Wednesday at Bernies | Ask the /r/formula1 community anything! - 04/26/2017

I heard Brundle talk about it in the Chinese GP, so I just took it from him. This article is very interesting though. Apparently, they still have spark plugs, but they can run without powering them for better fuel efficiency.

They separate the fuel chamber into two different, isolated volumes, one large and one small. When they don't ignite through the spark plugs, they manage to create an incredibly high pressure in the small chamber, like diesel engines. This smaller chamber has a fuel rich mixture, to aid ignition. The larger chamber has a fuel mixture that's less rich than the smaller one.

When the piston starts to move down, the two chambers are connected again, becoming on whole chamber. The small chamber is already igniting. When it comes to contact with the larger one, the ignition is continuing to ignite the fuel is the larger chamber too. This apparently creates better fuel efficiency (don't ask me why, I'm not an engineer).

When running in conventional ignition mode, they either don't fuel the smaller chamber, or they can retract a plunger that isolates the two chambers.

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