Gasoline Power Pack Calculations

A project log for Power Pack: Diversifying the Automobile

Powering the future is about diversifying our energy sources, including the vehicles that power or lives.

james-neeJames Nee 04/23/2016 at 22:320 Comments

Before going forward and designing the gasoline combustion engine module, I wanted to take a moment and think through the energy requirements and use that to drive the sizing of the engine.

My working theory is that to maintain a cruising speed of 100 KMPH (roughly 60 MPH) on a flat grade would require something on the order of 30 KW with an "average" vehicle (drag coefficient, weight, rolling resistance). If that is true, then a 40 HP engine (roughly 30 KW) would be enough to power the vehicle. Now note this is to maintain a cruising speed. Acceleration is a separate case and needs to be handled by studying the expected duration and magnitude of acceleration and to size the engine and capacitor banks accordingly. That is a much more complex issue and will be looked into a future time.

For now, I want to present a back of the envelope approach as to how I am viewing the issue and to see if my theory that a 40 HP engine will be sufficient to cruise at highway speeds.

Weight of the vehicle - 1850 kg

Drag coefficient of the vehicle - 0.35

Rolling Resistance of tires - 0.03

Distance traveled per second is 27.78 meters/second (100 Kilometers per hour)

Power consumed to overcome rolling resistance = rolling resistance * normal force * distance traveled per second

0.03*1823.9 kg *9.8 m/s^2 *27.78 m/s = 14896.37 J/s

Distance traveled per second is 27.78 meters/second

Power consumed by drag = 0.5*density of air (assuming 25 C)*velocity of the object (assuming still air)*area exposed to oncoming air*drag coefficient * distance traveled per second

0.5*1.1839 kg/m^3 * (27.78 m/s)^2* 3 m^2 * 0.35 * 27.78 m/s = 17766.82 J/s

14896.37 + 17766.82

Overall power consumption to maintain 100 KMPH = 32663.19 Watts or roughly 32.6 KW