Modern day diesel engines are quieter, more durable, and cleaner than before. However, they use heavy parts and expensive exhaust after-treatment systems. In order to solve this problem, Mazda changed the way diesel engines work with its SkyActiv-D technology.
Before we proceed, we need to explain what compression ratio is and how it affects the performance of an engine. Why? Because with the SkyActiv-D technology, Mazda deliberately reduced the compression ratio – making their diesel engine unique from other carmakers.
Compression ratio explained
Automobile engines produce energy through the up and down motion of the pistons inside the cylinders, compressing the air-fuel mixture.
Compression ratio is the correlation between the volumes inside the cylinder when the piston is at its lowest point (bottom dead center), versus when it’s on its highest point (top dead center). In a nutshell, the higher the compression ratio is, the more mechanical energy you could get from the air-fuel mixture inside the cylinder. That has always been the principle when we’re talking about compression ratios.
However, Mazda dared to defy that with the SkyActiv-D technology.
Low compression ratio
Instead of keeping the compression ratio high as it has always been believed, Mazda reduced it to 14:1 – the world’s lowest among diesel engines. Their intention is to lower compression ratio to enable air and fuel to mix more thoroughly, resulting to cleaner exhaust emissions, higher combustion efficiency, and better fuel economy.
How? They redesigned their diesel engine by using lighter components. The aluminum block is lighter by 25 kg, while the cylinder head has thinner walls resulting to 25% less weight. Moreover, the crankshafts and pistons are also 25% lighter. All these result to better drivability and efficiency – as opposed to the current Common Rail Direct Injection (CRDi) diesel engines.
You might think that Mazda’s bold move will affect the fuel economy of their diesel engine. However, they did otherwise and boosted it by delaying the combustion process by half a millisecond to allow better mixture of air and fuel. This makes the engine more efficient as it produces more power and consume less fuel.
Moreover, they also optimized fuel injection and combustion close to the top dead center of the cylinder which results to a higher expansion ratio, yielding more power and better performance.
It doesn’t stop there. They now use multi-hole Piezo fuel injectors that can customize the amount and timing of the fuel put into the cylinder. These types open and close quicker than the conventional solenoid type, making the process much more precise to adapt to different driving conditions. In addition to that, they used ceramic glow plugs to assure cold-start capability.
Lastly, to avoid knock at cold temperatures, Mazda used their patented variable valve lift (VVL) system on the exhaust side of the cylinder. This allows recirculation of hot exhaust gases back into the combustion chamber – increasing the air temperature for fast engine warm-up and stable ignition.
Just like the other CRDi engines, the SkyActiv-D uses turbochargers to boost performance by increasing its torque and power output. However, it uses two-stage turbochargers (small and large) that can be used interchangeably to fit certain driving conditions. During low speed drive, it will produce higher torque; it will then produce more power at high speeds.
This turbo system, along with the low compression design, allows optimally timed combustion with low soot and NOx emissions. They also reduced the fuel hotspots that end up as pollutants. With this, there won’t be any need for expensive exhaust after-treatment systems that are costly to maintain.
The introduction of the Mazda SkyActiv-D is a game changer, not only to their local lineup, but for the whole automotive industry as well.
Berjaya Auto Philippines (BAP), the local importer and distributor of Mazda vehicles, brought this technology into their showrooms this year with the new diesel variants of the CX-5 and the Mazda 6. If you’re curious as to how it is to drive these cars with SkyActiv-D technology, read our experience at the AutoDeal Blog.
For more information about Mazda and its vehicles, visit the AutoDeal Car Guide.