Re: Fuel cells (was Re: jeff's cyborg cells)

Eugene Leitl (
Mon, 7 Jun 1999 12:12:30 -0700 (PDT)

Michael S. Lorrey writes:

> > 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.

Yes, the efficiency goes up asymptotically with larger temperature delta between the opposite thermal reservoirs.

> > 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...

An internal combustion engine is really an obsolete monstrosity. It has a relatively low power density, low fuel efficiency due to being a Carnot machine, generates toxic exhaust, has lots of complex, expensive movable (vibration due to acceleration/decceleration) parts subject to friction losses/wear, leaks due to thermal cycling, is noisy, etc. It has required enormous expanses in R&D and support infrastructure to be as reliable and cheap as it is.

> > The gear box in a well designed car is better than 80 percent efficient,

The point is: you don't need one in an electrical car. And by stripping down radically (yet naturally: you can't put spike-capable ICEs into wheel hubs and simultaneously use them for braking) and using carbon (soon buckytube?) materials you can go into the ultralight regime where the whole car plus fuel weighs about the same as its passenger, resulting in riduculously low fuel consumption and/or extreme driving performance.

Compound frame cars _can_ be safe. Despite of extra protection available in Formula 1 cars (head support), they are extremely safe on impact, yet are mostly made from carbon compounds.

> > 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?
> Yes. I got those numbers off of a report done by the Washington State Energy
> Office 8 years ago, back when I was in the energy conservation biz. (Its the end
> result numbers that really matter, anyway.)

This is a nice instance how you can make new technologies look bad by introducing lots of unnecessary hidden assumptions. Electric car=battery car. Battery car=lead/acid cells. Mounted into a standard steel frame vehicle cum gear transmission et al.. Low efficiency controllers. Recharging losses+energy conversion losses+tranportation losses+Carnot process generation losses --> nonviable. Of course not. Nobody would compare a modern plasma drive to a Chinese bamboo stick filled with shooting powder, despite the working principles being quite similiar.

> Mike Lorrey