Skyactiv-X Compression-Ignition

Mazda Motors has announced a “Sustainable Zoom-Zoom 2030” vision. A plan aimed at cutting emissions and maintaining growth through the year 2030. A big part of this initiative is a new ultra-efficient and ultra-clean, yet powerful compression-ignited engine.

Combining the best traits of diesel and gasoline engines, Mazda calls it Skyactiv-X and experts are calling it the “holy grail” of powertrain technology. It is a risky yet necessary gambit for Mazda as it races to stay competitive on a shoestring budget. Meanwhile, rivals are investing heavily in costly electrified cars.

Typical of Mazda’s business model, it has a tendency to zig while the industry zags. They have a tradition of being more innovative than the competition. The company proved their aptitude in 1967 when they pioneered the revolutionary rotary engine and again more recently as an early adopter of lean-burning, high-compression combustion in the Skyactiv engines.

Mazda says the new engine will boost torque by up to 30 percent and also improve fuel efficiency by up to 30 percent over their current line of Skyactiv-G direct-injection engines. This Homogeneous Charge Compression Ignition engine (HCCI) actually works a lot like a diesel. Instead of using spark plugs to ignite the air-fuel mixture, it uses compression, which allows it to burn like a diesel engine, but without nasty nitrogen oxide or sooty emissions.

This technology has eluded engineers for years and is not without its challenges. If the engine is revving too quickly, there is the risk of misfire because of the high number of revolutions. If it revs too slowly, it can misfire because of low temperatures. Engine cooling is a challenge because of the HCCI’s high temperature and pressure. Additionally, the engines are more fickle about fuel and perform differently depending on fuel properties.

Mazda’s solution was a hybrid or crossover of sorts, hence the ‘X’ in Skyactiv-X. Engineers were able to expand the range at which the HCCI can work, but there are ranges where it still has difficulty, such as at high revolutions where Skyactiv-X still employs a traditional spark plug to help with combustion.

The transition between compression ignition and spark ignition is one of the biggest challenges. The transition must be absolutely seamless and unnoticeable to the driver. The compression-ignition mode is extremely sensitive to even the smallest changes in cylinder pressure and temperature, making it hard to manage in the wide-ranging road conditions of real-life driving. They have apparently figured it out though, and plan on beginning production in mid-2019.

Mazda also has outlined plans for a pure electric vehicle in 2019 and a plug-in hybrid after that, but they feel that the pursuit of the ideal internal combustion engine should come first and is the keystone to their growth plan.