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Old 09-14-2015, 10:55 AM   #1 (permalink)
MetroMPG
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Location: 1000 Islands, Ontario, Canada
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Blackfly - '98 Geo Metro
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Why hydrogen powered cars will have poor drag coefficients

Why? Well, have a gander at the gaping maw on this thing:


(Toyota Mirai hydrogen vehicle: a face only a mother could love)

Hydrogen vehicles need big grilles for cooling and also to take in air to process in the fuel cell:

Quote:
...cooling is a challenge, because fuel cells run at far lower temperatures--perhaps below 100 degrees Centigrade--than do internal-combustion engines.

The huge temperature differential between ambient air and the temperature of the engine coolant means [IC] engines are easy to cool: You can shed heat more easily from a given amount of airflow.

To shed heat from the [fuel cell] stack coolant at the lower temperature differential requires a greater amount of airflow--hence the large cooling inlets.
Source: 2016 Toyota Mirai Hydrogen Fuel-Cell Car: A Few Things We Noticed

And the Mirai's drag coefficient?

0.293

Oof! Not exactly class-leading. In fact, pretty far from class-leading.

One of the great things about (battery) electric cars is they don't need big cooling systems or exhaust systems, so you can dramatically cut drag using smooth underbodies and no (or much smaller, or fake) grilles.

Tesla Model S is a good example:



The Model S actually has a pretty big grille on its snout, but it's fake. It's just there for styling.

The car's 0.24 drag coefficient is actually top of the class for a production vehicle.

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