Thread: isuzu & LPG

Originally Posted by EchiDna

miracle of miracles - they get more range out of the same amount of diesel by adding another fuel source, plus re-tuning the engine to cater for more fuel gives more power... Sheesh anyone can improve the range of any car by putting another fuel tank on it... in terms of economy, gas is cheaper per joule that diesel, but in terms of energy, 1 joule of energy from gas = 1 joule of energy from diesel, it cannot chemically or physically be any other way.

I don't think that it is a miracle.

I think that people are just in violent agreement with respect to the basic issue of running cost. For whatever reason the energy content of lpg is charged at a lesser cost than that of diesel. This returns a saving at the fuel pump.

No matter what you do you will always run into issues that many will not agree on. Just one of the colourful aspects of life.

Originally Posted by EchiDna

and apparently 1 litre of gas = exactly the energy output of 1 litre of diesel... or so sayeth the mathematician who calculated the above example...

No, I think that if all things were equal with regards the 1000 kms covered in the example then a litter of diesel contains less energy than a litre of lpg.

On diesel only this Land Rover Defender returned 700km on average per tank resulting in average fuel consumption figures of 10.7 litres/100km.


700km for 75 litres = 10.7l/100km. Cost to refill = 75 litres @ $1.20 = $90
This means $90 buys 700km on diesel only
Running the system on diesel/gas and still using 75l of diesel plus 28l of LPG the Defender now consistently returns just over 1000kms an increase of 300km on diesel only scenario.
To cover the additional 300km on diesel only would cost:
300km @ 10.7l/100km = 32.10 litres required
32.10 litres @ $1.20 = $38.52
Therefore to cover 1000kms on diesel only the cost would be: 700km @ $90.00 + 300km @ $38.52 = $128.52


To cover the same distance (1000kms) with diesel/gas the cost would be:
75l diesel @ $1.20 = $90.00 + 28l LPG @ $0.40 = $11.20 So diesel + LPG = $101.20
So, the nett saving per tank would be $128.52 - $101.20 = $27.32 or 21% per tank.

This saving doesn’t take into account the extra power (the dyno showed 34% at this setting) giving you better drivability. Not to mention quieter, cleaner and with less wear on the engine!

So you can either accept that 1 ltr of lpg has more energy than 1 ltr of diesel (don't think so) or that the mix of lpg and diesel results in greater efficiency from a diesel motor (don't know that I am prepared to accept that but I am not ruling it out) or that the example given has numerous variables that have not been taken into account (I vote for this one).

Originally Posted by isuzurover

I can't see any fuel consumption numbers there???

A blind monkey with a spanner can get those sort of figures out of a VE injector pump.

Ben,

Even with the fuel consumption figures on the web site as EchiDna found, you cannot draw conclusions as I have pointed out in the example of the Defender 300 Tdi on diesel/gas would have us belive that where 32.1 ltrs of diesel are required to do 300 km you only need 28 ltrs of lpg.

I think that blind monkeys might struggle but then again as they would not see the black smoke it is very possible that they could get more power out of the 300 Tdi. Black smoke is the one thing that most people will see coming from a diesel with an over adjusted pump. Can't say that the pollution coming out of a diesel with additional lpg to get the same numbers as per the black smoke diesel example would be any less it is just that people will not see it.

I am not here to argue one way or the other, I just think that even when dyno plots and fuel consumption figures are put up they do not settle the argument as there are other bits of information that are not presented which would allow us to account for other variables, and mostly poor scientific method.

Originally Posted by slug_burner

Ben,

Even with the fuel consumption figures on the web site as EchiDna found, you cannot draw conclusions as I have pointed out in the example of the Defender 300 Tdi on diesel/gas would have us belive that where 32.1 ltrs of diesel are required to do 300 km you only need 28 ltrs of lpg.

I think that blind monkeys might struggle but then again as they would not see the black smoke it is very possible that they could get more power out of the 300 Tdi. Black smoke is the one thing that most people will see coming from a diesel with an over adjusted pump. Can't say that the pollution coming out of a diesel with additional lpg to get the same numbers as per the black smoke diesel example would be any less it is just that people will not see it.

I am not here to argue one way or the other, I just think that even when dyno plots and fuel consumption figures are put up they do not settle the argument as there are other bits of information that are not presented which would allow us to account for other variables, and mostly poor scientific method.

Sorry - just saw power and torque data.

I think that an ENGINE dyno run at constant load while the flow rate of each fuel is being measured accurately with mass flow meters would be very useful.

Originally Posted by isuzurover

Sorry - just saw power and torque data.

I think that an ENGINE dyno run at constant load while the flow rate of each fuel is being measured accurately with mass flow meters would be very useful.

Agree. Then we would only have the issue of does lpg do damage to your diesel engine and even that one will be dependant on the rate that it is injected at and if you can change the injection timing.

Originally Posted by slug_burner

Agree. Then we would only have the issue of does lpg do damage to your diesel engine and even that one will be dependant on the rate that it is injected at and if you can change the injection timing.

That is the crux of the problem, you can't change the injection timing of the LPG. It's there in the cylinder and will ignite as soon as the charge gets hot enough. Which I've shown it can on a cold engine at idle.

If LPG could be injected at the desired time with it's own injector, there would be no detonation issues regardless of rates. The only downsides would then be the install cost and having two tanks to refill.

The question for today is:
Does LPG fumigation have a lower rate which below no detonation occurs or does it simply drop the evidence below our detection methods of noise and vibration?

Originally Posted by Dougal

That is the crux of the problem, you can't change the injection timing of the LPG. It's there in the cylinder and will ignite as soon as the charge gets hot enough. Which I've shown it can on a cold engine at idle.

If LPG could be injected at the desired time with it's own injector, there would be no detonation issues regardless of rates. The only downsides would then be the install cost and having two tanks to refill.

The question for today is:
Does LPG fumigation have a lower rate which below no detonation occurs or does it simply drop the evidence below our detection methods of noise and vibration?

Would you pick up if detonation was happening via measurements with accelerometers by attaching a couple around the head and block?

Originally Posted by slug_burner

Would you pick up if detonation was happening via measurements with accelerometers by attaching a couple around the head and block?

I think you might, but the problem may be getting the signature of detonation so it is not confused with diesel knock, with the chosen location of the accelerometers.