Not all cars utilize MAF meters. Speed density cars use throttle angle, RPM, VE tables, barometric pressure, intake air temperature to compute the amount of air entering the cylinders to come up with a BPW.
And even with MAF meters, temperature, pressure and density do matter; the meter is calibrated to reflect the mass of air flowing at any given moment as it reacts to all of these "unseen" parameters.
But the exact value of any one of those parameters doesn't matter. The only thing that matters is the total
combination of those parameters. P1, T1, and V1 can be completely different from P2, T2, and V2, but if they both come out to the same mass flow rate, then they will be treated equally by the sensors and tune in determining how much fuel to throw at it. Hence, the mass flow rate, and ONLY the mass flow rate is what matters. There could be a thousand different ways of that mass flow rate manifesting itself, but the meter will treat them all the same way.
And what about intercooled turbodiesels using compression ignition instead of spark timing? They benefit hugely from charge cooling.
They have timing, too. Timing of the fuel injection.
And the density certainly is increased in that example, as it is regulated to maintain a certain amount of boost post intercooler. But that increase in airflow to the chamber is due to the fact that the turbo is spinning harder.
It does. I've already explained that while mass is conserved, the values of other parameters of the air stream are not assured to be equal on either side of the heat exchanger. Mass flow rate ~= V x d x A (velocity, density and area) and density, as noted, is approximated by P/RT. So, in essence, MFR ~= V x (P/RT) x A: The characteristics of the air stream ahead of the intercooler and after it can be markedly different in terms of temperature, velocity and density even as the mass flow rate is conserved.
If the mass is conserved (as you agree), then how can the intercooler itself increase the mass air flow!? The velocity and density before and after are irrelevant.
However, you've got me thinking: since the velocity / volume flow rate decreases, what effect does that have on the mass of air going into the chamber? We agree that the volume flow rate decreases across the intercooler. Would that not have to have a negative effect on volumetric efficiency? Let's say the motor is displacing 400 CFM (swept volume). That's a fixed number, no changing it. With no intercooler, let's say the power adder is supplying 700 CFM, resulting in a VE of 1.75. But add an intercooler, with no change in the power adder, and that 700 CFM falls to 600 CFM, then the VE is only 1.5. We know the volume flow rate has to decrease by the same amount (proportionally) that the density increases per the conservation of mass (mass flow rate = volume flow rate 1 * density 1 = volume flow rate 2 * density 2; 1 being before intercooler, and 2 being after).
Is any of this not true? And if so, wouldn't that account for the mass flow rate not changing, and thus no extra power?
Now, the way you DO increase the power is to bump up the output from the power adder to get that 600 CFM back to 700 CFM, but now at the higher density. This certainly results in a greater power output, and I haven't disagreed with this at any point.
Well, what you believe flies in the face of decades of mechanical and chemical intercooling theory and practice.
Bell Intercoolers engineers and makes these things. On their FAQ:
"
What is the purpose and/or advantage of an intercooler?
The purpose of the intercooler is to remove the heat in the air charge that the turbo/supercharger puts into the charge when compressing it. There are two advantages: Reducing the heat in the air charge increases the charge density (more molecules of air per cubic foot), thus increasing the potential for making more power. Reducing the heat decreases the tendency of the combustion process to knock (detonation)."
http://www.bellintercoolers.com/pages/techFAQ.html#FAQ_1
Let's do this. Positive displacement blower. By definition, it moves a fixed volume per cycle. So the mass flow rate going through the blower is equal to the displacement volume of the blower * rpm * density at inlet. Agreed?
Since the density at the inlet is fixed by the constant ambient conditions, and the volume flow rate is also fixed, then the mass flow rate across it is also fixed at a given rpm. Agreed?
So now explain how cooling the air down, AFTER the blower, which is moving a fixed mass of air per unit time, can possibly increase the amount of oxygen moving into the engine? I welcome Bell Intercoolers, engineers, college professors, or John Force to explain where I'm mistaken. Maybe I am mistaken, but I don't see it.
The same principle can be applied to a non-MAP regulated centrifugal supercharger or turbo, assuming it stays at the relatively same spot on the compressor map, which it will since downstream changes don't affect them much.
And FWIW, I agree that a cooler charge reduces the propensity of end-gasses to detonate allowing one to run additional spark timing which will help power but the gains from increase charge air density can't be ignored.
As I said, it's an approximation for the sake of discussion. But FWIW, a number of online sources indicate that gains of 15-20% with w/m in boosted applications is possible with all optimizations made.
Snow Performance makes w/m systems. On their diesel FAQ they write:
"Power is increased through:
• Air charge cooling - Water/methanol usually lowers air charge temps over 200 degrees F. Low air temps makes denser air charge which provides more molecules of oxygen for combustion.
• Combustion conditioning - the methanol acts as a combustion catalyst as well as a cooling agent. Water vaporization inside the combustion chamber increases torque and power output through "the steam" effect."
I personally see upwards of 20% gains on my car when I throw the timing at it. But that's because combustion event (and corresponding pressure spike) occurs closer to the crank angle where the geometry of the rod and crank arm allow for a greater torque to be produced on the crank.
But that air immediately becomes heated when it contacts the AC condenser, the radiator, the piping-hot engine and manifolds. It makes more sense to induct air from the cool, ambient surroundings than to suck air that's been pre-heated under the hood.
But for every pound of air pulled from the underhood, it's replaced by a pound of air from outside (conservation of mass, no?). And since the volume of the underhood is fixed (I mentioned this several posts ago), the density (fixed mass / fixed volume) has to be the same, hot or cold. The only way it'd change is if the ambient atmospheric changed.
I don't understand where my reasoning is wrong above, or how it can coincide with your "density = P/RT, therefore, higher T = lower density", but I'm certainly unable to argue against that.
For Christ's sake, this has turned into an episode of Bill Nye the Science Guy gone bad. Just f*cking Google it. lol
I have already. Both sides of this argument can be found all over. And I'm not very good at explaining why my side is correct, but with my real world experience, the other side has not convinced me yet either.
And I assure you, the people who understand these things pretty much always have cars that run better, for less money, than those that don't.
Not to mention, I freakin' love talking about and debating these things.
It's not common I run across someone else who can.
Cooler air is denser air and denser air, by definition, has more oxygen per unit volume.
