Compression Gasoline Engine?

[PTskier]

I drive a 2016 Mazda CX9 that gets about 26 mpg at 75 & 80 on I-90 from Seattle to Spokane. 4 cylinder 2.5 L turbocharged gasoline engine in a 4300# SUV. I also drive a Toyota Prius Prime plug-in hybrid that is getting us about 150 mpg...not accounting for the electric miles at about 3 cents per mile, about 25 miles per charge before the gasoline engine needs to run.

"compression ignition in addition to the standard spark ignition to achieve a super lean burn. Coupled with a supercharger," That's getting into a lot of touchy territory. Really easy to get something too hot to destruction if it goes wrong. Just to clarify, the Diesel cycle (from Rudolf Diesel) has the heat of compression of the air in the cylinder sufficient to ignite the fuel injected into the cylinder. The fuel is injected at the correct time and quantity to provide a strong, powerful power stroke. The Otto cycle (from Nikolaus Otto) has the fuel in the cylinder and a spark device at the correct time for the ignition and the strong, powerful power stroke. The Diesel cycle is anything that will burn sufficiently including diesel fuel, propane, other products, black heavy residual fuel oil. The Otto cycle is usually gasoline and sometimes propane and other gases. I've trained at two diesel engine makers. I've run diesel engines to 57,500 hp (straight 12, 2-stroke). Those and 2,700 hp generator diesels ran the heavy black residual fuel oil. They ran fine with this fuel that has up to 3.5% sulfur, which will be illegal after 2020. And, I've run diesel engines as small as hand cranked air cooled engines.

A diesel gets good fuel consumption because the fuel has more BTUs per gallon, and there is not a throttle plate to make the engine work harder pulling air into it. The diesel also has a harder time putting out clean exhaust, as we've seen. Also, gasoline is a cleaner fuel than #2 diesel fuel.

 

[Tom K.]

A diesel gets good fuel consumption because the fuel has more BTUs per gallon, and there is not a throttle plate to make the engine work harder pulling air into it. The diesel also has a harder time putting out clean exhaust, as we've seen. Also, gasoline is a cleaner fuel than #2 diesel fuel.

All good points, except I think that modern day ultra-low sulfur #2 diesel might approach gasoline's "cleanliness".

The throttle plate comment is a good one, too. BMW uses this approach in their gas engines through a system called "valvetronic" (IIRC). I've never had higher performance, more economical engines than BMWs. Sadly, other aspects of the vehicles drove me away from the brand five years ago.

 

[scott43]

All good points, except I think that modern day ultra-low sulfur #2 diesel might approach gasoline's "cleanliness".

The problem with diesel has always been the nature of the emissions..NOx is the big problem as we've seen. I think the US has seen this issue as more problematic than the gasoline engine's emissions.

 

[Magoo]

I got a 16 CX-5 and love it. The diesel will be here in the USA as the 18 model. I can't give my car enough praise and normally I'm eh its just a automobile.

 

[chilehed]

From what I've seen it looks like they're intentionally inducing detonation in a stratified charge. Ballsy move, that's really hard on parts. Generates more NOx, too. Plus I bet the N&V guys are having fits.

 

[Tom K.]

First drive report, in a "not quite ready for prime time" prototype:

https://www.autoblog.com/2018/01/26/mazda-skyactiv-x-review-compression-ignition-engine/

 

[CalG]

Honda did some work on this concept back in the late 90's .

Honda readies Activated Radical Combustion

ARC

 

[oldschoolskier]

My first car was a ‘74 Corolla tha gave 37mpg (yes I tracked it back then).

The difference be the old Corolla and the new is engine size, less complicated engine and lower hp and likely similar emissions due to the better mileage.

The biggest push by most manufacturers has been HP. Consider my 89 Chev S10 with the 4.3L v6had about 145hp and my 14 F150 with 3.7L v6 (no turbos) has 305hp. If the same effort is put towards shrinking engine size to reduce fuel usage without losing power, this should be possible.

Question becomes will the auto buying public agree.

 

[Dave Marshak]

First drive report, in a "not quite ready for prime time" prototype:

https://www.autoblog.com/2018/01/26/mazda-skyactiv-x-review-compression-ignition-engine/

I read that several weeks ago. According to that article, it uses compression ignition for low loads and spark ignition when more power is required.

The other explanation was that it uses a fuel/air lean mixture that is too lean for spark ignition, then it adds a little gas near the spark plug. Spark ignition causes enough pressure increase to ignite the lean mixture by compression, all at once without any flame front propagating through it, which minimizes NOx formation.

The second explanation sounds a lot more feasible than the first to me. Neither of those explanations imply that it is anything like a diesel. The diesel references are just marketing stuff to buy in to the perceived efficiency of diesel without owning the pollution of it.

dm

 

[pete]

I read that several weeks ago. According to that article, it uses compression ignition for low loads a........ Neither of those explanations imply that it is anything like a diesel. The diesel references are just marketing stuff to buy in to the perceived efficiency of diesel without owning the pollution of it.

dm

no, not a diesel, earlier link described it ... " the operation of the engine is a bit like an implosion-type nuclear bomb"

that's why it's so efficient!

I like technology but always a bit shy of a lot of complexity ... of course, I can no longer work on most any car due to this. Funny too is the domino effect on technology where one "improvement" drives fixes across other parts of a vehicle. sort of like buying new boots, now I need to upgrade my bindings which implies ski's .. now new coat, base layers ... ohhhhhh noooo!

 

[PinnacleJim]

This is really not a pure diesel engine or a pure spark ignition (Otto cycle) engine, but something that's a bit of a mix of the two. The fuel efficiency gains come largely from the higher compression ratio. Not quite high enough for the heat of the compression to self ignite the lean fuel-air mixture, but as close as they can get to that. Then a bit of injected fuel and spark ignites everything. The tricky part of all this is making this happen reliably under varying ambient conditions and sudden throttle changes. I will be very surprised it there are not a series of software updates to the early engines that come off the line.

 

[Dave Marshak]

This is really not a pure diesel engine or a pure spark ignition (Otto cycle) engine, but something that's a bit of a mix of the two. The fuel efficiency gains come largely from the higher compression ratio. Not quite high enough for the heat of the compression to self ignite the lean fuel-air mixture, but as close as they can get to that. Then a bit of injected fuel and spark ignites everything. The tricky part of all this is making this happen reliably under varying ambient conditions and sudden throttle changes. I will be very surprised it there are not a series of software updates to the early engines that come off the line.

This is a spark engine, not a diesel at all. In a diesel, fuel is injected AFTER compression, and ignites spontaneously. Combustion occurs along a flame front as fuel continues to be injected. IT has high NOx because all the combustion is on that flame front, and better torque because you can continue to inject fuel (and keep pressures higher) for a longer part of the power stroke.

The Mazda is a stratified charge system where spark ignition in the rich part of the charge causes compression ignition in a part of the charge that would otherwise be too lean. The whole lean charge goes off at once, which eliminates the flame front that generates NOx.

They must be able to get higher temperatures without NOx to get better efficiency. It's a slick deal if they can do it.

dm

 

[PinnacleJim]

This is a spark engine, not a diesel at all. In a diesel, fuel is injected AFTER compression, and ignites spontaneously. Combustion occurs along a flame front as fuel continues to be injected. IT has high NOx because all the combustion is on that flame front, and better torque because you can continue to inject fuel (and keep pressures higher) for a longer part of the power stroke.

The Mazda is a stratified charge system where spark ignition in the rich part of the charge causes compression ignition in a part of the charge that would otherwise be too lean. The whole lean charge goes off at once, which eliminates the flame front that generates NOx.

They must be able to get higher temperatures without NOx to get better efficiency. It's a slick deal if they can do it.

dm

And your point is? Didn't really need the lecture. With three degrees in mechanical engineering and having done my graduate thesis on the combustion of emulsified fuels in diesel engines, I think I understand the technology.

 

[Dave Marshak]

And your point is? Didn't really need the lecture...I think I understand the technology.

I didn’t mean to give you a lecture. Was anything I wrote not true?

dm

 

[chilehed]

IT has high NOx because all the combustion is on that flame front,...

NOx is generated due to high temperatures. The way the flame front propagates has nothing to do with it.

The article confirms what I expected: lots of noise and difficulty with handling transient throttle input. I bet long odds that NOx concentrations will be higher going into the converter, and that there's been more than one broken ring land on the teardown table.