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-----Original Message-----
From: Tom Bauer <tomb@ccpl.carr.org>
To: Military Vehicles List <mil-veh@uller.skylee.com>
Date: 18 January 2000 17:43
Subject: Re: [MV] Multifuel cold start?
>1) you need really good
>batteries, a diesel has to spin fast when it is cold or it may not
>start.
>
Quite true, because the air charge heat owing to compression is lost to the
metal surfaces very rapidly, even a good _cranking_ speed is much less than the
idle revs.
2) mine will start easily down to around 0 degrees if i hold the
>throttle down to about to where 1200 rpm would be when hot and then
>crank it. it starts right away.
>
Its often customary to floor the accelerator thereby ensuring maximum injection
and guaranteed pick up when any cylinder starts to fire.
> since diesels like to be hot to run
>properly you need to warm it up for a much longer time before you will
>get full power.
>
Likely some other effect, once the injected fuel burns the designed heat energy
is released. In actuality with a cold and therefore more dense air charge more
power is available, hence intercooling on supercharged diesels.
> if you are using the cold start system and ignition of
>that fuel does not take place then you are adding more fuel to the
>engine and this may make it harder to start.( i took mine off since here
>in maryland it never gets much below 0 )
>
That's a puzzle as the air/fuel ratio of a diesel CI engine is unimportant for
combustion to occur. The excess fuel actually makes it easier since it begins
to puddle on the pistons, adds to the piston sealing and compression ratio
thereby making significant increases to the CR and compressed air charge
temperature. This is the reason some well worn engines will eventually fire
after extended cranking albeit with a momentary large cloud of partially burnt
fuel smoke when combustion finally occurs.
Some small hand started diesels have this technique as the official cold start
procedure, the engine is rocked by hand some 10 - 12 times at the injection
point listening to the injector squeak as fuel is provided before winding up
de-compressed. Others have the injector fuel control rack extended outside the
pump with a gravity arrangement to defeat the max fuel stop setting giving some
300 - 500% over injection, winding the engine up de-compressed has the same
effect and the fuel stop re-engages as the governor takes over.
Richard
(Southampton UK)
This archive was generated by hypermail 2b29 : Mon Feb 21 2000 - 18:15:08 PST