Thread: LPG Fumigation in diesels revisited

FYI a bit of info on natural gas on stationary diesel engines:

DIESEL GAS AUSTRALIA

They claim no power loss, and up to 90% substitution of diesel with NG.

I have seen a local (Adelaide-Mt Gambier and return) delivery truck with a rack of CNG cylinders behind the cab and under the tray, it did 900km/day per fill so saved the company money at that level of use. The driver, a mate of mine, said it went better with the substitution in place, when it used around 10% diesel only.

CNG seems to be good for fleets operating from a base with a suitable refilling point.

LPG is easy to do and quite cheap if you don't fall for the hype from the big installers. Unfortunately emissions testing kills the idea of doing too many odd model vehicles with simple equipment as each one must be separately approved with each type of kit. Sorta kills the economics. Which is why I stick to older diesels for now.

Great info Ben.

Do you know how they quantified the 15-19% substitution? Was it on equivalent energy content or equivalent liquid volume?

It's also really interesting that they retard the timing when fumigating (either ethanol or lpg) and have some solid figures for knock limit.

Originally Posted by bee utey

FYI a bit of info on natural gas on stationary diesel engines:

DIESEL GAS AUSTRALIA

They claim no power loss, and up to 90% substitution of diesel with NG.

I have seen a local (Adelaide-Mt Gambier and return) delivery truck with a rack of CNG cylinders behind the cab and under the tray, it did 900km/day per fill so saved the company money at that level of use. The driver, a mate of mine, said it went better with the substitution in place, when it used around 10% diesel only.

CNG seems to be good for fleets operating from a base with a suitable refilling point.

LPG is easy to do and quite cheap if you don't fall for the hype from the big installers. Unfortunately emissions testing kills the idea of doing too many odd model vehicles with simple equipment as each one must be separately approved with each type of kit. Sorta kills the economics. Which is why I stick to older diesels for now.

CNG has a far higher octane rating than LPG. MAN (think house sized diesel engines) place a condensation limit on the gas allowable to fumigate their power generating diesels. The gas must not form any liquid under a certain pressure (which I forget, but it was much higher than LPG) to be an acceptable fuel in their diesels.

I have Diesel Gas version one fumigation on a 1996 300TDi in a Defender 130. Been in there for over 6 years and 110 000 km. quieter, cleaner, more power. I notice the gas run out. I get 11 litres diesel and 3 litres LPG per 100k around town and well down into 9s on the open road even when loaded up. Mine is tuned for longevity not power

Cost $4600 but govt gave back 2000. But back then LPG was 35cpl

I changed the TXFR ratio to 1.2 : 1 and cruises on 110 at 2600rpm. Engine runs very smooth.

Gets my vote.

Sent from my iPad using Tapatalk HD

Originally Posted by zwitter

I have Diesel Gas version one fumigation on a 1996 300TDi in a Defender 130. Been in there for over 6 years and 110 000 km. quieter, cleaner, more power. I notice the gas run out. I get 11 litres diesel and 3 litres LPG per 100k around town and well down into 9s on the open road even when loaded up. Mine is tuned for longevity not power

Cost $4600 but govt gave back 2000. But back then LPG was 35cpl

I changed the TXFR ratio to 1.2 : 1 and cruises on 110 at 2600rpm. Engine runs very smooth.

Gets my vote.

Sent from my iPad using Tapatalk HD

You get the difference between substitution and addition right?

Originally Posted by Dougal

You get the difference between substitution and addition right?

You can do both on the same engine, it depends on how far you press the accelerator. With auto transmissions substitution will mean the same power is achieved at a lesser accelerator position and some adjustment may be needed for the kickdown cable. I have suggested to some D1 owners that manual gear selection helps to maintain optimum engine speed if they want the trans to be normal on diesel only.

On a 300TDi the simplest way to achieve safe addition is to be conservative with the maximum diesel screw setting. An EGT gauge will help you judge safe limits. Dosage rates of LPG are set by the installer.

On one electronic system I was evaluating, the EGT probe is an integral part of the control system, cutting LPG at high EGT's. This was for a common rail engine with some connection to the vehicle ECU.

The difference as I see it is starting at your highest state of tune with diesel only is substitution.
Additional fuels are added and diesels is subtracted to give you the same power output, similar AFR's etc.
This is what Ben's results are about and the maximum substitution.

Addition is going beyond the diesel only state of tune, which is where the dragons lie.

The interesting part is, I haven't seen any lpg fumigation results putting out more power than tweaked up diesel on the same engine.

Originally Posted by Dougal

Great info Ben.

Do you know how they quantified the 15-19% substitution? Was it on equivalent energy content or equivalent liquid volume?

It's also really interesting that they retard the timing when fumigating (either ethanol or lpg) and have some solid figures for knock limit.

All values are based on equivalent energy content IRC. They have flow meters on all lines and the LPG or ethanol tanks are suspended from load cells.

The computer retards the timing automatically. If you set the engine to maintain a constant torque, it reduces injection volume and retards timing progressively as the (alternate) fuel is increased.


Chief - the consensus was that there is no real benefit, just that the minimal/no excise on LPG/NG/EtOH is lower, which makes it more attractive/economical in some cases. Seems there is little chance of harm if done sensibly, but the cleaner combustion (etc) claims seem to be unsubstantiated.