Aviation and the Global Atmosphere

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Much of the longer term combustion research is now aimed at what is termed "ultra-low NOx technology." This technology is defined as technology that produces NOx levels that are no more than 50% of the ICAO CAEP/2 standards. All major manufacturers of aircraft engines, with the sponsorship of associated government agencies, are currently pursuing combustor technologies aimed at reducing NOx emissions to these levels, under operating conditions typical of the next generation of engines. This approach entails pursuing technology that is relevant to engines with pressure ratios from current levels (30 to 40) to future levels (above 50). The aim is to reduce NOx production in the vicinity of airports and at subsonic cruise conditions. Two key programs are aimed at large, subsonic, high-pressure ratio aircraft engines:

Figure 7-24: Illustration of complex flow passages and blade cooling schemes in a typical turbine stage (after Rolls Royce, 1992).

Figure 7-25: Typical static temperature and static pressure histories downstream of the combustor (Lukachko et al., 1998).

These programs specify that there must be no compromise in performance, safety, or any other emissions parameters (smoke, CO, and HC).

Details of combustor technologies are commercially sensitive and are not openly available. However, three parallel strategies are being pursued. They vary in their NOx reduction potential and their associated increase in complexity, cost, and development challenge:

7.5.5. Future Technology Scenarios

As part of the preliminary work associated with this report, industry was asked to consider what advances in technology might be applicable for aircraft in the year 2050. Numerous projections were made by an expert group from the aeronautical industry (engine, airframe, and aerospace manufacturers). The group provided their best judgments of fuel efficiency and NOx technology scenarios for the year 2050 (ICCAIA, 1997f) to the ICAO Committee on Aviation Environmental Protection Forecasting and Economic Support Group (FESG) for use in Chapter 9 of this report. The assumptions for the 2050 scenarios were as follows:

Chapter 9 of this report considers the conclusions of the group in conjunction with FESG traffic scenario projections. Together, these considerations take account not only of long-term demand but also of fuel burn and emissions (see Chapter 9). The latter two depend on three factors:

The benefits arising from the first item influence projections in terms of fuel efficiency alone. The other two items take into account the net effects of cycle changes and emissions reductions strategies. Two potential long-term aircraft technology scenarios emerged from these deliberations. These scenarios are summarized in Table 7-6.

The outcome of these deliberations is that a basis now exists for the development and ongoing monitoring of future research strategies as air transport and concern about its environmental impact continues to grow.

7.5.6. Summary of Key Points Relating to Combustion Technology

Several important conclusions can be drawn from the present assessment of combustion technology in relation to emissions production and control:

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