Cold air VS Warm Air Intakes - what's the difference?

[Daox]

Originally Posted by AXMonster

How about utilising a WAI and putting a resistance in series with the intake air temp sensor to fool it into thinking the intake air isn't hot, but mildly warm. This should combat the retard function that some cars see??

You still have to deal with the knock sensor. And, you really don't want knock, so I'd recommend not doing this.


On another note about applying vacuum to the crankcase, I don't know what modern engine doesn't do this. Any modern engine is fitted with a PCV valve and anytime there is vacuum in the intake manifold theres vacuum in the crankcase.

[hondaworkshop]

My '00 Civic (with knock sensor) is showing ~10% mileage improvement with a WAI pulling hot air from right next to the exhaust manifold. Aside from driving style, it has been the best single thing I've done for FE.

[trebuchet03]

Originally Posted by Daox

On another note about applying vacuum to the crankcase, I don't know what modern engine doesn't do this. Any modern engine is fitted with a PCV valve and anytime there is vacuum in the intake manifold theres vacuum in the crankcase.

Measure the vacuum It's not throttled, so there's almost no vacuum at all. My gauge moved, but not enough to take a measurement - unless I plugged up the breather port. The PCV system is basically a high flow low vacuum system - at least in my car. If my breather was smaller than the PCV valve line, there'd probably be a bit more vacuum - but the PCV valve itself acts as the bottleneck :/

[LostCause]

The whole crankcase discussion is nice...I had never thought of that. In a multicylinder engine, isn't it kind of a moot point? When one piston descends, another rises. There shouldn't be any compression/expansion going on. The PCV valve exists solely for piston blow-by...

The retarded timing is definately to prevent knock, but I wonder how much of an effect WAI's have on chamber temperature. As far as I know, intercoolers and CAI are used mainly for increased charge density. I wonder how dependent knock is to these changes in temperature...

I've tried thinking of ways to decrease air density through expansion (i.e. increase a closed volume), but it always seems to be complex/power hungry. Everything has an opposite, right? Heat engine - heat pump. Black - white. Supercharger - subcharger?...

- LostCause

[Harpo]

Originally Posted by hondaworkshop

My '00 Civic (with knock sensor) is showing ~10% mileage improvement with a WAI pulling hot air from right next to the exhaust manifold. Aside from driving style, it has been the best single thing I've done for FE.

I'm up almost 2mpg after adding some baffles restricting cold ait flow. Around 5%, but then the ambient temps were a bit higher (8-10 degrees) as well.

I did some IAT monitoring last week as it relates to fuel flow. While it has a positive impact (45-115 degrees), the FWT increase has the biggest fuel flow affect across the range. Changing timing has less overall effect than friction reductions it appears. Now with summer approaching, the WAI may be icing on the cake.

http://forum.ecomodder.com/showthread.php?t=1506

[trebuchet03]

Originally Posted by LostCause

The whole crankcase discussion is nice...I had never thought of that. In a multicylinder engine, isn't it kind of a moot point? When one piston descends, another rises. There shouldn't be any compression/expansion going on. The PCV valve exists solely for piston blow-by...


- LostCause

That's a good point - (slaps forehead) and a bit of oversight on my part I imagine there'd be a tiny tiny pressure gradient given the piston velocities, but nothing to get bunched p about

[AXMonster]

Originally Posted by Daox

You still have to deal with the knock sensor. And, you really don't want knock, so I'd recommend not doing this.

AFAIK the knock sensor is only there to protect the engine, and will retard on a knock by knock basis (incipient knock), retarding a few programmed degrees when it gets a knock, then if it doesn't detect any further knock it advances back up slowly to the base map until it encounters knock again, then backs off again, then advances again.
The best systems have learning functions that populate steady state and transient knock limit correction maps. The normal way to get these maps to re-learn is to disconnect the ECU power supply so that it is starting again from zero.
Any engine modification to a vehicle that has a self learning function (even a fuel octane change) can benefit from a forced system reset.

Actually reaching the knock limit and staying there IS something we want for the engines to be as efficient as possible.

Originally Posted by Daox

On another note about applying vacuum to the crankcase, I don't know what modern engine doesn't do this. Any modern engine is fitted with a PCV valve and anytime there is vacuum in the intake manifold theres vacuum in the crankcase.

The vacuum in the engine is so small its virtually immesurable. To increase the vacuum in the crankcase to a level that will actually de-aerate the oil and reduce windage (the crank cutting through the oil mist in the crankcase and in effect a kind of aerodynamic drag) there needs to be a large vacuum source to the crankcase, such as multiple PCV valves in the rocker cover, exhaust extractors etc.

[DifferentPointofView]

cold air=more power, and you use less of the accelerator pedal, which is basically the throttle control. less use of the pedal= (basically) closed throttle plate. closed throttle plate means a restriction of the "air pump, or intake" you have a pumping loss in that air is not getting in efficiently.

Warm air=less power, and you use more of the accelerator pedal, which is basically a throttle control. more use of the pedal= a more open throttle plate. open throttle plate means there is less of a blockage that's letting the air in, reducing the pumping loss.

at wide open throttle, you have (basically) no pumping loss at the throttle plate. so warm air intakes won't do anything here. but unless 55mph makes you have to floor it to keep going 55, a warm intake will do something. that something depends on the vehicle.

Diesels don't have a throttle plate, so you don't have a pumping loss problem from the T-plate.

[tasdrouille]

WAI arguments

In favor:
- Pre-heated intake mixture at low rotational speed improves combustion. (Chiu and Horng, 1992)
- Specific fuel consumption varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher ambient temperature is found to increase the flame speed, the combustion reaction rate, the uniformity of the fuel-air mixture and reduce the heat transfer rate though the cylinder walls (Pulkrabek, 1997).
- For lower temperatures, only a small part of the injected fuel is vaporized, causing nonhomogeneity. As a result, lower flame speeds, higher unburned mixture, higher hydrocarbons and carbon monoxide emissions, and loss of power are observed (Pulkrabek, 1997; Heywood, 1988).


Against:
- Engine brake torque varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher intake air temperature increase the occurence of engine knock (heywood 1988).
- At high engine rotational speeds, higher intake mixture temperatures decrease the volumetric efficiency of the engine (Chiu and Horng, 1992).

References:
Chiu, C.P., and Horng, R.F., 1992, “Effects of Intake Air Temperature and
Residual Gas Concentration on Cycle-to-Cycle Combustion Variation in a
Two-Stroke Cycle S.I. Engine Equipped with an Air – Assisted Fuel Injection
System”, JSME International Journal, Vol. 37, N.4, pp. 957-965.

Nakajima, K., Shinoda, K., and Onoda, K., 1969, “Experiments on Effects
of Atmospheric Conditions on the Performance of an Automotive Gasoline
Engine”, SAE Transactions, SAE 690166, pp. 745-766.

Pulkrabek, W.W., 1997, “Engineering Fundamentals of the Internal
Combustion Engine”, Prentice Hall, Inc.

Heywood, J.B., 1989, “Internal Combustion Engine Fundamentals”,
McGraw-Hill Book Co.

[trebuchet03]

- At high engine rotational speeds, higher intake mixture temperatures decrease the volumetric efficiency of the engine (Chiu and Horng, 1992).

That's hardly an argument against (unless it's so low that there's no injector duty cycle to handle it) I mean, if I could have bought my car in a 1.0 liter (instead of 2.0)- I'd be much happier Something tells me that I'm not having a 50% decrease in volumetric efficiency though