New Radiator Thread

[fart can]

For those of us who have read the 5 year, 12 page thread...

I have a question.

According to the table on page 674 of 'Internal Combustion Engine Fundamentals', the coolant load, Qcool, should equal anywhere between 17-26% of the fuel heating value at maximum power.

I have two problems with this:

(1) Next to Qcool is Pb, which stands for brake power. It claimes that Pb ranges from 25-28% of the fuel heating value. This implies that Qcool approximately equals Pb. This violates the '1/3 HP' Law of Cooling. I am correct in reading that brake power roughly equals coolant load?

(2) The table does not specify which fuel heating value. There are upper and lower heating values ( LHV = 44 MJ/kg) for fuel listed in same book's table, and there is also a LHV for a stoich. mixture, listed as 2.83 MJ/kg. Which one should be used? The stoich value makes sense, but read on...

In the same book, on the same page, it reads that mdotfuel * QLHV * 26% = Qcool. This makes sense, until I introduce my mass flows for fuel.

According to Virtual 4 Stroke, our max fuel flow rate is 4.98 g/s. Applying this to the coolant load equation, using QLHV=44 MJ/kg, I get a coolant load of 57 kW. Performing a reality check, I do 57*3*1.34 = 229 HP. It is obvious there is something wrong.

Using the LHV of the stoich mixture, 2.83 MJ/kg, I get a coolant load of 3.66 kW. Converting to HP, I have 3.66*3*1.34 = 14.7 HP. This is also obviously wrong. Especially since Virtual 4-Stroke claims a peak power of about 85 HP for this fuel flowrate.

Can someone tell me what I'm doing wrong?

[Chris Allbee]

44 MJ/kg = 44000 J/g
44000 J/g * 4.98 g/s = 219,120 J/s
219,120 J/s * .26 = 56971.2 J/s (Watts)
56971.2 J/s * 1 hp/745.7 J/s = 76.4 Hp

76.4 Hp...Where's the problem? That sounds reasonable for a cooling load...

[fart can]

Thanks for braving a response Chris. Check this out:

From http://fsae.com/eve/forums/a/tpc/f/125607348/m/6746055451/p/5

jonno claims "Engine heat rejection is about 1/3 max engine power".

Assuming this max engine power is brake horsepower, then that would put my engine, with our calculated 76.4 HP of coolant load, making 3*76 = 228 HP . Not only is this number rediculous, but my engine simulator claims a peak corrected peak of about 85 HP.

I don't know where this 1/3 HP figure comes from for estimating coolant load, and it doesn't seem anyone else does either. The question has been posed on the 12 page 'radiator design' thread.

Any thoughts?

[Brett Neale]

The 1/3 max power theory comes from the total maximum power possible for the given amount of fuel injected. Approximately 1/3 of the power goes to drivetrain/friction losses, 1/3 goes to the cooling system and 1/3 goes out as usable "brake" power. My interpretation is that the cooling load is the same magnitude as the brake horsepower, so say your engine makes 50 brake kW then you have 50kW of heat rejection to deal with.

Anyone agree or am I interpreting this wrong?

[Matt N]

I'm not sure if this idea has been brought up before in the radiator thread but here is another idea.

Go through past enduro results and look at the fuel that was used. You should be able to deduce average engine horsepower by finding the heat energy of x.xx gallons of gasoline over the distance and time of the endurance event. As folks above stated you can expect your engine to reject 30-35% of its heat through the coolant.

Very basic (not really engineering) but it will get you in the ballpark.

Matt

[fart can]

If you have a copy of 'Internal Combustion Engine Fundamentals' by Heywood of MIT, you will find that this is exactly what the table I mention implies (table 12.1 on page 674).

He gives (percents are of fuel heating value):

brake power as 25-28%

coolant load as 17-26%

auxililary drives and friction loss as 3-10%

chemical enthalpy flux due to incomplete combustion as 2-5%

and finally sensible exhaust gas enthalpy as 34-45%.

This is exactly what you said Brett. This makes sense from a thermodynamic standpoint, where you have ballpark efficiency of about 30%, which is the ratio of actual power / available power.

The only reason I am freaking out is because this conflicts with the seemingly generally accepted 'coolant load is 1/3 brake horsepower', which I refer to as the '1/3 HP Law of FSAE Cooling'.

In short, I agree with Brett, but our thoughts conflict with the rule of thumb 1/3 HP Law of FSAE Cooling.

Please don't be shy with responses, we are all learning here.

[ad]

Originally posted by fart can:
If you have a copy of 'Internal Combustion Engine Fundamentals' by Heywood of MIT, you will find that this is exactly what the table I mention implies (table 12.1 on page 674).

He gives (percents are of fuel heating value):

brake power as 25-28%

coolant load as 17-26%

auxililary drives and friction loss as 3-10%

chemical enthalpy flux due to incomplete combustion as 2-5%

and finally sensible exhaust gas enthalpy as 34-45%.

This is exactly what you said Brett. This makes sense from a thermodynamic standpoint, where you have ballpark efficiency of about 30%, which is the ratio of actual power / available power.

The only reason I am freaking out is because this conflicts with the seemingly generally accepted 'coolant load is 1/3 brake horsepower', which I refer to as the '1/3 HP Law of FSAE Cooling'.

In short, I agree with Brett, but our thoughts conflict with the rule of thumb 1/3 HP Law of FSAE Cooling.

Please don't be shy with responses, we are all learning here.

This "1/3 Law" is actually a load of bs. I would pay no attention to it unless you want to find yourselves in a load of hurt during an enduro.

Heat dissipated to the water jacket varies significantly depending on operating conditions. Even the size of your radiator...

[Pete M]

1/3 of total thermal energy going to the cooling system is reasonable. Sizing a core for heat dissipation equal to power output (each 1/3 of the thermal energy produced by burning the fuel) will make it a bit oversized though, as you're sizing your cooling system assuming constant WOT peak power. In reality, it'll see considerable part throttle time too. The 1/3 of brake rule is an attempt at rule-of-thumbing this, but it's dodgy, the true fraction needed is heavily dependent on track and driving style.

[Maverik]

The best thing you could possibly do is put some temp sensors on your car or build a radiator dyno and figure out what the actual heat load is. You think the heat load for an f1 engine is the same percentage as a fsae one because a book has some general percentages in it?

[fart can]

Originally posted by Maverik:
The best thing you could possibly do is put some temp sensors on your car or build a radiator dyno and figure out what the actual heat load is. You think the heat load for an f1 engine is the same percentage as a fsae one because a book has some general percentages in it?

Probably different, but unless you can prove otherwise, I'd stick with the book as a starting point.

[fart can]

The 1/3 of brake rule is an attempt at rule-of-thumbing this, but it's dodgy, the true fraction needed is heavily dependent on track and driving style.

I see what you are saying. I'm guessing my fuel flowrates from virtual 4 stroke assume WOT. I'd have to get with the lap sim to check throttle position stats, I think it can do that.

Do you know of any good papers correlating coolant load to tracks or should i just use intuition?

Thanks for the response

[fart can]

Originally posted by ad:
This "1/3 Law" is actually a load of bs. I would pay no attention to it unless you want to find yourselves in a load of hurt during an enduro.

Heat dissipated to the water jacket varies significantly depending on operating conditions. Even the size of your radiator...

Do you have any sources you could point me to, Andrew?
Thanks

[ad]

Originally posted by fart can:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by ad:
This "1/3 Law" is actually a load of bs. I would pay no attention to it unless you want to find yourselves in a load of hurt during an enduro.

Heat dissipated to the water jacket varies significantly depending on operating conditions. Even the size of your radiator...

Do you have any sources you could point me to, Andrew?
Thanks </div></BLOCKQUOTE>

Yeah sure;

- Internal Combustion Engine Fundamentals (Heywood)
- Compact Heat Exchangers (Kayes and London)
- Review of Engine Cooling Techniques for Modern Engines (IMechE download)
- The Effect of Changes in Ambient and Coolant Radiator Inlet Temperatures and Coolant Flowrate on Specific Dissipation (SAE download)
and
- 2005 Ford GT- Maintaining your Cool at 200 MPH (SAE download)

They should get you started http://fsae.com/groupee_common/emoticons/icon_smile.gif

[fart can]

Originally posted by ad:
Yeah sure;

- Internal Combustion Engine Fundamentals (Heywood)
- Compact Heat Exchangers (Kayes and London)
- Review of Engine Cooling Techniques for Modern Engines (IMechE download)
- The Effect of Changes in Ambient and Coolant Radiator Inlet Temperatures and Coolant Flowrate on Specific Dissipation (SAE download)
and
- 2005 Ford GT- Maintaining your Cool at 200 MPH (SAE download)

They should get you started http://fsae.com/groupee_common/emoticons/icon_smile.gif

Thanks Andrew.

I was able to find all of the papers. Already have the books. I've only browsed the first two chapters of Kays and London, did you find any coolant load information in their book or is it all just heat exchanger info?

Thanks again