intake air temp - effects on torque

[HappyTime]

does anyone have the math on intake air temps effect on gasoline engine torque? i know there is not one equation that covers all motors in real life conditions, but im looking for the math that says for every 1F drop in temp increases air density, fuel consumption,and power by this much.

I ran my obd2 logger on my 2003 audi a4 quattro. intake temps were 40F+ above ambient air temp at freeway speeds. I installed some fiberglass header wrap around the fuel lines under the hood, and some heat shielding that looks like a carpet pad with a layer of aluminum on one side around the air filter box. sealed all the gaps with aluminum tape made for hvac ducts.

now intake temps are down to +12F above ambient at freeway speeds. the first thing i notice is that a slight press on the gas in 4th gear at 50mph almost got out of control. also fuel consumption is up 8% at freeway speeds, making for loss of 1.8mpg!

im thinking of removing the last part of the air intake ducting so it pulls in hot under hood air to see the fuel consumption effects of increasing the intake temps.

 

[bentheswift]

"i know there is not one equation that covers all motors in real life conditions, but im looking for the math that says for every 1F drop in temp increases air density, fuel consumption,and power by this much."

That is exactly the formula that you just said didn't exist.

A good place to start would be finding the density change that air undergoes over the temperature change you've experienced, and divide the new density by the old, hot density to find the approximate change in air mass entering the engine on each stroke. That is probably all the gain you're seeing (on the order of 2-5%). If the engine has a knock sensor and active timing control, then it may be bumping up the spark timing a bit too. That is the part that there is no formula for, since it changes from engine to engine.

I don't have any experience with Audis, but I do know that mpg gauges built into cars are, and have always been, notoriously inaccurate. The proper way is to log fuel that goes into the gas tank and divide it by odometer miles, and to do so accurately requires logging over several tanks. I personally wouldn't trust anything but real measurements when it comes to fuel economy.

 

[ivymike]

the density of air entering the engine isn't the only thing that affects fuel economy. have you considered the effect of air density on drag? on tire rolling resistance?

 

[dgallup]

SAE J1995 section 9 gives you the formulas necessary to correct observed engine power performance for deviations in inlet air conditions.

 

[patprimmer]

I would also guess that there is a lot written about it in the

http://naca.larc.nasa.gov/search.jsp

web site.

Cooler intake air from insulating the induction system will have very little if any influence on fuel economy when used at the same performance level, as the extra potential power will be throttled back in proportion to maintain the same cruise speed.

It will use more fuel in direct relationship to the increase in air density at WOT, but typically WOT is a very small portion of operating time except in race cars and low powered heavily loaded applications.

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[HappyTime]

thanks guys, i found that what I was really looking for was how air density changes with temperature. The fuel consumption changed based on other factors, im sure.

 

[PLeon]

OK, I know CLOSED LOOP. But how about MAP vs TPS map? especially at low loads.

 

[PLeon]

Sorry, wrong thread.

 

[globi5]

A lowered air density (higher temperature) reduces pumping losses and thus improves mileage.

Besides, a higher intake temperature accelerates fuel evaporation and also increases temperature at TDC and accelerates burning speed.