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-   -   Does downstream O2 sensor affect fueling and FE in Petrol Engines? (https://www.team-bhp.com/forum/technical-stuff/132889-does-downstream-o2-sensor-affect-fueling-fe-petrol-engines-2.html)

Ok, 1 is definitely placed right before the after treatment devices, that is called upstream. The 2nd is placed somewhere down / in between the after treatment devices (depending on the exhaust configuration), that is called downstream.

My earlier question remains unanswered, why do you think it is not required in a Diesel engine? My understanding can be wrong, please explain.

Spike

Unlike gasoline engines, there is no concept of stoichomertry in diesel engines and O2 sensor is definitely not used for fuelling.

AFR jumps around from 8 to 80 based on throttle %

Yes some diesels do have O2S and i think its there for the pollution control (decreasing NOx emission through EGR cycling) rather than fueling.

Lookie here, it says wideband O2S can be used in Diesels for fueling too, but its for the sake of smoke control and not for optimising engine performance.

Sankar is right, O2S is used to control the emissions by controlling the fuel spray. It is not just for NOx but also for CO, HC, PM.

Infact, I feel, diesel after treatments are more complicated than the petrol ones.

Spike

Does the BS4 Swift D have an O2 sensor?

How do you control the fuel spray and how does that effect emissions?

How do I know if Swift D has an O2 sensor? Ask me if Mahindra Thar CRDe BS-IV has one.:)

LOL, either you really do not know this or are trying to pull my leg. Either ways I will try to explain.

By fuel spray I meant -
a) The time at which fuel injection starts
b) The time for which fuel is injected
c) The quantity of fuel injected.

The O2 sensor's role becomes important as emissions become stricter. Have a look at some emission norms like Euro VI, EPA, CARB II, compare with BS-IV norms and you will understand what strictness I am talking about.

Fuel spray (all three factors above) effects emissions as the amount of fuel injected, the amount actually properly burnt, all determine what the exhaust gases will comprise of.

Ideally, a fuel on burning must only produce CO2 and H2O, but things are not ideal, which leads to unwanted emissions like CO, HC, NOx, PM, Formaldehydes etc. Hope that helps.

Spike

PS - If you are interested in reading, I can suggest you some books.

No, it doesn't. Hyundai Fluidic Verna CRDI and i20 CRDI has one.

Spike, does Thar BS4 has one?

Interesting, both are Hyundai. Any idea what kind of after treatment (catalyst) it uses ?

No.

Spike

Can "Fuel Spray" control emissions in diesels? How will changing Fuel spray parameters affect exhaust gas composition? Is oxygen content of the burning mixture more important in diesels? EGR?

Cheers

No idea man, not much info regarding Diesel exhaust after treatment.


Low oxygen content sensed by Oxygen sensor probably means more smoke and more smoke = more soot/particulate emission. The O2 sensor tells the ECU what it sees and the ECU might change the fueling accordingly.

Diesel engines run lean, that is a known fact. But how lean, when lean, how long lean all matters. The term "fuel spray" which I chose, was bad it seems, fuel injection could have been better (??) .

Is exhaust gas emission effected by fuel injection pressure? Does the fuel injection pressure effect the fuel spray? Does the nature of fuel spray have any effect on the combustion? Does the nature of combustion have any effect on the exhaust gases? Does the nature (quality) of exhaust gas have any effect on the emissions?

I wrote with what little understanding I have, please feel free to correct me if I am wrong. Or why don't you enlighten us on the same, as well as the EGR ?

Putting it in another way, what effects the exhaust emissions?

Spike

PS- Which exhaust parameter limits a diesel engines capability?

Assume a diesel engine under full load.

Parameters such as fuel quality, operating temperature, etc., causes excessive exhaust emissions.

What would you do to control the emissions? Run it leaner?

Cheers.

I really do not know. By rich / lean I hope you re referring to Lambda <>1.

Causes excessive exhaust emissions - what is excessive here - CO, HC, NOx PM ? Also, I think you missed my earlier query, how is the emission controlled then?

Spike

If the Thar BS4 itself does not have an O2 sensor, why did you think all diesels require one. Any reasons?

First you design the combustion chamber to promote optimal mixing. ie high swirl index coupled with fine droplet size & injector pressure is a key driver for this. Then you setup your lookup table to fuel up to the smoke line. Rest to left to God (ie aftertreatment)

Yes please send me your book recommendations. Thx

All diesels do not require but the diesel engines requiring stricter emission clearance do. Why? - Because they house devices like DPF which need this info for their proper operation (e.g. during regeneration). I never meant all diesel engines require an O2 sensor, sorry if I sounded so.

Regarding why some cars need an O2 sensor -
a) Due to their individual reasons (particular engine type , exhaust configuration etc). But this is a good question as to why the Hyundai cars use one, I will probe further in to this and update.

b) The components may be "carried forward" from their counterparts in other countries (with stricter norms). I won't be surprised if these cars meet BS-V without much changes.


Lol yeah, correct !

You have a PM.

Spike