LPG substition for diesel engine

[HydroScope]

Hi,

diesel engine runing with LPG seems like a great idea here in australia diesel is much more expensive then petrol and LPG. It makes financial sense to convert from petrol to LPG but not to diesel/lpg because available kits dont seem to uses high levels of LPG substitution, what is the limit? I know when it comes to diesel\Natural gas I have herd of 95% gas 5% diesel. It would be great to see a kit that could combine common rail turbo diesel with 95% subsitition of diesel with LPG, since they are now producing some nice small but powerful diesels.

 

[dcasto]

Here is paper labled LNG in diesels, but it also looks at LPG. Be sure to click on the "cetane number" hyperlink, its a good table of all typical fuel properties.

http://www.naftc.wvu.edu/NAFTC/data/indepth/LNG/LNG.html

 

[BrianPetersen]

With an otherwise-unmodified engine having compression ratios typical of automotive and light truck diesels, detonation is a big problem if an attempt is made to substitute too much diesel with LPG (propane).

This is not so much of an issue with CNG since methane is more resistant to self-ignition inside the cylinders.

Most "true" CNG conversions of diesel engines (example: city buses) completely eliminate the diesel fuel system, but operate stoichiometric with spark ignition, essentially like a gasoline engine but with a higher compression ratio.

I'm not aware of any full LPG conversions of diesel engines because of the detonation issue; all I've heard of are conversions of spark-ignition gasoline engines, but that doesn't mean it has never happened.

 

[patprimmer]

LPG will normally detonate at about 11 or 12:1 compression.

Diesels are are not my area, but I think typically compression ratios are 18 to 20:1. The timing of the fuel injection is critical re nature of combustion process in a somewhat similar vein to spark timing in a spark ignition engine.

LPG is added to the manifold so it is not timed, so it can ignite at the point in the compression stroke where the chamber is seeing somewhere in the ballpark 11 times atmospheric pressure.

Regards

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[j79guy]

Hydroscope: On my Cummins powered gravel truck, (444 engine.) Picker truck, (Brazilian 6-cylinder.) and personal pickup, (Navistar 7.3L) I'm running 60/40 propane to diesel. At the prices I'm paying here for LPG, it works out to a total of 27% cost reduction to keep these vehicles on the road. (Fuel, maintenance, purchase of the LPG equipment amortized over time, ect.) I've not become brave enough to go higher, as I'm approaching the inlet air Lower Explosive Limit. A local fellow converted his logging truck to straight CNG, by dropping the compression ratio, replacing the diesel injectors with spark plugs, and putting high tension ignition where the HP diesel pump was. The conversion to straight LPG would be similar. Nearly every natural gas pipeline compression facilities have thier own electrical power generation capability, which in turn are mostly converted diesels to run on straight natural gas. Lots of information out there. Lots of documented cost breakdowns.

j79 guy