At 05:27 PM 6/4/99 -0400, Michael S. Lorrey wrote:
>
>The turbines that the Army is testing for use by infantry are something
like 10
>watts per cubic inch. I wonder how the will compete with those new
radioactive
>powder plasma/dielectric batteries which supposedly have phenomenal power
>densities.
>
Concentrated power is a great thing - but military hardware is not often the most efficient thing around - it's more important to get the power quickly than cheaply..
The only radioactive 'batteries I know of are either thermionic or collect beta particles (very low current at a few thousand volts). Is this something new?
>>
>> Oh, a non-production room temperature cells could have well
>> beyond 90%. And electrical motors with 98% efficiencies are not
>> unheard of. Notice that Carnot machines will never make more
>> than 37%. A real-world car does much, much worse.
>
>Actually, current econo-speck car engines are at least 46% efficient, but the
>transmission and rolling and aerodynamic drag will drop it down to the 14-24%
>efficiency range. Even an electric car, all told, has a 30-45% efficiency.
>
Far as I know, Carnot engines are the at the theoretical maximum efficency - and in the real world cannot be produced. Some turbine cycles come close, though.
All automotive engines currently in production use the Diesel or Otto cycles - both are much less efficient that Carnot - and the best ceramic Diesels I have read of are around 30% efficient. These were made by Ford for the Army, and had no cooling system other than radiation from the cylinders, which ran at red heat. Hardly a low IR signature power source...but then I have never sean a 'stealthy' tank...
The gear box in a well designed car is better than 80 percent efficient, and rolling friction has been dropping steadily with new tire designs. Some body designs have extremely low drag coefficients at normal highway speeds - the reason most new cars look like rolling turds - that shape cuts the air best. The 14% overall fuel efficiency I can believe for a gasoline powered car, but 30-45% seems way too low for electric, unless you are figuring in lots of power accessories. When you say 'all told' are you including power generation and trarnsport losses?
Chuck Kuecker