|MadSci Network: Engineering|
When it comes to automobiles, there are a lot more requirements to the power train than just thermal efficiency and number of parts. There are a lot of things about today's internal combustion engines that you take for granted driving around every day, that you probably wouldn't think of until you really tried putting a jet turbine into your car.
First of all, a jet engine isn't quite as flexible as you think. They do a much better job at producing a constant output at a constant speed, and wouldn't be quite so happy in stop-and-go traffic. Have you ever watched top-fuel drag racing? Often times you'll see jet engine dragsters at these types of events, but have you ever noticed that they don't do any better than the ICE (internal combustion engine) vehicles. This is because it takes a relatively long time for those engines to come up to speed. Sure they make great power when they get there, but it takes time.
Next, have you ever stood close to a jet engine while it's running? Not very quiet is it? How about jet fuel? That stuff is not exactly cheap either. People are complaining now about gasoline approaching $2 a gallon, but compared to jet fuel, it's practically free.
These are just some of the things that must be considered for application in a vehicle. The engine must be readily capable at operating at a wide range of speeds. It must be easy to refuel, and fuel must be cheap. It must be compact, light weight, quiet, easily serviced, cheap to manufacture, produce low amounts of emissions, etc.
You say not to mention historical reasons, but when you think about it, that does have a lot to do with it. People are reluctant to change--on both sides of the table. The designers have always made ICE vehicles, and they know a lot about them, and are comfortable with them, so they will continue to produce them. Also, customers are used to ICE vehicles, and are reluctant to try something different or unproven. It's funny to see how much marketing really plays a part in engineering decisions in cases like this. I know it surprised me. Maybe if we had always used jet engines, jet fuel would be cheaper, and the engines would be more refined for use in a car, but that isn't the way things have worked out.
There are other power technologies that have failed in the auto industry too. For example, the rotary engine. It was a good idea, but it never caught on. Electric motors. They're light, quiet, produce a constant torque through a wide range of speeds. Butů.the power source didn't work out. Batteries are heavy and expensive. They have a short range, and you can't replenish the power quickly like you can refill a gas tank.
You may be right. There may be better options out there. I won't deny that at all. So if you have an idea, think about it a little more, and maybe you'll find a way around some of these details. As with almost all engineering projects, there are trade offs to be made everywhere, and it's finding the perfect mix which is the hard part. Good luck.
Your Mad Scientist,
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