Lasers and Engine efficiency

Very interesting topic. As in many others, Toyota brand is mentioned in the article...

 

IEEE Spectrum is usually a reliable source of well-presented technical information, with articles often written by the developers and engineers who are actually working on a project.

 

Thank you for the sharing.
I've found some inaccurate sentences, about the reason for the "ineffiency" of spark plugs.
In fact the increase in efficiency is not related to the spark-initiated incomplete combustion: as we know, only a very small amount of charge is not completely burned, due to quenching effect (wall of cylinders). It has to do with the timing and the A/F ratio allowed by the new laser system. IMPOV.

 

Anything with the word Laser in it sounds very high-tech, Cool!

Don't mean to change the subject, but I would ask: what happened to HCCI Gas engine research?

 

Still ongoing. Sounds like any commercial engine that makes it to market will likely be HCCI and spark ignition; switching between them to whatever is best for the demand on the engine.

We have laser head lights and now laser spark plugs. When do we just get to ride around on a laser beam? Or a sonic screwdriver?

"The increased energy output allows for leaner fuel-air mixtures, increasing overall fuel efficiency by 27 percent while lowering emissions." - the article

Do they mean a decrease hydrocarbon emissions? Because a lean mixture is going to result in the formations of more NOx.

 

If the peak temperatures are lower, possibly less NOx. But I agree with you, the leaner the mixture, more N and O are available for the chemical reaction.

 

Lean mixes burn hotter though. It is possible to burn through a cylinder running an engine lean that wasn't designed for it. I think it would take a different fuel to keep peaks temperatures lower. Or water injection.

Ford had an experimental V6 Ecoboost with both E85 and gasoline injection. As demand and rpms increased on the engine, it would inject a larger portion of E85 into the mix. E85 has a higher octane, allowing greater timing advance an turbo boost for more power. The ethanol also provided extra cooling in the cylinder.

 

Lean mixes burn hotter very close to stoichiometric combustion, but as A/F gets leaner, temperature drop. The same amount of energy diluted in more air...

 

Wasted some time 'googling', and all lean(and rich) mixtures of liquid fuels lead to cooler cylinder head temperatures. The lean mixture can lead to different dynamics going on during combustion that lead to knocking, and even pre-ignition, and how the temperatures are transferred to engine components. A lean burn could have a faster flame front than stoichiometric and rich. That extra speed puts the fuel mix between it and the cylinder under greater pressure. Exceed the petrol's octane limit, and then there is knocking.

Then a lean mix can be burning too efficiently. The tiny amount of unburnt fuel mix at stoich. due cooling from the cylinder walls forms a boundary layer between the combustion and walls. This layer insulates the walls from the combustion heat. With a lean mix the fuel for that boundary layer is being burned. Without the insulation, more heat is transferred to engine parts; leaving hot spots for pre-ignition and knocking. The knocking and pre-ignition alone can damage an engine. Then if the parts are getting hotter, they are likely weaker at those temperatures. On top of that, there is extra oxygen, in a hot environment, to potentially react with the metal.

That said, nearly all the car manufacturers had lean burning engines in cars at one time. Notably Chrysler and Honda during the '80s and early'90s. Some of those carbeurated, lean burn engines met the emission requirements of the time. Then fuel injection and tighter regulations came along. The higher NOx levels of lean burn just couldn't be handled by a three-way catalytic convertor. It seems the cat needs a balance of NOx and hydrocarbons to work properly. While NOx went up lean burn, HCs went down. Lean burn, natural gas engines from Cummings can be equipped with SCR to reduce NOx. https://www.cumminspower.com/www/literature/technicalpapers/PT-7009-LeanBurn-en.pdf (The paper claims reduced NOx without the aftertreatment, but not compared too)

Honda is still working with lean burn, others surely are, but it appears that it will require diesel emission control technologies to meet regulations.

 

Lean burns died not because they would burn through the walls, it died because NOx standards were raised. Compared to 2000 the average car emits less than 13% of the NMOG+NOx. Lean burn in a gasoline car, if done the old way would require the SCR used on diesels, and that would add more cost. For the modern 3 way cat a slightly rich mix is required to get lowest pollutants out.

Regulators may switch to NMOG + NOx instead of regulating both individually. That should allow direct injection engines to use stratified charges to do lean burns and still conform to regulations.

The water injection tech is actually really cool. It is actually methanol water. Injecting this is a hot engine not only reduces NOx and particulates by cooling it, it actually increases efficiency and power. Alternatively aggressive EGR robbing power and/or rich mixtures are used to keep engines in side pollution requirements.

I think the key is NOx formation, and current US regulation. Very lean mixes decrease the quality of combustion. Many other countries probably can have lean burn and comply with regulations. New pollution control devices can always be invented.

Still if you are going very lean, the gen III prius method of aggressive cooled egr with slightly rich mix probably produces much lower NMOG+NOx with similar efficiency. It does add another part, but denso - toyota's supplier - created a lower priced part for gasoline engines for the camry hybrid and aqua. the next gen volt is using this tech. The cooled egr reduces the pollution created, versus the more expensive SCR technology which allows a more efficient engine to produce more pollution but then must clean it up using more fuel or requiring urea.

 

HCCI research is still going on and is working in the lab. The problem is this requires a turbo charger and/or super charger and di which cost more (ford charges about $1000 more in its ecoboost). For the same size engine you can't get the same power output which adds more cost and weight, and has trouble at cold temperatures, so they are working on an engine that can run both the HCCI at low power and miller cycle at higher power which might bring the efficiency and power to make the extra cost worth it. Don't expect a production car with this kind of engine for at least 5 years, probably 10.

Bosch Hard At Work On Sparkless Ignition HCCI Engine

I guess lasers could be used instead of spark plugs in such an engine ;-) but that may make it take even longer to make it outside the lab.

 

A laser ignited car can produce a better combustion in very lean conditions. It has been attempted before in stratified charge engines, where the mix had to be near stoichiometric at the spark and globally leaner , I believe this energy source can allow further developments.

 

+1

Yes, it definitely is feasible to do laser ignition plus stratified charge to be lower in NOx than spark ignighted engines doing the same, and they are close with spark plugs.

I find the 27% figure hard to believe, unless you compare a heavily throttled port injected ice, to a valve controlled di with laser. The prius valving gets rid of most of the throttling losses, so it couldn't get close to this figure, but it can get di and laser improvements.

 

It is cool, and major use started in WWII fighter planes because the cooling prevented knocking while the engines produced high power. Methanol helps with the cooling, but it was likely first added as an antifreeze for the water. There are kits, and DIY methods of putting it in a car, but the aftermarket stuff can take a lot of work to the system working right for the best performance.