cooling for important

[foza_11]

what is the inlet temperture for air in silver stone ?is it 40 celusis ?
also,the maximum Q is 18 KW ?

[foza_11]

what is the inlet temperture for air in silver stone ?is it 40 celusis ?
also,the maximum Q is 18 KW ?

[whiltebeitel]

40* C is a decent upper limit, though I've never been to Siverstone myself. As for Q, I assume you mean required heat rejection? In that case, you can assume that the rejected heat should be at least equal to the peak power of your engine.

That should be a decent start, if I understand you correctly.

[Dart]

According to me, assuming d inlet temp as 40 C and designing for the heat rejection of max engine power will get your system over designed. Also how much heat has to be rejected will also depend on the weight of the car (load the engine is carrying) and also how much rich or lean the mixture is. Our radiator had pretty tough time when our car was running very lean and the temps were steadily rising.
Please correct me if m wrong

[Rex Chan]

Running leaner may initially get you hotter EGT, but past a certain point you're putting in less fuel, so less energy. The only reason to get hotter engine coolant temps would be the exhaust port transferring heat to the water jacket.

I would design for a 40C day. The rule of thumb is that 1/3 of fuel energy goes into mechanical power, 1/3 into the cooling system, and 1/3 into the exhaust. Unless you run at peak power all the time, the heat rejection needed is less than the peak power of your engine. How much less is up to you to decide...but you should be able to do some good estimations, even without a car/data.

[Wesley]

If your reply to the judges question "How did you size your radiator" is "We used the 1/3 rule" It better be followed up by "as a starting point for further testing and calculation."

Every time I mentioned 1/3, eyebrows shoot up waiting for a real answer. Whether it's fin density calculations or empirical heat rejection numbers from a dyno or test setup, you need numbers.

I used super-long dyno pulls from our car on a road car inertia dyno to calculate our engine heat rejection to the coolant at 100% throttle. Plotting coolant temperature knowing system volume and time elapsed, heat transfer to the coolant is easily calculable. We could start a pull at 170F and the temp would climb to 200F at the end of the pull. Disable the fans until that temp is reached and you have quantifiable power into the coolant, which was actually very close to engine power output (and the subsequent 1/3 rule by back-calculating from BSFC and power numbers)

Then figured how much load we were actually using on an average lap using TPS histograms. I scaled it roughly proportionally to TPS on an average course, with a minimum we determined at high idle, then considered average airspeed and heat rejection at that speed. (Using averaged data from previous cars) Sizing the radiator to reject heat at the same average rate per lap was enough to keep it running cool - plus one other factor.

Short term fluctuations (heavy-load straights and tight sections) were "absorbed" by sizing the cooling system volume to take in energy above the rejection limit without going over a specific design temperature. The system volume was designed to be capable of running two autocross laps without going over 210F even with no heat transfer from the rad.

There are better ways to model your rejection, but this is a good way to get a realistic ballpark when you're choosing from a handful of radiators.