3 ms·

> But, no joke, an engine with just one moving part, and no transmission, has one heck of an advantage in maintenance and reliability. I guess you could say th

> But, no joke, an engine with just one moving part, and no transmission, has one heck of an advantage in maintenance and reliability. I guess you could say the same thing about the Wankel engine as well. The problem is that a traditional engine is tuned to work well enough within the life time of a car these days, so it isn't really a problem. Fuel economy wise though, the traditional piston engine outperforms the Wankel engine.

graycat 12y ago
The Wankel was asking a lot of the seals at the edges of its special rotor; apparently it was asking too much. > Fuel economy wise though, the traditional piston engine outperforms the Wankel engine. Yes, piston rings work a lot better than the seals Wankel needs. And, now with pistons, we can use high compression ratios; the Wankel seals have problems which get much worse at higher compression ratios. Why high compression ratios? Simple, classic Carnot cycle physics: The higher the compression ratio, the more get out of the fuel. Why higher compression ratios now? Because now we can have direct fuel injection, directly into the combustion chamber, much as in a Diesel. So, then can do all the turbo charging and supercharging want, for still higher total compression ratios because don't have to worry about pre-ignition from the air being too hot from the compression it got before entering the cylinder. So, don't have to use an intercooler to cool the compressed air. Why supercharging or turbocharging? Because get more power out of the same basic engine of pistons, cylinders, etc., that is, more power without more friction from larger pistons. So save on friction. So two savings for fuel economy: Higher compression ratios and less friction. That's what Volvo and others are doing: Small engine, lots of boost, good power and good fuel economy. I suspect a good way to get both range and fuel economy with an electric car is to have a hybrid: So, have an internal combustion engine drive a generator to charge the batteries. Here can have an advantage: The engine need run at only one power setting, its most efficient. Then for such an engine? Sure, use a gas turbine so that we are back to basically just one moving part. Yes, in an axial flow gas turbine, the part that rotates, at, say, 30,000 RPM or so, is darned expensive, but that part is also designed for the engine to have some ability to have a throttle. If give up the idea of a throttle and have only one power setting, then we can return to centrifugal force for both the compressor and the turbine. Then the metal for the high temperatures is expensive, so can use some ceramic. Now we're talking: Just one major moving part, cheap ceramic, centrifugal force, single power setting (where the aerodynamics for the compressor and turbine work best). Might get 200 HP in a small package. Then run it only when charging the battery. Then never bother plugging the car to charge the batteries. When driving around town, nearly never run the turbine. On the highway at 65 MPH, occasionally run the turbine. Blasting across, say, Nevada at 110 MPH, run the turbine a lot. At top speed of 150 MPH or so, sure, run the turbine 100% of the time and still have the battery run down. Sure, get some losses when generate the electric power, when stuff it into the battery, when draw it out of the battery, and when drive the electric motor. Yup, several losses.
- lloeki 12y ago
  > I suspect a good way to get both range and fuel economy with an electric car is to have a hybrid: So, have an internal combustion engine drive a generator to charge the batteries. Isn't that how the Chevy Volt/Opel Ampera is operating?
  - graycat 12y ago
    I suspect so, and for some other hybrids as well, but I don't think anyone is using a gas turbine yet except maybe in a hybrid for, say, a city bus.

graycat 12y ago

The Wankel was asking a lot of the seals at the edges of its special rotor; apparently it was asking too much. > Fuel economy wise though, the traditional piston engine outperforms the Wankel engine. Yes, piston rings work a lot better than the seals Wankel needs. And, now with pistons, we can use high compression ratios; the Wankel seals have problems which get much worse at higher compression ratios. Why high compression ratios? Simple, classic Carnot cycle physics: The higher the compression ratio, the more get out of the fuel. Why higher compression ratios now? Because now we can have direct fuel injection, directly into the combustion chamber, much as in a Diesel. So, then can do all the turbo charging and supercharging want, for still higher total compression ratios because don't have to worry about pre-ignition from the air being too hot from the compression it got before entering the cylinder. So, don't have to use an intercooler to cool the compressed air. Why supercharging or turbocharging? Because get more power out of the same basic engine of pistons, cylinders, etc., that is, more power without more friction from larger pistons. So save on friction. So two savings for fuel economy: Higher compression ratios and less friction. That's what Volvo and others are doing: Small engine, lots of boost, good power and good fuel economy. I suspect a good way to get both range and fuel economy with an electric car is to have a hybrid: So, have an internal combustion engine drive a generator to charge the batteries. Here can have an advantage: The engine need run at only one power setting, its most efficient. Then for such an engine? Sure, use a gas turbine so that we are back to basically just one moving part. Yes, in an axial flow gas turbine, the part that rotates, at, say, 30,000 RPM or so, is darned expensive, but that part is also designed for the engine to have some ability to have a throttle. If give up the idea of a throttle and have only one power setting, then we can return to centrifugal force for both the compressor and the turbine. Then the metal for the high temperatures is expensive, so can use some ceramic. Now we're talking: Just one major moving part, cheap ceramic, centrifugal force, single power setting (where the aerodynamics for the compressor and turbine work best). Might get 200 HP in a small package. Then run it only when charging the battery. Then never bother plugging the car to charge the batteries. When driving around town, nearly never run the turbine. On the highway at 65 MPH, occasionally run the turbine. Blasting across, say, Nevada at 110 MPH, run the turbine a lot. At top speed of 150 MPH or so, sure, run the turbine 100% of the time and still have the battery run down. Sure, get some losses when generate the electric power, when stuff it into the battery, when draw it out of the battery, and when drive the electric motor. Yup, several losses.

lloeki 12y ago
> I suspect a good way to get both range and fuel economy with an electric car is to have a hybrid: So, have an internal combustion engine drive a generator to charge the batteries. Isn't that how the Chevy Volt/Opel Ampera is operating?
- graycat 12y ago
  I suspect so, and for some other hybrids as well, but I don't think anyone is using a gas turbine yet except maybe in a hybrid for, say, a city bus.