Thread: Diesel Gas

i was talking to derek and he said he is and his brother is woko.yes they live in dungog but they work in singleton but apparently derek is looking to move to the singleton area.

Since we have soo many advocates of the systems here. How about they provide some test data to show the gains in engine efficiency and fuel economy?

I'd also like to hear how they are avoiding detonation. Because diesel compression temps are above the autoignition point of the gaseous fuels they're using.

Originally Posted by Dougal

Since we have soo many advocates of the systems here. How about they provide some test data to show the gains in engine efficiency and fuel economy?

I'd also like to hear how they are avoiding detonation. Because diesel compression temps are above the autoignition point of the gaseous fuels they're using.

I have a table here to look at.

because the auto ignition temp of gas is higher it relies on the diesel firstly being ignited the lpg assists in the burn.
big diesel engines have been using gas for a long time now, My old boss was working on a big Cummins genset with gas on it

Originally Posted by lambrover

I have a table here to look at.

because the auto ignition temp of gas is higher it relies on the diesel firstly being ignited the lpg assists in the burn.
big diesel engines have been using gas for a long time now, My old boss was working on a big Cummins genset with gas on it

That doesn't really help. If the LPG can ignite on compression alone, then it can detonate before any diesel is injected.
The reason I ask is because my 4BD1T hates lpg being streamed into it. Audible detonation at very low concentrations even when it's cold and idling. A warm engine with boost makes things a whole lot worse. But those conditions also make it harder to hear.

Cummins has a range of westport engines which run on gas (lpg, cng etc). But they are designed for the purpose with compression ratios lowered significantly below diesels to avoid detonation and spark plugs for ignition (i.e. not a compression ignition engine).

I know an engineer who works for MAN with large diesels which can be run with gas. However they have steel pistons and may have other mods which no-one can tell me about (engines are built for each application).

Originally Posted by Dougal

That doesn't really help. If the LPG can ignite on compression alone, then it can detonate before any diesel is injected.
The reason I ask is because my 4BD1T hates lpg being streamed into it. Audible detonation at very low concentrations even when it's cold and idling. A warm engine with boost makes things a whole lot worse. But those conditions also make it harder to hear.

Cummins has a range of westport engines which run on gas (lpg, cng etc). But they are designed for the purpose with compression ratios lowered significantly below diesels to avoid detonation and spark plugs for ignition (i.e. not a compression ignition engine).

I know an engineer who works for MAN with large diesels which can be run with gas. However they have steel pistons and may have other mods which no-one can tell me about (engines are built for each application).

Don't forget LNG.
I work for an LPG distributor & even I can't say much. Because a lot of this gas substition is in its "infancy" ( its still being honed to perfection) most commercial operations - ie Murray Goulburn,Toll, Fox etc insist on confidentiality clauses. We can't get hard data feedback, unless we field trial trucks ourselves, and that ain't happening. Certainly earlier on (2 + years ago) there were instances of truck engines going Kaput, but investigation showed the cowboy element was at work & I'm not convinced the industry is rid of them. Lets face it, there were engine failures due to LPG at the same develpoment stage. Sure, the better HDV (Heavy Duty Vehicle) conversions are with highly modified engines, but most are heading toward 95% gas with 5% diesel for ignition and I believe compressions remain the same. Spark plug ignition is too expensive & a service nightmare, for HDV.
The bottom line is that it did work with N/A engines in a HDV environment.
Its just that by spending more on better technology, the payback is greater.
One thing for sure is, properly done, it will save millions off the fuel bills of these freight companies, there are 7X semi public LNG refuelling sites in W.A.(Kleenheat) & 5 going in to Tas right now (BOC)& these are trial sites. Not to mention all the Metro buses running around on CNG
I'm personally quite interested in converting my Isuzu Landie, but one of the guys at work used to be pretty high up at Isuzu Aus, and his statement to me about my Isuzu was "I wouldn't do it because of the potential to overfuel"
So I'm fence sitting
BTW, LPG does have better properties than LNG & CNG for engines, but of course its a lot dearer.

Originally Posted by Dougal

That doesn't really help. If the LPG can ignite on compression alone, then it can detonate before any diesel is injected.
The reason I ask is because my 4BD1T hates lpg being streamed into it. Audible detonation at very low concentrations even when it's cold and idling. A warm engine with boost makes things a whole lot worse. But those conditions also make it harder to hear.

Cummins has a range of westport engines which run on gas (lpg, cng etc). But they are designed for the purpose with compression ratios lowered significantly below diesels to avoid detonation and spark plugs for ignition (i.e. not a compression ignition engine).

I know an engineer who works for MAN with large diesels which can be run with gas. However they have steel pistons and may have other mods which no-one can tell me about (engines are built for each application).

Having experimented with diesel gas enhancement, there are a number of things I have learnt or observed.

Firstly, LPG will not burn on its own in a normal diesel engine. At no stage will it ignite unless diesel has been injected and ignited first. This is true up to a massive amount of LPG which would cause major problems due to over fuelling. I now fit a micro switch to stop LPG flow at zero accelerator mainly not to waste LPG, nothing to do with self ignition...

Secondarily, the correct amount of LPG for diesel enhancement is way leaner than the point at which a flame can occur in the cylinder with LPG alone.

Thirdly, there is a change of combustion noise with LPG added, which gets louder as more LPG is added. It mainly indicates faster combustion. In this way more of the diesel fuel is burnt, causing cleaner exhaust as reported by testing of emissions. As EGT indicates most closely what happens in a cylinder the maximum temperature for a specific engine should be monitored if there is any doubt of the engine handling the LPG. An engine that has been modified to put out increased power continuously would probably benefit from piston and compression ratio changes.

Lastly adding LPG to a cold engine to increase power is not a good idea, and can be prevented by electronic settings (complex systems) or driver education (simple systems). So long as turbo waste gate limits are not reached the best time to add LPG is under load with the turbo boosting. Then the extra fuel will add turbo pressure to increase excess air.

The pure LPG/CNG engines you mention are of course specifically engineered, using spark plugs to initiate combustion and so bear only a superficial resemblance to diesel engines.

There are many succesful LPG enhanced vehicles driving around, but each engine type should be tested for durability before selling a kit to a vehicle owner.

Over to you, forum members...

Originally Posted by bee utey

Having experimented with diesel gas enhancement, there are a number of things I have learnt or observed.

Firstly, LPG will not burn on its own in a normal diesel engine. At no stage will it ignite unless diesel has been injected and ignited first. This is true up to a massive amount of LPG which would cause major problems due to over fuelling. I now fit a micro switch to stop LPG flow at zero accelerator mainly not to waste LPG, nothing to do with self ignition...

Secondarily, the correct amount of LPG for diesel enhancement is way leaner than the point at which a flame can occur in the cylinder with LPG alone.

Why do you say LPG will not burn on it's own? Do you think it can't detonate below the LEL?

Again the reason I'm quite curious on this is my own experiments show that LEL is completely irrelevant for compression ignition. The LEL is for igniting cold gas with a hot ignition source. Quite different to the situation inside an engine.
I've had all sorts of nasty banging noises happening at concentrations of 1/5th the LEL.

Originally Posted by bee utey

Thirdly, there is a change of combustion noise with LPG added, which gets louder as more LPG is added. It mainly indicates faster combustion. In this way more of the diesel fuel is burnt, causing cleaner exhaust as reported by testing of emissions. As EGT indicates most closely what happens in a cylinder the maximum temperature for a specific engine should be monitored if there is any doubt of the engine handling the LPG. An engine that has been modified to put out increased power continuously would probably benefit from piston and compression ratio changes.

So faster combustion, faster pressure rise, giving much higher stress on the engine for the same power (or torque) generated?
Where does the line lie between faster combustion and knock?

I don't believe the cleaner exhaust claims at all. Any well maintained diesel can be tuned to run clean on diesel alone.

Originally Posted by bee utey

Lastly adding LPG to a cold engine to increase power is not a good idea, and can be prevented by electronic settings (complex systems) or driver education (simple systems). So long as turbo waste gate limits are not reached the best time to add LPG is under load with the turbo boosting. Then the extra fuel will add turbo pressure to increase excess air.

What are the potential problems adding lpg to a cold engine?

But the really interesting one. Australia seems to be the only country in the world with an LPG price low enough to make $ by substituting LPG energy in place of diesel.
The rest of the world appear to pay significantly more $/kJ in gas, which makes LPG as a fuel quite costsly compared to diesel.

Originally Posted by Dougal

Since we have soo many advocates of the systems here. How about they provide some test data to show the gains in engine efficiency and fuel economy?

I'd also like to hear how they are avoiding detonation. Because diesel compression temps are above the autoignition point of the gaseous fuels they're using.

Maybe you should know what you are talking about before you jump up on your high horse.I have D/gas fitted to my Tdi,I have for quite some time now and it does make a very large difference to the engine,for your information the gas is not injected until the coolant temp is over 45 degree's and not before the engine pulls 6 psi of boost and the system is alittle more technical than a hose shoved down the inlet.My engine has never detonated,never run hot or has given any trouble at all since the gas system was fitted and I do recommend based on my experience D/gas on a Tdi,my engine just ticked over 424,000k's which is near the most K's of any Tdi on this forum so your opinion that gas is bad for then doesn't hold much merit. Pat