Could you explain the effect of thermodynamics on a cars performance?

[dcredskins24]

Basically I was conducting an experiment to explain how thermodynamics effects a cars performance.

This was done going to a track on days whether the temperature varies. Anywhere from 0-21 degrees celsius. I was trying to see how the colder air affected the times of each run to see how the temperature truly affected the car. Basically my question is this...

Im trying to explain why the hot air is worse for the car and decreases its performance compared to cooler air
and how the thermodynamics explains it.

Im having some trouble with that portion the basic aspects I know are that the car is NA. So im trying to explain how the air is processed from the intake to the intake manifold through the engine to the headers down through hte exhasut and back into the air. But I only know very very basic concepts. Could you please explain this so I can get a better understanding?

Thanks.

 

[MortenA]

Why cool air is better - a couple of suggestions:

The colder the air the higher massflow you can get with a constant volume flow.

Also the overall expansion when heated will increase (assuming that the end temperature is constant - im not sure of this).

Best Regards

 

[DougMSOE]

You may want to chech with the airplane group as well
1. the colder the air the better the engine will run, denser air.
2. the colder the air the more air the car has to push out of the way when going around the track.

 

[dcredskins24]

thank you all so much. You have been very helpful.

 

[chino101]

I'm sure a chemical engineer can explain this better than I can, but I'll give it a try.

Cold air (at 10 degrees C) will have a higher density than hot air (at 35 degrees C). Since the air has a greater mass per unit volume at lower temperatures, it will also have more oxygen per unit volume at these temperatures. Giving an engine more oxygen will allow it to make more power. Probably because the combustion will be hotter, thus causing the combustion gasses to expand faster, and in turn, the gasses pushes the pistons down faster.

I'm sure you already heard of nitrious oxide a.k.a NOS. When NOS is injected into an engine, the oxygen in the nitrious oxide is mixed in with the gasoline, and air to create a hotter and more powerful combustion. Just like how adding oxygen to a blow torch will create a hotter flame. But becareful, carelessly adding pumping NOS or any additional source of oxygen ( using a turbo, or supercharger), can damage your engine beyond repair. Use in a moderate and/or a controlled manner is usually found to be safe.

 

[chino101]

Oh yeah almost forgot, with the added oxygen, there is also must be added fuel.

 

[jouch]

A couple of points...
The first is of course the density. The lower the temperature, the higher the density. That means you get more air into your inlet manifold per unit volume...
Thus, the more air yyou have, the more fuel you need. The more fuel you get, the more power you get.
That is the basic reason.

You should also consider whether your car is fuel injected with a map sensor or whether it is carburettored.

If it is carburettored, you will have to adjust the jets to compensate for the extra air under cold conditions....you dont want to run your engine lean!

Hope this helps.
Jouch