Easi/cold start

[Lakesailor]

Perhaps the butane propellants (if they still exist) work because it is a gas and is compressible so could attain the ignition temperature, whereas as you say if the injectors are a bit duff the diesel fuel may be still liquid (not atomised at least) and only air is being compressed.

 

[VicS]

[ QUOTE ]
work because it is a gas and is compressible so could attain the ignition temperature

[/ QUOTE ] The ignition temperature is reached by adiabatic compression of the air in the cylinder. I suppose if the fuel is admitted as a gas it will also be heated unlike a liquid fuel that is injected at the appropriate point in the cycle. Don't know when that is though! Anyway the ignition temperature of butane is so high I guess that it is just not going to get hot enough anyway to ignite in a diesel engine. I have never taken that much notice but i assume that LPG fired engines are always spark ignition. You don't get dual fuel diesel/lpg engines or do you?

 

[Lakesailor]

Oh well, just a thought.

 

[oakum]

Thanks all - I was going to follow up with 2 other queries but they seem to have been answered! 1st, will any aerosol start an engine - my mate seems to think so - mind you a spanish lifeboat tow cost him 700euros last week when his engine packed up - so i won't put too much faith in his opinions. 2nd, will covering air inlet help with cranking.

 

[VicS]

[ QUOTE ]
will covering air inlet help with cranking

[/ QUOTE ] You'd need to watch out for sump breathers going into the air intakes. The suggestion was to "put your hand over the intake" A single intake will very probably have the breather going to it.

4,6,8 cylinder engines with separate air intakes will need someone with an abnormally large number of hands /forums/images/graemlins/grin.gif

 

[oldharry]

<<will covering air inlet help with cranking>>

No - it will usually only make things worse on a diesel. Covering the air inlet on a petrol engine will increase the suction in the manifold, so that more fuel is sucked from the carburettor. Helpful if the jets are partially blocked, the choke mechanism isnt working properly, or there are air leaks in the manifold. It forces the carb to deliver more fuel, while reducing the volume of air. Its quite easy to flood a petrol engine doing this.

You cannot increase the fuel supply to an injection engine - petrol or diesel - by blocking the air inlet. This only has the effect of reducing the air supply, which might just bring the air/fuel ratio up enough to fire, but lack of air will stop it again almost immediately.

Be careful covering the air intake of a diesel. It uses a great deal of air when it is running, and can easily suck in rags, cloths or anything else used to block the air intake. You may end up having to strip the head down to remove the ingested remains! A big diesel can cause injury by stripping the skin off hands used to block the intakes, if it 'catches' with the throttle open causing it to race!

 

[VicS]

[ QUOTE ]
No - it will usually only make things worse on a diesel

[/ QUOTE ] 'twas not my idea. Billjeratt did explain the theory.
Because the intake is blocked the engine does not draw in any air so there is nothing for it to compress so no resistance on the compression stroke so it turns faster. He suggests doing it at full throttle so lots of fuel is injected, then when you unblock the intake with a bit of luck the extra speed coupled with the extra fuel will make it start. He also says to block the intake with your hand if you do that (but not advisable on big engines perhaps) there is no rag to get sucked in.
I am not going to comment on whether or not it'll work but there are times when anything is worth a try.

 

[Billjratt]

Air-starve-decompress ..... Unfortunately I have been doing it regularly recently and can vouch for its efficacy, however - point taken - when I access the single intake on my 4 cylinder perkins, I remove the air cleaner complete with breather pipe, so it's purely the inlet manifold I block. It's also a good way of getting oil through the system after a filter change without starting the engine, and of course, injector bleeding.
Just don't get your palm read for a while afterwards!

 

[oldharry]

Well, as I said, you might just be lucky to get the fuel air ratio high enough to get it to fire, but if thats the problem its probably time for an injector and fuel system overhaul anyway. Possibly worth a try in an emergency. Dont do it regularly though because the extra fuel will wash all the oil off the cylinder walls, so when it does fire you have no oil film to protect the bore and rings until its running properly.

 

[Heckler]

Vics!! ether, goes bang, same as a petrol engine pre igniting, pinking, pinging (US)
the piston is on its way up the bore, ignition occurs too early, it trys to stop the piston, the rings take most of the strain and break, lose compression, more easy start, BANG, more broken things, even less compression, more easy start etc etc. if you need to use something like this cause your engine is about shagged and you need to prolong the agony, use WD40, it is not as fierce and doesnt seem to do as much damage, i think the propellant is propane or something similar plus the atomised white spirit makes it a gentler thing. by the way if you want to do a james bond, WD is the kiddy to practise on, have done the flame thrower thing a couple of times but for gods sake be careful!!
stu