Most local free press tends to fall into the camp of hemp-wearing, patchoulli oil reeking, bongwater chuggin' moonbat hippies of all ages.
Our local Galveston free paper is much more centered, and a lot less political.
Call it a nice, happy, libertarian "live and let live" attitude, and you'd be pretty close. Some of their readers are heavily into the green agenda though, which shows clearly in some of their letters to the editor.
One such letter though, led me to a very fascinating website. Check this out.
I extracted the following lead from the pages of the Twisted Parrot, via a Letter to the Editor and the Ed. Reply. This site features news of a most interesting vehicular technology coming out of Spain. Here's where y'all come in.
I want to know if this has validity, or is just some tree-huggers wet dream? Or both!
The MDI Air Car claims to run on compressed air, powering a unique, articulated connecting-rod based, piston engine. Which, when speeds exceed approximately 35mph, can then run on various fuels in internal combustion mode.
They do seem to have ample documentation of the engine's development.
While I don't see the technology at this level taking over the market for 300 hp luxury sedans and SUVs, I do think it'd have great use for postal vehicles, golf carts and the like.
Obvioiusly, the MDI folks think it'll go much further than that. Fine.
I want to know what you think.
please define compressed air.
Posted by: marcus | February 25, 2004 at 10:39 PM
The engine starts on compressed air. Max torque is reached at only 700 rpm, but the torque and horsepower curves don't intersect until over 2000 rpm. The company doesn't say where in the cycle the change from compressed air to petroleum combustion happens. That's critical for estimates of fuel mileage.
The company also does not list the total energy cost of compressing the air supply for the stored air-energy that the engine starts on. My guess is that if you factored in the energy quotient of compressing that air (as well as the cost of the compressors, their attendant oils and lubes, etc), the overall cost wouldn't be much better than a diesel run on Compressed Natural Gas, which is extremely clean-burning and in good supply (at least a 400-year supply).
The articulated con-rod is clever, but could cause problems in maintenance cycle. The design is there to enable the use of relatively low pressure energy from the stored air to turn the engine, but the same design works against the higher pressures required by Dr. Diesel's engine, which can't be run at a compression ratio of less than 15:1 Maybe the design is an internal combustion with spark plugs, it doesn't say. Such an engine could run at compression ratios of as little as 6.5:1, which would be similar to the air pressure in the compressed air.
The worry with the articulated con rod was amply examined during the Age of Steam, when powerful locomotives were developed using articulated connecting rods (outside rods). That experience showed that the articulated joints were the most difficult to keep in service, and very low TBF (time between failure) times were recorded as the horsepower of these locomotives was increased. Even continuous lube feed as used on the final evolution of steam locomotives wasn't good enough to eliminate this weak point in the design.
The principle here is rudely known as "monkey-motion". The idea being that designs which conserve motion, the purest being a simple rotating body, are the easiest to maintain and are the most efficient. When "monkey-motion" is introduced into a design, energy is wasted because the motion is not conserved, but directed in directions that don't produce energy. Such designs are less efficient, by design. The Wankel rotary engine is a good example. Designed for rapid and large power outputs of horsepower, it's internal eccentric rotors waste energy, have sealing problems, and make for a short-lived engine. Mazda sticks with the engine because of the mystique, mostly, and the fact that you can stuff a powerful motor in a small space. Mercedes experimented with this eccentric-rotor engine with it's C-111 race coupe, but couldn't prove it's endurance on the racetrack, and so gave it up.
It seems to me that the squished jelly-bean car is simply another underpowered Euro design, designed to maximize fuel mileage. Sure, it gets huge mileage, but that's because the compressed air energy isn't being counted in the total. Count that, and the vehicle wouldn't be any more efficient than any of the current Euro "City-cars". That cost has to be counted, because to not do it is absurd and is cheating the fuel economy/exhaust pollution standards. The relatively high final speed of this car is a red herring: by it's power design, it would take a week to get to 110 mph. You can put tall gears in anything, but small engines pushing tall gears are a joke.
A vehicle running on stored (battery) electricity makes zero pollution at the car, but that electricity has to be generated and that makes pollution for the most part. The same with this compressed air business.
The bus-train design is intriguing, but not because of the hybrid engine, because it is a rail-less, high volume people mover that could bring high-capacity transit to cities without the huge cost of the rail installations.
Posted by: Rivrdog | February 26, 2004 at 07:04 AM
I am in general agreement with Rivrdog's analysis. The one thing I would point out is that altho they are going way overboard with the monkey motion, keeping the piston near TDC is a good thing. Grumpy Jenkins achieved significant horepower gains from his Pro Stock Chevy V8s by running longer connecting rods (which required other exotic changes) to gain a bit of this. Small engines pushing tall gears can be worthwhile, but you would need a many-speed transmission, and you would row the thing along with the shift lever.
I wouldn't want to be in one of those "jelly bean" cars when it was hit by a Mini or a Prius, let alone a real automobile.
Posted by: triticale | February 26, 2004 at 08:15 PM
Triticale, I'm with you on the whole thing. Rivrdog nails the engineering aspects, and you sure as hell have it right on those things being butt-ugly and paper-thin.
Like I said, I think they'd be okay for low-stress urban crawlers...i.e; postal vehicles and golf cart type conveyences.
That monkey motion engine probably wouldn't overstress at lower RPM/Cylinder pressures....but gawd help it on the high end of things.
And Marcus? Ask Moncia Lewinsky about compressed air. It blows. I think that's her specialty.
Jim
Sloop New Dawn
Galveston, TX
Posted by: Jim | February 26, 2004 at 10:44 PM