Periodic Reporting for period 3 - CHAiRLIFT (Compact Helical Arranged combustoRs with lean LIFTed flames)
Berichtszeitraum: 2021-01-01 bis 2022-11-30
The main objective of CHAiRLIFT project, funded by the CS2 programme, was to assess an innovative combustor concept capable to achieve ultra low NOx operations in future aeroengines a key goal for a sustainable and environmental friendly growth of air traffic.
The proposed concept permits to fully satisfy the requirements of ACARE Flightpath 2050. It comprises two novel features. The first is to adopt “low swirl” lean lifted spray flames with a high degree of premixing and consequently significantly reduced NOx. Inherent characteristics are the stabilization by outer recirculation zones, a strongly reduced risk of flashback and a reduced susceptibility to thermoacoustics instabilities compared to conventional systems.
Second novelty is an alternative arrangement of burners in the annular chamber by tilting the axis of the flames relative to engine axis. This design has the advantage of limiting pilot flames affecting NOx emissions. Additional benefit is the reduced length of the combustor that compensates the increased flame length due to lift-off. The pre-rotated combustor outflow may require a reduced number of turbine nozzle guide-vanes, permitting to save weight and turbine cooling demanding.
The two basic concepts were considered together in a possible new combustor layout.
Overall objectives of the project were:
- Detailed characterization of the new combustor concept by the means of experimental investigations on a dedicated multi-burner rig and by high-fidelity CFD investigations.
- Optimization of the inclined geometry with respect to combustor aerodynamics and sidewall cooling requirement
- Development of the Eulerian-Lagrangian-Spray-Atomization model to accurately describe typical airblast atomizers used in aeroengines.
- Assessment of flame stabilization process using sinusoidal and nanosecond repetitively pulsed plasma discharges
- Application of flame monitoring based on ion-current probe.
- Mapping of NOx emissions measured at lab scale conditions up to representative MTO conditions for reference engine cycles.
The project has confirmed by dedicated experiments the overall outstanding low NOx capabilities of the proposed concept and its good stability performances despite the lack of piloting flames and the high level of premixing. High-fidelity CFD models (combustion and spray atomization) were validated against experimental results permitting possible future design optimization of the solution also starting from innovative contouring of the combustor sidewalls. Non-conventional flame stabilization improvement based on plasma actuation was successfully tested on a gaseous flame version of the burner.
The proposed concept permits to fully satisfy the requirements of ACARE Flightpath 2050. It comprises two novel features. The first is to adopt “low swirl” lean lifted spray flames with a high degree of premixing and consequently significantly reduced NOx. Inherent characteristics are the stabilization by outer recirculation zones, a strongly reduced risk of flashback and a reduced susceptibility to thermoacoustics instabilities compared to conventional systems.
Second novelty is an alternative arrangement of burners in the annular chamber by tilting the axis of the flames relative to engine axis. This design has the advantage of limiting pilot flames affecting NOx emissions. Additional benefit is the reduced length of the combustor that compensates the increased flame length due to lift-off. The pre-rotated combustor outflow may require a reduced number of turbine nozzle guide-vanes, permitting to save weight and turbine cooling demanding.
The two basic concepts were considered together in a possible new combustor layout.
Overall objectives of the project were:
- Detailed characterization of the new combustor concept by the means of experimental investigations on a dedicated multi-burner rig and by high-fidelity CFD investigations.
- Optimization of the inclined geometry with respect to combustor aerodynamics and sidewall cooling requirement
- Development of the Eulerian-Lagrangian-Spray-Atomization model to accurately describe typical airblast atomizers used in aeroengines.
- Assessment of flame stabilization process using sinusoidal and nanosecond repetitively pulsed plasma discharges
- Application of flame monitoring based on ion-current probe.
- Mapping of NOx emissions measured at lab scale conditions up to representative MTO conditions for reference engine cycles.
The project has confirmed by dedicated experiments the overall outstanding low NOx capabilities of the proposed concept and its good stability performances despite the lack of piloting flames and the high level of premixing. High-fidelity CFD models (combustion and spray atomization) were validated against experimental results permitting possible future design optimization of the solution also starting from innovative contouring of the combustor sidewalls. Non-conventional flame stabilization improvement based on plasma actuation was successfully tested on a gaseous flame version of the burner.
T1.2,T1.3 (KIT/ITS)
A cost-effective URANS setup was conceived based on the use LES data. This model was used to carry out a detailed parametric study on the combustor aerodynamics.
LES reactive numerical approach was then setup and validated on a literature test case (see Figure 1). The approach was then used to investigate the CHAIRLIFT concept to optimize the contouring of the side wall (see Figure 2).
As an additional outcome of the task, a preliminary design of possible cooling concept for the sidewall was carried out (Figure 3)
T2.1 T2.2 (UNIFI)
The main goal was to define a representative numerical setup for LES investigations. Results related to the validation of the computed flowfield in isothermal conditions are reported in Figure 4.
LES turbulent combustion models were considered to validate basic low-swirl lifted flame prediction. Investigated models belong to FGM family (with heat loss and flame stretch effects ) and ATF. A hybrid ATF-FGM model was also tested. Figure 5 reports a comparison of some of the tested models against measured CO and temperature. LES results permitted to deeply investigate the flame stabilization process (Figure 6).
CFD investigations of the KIT multi-burner rig have been carried out in T2.2. Figure 7 reports a comparison with exp data. The developed CFD model was then used to investigate several inclination angles defining a performance parameter to assess flame stabilization capabilities (Figure 8).
T 2.3 (URN)
The goal was to provide the spray distribution to the reactive simulation. A workflow based on segregated multiple steps was developed (see Figure 9). A validation of the proposed model was carried out on a literature test case and then applied to the current prefilmer airblast.
T3.1 (KIT/EBI)
A series of experimental tests were conducted at a multi-burner array test rig consisting of up to five modular burners at different inclination angles, equivalence ratios, air pressure drop across the nozzle, and varied air inlet temperature at ambient pressure. Figure 10 reports the stability of studied solutions as a function of pressure drop. Figure 11 is summarizing NOx emissions for two cases varying inlet air temperature.
T3.2 T3.3 (KIT, UNILE)
To study the effect of plasma discharge on the flame stability for the lifted flames, experiments on a single burner were performed. A large test campaign was carried out mostly focusing on flame stability and emissions (Figure 12). Additional tests were carried out by installing an ion sensor probe developed by KIT to carry out an high frequency monitoring of the flame (Figure 13).
T4.1 (UNIFI, KIT)
A hybrid approach combining Chemical Reactor Network and best fitting of the exp data, was used to upscale measured NOx emission up to max take-off conditions for reference engine cycles. Figure 14 reports the obtained scaled NOx emission for cycles at 13bar and 33bar. For the target air fuel ratio (26) predicted emissions are below 2 g/kg.
T4.3 (UNIFI)
LES investigation of the LBO transient of the multi-burner rig was carried out for the inline case, confirming the key role of outer recirculation in flame stabilization. A series of temperature snapshots during flame blow-off is reported in Figure 15.
The overall value and impact of the obtained results are confirmed by the significant number of scientific papers produced (6 journal articles and 12 conference papers and 2 PhD thesis) as well as by the exploitation actions set up, with a patent pending and with the developed methods and rigs considered for new researches.
A cost-effective URANS setup was conceived based on the use LES data. This model was used to carry out a detailed parametric study on the combustor aerodynamics.
LES reactive numerical approach was then setup and validated on a literature test case (see Figure 1). The approach was then used to investigate the CHAIRLIFT concept to optimize the contouring of the side wall (see Figure 2).
As an additional outcome of the task, a preliminary design of possible cooling concept for the sidewall was carried out (Figure 3)
T2.1 T2.2 (UNIFI)
The main goal was to define a representative numerical setup for LES investigations. Results related to the validation of the computed flowfield in isothermal conditions are reported in Figure 4.
LES turbulent combustion models were considered to validate basic low-swirl lifted flame prediction. Investigated models belong to FGM family (with heat loss and flame stretch effects ) and ATF. A hybrid ATF-FGM model was also tested. Figure 5 reports a comparison of some of the tested models against measured CO and temperature. LES results permitted to deeply investigate the flame stabilization process (Figure 6).
CFD investigations of the KIT multi-burner rig have been carried out in T2.2. Figure 7 reports a comparison with exp data. The developed CFD model was then used to investigate several inclination angles defining a performance parameter to assess flame stabilization capabilities (Figure 8).
T 2.3 (URN)
The goal was to provide the spray distribution to the reactive simulation. A workflow based on segregated multiple steps was developed (see Figure 9). A validation of the proposed model was carried out on a literature test case and then applied to the current prefilmer airblast.
T3.1 (KIT/EBI)
A series of experimental tests were conducted at a multi-burner array test rig consisting of up to five modular burners at different inclination angles, equivalence ratios, air pressure drop across the nozzle, and varied air inlet temperature at ambient pressure. Figure 10 reports the stability of studied solutions as a function of pressure drop. Figure 11 is summarizing NOx emissions for two cases varying inlet air temperature.
T3.2 T3.3 (KIT, UNILE)
To study the effect of plasma discharge on the flame stability for the lifted flames, experiments on a single burner were performed. A large test campaign was carried out mostly focusing on flame stability and emissions (Figure 12). Additional tests were carried out by installing an ion sensor probe developed by KIT to carry out an high frequency monitoring of the flame (Figure 13).
T4.1 (UNIFI, KIT)
A hybrid approach combining Chemical Reactor Network and best fitting of the exp data, was used to upscale measured NOx emission up to max take-off conditions for reference engine cycles. Figure 14 reports the obtained scaled NOx emission for cycles at 13bar and 33bar. For the target air fuel ratio (26) predicted emissions are below 2 g/kg.
T4.3 (UNIFI)
LES investigation of the LBO transient of the multi-burner rig was carried out for the inline case, confirming the key role of outer recirculation in flame stabilization. A series of temperature snapshots during flame blow-off is reported in Figure 15.
The overall value and impact of the obtained results are confirmed by the significant number of scientific papers produced (6 journal articles and 12 conference papers and 2 PhD thesis) as well as by the exploitation actions set up, with a patent pending and with the developed methods and rigs considered for new researches.
According to the obtained overall results, the following main progresses beyond the state of the art can be remarked:
- Comprehensive experimental and numerical characterization of low-swirl lifted spray flames operating at ultra-lean, low NOx, conditions. Wide, open, datasets for future possible further validation and improvements released.
- Deep understanding of the role of inclined burners arrangement on combustor aerodynamics and flame stability. Definition of possible novel sidewall contouring and cooling solutions.
- Novel two-phase flow approach for airblast atomizer modelling based on a complete multiregime workflow
- First application of nano-pulsed plasma discharges to low-swirl flames with understanding of the impact on flame stability.
As for the impact related to the main objectives of the project, it can undoubtedly be said that expectations have been fully met: the potentiality of achieving EINOx lower than 2 [g/kg] at relevant Max Take-Off conditions when operating with an Air Fuel Ratio around 26.
The proposed low-NOx solution has therefore the potential to represent a possible design concept for future aeroengines, contributing to develop an environmental friendly civil aviation in the next decades.
- Comprehensive experimental and numerical characterization of low-swirl lifted spray flames operating at ultra-lean, low NOx, conditions. Wide, open, datasets for future possible further validation and improvements released.
- Deep understanding of the role of inclined burners arrangement on combustor aerodynamics and flame stability. Definition of possible novel sidewall contouring and cooling solutions.
- Novel two-phase flow approach for airblast atomizer modelling based on a complete multiregime workflow
- First application of nano-pulsed plasma discharges to low-swirl flames with understanding of the impact on flame stability.
As for the impact related to the main objectives of the project, it can undoubtedly be said that expectations have been fully met: the potentiality of achieving EINOx lower than 2 [g/kg] at relevant Max Take-Off conditions when operating with an Air Fuel Ratio around 26.
The proposed low-NOx solution has therefore the potential to represent a possible design concept for future aeroengines, contributing to develop an environmental friendly civil aviation in the next decades.