Seiji Yoshida

Emission Reduction of Fuel-Staged Aircraft Engine Combustor Using an Additional Premixed Fuel Nozzle

The Japan Aerospace Exploration Agency (JAXA) is conducting research and development on aircraft engine technologies to reduce environmental impact for the Technology Development Project for Clean Engines (TechCLEAN). As a part of the project, combustion technologies have been developed with an aggressive target that is an 80% reduction over the NOx threshold of the International Civil Aviation Organization (ICAO) Committee on Aviation Environmental Protection (CAEP)/4 standard. A staged fuel nozzle with a pilot mixer and a main mixer was developed and tested using a single-sector combustor under the target engines landing and takeoff (LTO) cycle conditions with a rated output of 40 kN and an overall pressure ratio of 25.8. The test results showed a 77% reduction over the CAEP/4 NOx standard. However, the reduction in smoke at thrust conditions higher than the 30% MTO condition and of CO emission at thrust conditions lower than the 85% MTO condition are necessary. In the present study, an additional fuel burner was designed and tested with the staged fuel nozzle in a single-sector combustor to control emissions. The test results show that the combustor enables an 82% reduction in NOx emissions relative to the ICAO CAEP/4 standard and a drastic reduction in smoke and CO emissions.

High-Frequency Flame Oscillation Observed at a Coaxial LOX/LH2 Injector Element

To study the mechanism of the initiation of combustion instability as hydrogen injection temperature decreases, a hydrogen temperature ramping test was conducted with a single coaxial injection element with LOX/LH2 at a chamber pressure of 8.0 MPa. Two types of injectors were used in the tests. One employed a straight bore LOX post and the other employed a taper-reamed LOX post for better atomization of LOX. The combustion flame was visualized with a high-speed video camera at a rate of 6,000 frames per second. Results showed that unstable combustion was initiated when the hydrogen injection temperature decreased to less than a certain cryogenic temperature. By observing the movement of the prominent pattern of OH emission on the flame, the flame was found to propagate downstream at a constant speed with the flame angle remaining constant during stable combustion. On the other hand, injection pressure peaks appeared during unstable combustion. In this case, a block of flame with strong OH emission was occasionally observed. A block of flame caught up with an anterior block and coalesced into a large block with strong OH emission. This coalesced block of the flame is herein termed “flame burst”.

Intense Tangential Pressure Oscillations Inside a Cylindrical Chamber

Intense tangential pressure oscillations due to oscillatory combustion are generated experimentally inside a cylindrical chamber and are analyzed to understand their characteristic features. To generate the tangential mode, a coaxial injector is installed offcenter on the closed side of the chamber. Hydrogen and nitrogen-diluted oxygen are used as working gases under atmospheric conditions. The features of the side-wall pressure in the first tangential mode (1T mode) at high amplitude, whose amplitude is over 30% of the chamber pressure, differ from those of the side-wall pressure in the 1Tmode at low amplitude in the followingmanner: 1) The positive half-wave of the pressure oscillation has twin sharp peaks. 2) The amplitude of the positive half-wave (zero to positive peak) of the pressure oscillations is larger than that of the negative half-wave (negative peak to zero). The acoustical features of the signals are reproduced and investigated by conducting an analysis and anumerical simulation under similar configurations. It is found that the characteristic feature of the intense signal is originated in the nonlinearity due to the large amplitude of the pressure oscillation.

On acoustic damping of a cylindrical chamber in resonant modes

Acoustic damping of a cylindrical chamber with open and closed ends in resonant modes is analytically and numerically investigated to understand the low damping characteristic of the chamber without chocked nozzle. First, on the basis of the analytic solution of resonant acoustic modes inside a cylinder, the damping by radiation from the open end is calculated analytically using simple acoustic source modeling for velocity fluctuation. The effect of viscosity is also considered as an attenuation mechanism. The values of acoustic damping calculated for the first longitudinal and tangential modes are in good agreement with the corresponding values obtained using numerical simulation. The damping is also investigated for a configuration of the chamber with an injector installed off-center. Finally, we numerically and semi-analytically investigate the acoustic damping for a configuration that includes a hot-gas injection. The obtained mode is found to be a spinning tangential mode and the radiated wave also has a spinning feature. The damping for the spinning tangential mode is found to be larger than that for the symmetric dipole-like radiation under a uniform standing condition, but much smaller than the chamber with a chocked nozzle. Therefore, the chamber with an open end has the low damping characteristic suitable for intentionally generating oscillatory combustion.

Combustion Characteristics of Fuel Staged Combustor for Aeroengines at LTO Cycle Conditions

In JAXA, combustion technologies have been developed with an aggressive target that is an 80% NOx reduction of CAEP/4. For the drastic reduction of NOx emissions, a fuel nozzle was designed based on the lean staged combustion concept. This paper describes single-sector combustor tests of a fuel staged combustor at ICAO LTO cycle conditions of an assumed engine with rated output of 40 kN and overall pressure ratio of 25.8. The results showed that the combustor enables a 77% reduction of the NOx standard of CAEP/4.Copyright

Theoretical and Numerical Estimation of Acoustic Damping of a Model Combustion Chamber

Acoustic damping of a cylindrical chamber with open and closed ends is analytically and numerically investigated. In the analysis, based on the analytic solution of resonant acoustic modes inside cylinder, the damping from the open end is calculated by a simple acoustic source modeling for velocity fluctuation. The effect of viscosity is also considered as an attenuation mechanism. Acoustic damping calculated for first longitudinal and tangential modes are in good agreement with that obtained by numerical simulation. When a longitudinal mode exists, the directivity of radiation becomes like monopole and the damping is large. On the other hand, when a tangential mode exists, it is found that the dipole like directivity is obtained and the damping is small compared to that for the longitudinal mode. A configuration of the chamber and an injector installed off-centered is also investigated. Under non-resonant condition between injector and chamber acoustics, it is found that the acoustic radiation from the open end of the injector is negligible but the viscous effect becomes important. Finally we investigate the acoustic damping with hot gas injection numerically and semi-analytically. The obtained mode is found to be a spinning tangential mode due to the asymmetry of the mean flow field. The radiated wave has also a spinning feature and the damping is found to be much larger than that for symmetric dipole like radiation under uniform condition. The simple acoustic radiation modeling applied for the analysis also works well for this general non-uniform mean flow condition.

Investigations of a Staged Fuel Nozzle for Aeroengines by Multi-Sector Combustor Test

The reduction of NOx emissions from aeroengines is very important to protect the local air quality near the airports and prevent the climate change. ICAO CAEP has been stepped up the NOx standard frequently. Therefore, the engine manufacturers and national research institutes are actively working on the low-NOx technologies to meet the lower NOx emissions standard. JAXA is conducting research and development of the aeroengine technologies for the environmental adaptation in the TechCLEAN project. As a part of the project, combustion technologies have been developed with an aggressive target that is an 80% NOx reduction of CAEP/4. For the drastic reduction of NOx emissions, the fuel nozzles were designed based on the lean staged combustion concept. At first, five fuel nozzles were tested in a single-sector combustor at LTO cycle conditions of small aeroengine and it was confirmed that one fuel nozzle enabled 72% NOx reduction of CAEP/4. This lean low NOx fuel nozzle was tested in the present work in a multi-sector combustor at the same conditions with the single-sector combustor test. Test results showed that the combustor had combustion characteristics enabling 70% NOx reduction of CAEP/4, which was almost same with the single-sector combustor. For the improvement of combustion efficiency at middle power conditions, fuel staging among the main fuel injectors was also investigated at the MCL condition. The results showed that the fuel staging among the main fuel nozzles is effective to improve the combustion efficiency of the annular combustor.Copyright

Detection of frequency-mode-shift during thermoacoustic combustion oscillations in a staged aircraft engine model combustor

We conduct an experimental study using time series analysis based on symbolic dynamics to detect a precursor of frequency-mode-shift during thermoacoustic combustion oscillations in a staged aircraft engine model combustor. With increasing amount of the main fuel, a significant shift in the dominant frequency-mode occurs in noisy periodic dynamics, leading to a notable increase in oscillation amplitudes. The sustainment of noisy periodic dynamics during thermoacoustic combustion oscillations is clearly shown by the multiscale complexity-entropy causality plane in terms of statistical complexity. A modified version of the permutation entropy allows us to detect a precursor of the frequency-mode-shift before the amplification of pressure fluctuations.

Evaluation of Lean Axially Staged Combustion by Multi-Sector Combustor Tests Under LTO Cycle Conditions of a Small Aircraft Engine

JAXA is conducting research and development on aircraft engine technologies to reduce environmental impact in the Technology Development Project for Clean Engines (TechCLEAN). As a part of the project, combustion technologies have been developed with an aggressive target that is an 80% reduction over the NOx threshold of the fourth Committee on Aviation Environmental Protection (CAEP/4) of the International Civil Aviation Organization (ICAO). Lean staged fuel nozzles have been developed and tested using a single-sector combustor under Landing and Take-off (LTO) cycle conditions of the target engine with a rated output of 40 kN and an overall pressure ratio of 25.8. A reduction of 82.2% in LTO NOx emissions relative to the ICAO CAEP/4 standard and drastic reductions in smoke and carbon monoxide (CO) emissions were resulted by single-sector combustor tests of a lean staged combustor with an additional premixed fuel nozzle (ECF: Emission Control Fuel nozzle). After the test, the pilot mixer of the single-sector combustor was improved and an additional 2.5% NOx reduction was achieved by combustion tests. As a next step, a multi-sector combustor with ECF was developed and tested. The test results show that the combustor enables a reduction of 82.2% in LTO NOx emissions relative to the ICAO CAEP/4 standard, though unburnt hydrocarbons (HC) and CO emissions are increased. Temperature distributions in the combustor exit plane were also evaluated.Copyright

Research and Development of Staging Fuel Nozzle for Aeroengine

Research and development of combustion technologies to reduce NOx emission of aero-engines to 20% of ICAO CAEP4 is progressing as a part of a project of JAXA (Japan Aerospace Exploration Agency), the Technology Development for Clean Engine (TechCLEAN). To realize such low NOx level on aero-engines, it is necessary to use not conventional combustion system such as rich-lean combustion but advanced one such as premixed combustion. We are conducting research and development of staging fuel nozzles that use diffusion combustion for the pilot nozzle and premixed combustion for the main nozzle. As the first step, five fuel nozzles were tested experimentally in the form of single-sector combustor. Test conditions were selected as the LTO cycle of presumed small-class engines. From the result of tests, to combine the combustion efficiency in low engine power condition and low NOx emission in high power one, fuel nozzle models that have triple contrary swirler are suitable. However, the combustion efficiency in 7%MTO is lower than that of current engines. It is necessary to decrease the emission of CO.Copyright