[Diy_efi] Re: Diy_efi Digest, Vol 6, Issue 23
Mike
niche
Wed Aug 24 13:40:18 UTC 2005
As far as I understand this applies to diesels, its an
interesting point (as well) if it applies to diesels,
Excuse my ignorance, any diesels out there with CATs,
if so how do they handle particulates, anyone have
experience of servicing their older diesels... ?
Regards from
Mike
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
Twin tyres for most sedans, trikes and motorcycle sidecars
http://niche.iinet.net.au
At 08:49 PM 8/24/05, you wrote:
>Isn't it common on the newer catalytic equiped
>vehicles to use a pair of O2 sensors to monitor
>effectiveness of the cat and feed this info via
>computer for alerting the driver via a CEL/MIL/DIC
>presentation?
>
>--- Bill Washington <bill.washington at nec.com.au>
>wrote:
>
>> Mike,
>> In my experience even when the diesel is pumping
>> out lots of black
>> smoke - ie unburned or part burned fuel - there is
>> still lots of excess
>> oxygen - the reason for the smoke is usually droplet
>> sizes that are too
>> large to burn in the available time - ie inadequate
>> atomisation so the
>> oxygen can't get to all the fuel during the power
>> stroke - In this
>> scenario, for a mechanical injection diesel, even if
>> more fuel is
>> injected than there is oxygen to burn there will
>> still be excess oxygen
>> because of the droplet size.
>> The big adavantage with the latest generation
>> of common rail
>> diesels is the superior atomisation achieved by
>> raising the fuel
>> pressure in the distribution rail to extremely (even
>> dangerously) high levels and changing from
>> mechanical injection to
>> electronic injection - the mechanical injection
>> pumps had no hope of
>> achieving the injection pressures the common rail
>> designs use as normal
>> - the pressure difference from mechanical injection
>> to common rail is
>> orders of magnitude.
>> Therefore I believe that a normal O2 sensor
>> (narrow or wideband)
>> will not work on a diesel because there is always
>> 'excess' oxygen. Note
>> also that normally, diesels have wide open air
>> induction - ie no
>> throttle butterfly and engine speed and power are
>> controlled solely by
>> the volume of fuel injected, therefore the amount of
>> air inducted in a
>> normally aspirated diesel per stroke is essentially
>> the same across the
>> entire rev/power range (neglecting restrictions in
>> the air filter and
>> intake tract) - including these effects means that
>> the volume of
>> inducted air will reduce slightly as the revs
>> increase.
>> Adding a turbo changes this, of course
>> That being said, I seem to recall reading
>> somewhere about some of
>> the common rail diesels using an oxygen sensor but
>> no details of type or
>> purpose though it stands to reason that it would/
>> could only serve any
>> purpose in a maximum power condition in a modern
>> common rail diesel when
>> it may be possible to inject more very finely
>> atomised fuel than there
>> is air to burn it, then an oxy sensor could come
>> into play to limit the
>> volume of injected fuel.
>> Regards
>> Bill
>>
>> >----------------------------
>> >
>> >Message: 7
>> >Date: Mon, 22 Aug 2005 22:10:37 +0800
>> >From: "Mike" <niche at iinet.net.au>
>> >Subject: Re: [Diy_efi] Wide band sensor, F1
>> >To: diy_efi at diy-efi.org
>> >Message-ID:
>> <6.2.1.2.0.20050822220408.02951220 at 203.0.178.192>
>> >Content-Type: text/plain; charset="us-ascii"
>> >
>> >At 03:01 PM 8/22/05, you wrote:
>> >
>> >
>> >>I would say "no", assuming you mean the usual WBO2
>> sensor used in petrol engines. I have two reasons:
>> >>
>> >>1. It's calibrated to provide a response which,
>> while almost linear immediately about the
>> stoichiometric mixture for petrol (c. 14.7: 1?
>> memory fails) its response goes rapidly non-linear
>> on either side of that figure. Diesel engines,
>> AFAIK, run in a regime where there is always excess
>> air to burn the fuel which is expected to be metered
>> by the injection pump. So the sensor would be stuck
>> "on the end stops" of its response curve.
>> >>
>> >>
>> >
>> >Damn good point, I forgot all about this,
>> power=fuel, not air flow based.
>> >
>> >I should have known as the first thing I did in
>> Malaysia was rent a diesel
>> >with turbo and jammed the wastegate off - tut
>> tut...
>> >
>> >
>> >
>> >>2 Even if the injection pump is injecting
>> excess fuel which cannot all be burnt, it tends to
>> come out the exhaust as fine particles of carbon
>> rather than as unburnt fuel, which is what the
>> sensor is looking for. I'm not convinced the sensor
>> would notice, because of the different combustion
>> process (chemically and physically) going on in a
>> diesel.
>> >>
>> >>
>> >
>> >mmmm Surely though if there is excess fuel any O2
>> sensor will indicate
>> >when (allowing for response time) and how far
>> assuming it isnt jammed up
>> >against the 'rich' stop so quickly... ?
>> >
>> >So under those conditions would a wideband show
>> lower than say 11:1
>> >and not have its judgement clouded (pun) by soot
>> particulates ;) ?
>> >
>> >ie. Even though its nonlinear wouldnt it be
>> mappable, ie Calibrated to give
>> >a known output, with an error margin, at extreme
>> ends of the scale, its been
>> >a long time since I looked at any O2 sensors
>> admittedly...
>> >
>> >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
>> >isnt that important,
>> >
>> >
>> >
>> >Regards from
>> >
>> >
>> >Mike
>> >Perth, Western Australia
>> >VL Commodore Fuse Rail that wont warp or melt !
>> >Twin tyres for most sedans, trikes and motorcycle
>> sidecars
>> >http://niche.iinet.net.au
>> >
>> >
>> >
>> >
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>
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