306oc - Peugeot 306 Owners Club & Forum

Hi guys, I have just been reading info about cold air intakes etc and how intake temperatures affect a diesel.

I am curious as to how these engines know what the intake temperature is. I know that the MAF sensor has a temperature probe in it which is used to determine density of the intake air. It is also used to advance or retard the injection timing to allow the engine to compensate for the slower burn with cold air and faster burn with hot air.

Here is the bit that confuses me though. These engines originally don't have an intercooler. Is there some generic setting somewhere that says that the turbo at max boost will always increase the intake air temperature by a certain amount.


For example,
15c + (generic turbo temperature increase) = 65c intake manifold temperature.  = Injection 12* before top dead centre 
24c + (generic turbo temperature increase) = 74c intake manifold temperature.  = Injection 8* before top dead centre

(I have no idea actual injection starts just showing an example)

Now imagine then that you throw an intercooler into the mix. You still only have that MAF sensor reading, and then the generic turbo temperature rise setting in the ECU.

15c + (generic turbo temperature increase) = 65c before intercooler temperature = Injection 12* before top dead centre.
But then if you say measured the temperature after the intercooler and it was say 22c.
65c - 22c = 43c difference between what the ECU thinks is entering the engine and what actually is entering the engine.

Then you could get away with more timing advance than what the ECU thinks is actually required? Meaning you could have better fuel burn, higher cylinder pressure, better mpg from the same amount of fuel but just injected earlier than the car though it could be?

What are your thoughts guys? Would it be possible to have a temperature probe like the one in the maf and get it fitted into the entrance to the manifold to then map the car suiting the actual temperature of the intake temps?

Jack

What you say is true but if you measure the intake temp you are able to tell within a reasonable amount what it will be at the inlet after the turbo. If you fit an intercooler you do lower these temperatures but you wouldn't do this without a remap really and these variables "should" be taken into account from the mapper you choose. Therefore the extra sensor would not be needed.

I think it'd be more worthwhile to fit a map sensor after the turbo to accurately measure boost pressure rather than temperature.

A map sensor would only measure the pressure wouldn't it? And not the temperature of the air? Need Pro-Steve to have a look

Spoke to a couple of HDI tuners about this. Neither really had much info regarding the temp. Dervtech said that they could measure the density as it still measured the amount of air going into the engine. They didn't however say anything about temperature and the possibility of advancing the timing as well.

You seem to be mistaking timing a compression ignition engine with a spark ignition engine...

Why do you want to add timing?

To compensate for the slower ignition of the diesel when in colder air.

negligably slower..

and yes... there is most likely a standard values table which has a pressure - in take temperature calculation to compensate for Air temperature..

under standard conditions however the air temperature will never be as high as the engine running temperature anyhow..

even pre-intercooler stage1 setup..

after the IC my inlet pipes after a fast run if i stop quickly are almost ambient temperature because i have a sensible sized intercooler for the power i am looking to run.

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http://opus.bath.ac.uk/17232/1/thesis.pdf << written by a friend (Aquantence) of mine

Yeah I see what your saying but if the engine doesn't know that the intercooler is there it will still be asuming the high intake temps it's used to from a non intercooler engine. That means then your feeding cold air to an engine asuming hot air. Which would give some availability to move the injection period forward for more power with same fuel?

no? because the change in flame front speed of atomized fuel at different temperature of heated fuel is negligible..


you simply get more dense air charge and hence more oxygen per CC