[Bonemechanic]

I drive a Marazzo M8 diesel. In Kerala, the temperature soars to 40 °C during noon. I noticed a change in the FE numbers of my car during the morning and noon hours.

Traffic is higher during the morning drive, but the outside temperature is around 26 °C. Non-time traffic is less compared to morning time, but the temperature is high around 38 °C.

I drive alone with the ACC set to 24℃ and 100% time. The driving pattern is also almost the same for to-and-fro driving.

But I get a higher FE during the morning and a lower FE during noon. I assume the FE drop is because ACC works more.

Attaching MID pictures for the last 3 days.

February 7


February 8


February 9


Upper photo is noon drive and lower photo is morning drive.

Juat, like an EV, consumes more power during the winter to heat, while an ICE uses more fuel to cool during the summer.

[Aditya]

Thread moved out from the Assembly Line. Thanks for sharing!

[Shreyans_Jain]

The extra electrical load due to the radiator fans running full time has minuscule effect on fuel consumption. Two other factors have a greater role.

1. The AC system. High ambient temperatures reduce the temperature difference against peak compressed gas temp. This reduced delta T lessens the efficiency of the AC and makes it work harder, which is extra load on the engine. Effect increases progressively with temperature.

2. The hot ambient air going into the engine is less dense, which makes for lower availability of oxygen which means lower output. Ergo, engine has to work harder to ferry the same load. Effect increases progressively with temperature, and also creates a positive feedback loop with point 1.

Overall, performance and fuel efficiency both get adversely affected with high ambient temperatures.

[Neversaygbye]

Originally Posted by Bonemechanic

Juat, like an EV, consumes more power during the winter to heat, while an ICE uses more fuel to cool during the summer.

I agree with your findings - in peak summer with my car's AC on the mileage drops perceptibly in the afternoon and sometimes goes down to as less as 11 kmpl (MID reading). I have overlap with a US shift so usually reach office between 2-3 pm when it is quite hot outside. While returning from work (after 11 pm) the MID usually shows 14. In winter, without the AC on in either leg, the difference is very less - usually 0.5 kmpl. T2T mileage in summer is also less than in winter - typically 13kmpl in summer and 15kmpl in winter. I have a routinized route with similar traffic patterns so it is easy to take that out of the equation.

[Sameergarg]

Winters actually lead to reduced FE. Engine takes longer time to warm up. Tyres have higher rolling resistance. Cold air has more aerodynamic drag. Car fluids are cold and dense. Battery performance os also reduced. About 20 percent reduction

[Hemantteen]

Originally Posted by Shreyans_Jain

2. The hot ambient air going into the engine is less dense, which makes for lower availability of oxygen which means lower output. Ergo, engine has to work harder to ferry the same load. Effect increases progressively with temperature, and also creates a positive feedback loop with point 1.

Regarding point 2, can a mechanism be devised wherein intake air be routed through ac making it colder resulting in better fuel burn/efficiency?

[Safedriver2023]

The distance covered is less so it makes a big difference. You have to cool the complete cabin and it has to continuously cool the car as it is a green house. You will see lesser difference in highway trip, but the higher temperature difference for set temperature and outside temperature is the key factor for the fuel consumption - similar to running ac in your house during summer and winter

[TORQUEINDUCTION]

Originally Posted by Sameergarg

Winters actually lead to reduced FE. Engine takes longer time to warm up. Tyres have higher rolling resistance. Cold air has more aerodynamic drag. Car fluids are cold and dense. Battery performance os also reduced. About 20 percent reduction

I don't think that the reduction will be 20 percent. Car or any vehicle reaches to its optimum operating temperature in few minutes unless the temperatures are sub freezing like -20 Deg C or lower.

Originally Posted by Hemantteen

Regarding point 2, can a mechanism be devised wherein intake air be routed through ac making it colder resulting in better fuel burn/efficiency?

Engines do have intercoolers which reduce the temperatures of the intake air by a certain margin. Post turbochargers, the temperature of the air do rise to 75 to 85 Deg C. It can be more. Intercooler mostly are liquid to air cooled, but also can be air to air cooled. Intercooler helps to main the air density and in turn the oxygen content.

[Jeroen]

I think the difference if FE can not be explained by ambient temperature alone. Check a map and see what the vertical distance between your departure and arrival point is.

You will find you are probably driving a bit uphill one way and down hill the other way. Not enough to notice when your driving. But even a small gradients has a big impact on fuel efficiency.

Jeroen

[Redex]

Originally Posted by Hemantteen

Regarding point 2, can a mechanism be devised wherein intake air be routed through ac making it colder resulting in better fuel burn/efficiency?

Yes it can but is pointless. The energy required to run the A/C compressor would be greater than the power/efficiency gain.
The MAF sensor automatically compensates for changes in inlet air temperature anyway.

[Redex]

Just, like an EV, consumes more power during the winter to heat, while an ICE uses more fuel to cool during the summer.[/quote]

I don't understand why EV manufacturers don't harvest the heat wasted from battery and transmission cooling to reduce the load required for heating the cabin.

No, I do understand. It's not worth the effort or cost

[dhanushs]

Originally Posted by Bonemechanic

...I noticed a change in the FE numbers of my car during the morning and noon hours.....

2+kmpl only because of a change in temperature is unlikely. If it's possible, as a test, try driving with AC off up and down the next time. That will eliminate one variable.

Like Jeroen suggested, I too think that there is a difference in altitudes between the starting and ending points. That can hugely affect FE, even though it's not perceivable while driving.

[antz.bin]

Winter mornings have better efficiency on ICE cars than summer afternoons.

Colder air is denser and when the engine breathes that air, the combustion is better generating more torque for every combustion stroke.

This has been experienced since ages. It has nothing to do with engine being warmed up.

The other loss at a hotter time of day the one to cool the cabin. Air conditioner actually uses a lot more Diesel than us Diesel heads realise. As per my calculations, it uses 250-300ml per hour of running for my sub-4 m car on automatic mode even on a cold December night. Daytime usage at 40°C ambient temperature in a substantially larger car will be even higher per hour.

Both these factors should explain the lower efficiency in the afternoon time compared to the morning which is presumably substantially colder these days.

[Jeroen]

The notion that an IC engine is more efficient at lower ambient temperatures is, from a physics point of view, strictly speaking not necessarily true at all.

As members have pointed out at lower ambient temperature the air is denser. That allows the engine to produce more power. Effectively at a lower ambient temperature every intake stroke a relatively higher number of air molecules is behind drawn in compared to higher ambient temperature. That means you can also burn inject more fuel. But the ratio air to fuel needs to remain the same of course. No efficiency gain, only extra power. So don't confuse extra power with extra efficiency.

As some members have pointed out, lower ambient temperature leads to other effects, less power consumption from the AC, less tire resistance, but also less drag. Drag coefficient rises with the rise of ambient temperate.

Fuel efficiency of your car, is a the result of many factors. The actual efficiency of the engine is just one part of it. Many other external factors have in fact a larger impact on the overall fuel efficiency of your car than just the engine.


Jeroen

[DarthVeda]

Driving an EV for past few years has taught me the range is influenced by the environmental changes too, first time I noticed how much the wh/km increased when the road was wet, the same I noticed during cold temperatures too, when i say cold i mean around 12C. Even though I did not use AC, the wh/km was higher than before.
All these very evident in EV vehicle as we get measurable changes in wh/km, since liquid fuel have a very high density, it doesn't catch our attention in ICE.