I would say that they started 2015 with a fuel hungry engine with a weak ERS, and 2016 improved on this in every respect. The 2017 was a brand new architecture, and a brand new combustion concept based on the pre-chamber, they took a step backwards and it led them to a net step forward at the end of 2017. 2018 first spec engines are a new combustion concept that was developed with lessons learned in 2017, and this has led them to the development of the next evolution that's planned for mid season. New means same concept but new hardware to exploit the things you learn along the way.bigblue wrote: ↑Sat Feb 10, 2018 10:34 pmThe words "completely new combustion process" obviously brings concerns. Is it even possible to explain the progression from 2015 to this mid-2018 engine, in terms of combustion process ? Does one process evolve into another, or is it a sort of "start again from scratch" scenario ? It's quite worrying if it's the latter as often things don't work out as intended, then again I guess you have the previous versions as a benchmark, and all the lessons learned from those engines, if only in terms of reliability, layout, and energy recovery philosophy. I suppose the glass half-full view is that there is still the potential for big gains if rather different combustion is on the cards going forwards ? Anyway, I'm sure you can understand the caution after the last few years.
What if 1 gigantic intake valve was used with a smaller valve for the prechamber. 5.1.8 states the engine must have 2 intake and 2 exhaust valves per cylinder so I don't think you could get away with a 3rd smaller intake valve for the prechamber.
Good point. I didn't think about the increased weight. Was just wondering how effective a "normal" CC/cylinder design would be at ensuring fresh air for the prechamber. Than again maybe it's not even an issue.godlameroso wrote: ↑Sun Feb 11, 2018 4:40 amNot really, engine speeds are relatively low, two smaller valves however have lower inertia, and less mass than one big valve. Flow, seal, and valve inertia are more engineering challenges when using one valve, and not power or efficiency dead ends. However time is of the essence,
Don't the intake valves clash once both opened?
The angle between the intake valves is very small - they do come close as they open but won't touch.Brake Horse Power wrote: ↑Sun Feb 11, 2018 1:00 pmDon't the intake valves clash once both opened?
It is a challenge, maybe a side injector with a pocket in the piston for the injector, the combustion chamber is almost diesel like, very little curvature, not at all like the conventional pent roof chambers. The pre-chamber could sit just above the injector, and the injector uses a "pre-chamber spray pattern". Prior to this during the intake phase the main charge of fuel is sprayed with the "main chamber spray pattern", the swirl during intake segregates the main chamber mass, and allows a tiny and precise spray into the prechamber during the compression stroke. During this period the swirl will be transitioning to tumble/squish to aid mixing(if the engineers designed the system properly), the pre-chamber begins to ignite ~34 degrees BTDC, at ~16 degrees BTDC the flame jets begin penetrating across the chamber volume, at ~7 degrees BTDC the mixture begins igniting from outside in, and the pressure begins to rise dramatically until a few degrees ATDC where maximum heat release happens. With luck you timed everything well enough that maximum heat release happens just as the piston begins moving down, so that the combustion aids the crank's inertia.1158 wrote: ↑Sun Feb 11, 2018 5:06 amGood point. I didn't think about the increased weight. Was just wondering how effective a "normal" CC/cylinder design would be at ensuring fresh air for the prechamber. Than again maybe it's not even an issue.godlameroso wrote: ↑Sun Feb 11, 2018 4:40 amNot really, engine speeds are relatively low, two smaller valves however have lower inertia, and less mass than one big valve. Flow, seal, and valve inertia are more engineering challenges when using one valve, and not power or efficiency dead ends. However time is of the essence,
Yes, more than a fair amount of NOx.godlameroso wrote: ↑Sat Feb 10, 2018 8:23 pmDo these engines produce a fair amount of NOx?
Higher injection pressures would allow better atomization, otherwise you have to rely on air dilution and natural EGR to aid fuel vaporization. The spray pattern of the injector could feed the pre-chamber and main chamber independently, but it requires a very precise injector because the timing is critical.
The pre chamber nozzles are also very important, you need to size them accordingly. Too many nozzles and the jets won't have enough penetration across the cylinder volume, to few and you won't have enough sources to consume the lean mixture. The opening into the pre-chamber is also important.
The pistons probably have to deal with several compromises as well.