Diesel - Warm or Cold?

[PAFirefighter11]

With a diesel motor is a warm or a cold air intake going to provide better fuel economy? I've seen mixed responses on some other forums so I figured I'd post here. Does anyone have personal experience with this?

Thanks.

[arcosine]

My guess is warm air in the winter would be better, try it.

[Jyden]

Originally Posted by PAFirefighter11

With a diesel motor is a warm or a cold air intake going to provide better fuel economy? I've seen mixed responses on some other forums so I figured I'd post here. Does anyone have personal experience with this?

Thanks.

Cold - all the time, the colder the better. Cold is more oxygen for the combustion.

[NachtRitter]

Yep, colder is better... no WAI for the TDI.

[arcosine]

Originally Posted by NachtRitter

Yep, colder is better... no WAI for the TDI.

So you are saying that diesels get better mpg in the winter, -0F temperatures? I find that hard to believe.

[PAFirefighter11]

Originally Posted by arcosine

So you are saying that diesels get better mpg in the winter, -0F temperatures? I find that hard to believe.

I think the winter thing is hard to determine because they switch from #2 diesel to the winter blend of #1 or a mix of both. This reduces FE in and of itself.

[NachtRitter]

Originally Posted by arcosine

So you are saying that diesels get better mpg in the winter, -0F temperatures? I find that hard to believe.

No, I am not saying that and I did not say that. The engine itself needs to be warm while the intake air needs to be cold. In the winter, the diesel engine has a hard time getting warm; if the engine can't get up to operating temp there will be a negative effect on FE. However, a WAI still doesn't help; the biggest contributor to keeping the engine temp down is the radiator/coolant. So to get the best winter FE you want to have an engine block / coolant heater, a grill block, and no cabin heat. And cold intake air so that you get the most complete combustion (and therefore best power output for the fuel consumed). This is particularly important for a turbodiesel since the intake air is heated by running through the turbo.

Of course there are additional contributors to lower FE in winter, such as the fuel difference mentioned by PAfirefighter. I'd guess running without cabin heat might be unacceptable to some drivers too.

A study of the effect of intake temp on a normally aspirated diesel engine was done and is available here: http://www.oricpub.com/SE-1-1-2-3.pdf

[arcosine]

So you are saying that more air in the engine the better the mpg, well then why not have a big engine that sucks a lot of air in and that should get better mpg than a small engine that sucks less air in at a given output. I still don't follow the logic, since at partial throttle there is more excess air in a Diesel and less fuel but yet the sbfc is not better.

In the report that you site, they don't mention changing the injection timing for optimum torque at the different temperatures tested.

[NachtRitter]

Sorry, not seeing how you're coming to the conclusion that a bigger engine should get better mpg than a smaller engine based on the idea that higher air density is beneficial for FE. It's the ratio of air to fuel; the larger engine would presumably consume more fuel along with more air so the ratio would essentially be the same as the smaller engine.

Is it your belief that warmer intake air in a turbodiesel will get you better FE than cooler intake air? If so, do you have some data supporting that? Does that mean turbodiesels should not be seeing a benefit from intercoolers?

[TexasCotton]

cold air intake is way way over sold. Ebay has plenty of them. The benefit is marginal if not nothing on some vehicles