Mazda’s New Breed of “Sky” Engines Cometh

Escalating fuel prices had people literally rushing for smaller displacement vehicles around the world.

As emission standards draw closer to their enforcement dates, automakers are forced to look to the future and try to achieve lower emissions for their vehicles in order to allow their vehicles to remain in contention for a longer period of time and are, thus in a frenzy to offer better fuel-economy through technological-innovations for the numerous variations of the internal combustion engine.

With many manufacturers opting to bolt on turbos, superchargers and electric motors to supplement and/or increase the performance capabilities of the internal combustion engine, Mazda will be launching their new breed of four-cylinder NATURALLY ASPIRATED engines, which practically powers all their vehicles within their stable, sans the Rx-7 and 8 of course.

These new engines known as the Sky-G (gasoline) and Sky-D (diesel) can be paired to with the latest version of Mazda’s six-speed manual. These engines will be considerably lighter (estimated 60kg lighter) through meticulous optimization of material thickness and mounting points within the engine bay and of course, there are future plans of variate and offer displacements as low as 1.3L to 2.5L engines.

In addition to this, Mazda has an agreement to take supply of Toyota’s hybrid tech in order to help produce Mazda’s future Sky-based hybrids. For starters, Mazda was able to optimize their current Sky-equipped Mazda 3 to attain a fuel economy rating of 8L per 100km for city and 6L per 100km for high-way use.

Sky-G Engine Variant
In order to achieve such figures, Mazda upped the 2.0L’s compression ratio from 11:1 to 14:1 (higher than Kawasaki’s 13.9:1 compression ratio found in a 2008 ZX-6R sportbike). A longer than usual 4-2-1 exhaust was implemented in order to minimize the excess heat build-up in the cylinders, which could cause engine-knocking to occur, in order to also prevent exhaust gases from re-entering the combustion chambers during the engine’s intake-stroke. Even the exhaust headers have a rather “bulbous” look to it, which also means that the Sky engine could miss out on small-car applications, such as Mazda’s Miata, with the engine mounted longitudinally. It’d be jutting out of the bumper if it did, if only it had Peugeeot’s 308 hood, then perhaps it’d fit.

The use of direct injection (Thank you VW) has been included with a reduction in heat loss from the engine, because if too much heat gets dissipated by the engine, burning fuel becomes problematic making the engine inefficient. It can be said, that heat is the engine’s ally as well as the enemy, so maintaining it at a certain level becomes difficult and tricky for engineers. Such heat-loss reduction is obtained through the use of a smaller bore and a more complex piston shape that looks more like a cavity in the piston’s centre, which travels directly up towards where the engine’s spark plug ignites the fuel – much like BMW’s precision-injection engine technology.

So with heat becoming a major factor for the engine, the friction levels from the piston, rods, and crankshaft (which is now forged steel instead of cast iron), and roller finger followers have been reduced in the valvetrain.

The engine uses 0W20 oil as standard, and that’s going to be a tad difficult for us here in Malaysia, since not many people sell these particular lubricants that look like water with some colour in them.

The new Sky engines will also have dual variable-valve-timing, electronically varied (as opposed to using oil pressure) on the intake side, so that rapid adjustments can be made even during cold starts. Overall weight has been reduced by about 7kg, including 4.5kg saved by thinning out the block where additional strength wasn’t needed.

The Sky engine is capable of receiving a Research Octane Number (RON)as low as 91, which shouldn’t be a problem since we’ve got RON95 as a minimum here, so we should be able to attain the figures rated by Mazda of 163bhp at 6,000rpm and 210Nm of torque at 4,000rpm. However, Mazda does pride itself over its exceptionally wide torque band or pulling power that exists predominantly in the mid RPM range, much like it was found in our test drive for the Mazda 2 recently, which displayed a rather gentle acceleration where power delivery begins to be felt around 3,000 rpm onwards.

Though Mazda isn’t getting on the band-wagon of down-sizing engine capacities and adding a turbo charger, much like VW’s 1.2L turbocharged Polo, they were adamant in sticking to a higher 2.0L naturally-aspirated engines when employing HCCI (Homogenous Charge Compression Ignition), which combusts petrol much like how its done in a diesel-based engine (without spark plugs). Mazda claims that it will erode the benefits of down-sized engines, where smaller engines reduce pumping losses by opening the throttle more than usual. Similarly, HCCI engines will have to flow more air to realize better fuel-economy, by burning lean. Due to the way the Sky engines have been engineered, it would require greater than usual amounts of air to enter the combustion chamber, which it isn’t capable of doing unless the engine got up-sized and in doing so, you’ll get more fries and a larger cup of your favourite soft-drink. But on a more serious note, Mazda did indicate that by adding a turbo and an intercooler would make them loose their price-competitiveness.

Sky-D Engine Variant
As for the diesel side, their 2.2L Sky-D engine variant, more displacement variants will also follow, was able to achieve a whopping 20% increase in fuel-economy over the current engine and will meet Euro 6 emission standards as well as US Tier 2 Bin 5 emission standards without the use of any NOx (Nitrogen Oxide) after-treatment such as urea injection. You follow?

Instead of upping the compression ratio as was done in the Sky-G engine, they’ve instead lowered in from 16.3:1 to 14:1, which is now the same as the Sky-G engine, effectively making the Sky-D engine having the lowest compression ratio amongst other diesel running engines in the world. Mazda claims that by reducing cylinder pressures, reduces NOx production and would also allow the denser diesel to mix better with the air, thereby reducing soot production after combustion.

With the reduction in friction thanks to lower compression ratios, Mazda was able to gain a 4-5% increase in fuel economy, couple that with reduced internal forces also allow components such as the rods and pistons to be substantially lighter. Similarly enough, the cast-iron crankshaft was also replaced with one that’s made of steel.

However, by reducing the compression ratio for a diesel engine, it may not be able to combust properly due to lower temperatures, especially during start-ups, resulting in mis-fires. In order to rectify this, Mazda added a two-stage variable valve-lift system, catered for the exhaust-stroke in order to be able to create additional valve overlap, allowing the hot exhaust gases to be drawn back into the combustion chambers, thereby helping the engine attain a higher temperature during during start-ups.

Other new features for the Sky-D engine are a pair of sequential turbos — one small and one large — which outperforms the old single, variable-geometry unit; 12-hole piezo injectors that disperse fuel into the cylinder in exacting quantities during two to eight separate injections per cycle at pressures up to 2900 psi; and an exhaust manifold that’s completely integrated into the block. Here, too, fuel-economy claims are impressive: 7-7.5L per 100km for city and 5.5L per 100km for highway use. Talk about savings! Assuming the tank holds about 60L worth of diesel, you’d be filling up after doing about 1,000km! Travel from KUL-PEN-KUL…then fill up = Under RM100 at current diesel prices.

The Sky-D engine is capable of producing an extra 10bhp and 210Nm over the Sky-G engine, standing at 173bhp at 4,500rpm and 420Nm of torque at 2,000. Currently, Mazda’s diesel engines will stop screaming at 4,500rpm, but this time round, its been pushed to scream till it hits 5,200rpm. The torque levels will make this car exceptionally responsive, and thankfully, Mazda has made the Sky-D engine more more quieter with very little clatter, even when accelerating from engine speeds below 1,500rpm.

To sum things up, it looks like the internal combustion engine still has a lot more levels of evolution that it can reach. Let us hope and pray that one day engineers will somehow find a way to turn petrol / diesel into water! Can I get an A-Men?