Mazda's engine development

[pwd72s]

Sounds weird to me...kind of a gas engine, but semi diesel design?

https://www.caranddriver.com/reviews/2019-mazda-3-with-skyactiv-x-compression-ignition-gas-engine-prototype-drive-review

[aschen]

Engineering explained always does a good job braking down new car tech. "lean burning" gasoline engines has been one of those techs that have been pursued forever. It seems mazda has commercialized it for at least part of the engines operating conditions

https://www.youtube.com/watch?v=yNSxow3W7ek

[flipper35]

Not a new concept, but Mazda seems to be able to make it work commercially.

[sammyg2]

A friend of mine had one of those in high school. Darned thing would ping like crazy every time he pushed on the gas.
Took 30 seconds to shut down after he turned off the key too!

[RKDinOKC]

Mazda goes mmmmmmmmmmm

They have been calling their variable cam timing SkyActive for some time now.
My general description is it's load based variable cam timing with mixture and ignition to match.

Friend as a year old Mazda 3. It does pretty well. Seems to have plenty of power when needed and gets great gas mileage cruising.

[red-beard]

Ford is doing an Achates opposed Piston engine. The plan is to make a 2.7l engine with 42-45% thermal efficiency. This will mean mileage in the 40+ mpg range with a Ford F150, on gasoline.

[Jims5543]

A lot of the articles refrain from speculating on gas mileage, I think I read to expect Prius type of gas mileage, like 50+ MPG with 60 MPG not out of the question.

If they hit that mark it will be a game changer.

[onewhippedpuppy]

30% improvement would be pretty substantial. Mazda is such a cool company, the smallest of the Japanese manufacturers but possibly the most innovative.

[daepp]

Variable compression, right?

[Tobra]

45% thermal efficiency?

[Arizona_928]

Almost like a common rail.

I like

[porsche4life]

Originally Posted by red-beard

Ford is doing an Achates opposed Piston engine. The plan is to make a 2.7l engine with 42-45% thermal efficiency. This will mean mileage in the 40+ mpg range with a Ford F150, on gasoline.

Ooo? What’s the timeline on that. I’ve been saying I want an f150 sometime in the next 5 years....

[onewhippedpuppy]

Carnot Cycle! About the only thing I remember from my ME classes.

[Tervuren]

Originally Posted by daepp

Variable compression, right?

The article did not mention variable mechanical compression.

However it using an explosion of richer fuel/air near the spark plug to further compress the leaner fuel/air that was taken in during the intake stroke.

[berettafan]

so I read the first few paragraphs and I'm not clear on what's new here?

mazda wanted to use compression only to ignite an ultra lean fuel/air mixture but it wouldn't work so they brilliantly introduced spark to the mixture and boom, skyactiv x!

[onewhippedpuppy]

Originally Posted by Tervuren

The article did not mention variable mechanical compression.

However it using an explosion of richer fuel/air near the spark plug to further compress the leaner fuel/air that was taken in during the intake stroke.

I think Infiniti has come out with a variable compression engine, also a cool idea.

Originally Posted by berettafan

so I read the first few paragraphs and I'm not clear on what's new here?

mazda wanted to use compression only to ignite an ultra lean fuel/air mixture but it wouldn't work so they brilliantly introduced spark to the mixture and boom, skyactiv x!

It's both a compression and spark ignition engine, and goes between the two modes depending on load. Best of both worlds between a diesel and gas engine, but using gas and at a cost comparable to a standard gas engine.

[Tervuren]

Originally Posted by berettafan

so I read the first few paragraphs and I'm not clear on what's new here?

mazda wanted to use compression only to ignite an ultra lean fuel/air mixture but it wouldn't work so they brilliantly introduced spark to the mixture and boom, skyactiv x!

Think of it like a thermonuclear bomb.

A fission bomb creates the environment for a fusion bomb to go off.

The combustion chamber has a fuel/air ratio for compression ignition.

A precise second direct injection fuel pulse creates a small area near the spark plug that fires off like a conventional gasoline engine, this explosion raises the compression of the remaining leaner fuel/air in the cylinder and allows it to combust from compression rather than ignition spark.

Did that make sense?

[berettafan]

Originally Posted by Tervuren

Think of it like a thermonuclear bomb.

A fission bomb creates the environment for a fusion bomb to go off.

The combustion chamber has a fuel/air ratio for compression ignition.

A precise second direct injection fuel pulse creates a small area near the spark plug that fires off like a conventional gasoline engine, this explosion raises the compression of the remaining leaner fuel/air in the cylinder and allows it to combust from compression rather than ignition spark.

Did that make sense?

yes. we had fuel and air in the cylinder as it compressed but it wasn't going to ignite under just the pressure so we injected more fuel and added a spark.

it this really a variable compression engine now?

[Tervuren]

Originally Posted by berettafan

yes. we had fuel and air in the cylinder as it compressed but it wasn't going to ignite under just the pressure so we injected more fuel and added a spark.

it this really a variable compression engine now?

That is like asking if a thermonuclear bomb does not have a fusion reaction.

It is a dynamic variable compression in that the compression required to light off the majority of the chamber is higher than the fixed compression ratio of the piston motion.

Reaction one is used to create the conditions for reaction two.

[Tervuren]

One more attempt in case that doesn't stick.

In the conventional engine the spark creates a higher temperature as the source of ignition, heat radiation is how the reaction spreads through the combustion chamber.

In this Mazda engine a small reaction in the combustion chamber creates an increase in pressure, and compression is how the remaining fuel/air mixture burns.

So in the conventional engine it is heat radiation for ignition at a given compression.

In this Mazda engine it is heat radiation with a small part of the chamber in fuel air mixture ratio 1 that is ignited. This combustion expansion changes the compression ratio for fuel air ratio 2 that fills the remaining area of the chamber. This change in compression ignites fuel air ratio 2.

So the part of the chamber at fuel air 1 ignites by heat at compression level A, the part of the chamber at fuel air 2 ignites by increased compression to compression level B.

The compression ratio for ignition of fuel air 2 is higher than that of fuel air 1.

Fuel air mixture 1's combustion is used to control the compression of fuel air mixture 2.

If you spray food coloring into water, there is time for it to dissipate to median levels.
The second injection of fuel does not have time to mix with the remaining part of the chamber.
This results in two different fuel/air ratios in the chamber at the same time, one of which is used to raise the compression of the other.