I don't quite like the fact that the spark plug is burried deep inside the engine which makes servicing difficult. Reminds me of Porsche boxer spark plug changes for which you need to unmount the rear wheels.

Looks to me from image 3 at the bottom of the page that the whole unit unthreads: http://www.mahle-powertrain.com/en/experience/mahle-jet-igni...

Sounds interesting. I'm very curious, though, to see an ignition profile of the compression ignition concept: it seems to me that compression would be even throughout the ignition chamber, leading to a somewhat (within the bounds of statistical deviation in fuel/air pressure) simultaneous ignition of the fuel/air mix. Meaning that I think Mazda's technology would combust more efficiently.

- over 40% thermal efficiency

- significant reduction in CO2

CO2 production is directly inverse-linearly related to thermal eficiency. It is silly to list both.

This is far from a universally-realized/appreciated fact; it's good to list both for those that weren't aware.

Would you mind explaining why (to a layman)? The Wikipedia page on thermal efficiency makes no mention of the CO2 relationship.

Thermal efficiency basically refers to just the efficiency of an ICE (or any heat engine for that matter) – i.e. how much of the chemical energy of the fuel you manage to convert into mechanical energy in the drive train. The better the efficiency, the less fuel you need to produce the same power output, obviously producing less CO2 in the process.

(To be more specific, the terms are often used interchangeably. Thermal efficiency has an exact definition in an ideal heat engine and even ways of calculating the theoretical maximum for given conditions – but CO2 or chemical reactions have nothing to do with an ideal heat engine to start with. I'd personally perhaps prefer to talk about just the efficiency in an actual ICE – even if just to be clear none of the losses are conveniently left outside the calculation.)