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Arouse the DAMPFHAMMER!
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That's an awesome work Scider. I really appreciate your measurement!

It's somewhat interesting to see the offset between the lobe centers for high and low speed...This is probably designed around the factory VTEC switching point so the cam phaser doesn't have to move.
The setting of the centerline is mainly driven by mean VE and peak VE for each cam and the application. Of course it is also depended on the cam duration and profile shape. The lower the speed, the less gas dynamic support comes from impulse of the gas column, it's more related on the pressure swing. This is the main driver for VE and therefore the camshaft centerline. At higher speeds, even with higher duration of valve opening, the gas impulse and the the more retarded pressure wave helps to keep the air inside when piston is already moving up.

It makes me curious what aftermarket manufacturers are doing with their cam designs, and what design philosophy they use for the low speed cam profiles.
I know it exactly from TODA A3: low speed cam exhaust centerline is advanced by 4° compared to high speed cam. Centerlines of low speed and high speed are almost the same, as it is just a VTC work thing. A note, the low speed intake camshaftes have different centerlines by 2.5° difference, to start a sort of swirl for an faster combustion when the intake gas speed is low (part load - emission game). TODA overtakes that from the OEM camshafts.
 

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Arouse the DAMPFHAMMER!
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5,943 Posts
Ideally you want the flame to consume the end gas near the exhaust side before the intake, but this doesn't always happen based on port geometry and valve events.
Larry Widmer of ENDYN worked on that approach with his Roller Wave piston and head design. Knock location and activation has many parameters as you mentioned Scider. But this means it has also many options to depress it. These are the good news. The bad news all measures against knock cost something: emissions, efficiency or performance. Combustion design is finding the best compromise of those. One of my ideas lead to the highest compression ratio combustion systems in the market (Industry, CHP plants) while keeping emissions below limit at the highest available thermal efficiency of the market for such a combustion system. It's a different approach then Larry used for the Roller Wave concept, which is activation energy driven. My idea is mainly driven by turbulent kinetic energy. So two total different approaches for the same goal.

What OEM automotive combustion designs for down sized engines often miss is an idea to prevent knocking with more then the conventional primaries: retard ignition timing and adding fuel. There are so many options available and known, one of the OEM's I really appreciate is Mazda. They didn't follow that dead end strategy of down sizing and went into an high compression ratio design with all disadvantages and fought them successfully. The SkyActive gasoline engine is one of my favorite combustion designs in mass production engines.

Regarding fuel to cool turbine blades, the temperature level declines on both side of the optimal combustion velocity lambda. The right side is a much more difficult side, running lean means alot of effort, but it has an huge impact on efficiency too. I was involved in designing highly boosted lean burn combustion concepts and the main key to handle is ignition. Many OEM's have no experience in this field and even don't know technologies to handle it. The Corona Ignition System (Corona coming from the Sun-Moon-constellation not from the flue) is the wrong way into that. It's limited, expensive, and effectiveless to go really further. Formula One did the right step, pre-chamber combustion design. In industry this is common since the 80'ies 😂 . Just imagine, on a 27 bar BMEP engine having an exhaust temperature of 580 °C. This means alot to the boost concept and pressure drop over the engine. Finding positive pressure drops (= exhaust pressure - intake pressure < 0) concepts need some serious turbo technology. Anyway, running lean at almost a lambda of 2 and having a smaller (!!!) combustion duration compared to lambda 0.9... is included in a pre-chamber combustion design. I saw up to 20° less, just by shorting the combustion length. Faster is only HCCI, which is load limited.
 
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