Pursuing engine perfection

By introducing SkyActiv technology to all its next-generation Mazda vehicles (starting with the new CX-5), everyone can now drive an environment-friendly vehicle, not just those who are prepared to pay the price premium charged by other brands.

Until most of us are driving cars that run solely on electricity, Mazda will continue improving what has served the motoring world so well for over 100 years: petroleum-powered internal combustion engine.

The Japanese automaker has a point. While hybrids and plug-in electric vehicles hold promise, currently they are expensive and yet to be fully embraced by the market. Moreover, developing future powertrains is quite expensive and would-be investors must first be convinced of high returns before they start pouring in money.

Believing that by 2020, 80 percent of vehicles will still be powered with internal combustion engines, Mazda a couple of years ago, embarked on a mission on the premise that there are still significant opportunities for further development of current gasoline- and diesel-fed engines, along with benefits that could be gained from transmission and chassis refinement.

The result is SkyActiv.

SkyActiv consists of innovations that Mazda developed in order to refine its existing engines and transmissions, come up with sleeker external designs and bring down the weight of structural components in order to deliver substantial fuel-economy, safety and other benefits to upcoming Mazda vehicles.

With SkyActiv, Mazda engineers set themselves the task of increasing fuel efficiency in a number of ways. Among these was to raise the compression ratio of SkyActiv gasoline (SkyActiv-G) engines to an industry-high 14:1 (for comparison, Ferrari’s super cars have 12.5:1 while average family cars have between 9 to 11.1).

Compression ratio simply means the amount of air that an engine can squish in preparation for the “bang” phase of combustion. Hence, a 14:1 compression ratio simply means that 14 units of air will be compressed into the space of just 1 unit.

Caveat

Mazda’s breakthrough SkyActiv technology has already won numerous motor industry awards.

However, there is a caveat: Compressing the air/fuel mixture so high could create excessive heat buildup in the cylinder, which in turn, leads to premature auto-ignition or knock (engine knocking) and causes irreversible engine damage.

Before the breakthrough at Mazda, developing a technology to address engine knocking while maintaining high compression ratio has not been commercially feasible.

To keep the temperatures down and solve the issue of engine knocking, Mazda employed an innovative piston cavity design as well as fitting a seriously lengthy but sophisticated four-into-two-into-one exhaust manifold, which is designed so that the hot exhaust gases don’t get pulled back into the next cylinder’s intake stroke.

Moreover, Mazda employed lighter engine materials, more precise engine tolerances and other techniques to mitigate misfiring, exhaust, cooling, mechanical and pumping loss in the engine’s operation.

Such innovations could now be enjoyed in the 2.5-liter SkyActiv-G engine that powers both the P1.705-million (six-speed automatic version) Mazda 6 sedan and the P1.685-million CX-5 (AWD Sport version) crossover that are now available here in the Philippines.

More impressive feat

On the diesel side, Mazda has pulled off an even more impressive feat. As opposed to what it did in the gasoline, Mazda decreased the compression ratio of SkyActiv diesel (SkyActiv-D) from 16.3:1 to just 14:1.

With a similar compression ratio as that of SkyActiv-G, the result is a diesel engine that generates reduced cylinder pressure as well as temperature. Because of the lower compression ratio, combustion is more uniform and at the same time minimizes nitrous oxide and soot emissions. This negated the need for developing an expensive aftertreatment system.

Mazda claims that the lessened friction from the reduced cylinder pressure alone is worth a 4- to 5-percent gain in fuel economy. And the reduced internal forces also allow Mazda engineers to use components such as the rods and pistons that are substantially lighter.

Just like what is employed in its gasoline counterpart, the SkyActive-D engine also uses forged steel crankshaft instead of cast-iron. This results in overall weight savings of a whopping 25 kilograms.

To deal with misfires that are inherent in diesel engines with lower compression ratio, Mazda added a two-stage variable valve-lift system on the exhaust side and created additional valve overlap. This causes the hot exhaust gases to be drawn back into the next cylinder to warm it up.

Other new features employed in the SkyActiv-D include a two-stage turbocharger in which one small and one large turbo are selectively operated according to driving conditions (this setup achieves high torque and response at low speeds as well as high power at high speeds, and outperforms the old single, variable-geometry diesel engine unit); and  newly adopted multihole piezo injectors that allow a wide variety of injection patterns and precise amount of fuel injected.

No mystery

Indeed, it’s no mystery why many car buyers are not yet so enamored with the near-term promise of electric vehicles and hybrids. Apart from the hefty prices that both types of vehicles command, those who will be driving cars strictly powered by batteries are facing a steeper uphill battle because of the limited driving range and dearth of public charging stations around the country.

Mazda has proven that automakers could still refine and rethink the conventional internal combustion blueprint. With what the company did and is still refining, the Japanese carmaker is confident it can improve fuel economy and cut emissions by some 30 percent by 2015 when compared with its 2007 figures.

This is great news for car buyers who demand fuel efficiency but don’t want to compromise on performance.