radiator design

[mshorter]

Before just giving you an answer, I would ask you to reconsider the source of the heat you are trying to reject. Is the heat necessary for rejection directly proportional to the RPMs of the engine? If not, then in what case(s) would it diverge?

I'm from Brown University and this is my second year on the team but my first year actually doing design work. I'm not a powertrain expert by any means, but I'm pretty sure that the engine power is divided among the exhaust, coolant/oil (someone else is doing oil on my team), and the drivetrain itself. Since horsepower is positively correlated with RPM, RPM should be the primary driver of heat to the radiator, but I'm having a hard time figuring out how that might be effected by other factors, unless running the engine at high rpm at idle means that power is going out the exhaust and water hose instead of the drivetrain. I can talk to our team's powertrain people about it.

[Swiftus]

Matthew - You have what sounds like a pretty fun project. I would like to you to remove some pressure from yourself by admitting now that you will never find an exact solution. It does not mean that you won't find a great solution for your car, it just means that it cannot be 'optimised'. Computers doing trillions of calculations in CFD still get it very wrong. Hand calcs with good factors of safety should be your primary driver on your design.

Additionally, have you started researching general engine theory or cooler design much? Back in the depths of this thread are a lot of good, free literature resources that may prove invaluable in your learning and understanding of your system. I know that a number of them have been helping me stumble through my formula career.

On to some fun stuff. You sound like you have heard the energy conversion in thirds assumption. The assumption goes, the amount of energy extracted from the fuel which is burning in a spark ignition engine is split evenly into 3 pathways: 1/3 is delivered as mechanical work via the crankshaft, 1/3 is moved through the exhaust, and 1/3 is emitted as heat into the cooling system. So, if you are seeing 75 HP at the crank, you have 75 HP to reject from your coolers. Thats (75hp x ~750Watts/hp) ~56000 Watts! Compare that to the amount of heat you can feel off the end of a 1500 Watt heat gun and you can see how big of a task the coolers have to do (56000/1500 ~37 Heat guns!)

So now you know the heat that needs rejection at maximum power.

Review the power and torque curves in the image below

http://image.sportrider.com/f/18817320/146_03+sportbike_performance_dyno_charts+yamaha_YZ F_r6_horsepower_torque.jpg

Does the power keeping going up for all RPMs? Do you think more or less heat is being generated when the power starts to drop?

If I were to tell you that RPMs are not indicative of heat emitted by the engine, what other parameter might be a better fit?

[sid]

hey we are using a cbr 250 engines and cbr 600 radiators but cannot decide on the fans to be used any suggestion on how to go about it

[jlangholzj]

Matthew - You have what sounds like a pretty fun project. I would like to you to remove some pressure from yourself by admitting now that you will never find an exact solution. It does not mean that you won't find a great solution for your car, it just means that it cannot be 'optimised'. Computers doing trillions of calculations in CFD still get it very wrong. Hand calcs with good factors of safety should be your primary driver on your design.

Additionally, have you started researching general engine theory or cooler design much? Back in the depths of this thread are a lot of good, free literature resources that may prove invaluable in your learning and understanding of your system. I know that a number of them have been helping me stumble through my formula career.

On to some fun stuff. You sound like you have heard the energy conversion in thirds assumption. The assumption goes, the amount of energy extracted from the fuel which is burning in a spark ignition engine is split evenly into 3 pathways: 1/3 is delivered as mechanical work via the crankshaft, 1/3 is moved through the exhaust, and 1/3 is emitted as heat into the cooling system. So, if you are seeing 75 HP at the crank, you have 75 HP to reject from your coolers. Thats (75hp x ~750Watts/hp) ~56000 Watts! Compare that to the amount of heat you can feel off the end of a 1500 Watt heat gun and you can see how big of a task the coolers have to do (56000/1500 ~37 Heat guns!)

So now you know the heat that needs rejection at maximum power.

Review the power and torque curves in the image below

http://image.sportrider.com/f/18817320/146_03+sportbike_performance_dyno_charts+yamaha_YZ F_r6_horsepower_torque.jpg

Does the power keeping going up for all RPMs? Do you think more or less heat is being generated when the power starts to drop?

If I were to tell you that RPMs are not indicative of heat emitted by the engine, what other parameter might be a better fit?

Awesome points!

Also, (directed towards matthew) how does that "power" output change with load on the engine? Say that I personally can bench-press ~200lbs. If I press ~50lbs I still have the same potential to lift those 200lbs but will be sweating considerably less than if I were lifting 200lbs....see where I was going with than analogy? Hopefully that should answer your "dynamic vs static" event question.