Thread: isuzu & LPG

Originally Posted by bee utey

Dougal, in their infinite wisdom Isuzu/Land Rover have not seen the need to supply a tacho. The rev limit is quite easy to reach so must be safe in normal operation.

I agree the rev limit (3200-3600 depending on your engine) is safe for the engine. I just can't imagine hearing anything over the engine and pump noise at those rpm's.

Which is another reason why I conducted those tests at idle.

Originally Posted by Dougal

I agree the rev limit (3200-3600 depending on your engine) is safe for the engine. I just can't imagine hearing anything over the engine and pump noise at those rpm's.

Which is another reason why I conducted those tests at idle.

I can and do hear quite well as I have always worn quality ear protection when required. When I am less that 3 feet from the engine in a deefer I can sort out the types of noises quite clearly.

Please be kind to Pat, his engine is running well and the "research" clearly shows engine damage at continuous overload NOT under economy conditions.

This is just going round in circles. But there is a lot of good tech in this thread.

Let's summarise what we know:

1) There are lots of happy customers driving around with LPG Fumigation systems installed (at least in AU). There are no reports of catastrophic engine failure (at least from modern/AU systems). There are others who have fitted such systems, then later removed them as they found little/no benefit.

2) There are a number of installers who seem to be making a good business out of installing such systems.

3) Most of the installers/manufacturers of such systems are small companies, who do not have large R&D budgets to develop their systems - so in a way many of their (early) customers are Beta testers. Which is not necessarily a bad thing as it means that the kits are cheaper, however it does mean there is no conclusive proof/disproof of the issues raised here.

4) There appears to be no interest from diesel engine manufacturers in such systems.

5) Fumigation systems have been shown - in general, to reduce NOx and Soot, but CO emissions remain about the same and HC/VOC emissions increase. Which refutes the "cleaner burn" argument somewhat.

6) The sample sizes from customers seem too small to provide anything conclusive at present. If they all had EGTs and did oil analysis, we would have some great data. However most only have the "Butt Dyno" and fuel consumption data (where collected). These results are also confounded by the "placebo effect" - unless someone did a double blind study.

7) There is clear evidence from other studies that under SOME operational conditions at least, adding LPG/Propane/NG to a diesel can produce harmful detonation/pre-ignition.

8) Until someone puts an engine with one of these systems fitted on a dynamometer with mass flow meters for each fuel (and diesel return) and accurate detonation measurement, then I doubt we will get much further with the discussion.

Have been keeping tabs on this thread for a while, so time to add my own 2c worth.

First off, I do not own a vehicle with gas fitted. As a few others mentioned here, until I see some real proof of concept with min / max fumigation rates relative to load / RPM and some way of monitoring the amount fed in, I'll stick with turbo charging.

Having said that, a friend has a 300Tdi Defa with LPG fumigation that I've done a fair bit of work on, so this is the vehicle I will refer to. At present it is running 18PSI boost pressure aided by a non standard intercooler, the fuel pump has been wound up a little to far (considerable smoke off boost, slight black haze on boost under full throttle) and he basicly drives by the EGT when giving it a hard time. As far as I know the fumigation rate is still for factory boost levels. The system fitted uses a stepper motor / valve to control gas flow and a MAP sensor to control when to fumigate.

We recently removed the head to find the source of what sounded like a gudgeon bearing failure (turned out to be a dead vac pump, oops), but after 50,000km with the gas fitted it gave us a chance to check the condition of the pistons etc.
Wish I took photos, but the piston crowns and cylinder head are in perfect condition, all coated with a thin deposit of carbon, and showing no signs of pitting etc. normally associated with detonation. No checks done on the bottom end, as once we had the head off the source of the noise became obvious.

He states that for highway driving, the combined fuel consumption (diesel + LPG) is about the same as for diesel alone, so slightly reduced running costs as a result. Cruise EGT is about the same but under heavy load the fumigation causes it to increase a little faster until he is forced to back off before it goes too high. He can exceed the normal limit with diesel alone but the LPG causes a faster rise rate, similar to winding up the IP further.

Okay, so my own questions / theorys.

The fitter of the system mentioned above, after I pestered him enough, told me the ratio of LPG / diesel was more important the the ratio of LPG / air.

For LPG into idling diesel, the above statement may be valid, as you inject LPG into the engine, the IP senses the increased idling speed and reduces the amount of fuel to the point that the engine is running almost on LPG alone. Could this be the source of detonation? What is the A/F ratio of an idling diesel?

As for detecting detonation, I have a knock sensor off a petrol engine that screws into the block off an early injected car, this is basically a piezo disc with a mass attached so it acts as a microphone. This is used in conjunction with the crank position sensor to monitor for knock from approx 20 degrees before the spark plug fires to 30 degrees after. I can see no reason this setup wont work on a diesel, fit a crank position sensor, monitor the output with a digital scope with diesel alone, then add the gas and compare results. Crank position sensor gives a reference signal to determine TDC and firing point. This should also show the increased burn rate with LPG advancing the timing.

Whilst fiddling with a 3.5 V8, it appears no one will now go above 13:1 C/R for a straight LPG engine (not dual fuel), a few years ago it was possible to push 15:1 C/R with a little care. The reason given was that the composition of LPG has changed and will detonate above 13:1, and yet we can feed it into a diesel at much higher C/R. This may be due to the low fumigation rates used but seems a little contradictory.

Will leave it there as I think I've exceeded my 2c worth, even if I never fit fumigation to one of my vehicles its still an interesting subject.

Should add the 300Tdi mentioned has done about 150000km since rebuild and 50000 with increased boost / intercooler / LPG.

Lyle.

Hey Dougal, any chance you might be able to do a moving test with your Rangie and the original Barbie gear, at say 80kays, to see if there is much difference off idle?. I know what I'm asking is risky, like risking it all really, but it may give us further insight and you've got all the gear to make it half accurate. Could be really interesting.

Originally Posted by 1103.9TDI

Hey Dougal, any chance you might be able to do a moving test with your Rangie and the original Barbie gear, at say 80kays, to see if there is much difference off idle?. I know what I'm asking is risky, like risking it all really, but it may give us further insight and you've got all the gear to make it half accurate. Could be really interesting.

Not driving because I don't have enough hands or eyes to do it safely for myself and other road users.
I also have a lot of sound insulation which would make detonation hard to hear and the driveline influence will make it harder to pick up the vibration.
But if I get the chance to repeat it on a rolling road I will.

Does anyone know if the idling position on these Isuzu engines corresponds to a rack stop (i.e. fixed minimal fuelling) or governor stop (can drop fuel further if rpm tries to rise)?

Originally Posted by Dougal

Not driving because I don't have enough hands or eyes to do it safely for myself and other road users.
I also have a lot of sound insulation which would make detonation hard to hear and the driveline influence will make it harder to pick up the vibration.
But if I get the chance to repeat it on a rolling road I will.

Does anyone know if the idling position on these Isuzu engines corresponds to a rack stop (i.e. fixed minimal fuelling) or governor stop (can drop fuel further if rpm tries to rise)?

rack unless the idle has been ajusted by the throtel cable then it would be governor

Originally Posted by Dougal

Does anyone know if the idling position on these Isuzu engines corresponds to a rack stop (i.e. fixed minimal fuelling) or governor stop (can drop fuel further if rpm tries to rise)?

Pretty sure its governor, looking at the diagrams in the manual shows it will increase fueling if it drops below 290 IP RPM and decrease it if it goes above.

Does anyone know how far the rack has to move to start injection, there is a certain amount off the start to cover the stop position so where does injection start in relation to rack position, or is rack position measured in relation to the point that injection is started.

Lyle.