More thrust, less whine

British Airways' latest aircraft, the `Treble Seven', dramatically reduces the levels of noise and pollution, writes Tom Loosemore

Last week, British Airways proudly showed off the first of its new fleet of 325-seat Boeing 777 "Treble Sevens". These new aircraft, set to enter service this autumn, are fitted with the largest and most powerful turbofan jet engines yet produced. The new General Electric GE90 engine has a fan diameter of more than 3 metres and it produced over 110,000lb of thrust during testing - a new world record.

Today's jet engines are radically different from those fitted to early jet airliners. In modern high by-pass turbofan engines, the huge fan at the front of the engine acts more and more like an old-fashioned propeller, driven by the smaller jet engine in the middle. The rotation of the fan generates much more thrust than the expulsion of hot gases which have passed through the combustor in the core of the engine. In the case of the GE90, only 11 per cent of air sucked in at the engine's entrance is used in combustion, giving a by-pass ratio of 9 to 1, the highest yet for a commercial engine.

Generating most of the thrust in this way has several advantages. Fuel consumption, exhaust emissions, and engine wear and tear are all reduced. But the most dramatic impact has come in noise reduction.

Noise in a jet engine is very complex, with different sounds radiating from different parts of the engine. The large-diameter fan at the front of turbofan engines tends to create deeper toned, buzz-saw noises. The high-pitched whine that people often find particularly annoying comes from other rotating parts, deeper within the engine. Designers counter the buzz-saw noise by reducing the speed of the fan tips, and employing highly efficient sound absorption materials in the outer casing of the engine.

However, it is the small percentage of hot exhaust gases that make the most noise. The compressed, high-velocity gases shear through the surrounding air with a violent turbulent roar. Modern engines envelope this stream of hot gas with a cloak of slower, colder air from the turbofan, which helps to reduce the noise. In addition, the hot exhaust gases from the latest generation of aircraft engines are expelled with a lower velocity than in previous designs. The two factors combine to reduce noise dramatically.

There will never be a totally silent engine, but General Electric claims that the GE90 gets close to a practical limit in terms of minimising noise. Speaking at Heathrow last week, James Barrett, deputy chairman of GE Aircraft Engine Services, said: "We are now getting to the point where noise generated by the airframe - the `wind-rush' if you like - is of the same magnitude as that caused by the engines themselves." The results certainly appear impressive. Mr Barrettsuggests that the take-off of one of BA's new Boeing 777s, fitted with two GE90s, will barely be noticed by those living outside Heathrow's perimeter fence.

The new generation of jet engines are also much cleaner than before. The control of emissions has become increasingly important because European countries will soon adopt tough new standards governing the pollution emitted when an aircraft takes off. These regulations were first recommended nearly 10 years ago by the International Civil Aviation Organisation (ICAO). Sweden has already gone one step further and now levies a tax on emissions from commercial jets in all phases of flight.

According to General Electric, jet engine emissions can be classified into four categories: soot, unburned hydrocarbons, carbon monoxide, and various oxides of nitrogen (NOx). Over the past two decades, all emissions other than NOx have been reduced to relatively low levels. But NOx emissions are of particular concern since they tend to react readily with other pollutants in the lower atmosphere to create a chemical "soup" that, when exposed to sunlight, forms ozone and smog.

The GE90 incorporates a new design of combustor whose NOx emissions are 22 per cent below the proposed ICAO standard. In the past, increased power typically meant hotter engines and hence greater NOx pollution. Designers at General Electric believe that they have found a way of mediating this problem by employing a combustor that burns the fuel at lower temperature in two concentric chambers, instead of the single high temperature stage found in current engines.

The "Treble Seven" is the first Boeing to incorporate "fly by wire" all- computer control systems. Although the European Airbus has had computer control for several years, some pilots have expressed concern over the role computers play in the control of such aircraft. On board computers monitor every aspect of the aircraft to detect any abnormalities, and can be programmed to take over from the pilot should the computer calculate that the plane is in any danger. Pilots can feel nervous when using this system, and in response Boeing has ensured the pilot can if need over- ride the computer's instructions.

British Airways will pay out £2bn for the first 15 "Treble Sevens", although the price includes options to buy 15 more. The company hopes to use them to increase capacity on busy routes to the Gulf and the United States. Quiet computer controlled jets will be dominating our skies within a very few years.

Start your day with The Independent, sign up for daily news emails
ebooks
ebooksA special investigation by Andy McSmith
  • Get to the point
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

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

iJobs Job Widget
iJobs General

Recruitment Genius: Electronics Test Engineer

£25000 - £27000 per annum: Recruitment Genius: An SME based in East Cheshire, ...

SThree: Graduate Recruitment Resourcer

£20000 - £22500 per annum + OTE £30K: SThree: SThree Group have been well esta...

Recruitment Genius: Business Development Manager - OTE £40,000

£28000 - £40000 per annum: Recruitment Genius: A fantastic opportunity has ari...

Recruitment Genius: Contracts / Sales Administrator

£19500 - £25000 per annum: Recruitment Genius: Knowledge of and ability to use...

Day In a Page

Not even the 'putrid throat' could stop the Ross Poldark swoon-fest'

Not even the 'putrid throat' could stop the Ross Poldark swoon-fest'

How a costume drama became a Sunday night staple
Miliband promises no stamp duty for first-time buyers as he pushes Tories on housing

Miliband promises no stamp duty for first-time buyers

Labour leader pushes Tories on housing
Aviation history is littered with grand failures - from the the Bristol Brabazon to Concorde - but what went wrong with the SuperJumbo?

Aviation history is littered with grand failures

But what went wrong with the SuperJumbo?
Fear of Putin, Islamists and immigration is giving rise to a new generation of Soviet-style 'iron curtains' right across Europe

Fortress Europe?

Fear of Putin, Islamists and immigration is giving rise to a new generation of 'iron curtains'
Never mind what you're wearing, it's what you're reclining on

Never mind what you're wearing

It's what you're reclining on that matters
General Election 2015: Chuka Umunna on the benefits of immigration, humility – and his leader Ed Miliband

Chuka Umunna: A virus of racism runs through Ukip

The shadow business secretary on the benefits of immigration, humility – and his leader Ed Miliband
Yemen crisis: This exotic war will soon become Europe's problem

Yemen's exotic war will soon affect Europe

Terrorism and boatloads of desperate migrants will be the outcome of the Saudi air campaign, says Patrick Cockburn
Marginal Streets project aims to document voters in the run-up to the General Election

Marginal Streets project documents voters

Independent photographers Joseph Fox and Orlando Gili are uploading two portraits of constituents to their website for each day of the campaign
Game of Thrones: Visit the real-life kingdom of Westeros to see where violent history ends and telly tourism begins

The real-life kingdom of Westeros

Is there something a little uncomfortable about Game of Thrones shooting in Northern Ireland?
How to survive a social-media mauling, by the tough women of Twitter

How to survive a Twitter mauling

Mary Beard, Caroline Criado-Perez, Louise Mensch, Bunny La Roche and Courtney Barrasford reveal how to trounce the trolls
Gallipoli centenary: At dawn, the young remember the young who perished in one of the First World War's bloodiest battles

At dawn, the young remember the young

A century ago, soldiers of the Empire – many no more than boys – spilt on to Gallipoli’s beaches. On this 100th Anzac Day, there are personal, poetic tributes to their sacrifice
Dissent is slowly building against the billions spent on presidential campaigns – even among politicians themselves

Follow the money as never before

Dissent is slowly building against the billions spent on presidential campaigns – even among politicians themselves, reports Rupert Cornwell
Samuel West interview: The actor and director on austerity, unionisation, and not mentioning his famous parents

Samuel West interview

The actor and director on austerity, unionisation, and not mentioning his famous parents
General Election 2015: Imagine if the leading political parties were fashion labels

Imagine if the leading political parties were fashion labels

Fashion editor, Alexander Fury, on what the leaders' appearances tell us about them
Phumzile Mlambo-Ngcuka: Home can be the unsafest place for women

Phumzile Mlambo-Ngcuka: Home can be the unsafest place for women

The architect of the HeForShe movement and head of UN Women on the world's failure to combat domestic violence