Yep Water injection is good - actually Dave - if you fit a water meth kit you may not need LPG - you can add a 50/50 water meth mix and use the meth as the added fuel with the water and meth cooling the intake charge and stabilising the mix. (I dont know the chemistry but it works)
As we have said before - Rich and Lean are not really terms we can use with a diesel as it works so differently from a sparker in this situation.
OK mamoth post - sorry guys trying to get it all down - please correct me as you see fit.
With the LPG mix on a sparker we want a mix that will go bang easily and use as much of the oxidiser and fuel as possible the whole thing is set off by a flash of electricity.
On a diesel you dont want too much extra fuel as you are going to inject a LOAD of fuel into the cylinder directly, you also dont want too fast a burn of the LPG.
From what I understand of problems with detonation in petrols and how the diesel works as well as stuff I have picked up Detonation may not be strictly the right term to use on a diesel just like rich and lean.
The effect of an amount of LPG almost appropriate for a sparker is sort of a bang from the LPG using most of the oxidiser ahead of the diesel burn which is slower, MUCH slower now due to the lack of oxidiser from the LPG ignition. AND several droplets of diesel will enter the cylinder in different directions, start burning and ignite several different areas of the LPG mix - from what I have learned so far this is a BAD thing having several flame fronts.
With less LPG then it burns slower as you say Nige but this works as the separate flame fronts could be enveloped by the diesel flame or just be part of the diesel flame - no detonation just more power.
If you use liquid LPG then you end up with WAY too much LPG causing issues. The amount of LPG that is added is really small. You would end up with something like a 2-5 size jet in the LPG and a 100 jet in the Nitrous and that could still be too much. I havent tried calculating it but it is a REALLY small amount of LPG compared.
I have spoken to quite a few LPG specialists - all people who fit kits to petrol and diesels
ALL the LPG specialists I have spoken to say you MUST NOT allow liquid LPG into a diesel engine even with nitrous and make sure you only use a little vapour, then turn up the added amount slowly and carefully monitoring for det rattles.
I know this isnt true of sparkers - I have had my fuel solenoid stick quite a few times at the end of the 1/4 - all that happens is the engine DIES.
So far on the Fabia I have had a few things that back up what I have been told.
At tick over I released too much LPG - the engine started to pick up then rattled loudly at me - I VERY quickly turned off the LPG and it took a few seconds to settle back down and several minutes for my pulse to slow and my heart to get back to the right place
. At higher revs I noticed the rattle so again backed off the LPG.
The rev limit is 4500 and diesel alone this cannot be exceeded - On a road test it got to 5000 with LPG only turned on and would have carried on if I had not stopped the driver (I wasnt driving btw) I have now turned the LPG down some more so this CANNOT happen again.
Why can you run a diesel really lean and not melt it? I can sort of get my head round diesel rich making more power and therefore heat,until you get too high a temp.I understand the different type of burn involved in a diesel-which leads to no evaporative cooling effect.But why is it so different to petrol? run lean, even na, on petrol and you can melt things,run rich and upto a point you'll make more power,then power will drop of and so will heat.