The first information about motors Skyactiv (then still just Sky) appeared in 2010. Nowadays, Skyactiv technology includes the following: platforms, power structure of the car body, engines and transmissions. Surprisingly, but less than four years later the Japanese began talking about a new stage of its development: the second generation Skyactiv engines.
Magicians from Mazda have already surprised the world with their Skyactiv-G engines. The compression ratio of 14:1 is very much by the standards of civil gasoline engines. A lot of sweat went into that job: engineers were working at an ensuring stable combustion mixture, detonation suppression, and temperature balance. So, what else could we ask for in the motors of Skyactiv-G Generation 2? They will achieve a compression ratio of 18:1 on ordinary gasoline!
Such a high degree of compression is chosen because the Japanese intend to apply HCCI, Homogenous Charge Compression Ignition, in the second generation of Skyactiv units. That is, these will be petrol engines, operating on the principle of diesel. They must combine the advantages of two cycles. The idea of HCCI itself is not new. For example, seven years ago HCCI experiments were conducted by GM, when the same unit called DiesOtto was developed and tested by Mercedes-Benz company. However, no brand has brought this principle to the production car implementation yet.
In 2007 the Germans put DiesOtto engine under the hood of the concept Mercedes-Benz F 700. The car accelerated in 7.5 seconds, top speed was 200 km/h (electronically limited), and average fuel consumption was 5.3 l/100 km. This is really stunning for the car of 5.18 m length.
The fact is that although the HCCI promises 30% reduction in fuel consumption compared to current engines, it is more difficult to provide the desired parameters of mixture combustion in such engines. At the moment, experienced HCCI engines from Mazda operate stable only within 50% of maximum power. If more, it is necessary to activate the stored spark plugs (GM and Mercedes have made the same decision). Once such a motor has become commercial, then an average passenger car will emit carbon dioxide in an amount of 80 g/km, the Japanese developers say.
Mersedes turbo ‘four’ DiesOtto 1.8 was equipped with direct injection and variable valve timing mechanism, developing 238 hp., paired with an additional 20-horsepower electric motor in F 700, and reaching summary powerplant torque of 400 N • m.
