Thread: isuzu & LPG

oops, double post

Originally Posted by Sparkie

In relation to A/F ratio, how does 162:1 air/diesel compare to 0.4% lpg? I'll assume 200:1 air/LPG but thats a guess only.

We have
4.5 l/min of lpg which is 0.00938 kg/min
1092 l/min of air, which is 1.29 kg/min
Diesel at 150:1 A/F ratio is 0.0086 kg/min
Air/LPG mass ratio = 137:1

LPG/Diesel mass ratio = 1.09:1
At 100:1 A/F ratio it becomes 0.72:1

Do you propose the LPG is more likely go bang with less diesel burning?

Originally Posted by Dougal

Do you propose the LPG is more likely go bang with less diesel burning?

As I mentioned previously, after pestering the guy who installed the system on my mates Defa, he indicated the ratio between diesel / LPG was more important than LPG / air. This was about all he was willing / able to tell me.

But it does, in a way, agree with what a few of the proponents of these sytems are saying.

To understand what is really going on have a look at or look up "propane decomposition under pressure" that will sort of explain all.

Havent had a look at this myself, but the gist is that the two fuels either mix and burn together, or at least components of them do at the normal low levels of LPG / Diesel.

If the calcs I did for idle diesel / LPG ratio are correct, then maybe at the higher ratio (more LPG than diesel) something goes pear shaped.

Hopefully someone can explain this. HINT HINT

Lyle.

I'm not going to pretend I understand whats being written in this thread but I do follow that some believe that LPG will detonate before Diesel is injected.
Now this is a laymans question, but the flammability of LPG at atmospheric needs 2.1% to 9.6% air ratio or it wont ignite.
Wouldn't this apply regardless of pressure?
Are the volumes discussed here within those limits?

Originally Posted by Sparkie

avent had a look at this myself, but the gist is that the two fuels either mix and burn together, or at least components of them do at the normal low levels of LPG / Diesel.

If the calcs I did for idle diesel / LPG ratio are correct, then maybe at the higher ratio (more LPG than diesel) something goes pear shaped.

Hopefully someone can explain this. HINT HINT

Lyle.

As it seems that every thing I post gets bagged out of hand.
I have tried to explain what is going on in the combustion chamber when LPG is added and that LPG isn’t burning, that all the assumptions or what is generally known about LPG as a fuel is not applicable when used in fumigation.
basically because LPG isn’t LPG for very long. It very quickly ( quickly when over 900 Kevin) reorganizes its self into methane and hydrogen with a few others tossed in for good measure. sheesh you can even get acetylene.

Besides the argument now bores me, I know what I am getting and I am happy. There is just to much misinformation posted and some very bad assumptions, for what reason? I don’t know! Maybe just Ego? the net effect is that this thread is of no value to anyone who wishes to make an informed decision based on other members experiences since those with no experience seem to have the loudest voice.

Originally Posted by DeeJay

I'm not going to pretend I understand whats being written in this thread but I do follow that some believe that LPG will detonate before Diesel is injected.
Now this is a laymans question, but the flammability of LPG at atmospheric needs 2.1% to 9.6% air ratio or it wont ignite.
Wouldn't this apply regardless of pressure?
Are the volumes discussed here within those limits?

correct yes yes

What happens is that the LPG brakes down into other flammable gasses that will assist the diesel to burn more completely. In this thread along we have one poster stating the diesel is completely burnt in the combustion process >90% and we have an attachment to an article stating that <>75% is about the norm. In short the unburned fuel ( is wasted). is not burned because its to 1. To cold, 2 to larger droplets to be burnt though, 3 is far from the flame front.
The addition of LPG 1. Assists the diesel to ignite at a colder temperature, 2. has less "solids" so assists in moving burnt matter away from large ( relatively speaking) droplets of diesel allowing the burn to consume more if not all of the droplet. 3, speeds up the flame front so that diesel frutherest from the ignition point has more time to burn.

Originally Posted by clean32

As it seems that every thing I post gets bagged out of hand.
I have tried to explain what is going on in the combustion chamber when LPG is added and that LPG isn’t burning, that all the assumptions or what is generally known about LPG as a fuel is not applicable when used in fumigation.
basically because LPG isn’t LPG for very long. It very quickly ( quickly when over 900 Kevin) reorganizes its self into methane and hydrogen with a few others tossed in for good measure. sheesh you can even get acetylene.

Besides the argument now bores me, I know what I am getting and I am happy. There is just to much misinformation posted and some very bad assumptions, for what reason? I don’t know! Maybe just Ego? the net effect is that this thread is of no value to anyone who wishes to make an informed decision based on other members experiences since those with no experience seem to have the loudest voice.

I know this thread got a bit personal for a while, hopefully that is over and we can get back to the science.

If I personally have insulted you then I apologise, this was never my intention.

As you suggest, there seems to be a lot of misunderstanding of whats going on inside an engine fitted with fumigation, you seem to have a good handle on this and I hope you will explain it to me, as although I dont have it fitted to my vehicle, and may never do so, I would like to understand how it works, as do a few others if I'm not mistaken.

Many people have these systems fitted and seem quite happy with them, my mates 300tdi Defa being the one I have been using as a reference, and it done 50,000km with no detremental effects we can detect. (see earlier post for details)

So in reference to some of the recent questions:

Does the ratio of LPG / Diesel affect combustion? and would having more LPG than diesel, as Dougals and Bee_Uteys tests at idle indicate, cause a problem.

At what percentage would adding LPG cause compression ignition if it can?

Does it significantly speed the rate of ignition?

Do you have the results of the oil analyses back?

Lyle.

Originally Posted by Sparkie

So in reference to some of the recent questions:

Does the ratio of LPG / Diesel affect combustion? and would having more LPG than diesel, as Dougals test and Bee_Utey(I think) test at idle indicate, cause a problem. .

Defiantly but then you have left the world of fumigation and entered the world of duel fuel.

Originally Posted by Sparkie

At what percentage would adding LPG cause compression ignition if it can? .

yes it can, temperature ignition is no mystery see DeeJay's post, he’s correct there are a few other variables but that’s the guts of it.

Originally Posted by Sparkie

Does it significantly speed the rate of ignition? .

yes and no, air/diesel/ compression /temperature /turbulence are all variables.

or should I ask what do you call significant?


About 1deg depending. i should say 1 deg of timeing for example

Focus on the complete burn and increased midrange rather than over all KW ( leave that to the domain of the forced induction) chasing detonation is just barking up the wrong tree.


[/QUOTE]