Lasers set to zap engines into running more efficiently

new scientist ^ | 20 February 2015 | by Hal Hodson

[ckilmer]

PEW pew! For a week last November an internal combustion engine hummed away in a lab near Chicago. Why the excitement? This particular engine sets fire to fuel with lasers instead of spark plugs, burning fuel more efficiently than normal. Laser-fired engines could lead to cleaner, greener cars.

[IronJack]

It wouldn’t have to be “pumped.” The vacuum created by the intake cycle would pull it from a reservoir into the cylinder.

[IronJack]

You wouldn't have to use heat necessarily. You could use sound waves or vacuum. Gasoline vaporizes at something over 100 degrees. The equivalent vacuum wouldn't be that hard to draw.

I suppose the biggest challenge would be to keep the vapor from exploding prematurely when it was pulled into a superheated combustion chamber.

[IronJack]

Yes, but the energy yield from propane isn’t nearly as much as hexane, heptane, or octane.

[IronJack]

But wouldn't introducing gaseous gasoline enable GREATER compression, since liquids don't compress but gases do?

I'll admit the pre-ignition problem is a big one, but not insurmountable, I don't think.

[bunkerhill7]

I`m gonna put a couple of lasers in my tailpipe so I can have an afterburner for climbin` them steep mountain roads.

[Lazamataz]

Liquids don't compress.

Untrue.

Solids compress, too.

cf: Neutron matter.

[painter]

The major limit to the efficiency of fuel-burning engines is the limted attainable compression ratio. It’s about thermodynamics. Diesels are more efficient than spark-ignited engines because of their higher compression ratio.

Bill and Ernie Elliot actually proved that in 1985 stock car racing in Nascar. This is before restrictor plates. Ernie, Bill's engine builder discovered a way to shape the combustion chamber to work at 13 to 1 compression. The result was more horsepower and better fuel mileage. Not only was Bill's T-bird faster than every one else's car he could stay out on the track longer. This was on the Super Speed Way tracks.

[Arlis]

Won’t work on diesels. Their combustion is not a result of ignition from an outside source, but from the heat of the high compression.

The ignition from the high compression essentially already does to diesel fuel what the laser approach proposes to do with gasoline engines.

That’s why diesel engines are more efficient than gasoline engines - a more complete and thorough combustion of the fuel - albeit with worse combustion byproducts/emissions.......

[arthurus]

My cousin demonstrated to me 40 years ago a vapor system. He had a lawn tractor with a non functioning carburetor. He essentially changed the main jet, I think he put in a bigger one, and ran the gas line to the top of a gallon gas can in which he put, of course, gasoline. The rig worked well and cut his very large yard on about half the gas he had normally used. It was strictly single speed and I guess he got the ratios right for that speed. Tom hooked up the throttle but couldn’t get it to run right at all using the throttle so he removed it and just ran single speed. I can’t get terribly technical about all this because I don’t know much about it, just what I saw him do. I rode it around once.

[thackney]

Liquids don't compress. Gases do.

The liquid form is already more dense than the highest gas pressure. The expansion of liquid into hot gas is greater than starting with gas under any pressure.

which would result in a much more powerful ignition

The same number of molecules only expand so much during the combustion. If the combustion is complete, the expansion does not get any greater. If the initial condition is more dense, such as cooler, starting first with a liquid, the ratio of expansion is greater delivering more power per rotation cycle.

By the way, water does not compress but some other liquids do.

http://www.insidersecretstohydraulics.com/hydraulic-decompression.html

[Red Badger]

They weren’t looking for ‘power’ they were looking for fuel efficiency, since the Arab oil embargo of the 70’s had gasoline at the horrendous price of $1 a gallon.....................

[Red Badger]

Nowdays they have little ultrasonic devices that create ‘fog’ in water. You see them in little fountains and such..................

[thackney]

Greater expansion of the same amount of fuel into exhaust gases inside the combustion chamber is greater efficiency.

[IronJack]

I would like to see the theory tested out in a lab.

Certainly the molecular density of the liquid will be vastly greater than a gas, but I wonder if the energy absorbed by the state change doesn’t offset that.

I also wonder if compressing the vapor would simply cause it to liquefy again.

[The Duke]

"Maybe somebody could invent a device that would mix the gasoline with air before it reached the cylinder."

Brilliant...we could make it in both "four barrel" and "two barrel" versions! And we could call it the ... "Gas/air mixing thing-a-ma-jig"! We'll sell millions!

[wally_bert]

Chilling fuel is an old hot rod trick.

[cpdiii]

“Power needs to be high enough to ignite fuel in ms and optics would malfunction with carbon buildup in cylinders.”

I would suspect that the laser cleans itself by burning off the carbon deposits. Otherwise we have a real problem.

[reed13k]

I had an issue with an air related component at one point, but no seal issues and got about 20-25mpg depending on how much of a “young man driving” I was being. I think I put over 200K on that sucker before selling it to my sister who put another 50K or so on it - never rebuilt, just maintained.

Don’t doubt it could be improved, but it’s there if needed.

[Abathar]

<><><><><> And I’ve often wondered about injecting gasoline VAPOR into the combustion chamber instead of particulate (atomized) gasoline. <><><><><>

https://www.youtube.com/watch?v=58IkmPK6ikc

[JoeFromSidney]

optics would malfunction with carbon buildup in cylinders.

This was my first thought.Carbon buildup on the laser lens.