improved sfc from charge air cooling

[opsguy]

are there any rules of thumb on what benefit I could reasonably expect in SFC by lowering charge air temperature by 10 decgrees C - 4 MW land based diesel engine running on 180cst HFO 1200M above sea level

 

[black2003cobra]

Don't see why it would matter. Diesels run lean and without a throttle. Lots of extra air, and just add fuel to meet needed torque output. So fuel consumption just depends on how much is required to meet torque/power demand.

 

[dgallup]

You will definitely see improved BSFC with lower charge air temp. I ran extensive dyno mapping of BSFC vs many variables including charge air temp in a previous job. It was a significantly smaller motor, about 1/10th the power rating, but the trend should be the same. The test was also not at altitude but again I think the trend is the same. I'm assuming this is a 4 stroke intercooled turbo diesel.

Someone may have an equation for you but I'll try to find my test data, I think I have the it at home.

 

[black2003cobra]

Go figure. Interesting. A couple possible reasons that came to my mind for improved efficiency were, 1) more air for a given amount of fuel means cp/cv of the mix gets higher and closer to that of just air, and 2) lower starting temps mean lower temps throughout the cycle, which would reduce heat loss. But I wouldn't think a drop of 10C would make a big difference in those couple things.

There is a graph in Heywood, (Fig. 15-24), which shows improvements in efficiency with AFR. Going from, say, 27C to 17C would mean a mass-flow rate improvement of about 1.7%, (sqrt[300/290] - 1), so for a given fuel-flow rate, AFR would go up by that percentage. From that graph in Heywood, doesn't look like that would be a significant change at all.

But maybe there are some other reasons for it? Look forward to seeing the data.

 

[ivymike]

I think it may depend on what's driving your injection timing. If you're unable to advance timing because of a NOx limit (emissions), then 10deg cooler air may let you get a few degrees injection advance, which could reduce your sfc by several g/bkw-hr. If you're up against a cylinder pressure limit, then the denser charge air might cause you to violate that limit (or retard timing).

 

[black2003cobra]

I hadn't considered injection timing, thanks Mike.

(And OP...please scratch my comments regarding figure referenced. I misread it!)