Effect of Intake Air Filter Condition on Vehicle Fuel Economy

[Diesel_Dave]

I've been doing some research on cold air & ram air intakes for my truck. I came accross this study done in 2009 at Oak Ridge National Labs. It's for gas engines, so it doesn't really apply to my diesel, but I thought I'd pass it along to my Ecomodder friends who still need the crutch of spark plugs.

The study looked at 4 vehicles:
-2007 Buick Lucerne
-2003 Toyota Camry
-2006 Dodge Charger
-1972 Pontiac Grandville

The first 3 are fuel injected, the last carbureted. Bottom line was that they found the the air filter restriction effect on fuel economy was insignificant on the fuel injected cars, but did hurt the carbureted car. This is because the fuel injected cars have closed-loop control on air-fuel ratio, so you get the same AFR (and intake pressure) regardless of intake restriction.

Here was the take-away quote for me:

Results show that clogging the air filter has no significant effect on the fuel economy of the newer vehicles (all fuel injected with closed-loop control and one equipped with MDS). The engine control systems were able to maintain the desired AFR regardless of intake restrictions, and therefore fuel consumption was not increased. The carbureted engine did show a decrease in fuel economy with increasing restriction. However, the level of restriction required to cause a substantial (10–15%) decrease in fuel economy (such as that cited in the literature) was so severe that the vehicle was almost undrivable.

Here's the full report:
http://www.fueleconomy.gov/feg/pdfs/...02_26_2009.pdf

[suspectnumber961]

At 37.7 mpg for the last 2 tanks and and ~ a 35 mpg summer avg last year...and if the next full tank comes in at a similar level (3 tank avg)....I'll have managed a 7.8% gain from adding a cone filter....A-B test complete.

Warmer temps have probably helped though....

2003 Ford Focus ZX3 w/Zetec DOHC engine Gas Mileage (Elroy) - EcoModder.com

[Diesel_Dave]

Originally Posted by suspectnumber961

At 37.7 mpg for the last 2 tanks and and ~ a 35 mpg summer avg last year...and if the next full tank comes in at a similar level (3 tank avg)....I'll have managed a 7.8% gain from adding a cone filter....A-B test complete.

Warmer temps have probably helped though....

2003 Ford Focus ZX3 w/Zetec DOHC engine Gas Mileage (Elroy) - EcoModder.com

A while back some of us who keep weather data in our daily logs compared notes (http://ecomodder.com/forum/showthrea...cts-20561.html). A rule of thumb that emerged was ~1% change for every 2 deg F change in temperature.

[suspectnumber961]

Not driving much in the warmest weather though. Notice that when checking "fuel used" that I had to set the SG back last 2 tanks.

[slowmover]

This is not so argumentative as it may sound; am looking for context:

I didn't read the .pdf, DD, but I'm suspicious where a personal vehicle is under load. I know that even in 1972 that the OEM's were oversizing air intakes/filters somewhat, but even todays sophisticated electronics are going to have a hard time keeping up with a dirty filter once loaded to capacity and/or towing. Add in an ascent when already at altitude and the filtering surface is being called upon at maximum.

Big trucks running dual VORTEX aircleaners (379 Pete's and W900 KW's), -- about as low restriction as one can get for volume -- still notice a point where filter restriction is significant (not unusual for an O/O to change filters based on restriction with a quality in-cab gauge).

For light load FE purposes, yeah, okay . . . but for a bit of real world, better sooner than later on changing. An oil analyst would tell us that the air filter always trumps the oil filter for importance (which really isn't capable of much work) as even a pencil point hole can trash a motor. A $17k longblock is not in my future.

The past couple of years I change the air & fuel filters annually along with a single oil change (not running many miles, so am well within the 7.5-15k OCI) as the local caliche dust is not to be trifled with.

Anyone who ever parks on unpaved surfaces (not just drives them) is better off with factory guidelines. I'd say that anyone whose engine fan even once kicks up some dust is better off with factory-only filtration (as the aftermarket is more than suspect in it's claims short of DONALDSON-sourced nanofiber pieces).

If you are looking to lower restriction without changing filtration as often in that Dodge, then have a look at the VOLANT piece. The OP does a nice job, and was kind enough to respond to my requests for data over time.

Frankly, I doubt it would make much difference past the revised 4" deep MOPAR piece available for the stock air box this past year (which has also been shown to be good past 400 RWHP). If I were looking to spend a lot to gain a little on the intake side then I might try this piece along with "known" better intake tubing and a TAG ahead of the turbocharger.

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[Diesel_Dave]

I haven't found any similar studies on diesels, but I'd be willing to bet that there is a FE effect on diesel. The reason being that most diesels don't have closed loop control on air-fuel ratio. On a typical gas engine, if you decrease the intake air restriction, the throttle will close down in keep the AFR the same, thereby negating the lower intake air restriction.

On most diesels, lower intake air restriction mean higher AFR and therefore better FE. That's with diesels that are naturally aspirated, or have a fixed geometry/wastegated turbo. In some cases, engine with VG turbos (such as mine) do have closed loop AFR control. In those cases, I think there's still a FE benefit, becausse the VG turbo won't have to close down as far, thereby decreasing pumping losses.

BTW, slowmover, I'm not looking at changing my filtration--only the restriction upstream of the filter. Also, I never drive on any unpaved roads.

[slowmover]

In some cases, engine with VG turbos (such as mine) do have closed loop AFR control. In those cases, I think there's still a FE benefit, becausse the VG turbo won't have to close down as far, thereby decreasing pumping losses.

Thanks for pointing this out. Earlier HPCR CTD's can be fitted with the later VG turbos with a stand-alone controller, and perhaps with EFI-Live software could also be an addition in search of better economy / overall better "performance".

And the info about DONALDSON Powercore filters (developed from the experience in Iraq with helicopter turbine engines) is offered as FYI for those who are contemplating such a change. The OP in that thread found no worthwhile gains which was not surprising for a stock, or nearly stock, engine. But I'd expect the filter in question could travel a longer set of miles prior to changeout (one would need to seach the FORD boards where the filter is most commonly encountered).

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[Tesla]

Old thread dig, but just found article/study related to topic for diesel air filtration:
http://www.fueleconomy.gov/feg/pdfs/..._AirFilter.pdf

Doesn't agree with my experience, they indicate on vehicles tested there was little adverse effect on FE with a dirty filter, main effect was reduced performance.

Here's another Diesel article on air restriction and intakes, not as related but good info:
http://www.genosgarage.com/GenosGara...tems-Part2.pdf