Mazda’s High-Compression ‘SkyActiv-X’ Engine

If you pursue the car industry to any degree, you’d feel the age of internal combustion engine over. But Mazda is a no ordinary company. The company is not racing into the realms of hybrid and electric cars with all their might. It has not been bothered with downsizing, choosing instead to stay with much larger engines with all petrol being aspirated. The company hasn't announced a date when it’ll quit making cars powered by internal combustion. But unbelievably, it has made a revolutionary new petrol engine under the skin of the SkyActiv-X hatchback. We talked to engineers behind the project, and here is what we learned:



1. The spark is the key


The idea of Homogenous Charge Compression Ignition (or HCCI) has been around for some time now. The concept is you ignite a considerably much leaner fuel/air mixture using a very high rate of compression with no spark plug, which is as much as you would in a diesel engine. The trouble is, you can’t control when the blast occurs, and that increases the danger of engine knocking - which is when an explosion happens the piston might not be at the top centre. Mercedes tinkered around with their engineers for a while before quitting, so how has Mazda overcome it? By doing something that is not exactly HCCI, is the solution.

Mazda names it, Spark Controlled Compression Ignition or SPCCI, and that “spark” bit was the eureka moment for the company. Under the guidance of a spectacularly complicated ECU, spark plugs are brought into the mix, giving the control needed to stop when the chance of pinking happens.

A lean mixture comprising of more air than fuel - about double the amount of air you'd find in “stoichiometric” mixture used by ordinary petrol engines - is packed near to the conditions required for combustion. The ECU utilizes sensors to perceive this point, responding by igniting the spark plugs. This causes an extending fireball, triggering the right conditions for combustion to occur.


The outcome is a far leaner burn, giving approximately 20% - 30% increase in effectiveness. That’s a reduction in emission to provide Mother Nature lesser kicking as well as lower fuel consumption.



2. It sounds like other petrol inline-four



You may think an ultra-high compression proportion would give SkyActiv-X a clattery, but no: it sounds like any old inline-four engine, generally. It’s not the most muscular sounding four-banger, but rather it is tranquil and extremely smooth, which may be partly due to the newer platform’s better sound-deadening. The angry noise might be given in the early days, but the final version of SkyActiv-X ends up with a quite opposite character.



3. Efficiency increases with big window of operation


At first, downsizing was acknowledged by the world. However, until Mazda’s engine came, now the world is starting to realise downsizing generally does not work. Without a doubt, with downsizing there are efficiency savings to be had but only in a very narrow window. With Mazda’s engine, there’s no such issue with SPCCI as the working window is enormous, assisted by a small supercharger keeping up the air supply. It’s only under high load at high RPM which the ECU changes to traditional spark ignition; thus, the rest of the time, you can still enjoy that beautiful lean burn.


4. The air/fuel mix is swirled as if hurricane



All of the above seems not enough to say about how engineering wizard Mazda’s SkyActiv-X’s engine is, there is one more interesting piece I would like to share with you: it is the fuel. The fuel is swirled when it is injected. Mazda Europe’s R&D Chief Heiko Strietzel compared this with a typhoon – a vortex which has an extremely steady “eye” in the centre where there is almost no movements. This creates a lesser lean area around the spark plug – which unlike the fuel/air mix in the rest of the cylinder. It’s then the fireball, which we talked about before, is started, creating the right conditions for compression ignition to ignite.


5. There’s more low-mid end torque



Much like a turbocharged motor, there’s a healthy and handy delivery of low and mid-range torque running here. However, there isn’t a lag nor the boost threshold step, which makes SkyActiv-X an almost engine to experience at this first kind. The engine picks up briskly from about 2500rpm, and after that it’s a direct force pull all the way up to the red line. The change from SPCCI to conventional ignition is indiscernible.



6. Expected to debut in 2019


The new engine is proposed to debut in the next generation 3 hatchback in 2019, and it should inevitably be available for each new Mazda. “If it’s well accepted, this technology will be available in all of our next models.” Mazda Europe CEO Jeffrey H. Guyton affirmative while he addresses at a driving event.

So, it will not be installed in the ND-generation MX-5. But soon it will be thrust into the automotive mainstream, proving to the world the age of the petrol engine far from over.

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