Mazda has always been the outlier in the auto industry when it comes to internal combustion engines. It built its reputation on the quirky Wankel rotary engine that NSU never could get right. Mazda’s amazing rotary was half the size and half the weight of a conventional piston engine, which made it the ideal choice for Mazda’s first sports car, the iconic RX-7.
The one thing Mazda could never tame, though, was the rotary’s thirst for gasoline. As fuel prices rose and miles per gallon became important to consumers, Mazda turned its attention to developing more efficient piston engines, leading to its current lineup of so-called SkyActive engines.
Last January, Mazda announced a new generation of gasoline engines that ran without spark plugs. Called HCCI, which stands for homogeneous charge compression ignition, the new engine used compression ratios as high as 18:1 to ignite the fuel mixture. It was said to have 30% better fuel economy with lower emissions.
This week at the Tokyo motor show, Mazda has once again announced new internal combustion technology, this time known as Spark Controlled Compression Ignition or SPCCI. Dubbed SkyActive X, this latest power unit combines the HCCI technology with the tried and true spark plug. It still uses a very high compression ratio and a combustion chamber similar in shape to the those used in diesel engines.
Mazda says it can switch seamlessly between compression and spark ignition, depending on load. It uses a new split fuel injection system and an in-cylinder pressure sensor to keep stabilize combustion and control the heat of the cylinder head. Mazda claims 30% more torque from a given quantity of gasoline and 20% better fuel economy. Here’s how Mazda explains it:
“The SKYACTIV-X controls the distribution of the air-fuel mixture in order to enable lean burn using the SPCCI mechanism. First, a lean air-fuel mixture for compression ignition is distributed throughout the combustion chamber. Next, precision fuel injection and swirl is used to create a zone of richer air-fuel mixture—rich enough to be ignited with a spark and to minimize nitrous oxide production—around the spark plug. Using these techniques, SPCCI ensures stable combustion.”
But how does it work? This is a case in which a video is worth ten thousand words. Enjoy!
So, what does any of this have to do with the coming electric car revolution we are all hoping for? Not much, actually. But despite our fondest wishes, internal combustion engines will be with us for many more decades. If they all used significantly less fuel and created fewer carbon emissions in the meantime, that would be a good thing, right?
And if Mazda were to combine its new SPCCI engine with its stunning Vision Coupe Concept on display this week at the Tokyo motor show, that would be a very good thing.
Source: Road & Track