Automobile fuel consumption in winter / summer...

[Externet]

It's been about 20 years since they do not manufacture automobiles any more; they make computers with wheels since then.

 

The on-board engine control unit measures intake air mass by its flow and its temperature, and sets the fuel amount for combustion.

Being cold winter air more massive, does it feed correspondingly more fuel then, than in hot summer thinner air ?

 

If yes, preheating intake air would decrease the fuel ratio,

If not, is it because the oxygen content exhaust sensors action ? Hey ! but if there is more air mass intaken, then the 14:1 ratio could not be sustained ! What am I missing ? Is the throttle position working less open in winter for the same performance, or there is another compensating control ?

[alpha2cen]

This is a method to reduce the cold air effect.

Is it difficult to control the valve opening time?

Edited January 19, 2013 by alpha2cen

[efzauner]

Sure modern EFI takes care of all that. Lower air temperature means denser air and more fuel required.

MASS air flow sensor means what it says. It monitors the MASS of the air, not the volume. It is a heated wire whose current is monitored. As the air flows by it, it is cooled thereby decreasing the resisitance.

But you dont want to preheat the air. You want cool air! thats why turbos often have intercoolers

 

As for valve opening time. its called variable valve timing and is very common also. Usually linked to RPM but no reason it cant be varied for other reasons.

[Externet]

Thanks.

Well, then, comparing same exact driving/road conditions, will winter cold use more fuel than hot summer ? ( having no fast valve closure implemented )

[alpha2cen]

Thanks.

Well, then, comparing same exact driving/road conditions, will winter cold use more fuel than hot summer ? ( having no fast valve closure implemented )

During the induction stage more air is entered into the cylinder. This makes the trouble. Originally, auto engine is not desigined only for the cold winter.

We can estimate the amout of fuel by using the state equation of ideal gas.

PV=nRT

At the final sep of the induction stage the values P, V are the same as the values in the summer.

n=PV/(RT)

n=k (1/T)

However, decreased temperature condition leads to increasing the amount of air entering into the cylinder.

 

This is expansion reaction equation in the cylinder.

A Air + B fuel---> C CO2 + D others

To make this reaction to be done well, reactant ratio, alpha x A/B, must be keeped constant.

Therefore, we must input more fuel into the engine.

Edited January 20, 2013 by alpha2cen

[Externet]

Clear ! Thanks.

 

Then, if in cold air induction A + fuel B, we partially replace some A with some 'E' (exhaust gases recirculated into the intake), the fuel amount B can be reduced accordingly to the amount of oxygen as the amount of A is less.

 

Some amount of E + less mass of cold A + less fuel B ---> E + C CO2 + D others

 

The amount of E, controlled by the engine control unit ECU depending on the ambient air temperature sensor reading. Is that the way it is currently implemented , or exhaust gas recirculation EGR is used only to reduce emissions with no intention to compensate for extra fuel consumption in cold air temperature ?

Edited January 20, 2013 by Externet

[alpha2cen]

Is that the way it is currently implemented , or exhaust gas recirculation EGR is used only to reduce emissions with no intention to compensate for extra fuel consumption in cold air temperature ?

EGR is good for reducing emission and decreasing fuel consumption. Except adding much more complex structure on the engine block, EGR is better than the exhaust valve control.

Practcally, without reintroducing hot exhaust gas, liquid fuel vaporization is not done so well during the short induction time.

[John Cuthber]

To make this reaction to be done well, reactant ratio, A/B, must be keeped constant.

Therefore, we must input more fuel into the engine.

Not really.

It's perfectly possible (and common) to run the engine with less fuel added than would be needed to use all the oxygen.

http://en.wikipedia.org/wiki/Lean_burn

 

 

For a given power requirement, you can use a smaller engine if the air is fed to it cold. Recirculating exhaust gas will have the opposite effect and will reduce the available power.

It's also likely to lead to increased CO emission if used in the way you suggest. (Though it reduces NOX formation)

[alpha2cen]

Not really.

It's perfectly possible (and common) to run the engine with less fuel added than would be needed to use all the oxygen.

http://en.wikipedia.org/wiki/Lean_burn

 

 

For a given power requirement, you can use a smaller engine if the air is fed to it cold. Recirculating exhaust gas will have the opposite effect and will reduce the available power.

It's also likely to lead to increased CO emission if used in the way you suggest. (Though it reduces NOX formation)

For the complate fuel combustion, excess air introducing is common thing. I mean constant excess air ratio. Not vaporized liquid can be turned into solid pollution material on that reaction.

I think experiment and parameter optimization are the best way to solve that problem. Power, pollution gas generation and fuel consumption must be considered at that engine design and operation condition.

Edited January 20, 2013 by alpha2cen

[John Cuthber]

They are considered in real time by the engine management system.

As the OP says, "It's been about 20 years since they do not manufacture automobiles any more; they make computers with wheels since then."