13:1 Compression and 40 mpg on 87 Octane fuel? Introducing Mazda’s Skyactiv Technology

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 mazda skyactiv engine
The cat is located under the curve of the exhaust manifold, pretty far away compared to today’s typical close-coupled cat.  We feel that this engine is going to be a bit hard to modify!

This cross flow of cool intake air adds extra combustion chamber cooling to further reduce the propensity for detonation.  The additional cooling also helps keeps the production of the pollutant NOx low.  NOx is a byproduct of the high combustion temperatures created by efficient combustion and high compression ratios.  The cooling effect of tuned overlap and conventional EGR keeps NOx low, even in this high compression motor.

 mazda skyactiv engine
The high pressure injector has six spray holes for good atomization and fuel mixing.

With direct injection, fuel can also be injected during the intake stroke.  As the fuel vaporizes, it cools the air in the combustion space which contracts with the drop in temperature.  This also causes a drop in pressure and allows for more air to be taken into the cylinder improving volumetric efficiency.

 mazda skyactive engine
The intake port is shaped for tumble into the cylinder as the piston drops from TDC.  This helps ensure good mixing of the fuel and air by increasing cylinder turbulence.

With lots of cylinder cooling, through direct injection, variable cam timing and exhaust tricks, along with a very homogeneous fuel air mixture due to the turbulent combustion chamber, smooth combustion with no detonation is assured even with 87 octane pee water fuel.  The tricks to improve VE through super high compression (yes high compression improves VE), intake stroke cylinder cooling, variable cam timing tricks and efficient exhaust, plus the gains in thermal efficiency due to the high compression ratio, also yield pretty decent power output.  To further increase thermal efficiency, the bore size has been reduced from 87 to 83.5mm to reduce the piston’s surface to volume ratio.

 mazda skyactive engine
The tuned intake manifold is conventional and unremarkable.

 

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