Why do diesel cars get good gas mileage?



  1. 0 Votes

    The Helium site has answered this well.

    In sum, diesel fuel is more powerful than gas, and when it ignites in the cylinder fumes — the whole cylinder fumes — explode all at once. That’s because the whole volume of gas has reached a critical state. With gas, the explosion only happens because a spark is ignited at one end. The resulting explosion doesn’t quite finish by the time it’s necessary open the cylinder and vent the (mostly) combusted gas.

    When the Helium article was written, one of the big downsides of diesel wasn’t recognized: Diesel exhaust is far more carcinogenic than gas exhaust.

    • 0 Votes

      I made a slight mis-statement that I can’t correct in the text, now. Darn, I almost had it. (“Gas” has two meanings, and they got slightly confusing, as written.)

      The third sentence would be better as: “That’s because the whole cylinder of gaseous diesel has reached a critical state.”

      The idea is that when a chamber of gassy stuff is compressed, it’s all compressed equally. So when one part is ready to blow, the whole thing is ready to blow.

      But gasoline never gets to such a state. To explode, a compressed cylinder must be set off with a spark. That only happens at one end of the cylinder, and it takes a small, but significant, amount of time for the fire to reach the other end.

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