MAZDA ROAD TESTS ENGINE TECH
Prototypes fitted with latest Skyactiv-X architecture unveiled ahead of 2019 launch
Mazda has revealed the latest version of its innovative 2.0litre Skyactiv-X engine, which is expected to deliver a 20% improvement in fuel consumption over the existing Skyactiv-G petrol during general driving.
That figure could increase during low-speed driving to as much as 30%, the company claims. The target outputs for when the engine hits the market in 2019 are 190hp and 230Nm.
Development engines have been installed in six prototype cars comprising Mazda 3 bodies underpinned by the new Skyactiv architecture.
The new Skyactiv-X engine relies on two technologies — lean burn combustion and compression ignition — to reduce fuel consumption and CO2 emissions while delivering good performance.
A conventional internal combustion engine mixes air with fuel at a ratio of 14.7:1, the perfect mixture to burn petrol in the cleanest possible way. Fuel is ignited by a spark inside the engine’s combustion chamber and burns progressively until it is used up in a split second. A leaner mixture can improve economy, but can be more difficult to ignite and leads to faltering combustion.
The Skyactiv-X technology successfully sidesteps those problems with spark-controlled compression ignition (SPCCI), which reliably ignites the entire lean air/fuel mixture of between 30:1 and 40:1 in one go. Extra air to feed the lean burn running is supplied by y a small, , belt-driven, Rootes-type air pump.
A higher-than-normal compressi on ratio of 16:1 produces almost enough pressu ure to combust the lean fuel-air mixture spont taneously, but not quite. That happens when a se econd dose of fuel is injected and fired by a spark to create a mini fireball. The extra pressure crea ated by the fireball tips the simmering main ch harge over the edge and it ignites.
The engine can run in this mode th hroughout a large part of the operating range but t, when the driver accelerates very hard, the engin ne switches to a conventional mode burning a spa ark-ignited 14.7:1 air fuel mixture like any other p etrol internal combustion engine.
SPCCI is an evolution of a conc ept called HCCI (homogeneous charge com mpression ignition), which a number of manu ufacturers tried but failed to perfect more than n a decade ago. The main problem was switchin ng between HC CCI mode and conventional mode, now sol lved by Mazda with SPCCI.
The new Skyactiv vehicle architecture is lig ghter to improve energy efficiency. It is also aim med at improving driver control by giving a sm moother ride by reducing road shocks into the cab bin. A stiffer structure using more lightweight ste eel components helps improve handling and rid de, and the introduction of thimble-sized str ructures called ‘damping nodes’ at crucial joi ints reduces noise and vibration in the cabin.
This engine’s reveal was accompanied by a sec cond look at the Kai concept first shown at the Tokyo motor show last year. The Kai’s clean lines are designed to exploit the light falling on the car’s surfaces and hint at how the next Mazda 3, based on the Skyactiv architecture, could look.