3 ms·

There's actually a subtle difference, with an ICE you pay for the larger displacement with more fuel usage at idle and inefficient RPM ranges(things like VVT he

There's actually a subtle difference, with an ICE you pay for the larger displacement with more fuel usage at idle and inefficient RPM ranges(things like VVT help mitigate it but physics is physics). For EVs you're largely just fighting against Ohm's law(constant voltage requires that you draw more amps which means resistance generates heat, etc) and to a lesser degree weight. Which has much less impact like you note. My basic understanding of ICEs is that they are most efficient when you can run them at a specific RPM(and tune for that RPM) which is why you see Diesel-Electric Locomotives where the ICE largely acts as a generator.

jacquesm 11y ago
> My basic understanding of ICEs is that they are most efficient when you can run them at a specific RPM(and tune for that RPM) which is why you see Diesel-Electric Locomotives where the ICE largely acts as a generator. That's spot on. This is why you can't use the cam from a generator on a car and vice versa (even if it is otherwise the exact same engine, such as with the Willy's engine). The cam on a generator will be very pointy to open and close the valves across a very sharply defined moment in the engine cycle, whereas on the car version the cam is much more smooth giving a wider operating range (but at lower efficiency). The reason why Diesel Electric locomotives use the electric motor to drive the wheels rather than using the diesel directly is twofold, one the efficiency that you already noted, the second reason is that the electric motor does not need a clutch and has a torque curve much better suited to getting a large weight accelerated (much like steam power is better than ICE's at this, it's the exact same reason).
- vvanders 11y ago
  Yup, was aware of point #2 as well. They mitigate that in part by backing up too(thus putting slack in the cars) before moving forward. Always fun to hear the cars going thunk, thunk, thunk as they get ready to head out.

jacquesm 11y ago

> My basic understanding of ICEs is that they are most efficient when you can run them at a specific RPM(and tune for that RPM) which is why you see Diesel-Electric Locomotives where the ICE largely acts as a generator. That's spot on. This is why you can't use the cam from a generator on a car and vice versa (even if it is otherwise the exact same engine, such as with the Willy's engine). The cam on a generator will be very pointy to open and close the valves across a very sharply defined moment in the engine cycle, whereas on the car version the cam is much more smooth giving a wider operating range (but at lower efficiency). The reason why Diesel Electric locomotives use the electric motor to drive the wheels rather than using the diesel directly is twofold, one the efficiency that you already noted, the second reason is that the electric motor does not need a clutch and has a torque curve much better suited to getting a large weight accelerated (much like steam power is better than ICE's at this, it's the exact same reason).

vvanders 11y ago
Yup, was aware of point #2 as well. They mitigate that in part by backing up too(thus putting slack in the cars) before moving forward. Always fun to hear the cars going thunk, thunk, thunk as they get ready to head out.