More than six years ago, Mazda debuted a technology that promised to revolutionize internal-combustion. Now, we’re wondering if it was a false dawn. Skyactiv-X, as Mazda calls it, represented the culmination of decades of auto-industry research and development into a compression-ignition gasoline engine. For years, major automakers and research groups worked toward creating a homogeneous-charge compression-ignition (HCCI) engine, which held the promise of diesel-like fuel economy with far fewer emissions. Ford, GM, Nissan, Honda, Mercedes-Benz, and Hyundai all developed prototype HCCI engines, and even the US Department of Energy funded research into the technology. While most efforts seemingly petered out,...
