Diesel air intake warm or not

[Piwoslaw]

Originally Posted by vacationtime247

My idi 2.0L Mazda RF diesel engine has an air heater plate between the intake and the air filter. Get's pretty warm to the touch.

Intake air heaters before or inside the filter are usually for cold starts, and (in newer diesels) for burning out the DPF.

[Tesla]

Think I've said it before, cold air intake is generally preffered for diesels, but that is within reason, depending on the engine tune & fueling map.
I think ideally an intake that could maintain a constant temp year around would be best, and then adjust the tuning, intake, exhaust etc. around this particular temp range.
Getting more air into a diesel increases efficiency until the point is crossed where pumping losses start to pull the power curve back down.
Warming air up from below 0C will definately improve combustion efficiency, but once you get over 50C, then you will start to have a significant effect on the actual air mass going to the cylinder and this will have a major effect on both efficiency as well as power.
Absolute Zero is -273C, so if the same pressure & volume is maintained, going from 0-50C will be a decrease of about 18% air mass actually entering the cylinder.

[Diesel_Dave]

Originally Posted by Piwoslaw

Intake air heaters before or inside the filter are usually for cold starts, and (in newer diesels) for burning out the DPF.

Yes, the intake heater is for cold starts. My truck has a grid heater. It's an alternative to glow plugs for a cold start. Mine comes on whenever the intake manifold temperature upon turning the key on is below 66 deg F. I've never heard of it being used for DPF regens.

Warming the air is strickly to help the engine start, though--not to improve efficiency. A diesel is compression ignited, so when it's really cold, sometimes the pressure at the end of the compression stroke isn't enough to raise the temperature up to the point where it will ignite the first fuel injection. That's where the grid heater/glow plug comes in--warming the air prior to compression results in higher post-compression temperatures, therefore you can get ignition. This is also why higher compression ratio engines tend to start better in cold weather. Once you get the first few firing events to take place the cylinders, head(s), etc. warm up enough that the starting aids aren't needed anymore.

That's why I said colder air is alwars better--within reason (until you get down where you're really affecting ignition delays.

[oil pan 4]

For every degree (F or C it doesn't matter) you increase intake air temp your EGT see the same increase.
With DPF you need as much EGT as you can get to burn off the soot, I wouldn't be surprized if some diesels fired up their intake heater to help burn off the DPM.

My solution, ax the DPF. On larger diesels it can take up to 17 liters, 4+ gallons of fuel, $16 worth of fuel, to torch the DPM off the DPF.
This is a great deal for the government, they get over $2 in taxes for 0 miles driven on your part every time your DPF lights up.

[Piwoslaw]

Originally Posted by oil pan 4

For every degree (F or C it doesn't matter) you increase intake air temp your EGT see the same increase.
With DPF you need as much EGT as you can get to burn off the soot, I wouldn't be surprized if some diesels fired up their intake heater to help burn off the DPM.

According to this site, normal exhaust gas temperatures in a turbodiesel are above 200°C, natural regeneration of the DPF happens at 400°-500°C, while 500°-600°C is needed for forced regen. Many things are done to get EGT that high, among them is warming of the intake air. Euromodder mentioned that a heater in the air filter box may be responsable for the higher temps in his intake he sees during regen.
Some TDs also have an intercooler bypass valve keep the post-turbo air warm, and sometimes restrict the intake to allow more EGR into the cylinders.

But this is all for DPF regen, not "normal" operation, so emissions in this case are more important than fuel consumption.

[AXMonster]

For modern cars the old rule of fuel in = power out still applies. The difference that air intake temperature makes is in the variable turbine geometry turbo.

When the engine is running the sensors feed back all the data to the ECU, which calculates the boost requirement based on an air density map. Basically the VGT is set to produce sufficient boost based on the fuel demand and the density of the incoming air. If the air is warm it will need more boost pressure to reach the density to ensure no smoke. Conversely if it is cold it will require a lower pressure.

This has a knock on effect on the pre-turbine exhaust pressure, and in fuel economy terms the amount of work the piston has to do to push the exhaust gasses out of the cylinder and past the exhaust turbine. If the turbine does not need to drive the compressor produce as much boost pressure then the amount of work done on the exhaust stoke is less. So..... lower air intake temperature (post intercooler) = less energy absorbed on the exhaust stroke.

[Vekke]

Here you can find also some information on the topic:
The Common Rail - where maritime professionals meet • The forum area of www.dieselduck.net

[ecomodded]

I read that Vekke, My perception is that the hotter the air the more moisture it can hold. Cold air cannot hold as much water as warm air so cold air would contain less moisture.
I must of missed the point.

[rmay635703]

Originally Posted by ecomodded

I have read that diesel motors run most efficiently on cold air and I have read that they run most efficiently on warm air.
Most who drive a diesel notice mpg losses threw winter. Could the cold ambient outside air be responsible ? or has it nothing to do with cold air and more to do with winter mixed diesel.

Here is some food for thought, if running warmer intake air causes higher combustion chamber temperatures could it mean a more complete (hotter) burn occurred?.

I would bank more on increasing the temperature of the fuel not the air.

Combined with a decent fuel water separator and filter there are many more possibilities/benefits with heated fuel.

Another good suggestion would be to preheat the motor and transmission with a block or blanket heater of some sort. That helps reduce the winter FE hit.

Cheers

[Duffman]

Ive been watching my scangauge since reading this a few months ago and I can see no real difference at idle and my intake temperatures go up 10C or more when sitting still and there seems to be no change at all (there is scatter in the readings). Biggest two that I see are both Oil and Coolant making a big difference (even 10C there).