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Old 07-14-2010, 05:04 PM   #1 (permalink)
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Do you like your Diesel warm or cold ?

Quick and simple question - WAI for a Diesel - good idea or not ? I've seen a few posts that suggest WAIs for diesels are either a good idea and to be encouraged, or a bad idea that will cause really poor FE.

Examples include :

this from ConnClark where he suggests WAI for Diesels is not good

and

this where Piwoslaw is thinking of bypassing his intercooller.

What is the truth, anyone know before I block my grill ?

Apologies if I am missing something fundamental, it wouldn't be the first time.

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Old 07-14-2010, 08:18 PM   #2 (permalink)
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The Otto cycle requires an A/F ratio close to stoichiometric to run. If you want less fuel, you can lean it out some, but you really need to have less air flow into the cylinders. One way to do that is to warm up the intake charge and make it less dense.

With the Diesel cycle, it will run with a much wider range of A/F ratio, and there is no need to reduce airflow into the cylinders. A WAI should do either nothing, or possibly reduce efficiency if there isn't enough air to burn all the fuel.
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Old 07-14-2010, 08:35 PM   #3 (permalink)
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Warm air, being less dense, will reduce the smoke limit and overall power.
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Old 07-15-2010, 12:00 AM   #4 (permalink)
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Don't bother. A diesel isn't throttled, so there's nothing to gain in terms of pumping losses. The warmer, less dense air simply reduces the amount of fuel that can be burned fully (any more and it starts smoking), meaning you get less power, and the same mpg.
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Old 07-15-2010, 01:24 AM   #5 (permalink)
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GO COOL.

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Old 07-15-2010, 03:49 AM   #6 (permalink)
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I'm also in the CAI group, just to make things straight. My intercooler bypass idea is mostly for quicker warm-up. At load the intake air would go through the IC. My grille block has two independently operable openings, for the IC and for the radiator, and the latter gets opened much less often than the intercooler side.

Now that you've started this thread...
I wonder what the best temperature for the engine itself is? During normal driving my coolant temperature is 78-80C (172-176F), rises to 95-105C (203-221F) in hot weather, stop&go traffic, or hillclimbing. The fan is supposed to kick in at 95 (1st speed) and 105 (2nd speed). When the fan was disconnected the temperature once rose to 115C (239F) but nothing happened. So my question is: Does a diesel like to be warmer (like above 90C/194F), or should I try to keep it closer to 80C/176F?
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[Old] Piwoslaw's Peugeot 307sw modding thread

Last edited by Piwoslaw; 07-15-2010 at 09:52 AM.. Reason: Added F
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Old 07-15-2010, 04:13 AM   #7 (permalink)
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Piwoslaw - thanks for clarifying - I will leave a gap in the block for the intake.
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Old 07-15-2010, 07:03 AM   #8 (permalink)
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As ambient temp drops the air is more dense, and when it really gets cold like 40 below
(farenheit and centigrade are both the same temp at 40 below so it does'nt matter), diesels need some real innovative treatment to start at all.

I would say if you have plenty of power and a precise method of measuring intake temps, it would be a worthwhile experiment.

The benefit would be (more than likely) at lower ambient temps compared to atmospheric.

It may be significant when the differences between the two become significant, but if you can control the incoming air temp fairly precisely then you can tell us what you found.

It might be surprising.

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Old 07-15-2010, 07:35 AM   #9 (permalink)
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What about the effects of warm air on combustion burn speed? I believe this is a benefit in gassers.
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Old 07-15-2010, 08:22 AM   #10 (permalink)
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Diesels like cold air and hot coolant. Most modern diesels use 195* thermostats, a few even use 203* (common performance mod on powerstrokes). In a diesel, the hotter engine burns fuel better, giving better power and mpg, as long as the intake charge is cool enough.

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