Compression Ignition’s efficiency and simplicity on gasoline is near commercialization. Maybe? Wayne Gerdes – CleanMPG – Aug. 7, 2017 2019 SKYACTIV-X Fingers crossed… Again. Mazda just announced, “Sustainable Zoom-Zoom 2030,” a long-term vision for technology development to 2030. Within this announcement, they stated they have created and will introduce a next-generation engine called SKYACTIV-X, the world’s first commercial gasoline engine to use compression ignition in 2019. SKYACTIV-X Engine According to the company’s release, SKYACTIV-X is/will be the world’s first commercial gasoline engine to use compression ignition, in which the fuel-air mixture ignites spontaneously when compressed by the piston. A proprietary combustion method called Spark Controlled Compression Ignition overcomes two issues that had impeded commercialization of compression ignition gasoline engines: maximizing the zone in which compression ignition is possible and achieving a seamless transition between compression ignition and spark ignition. This new combustion engine combines the advantages of gasoline and diesel engines to achieve outstanding efficiency and power. Compression ignition with a supercharger improves efficiency, engine response, and in particular, increases torque between 10 and 30 percent over the current SKYACTIV-G gasoline engine family. Compression ignition makes possible a super lean burn that improves engine efficiency up to 20 to 30 percent over the current SKYACTIV-G gasoline engine of the same displacement. SKYACTIV-X even equals or exceeds the latest SKYACTIV-D diesel engine in fuel efficiency!!! The engine is still under development and figures are subject to change. With high efficiency across a wide range of rpms and engine loads, the engine allows much more latitude in the selection of gear ratios, providing both superior fuel economy and driving performance. Homogeneous Charge Compression Ignition (HCCI) Let us assume Mazda is using HCCI using conventional gasoline in an engine without spark. Meaning the heat of compression > 15:1 compression ratios are high enough to auto ignite the air-fuel mixture in a controlled manner which in turn creates the downward driving force on the piston. Because HCCI injects fuel later in the compression stroke, combustion normally occurs at the boundary of the fuel and air, producing higher emissions, but allowing a leaner and higher compression burn, producing up to 30 percent more efficiency than a std. gasoline engine. Think TD vs a std. SI ICE. Controlling HCCI through a range from idle to full power is a bitch however. The trick is to control the HCCI process to achieve the efficiency, extremely low NO, and run over wide load and speed ranges. Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. Because peak temperatures are significantly lower than in typical SI engines, NOx levels are almost negligible. Additionally, the technique does not produce soot so no DPF would be required. The hard parts include how to create the auto ignition temperature from a cold start, a much tighter load range where the lean fuel-air can provide usable power due to in-cylinder pressure restrictions, and both CO and HC pre-catalyst emissions are higher due an incomplete combustion event thanks to how fast it occurs and the low in-cylinder temperatures. So how is it controlled to allow cold starts, a wide powerband, and low emissions of all types? I have no idea what Mazda is doing? While we still await the 2.2L SKYACTIV-D with SCR and a DPF, maybe the SKYACTIV-X using HCCI possibly will be offered almost immediately - as a 2019 - in the CX-5 or new Mzda3 instead? A super lean mixture usually introduces sky-high NOx output which may indicate the need for a gasoline SCR solution to cure that hurdle. Except with an HCCI off-shoot... And what about its drivability near idle, high torque at low RPM, or max power at WOT? Mazda has a penchant for curing combustion problems. Cold temperature starting? Does it use very expensive 30k psi CI injectors or more std. 2.7k SI ones? Like the 14:1 CR on gasoline in their European and Asian SKYACTIV-G engines - 13:1 here, maybe they have just done it again?