Quote:
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.
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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.