Submitted via IRC for AndyTheAbsurd
It's called Spark Controlled Compression Ignition, and Mazda made it work.
Despite rumors to the contrary, the internal combustion engine is far from dead. Recently we've seen several technological advances that will significantly boost the efficiency of gasoline-powered engines. One of these, first reported back in August 2017, is Mazda's breakthrough with compression ignition. On Tuesday, Mazda invited us to its R&D facility in California to learn more about this clever new Skyactiv-X engine, but more importantly we actually got to drive it on the road.
The idea behind Skyactiv-X is to be able to run the engine with as lean a fuel-air mixture (known as λ) as possible. Because very lean combustion is cooler than a stoichiometric reaction (where λ=1 and there is exactly enough air to completely burn each molecule of fuel but no more), less energy is wasted as heat. What's more, the exhaust gases contain fewer nasty nitrogen oxides, and the unused air gets put to work. It absorbs the combustion heat and then expands and pushes down on the piston. The result is a cleaner, more efficient, and more powerful engine. And Skyactiv-X uses a very lean mix: a λ up to 2.5.
(Score: 5, Interesting) by Corelli's A on Wednesday January 31 2018, @02:32AM (1 child)
It's a clever design. If I read the design parameters correctly, that's a 16:1 compression ratio. To set proper spark timing, they specify an "in-cylinder pressure sensor" to measure the spark-initiated and compression-initiated combustion pressure curves for each stroke.
Although they tout lower cylinder temperatures, I also note that one of the graphs indicates that a given engine switches between combustion regimes depending on load/rpm so I don't know if those lower temperatures always obtain. I am exceedingly curious what kind of lifetime a mass-produced in-cylinder pressure sensor can have. What are the failure modes? If one of these sensors fails, can the engine run at all?
(Score: 2, Interesting) by Anonymous Coward on Wednesday January 31 2018, @03:13AM
> If one of these sensors fails, can the engine run at all?
Might have a limp home mode in the software that runs things from an open loop calibration table? But certainly can't run well without the feedback sensor, everything in this engine is on the edge.
Another possible failure mode is a sticky/leaky fuel injector -- too much fuel combined with 16:1 compression is going to make a bigger bang than the materials of the engine can withstand (for very long).