This past week Mazda announced it will introduce its next generation engine called SKYACTIV-X in 2019. While all manufacturers make similar announcements for new products, Mazda’s announcement was something special.
This new engine will be the first commercial gasoline engine to use compression ignition.
Compression ignition is used all the time, but not in gasoline engines. Diesel engines use compression ignition. When the diesel piston goes up in the cylinder, it compresses the air in the cylinder several times. Compression ratios vary from a low 15:1 to around 23:1. This squeezing of the air makes it very hot. When the diesel fuel is injected into the cylinder, the hot air ignites the fuel instantly.
Compression ignition in gasoline engines isn’t quite as simple as in diesel engines, but it does offer similar advantages.
Mazda is utilizing a proprietary combustion method called Spark Controlled Compression Ignition which allows the engine to have a seamless transition between conventional ignition where the fuel is ignited by a spark plug to compression ignition where the fuel is ignited by the heat of compression.
While details of how the compression ignition works, it is safe to say that the shape of the piston head and combustion chamber will be critical along with the timing and position of the injection of fuel into the cylinder.
When a supercharger is added to the compression ignition engine, torque will increase from 10 to 30 per cent above the current SKYACTIV gasoline engine and it will have even better engine response and fuel economy. Compression ignition allows an extremely lean burn in the cylinder, with excess air in the cylinder and very little fuel. Only the fuel needed to keep the engine running at the demanded power levels will need to be injected, instead of a richer mixture that is needed for spark ignition to take place.
This very lean fuel delivery will improve engine efficiency from 20 to 30 per cent over the current SKYACTIV engine and from 35 to 45 per cent over a 2008 Mazda engine with the same displacement. Fuel economy even exceeds that of the latest Mazda diesel engines.
The strong engine torque over a wide power band range enables a wider selection of transmission gear ratios, which will also improve fuel economy and vehicle performance.
The compression ignition will also be good for the environment. Carbon dioxide, a greenhouse gas, is a byproduct of fuel burning in the engine. By decreasing the amount of fuel needed to create the combustion process, fewer greenhouse gases are produced.
This compression ignition engine is only part of Mazda’s long-term vision for technology development. Mazda calls it “Sustainable Zoom-Zoom 2030” in which everything from driver enjoyment to proactive safety to autonomous vehicles will be developed for the future.
While hybrids and electric cars are seen as the future of environmentally friendly automobiles and will be part of Mazda’s ongoing initiatives in 2019, the gasoline engine will be with us for a long time.
Innovative engineering such as Mazda’s Compression Ignition gasoline engine will keep them in our future for a long time while providing lower emissions, better fuel economy and outstanding performance all at the same time. Who can want for more?