Mazda Skyactiv

In the quest to build vehicles that are economical, efficient and greener, this Japanese carmaker has taken an intriguing approach

We all know that cars need to become more economical and more efficient. We know that this must be achieved while keeping exhaust emissions at least at their present level of near-squeaky cleanliness.

So carmakers develop downsized engines with turbochargers, hybrid powertrains, and electric cars, they devise ever more complex ways of dealing with a diesel's dirt, and the cost goes up and up.

In a refreshingly detached look at the obvious, Japanese carmaker Mazda has embarked upon an intriguing new approach. It brands this whole approach "Skyactiv", which covers many bases but which contains some intriguing new takes on existing methods. This means that Skyactiv cars need cost no more than their predecessors, yet they will be much more fuel-efficient and quite a lot more fun to drive.

Some of these ideas (and their 135 patents) come under the "Why has no one done this before?" category, while others refine what is already known. Forming the body shell's reinforcement channels out of more pieces of straight, lightweight steel sections, is one example of the latter. Devising a new automatic gearbox to mimic the positive feel and fuel-economy benefit of a Volkswagen-type DSG system but without the weight, is another. Creating a new manual gearbox for front-wheel-drive cars with a shift so precise it mimics that of the rear-wheel-drive MX-5 sports car is a third.

The main news, however, lies with the engines. Here, it's all about compression ratios. Stay with me here, because the higher the ratio the bigger the bang when the fuel/air mixture ignites and more power is the result. Up to a point.

Petrol engines in the 1960s typically ran at a ratio between eight- and nine-to-one. Nowadays over 10-to-one is commonplace, and with direct fuel injection, which cools down the cylinder air heated as the piston compresses it, it can be as high as 12-to-one. Beyond that, however, it's hard to avoid "detonation", in which the huge heat of compression ignites the fuel too soon and tries to force the piston down before it has finished coming up. This makes a nasty clatter and robs the engine of power.

The new Skyactiv G (for gasoline) engine, however, runs at an extraordinary 14-to-one, yet still manages to use standard-grade fuel. It's tantamount to turbocharging without the expensive and complex turbocharger. The result of all this is an engine with both economy and mid-range pulling power around 15 per cent better for the same 2.0-litre capacity. It certainly feels lively to drive, although it's at its best in the middle speed ranges and loses its enthusiasm at high revs. So far, then, so commendable. Now, though, I'm going to tell you about the best part of Mazda's new philosophy: the Skyactiv D diesel.

Here, again, the story centres around compression. In a diesel this is very high, because the engine works by using the heat generated by compression to ignite the fuel. This is injected just after the piston has started to descend on its power stroke; any sooner and the huge pressures would cause detonation. It would be good to inject the fuel sooner, but that's possible only if the compression ratio is reduced. And then it might be difficult to get the engine to run properly when it's cold, because it would misfire.

So the clever part here is to succeed in lowering the compression ratio from the 17-to-one that a turbodiesel typically runs at. The Skyactiv D engine, with twin sequentially-operating turbochargers (small first, then the larger one joins in) runs at, yes, 14-to-one – the same as the petrol engine.

It's able to do so by injecting the fuel earlier, just before the piston reaches the top of its stroke. Because the combustion space is still decreasing, pressure is still rising enough to ignite the diesel fuel. So the rapidly-expanding, burning gases can now push the piston the whole way down rather than missing out on the first part of the movement. The peak combustion pressure is less, because the compression ratio is less, but it is sustained over a longer period which means more power and torque – 175bhp from 2.2 litres, and 310lb/ft – while using around 20 per cent less fuel.

There are big benefits here. The lower peak pressures allow components to be less massive, so the engine weighs less and can have an aluminium, instead of iron, cylinder block. The peak combustion temperatures are lower, so there are fewer nitrogen oxides – the engine will pass the next round of emissions regulations without needing exhaust after-treatment. As for the misfiring when cold, this is eliminated by making the exhaust valves open only very slightly after a cold start so trapping the hot exhaust gases and bringing the combustion chamber quickly up to temperature. Problem solved.

Perhaps the most remarkable thing, though, is the way the engine reaches revolutions per minute previously unthinkable in a diesel.

Mazda's engineers say it will run to 5,200rpm, but on a quick test run I briefly saw 5,800rpm at which the engine was still pulling strongly and smoothly. Its response to the accelerator is as crisp as a good petrol engine's, and its muscular eagerness made the Skyactiv prototype (new, lightweight structure clothed in current Mazda 6 outer panels) great fun to drive.

This is a brilliant engine, a diesel revolution. Its first production application comes in next year's Mazda CX-5 "crossover" car. It will be worth the wait.

Mario Balotelli pictured in the win over QPR
footballInternet reacts to miss shocker for Liverpool striker
Sol Campbell near his home in Chelsea
Kimi the fox cub
newsBurberry under fire from animal rights group - and their star, Kimi
Arts and Entertainment
Ella Henderson's first studio album has gone straight to the top of the charts
<p>Jonathan Ross</p>
<p>Jonathan Ross (or Wossy, as he’s affectionately known) has been on television and radio for an extraordinarily long time, working on a seat in the pantheon of British presenters. Hosting Friday Night with Jonathan Ross for nine years, Ross has been in everything from the video game Fable to Phineas and Ferb. So it’s probably not so surprising that Ross studied at Southampton College of Art (since rebranded Southampton Solent), a university known nowadays for its media production courses.</p>
<p>However, after leaving Solent, Ross studied History at the School of Slavonic and East European Studies, now part of the UCL, a move that was somewhat out of keeping with the rest of his career. Ross was made a fellow of the school in 2006 in recognition of his services to broadcasting.</p>

Rumours that the star wants to move on to pastures new

Life and Style
Paul Nuttall, left, is seen as one of Ukip's key weapons in selling the party to the North of England
Arts and Entertainment
Russell Brand labelled 'left-wing commie scum' by Fox News
Arts and Entertainment
BBC's Antiques Roadshow uncovers a TIE fighter pilot helmet from the 1977 Star Wars film, valuing it at £50,000

TV presenter Fiona Bruce seemed a bit startled by the find during the filming of Antiques Roadshow


Comedian says he 'never laughed as hard as I have writing with Rik'

Steven Caulker of QPR scores an own goal during the Barclays Premier League match between Queens Park Rangers and Liverpool
Arts and Entertainment
artKaren Wright tours the fair and wishes she had £11m to spare
Life and Style
Kirsty Wark and Camila Batmanghelidjh been invited to take part in Women Fashion Power, a new exhibition that celebrates the way women's fashion has changed in relation to their growing power and equality over the past 150 years
fashionKirsty and Camila swap secrets about how to dress for success
Arts and Entertainment
Joy Division photographed around Waterloo Road, Stockport, near Strawberry Studios. The band are Bernard Sumner (guitar and keyboards), Stephen Morris (drums and percussion), Ian Curtis (vocals and occasional guitar), Peter Hook (bass guitar and backing vocals).
booksNew book on Ian Curtis sheds fresh light on the life of the late singer
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

ES Rentals

    iJobs Job Widget
    iJobs General

    Operational Risk Manager - Asset Management

    £60,000 - £80,000: Saxton Leigh: Our client is an leading Asset Manager based...

    Year 5/6 Teacher

    Negotiable: Randstad Education Sheffield: Permanent Year 6 TeacherThe job:This...

    KS1 & KS2 Teachers

    Negotiable: Randstad Education Sheffield: KS1+KS2 Teachers required ASAP for l...

    Year 2 Teacher

    Negotiable: Randstad Education Sheffield: Year 2 Teacher The position is to wo...

    Day In a Page

    Oscar Pistorius sentencing: The athlete's wealth and notoriety have provoked a long overdue debate on South African prisons

    'They poured water on, then electrified me...'

    If Oscar Pistorius is sent to jail, his experience will not be that of other inmates
    James Wharton: The former Guard now fighting discrimination against gay soldiers

    The former Guard now fighting discrimination against gay soldiers

    Life after the Army has brought new battles for the LGBT activist James Wharton
    Ebola in the US: Panic over the virus threatens to infect President Obama's midterms

    Panic over Ebola threatens to infect the midterms

    Just one person has died, yet November's elections may be affected by what Republicans call 'Obama's Katrina', says Rupert Cornwell
    Premier League coaches join the RSC to swap the tricks of their trades

    Darling, you were fabulous! But offside...

    Premier League coaches are joining the RSC to learn acting skills, and in turn they will teach its actors to play football. Nick Clark finds out why
    How to dress with authority: Kirsty Wark and Camila Batmanghelidjh discuss the changing role of fashion in women's workwear

    How to dress with authority

    Kirsty Wark and Camila Batmanghelidjh discuss the changing role of fashion in women's workwear
    New book on Joy Division's Ian Curtis sheds new light on the life of the late singer

    New book on Ian Curtis sheds fresh light on the life of the late singer

    'Joy Division were making art... Ian was for real' says author Jon Savage
    Sean Harris: A rare interview with British acting's secret weapon

    Sean Harris: A rare interview with British acting's secret weapon

    The Bafta-winner talks Hollywood, being branded a psycho, and how Barbra Streisand is his true inspiration
    Tim Minchin, interview: The musician, comedian and world's favourite ginger is on scorching form

    Tim Minchin interview

    For a no-holds-barred comedian who is scathing about woolly thinking and oppressive religiosity, he is surprisingly gentle in person
    Boris Johnson's boozing won't win the puritan vote

    Boris's boozing won't win the puritan vote

    Many of us Brits still disapprove of conspicuous consumption – it's the way we were raised, says DJ Taylor
    Ash frontman Tim Wheeler reveals how he came to terms with his father's dementia

    Tim Wheeler: Alzheimer's, memories and my dad

    Wheeler's dad suffered from Alzheimer's for three years. When he died, there was only one way the Ash frontman knew how to respond: with a heartfelt solo album
    Hugh Bonneville & Peter James: 'Peter loves his classic cars; I've always pootled along fine with a Mini Metro. I think I lack his panache'

    How We Met: Hugh Bonneville & Peter James

    'Peter loves his classic cars; I've always pootled along fine with a Mini Metro. I think I lack his panache'
    Bill Granger recipes: Our chef's heavenly crab dishes don't need hours of preparation

    Bill Granger's heavenly crab recipes

    Scared off by the strain of shelling a crab? Let a fishmonger do the hard work so you can focus on getting the flavours right
    Radamel Falcao: How faith and love drive the Colombian to glory

    Radamel Falcao: How faith and love drive the Colombian to glory

    After a remarkable conversion from reckless defender to prolific striker, Monaco's ace says he wants to make his loan deal at Old Trafford permanent
    Terry Venables: Premier League managers must not be allowed to dictate who plays and who does not play for England

    Terry Venables column

    Premier League managers must not be allowed to dictate who plays and who does not play for England
    The Inside Word: Brendan Rodgers looks to the future while Roy Hodgson is ghost of seasons past

    Michael Calvin's Inside Word

    Brendan Rodgers looks to the future while Roy Hodgson is ghost of seasons past