SKYACTIV Compression Technology Features in the Mazda G Engine
Mazda engineered a series of engines to increase fuel efficiency. Using SKYACTIV technology, these engines are able to compress the air-fuel mixture inside the cylinders to an extraordinary degree.
SKYACTIV engines can harness up to 15% more energy from every drop of fuel than conventional engines. This helps Mazda achieve their Sustainable Zoom-Zoom philosophy.
Compression Ignition
Compression ignition is an innovative method of fuel combustion that uses pressure to ignite the air/fuel mixture. It is found in many diesel trucks, trains, construction equipment and other diesel-powered machines.
Automakers have been working on developing compression-ignition engines for decades. However, they haven’t been able to put them into production due to a variety of challenges.
Mazda figured out how to overcome these problems and rolled out the world’s first commercially available compression-ignition gasoline engine, the Skyactiv-X.
To accomplish this, Mazda changed the way it combines air/fuel mixtures for spark and compression ignition. It traded HCCI for SPCCI, or Spark Plug Controlled Compression Ignition.
SPCCI, or spark-controlled compression ignition, allows the engine to use extremely lean fuel mixtures, like HCCI, but over a much wider swath of driving conditions, including under moderate load and higher engine speeds. It also solves the problem of soot production in CI operation. This new system combines a high-response air supply and super-high-pressure fuel injection to support compression ignition.
Dual Sequential Valve Timing
The Dual Sequential Valve Timing feature of the Mazda G engine allows the cams to be opened earlier for intake and closed later for exhaust. This ensures that the engine is able to breathe more efficiently as it goes through its full range of revs, helping it to create more power and torque while improving fuel efficiency.
The SKYACTIV-G 2.0-litre engine features multi-hole injectors that enhance fuel spray and the evaporation of the injected fuel in the combustion chamber after injection to reduce pumping losses caused by internal exhaust gas recirculation (EGR). It also uses specially designed piston cavity shapes to avoid knocking, which can occur due to high temperatures and compression.
Besides, the engine also has an unusual Miller cycle that delays the closure of intake valves, which is an advanced way to improve efficiency. Moreover, it is equipped with Spark-Controlled Compression Ignition, a never-before-seen combustion method that Mazda engineers have developed. This is a step forward in their quest to develop an ideal internal combustion mechanism.
Variable Valve Timing System
The Variable Valve Timing System (VVTS) feature of the Mazda G engine is designed to improve fuel efficiency. It increases horsepower and reduces emissions.
The valve timing can be controlled by adjusting the position of each intake and exhaust valve on the cylinder head. This can be done for different situations to make the vehicle more efficient.
The VVTS can be achieved using a simple cam-phasing VVT or a continuously variable VVT that adjusts the shifting of each intake and exhaust valve. The latter is a better option because it offers continuous valve timing and duration changes, which greatly enhance engine flexiblility at low to high rpm.
High Compression Ratio
The High Compression Ratio feature of the Mazda G engine enables a 15% increase in fuel economy and additional torque in low- and mid-speeds. This ratio also helps reduce exhaust, cooling, pumping and mechanical-friction losses by eliminating unwanted abnormal combustion or knocking.
To reduce knocking, Mazda engineers adopted a 4-2-1 exhaust system that prevents hot residual gases from re-entering the cylinder, lowering the temperature inside. They also redesigned the combustion process by using multi-piezo injectors to enhance the air-fuel mixture, quicken its combustion and help cool the cylinder.
Another key to the engine’s efficiency is its dual sequential valve timing (S-VT) intake that minimizes pumping loss. During the first 20% of the compression stroke, inlet valves remain open until BDC (bottom dead center), when the piston is at the bottom of the cylinder.
