International Civil Aviation Organisation (ICAO) is the global forum for international civil aviation and has succeeded for more than 40 years in bringing the world together around increasingly stringent regulations for aircraft emissions and noise. Besides ICAO that works in close co-operation with various UN bodies, there exist other regulatory governance bodies that set regulatory standards for the civil aviation industry in aspects of noise and emissions regulations. These bodies include the influential Federal Aviation Authority (FAA) who imposes strict Federal Aviations Regulations (FARs) on aircrafts flying to and within the United States of America (USA) and these FARs are at the same time widely adopted by air carriers worldwide. The Environmental Protection Agency (EPA) of the USA standards are equivalent to the NOx emission standards of the UN International Civil Aviation Organization (ICAO) too. Hence, it may seem that there exist various agencies whose regulatory standards aircrafts must adhere to but, eventually, they originate back to those of ICAO’s.
According to the recent publication of the ICAO environmental report, initiatives to promote the sustainability of aviation activities in synchronization with the growth of the industry over the past four decades have successfully reduced aircraft noise by a whopping 75%, and CO2 emissions intensity by 70%. While research and development work in improving environmental standards in the aviation industry has been intensely ongoing for major turbine manufacturers such as General Electric (GE) and Pratt & Whitney (P&W), regulatory standards must definitely be in place, stringent as ever, and constantly looked into to review them according to current and projected trends in aviation travel. Of these regulatory standards, amongst are aircraft engine emissions and noise control standards that are of most relevance to the UEET program and in producing ‘the engine of the future’ as aircraft engines’ designers strive for a more environmental approach towards their conceptualization of their future engines.
4.3.1 Aircraft engine emissions
While engine emissions of aircraft may seemingly be grouped together with those of automobile vehicles on the road, it is more accurate to identify aircraft engine emissions with a significant portion emitted at altitude. With relations to the turbofan engine that is widely used in commercial aircrafts today. Figure 4.3.1.1 below shows the schematic production of emissions from the engine.
These emissions at high altitude will alter the atmospheric concentration of greenhouse gases and trigger the formation of condensation trails and may increase cirrus cloudiness, all of which will contribute to the change of climate. Indirectly, aircraft engine emissions have also greatly contribute to the consequences felt by the world as with rising sea-levels and extreme weather changes.
The jet exhaust usually contains harmful gases like oxides of nitrogen, carbon monoxide and particulate matter. These components can lead to ozone depletion and global warming. Other components of the exhaust such as aerosols and particulates are harmful as they are suspected of producing clouds that could affect the earth’s climate changes. Currently, most combustors in engine meet the 1996 International Civil Aviation Organization landing and takeoff NOx limits by small margins.
The famous Kyoto Protocol signed in Japan in 1997 has excluded international aviation emissions from their targets, while also stating that the responsibility for cutting down or limiting greenhouse gases from aircrafts will work through ICAO.
The Council of ICAO and the Committee on Aviation Environmental Protection (CAEP) has hence adopted engine certification standards contained in Annex 16 – Environmental Protection, Volume II – Aircraft Engine Emissions to the Convention on International Civil Aviation. Since this inception, technological innovations in aircraft engines have resulted in reductions of key air pollutants.
As can be observed in figure 4.3.1.2 below with respect to P&W’s engines, pollutant especially that of unburned hydrocarbons (UHC) has dropped significantly for the transformation of the older JT8D-200 to the more technologically sound JT8D-EKIT.
To achieve certification, it must be demonstrative that the characteristic emissions of the engine type for HC, CO, NOx and smoke are below the limits defined by ICAO. The certification process is performed on a test bed, where the engine is run at four different thrust settings, to simulate the various phases of the LTO cycle, as follows:
- take-off (100% available thrust) for 0.7 min;
- climb (85% available thrust) for 2.2 min;
- approach (30% available thrust) for 4.0 min; and
- taxi (7% available thrust) for 26 min.
The test bed process is as depicted in figure 4.3.1.3 below:
With certification, the next step for these OEMs is to work towards the goal of UEET’s aim to fulfill several emissions criteria. The engine should have a combustor that can reduce the NOx emissions by 70% over the landing and take-off cycles from the 1996 International Civil Aviation Organization standards, with no increase in other emission constituents such as smoke, unburned hydrocarbons and carbon monoxide. Gas turbine propulsion technologies that allow carbon dioxide reductions will be developed. With regards to the problems caused by aerosols and particulates, levels of emission will be assessed and reduced if possible. The operability for safe flights, cost of engines and ease of maintenance should not be affected by this emission reduction. The ultra efficient engine should also reduce the threat of ozone depletion by 90% through the use of combustor technologies.
The effect and impact the UEET had created is apparent in the present day. Of technical achievements accomplished most recently, Rolls Royce’s Trent 1000 engine, used in the new Boeing Dreamliner B787, is designed and built such that the fuel burnt during operation in 15% lesser compared to engines 1 decade ago. In addition, emissions will be decreased by 40% as compared to current international legislation and regulations. Airbus, on the other hand, is not lagging in this competitive race. Its brand new A380, the largest civil commercial aircraft to date, has the lowest fuel consumption per passenger of any large commercial aircraft yet built.
While OEMs work on the technical and engineering aspect of such improvements, researchers are in search of an alternative fuel that might cut down on the harmful emissions that contribute to the greenhouse effect. Presently, the fuel used in the civil aviation industry is kerosene that is derived from crude oil, providing a good balance of energy density, operational issues, cost and safety, all properties required of an aviation fuel. As fuel costs rise and the future looks bleak for the downtrend of the fuel prices and the depleting supply of fuel, R&D work are in process to find a fuel replacement. Apart from better economical and environmental-friendly impacts, a viable alternative aviation fuel could possible stabilize world fuel price fluctuations and hence, reduce uncertainties and vulnerabilities from over-reliance on a single type of fuel.
Aircraft and engine manufacturers are currently looking into the possibility of using synthetic jet fuels from coal, natural gas or other hydrocarbons feedstocks and also biogas. Ideally, the fuel should not require OEMs to change or re-design the engines.
As we can see, the trends for the designs of new aircrafts are heading towards that of economical and environmentally friendly at the same time. Perhaps, the ‘engine of the future’ will have even better performance than the B787 and A380 economically-wise and also more environmentally friendly.
4.3.2 Aircraft noise
Besides aircraft emissions, the other aspect of regulatory standards most often discussed and focused on is aircraft noise. Aircraft noise is the most apparent source of aircraft pollution for many, especially felt by residents residing near airports. This is a significant cause of adverse community reaction related to the operation and expansion of airports both in developed and developing countries.
ICAO has been addressing the issue of aircraft noise since the 1960s. The first Standards and Recommended Practices (SARPs) for aircraft noise certification were published in 1971. They are contained in Annex 16 to the Convention on
International Civil Aviation (Volume I - Environmental Protection — Aircraft Noise). These Standards have been updated since then to reflect improvements in technology.
Reducing or limiting noise originating from aircraft is therefore paramount and one of ICAO’s important goal set out to achieve. Although aircrafts coming out of production lines these days are 75% quieter than 40 years ago according to ICAO’s researchers, aircraft manufacturers are still competing to design even quieter aircrafts to market their products as the world becomes more environmentally conscious. For instance, Boeing’s new Dreamliner aircraft (B787) is also expected to deliver significant improvements in noise, about 15 to 20 decibels (dB) below the Chapter 4 limits, and therefore at least 10dB better than the older aircraft (e.g. B767, A330) it replaces. Figures 4.3.2.1 and 4.3.2.2 below show the progress of noise reduction at source over the last 40 years.
As depicted above, noise has been greatly reduced over the last four decades since the inception of aircraft noise regulation. There is substantial belief that the ‘engines of the future’ will probably have even greater reduction of noise as compared to present standards.
The number of people exposed to aircraft noise is the metric normally used to estimate aircraft noise impact. ICAO’s Committee on Aviation Environmental Protection (CAEP) has developed a computer model for assessing global exposure to the noise of transport aircraft, known as MAGENTA Recent estimates from the MAGENTA model have shown an improvement in the global noise situation with a reduction in the size of the population within the 65 dB DNL1 contours of about 30 percent in 2006, relative to the 2000 level. Noise insulation programs and other noise management and reduction initiatives are often developed around airports to reduce the noise experienced by the exposed population.
Aircraft acoustic certification involves measuring the noise level of an aircraft in
Effective Perceived Noise Level (EPN) dB at three points: two at take-off (flyover and sideline), and the third during the approach. These steps are illustrated in figure 4.3.2.3 below.
