[Diy_efi] Re: Diesel A/F and F1?

[Phil Lamovie]

Hi,

It's that time again...

>>> As I understand it from NTK, there are no problems using
>>> a WBO2 on diesels, and to make things even nicer, the AFR
>>> for diesel is ~14.5.

As long as you're paying for the sensors there is no problem with
dropping them into a volcano as well.

There is no such thing as an AFR of 14.5:1 for diesels
Running at 14.5:1 would produce clouds of smoke, soot,
and unburned fuel.  There is no attempt to create an A/F
"mixture" prior to combustion. There is simply a pocket
of air at 450 deg and some fuel is squirted into it.

Total time allowed for mixing and combustion is about 1.5 ms

Seriously though, they are not A/F sensors they are O2 sensors.
That's why you don't see them used even on experimental diesel
engines.

Diesel run from 50:1 down to as low as 18:1 A/F.

They can run at 1000:1 without any combustion issues.
(emissions aside)

The chemistry that is at work is entirely different from petrol
ignition. All the air in the diesel combustion chamber is at
a temperature in excess of the self ignition temp of the fuel.

In order to avoid soot / smoke 80 - 100% excess air has been
the std for many years. i.e. twice the air that is "chemically"
required to  supply oxygen for combustion.

Huge sums of money and millions of hours of work have gone into
changing this. The very high pressure, 25,000 psi injection systems
and their multiple injection per cycle are being developed to counter
this phenomena.  At last count some piezo injectors were doing 6 (six)
injections of differing periods during the one cycle.

Reasons for this are the desire to raise the power density of the engine
to petrol levels. Current SOTA (state of the art) petrol engines can do
a pretty clean 100 hp per litre, if diesels are stuck at 100% excess air
they can only do half of that.

This mitigates against the use of diesel in FWD passenger cars as
the extra size plus extra strength causes lots of extra weight.

>>> conversion for lambda to actual AFR for diesel fuel if you
>>> want an AFR number.  I suspect that since you're looking at... (snip)

Lambda has no meaning in diesel talk. The smoke would be out of
control at Lambda 1.3 in most cases.

>>> I wonder what they use for F1 (or do they) when running 4:1 or
>>> is it with that exception so they use such very rich mixtures
>>> just to cool the exhaust valves at selected parts of the race
>>> when acceleration isn't that important,]

F1 uses a fuel with a composition very close to premium unleaded
available at the pump in most countries. See FIA web site for full
specifications. its stoich would be 14.7:1 +/- a few %

F1 never uses fuel to cool exhaust valves. The valves are discarded after
1300 kms so are totally sacrificial as are cranks and heads and
valve seats and everything else you care to name.

There are instruments specifically designed for testing the combustion
efficiency of diesel engines. There are smoke meters that test the colour
(opacity) of the exhaust and soot filters that are weighed with very
expensive scales after controlled dyno runs and NOX sensors as well as
in cylinder pressure sensors etc.

HTH

phil

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