Hi,
Quote:
Originally Posted by chesterakl
There are a ton of things that the colder air/dense air can affect.
- Drag on the aerodynamic properties of the vehicle.
- Changes to fuel use due to the fuel/air mixture changes using denser air.
- The temperature of the fuel itself affects how it atomizes before combustion.
- Colder air going through the radiator and pulling more heat out of the cooling system, thus needing more heat input from the engine to maintain an optimum temperature. Normally not a real big deal on non-hybrids because they usually generate more heat than they need, but when the ICE of a hybrid kicks in, or it doesn't let you get into EV at all, only because the temperatures are too low for optimum operation - that's fuel used for things other than normal operation that would not be needed in warmer weather.
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Actually I have a Graham miniscanner in my Prius and was monitoring:
- ICE coolant temperature
- MG1 temperature
- MG2 temperature
At highway speed, 65
mph, and using a 'water noodle' lower grill block, the car reached thermal equilibrium within 30 minutes. Thereafter, the changing temperature effects were visible on in the MPG display. BTW, aerodynamic drag is proportional to the air density, which was a function of the air temperature. I was driving from one edge to the other edge of a high pressure sensor.
The fuel-air mixture is handled by mass-flow sensor and the Atkinson cycle pushed part of the charge from the hot cylinder back into the hot manifold. It is pretty well warmed up during the evaporation cycle. You're normally right about heat being needed at lower speeds but at 65
mph the energy demands provides a surplus of waste heat.
Bob Wilson