What engines would an airborne vehicle use in a setting <200 years in the future?

Question

In a setting <200 years in the future could airborne military vehicles(fighter-jets), mass-transportation vehicles (planes, buses etc.), and personal vehicles (cars, motorcycles) use something like an ion-engine as a viable main-engine for transportation?

The vehicles should only travel inside the planets atmosphere, if at all only planes and jets should be able travel outside of it and go to space but not interplanetary-space.

Could <200 years from now be a long enough time for personal vehicles to be airborne and ion-engines or a new engine to be developed for (very)low fuel consumption, good acceleration (like equivalent vehicles today or better, (very)long range and very low pollution?
If it would be a new engine, what kind of fuel would it be using?

Answer 1

As others have said ion thrusters are not suitable for use in atmosphere but there is something similar. Ionocrafts use a large voltage between two electrodes to ionise the air around them, which is then accelerated by the electric field to provided thrust. They don't work in a vacuum so would not work in space (Although a ionocraft-ion thruster hybrid might be possible but you would still need another engine to get you into orbit). Currently the only once that exist are made of foil but in 200 years time they could be viable for large vehicles.

They are very efficient, which means they save energy and money but they would require huge voltages to be able to lift people and cargo. This should not be an issue as we are close (20-50 years depending on who you ask) to achieving self-sustaining fusion which could provided the energy needed cheaply (once it has been around long enough for the technology to be able to fit in a car). Fusion uses hydrogen isotopes as a fuel (There are other isotopes you can use) which would probably be obtained from sea water through hydrolysis powered by solar cells. (So you'll still have places to refuel your vehicle, just not with petrol. As hydrogen cars could be popular in the near future the infrastructure for this would probably already be in place) They should have an extremely long range using this as a power source.

Vehicles using this set-up would not produce CO2 or particulates (A reason companies might develop them) but they will produce ozone which is toxic but the volume produced can be minimised by planing the placement of the electrodes. The insides of the fusion reactor would become radioactive due to neutron activation so they would have to be decommissioned at the end of the vehicles life (You wouldn't want old vehicles to be abandoned) but it wouldn't be an issue during normal use. (It might be in crashes, but everything will probably be self-driving by then so crashes would be very rare)

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Source: A study on the performance of ionocraft

Answer 2

Ion engines? Absolutely not. The thrust generated by an ion engine is so ridiculously low, it would be impossible to get something off the ground. Even the ion engine in KSP is overpowered, since a burn doesn't last upwards of a year...

However, in the future, there is an alternative: pulse-detonation engines.

The big difference is that right now, jet engines are burning fuel, which releases gas and smoke and all that. But doing so releases all that energy over time and in an inefficient manner, burning things uncleanly.

What make a PDE so helpful though, is its use of many many (thousands per second) small explosions rather than the burning of petrol. Using a pulse detonation engine, your craft can travel significantly faster (upwards of Mach 6), use significantly less fuel, and unfortunately, make a ridiculous amount of noise.

Basically, the concept of the PDE is that you take small amounts of fuel, drop them into a cavity, and explode the fuel, generating thrust. Due to the adiabatic expansion curve of the explosion, it is much more efficient than conventional turbine-based engines today.

The catch though, is making each explosion small enough and the explosions fast enough that the vibrations caused by a discernable pulse are gone. With a cycle speed in the 1000s of hertz, the problems of having a pulse then a wait and another pulse go away quickly.

The fuels which an engine such as this would use are likely to be the same kinds of petrol used today. An experimental flight was undertaken in 2008 using octane fuels travelling at low speed. However, many aeronautic engine companies, NASA, and the government are attempting to develop these engines due primarily due to the efficiency gains and the ability for them to maintain speeds in excess of Mach 6.

Within 200 years, this should absolutely be developed, especially since prototypes already exist. Beyond the timeframe of 100 years, however, the technology would likely be obsolescent due to something as of yet unknown.

Answer 3

At the present day, ion engines have a very low thrust-to-mass ratio, but they are fuel-efficient. That makes them attractive for long-range space missions, but not for atmospheric use. Even if that could be overcome by future engineering, some problems remain.

• Ion engines have a very hot, very fast exhaust. Standing behind an ion engine with enough thrust to lift a personal vehicle is going to be bad for the bystanders or the scenery.
• Ion engines proposed today use fuels like xenon, mercury, bismuth, or iodine. Difficult to handle, expensive, and nothing you want to release in your ecosphere.

That means the "or a new engine" part of your question sounds better, but as SJuan76 points out that's difficult to predict.