3 ms·

Just like "good, fast, cheap: pick two" there's a similar rule in automotive tuning: "Fast, efficient, clean: pick two" VW decided to go for all three.

chao- 11y ago
That's an interesting comparison. What would it mean, from a mechanical or chemical perspective, for an engine (or the whole car?) to be both very fast and very clean, but not efficient? Does not the inefficiency also lead to a lessening of cleanliness? I know that would probably require defining "clean" as distinct from "efficient", I simply know very little about cars and so the fast+clean idea feels a little off, and I'd like to know where I'm wrong.
- ars 11y ago
  > and very clean, but not efficient ... Does not the inefficiency also lead to a lessening of cleanliness Not at all. You can burn tons of fuel, while making no pollution at all. It might not be efficient, but it will be clean. In a car, they use some of the energy to clean the waste product of burning the fuel, so that all that comes out is Water and CO2. But it costs energy to do this cleaning, it's easier not to. For an internal combustion engine higher temperature means more efficient, but higher temperature also makes more NoX (i.e. nitrogen that burned in air). So you can lower the temperature, or try to clean the exhaust.
- function_seven 11y ago
  > Does not the inefficiency also lead to a lessening of cleanliness? All depends on what we're measuring. In the case of VW, it's the NOx limits that they were cheating on. In order to reduce NOx, you can run a richer air/fuel mixture, which consumes more fuel and is thus inefficient. If you're instead talking about C02, then you're generally right. Efficiency and cleanliness are aligned. And my original comment could probably be rephrased as, "fast, clean, efficient, reliable, cheap: pick any three". But that doesn't have zing to it :-)

chao- 11y ago

That's an interesting comparison. What would it mean, from a mechanical or chemical perspective, for an engine (or the whole car?) to be both very fast and very clean, but not efficient? Does not the inefficiency also lead to a lessening of cleanliness? I know that would probably require defining "clean" as distinct from "efficient", I simply know very little about cars and so the fast+clean idea feels a little off, and I'd like to know where I'm wrong.

ars 11y ago
> and very clean, but not efficient ... Does not the inefficiency also lead to a lessening of cleanliness Not at all. You can burn tons of fuel, while making no pollution at all. It might not be efficient, but it will be clean. In a car, they use some of the energy to clean the waste product of burning the fuel, so that all that comes out is Water and CO2. But it costs energy to do this cleaning, it's easier not to. For an internal combustion engine higher temperature means more efficient, but higher temperature also makes more NoX (i.e. nitrogen that burned in air). So you can lower the temperature, or try to clean the exhaust.
function_seven 11y ago
> Does not the inefficiency also lead to a lessening of cleanliness? All depends on what we're measuring. In the case of VW, it's the NOx limits that they were cheating on. In order to reduce NOx, you can run a richer air/fuel mixture, which consumes more fuel and is thus inefficient. If you're instead talking about C02, then you're generally right. Efficiency and cleanliness are aligned. And my original comment could probably be rephrased as, "fast, clean, efficient, reliable, cheap: pick any three". But that doesn't have zing to it :-)