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Old 04-14-2022, 02:17 PM   #120 (permalink)
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Originally Posted by aerohead View Post
On purpose, I gave a math breakdown so everyone could learn to 'fish'.
I'd like you to see if you can figure the new numbers.
If not, I jump in.
1) The aero power varies as the Cd at any given speed.
2) If you already know the Cd, and the aero power at the target speed, multiplying the original aero power, by the fraction created when the new Cd is divided by the 'original' Cd, will spit out the new aero power.
3) Rolling-resistance power never changed, so that's just added back for the total Road Load horsepower.
4) Total efficiency ( 95% ) didn't change, so dividing by that gives you the ' brake-horsepower equivalency ( Bhp-e ).'
5) Bhp-e multiplied by it's conversion constant ( 2546-Btu/hp ) yields your Btus per hour.
6) I allowed a thermal efficiency for the IONIQ's engine @ 40% ( 60% of the heat energy lost to cooling and exhaust ). So the Bhp-e divided by 40% (0.40 ) gives gross Btus available from the gasoline.
7) The gross Btus/hour divided by the specific heat content of 111, 836- Btu/gallon gives your new gallons/hour.
8) You're still going 80-mph.
9) 80 mph divided by your new gallons per hour = your new mpg.
This is an 'energy-balance' method of estimating, same as Chrysler Corporation used to calculate the aerodynamics of their 1934 DeSoto Airflow mule's modifications.
It's actually more simple to do than to explain.
I use a cheap CASIO, scientific pocket calculator from the thrift store, with ten decimal point accuracy and a single memory.
Once a value is obtained, it's used for the next operation, all the way through.
How do I know my aero power?
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aerohead (04-14-2022)