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Old 06-24-2009, 01:42 AM   #11 (permalink)
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Originally Posted by cfg83 View Post
delslo -



Yeah, I've heard of some people at higher altitudes (i.e. Colorado) getting great MPG, because they are "running lean" as a function of their altitude. They are not actually "lean" per se, but they are using less fuel than they would be at sea level.



For OBDII controlled cars (1996 to present), the AFR is controlled by the 02 sensor, which shoots for the magic 14.7 stoichiometric ratio. If the cold air is denser, there is more "air" being drawn into the car. The 02 sensor will report this to the ECU/PCM, which will increase the amount of fuel injected.

I lost the "perfect URL" for this, but here is a good explanation :

Tips on Reading Gauges; Air-Fuel Ratio Monitor




Other people have posted that this was done on some full size trucks in the 1970's. It used the WAI when the engine was cold, and switched to the CAI (with a flap, just like you said) once the engine was all warmed up. All mechanical stuff in those days, no carputer. I think that some Hondas use WAI by placing the intake deliberately close to "hot stuff", but I don't know the details.

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Any vehicle with a "heat riser" on the intake piping switches from HAI to CAI based on engine temps. The warmer the engine gets, the more the valve closes to allow colder air from the end of the piping to enter the intake. When the engine is cold, the thermal valve is completely open, which only accepts air from near the engine, so that the thermal cycling warms up the engine faster. (Each degree the engine warms up also warms the intake temperature, creating an effect of non-linear heating, or a "heat curve", since intake temperature effects engine warm-up times, until the thermal valve begins to close, which allows cooler air intake. In the event that the thermal valve is stuck open, allowing only hot air to enter the intake system, the net effect of engine cooling would become the determining factor in overall intake temperature, all other things equal.)

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Old 06-24-2009, 02:15 AM   #12 (permalink)
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Quote:
Originally Posted by cfg83 View Post
Yeah, I've heard of some people at higher altitudes (i.e. Colorado) getting great MPG, because they are "running lean" as a function of their altitude. They are not actually "lean" per se, but they are using less fuel than they would be at sea level.
I've heard both ways. Also, the air being thinner is similar to the gains achieved from aero mods, so its difficult to determine exact causation.

In the other thread you say it exactly right - hotter air intake temps are reducing output.

So using that, the whole reason I can't wrap my head around an endorsement for an HAI is simple: if you're limiting output, yet it still requires x amount of tq to achieve the speed/distance you need, you need to increase throttle/revs to do the same amount of work. This is the same as saying you're putting the engine under more load. More load = more fuel consumption.

Also, the burn efficiencies of heated fuel vapors on a fully warmed motor I would have to imagine are completely negated by the aforementioned reduction in dynamic compression ratio.

Please, keep going. I need to make sense of this. I love making intakes
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Old 06-24-2009, 02:27 AM   #13 (permalink)
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By opening the throttle more, you're inducing less pumping loss in the engine. The pumping loss isn't the sole source of the reduction in consumption, but it's one piece of the puzzle.

By adding warm air, you are in fact changing the volumetric efficiency of the engine, which, in this case, means you're creating less power (with less fuel) for the same amount of engine speed, with more throttle angle. A higher throttle angle decreases parasitic load on the engine, again, due to a reduction in pumping losses.

Hotter air flows with increased velocity, due to the heat induced expansion of gasses. Increased velocity allows for less necessary vacuum to achieve the same result. Again, less pumping losses.

If the intake air is already hot, less calories (energy, not fat) are consumed to heat the intake charge to the necessary temperature for combustion, and to keep the engine at the proper operating temperature. The decreased differential between engine temps and intake temps means, effectively, that less energy calories must be consumed in heating/expanding the air in the combustion charge, so that more of the energy exchange can be focused on pushing on the piston, rather than heat-exchange taking place with the cylinder walls. (Yes, this does happen. When you eat cold food, your body's first exercise is to heat the food to your body temperature, which takes more calories to maintain your core temperature. If you eat food that is at your core temperature or warmer, less calories are necessary to digest/fully consume the food, so you get more energy content from it, comparatively.)

HAI's work on the "less is more" principal. You're only getting a percentage of the charge, but for that percentage, a higher percentage of the exchanged energy (see: law of conservation of energy) can be used to perform the desired task, with less waste generated.

In essence, a hot cycle is a more efficient cycle, although producing less power per cycle.

I hope that helped, I think it made my carpal tunnel flare up.
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Old 06-24-2009, 02:40 AM   #14 (permalink)
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delslo -

(Christ, I was trying to answer the question from my low-skillzz standpoint, but I wonder if I am alluding to a similar thing when I conjecture that the "BSFC topo map" is moving)

Quote:
Originally Posted by delslo View Post
...

In the other thread you say it exactly right - hotter air intake temps are reducing output.

So using that, the whole reason I can't wrap my head around an endorsement for an HAI is simple: if you're limiting output, yet it still requires x amount of tq to achieve the speed/distance you need, you need to increase throttle/revs to do the same amount of work. This is the same as saying you're putting the engine under more load. More load = more fuel consumption.

Also, the burn efficiencies of heated fuel vapors on a fully warmed motor I would have to imagine are completely negated by the aforementioned reduction in dynamic compression ratio.

Please, keep going. I need to make sense of this. I love making intakes
Ok, I'll take a different stab, but please be kind, I'm not a car guy (I mostly vomit my internet-learned info-worms like a mommy bird).

One thing we like to complain about in Ecomodder is that the engines are "too powerful" for our needs. We are deliberately driving in lower load conditions. Many of us would like to have cars with lower HP.

Mayyyyyybee, the HAI causes the engine to operate in a different state of BSFC. That is to say, we are at lower HP, but because our engines and ECU/PCMs are operating "outside the norm", we can get good MPG. This may be why some cars like HAI and some don't. It's like finding an exploit in the engine and/or ECU/PCM.

Does that make sense?

Question: When BSFC charts are made, is IAT always uniform? I would expect yes, and I would expect some kind of "standard" intake temp. Maybe atmospheric conditions would be taken into account during the test in order to account for humidity. Do BSFC charts "move" as the humidity changes?

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Old 06-24-2009, 04:39 AM   #15 (permalink)
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Ok here's the conclusion I've reached:

+ reduced pumping losses from throttle position = more efficient
+ improved thermodynamic energy transfer = more efficient
- higher load to compensate for lower output = more fuel = less efficient
- lower dynamic compression = less efficient

It's a trade-off and difficult to determine which set is more significant - especially given other variables such as vehicle absolute gearing, road grade, environment, etc, etc.

Additionally, when you throw in OEM ECU parameters, everything goes out the window. Dependent on tps/revs/load/iats, etc, the ECU may or may not add or subtract timing and fuel - totally up to the OEM.

So... it may work, and it may not. Completely dependent on application.

The reason for the OP was if an OEM had done as such, I could totally get on board as they have the knowledge and resources to exhaustively test ideas more-so than enthusiasts. Not to discredit enthusiasts or things done outside the real of OEM, just always helps settle a debate easier.

other:
+ decreased warm up time
+ aids high operating (h2o) temps = more efficient
- higher risk of pre-ignition
- reduced output at all times (ever drive in traffic so bad you can't pull out unless you gun it or completely cut-off someone?)

Personally, I'd rather avoid risk of detonation and reduction of power at all times for speculative or modest gains. If anything, some sort of OEM intake to HAI valve is what I'd like to experiment with.

If it works for others, that's awesome! Thanks for the explanations. Always nice to learn new things
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Old 06-24-2009, 01:51 PM   #16 (permalink)
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Quote:
Originally Posted by delslo View Post
Ok here's the conclusion I've reached:

+ reduced pumping losses from throttle position = more efficient
+ improved thermodynamic energy transfer = more efficient
- higher load to compensate for lower output = more fuel = less efficient
- lower dynamic compression = less efficient

It's a trade-off and difficult to determine which set is more significant - especially given other variables such as vehicle absolute gearing, road grade, environment, etc, etc.

Additionally, when you throw in OEM ECU parameters, everything goes out the window. Dependent on tps/revs/load/iats, etc, the ECU may or may not add or subtract timing and fuel - totally up to the OEM.

So... it may work, and it may not. Completely dependent on application.

The reason for the OP was if an OEM had done as such, I could totally get on board as they have the knowledge and resources to exhaustively test ideas more-so than enthusiasts. Not to discredit enthusiasts or things done outside the real of OEM, just always helps settle a debate easier.

other:
+ decreased warm up time
+ aids high operating (h2o) temps = more efficient
- higher risk of pre-ignition
- reduced output at all times (ever drive in traffic so bad you can't pull out unless you gun it or completely cut-off someone?)

Personally, I'd rather avoid risk of detonation and reduction of power at all times for speculative or modest gains. If anything, some sort of OEM intake to HAI valve is what I'd like to experiment with.

If it works for others, that's awesome! Thanks for the explanations. Always nice to learn new things
For higher load - engines tend to operate more efficiently under higher load. I remember that specifically, but I don't remember the theory of engine operation which supports it.

Driving in traffic so bad... - Don't drive during peak traffic hours, if you can avoid it. You *could* get up to 15% better fuel economy just by avoiding peak traffic hours or taking your lunch break 1/2 hour later. You'll also be less stressed, and have more time.
Example: I could leave to take my wife to school at 7 AM, and be there at 8.30AM. OTOH, I could also leave at 6.20AM, and still only get her there at 8.30AM. Try to graph your local traffic conditions and patterns, and you'll find similar occurrences.

If you want to test with an OEM intake vs HAI, there are a few options I can think of.
One is a simple flapper valve. Open it to hot air, close it to OEM.

The second is one that I've suggested before, but it isn't as efficient as recovering exhaust heat: If you have an intake box large enough, you can insert a second heater core into it. Run it off your original heater core in series, and as your engine heats up, it heats the incoming air (once the thermostat is opened). You can't claim faster warmup with this method, and it partially cools your coolant as it heats the air. The more temperature differential there is between the intake air and the intake heater's temp, the more cooling effect the system will have on your coolant, so there is a partial trade off. The heating effect can be controlled with a coolant valve, commonly found on vehicles of Japanese origin, that don't have automatic climate control. Another option to control the heating effect is using the flapper valve method with this mod, so that you can control where the air is coming from, instead of the coolant flow through the intake heater.

While there are still other methods, those are the two most pronounced in my mind at the moment.

CFG - I wish I could answer that question about BSFC, but I can't speak to it in good conscience, because the only information that I have about BSFC is that peak torque usually coincides with it in gas engines, and peak VE is usually close to that island as well...

What this tells me about BSFC: The occurrence of the lowest BSFC per engine speed usually is at the point where, per RPM, the most torque is produced with the least losses. This could be partially shown as a function of cam profile, partially as a function of fluid dynamics, engine speed, etc.

There are still too many factors in the "system" for me to definitively say that BSFC would or wouldn't be affected by changing a given parameter.

Hope that helps. Carpal Tunnel is getting worse. LOL.
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Old 06-24-2009, 05:00 PM   #17 (permalink)
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Quote:
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For higher load - engines tend to operate more efficiently under higher load. I remember that specifically, but I don't remember the theory of engine operation which supports it.
I saw this in one of the other threads, and there's a rather large caveat overlooked IMO. Sure, higher loads lend themselves to greater efficiency and lower BSFC due to the improvements in pumping loss. However, this does not necessarily lend itself to lower fuel consumption.

If you look at any 3d fuel map, there is always more area under the curve, and therefore more fuel, whenever throttle/airflow and rpm's increase (ie load). Honda's lean burn capitalizes off greater load/throttle openings because the ECU is simultaneously running higher than stoichymetric air:fuel ratio's, permissible by their head design. This is generally not the case for other auto's.

If load was conducive to FE, then there wouldn't be so much emphasis on DWL techniques and reducing weight (load).

So again, reduction in output via HAI requires more load to compensate which requires more fuel. IMO it's really dependent on the OEM fuel parameters, application and other variables to determine if the reduction in pumping loss is providing net FE +/-.

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Old 06-24-2009, 05:04 PM   #18 (permalink)
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- higher load to compensate for lower output = more fuel = less efficient
deslo, why do you think HAI means more load and more fuel? Something isn't quite adding up with your analysis.
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Old 06-24-2009, 08:10 PM   #19 (permalink)
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deslo, why do you think HAI means more load and more fuel? Something isn't quite adding up with your analysis.
Because you're crippling output. If the output required to achieve desired speed/distance is fixed, then you need more throttle and rpms to compensate for a reduction in output with a HAI. More throttle/airflow and more revs is load by definition as I understand it. More load requires more fuel as programmed into the ECU by the OEM.

Similarly, the reduced compression effect of less denser air cripples output, compounding the matter.

This is my largest quandary.
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Old 06-24-2009, 09:40 PM   #20 (permalink)
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Because you're crippling output. If the output required to achieve desired speed/distance is fixed, then you need more throttle and rpms to compensate for a reduction in output with a HAI. More throttle/airflow and more revs is load by definition as I understand it. More load requires more fuel as programmed into the ECU by the OEM.

Similarly, the reduced compression effect of less denser air cripples output, compounding the matter.

This is my largest quandary.
You appear to be assuming that the engine's ouput isn't variable per the same RPM...

You're correct in that it takes a given output to maintain a given speed, but most engines produce MORE than that given output per the RPM at which they produce the required speed (via the drivetrain).

Therefore, since RPM is fixed per vehicle speed, and necessary output is a constant, the variable is actually throttle position.

If you open the throttle more, (under normal circumstances) you're creating more output, due to more availability of air, and thus more fuel input.

With hotter air, you have to open the throttle just that much more to maintain the same output and engine RPM.

Remembering that RPM and engine output need to remain constant when speed remains constant (on a flat, level surface, assuming that losses are also a constant), the difference between the HAI's apparent effect on power production and the CAI's apparent effect on power production is simply stated by showing the same power production at differing throttle positions.

Once again, if the throttle is opened more, there are less pumping losses per the same output.

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