Mazda eyes 18:1 petrol compression

Mazda’s second-generation SKYACTIV-G petrol engines could emerge within four years with compression ratios as high as 18.0:1.

What’s more, the heavily reworked four-cylinder engines will employ diesel technology -- including a combustion process ignited not by a sparkplug but compression -- to reduce fuel consumption by a further 30 per cent.

Mazda shocked industry observers when its first-generation SKYACTIV-G petrol four emerged in late 2010 with a compression ratio of 14.0:1, matching many diesel and motorcycle engines and setting a new benchmark for a mass-produced petrol engine.

At the same time, as part of the push to reduce its fleet-average fuel consumption by 30 per cent between 2008 and 2015 (the same figure it achieved between 2001 and 2008), Mazda revealed its first SKYACTIV-D diesel engine with a super-low 14:1 compression ratio.

The 2.0-litre SKYACTIV-G made its Australian debut in the Mazda3 SP20 in 2011 and, alongside the 2.5-litre SKYACTIV-G petrol four, will power the third-generation Mazda3 small car range due for launch in February.

Mazda has previously identified homogeneous charge compression ignition (HCCI) as the next step for its SKYACTIV-G petrol engine, and similar technology has been investigated by GM, Mercedes-Benz and Hyundai/Kia.

Like those car-makers, Mazda says the diesel-like HCCI technology works by using the heat and pressure inside the cylinders to ignite the air/fuel mixture without requiring a spark plug for ignition.

However, Mazda has gone two steps further than GM and Mercedes by confirming it will enter production in its second-generation SKYACTIV-G engine, as part of its drive to meet ever-tightening global emissions standards.

Europe has the world’s most stringent fleet-average CO2 emissions laws, which call for 95g/km by 2020 and 65g/km by 2025 – well below all current vehicles, including Australia’s most fuel-efficient car, the Toyota Prius hybrid (89g/km).

The US and China are expected to follow and electric vehicles will be mandatory for all brands in California by 2018.

Instead of following other car-makers down the downsized turbo engine path, HCCI will be the centrepiece of Mazda’s plans to cut the fuel consumption of the internal combustion engine, which it says will still power 90 per cent of passenger cars in 2020, by another 30 per cent beyond 2015.

“We decided not to follow the downsizing approach because our SKYACTIV engines will be competitive without that,” said the general manager of Mazda’s product strategy division, Hidetoshi Kudo, at a Mazda technology forum in Yokohama on Friday.

Indeed, Ichiro Hirose, the vice-president of Mazda’s European R&D Centre, said Mazda would not be able to meet future emissions laws without HCCI, which more effectively reduces fuel consumption in the real world compared to downsized engines.

“In order to improve efficiency we have no choice but to go to HCCI,” he said. “The aim is to get another 30 per cent in thermal efficiency with HCCI.

“This statement is not based on a wish but based on many tests already in our research activity.

“We’re going to build the ideal internal combustion engine, with vastly reduced well-to-wheel CO2 emissions. [We can achieve] hybrid-like fuel consumption with HCCI in the second-generation.”

Hirose-san said Mazda’s lean-burn HCCI technology, which he describes as diesel technology for petrol engines, will include compression ratios of between 16:1 and 18:1.

He said HCCI, which aims to make petrol engine combustion as lean as possible without misfiring, could lead to fuel savings of up to 30 per cent, reduce friction losses by 20 per cent and eliminate both pumping losses and harmful NOx emissions.

However, he cited challenges including managing heat loss and the smooth transition between compression ignition at low to mid-range engine speeds and spark ignition at higher revs.

Beyond HCCI for its second-generation SKYACTIV-G engines, Mazda is already working on third-generation SKYACTIV technology, which will include adiabatic combustion chamber technology.

Mazda said this would lead to another dramatic reduction in fuel consumption by improving low-speed efficiency and reducing exhaust energy and cooling losses, but would not reveal the type of cylinder wall and/or piston coatings it is investigating.

It says the wider ‘sweet spot’ of petrol engines incorporating lean diesel-like air/fuel ratios and adiabatic combustion chambers will negate the need for continuously variable automatic transmissions (CVTs) and multi-speed automatics.

Hirose-san said that although some of Mazda’s rivals were developing automatics with 10 or more ratios, “six (speeds) is enough from a fuel consumption view”.

Further, in terms of their impact in hybrid applications, the broader performance spread of its MkII SKYACTIV engines requires electric assistance only at very low loads, where the energy required could be covered by brake energy regeneration, leading to downsized motors and batteries.

Thus, Mazda says its third-generation SKYACTIV engines will offer EV-like well-to-wheel emissions levels (depending on the power source).

Before its second- and third-generation SKYACTIV engines arrive, Mazda will broaden the rollout of its ‘i-stop’ idle-stop system. Introduced in 2009, it was employed in 70 per cent of its passenger cars built in 2012, rising to 80 per cent in 2013.

The innovative Japanese brand’s world-first capacitor-based regenerative braking system, i-ELOOP, debuted in this year’s new Mazda6 but will not feature in next year’s new Mazda3, which nevertheless consumes just 5.7L/100km in 2.0-litre auto form.

Mazda is also working on electrification, having just released in Japan its first mass-production petrol-electric vehicle, the 3.2L/100km Mazda3 Hybrid, and fitted its battery-electric Mazda2 prototype with a rotary range-extender.

It also revealed a compressed natural gas-powered Mazda3 concept at last week’s Tokyo show, as part of its development of alternative fuel systems.

Asked when its second-generation SKYACTIV-G petrol engines would become available to customers, Mazda’s managing executive officer of R&D Takahisa Sori said: “We began our SKYACTIV research in 2006 and it reached production in 2011, so maybe you can imagine the timing.”

Therefore, given it has already started SKYACTIV II development, expect to see Mazda’s lean-burn HCCI petrol engines to emerge within four years – in time for the next generation of its core 2, 3 and 6 passenger models.

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