Story & Photo by Randy S. Peregrino
JUST when you thought Mazda already succeeded advancement-wise in their current Skyactiv powertrain lineups, another major breakthrough is under way—the next-generation Skyactiv-X engine.
Imagine a gasoline motor which is greatly more efficient and, at the same time, more responsive, minus the aid of a forced induction system. But, in order to achieve this milestone, Mazda turned to the very concept of diesel engine’s ability to produce combustion from compressed hot air to ignite the fuel.
For years, car manufacturers took into consideration the idea of High Compression Combustion Ignition (HCCI), but it proved to be difficult in attaining a lean mixture in favor of fuel efficiency. Now, Mazda took the giant step and came up with the solution by adapting its very own “Spark Controlled Compression Ignition”. This means that the Skyactiv-X system is not completely letting go of the conventional spark plug but rather utilize it to assist in producing spark on certain conditions. As such, the new technology will not rely on compression ignition alone to produce a combustion.
Complex as it may, there is no better person to expound these mechanics than a company subject matter expert. We recently had the privilege to be enlightened by no less than Mazda’s Product Strategy Division General Manager and Research and Development Head Hidetoshi Kudo. In a brief yet detailed presentation, he was able to share the innovations behind the new technology. “As you may know, gasoline and diesel engines each have strong points. With diesel engine, the response and torque is better. On the other hand, the peak power and high-speed performance with clean exhaust is for the gasoline engine. In SkyActiv-X, ‘X’ means a crossover between diesel and gasoline engines,” he explained.
While using lean mixture of fuel is good for efficiency, it is also known to be detrimental for the engine itself. “We realize that the transition to a complete compression ignition is very difficult. Then we tried to breakthrough HCCI. In common sense, spark is not needed for compression ignition, but, in this case, we tried to use spark ignition to control the compression issue,” Kudo added. The key is utilizing a spark-assisted combustion compression ignition in SkyAtiv-X. There will be complete control of switchover where the use of a spark plug is considered as a control factor. Think of it as an endless transition between the two ignition process in order to produce the ideal combustion.
Kudo further tackled the relationship between the two different motors. “We all know that gasoline and diesel engines respond differently. For the conventional gasoline engines, when you press the pedal, there’s a delay in the air coming in and response is not so good. On the other hand, diesel engine is always almost opened, therefore, the torque can be controlled by the fuel injection and response is good. The Skyactiv-X has the same characteristics like the diesel engine by utilizing the lean operation,” he said.
In one of the slides, graph showed that the acceleration curve of Skyactiv-X is almost similar to that of the Skyactiv-D (diesel). Moreover, compared to current Skyactiv-G (petrol) powertrains, which already attained around 15-percent increase in performance, the new Skyactiv-X technology can add up from 10 percent to 30 percent more on torque versus the current technology and claimed to be 20 percent to 30 percent more fuel efficient. While fuel efficiency falls closely with the current Skyactiv-D powertrains, the acceleration characteristic of the Skyactiv-X is steadier toward higher rpm.
Interestingly, there will be no major changes in terms of engine components. Kudo simply stated “The system is very simple—no special hardware.” But when asked how can the motor handle the lean mixture, he clarified that the compression is not high, therefore, the engine is not heavy built and rather comparable to the current ones. “We understood the mechanics by utilizing the modern ways of development then we can fully understand that it can control preignition. We only applied pressure sensor to the system,” Kudo explained.
The upcoming Skyactiv-X will coexist with Mazda’s current powertrain lineup. However, there’s no clear information yet as to the different displacement offerings, including segment applications. Instead, it would be a continuing development and that Mazda will deploy the technology one step at a time until there’s a capability to deploy it to every displacement area. Slated to be released in 2019, pricing of vehicles with this motor would be somewhat higher, but it would be commensurate to the performance and driving sensation enhancements. It was also claimed that Skyactiv-X is built to meet future Euro emission standards and while it shares the same characteristics with diesel mills, it will definitely not sound like one.