If you're as fascinated by Mazda's SKYACTIV-X Spark Controlled Compression Ignition engine as I am, then you're going to want to take a break from whatever Miata-Is-Always-The-Answer comment you were writing and watch this video. It's borderline pornographic.
At the end of August, Mazda flew me to Frankfurt, Germany, and let me drive two of its SKYACTIV-X prototypes (here's my review). More importantly, I got to speak with the company's engineers, who walked me through how Spark Controlled Compression Ignition, SPCCI, actually works. I used that information to write an in-depth technical explainer on the "holy grail" engine.
But pictures and words only go so far in explaining how a complex mechanical/thermodynamic system works, which is why Mazda has released this awesome video showing what happens in the combustion chamber, and comparing SPCCI with traditional gasoline and diesel motors.
I know it's just an animation, but look at the shape of that piston! And check out how it helps generate swirl!
The most important bit of the video, though — the part that actually provides insight into how SPCCI works — is fairly easy to miss. If you look closely during the intake stroke, you'll notice a short burst of fuel from the injector. This combines with the intake air, and mixes thoroughly in the "cyclone" to create a homogenous lean mixture throughout the cylinder.
This lean mixture won't ignite from a traditional spark plug, which is why, just as the piston reaches the top of its compression stroke, the injector shoots a bit of fuel near the plug to create a localised rich mixture, which ignites via the spark plug. The resulting "fire ball" compresses the lean mixture in the rest of the combustion chamber, resulting in rapid and homogeneous combustion.
It's a great visual explainer of how SPCCI combines the spark-induced fireball effect seen in traditional gas cars with the "rapid and simultaneous combustion at multiple points" of diesels, and it's great that Mazda has managed to make it work for its upcoming production cars.