heating intake air to improve mpg? 1

[86corolla]

been curious for a while about how much fuel economy can be gained by having an engine intake from a hot spot in the engine bay. I'm sure there have been many experiments in this field, can anyone point me in the right direction, or give thoughts. The idea is to have two intake pipes; one cold air, the other a hot air when absolute power is not needed, and a way to switch between the two.


thanks

 

[patprimmer]

How does preheating air improve fuel economy under normal conditions on a well designed and tuned relatively modern car.

Regards
Pat
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[Lou Scannon]

That's not really new. Late 60's and later carbureted engines had a thermostatically controlled intake air mixing system that blended warmed air from a shroud on the exhaust manifold with underhood, or later on, ambient air to maintain a constant temperature at idle and part throttle. At WOT, the vacuum controlled valve closed fully to block the warmed air.
I'm not aware of a closed loop fuel injected system that uses this system; that tells me that the main benefit was open loop carburetion accuracy; evidently the fuel economy improvement for fuel injected systems is minimal, or they would be using it.

 

[patprimmer]

Hem

As far as I know, that system was a quick warm up device to improve drive ability and reduce cold star emissions.

It could have a very minor impact on fuel economy by reducing the time it was necessary to run the choke.

Regards
Pat
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[GregLocock]

http://www.metrompg.com/posts/wai-test.htm

Simple question. Given that it is very cheap to blend warmer and rather cooler air do you not think that manufacturers would have done this rather than indulging in variable cam timing etc if it had a worthwhile effect on mpg?

Cheers

Greg Locock

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[IceStationZebra]

I agree with Pat and Greg. The warm air intake was just to improve vaporization in a relatively cool carburated engine.

And I'm sure somebody will correct me if I'm wrong, but doesn't warm intake air lower the overall thermodynamic efficiency of an engine?

ISZ

 

[black2003cobra]

Previous discussion here:

http://www.eng-tips.com/viewthread.cfm?qid=220747&page=7

 

[Lou Scannon]

To clarify my previous post, I did not intend to give the impression that I agreed with the premise that preheating improves fuel economy in general. My main point is that the preheating concept itself is not new. I am in full agreement with all the posts between this one and my first reply.

 

[pmtoo]

I have preheated intake air to over 100°C in an exhaustive study of a single two-stroke. The result was a drastic decrease in fuel consumption, but it was a crude engine to begin with and all the heated air was doing was assisting in fuel evaporation and reducing pre-ignition droplet size (it was a heavy/thick fuel). In my test my high HC emissions dropped to low levels with the heated air because I was not sending as much fuel out the exhaust. A normal engine would not see this improvement, this test did because the engine was junk to begin with. As far as for a "normal" engine, the only improvement I see is in a slight reduction of pumping losses. This will come with increased NOx emissions from the increased combustion temps (the reason why most modern cars intake cold air).

The metrompg link summarizes the small difference well.

 

[turbocohen]

Years ago I worked for a guy some of you may have heard of named Smokey Yunick as a techicians assistant. Years after the second time I was fired I built my own hot vapor cycle engine and experimented with intake heat as high as 450F on a blower/checkvalved engine. The heat expanded the intake air of course and there was some improved efficiency potential but NOX was off the charts no matter what anyone else claimed. In the end I found more useful gains from better transmissions improved fuel spray/targeting/timing and efficient combustion chamber designs.

The pro was better part throttle efficiency, the con was melted parts and hot fuel handling disaster.

 

[patprimmer]

You could get the similar part throttle economy by simply reducing the size of the engine by the change in VE that results from the intake air preheating.

For difficult to evaporate fuels, or in very cold climates, preheating may help, but for highly volatile fuels, in warm weather you get virtually 100 evaporation anyway, so preheating simply reduces VE which requires wider throttle opening which reduce pumping losses.

I am ure this has all been said before.

Regards
Pat
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[dmelacom]

HI guys. I'm new here and find this forum to be very informative. Thanks..

There is definitely an optimum air temp. My guess it's right about 130-140 f. I say this because of many years of forced induction product design with an emphasis on emissions standards and meeting strict California smog testing standards. I find this window to be the optimum for best (low) HC and reduced nox emissions.

 

[tomt2]

I heard that heated intake air works well on Saturns. I tried it on my 1.9L DOHC Saturn and saw a consistent 3mpg improvement on my short drive to work. I recorded the same 3mpg improvement on 3 tanks of gas until the weather started getting cold. Then my mileage went to hell. I believe the car was leaning out the A/F mixture due to less volume of air per piston stroke. I noted the intake air would get up to around 130-140F on my short 3 mile drive in the summer. In city driving longer distances the temp would go up to 150-155F. I think a good engine coolant heater, perhaps an oil heater, and heated intake air would all help to improve mileage in colder climates especially. I think I saw a good benefit because my trip is so short, the car wasn't warming up to full operating temperature by the time I shut it off. The AIT sensor was reading a higher than normal reading so it could start to taper off fuel enrichement. Now i just need to get a coolant heater and I think I will start to get decent fuel mileage in the winter.

 

[ivymike]

a coolant heater? you mean to plug into the house at night?

 

[j79guy]

Yeah, it's a Canadian thing eh?

Robin.

 

[Bribyk]

When I was in Australia some locals were quite amused by this "electric blanket" on our engines that we had to plug in at night to keep them warm.

 

[winterpeg1]

Had some experience with pre-heating intake air to an engine for both a carbureted 2.4 liter engine on my 1984 Nissan king cab in Brandon Manitoba and on my 1989 Dodge 150 full size pick up's 5.2 liter engine with throttle body fuel injection. With temperatures in the winter as low as minus 40*C it did make a significant increase on the Nissan truck and a marginal on the Dodge. The method used was to draw warm air off of the exhaust manifold's modified heat shield into the main air intake through the air filter. This made no significant improvement for fuel economy in warmer weather. Basically had summer like fuel economy overall. Currently have a 95 Dodge pickup with a 5.2 liter engine, multiport injected modified with this type of intake. In Winnipeg now and have a very minor increase for fuel economy this winter.

 

[tomt2]

Yeah, I was referring to a coolant heater you could plug in to warm the engine a few hours before you need to start the car in the morning. An oil heater would be more for reducing engine wear at startup when it is very cold out.

I downloaded the calibration data from a ROM on a 1987 Dodge Daytona 4 cylinder (batch fired injectors) and looked at the values using Chem2 software. I noticed the computer automatically richens the A/F mixture when the coolant is cold. As the temperature of the coolant increases, the fuel enrichement decreases. At around 118 deg F the fuel enrichement levels off and does not decrease anymore. I imagine my Saturn has the same type of deal. Another interesting thing is the Daytona doesn't go into closed loop until the coolant reaches 66 deg F and a delay time of 20 seconds is reached (it does use a heated 02 sensor). I am half way to work by then (when the outside temp is around 30 deg F)!

I think if i had a longer commute to work, i would see less of a mileage improvement with the warm air intake (WAI). Since my commute is short my engine is not warmed up fully by the time I get to work. The warmer air probably helps vaporization while the intake and head are still cool. Once everything is warmed up, the WAI probably makes little difference in mileage. Keep in mind that my car uses sequential fuel injection, not a carburator, and I'm still seeing an improvement.

It really hasn't made a very noticeable decrease in performance during summer days, so I don't worry about having a valve to turn off the warm air and pull in cool air on hot days. I also hear no pinging and no noticeable spark retard (using a Scangauge II).

 

[winterpeg1]

One of the things of note is in Alert Nunavut, the most northerly settlement in the world. It has the exclusive use of some of the most unique pre-heating systems on a vehicle I have ever seen. Was there for 8 months as the Power plant supervisor till May 2008 with a couple of vehicles we use regularly out of our maintenance bay.

Almost all wheeled and tracked machines burned JP-8, the same fuel the C-130 use when bringing in our supplies on a less than frequent basis. 2 Block heaters for starters on some engines! There were adaptations of mullion heaters normally used on fridges to defrost them on the transmission pan and on the Tran’s axles plus difs. All were insulated and the power draw on some was a 20 amp circuit breaker. There was also an interior warmer in most of the ford F-350's Diesel crew cabs as well.

All vehicles had 3 flaps that open on the radiator blankets on the exterior of the front grill increasing heat to the engine. Vehicles burned more fuel idling than actually moving on the 45 Km of roads in the area. Part of the reason it is 24 hours nighttime in the winter for almost 6 months, so you leave your lights on. This to see if polar bears and wolfs are in the area, your key safety concern.