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

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mazda skyactiv engine
The addition of roller rockers greatly reduces valvetrain friction.  A hydraulic lash adjuster greatly reduces maintenance over the life of the car.

To eliminate the problem of intake valve deposits that plague current direct gasoline injection engines, the engineers at Mazda determined that deposits are formed when intake valve temperatures fall below 400 degrees C.  Measures were taken so that the intake valve would operate above this point to reduce deposit formation.

mazda skyactive engine
One of the biggest issues with direct injection engines is a build up of deposits on the intake valve.  Mazda determined that this was largely due to the intake valve being too cool.  A lot of analysis went into designing the heat paths away from the valves to keep them at the proper temperature to avoid deposit formation.

Friction reduction was also aggressively pursued in the Skyactiv G engine.  There is 50% less valvetrain friction though the use of roller rockers, 37% less ring friction with narrow low tension rings, a small bore and slipper skirted pistons and 30% less overall friction for the entire engine using tricks like narrow main and rod bearings and superfinishing.  Less friction also fits into the scheme of greater overall efficiency which is amazing for this engine. 

mazda skyactive engine
As you can see here, the cylinder volume is very minimal but the combustion chamber is very different from a modern, shallow included angle pent roof quench chamber you typically see.

The Skyactiv G engine has an astounding BSFC or Brake Specific Fuel Consumption of 0.28, (this is a measurement expressed as pounds of fuel per horsepower per hour) which approaches that of a diesel.  A few years ago, a BSFC number of 0.45 was considered to be good for a gas engine!  More efficiency means great fuel economy.

mazda skyactive engine
You can see how little of an area of the piston actually contact the cylinder walls.  You can also see the reduced contact area of the wrist pin and how the piston and rod tapers have been carefully engineered to cause less distortion to the piston under load.

Performance-wise, the Skyactiv G engine produces 15% more torque from 1000 to 4500 rpm over the best in class gasoline 2 liter engines while using 15% less fuel and producing 15% less CO2.  In a Mazda 3, the projected fuel mileage will be in the 40 mpg range in highway use, equal to what our Project TDI Golf currently produces.

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