Mazda has been sharing bits and pieces of its revolutionary SkyActiv-X technology, a gas engine that doesn't need spark plugs under heavy loads. Other than a few details released in its recent powertrain plan, we’ve been kept in the dark on the how it actually works. Luckily, a recently published patent may give us a better idea of how the engine runs and has details of a brand-new, never used, device that could be employed to reach Mazda's lofty fuel economy and emissions goals.
was published just a couple of weeks ago and it describes a powertrain control module for a compression ignition-type engine. The patent references a few older patents describing homogeneous charge compression ignition–or HCCI–but delves much deeper into Mazda’s plans as it describes all of the sensors and devices that the engine will need to run.
One of the big questions related to HCCI is how Mazda will regulate temperatures to make sure engine knock doesn't occur. That is answered right off the bat since the patent shows the deployment of a multitude of temperature and pressure sensors. We start off with the usual mass air flow and intake temperature sensors that can be found on just about any modern car, but Mazda adds another intake temperature sensor on the downstream side of the intercooler that is forcing cooled air from the supercharger they plan to use.
Sensors in the intake give the PCM some data as the air is hurling towards the engine. But the actual high temperature explosions happen inside the cylinder, so Mazda is monitoring that by adding a temperature sensor on the intake and exhaust ports as well as the EGR inlet, along with pressure sensors in the cylinder and the exhaust. All of the sensors will provide important data to the PCM to make sure the engine performs within its limits. However, the one that solves one of the biggest tuning challenges is the cylinder pressure sensor.
Timing can be controlled easily in a standard Spark Ignition (SI) engine due to the use of spark plugs. A compression ignition engine, or in this case, a compression ignition cycle, runs based on auto-ignition and it is much more difficult to control the timing. The in-cylinder pressure sensor helps solve this issue by providing feedback to the PCM along with the temperature sensors so that the ignition control strategy can be deployed via valve timing and EGR control.
The patent describes an engine control strategy that uses the information from these sensors to control valve opening along with EGR injection in order to control the temperature inside the cylinder. The description of the spark ignition mode is pretty similar to their current SkyActiv engine tuning; we can see some of the same valve control mechanisms in place. Mazda takes these a step further and describes how the EGR system can inject hot or cooled air inside the cylinder in order to raise the temperature and transition to HCCI mode in low load situations. Once the engine is in HCCI mode, the combustion is controlled by the amount of fuel injected combined with the amount of cooled or hot air that is introduced from the valves or the EGR system.
This tells us a bit more about the operation and transitions of the new engine. That said, there is one last part that may tell us how Mazda is able to making such high increases in fuel economy while or from incomplete fuel burn. The key could be a device listed as part 76 in the patent, which is called an O3 Generator, or Ozonator. It may be familiar to you as a device used by cleaning companies to remove bad smells or mold from a home or car. One has never been used in automotive powertrain applications.
Adding the ozonator to the powertrain control scheme helps to solve several shortcomings of the hybrid HCCI design along with adding improvements in fuel economy. Since ozone (O3) than the fresh (O2) that is usually brought into the cylinder, it can be injected in order to run the low-load compression mode when the ambient temperature is cool. Extending the running time of the low-load mode helps to improve fuel economy along with reducing emissions.
The second part of the equation is that injecting ozone allows for the engine to run under stoichiometric conditions when in low-load which allows the implementation of a instead of using an expensive after treatment system like you might find on a diesel vehicle. Another benefit of ozone injection is an overall reduction in the output of nitrogen oxides (NOx). that NOx is greatly reduced when combined with ozone and directed to a catalytic reactor.
When asked, Mazda acknowledged the existence of the patent but told us they would not confirm any additional technical details until an official release in September.
The combination of an advanced array of sensors along with the introduction of an ozonator makes the powertrain control scheme of the SkyActiv-X more apparent. That's how the transition from spark ignition to compression ignition can be controlled and explains how they are able to reach such high fuel economy targets. This could be the innovation that extends the life of the combustion engine far in to the future.