As I see it, a problem with an automobile?s internal combustion engine comes from the engine?s need to run at different speeds. In stead, I like the idea of a diesel railroad engine. I understand that the train?s engine has two modes of operation. The engine runs at idle or all out. The engines generate electricity and the electricity powers motors that move the train. This has a strong appeal for me. I don?t know why but I suspect it has to do with boyhood dreams and electric trains. .
During discussions with fellow train enthusiasts, another obsession inserted itself. The obsession deals with my thing for gas turbines. ( I have spelled that right haven?t I? I mean engine things not head gear things. )
I fantasize about gas turbines turning generators which power electric motors. I like gas turbines because of the decreased number of parts compared to the current piston type engine. It just seems simpler to me.
Sounds like time for you to begin r&d, patent it, and make the next million bucks.
But first you must figure out how to capture all the waste heat a typical gas turbine produces…I thought about (years ago) using that heat to boil water and run another steam turbine and thereby get the overall efficiency over 50% capturing as many BTU’s as possible. That’s the name of the game. With any fuel, you are paying for BTU’s and you can’t waste them or let them escape through radiators and exhaust pipes…
Back in the 1920s in the US, there was a car called the Owen Magnetic.
It featured a gasoline engine that turned a large generator. Cables carried electric current from the generator to an electric motor mounted on the front of the drive shaft, and thus, it used electric power to turn the rear drive wheels. In effect, the car used electricity in place of a transmission. Unfortunately, it was not very successful and was discontinued after about 5 years.
Even earlier, Dr. Ferdinand Porsche designed the Lohner-Porsche which used an electric motor in each of its 4 wheel hubs . The Lohner-Porsche won several early hill-climb races, but it was not successful as a consumer product. While this design was more complex than the Owen Magnetic, it is possible that Porsche’s design from 1900 inspired the Owen Magnetic.
Anyway, as you can see, this basic concept is not new.
The more things change, the more they stay the same.
Gas turbines are extremely simple yet expensive machines. The hotter the exhaust, the more efficient the engine will be. In a modern jet engine, the exhaust temp can reach above the melting point of the turbine blades during takeoff. Without passing cooling gas inside the turbine blade, the blades would melt. You can also coat the blade with that space shuttle ceramic. Rolls Royce, the jet engine maker, says that each one of their turbine blade is made up of a single crystal, which mean no micro defects whatsoever. Making a blade like that takes time and that’s expensive. As mentioned in another post, you should recover some of that exhaust heat with a steam or Stirling engine. Since you’re using electric motors to power the car, it makes sense to recover some energy during braking since traction motors can become generators. So you’d need a battery pack or a supercapacitor. Add them all up and you’re looking at some serious money.
However, gas turbine is a theoretically great idea. Gas turbines are much smaller than a regular car engine of the same power so the car can shrink around it, provided that your customers are not looking for size to compensate their anatomical shortcomings, and improve on aerodynamics. The engine itself is lighter. Small car => less metal => less weight => smaller brakes (especially if you use regenerative brakes as well), suspension, and tires requirements. So if you can balance the high propulsion cost with smaller component costs elsewhere, you can make this work. I believe that GM put a gas turbine in one of the lease return EV1 as a research project.
Seeing Turbine Powered Cars On The Street Was Not Uncommon When I Was A Kid.
They were all copper-color, as I remember, and Woodward Ave., in and out of Detroit, is where one was likely to come upon these. I spent many tanks of gas “Woodwarding” (drag race capitol of Michigan). I remember hearing that one drawback was that they had a delay between pressing the accelerator and starting to move.
I grew up where Chrysler had a number of these experimental cars on the road. These were not turbine/electric, rather just turbine powered.
Here’s a link to the new car brochure:
And, before Chrysler’s flirtation with experimental turbine power, Rover of the UK was actively exploring this area of technology.
Turbine engines had a lot of promise for cars in the era of cheap fuels and lack of concern for the environment. Unfortunately, the advantages of turbine engines for cars were outweighed by their high fuel consumption and the emission of HUGE quantities of carbon dioxide.
The generator-motor link between the diesel engine and the locomotive wheels amounts to nothing more than a continuously variable transmission. The traction motors have a series wound field while the generator has a differntially compounded field. At low speeds, the series motors draw a lot of amps and since those amps go through the field as well as the armature, the field is strong which means high torque and low rpm. The generator has a compound field, a separately exited shunt field and a differentially compounded series field. When the current draw is high, the generator’s series field weakens the field of the shunt winding causing the voltage to stay low and lets the diesel engine rev at its most efficient rpm.
As the train speeds up, the series traction motors draw less amps and the generator’s series field weakens the generator field less and allows the voltage to rise.
It all adds up to a continuously variable automatic transmission.
Why not use it in cars? My guess is cost and weight of the system plus it’s a lot harder to design an efficient 100 horsepower generator and electric motor than it is to design an efficient 1500 horsepower generator and electric motor.
Scale effect favors large motors and engines when it comes to efficiency.
The variable field generator is also used to power the dc hoist motors used in high speed elevators. A 3 phase induction motor turns a dc generator with a variable externally exited field winding and that generator powers the elevators dc hoist motor. This setup is often called a Ward-Leonard drive.
Electric motor/generator has a efficiency of 90% each. So 90% x 90% ~ 80%. This is compared to 98% of a conventional transmission. However, a locomotive engine is design to operate at a very narrow range and varies its torque. This means its engine turns at the most efficient speed and, if done properly, the increased engine efficiency more than offsets transmission loss. A train engine is design for efficient cruising instead of blazing acceleration–they don’t need to merge onto freeways like we do.
In a gas turbine/electric propulsion, the gas turbine would be designed and optimized for one speed, as a gas turbine is slow to respond. Unlike the train, the car would need a battery pack to store extra power for highway merging. When Chrysler didn’t have the electronics to build a hybrid, its turbine car had an engine that was out of place. With the hybrid technology we have today, I think turbine electric makes sense.
One of the biggest drawbacks to turbines is that there is a huge thermodynamic efficiency drop off when throttled back to cruise power and the idle fuel consumption is very high compared to piston engines.
When driving through hill and dale country on roads with 45-50 mph speed limits, a car engine is making zero power nearly half the time. Highway cruising only demands about 15 horsepower so our engines are spending a large percentage of the time at a power that is way below the engine’s maximum efficiency. This is why most gas mileage records are set with intermittent engine runs. Accelerate at about 60-75% full throttle and then coast with the engine off and repeat. Don’t use the engine unless you really mean it.
A turbine might make sense to recharge the batteries on a series hybrid but a 15 horsepower piston engine doing the same would probably beat the turbines efficiency, especially in that horsepower range.
Turbines are great engines for airplanes, where the engine is running at nearly full power for the whole trip and where light weight is extremely important. What good is the world’s most efficient diesel engine in an airplane if that engine is so heavy that it is the airplane’s entire payload?
Jay Leno on he Turbine Motorcycle.