School Me: WAI vs CAI

[Joeggernaut]

Okay first let me say I know there are ton of wai vs cai threads but none of them seem to address new technologies and account for them. School me or provide your input on cai vs wai in the different applications.


This thread is only concerning mostly gasoline engines and applications.

Few definitions first:
Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.
Air

The Engine Control Unit (ECU) adjust air flow or fuel flow to meet this ratio as close as possible. This measurements are based on oxygen sensor, fuel pressure, and map/maf sensor. Stoich takes into account volume and oxygen readings.

Stoich ratios are achieved based on open and closed loop. Open loop means only the maf/map sensor is dictating ratios. Closed loops means the maf/map and oxygen sensors are dictating ratios.

Cold Air Intake (CAI):
A intake designed to draw cooler air from parts of the engine bay that are cooler than the factory design air intake draw air from. Often these are located near the bottom of the engine compartment where the air is not as hot.

Warm Air Intake (WAI):
A intake designed to draw warmer air from parts of the engine bay that are hotter than the factory design air intake draw air from. Often these are located near the top or exhaust of the engine compartment where the air is hotter.

MAF/MAP Sensor
MAF sensor: measures the amount of air flow in terms of volume. It does not measure the amount of oxygen entering the engine.
MAP sensor: measures the amount of air flow in terms of volume based on predetermined calculations based on air pressure/intake temps/etc. It is not exact or a direct approach like a MAF but it does not interfere with air flow and is cheaper to service/produce.

Conventional Throttle
A butterfly valve is controlled via a cable connected to the accelerator that driver physically controls.

Drive-by-wire
A butterfly valve is controlled by the ECU based on given parameters such as user accelerator input, gear, and engine readouts (rpm,air temp,etc).

DBW is able to improve efficiency by providing the optimal butterfly valve opening conditions. Downside is that it does not allow full direct control(sensors regulate the butterfly valve instead of a cable) for hyper-milers but is more efficient for the masses.

Butterfly-valve
A valve that opens and closes often inside the air intake to allow air to enter the engine.

Camshaft profile
The profile of the camshaft lobes that allow how far a valve opens or closes. Think "how wide"

Camshaft phasing
The phasing or adjust of the camshaft angle to allow for changes in duration that a valve is open or closed. Think "how long"

Valvetronic/VEL
BMW/Nissan designed actuators that allow for infinite camshaft profiles. This means the valves open as high or as low as they want based on engine conditions allowing. It eliminates the need for typical/old camshaft profile designs that are often bought by v8 grurus to increase horsepower.

This gives the engine ability to eliminate a butterfly valve completely since the valves can now control air intake. Throttle losses essentially become minimal and efficiency is increase in terms of MPG and Power.

Note: There is often still a butterfly valve present as a backup in-case the system fails so the car can be limped home but in normal operation it is always completely open.

Intake/Exhaust Variable Valve Timing
Intake and exhaust cam phasing is adjusted meaning retarded or advanced to allow for shorter or longer durations the valves are open or closed.


School Me Part/My Theories (Provide input or ideas on each part):

1. Theory CAI:
Colder dense air has more oxygen. The more oxygen the more powerful the combustion process is and more power is produced. In open loop Stoich, more air needed to meet the volume so it sucks in more air. More air and fuel is compacted in the combustion chamber but the same amount of fuel volume is still used so a slight fuel savings.
In closed loop Stoich (most cars), the ECU sees more oxygen so it adds more fuel to match stoich so more fuel is burnt and more power is created. A slight decrease in mpg but is negated by the fact the engine can run at a lower rpm and make the same amount of power thus a net slight increase in mpg and power.
The net effect is based more on engine applications and RPM speed to see a true increase in mpg but there is always a slight increase in HP.

2. Theory WAI:
Hotter dense air has less oxygen. The less oxygen means less power is made. In open loop stoich, there is too much air entering so the ecu decreases fuel to maintain stoich.
In closed loop stoich (most cars), the ECU sees it needs more oxygen so the butterfly opens more which results in more air volume and decrease fuel to also meet stoich. The results of the butterfly opening more is a decrease in throttle losses caused by back pressure created by vacuum and turbulence.
The net effect is throttle losses outweigh the power decrease and fuel economy improves more than CAI.

3. DBW improves throttle losses but they are still there with CAI. Basically same affect as conventional throttle just a slight efficiency increase.

4. Valvetronic/VEL reduces the need for a WAI because the warm intake strives to decrease throttle losses but since there is no butterfly valve or turbulence the WAI hurts the engine more than it helps. WAI only apply to DBW and conventional throttle vehicles but are a hindrance on new cars with infinite cam profiles. Car engineers don't put WAI on new cars since this holds true but some do put ram air ducts and cold air ducts to improve power.

Thanks for any input and ideas. I am curious to see others people theories on these concepts and any scientific experiments to prove them.

[gone-ot]

...since you seem to be asking about a BOSCH system, contact them.

[oil pan 4]

ABA test both since WAI usually provides an MPG boost to gasoline engines, but not always.

If you have a diesel don't bother with WAI, unless its really cold.

[Diesel_Dave]

You say that cold air has "more oxygen" and warm air has "less oxygen". That's sort of true. Cold air does have more oxygen per unit volume--but only because there's more air per unit volume. The temperature doesn't affect the percentage of oxygen in air--therefore the amount of oxygen per unit mass doesn't change.

Now, you might be tempeted to think that because the stoke of the engine is a fixed volume, that volume is what matters. However, closed loop control keeps the air-fuel ratio basically constant (near stoich)--and AFR is mass-based, not volume based--the throttle will adjust to keep the same mass of air regardless of temperature (by changing the intake pressure). So warmer temps mean higher intake pressures--to keep the density the same. Higher intake pressure means lower pumping losses and also lower throttle losses, therefore, better fuel efficiency.

Also, warmer air increases the flame speed, so the combusion happens more quickly, giving it more room to expand. That also increases fuel efficiency.


Diesels are a different story because they're typically not at constant AFR and also don't have flame propogation. I've gone into the details on how a CAI benefits a diesel in other threads, but since you asked about a gasser, I'll stop now.

[user removed]

Originally Posted by Diesel_Dave

You say that cold air has "more oxygen" and warm air has "less oxygen". That's sort of true. Cold air does have more oxygen per unit volume--but only because there's more air per unit volume. The temperature doesn't affect the percentage of oxygen in air--therefore the amount of oxygen per unit mass doesn't change.

Now, you might be tempeted to think that because the stoke of the engine is a fixed volume, that volume is what matters. However, closed loop control keeps the air-fuel ratio basically constant (near stoich)--and AFR is mass-based, not volume based--the throttle will adjust to keep the same mass of air regardless of temperature (by changing the intake pressure). So warmer temps mean higher intake pressures--to keep the density the same. Higher intake pressure means lower pumping losses and also lower throttle losses, therefore, better fuel efficiency.

Also, warmer air increases the flame speed, so the combusion happens more quickly, giving it more room to expand. That also increases fuel efficiency.


Diesels are a different story because they're typically not at constant AFR and also don't have flame propogation. I've gone into the details on how a CAI benefits a diesel in other threads, but since you asked about a gasser, I'll stop now.

Great explanation. I would only add that the hotter the intake charge at the point of injection, the better atomization of the fuel.

regards
Mech

[jamesqf]

Originally Posted by Joeggernaut

Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.

No, for economy a modern engine will try to enable lean burn, where the A/F ratio might be up to 22:1, when conditions allow. Warmer intake air apparently increases the RPM/load range where this is possible.

[gone-ot]

Let me add that todays' modern engines try to maintain 14.7:1 mass air/fuel ratio, not for economy or power, but rather for EMISSIONS COMPLIANCE.

That's *why* individuals have to 'circumvent/trick' the engines normal "closed-loop" operational mode to make them "more efficient," by getting the ECM to operate closer to "lean" A/F ratio (16-18:1) than the 'chemical correct' stoichiometric (14.7:1) ratio needed for EPA requirements and catalytic converter "longivity."

[Joeggernaut]

Originally Posted by Diesel_Dave

You say that cold air has "more oxygen" and warm air has "less oxygen". That's sort of true. Cold air does have more oxygen per unit volume--but only because there's more air per unit volume. The temperature doesn't affect the percentage of oxygen in air--therefore the amount of oxygen per unit mass doesn't change.

Now, you might be tempeted to think that because the stoke of the engine is a fixed volume, that volume is what matters. However, closed loop control keeps the air-fuel ratio basically constant (near stoich)--and AFR is mass-based, not volume based--the throttle will adjust to keep the same mass of air regardless of temperature (by changing the intake pressure). So warmer temps mean higher intake pressures--to keep the density the same. Higher intake pressure means lower pumping losses and also lower throttle losses, therefore, better fuel efficiency.

Also, warmer air increases the flame speed, so the combusion happens more quickly, giving it more room to expand. That also increases fuel efficiency.


Diesels are a different story because they're typically not at constant AFR and also don't have flame propogation. I've gone into the details on how a CAI benefits a diesel in other threads, but since you asked about a gasser, I'll stop now.

Thanks for that explanation. It is hard to find a legit explanation that doesn't just say it "works because it works".

So the question comes down to new technologies now.

With infinite cam profiles the cam profile is optimized to virtually eliminate pumping losses. Since it is 99% optimized the need for a wai is basically negated besides the slight minimal increase in flame speed (DI helps with this more). A cai though is still beneficial. Thoughts on this?

Side Note: For other readers, pumping losses are inefficiencies caused by vacuum created when the valve closes causing air to back track within the intake system. The engine has to work a little harder to draw back in this air which are pumping losses. Back in the day car tuners would run intake runners which were designed to eliminate this back pressure. Some new cars still use this idea but use an extra butterfly valve to simulate intake runners.

[Joeggernaut]

Originally Posted by Old Tele man

Let me add that todays' modern engines try to maintain 14.7:1 mass air/fuel ratio, not for economy or power, but rather for EMISSIONS COMPLIANCE.

That's *why* individuals have to 'circumvent/trick' the engines normal "closed-loop" operational mode to make them "more efficient," by getting the ECM to operate closer to "lean" A/F ratio (16-18:1) than the 'chemical correct' stoichiometric (14.7:1) ratio needed for EPA requirements and catalytic converter "longivity."

Yes thanks for clarifying. I was aware of this already as I know stoich does fluctuate and sometimes other air fuel ratios are targeted but other readers will find this useful to know.

[baldlobo]

Originally Posted by Joeggernaut

Okay first let me say I know there are ton of wai vs cai threads but none of them seem to address new technologies and account for them. School me or provide your input on cai vs wai in the different applications.


This thread is only concerning mostly gasoline engines and applications.

Few definitions first:
Stoich:
The modern engine is trying to keep a 14.7 to 1 mass ratio of air to fuel.
Air

Stoich, is a ratio of fuel to oxygen that will allow fuel to ignite; now when it comes to modern engine controls; it depends on engine coolent temp, intake temp, map/maf, tps and o2.

Cold Air Intake (CAI):
A intake designed to draw cooler air from parts of the engine bay that are cooler than the factory design air intake draw air from. Often these are located near the bottom of the engine compartment where the air is not as hot.

most cold air intakes do not go down past the engine(because lower means water getting sucked up/hydrolocking/getting sued). "cold air" is subjective.

Warm Air Intake (WAI):
A intake designed to draw warmer air from parts of the engine bay that are hotter than the factory design air intake draw air from. Often these are located near the top or exhaust of the engine compartment where the air is hotter.

most engines from the 80 and earlier had some variation of this, to help with cold start issues(too much oxygen to fuel). Still questioning why they got away from thermac's for fuel injection.

MAF/MAP Sensor
MAF sensor: measures the amount of air flow in terms of volume. It does not measure the amount of oxygen entering the engine.
MAP sensor: measures the amount of air flow in terms of volume based on predetermined calculations based on air pressure/intake temps/etc. It is not exact or a direct approach like a MAF but it does not interfere with air flow and is cheaper to service/produce.

the only maf i've seen that interferes with airflow is the spoon type that ford used in the late 80's/early 90's

MAF systems use the same sensors to calculate air flow as the map does, just uses a different way to determine fuel; it's also an indirect method.

Camshaft profile
The profile of the camshaft lobes that allow how far a valve opens or closes. Think "how wide"

nope, the camshaft profile is when it open's and how long it stays open per cycle.

LIFT is how far the valve opens and closes

Camshaft phasing
The phasing or adjust of the camshaft angle to allow for changes in duration that a valve is open or closed. Think "how long"

Camshaft phasing is the change of camshaft timing in relation to it's static position; does not change duration

Valvetronic/VEL
BMW/Nissan designed actuators that allow for infinite camshaft profiles. This means the valves open as high or as low as they want based on engine conditions allowing. It eliminates the need for typical/old camshaft profile designs that are often bought by v8 grurus to increase horsepower.

This gives the engine ability to eliminate a butterfly valve completely since the valves can now control air intake. Throttle losses essentially become minimal and efficiency is increase in terms of MPG and Power.

Note: There is often still a butterfly valve present as a backup in-case the system fails so the car can be limped home but in normal operation it is always completely open.

might want to read this

AutoZine Technical School

Intake and exhaust cam phasing is adjusted meaning retarded or advanced to allow for shorter or longer durations the valves are open or closed.

nope; duration doesn't change, phasing a cam changes when it opens and closes(eg crankshaft rotates 720 for every 360 of the camshaft; phasing means a camshaft the opens at 208 normally would move 10 or more degrees +/- so 208 could end up phased at 198 or 218 depending on the computer)

School Me Part/My Theories (Provide input or ideas on each part):

Schooled