Mazda’s Skyactiv to wring out more efficiency
HIROSHIMA, Japan — Look at the typical internal combustion engine and only around 30 per cent of the fuel it consumes is put to good use. The remainder is squandered in the form of mechanical and heat losses (in the exhaust stream and engine). Mazda wanted to reduce the waste portion. Enter the company’s Skyactiv engines — a range of power plants aimed to compete with the ever-increasing number of smaller displacement, turbocharged engines on an even footing.
To compete, Mazda’s Skyactiv family of directinjected gasoline engines use an ultra-high 14:1 compression ratio (13:1 in Canada). To reduce the risk of engine knock, the bane of high-compression engines, Mazda adopted a headerstyle four-into-two-into-one exhaust manifold and optimized the fuel injection by using multi-hole injectors. The net result was a huge 15 per cent increase in low- and mid-range torque while slashing fuel consumption by 15 per cent. Now that is a step forward by any standard.
Combine this with the rest of the Skyactiv thinking — the use of more efficient transmissions and mass reduction, particularly in the body — and you have a naturally aspirated car that can compete with anything on the road from an economy perspective.
At present, 95 per cent of the vehicles on the road use gasoline or diesel as fuel. According to Mazda, 90 per cent will still be burning fossil fuel in 2020. To cut the environmental impact of this reality, the only way to improve things is to increase the efficiency of the engine. At this point, adding idle stop and brake regeneration technology are supplementing the conservation efforts. Adding a capacitor and harvesting otherwise wasted energy and using it to recharge the battery and power the electrics (i-ELOOP in Mazdaspeak) and using idle stop to prevent needless consumption when the car comes to a standstill cuts real-world fuel usage by up to 10 per cent. Mazda will also add cylinder deactivation to its Skyactiv gas engines in the near future, which will further improve fuel economy.
In the longer term, Mazda will transition into Skyactiv 2.0, and ultimately, Skyactiv 3.0. Skyactiv 2.0 increases the efficiency of the current engine from 37 per cent to a staggering 48 per cent, which represents an improvement of 30 per cent. The implementation of the next-generation Skyactiv technology will arrive in Mazda’s Gen 7 products (the current product range is known as Gen 6) due for launch by 2020.
The first move will be to increase the already lofty 14:1 compression ratio to a staggering 18:1 — you’re talking a diesel engine-like number here! The second step will be to introduce HCCI, or homogeneous charge compression ignition and reduce internal friction by a further 20 per cent (Skyactiv 1.0 has already reduced this by 30 per cent).
In very simple terms it takes a gasoline engine and allows it to operate like a compression-ignition, or diesel, engine under specific operating conditions. In other words, compressing the air/ gasoline mixture sees it auto-ignite — the combustion is spontaneous and complete without the need for a spark plug. In many regards, this technology blends the best of both a conventional gas engine with those of a diesel engine.
HCCI is not a new technology by any means; however, early attempts to put it to meaningful use ran into what proved to be insurmountable obstacles. However, time and sophisticated computer-controlled electronics have come to the rescue.
HCCI advantages are many. Unlike conventional engines, the combustion process uses a lean mixture and lower internal temperatures. The entire fuel mixture is burned simultaneously producing the same power as a conventional engine while consuming less fuel and producing far fewer emissions in the process.
HCCI is also well suited to operating on alternate fuels such as ethanol, propane and natural gas. Finally, the HCCI principle reduces the pumping losses. In the long run, the gas/electric hybrid could end up being cleaner than an all-electric ride if the electricity needed to fully recharge it is generated from a less-than-clean source — a coal-fired generator. In short, the demise of the internal combustion engine and its ability to power the future has been greatly exaggerated.