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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: 2) by Whoever on Wednesday January 31 2018, @06:26AM (1 child)
But this engine runs with excess O2 and naturally there is nitrogen in the air intake, so how does more complete burning of the fuel reduce NOx emissions?
There is also mention of lower combustion temperatures, perhaps this is the reason?
(Score: 3, Interesting) by ElizabethGreene on Wednesday January 31 2018, @03:42PM
NOx forms when you have heat, oxygen, and nitrogen. You can demonstrate this by firing an arc furnace in an enclosed space. The air in the vessel will turn brown from NOx compounds.
The minimum temperature for this reaction is ~2800 F. Below that it doesn't happen in quantity.