Thread: DieselGas - how's it going?????

Originally Posted by p38arover

What are those conditions? Not just pressure as LPG is under much higher pressure in a tank.

Wouldn't preignition be audible? It is in a petrol engine.

The autoignition temp of LPG is 468 deg C according to the shell MSDS.
http://cms.shellgaslpg.com/files/NZ/...Data_Sheet.pdf

That's lower than the compression temps in a diesel and is not tied to a stoich a/f ratio.
Good luck hearing it over your average diesel engine. If you can hear it outside, it's a hell of a bang going on inside.

Originally Posted by Dougal

The autoignition temp of LPG is 468 deg C according to the shell MSDS.
http://cms.shellgaslpg.com/files/NZ/...Data_Sheet.pdf

That's lower than the compression temps in a diesel and is not tied to a stoich a/f ratio.
Good luck hearing it over your average diesel engine. If you can hear it outside, it's a hell of a bang going on inside.

A quick search agrees with this figure, but shows that the autoignition temperature does vary with the air fuel ratio, although only the abstract of that paper is available without paying, so I can't say whether that variation is significant, but also revealed that the the minimum auto ignition concentration is about 10% of the stoichiometric mixture. Proportions below that will not detonate.

John

Originally Posted by JDNSW

A quick search agrees with this figure, but shows that the autoignition temperature does vary with the air fuel ratio, although only the abstract of that paper is available without paying, so I can't say whether that variation is significant, but also revealed that the the minimum auto ignition concentration is about 10% of the stoichiometric mixture. Proportions below that will not detonate.

John

They also list an upper and lower explosive limit, presume this is at atmospheric pressure. Roughly 2% and 10% by volume.

Originally Posted by JDNSW

Pressure in an LPG tank is quite low compared to compression pressures in a diesel - like about one tenth as much (CNG is another matter!), as the Liquefied Petroleum Gas is stored in liquid form.

I mis-read Dougal's post. I was thinking after the turbo but before going into the cylinder.

i have recently had gas fitted to mt 300tdi. I have found an increase of 200km per tank normal now with an increase in power. When it was first fitted the 110 went like a train...a lot of extra power with increased km/tank of diesel. However the gas usage was high. I had the gas inlet pressure to the gas injector tested and it was set at 25psi. The system I have fitted is supposed to be factory set at 15psi. However after having the pressure readjusted to 15psi the advantages of gas disappeared so I bought a pressure gauge and now I have been experimenting with different pressures myself. At present I have it adjusted at around 22psi and I find I have both power and economy back, using 1l of gas per 40km. More testing to come but I feel around this figure gives me best results. Jim

Originally Posted by Dougal

They also list an upper and lower explosive limit, presume this is at atmospheric pressure. Roughly 2% and 10% by volume.

Yes, that is about right - I don't know how they vary with pressure, probably not much seeing ignition temperature doesn't seem to, although interestingly, heavy oils will ignite at room temperature if the pressure is high enough (a hazard for high pressure compressors)!

Since the stoichiometric mix is about 15:1 (I may be getting proportion by mass and proportion by volume mixed up here, but the difference is probably not that significant, seeing the molecular weight of propane is not too dissimilar from air) or 7%, the lower limit is in fact 28% (this time I calculated it instead of guessing conservatively) of it, which is about as high as would ever be used in dieselgas - suggesting that detonation is probably pretty rare.

John

Originally Posted by jx2mad

i have recently had gas fitted to mt 300tdi. I have found an increase of 200km per tank normal now with an increase in power. When it was first fitted the 110 went like a train...a lot of extra power with increased km/tank of diesel. However the gas usage was high. I had the gas inlet pressure to the gas injector tested and it was set at 25psi. The system I have fitted is supposed to be factory set at 15psi. However after having the pressure readjusted to 15psi the advantages of gas disappeared so I bought a pressure gauge and now I have been experimenting with different pressures myself. At present I have it adjusted at around 22psi and I find I have both power and economy back, using 1l of gas per 40km. More testing to come but I feel around this figure gives me best results. Jim

Jim, is yours computer controlled? Who installed yours?

Originally Posted by JDNSW

Yes, that is about right - I don't know how they vary with pressure, probably not much seeing ignition temperature doesn't seem to, although interestingly, heavy oils will ignite at room temperature if the pressure is high enough (a hazard for high pressure compressors)!

Since the stoichiometric mix is about 15:1 (I may be getting proportion by mass and proportion by volume mixed up here, but the difference is probably not that significant, seeing the molecular weight of propane is not too dissimilar from air) or 7%, the lower limit is in fact 28% (this time I calculated it instead of guessing conservatively) of it, which is about as high as would ever be used in dieselgas - suggesting that detonation is probably pretty rare.

John

Have you seen the threads I linked into this post: http://www.aulro.com/afvb/technical-...tml#post677516