Hot air flow vs. Cold air flow

[Begle1]

How much faster does a volume of hot air flow through a valve than cold air?


How many more molecules does a volume of cold air have in it than a volume of warm air?

 

[triton]

what I know and something I found.....


don't know about flow but, heat excites atoms and causes them to occupy more volume in space. For that reason, the hotter the air is, the thinner it is and why hot air rises. Cold air molecules are packed closer together which is why cold air is more dense. Water vapor also plays a part in density.

When the temperature increases, the higher molecular motion results in an expansion of volume and thus a decrease in density.

moving hot air through a valve would probably be easier since it's thinner

 

[Begle1]

I would imagine that hot air's tendency to expand (diffuse) gives it a better tendency to expand into the low-pressure cylinder.

We're trying to get molecules into the cylinder. If it's hot air, there's less molecules in a volume, but that volume flows faster. If it's cold air, there's more molecules in the volume, but that volume flows slower.

Are we totally sure that cold air nets more molecules? Or is cold air more important due to EGT reduction?

 

[displacedtexan]

I'm guessing that molecule counts aren't significantly different, at least on a blown engine.

You'll see much more of a difference in EGTs. And the gain from that.

 

[triton]

cold air only has more volume if there's more cold air than hot. Since hot air is less dense, it has more volume.

I agree... the injection of cold air is likely for the purpose of lowering EGT's

 

[Begle1]

I agree... the injection of cold air is likely for the purpose of lowering EGT's

And yet we hear stories about guys getting significantly more power just by installing intercoolers.

So that would mean that it has to give a net increase in molecules, right?

 

[triton]

I've never heard about any significant increase in HP from a IC. If anything, it helps lower EGT dues to the colder denser air. Also a aftermarket IC can handle more psi and likely has the ability to move more volume

I'm surely no expert but, we're taking hot air ( less dense ) from the turbo and making it cold air through the IC. It comes out with more volume and more density.

If we injected only hot air it would be so thin you wouldn't get as much compression from it.

 

[Hurley]

I've never heard about any significant increase in HP from a IC. If anything, it helps lower EGT dues to the colder denser air. Also a aftermarket IC can handle more psi and likely has the ability to move more volume

I'm surely no expert but, we're taking hot air ( less dense ) from the turbo and making it cold air through the IC. It comes out with more volume and more density.

power is increased due to a lower inlet temperature = more dense air= higher mass flow rate through the engine. higher mass flow of air (and corresponding fuel)=more power

 

[triton]

power is increased due to a lower inlet temperature = more dense air= higher mass flow rate through the engine. higher mass flow of air (and corresponding fuel)=more power

you would think. I saw zero increase in power by adding my IC. I did see a drop in EGT's though. This is when my motor was totally stock

 

[Begle1]

Conjecture is that, once you get to the point that the stock valves are not flowing enough, you might be better off with a hot air charge.

But if that was true, wouldn't close-to-stock engines be the ones that see the most benefit from an intercooler?

 

[dragnsled]

you would think. I saw zero increase in power by adding my IC. I did see a drop in EGT's though. This is when my motor was totally stock

You probably upgraded the intercooler...if you went from not having one to having one there would definitely be a difference and if there is a way to lower EGT's you can add fuel to make more power

 

[Joesixpack]

Conjecture is that, once you get to the point that the stock valves are not flowing enough, you might be better off with a hot air charge.

But if that was true, wouldn't close-to-stock engines be the ones that see the most benefit from an intercooler?

hot air never better, high boost = hot air, and charge air cooling most effective

 

[zstroken]

cold air is better, will burn more fuel and make more power. This isn't smoke and mirrors, look at the cars that let their carbs sit in an ice bath. It has been proven on a dyno that a cold engine makes more power than a warm one.

 

[triton]

this think he was just trying to figure out why

 

[Begle1]

It's just always struck me as counter-intuitive, that's all.

Ideally I think that you'd want to have it flow through the valve really hot, and not cool it off until it was inside the cylinder...

 

[Hurley]

you would think. I saw zero increase in power by adding my IC. I did see a drop in EGT's though. This is when my motor was totally stock

And you didnt attribute the lack of power increase due to it being a stock vehicle?

This isn't smoke and mirrors

Indeed it is not. No matter how you cut it and flip it, an increase in power is due to an increased mass flow rate of fuel and air. How that mass flow rate is accomplished is all dependent on the style of tuning.



increased mass flow rate=increased energy density=greater combustion=more powa

 

[Begle1]

Ideally I think that you'd want to have it flow through the valve really hot, and not cool it off until it was inside the cylinder...

For the record, I retract that conjecture...

 

[GLHS]

FWIW, I tested my truck with that theory a few years ago.
Had a baseline of what kind of boost and power my truck had with a Banks intercooler installed for a couple years (about 34). I then made a crossover pipe with same size as stock intercooler piping. The result; truck picked up 3 psi more boost but in fact had less power. Smoke was a lot more even right off idle.
I ran it like that for 2 days and that was enough "testing".

 

[chasespeed]

Density of air 1) (lb/ft3)
Air temperature (oF) Gauge Pressure (psi)
--- 0---- 5---- 10--- 20--- 30--- 40--- 50--- 60--- 70--- 80--- 90--- 100
30 0.081 0.109 0.136 0.192 0.247 0.302 0.357 0.412 0.467 0.522 0.578 0.633
40 0.080 0.107 0.134 0.188 0.242 0.295 0.350 0.404 0.458 0.512 0.566 0.620
50 0.078 0.105 0.131 0.185 0.238 0.291 0.344 0.397 0.451 0.504 0.557 0.610
60 0.076 0.102 0.128 0.180 0.232 0.284 0.336 0.388 0.440 0.492 0.544 0.596
70 0.075 0.101 0.126 0.177 0.228 0.279 0.330 0.381 0.432 0.483 0.534 0.585
80 0.074 0.099 0.124 0.174 0.224 0.274 0.324 0.374 0.424 0.474 0.524 0.574
90 0.072 0.097 0.121 0.171 0.220 0.269 0.318 0.367 0.416 0.465 0.515 0.564
100 0.071 0.095 0.119 0.168 0.216 0.264 0.312 0.361 0.409 0.457 0.505 0.554
120 0.069 0.092 0.115 0.162 0.208 0.255 0.302 0.348 0.395 0.441 0.488 0.535
140 0.066 0.089 0.111 0.156 0.201 0.246 0.291 0.337 0.382 0.427 0.472 0.517
150 0.065 0.087 0.109 0.154 0.198 0.242 0.287 0.331 0.375 0.420 0.464 0.508
200 0.060 0.081 0.101 0.142 0.183 0.244 0.265 0.306 0.347 0.388 0.429 0.470
250 0.056 0.075 0.094 0.132 0.170 0.208 0.246 0.284 0.322 0.361 0.399 0.437
300 0.052 0.070 0.088 0.123 0.159 0.195 0.230 0.266 0.301 0.337 0.372 0.408
400 0.046 0.062 0.078 0.109 0.141 0.172 0.203 0.235 0.266 0.298 0.329 0.360
500 0.041 0.056 0.070 0.098 0.126 0.154 0.182 0.210 0.238 0.267 0.295 0.323
600 0.038 0.050 0.063 0.089 0.114 0.140 0.165 0.190 0.216 0.241 0.267 0.292

Okay, here ya go, on the density thing...

Top row, PSIG, left hand column, air temperature.

These numbers are pounds per cubic foot of air at said temperature, and pressure.

FWIW, 1 lb of air @ 70* @ 29.92 in/Hg, is 13.3 ft/3, and these numbers change with humidity as well.

 

[Ragged Edge]

It's just always struck me as counter-intuitive, that's all.

Ideally I think that you'd want to have it flow through the valve really hot, and not cool it off until it was inside the cylinder...

If your a diesel pro why do ask such a question