Intake Air Temperature.

[JockoT]

As I struggle to get to grips with my ScanGauge I was wondering why I would want to know the Intake Air Temperature? I have no control over it, as it is dependent on ambient temperature, so why would I want to follow it. Or is it just something that OBM II can display, so ScanGauge do!

[Daox]

OEMs use intake air temperature to control the fuel injection and ignition timing on the engine. The Scangauge gives you access to any sensor that the ECU has available. You can use the intake air temperature for troubleshooting (bad sensor, short in the wiring, etc), or you can use it for monitoring a fuel economy modification like a warm air intake, or performance modification like a cold air intake.

[JockoT]

I appreciate that the fuel injection system uses the air temp to get the correct fuel density, I just wondered why ScanGauge gave the option of displaying it. There are lots of other things they allow you to scan but don't display on a gauge. Regarding warm air intake, I was always under the impression that a colder air intake temperature gave better performance and fuel economy. I read a thesis on air intake temperature and the published results clearly showed that increasing the inlet air temperature caused the fuel consumption to get worse. I am open to persuasion, however.

[Daox]

I'd be interested in reading this paper if you can find it.

On gasoline cars, warm air does a couple things, some are positive and others are negative. Mainly, it reduces the density of the air coming into the engine. This essentially doesn't allow the engine to make as much power. The lower output of the engine therefore requires increased engine load to do the same work. Increased engine load causes a reduction in pumping losses which increases efficiency. This is the same reason smaller engines get better fuel economy than larger ones (all else being equal). Warmer air also speeds up the combustion process. This is a good thing to a point, but if you get too much heat in there, you start having to alter ignition timing which can hurt efficiency.

Thats kind of the short answer. Others can fill in with what I haven't remembered off hand.

[oil pan 4]

Cold air gives better power and fuel economy on diesel.
On a gas engine cold air gives more power and typically less power.
And you can control the intake air temperature.
Of course any one trying to sell you a cold air intake is going to tell you there is no negative side effects.
Typically, not always, cold air reduces fuel economy.

[redpoint5]

Originally Posted by oil pan 4

On a gas engine cold air gives more power and typically less efficiency.

.

[JockoT]

I realise you can change the air intake temperature, I have had cars where the air cleaner has a summer and winter position. But how and why would I adjust it on the move?

[California98Civic]

Originally Posted by JockoT

I realise you can change the air intake temperature, I have had cars where the air cleaner has a summer and winter position. But how and why would I adjust it on the move?

The why: if intake air is not very high, the theory goes, the beneifit to fuel economy from decreased pumping losses cannot occur. If it is too high, some fear engine damage. I typically went for 30-50*F over ambient.
The how: some guys have a shutter system on the grill, or a redirect system on the intake tube. Both are to allow selecting for hotter or cooler intake air (often using a solenoid or some sort of wire-pull switching mechanism).

I have gained a little more skepticism about my warm air intake in the last year, since I was forced to run without it for a while and was unclear what affect its removal had on my FE (possibly it got better, but there are too many variables to feel confident of that educated guess). So, I too would love to see the thesis on warm air and fuel efficiency that you mentioned. Can you find it?

james

[JockoT]

Originally Posted by California98Civic

I too would love to see the thesis on warm air and fuel efficiency that you mentioned. Can you find it?

I downloaded the pdf
EFFECTS OF AIR INTAKE TEMPERATURE ON THE FUEL CONSUMPTION AND EXHAUST EMISSIONS OF NATURAL ASPIRATED GASOLINE ENGINE | Abdullah | Jurnal Teknologi