The world's lowest diesel-engine compression ratio, it's clean, highly-efficient diesel engine will comply with strict exhaust gas regulations globally without the need to use expensive Nitrogen Oxides.

Features of SKYACTIV-D

  • 20% better fuel efficiency
  • A new two-stage turbocharger realizes smooth and linear response from low to high
  • Complies with global emissions regulations without expensive NOx after treatment

Causes of NOx and Soot Formation

Diesel engines generally have a high compressions ratio; the compression temperature and pressure at piston top dead centre are very high. If fuel is injected under these conditions, ignition will take place before an adequate air-fuel mixture is formed, which results heterogeneous combustion to occur.

There are strict emission regulations which makes it difficult to ignite the mixture at the optimal timing, which leave no other choice but to delay combustion until the piston begins to descend and lower the cylinder pressure and temperature, however, this causes fuel economy to worsen.

Optimization of Combustion Timing by Lowering Compression Ratio

When the compression Ratio is lowered, the temperature for both the compression and pressure at TDC decreases. Therefore, ignition takes longer even when fuel is injected near TDC, enabling better mixture of air and fuel. This actually relieves the formation of NOx and soot because the combustion becomes more uniform without localised high-temperature areas engine, at which a large amount of work is obtained than in a high-compression-ratio diesel engine. 

Reduction on Weight and Mechanical Friction by lowering Compression Ratio

As a result of its low compression ratio, the maximum in-cylinder combustion pressure for SKYACTIV-D is lower than the current diesel, realizing significant weight reduction through structural optimization.

It became attainable to change the cylinder block's material to aluminum, which saved 25kg (vs. current diesel). The cylinder head became 3kg lighter with thinner walls and an integrated exhaust manifold. As for the reciprocating parts, the weight of the pistons was reduced by 25%.

The crankshaft has its main journal diameter reduced from 60mm to 52mm, achieving a 25% weight reduction. The outcome is that the mechanical friction was greatly reduced to the same level as an average gasoline engine.


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