Thread: isuzu & LPG

Originally Posted by Dougal

Gee I don't know. Maybe to make sure your pistons aren't going to melt.

Your NA engine at full power on diesel will still have about 25% excess air going through it. This air is used for internal engine cooling and the effect is keeping internal temps low enough to not melt pistons. Measuring EGT's is the common way of knowing that your internal temps aren't dangerously high.

Adding lpg to burn this 25% cooling air both removes the cooling effect it had and adds the heat of the LPG.

Which is a very good reason to measure EGT's with any fuelling mods.

That said, I'm still against LPG as a fuel for diesel engines.

Too high a EGT's can cause damage, but the way a diesel engine works is actually by way of compressing the air and just before TDC, diesel is injected.
The compressed air in the cylinder creates the heat and aides in ignition.

There is no comprehensive technical proove that adding LPG will harm a diesel engine given its added at very low dosage.
There is insufficient gas to ignite and the gas that is present is to aid a cleaner burn and hence less emmissions.

See below.
The diesel internal combustion engine differs from the gasoline powered Otto cycle by using highly compressed, hot air to ignite the fuel rather than using a spark plug (compression ignition rather than spark ignition).

In the true diesel engine, only air is initially introduced into the combustion chamber. The air is then compressed with a compression ratio typically between 15 and 22 resulting into a 40-bar (4.0 MPa; 580 psi) pressure compared to 8 to 14 bars (0.80 to 1.4 MPa) (about 200 psi) in the petrol engine. This high compression heats the air to 550 °C (1,022 °F). At about this moment, fuel is injected directly into the compressed air in the combustion chamber. This may be into a (typically toroidal) void in the top of the piston or a pre-chamber depending upon the design of the engine. The fuel injector ensures that the fuel is broken down into small droplets, and that the fuel is distributed evenly. The heat of the compressed air vaporizes fuel from the surface of the droplets. The vapour is then ignited by the heat from the compressed air in the combustion chamber, the droplets continue to vaporise from their surfaces and burn, getting smaller, until all the fuel in the droplets has been burnt. The start of vaporisation causes a delay period during ignition, and the characteristic diesel knocking sound as the vapor reaches ignition temperature and causes an abrupt increase in pressure above the piston. The rapid expansion of combustion gases then drives the piston downward, supplying power to the crankshaft.[15]. Model aeroplane engines use a variant of the Diesel principle but premix fuel and air via a carburation system external to the combustion chambers.

As well as the high level of compression allowing combustion to take place without a separate ignition system, a high compression ratio greatly increases the engine's efficiency. Increasing the compression ratio in a spark-ignition engine where fuel and air are mixed before entry to the cylinder is limited by the need to prevent damaging pre-ignition. Since only air is compressed in a diesel engine, and fuel is not introduced into the cylinder until shortly before top dead centre (TDC), premature detonation is not an issue and compression ratios are much higher.

Originally Posted by big guy

There is no comprehensive technical proove that adding LPG will harm a diesel engine given its added at very low dosage.
There is insufficient gas to ignite and the gas that is present is to aid a cleaner burn and hence less emmissions.

With that I disagree.
The tests I've run with my Isuzu show audible detonation occuring with LPG fumigation rates as low as 0.4% (volume/volume of intake air). If you've ever smelt the exhaust of a detonating engine you'll know it's unmistakable.
Many people claim detonation can't occur below the 2% LEL, but a simple test shows it can and does.

I understand quite well how diesel engines work. If you compare the auto-ignition temperatures of LPG to the compression temperatures of a diesel you will see why the detonation occurs and how it is unavoidable with the compression ratios that diesels run.

Do you have a reason why extra fuel by way of LPG won't increase the EGT's in a diesel?

Originally Posted by Dougal

Gee I don't know. Maybe to make sure your pistons aren't going to melt.

Your NA engine at full power on diesel will still have about 25% excess air going through it. This air is used for internal engine cooling and the effect is keeping internal temps low enough to not melt pistons. Measuring EGT's is the common way of knowing that your internal temps aren't dangerously high.

Adding lpg to burn this 25% cooling air both removes the cooling effect it had and adds the heat of the LPG.

Which is a very good reason to measure EGT's with any fuelling mods.

That said, I'm still against LPG as a fuel for diesel engines.

not worth it

Originally Posted by clean32

Gee I don't know Dougal??
Maybe its because EGT although is a measure of temperature it is in reality an indicator of pressure density created by the turbo trying to squirt the gasses onto a turbine. Once the pressure has been removed as would be indicted by post turbo EGT temps (normal 200deg drop) remove the pressure or increase the area the gasses can expand into and guess what MAJIC the temp drops.

The temp drop across a turbo is the energy being extracted from it. Turbos feed on both heat and pressure. It's got nothing to do with putting in more fuel and not monitoring exhaust temps.

Last I read your Isuzu doesn't have a turbo.

Originally Posted by clean32

But I think with your concern you are more interested with combustion temps or head temp. I don’t think this a concern mainly because not only would extremely high temps be required but also a reasonably long soak time. This is easy to identify and avoided, IE rolling cole up a very long hill.

Your engine has a fixed expansion ratio, this means higher exhaust temps are directly linked to higher combustion temps.
Dangerous combustion temps can be reached in seconds with too much fuel. They don't need a long soak time and they don't need black smoke either.

Originally Posted by Dougal

The temp drop across a turbo is the energy being extracted from it. Turbos feed on both heat and pressure. It's got nothing to do with putting in more fuel and not monitoring exhaust temps.


Last I read your Isuzu doesn't have a turbo. maybe a coffee will help\/



Your engine has a fixed expansion ratio, this means higher exhaust temps are directly linked to higher combustion temps.
Dangerous combustion temps can be reached in seconds with too much fuel. They don't need a long soak time and they don't need black smoke either.

the only thing correct there, is that i doint have a turbo

Originally Posted by Dougal

With that I disagree.
The tests I've run with my Isuzu show audible detonation occuring with LPG fumigation rates as low as 0.4% (volume/volume of intake air). If you've ever smelt the exhaust of a detonating engine you'll know it's unmistakable.
Many people claim detonation can't occur below the 2% LEL, but a simple test shows it can and does.

I understand quite well how diesel engines work. If you compare the auto-ignition temperatures of LPG to the compression temperatures of a diesel you will see why the detonation occurs and how it is unavoidable with the compression ratios that diesels run.

Do you have a reason why extra fuel by way of LPG won't increase the EGT's in a diesel?

Disagree is fine, finding true and relative facts for any one argument is another.

I also have Diesel gas and a EGT gauge fitted at same time.

I have done many different runs now with LPG on and off and the difference in terms of temperature increase is very little.
I measured may-be 20-40 degeree C at full boost over a steep hill.
Done severel times with same numbers.
The increase in power is quite amazing and for that we must have more temperature, thats a given.
The gas research I have done has not shown any detromental affect on engine wear on engines, bearings, valve or combustion chambers.
In fact its has reduced glazing on barrels if I listen to the comments from a reputable diesel fitter, who in turn has first hand experience.

So, my conclusion is that my 12 year old diesel will not be adversely affected and by all accounts, an even older truck donk(Isuzu 4bd1 or 4bde or whatever) will have even less issues if not prelong the life even further.

I am very happy with my set up which incidentally was also done by same reputable gas fitter Bee utey.

Thanks

Originally Posted by big guy

Disagree is fine, finding true and relative facts for any one argument is another.

I also have Diesel gas and a EGT gauge fitted at same time.

I have done many different runs now with LPG on and off and the difference in terms of temperature increase is very little.
I measured may-be 20-40 degeree C at full boost over a steep hill.
Done severel times with same numbers.
The increase in power is quite amazing and for that we must have more temperature, thats a given.
The gas research I have done has not shown any detromental affect on engine wear on engines, bearings, valve or combustion chambers.
In fact its has reduced glazing on barrels if I listen to the comments from a reputable diesel fitter, who in turn has first hand experience.

So, my conclusion is that my 12 year old diesel will not be adversely affected and by all accounts, an even older truck donk(Isuzu 4bd1 or 4bde or whatever) will have even less issues if not prelong the life even further.

I am very happy with my set up which incidentally was also done by same reputable gas fitter Bee utey.

Thanks

So you're running a turbo diesel, where Clean32 is not. Were fuel and/or boost tuned with the gas fitment?
A 12 year old engine will certainly not be an Isuzu 4BD1, is it one of the last 300tdi's or one of the first TD5's?
Did you have a cylinder glazing problem?

The interesting thing about the Isuzu's is the power gain possible just by tweaking the injection pump is beyond what most people require (over 200hp and 600Nm depending on your injection pump) so the "more power" reason isn't really a good one.

What do you think of dumping more fuel as gas into a non turbo diesel and not monitoring EGT's?

Originally Posted by Dougal

What do you think of dumping more fuel as gas into a non turbo diesel and not monitoring EGT's?

Dougal this has been answered by myself and others in the past. Please either up your knowledge or leave the topic alone

you are wrong, if you doint get it, so what! you are still wrong!!!!