2000 2005 2010 2015 YEAR
Figure 1-.1. Projected natural .as consumption 2000-2020.
.nvironmental .ffects
The use of natural gas and the use of the new dry low N0x combustors have reduced N0x levels below 10 ppm. Figure 1-33 shows how in the past 30 years the reduction of N0x by first the use of steam (wet combustors) injection in thecombustors， and then in the1990s， the dry low N0x
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0
ASIA PACIFIC EUROPE LATIN AMERICA NORTH AMERICA
ASIA
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Figure 1-... Technolo.y trends indicate that natural .as is the fuel of choice.
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0 1970 1975 1980 1985 1990 1995 2000 2005 2010 Years
Figure 1-... Control of .as tur.ine .Ox emissions over the years.
combustors have greatly reduced the N0x output. New units under devel-opment havegoals， which would reduce N0 x levels below 9 ppm. Catalytic converters have also been used in conjunction with both these types of combustors to even further reduce the N0x emissions.
New research in combustors such as catalytic combustion have greatpromise， and values of as low as 2ppm can be attainable in the future. Catalytic combustors are already being used in some engines under the
U.S. Departmentof Energy"s(D0E)， Advanced Gas Turbine Program， and have obtained very encouraging results.
Turbine .xpander Section
There are two types of turbines used in gas turbines. These consist of the axial-flow type and the radial-inflow type. The axial-flow turbine is used in more than 95% of all applications.
The two types of turbines-axial-flow and radial-inflow turbines-can be divided further into impulse or reaction type units. Impulse turbines taketheir entire enthalpy drop through the nozzles， while the reaction turbine takes a partial drop through both the nozzles and the impeller blades.
.adial-Inflow Turbine
The radial-inflow turbine， or inward-flow radial turbine， has been in use for many years. Basically a centrifugal compressor with reversed flow andopposite rotation， the inward-flow radial turbine is used for smaller loads and over a smaller operational range than the axial turbine.
Radial-inflow turbines are only now beginning to be used because little was known about them heretofore. Axial turbines have enjoyed tremendousinterest due to their low frontalarea， making them suited to the aircraftindustry.However， the axial machine is much longer than the radialmachine， making it unsuited to certain applications. Radial turbines are used in turbochargers and in some types of expanders.
The inward-flow radial turbine has many components similar to a cen-trifugal compressor. There are two types of inward-flow radial turbines: the cantilever and the mixed-flow. The cantilever type in Figure 1-34 is similar to anaxial-flow turbine， but it has radial blading.However， the cantilever turbine is not popular because of design and production difficulties.
Mixed-Flow Turbine.The turbine as shown in Figure1-35， is almost identical to a centrifugal compressor-except its components have different functions. The scroll is used to distribute the gas uniformly around the periphery of the turbine.
Figure 1-... Cantilever-type radial inflow tur.ine.
Figure 1-.5. Mixed flow type radial inflow tur.ine. Figure 1-... Components of a Radial Inflow Tur.ine.
Thenozzles， used to accelerate the flowtoward the impellertip， are usually straight vanes with no airfoil design. The vortex is a vaneless space and allows an equalization of the pressures. The flow enters the rotor radially at the tip with no appreciable axial velocity and exits the rotor through the exducer axially with little radial velocity. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 1(21)
