Can Lasers Ignite Fuel/Air Mixture?

[Scrambler]

Is it possible to detonate or to ignite a fuel and air mixture using lasers, or a laser pulse, any type of laser, CO2 or other wise ?

or is there any possible way of using Lasers for the propulsion of an aircraft, i am already aware of several methods, but they do not include ignite fuel, any possible way to ignite fuel with a laser, or a fuel air mixture ?

 

[Scrambler]

or is this idea of igniting fuel using a laser too sci-fi?

 

[Su Solberg]

personally, I believe it's the problem of whether it's easy for fuel to absorb light enengy easily.

U c? laser has already been used in metal cut, there is no doubt that laser have such high power output.

another problem is the ignition time, i think. Is it fast enough to react with the order signal?

 

[Scrambler]

Thank you for that quick answer, that's exactly what i was looking for , is if there is a fuel that can potentially use the power of a laser to ignite! I guess I'm back to the drawing board!

 

[Danger]

I think that Su nailed it pretty well. A laser would be great for igniting solid fuel (as in proposed fusion installations), but a gaseous mix probably wouldn't have the optical absorption needed for detonation.
The only way that I can think of it possibly working would be if you have some sort of laser-activated ignition device in either the head or the top of the piston, but that would really only be a very high-tech and expensive replacement for a good ol' spark plug. That would have problems as well, though, such as potential scattering of the beam by the fuel mixture and the lack of timing control that Su already pointed out.

 

[Scrambler]

Thank you very much ! All i wanted to know and more ! :)

 

[Integral]

Beyond all of that lasers are expensive, inefficient and sensitive to vibrations. It takes a lot of power to produce a reasonable laser pulse. We spend hundreds of watts to produce a 30W beam. there are just so many better ways to ignite a air fuel mixture, a laser would be at the bottom of the list of useful solutions to the problem.

 

[FredGarvin]

Why not just a cheap and easy piezo igniter? Not cool enough I guess.

 

[LURCH]

There has been work on using a laser propulsion system that does not need any fuel. The laser causes a sudden heating of air, which expands rapidly like an explosion, and propells the craft.

Here's a http://en.wikipedia.org/wiki/Laser_propulsion" .

 

[Scrambler]

LURCH - that might just work, in searching for an alternative source of propulsion, because of the rising price of fuels, air would be very cheap. Another method would be , correct me if I'm wrong, is to use somesort of reflective surface on the craft and shine the laser on that, more complex than that , but you get the idea !

 

[LURCH]

That is indeed the idea behind one of the approaches mentioned in the Wiki article. The main savings comes from the fact that the propulsion system (the laser) stays in place and sends the energy to the vehicle. It's essentially an engine that does not have to pull its own weight.

 

[Scrambler]

Therefore less fuel is used to accelerate the vehicle because of a smaller mass, however, just how far can this laser propel it, are there any technologies (laser) that for example can be based on Earth or the ISS and "push" it possibly to the moon, or from the moon to mars. I am aware that once powered the vehicle can "coast" , but can this "coasting" be sustained on such extended missions! ?

 

[redargon]

I'm sure I saw some footage of them launching a conical type disk upwards on a laser. Maybe on mepipe... I mean youtube. The problem that you may face using this system to get something to Mars or the moon is: how do you get that something back. You either have to carry conventional propulsion with you or a secondary laser kit to setup where you land so you can get back home. If coming home isn't a problem (like for a rover or something, this could be ideal). I'm not sure, but I would guess that the force generated by the laser would decrease and like most power equations, the decrease will probably be related to the inverse squared distance of travel. Ie. large distances may be difficult (especially from earth,through our atmosphere). In space, however, like your suggestions, it could work.

 

[Danger]

how do you get that something back. You either have to carry conventional propulsion with you or a secondary laser kit to setup where you land so you can get back home.

Larry Niven, one of the greats of SF writing, addressed this issue. His idea is that the solar sail is in two parts. For the return trip, or even just braking upon arrival, the centre parabola disengages from the sail, travels ahead of it, and then reflects the incoming propulsion beam back to the main sail.
(Yes, I can see the inherent problems, but it's not a bad idea overall.)

 

[Scrambler]

not a bad idea at all, i know quite a bit about solar sails but its still within the grasps of SF,

redargon

Thank you for pointing out the obvious flaw of flying back, i had not thought of it! And for this idea to work i was thinking STRICTLY launched from space.

1. Vehicle is conventionally launched into orbit! (rockets etc.)
2. Vehicle docks with the ISS. (ISS Will have the laser equipment installed on board)
3. The ISS used as a launching pad for the vehicle!
4. To come back , well other than setting up another laser like redargon mentioned, i have no other ideas !

I think its a fairly good idea, but the math still needs to be worked out !

 

[LURCH]

4. To come back , well other than setting up another laser like redargon mentioned, i have no other ideas !

If you're going to a planet, you don't need another laser, you just need a mirror (or two) toredirect the beam. If the mirror is left in proximity to the planet, and gravity holds it in place. The beam fronm the original emmitter reflects off the mirror, back in the direction from which it came. Place your vehicle in the beam, and you get propulsion in that direction.

 

[redargon]

just like danger said.

i was wondering, my knowledge of lasers is not perfect, but what kind of mirror would you need to reflect such a powerful laser (I'm guessing it would have to be pretty powerful).

Also, if you put a laser on the ISS and then use it to generate a force on an object, is there a reaction force on the ISS at all?

 

[Danger]

Also, if you put a laser on the ISS and then use it to generate a force on an object, is there a reaction force on the ISS at all?

There would have to be, as far as I know. Photons exert pressure, which is why the sail works in the first place. There would have to be, therefore, an equal and opposite force upon the launcher.

 

[redargon]

So you could put the ISS out of orbit unless you steadied it during launch using jets or something. Interesting. I think this laser launch module could be a pretty big one :smlie:

 

[Scrambler]

. If the mirror is left in proximity to the planet, and gravity holds it in place. .

This idea you propose might work, but as you know things left in orbit go around the planet and orbit , so the beam will not be constantly reflected back, this mirror or reflective surface will need its own fuel to maintain its position between the planet and the vehicle! Correct me if I'm wrong !

 

[Scrambler]

redargon and Danger !

This is an excellent point you have pointed out ! Newton's third law, which I have avoided using because in space it causes a headache according to it, The ISS would have to exert an equal force at the "back" and that should solve the problem, so there will need to be a laser module and an extra fuel module, or this opportunity can be taken to launch TWO vehicles directly opposite to each other and avoid this problem !

 

[Scrambler]

, but what kind of mirror would you need to reflect such a powerful laser (I'm guessing it would have to be pretty powerful).

To answer the mirror question, well no MIRROR is 100% reflective, so some heat will be absorbed, the only way i can think of is :

To use a mirror with a material so the particles aren't close enough to trap the heat and allow the heat to dissipate away from the reflecting surface, and out the "back", another way would be to somehow cool the mirror without affecting its ability to reflect light, after all a laser is just another form of light, my knowledge of mirrors is limited, does anyone know if this sort of mirror exists or what type of material can be made for the back of the reflective surface ?