blame the glass of whisky sitting beside me.