Diesel Consumption: How Temperature Affects Fuel Use

Hello fellow mechanics,

'Since I aim for minimal fuel consumption, I usually drive according to my MFA (Multi Function Display), except for highway trips. Now that the temperatures have returned to more comfortable levels, I've noticed that my AKN engine seems less thirsty. When the outside temperature was around 30-35 degrees Celsius, my AKN averaged about 7.8 - 8.1 liters per 100 kilometers. Currently, it's only about 6.8 - 7.1 liters. Is the lower fuel consumption due to the more favorable outside temperatures, meaning more oxygen in the cylinders -> better acceleration -> shorter acceleration times, etc.? Or is it because the air conditioning system doesn't have to work as hard? Another possible reason could be my recently failed AGR (Acoustic Resonance Control) valve, but could it really make that much of a difference? Has anyone else had similar experiences? Subjectively, the engine performance wasn't significantly worse at higher temperatures (the system seems to be doing its job). If anyone here doubts these fuel consumption figures, my A4 Avant with engine code AKN does not have Quattro all-wheel drive or an automatic transmission, and no other features that would reduce power.'

The difference in energy consumption is likely due to the air conditioning system, as its cooling power has to come from somewhere. Since energy is never lost but only transformed, the motor has to work harder than usual and therefore consumes more energy.

The difference in energy consumption is likely due to the air conditioner, as the cooling power has to come from somewhere. Since energy is never lost but only transformed, the motor has to work a bit harder than usual and therefore consumes more.

Hi!

Yes, I suspect the same thing... My summer consumption has usually been lower (for the past 3 summers). This summer, however, it was very high, almost 11.5 liters of diesel (engine code AFB). Normally, in the summer, I manage with 10 liters, and in the winter with 12 liters (which is due to the automatic transmission and quattro all-wheel drive).

Regards,
Felix.

Hello everyone...

Are you sure your engine is in good condition?

I have the same machine, and I would describe myself as a 'dynamic' driver.
Average 8.1 (Modified/Chip-tuned).

I haven't seen such high fuel consumption in customer vehicles before either.

Best regards, Steve.

I would like to know how the AGR handled their service request, as I am looking for a reasonable solution to my problem with AKN.
Thank you for the response.

mfdk

Okay, I'm ready. Please provide the German text you want me to translate into English. Just paste it here, and I will give you the translation.

Okay, it's not the oxygen content, because that remains constant regardless of temperature (are you perhaps confusing it with oxygen solubility in water?). However, at lower temperatures, the air has a higher density, but this doesn't play a role in the high compression within the cylinder. But higher density means greater air resistance -> more fuel consumption.

I'm betting on the air conditioning - if I activate the 'eco' mode while driving at 100 km/h on a warm summer day on the country road, my car's fuel consumption drops from approximately 5.5 to below 5 liters per 100 kilometers.

@chris_s

Higher density -> higher oxygen content per stroke?

Hello,

Marco wrote:

@ chris_s higher density -> higher oxygen content per stroke volume.

A higher density means more oxygen atoms per unit volume.
The percentage of oxygen atoms/molecules remains the same compared to the other atoms/molecules that make up the air (nitrogen, carbon dioxide, noble gases, etc.).

Best regards, Rainer.

@Rainer.K

That was the commented version of my answer, thank you for that!

Thank you for the tip/link with the very good explanation of the AGR function and decommissioning process.
I have already read this page and also browsed the excellent forum on this topic. My problem lies in identifying the correct hose at the vacuum sensor and finding a practical way to 'seal' the hose and allow for pressure equalization through a hole or similar. Since there are very few articles specifically about the AGR (Exhaust Gas Recirculation) system on AFB or AKN engines, I took the liberty of asking Marco how he managed it on his AKN, because I don't want to install a metal plate.

Thank you and best regards.
mfdk

What I wanted to say is that the compression ratio in the TDI engine is so high (19.5:1?), that the density difference of the intake air due to temperature should not have a significant impact on the number of oxygen molecules in the combustion chamber. However, I would be happy to be proven wrong, as I only came up with this idea myself.

@mfdk

Hello,

A sheet of metal that is 1.5 mm thick is doing its job for me.

Everything you need should be on page 2 of the thread.

/viewtopic.php?t=3447&highlight=agricultural+material

I actually found this thread using the search function!

Hi,

chris_s wrote:

What I wanted to say is that the compression ratio in the TDI engine is so high (19.5:1?), that the density difference of the intake air due to temperature should not have a significant impact on the number of oxygen molecules in the combustion chamber. However, I would be happy to be proven wrong, as I only figured this out myself.

It is independent of the compression ratio. With colder air (higher density), more oxygen molecules are drawn in or forced in via turbocharging into the cylinders. How much this air is then compressed doesn't matter; the number of oxygen molecules does not change as a result, only the volume.

Best regards, Rainer.

Thank you for the reply and the link to the thread. I am familiar with that thread and have already printed it out. I would like to close off the AGR valve without using a metal plate, but it doesn't seem possible. Therefore, I am looking for a solution: disconnect the hose, insert a screw, and create a small pressure equalization hole in the correct location. However, I cannot reliably identify which hose to disconnect, and I don't know where I should place the small pressure equalization hole.

Thank you, Marco.

Regards,
mfdk

Hello,

Here's another picture of the AKN.

http://www.brain-storm.net/dieselschrauber/agr.jpg