Why do engines with a MAF sensor still use an o2 sensor?

[ELS]

I stick by my statement; EGR is inert, it has no affect on the amount of oxygen in the exhaust. Look no further than your 5 gas exhaust analyzer. With the probe out of the exhaust, 20.7% oxygen, with the probe inside the exhaust, 0.3% oxygen. Where is this "other" oxygen of which you speak coming from? Hint, it's simply not there.

With respect to "Hot O2," you do realize that EGR COOLS the combustion process, right? Because the main purpose of EGR is to reduce oxides of nitrogen emissions formed by high combustion temperatures. Ideal gas laws (Charles's Law, to be exact) are not germane to this discussion.

And if you somehow think that disconnecting the EGR valve from a properly running system would increase mileage, you lack the basic understanding of pumping losses and the effect of introducing an inert gas into the intake charge of an engine. Conduct the experiment for yourself. Go disconnect the EGR system on your daily driver and compare the mileage before and after.

Diesel EGR is entirely different because Diesels don't require a homogeneous fuel air mixture for the flame front. And where is the oxygen sensor on a Diesel?

Where do you get the idea that I said any of that?
I told you I already understood why it doesnt' change the O2 sensor reading, And my theory was that adding EGR would INCREASE fuel efficiency by reducing pumping losses at low throttle.

[Tuner]

I stick by my statement; EGR is inert, it has no affect on the amount of oxygen in the exhaust. Look no further than your 5 gas exhaust analyzer. With the probe out of the exhaust, 20.7% oxygen, with the probe inside the exhaust, 0.3% oxygen. Where is this "other" oxygen of which you speak coming from? Hint, it's simply not there.

When the exhaust gas being recirculated is the product of a lean of stoichiometric combustion process it contains unburned O2

With respect to "Hot O2," you do realize that EGR COOLS the combustion process, right? Because the main purpose of EGR is to reduce oxides of nitrogen emissions formed by high combustion temperatures. Ideal gas laws (Charles's Law, to be exact) are not germane to this discussion.

Exhaust gases are hot compared to intake gasses. Ergo, in the right circumstances such as lean light-load cruise at highway speed, hot exhaust gas helps vaporize gasoline in the intake charge, and, if the hot exhaust gas contains O2 because it is the product of a lean of stoich combustion cycle, the subsequent combustion cycle containing the hot O2 is enhanced, caused to be more complete, irrespective of the actual combustion temperature (which you refer to in the production of NOX). In contrast is the situation of EGR from rich combustion which contains no O2 and interferes with the combustion process, such as at low idle speed with a radical cam and rich A/F.

And if you somehow think that disconnecting the EGR valve from a properly running system would increase mileage, you lack the basic understanding of pumping losses and the effect of introducing an inert gas into the intake charge of an engine. Conduct the experiment for yourself. Go disconnect the EGR system on your daily driver and compare the mileage before and after.

Are you reading impaired? I clearly described the early and mid '70s crude EGR systems which killed mileage to the later systems which are much improved and enhance mileage.

Diesel EGR is entirely different because Diesels don't require a homogeneous fuel air mixture for the flame front. And where is the oxygen sensor on a Diesel?

[Tuner]

Diesel EGR is entirely different because Diesels don't require a homogeneous fuel air mixture for the flame front. And where is the oxygen sensor on a Diesel?

https://trucksauthority.com/6-7-cummins ... locations/

Mass air flow and intake air temperature sensors are located on the intake manifold of the Cummins 6.7L engine. NOx, O2, and differential pressure sensors are present on the exhaust manifold. You can find the crankshaft and camshaft position sensors on the left-hand side of the crank pulley beside each other. Furthermore, the EGR temperature sensor has a location on the crossover tube.

https://www.energy.gov/eere/vehicles/ar ... gen-sensor

2014 DOE Annual Merit Review REGIS
Objectives and Relevance
Objectives
 Develop an Intake Air Oxygen (IAO2) sensor which directly and accurately
measures the oxygen concentration in the intake manifold
 Demonstrate the potential of the sensor in combination with system
adaptation and cEGR control strategies in a target engine application
Relevance of cEGR
 cEGR enables improved fuel economy in most driving conditions
(on and off cycle) supporting the mainstream trend of Downsizing
 Improvement of up to 5% in engine peak thermal efficiency
 Other future combustion technologies will utilize cEGR
Relevance of IAO2
 IA02 aims at providing a significant improvement in control accuracy of
cEGR to maximize the fuel economy potential of the system

[ELS]

Couldn't you instead of using another oxygen sensor in the intake, just plumb the reference air port from the O2 sensor to the intake.
It will automatically compensate for differences in the intake oxygen content from any EGR.

[gunt]

alot of big agro here
so begin , which stuff are we talking about , early i'd say , narrow band lamda , EGR is generally only on full on over run and only percentages come in otherwise ,depending on criteria , and that includes the fan cutting in , we will often see 30% egr and the air flow MAF will decrease by near enough the amount % , large variations , will bring an engine light , now narrow band lamda , like EGR is only used at set parameters , other than that its ignored , so warm up / choke , and loads from the MAP , and % of throttle all set in stone in the ecu , so at certain points the O2 is ignore the data will be fully on the MAP , i never checked when the EGR was in , was the ecu programmed to ignore lamda too , but essentially , one is before the even and the other after , say you have an air leak from the MAP to the cylinder , the ecu has know other way to figure that out other than after the event

[rebelrouser]

alot of big agro here
so begin , which stuff are we talking about , early i'd say , narrow band lamda , EGR is generally only on full on over run and only percentages come in otherwise ,depending on criteria , and that includes the fan cutting in , we will often see 30% egr and the air flow MAF will decrease by near enough the amount % , large variations , will bring an engine light , now narrow band lamda , like EGR is only used at set parameters , other than that its ignored , so warm up / choke , and loads from the MAP , and % of throttle all set in stone in the ecu , so at certain points the O2 is ignore the data will be fully on the MAP , i never checked when the EGR was in , was the ecu programmed to ignore lamda too , but essentially , one is before the even and the other after , say you have an air leak from the MAP to the cylinder , the ecu has know other way to figure that out other than after the event

And really egr is old technology, most modern engines use variable cam timing to take the place of an egr valve.

[Rick!]

Couldn't you instead of using another oxygen sensor in the intake, just plumb the reference air port from the O2 sensor to the intake.
It will automatically compensate for differences in the intake oxygen content from any EGR.

The oxygen pump in an O2 sensor works at an ionic level, not at a macroscopic level.
Is the oxygen content of air in an uncompressed state any different than freestream air or the ambient air in the O2 sensor? How so? How do u plumb this circuit while enduring temps of over 400C and avoid failures due to vibration/modal stresses?
Tuner described a diesel intake O2, not a gasser. What engine are you inquiring about?
What is your end goal?
If OEMs could meet emissions without an O2, do u think they would have done so by now?
Hell, I use two O2s and closed loop on my brother’s methanol dragster for the more precise fuel control and extra level of performance consistency.
With a bit more forethought and properly formulated questioning, you can get equally clear responses. ( No MAF so not apples to apples.)

[ELS]

Couldn't you instead of using another oxygen sensor in the intake, just plumb the reference air port from the O2 sensor to the intake.
It will automatically compensate for differences in the intake oxygen content from any EGR.

The oxygen pump in an O2 sensor works at an ionic level, not at a macroscopic level.
Is the oxygen content of air in an uncompressed state any different than freestream air or the ambient air in the O2 sensor? How so? How do u plumb this circuit while enduring temps of over 400C and avoid failures due to vibration/modal stresses?
Tuner described a diesel intake O2, not a gasser. What engine are you inquiring about?
What is your end goal?
If OEMs could meet emissions without an O2, do u think they would have done so by now?
Hell, I use two O2s and closed loop on my brother’s methanol dragster for the more precise fuel control and extra level of performance consistency.
With a bit more forethought and properly formulated questioning, you can get equally clear responses. ( No MAF so not apples to apples.)

The o2 sensor messures oxygen content in a specific "sample" size. So the reading is a percentage of content Not like total grams or whatever.
Oxygen sensors have a reference side.
Also
"How do u plumb this circuit while enduring temps of over 400C and avoid failures due to vibration/modal stresses?"
How dumb is that? has nobody ever plumbed an exhaust system that doesn't fail? ah yes, most have been doing that for centuries.

[gunt]

Everyone forgot sensor redundancy including em , at that time it would have being 2 sensor redundancy now its 3 , so while it has a function it is also the back up for another failing and also a tool for the computer to flash the engine light

[rebelrouser]

Everyone forgot sensor redundancy including em , at that time it would have being 2 sensor redundancy now its 3 , so while it has a function it is also the back up for another failing and also a tool for the computer to flash the engine light

At the tech school I used to take a newer car running in the classroom on a roll dyno, hook up a 5 gas analyzer and I would start unplugging sensors, you usually had to unhook several before the engine even started to have a problem controlling the air fuel ratio. Part of the lesson was it sometimes makes problems had to fix because in testing you may find codes and issues with multiple sensors before finding the root cause of the problem, because the system is really good at using other sensors for info to keep running right. And the average customer who drives with a check engine light on until the car actually lays down on them, may not understand the accumulated parts failures.

[naukkis79]

Can't you just calculate the required injector duty cycle depending on the MAF reading?

No you can't even in ideal conditions because you have variations in fuel. O2 sensor gives a feedback loop which is used to calibrate every other sensor and fine tuning for fuel used. Gasoline isn't regulated - it's formulation varies a lot and only sane possible way to adapt to fuel variation is feedback loop - with O2 sensors.

[David Redszus]

EGR is an inert gas which, when injected into the combustion chamber,
will reduce chamber temperature. The reduction of temperature serves to reduce
the formation of NOx. EGR has no effect on O2 readings.

The primary source of ECR is from the exhaust port during the overlap period.
A late closing exhaust valve will increase EGR; which is characteristic of a
racing camshaft with a long duration and late EV close. Overlap pressure ratio
will affect EGR. If Pe>Pi, exhaust gas reversion will produce increased EGR.

A Lambda sensor does not read the amount of oxygen or fuel ratio.
What it does is compare the partial pressures of oxygen, inside the exhaust
to that of ambient air. The sensor output is millivolts, (10mv-950mv),
depending on sensor temperature. The Lambda controller (which controls
the sensor heater current) serves to also convert millivolts to voltage which can
be read by the ECU.

In street vehicles, the primary purpose of Lambda is to keep the exhaust gas to
within +-1% of stoich, so that the catalytic converter will function properly.
Without a cat the objective is quite different. To obtain an A/F reading, from a
Lambda voltage, it is necessary to know the stoich value of the fuel being used.

An Air Mass Flow sensor does exactly that; it measures air mass-- not air flow.
The output from a MAF is a voltage signal (1.0v-5.0v) which is read by the
controller and converted to engineering values such as mass and volume
(it knows air density).

The MAF automatically compensates for changes in air temperature, density
and humidity. It is very accurate and responds very quickly, but is confused
if presented with reversed pulsed flow. Installation location becomes important.
.

[Tuner]

Does a MAF sensor compensate for humidity?

[David Redszus]

Does a MAF sensor compensate for humidity?

Yes. A change in humidity will produce a change in air density, which is read by the sensor as a change in mass flow.

A change in relative humidity from 0 to 50 will cause a reduction in air density from 1.20442 kg/m^3 to 1.18352 kg/m^3.

[Tuner]

I thought the question would be more obvious. I should have been more specific.

Humidity has significant effect on O2 per unit mass of air. Higher humidity = less O2 per gm mass. On a hot day a large swing in humidity can require changing carb jet several sizes, as much as 6 to 8 jet sizes in a Holley at 100 deg. F and 100% humidity, compared to 60 F and 40% to 50%. It appears a MAF sensor cannot compensate for humidity.