Flameless combustion is a new technology with the following advantages:1)Ultra-low emissions of both NOX and CO;2)fuel flexibility,from liquid fuels,natural gas to hydrogen-rich syngas;3)lower possibility of flashback...Flameless combustion is a new technology with the following advantages:1)Ultra-low emissions of both NOX and CO;2)fuel flexibility,from liquid fuels,natural gas to hydrogen-rich syngas;3)lower possibility of flashback and thermoacoustic oscillations.In this paper,we focus on the dynamic characteristics of a flameless model combustor.Experimental results show that flameless combustion can lower emissions while maintaining combustion stability.However,combining a pilot flame with flameless combustion may excite thermoacoustic instability.展开更多
This paper presents the experimental and numerical results for a two stagecombustor capable of achieving flameless combustion with liquid fuels for different thermalheat inputs of 20,30,40 and 60 kW and heat release d...This paper presents the experimental and numerical results for a two stagecombustor capable of achieving flameless combustion with liquid fuels for different thermalheat inputs of 20,30,40 and 60 kW and heat release density of 5-15 MW/m^(3).Combustioncharacteristics and pollutant emissions are studied for three different fuels,kerosene,diesel andgasoline.The influence of droplet diameter on pollutant emissions at all conditions is studied.The fuel and oxidizer are supplied at ambient conditions.The concept of high swirl flows hasbeen adopted to achieve high intemal recirculation rates,residence time and increased dilutionof the fresh reactants in the primary combustion zone,resulting in flameless combustion mode.Air is injected through four tangential injection ports located near the bottom of the combustorand liquid fuel is injected through a centrally mounted pressure swirl injector.Computationalanalysis of the flow features shows that decrease in the exit port diameter of the primarychamber increases the recirculation rate of combustion products and helps in achieving theflameless combustion mode.Based on preliminary computational studies,a 30 mm primarychamber exit pont diameter is chosen for experimental studies.Detailed experimentalinvestigations show that flameless combustion mode was achieved with evenly distributedcombustion reaction zone and unifom temperature distribution in the combustor.Pollutant emissions of CO, NO_(x),C_(x)H_(y) are measured and compared for all operating conditions ofdifferent fuels and different thermal inputs. The acoustic emission levels are reduced by6-8 dB as combustion mode shifts from conventional mode to flameless combustion mode.展开更多
Moderate or intense low oxygen dilution(MILD)combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs.However,due to the lac...Moderate or intense low oxygen dilution(MILD)combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs.However,due to the lack of the fundamental knowledge on this combustion,there is a misconception that MILD combustion should be established by high preheating of the air,which has limited its application.Our research and development on this combustion has been performed for several years. We have found that the requirements for establishing the MILD combustion are more relaxed than previously.It is also revealed that this combustion of different type,i.e.,non-premixed,partially premixed and fully premixed,can be achieved by firing various fuels(i.e.,gaseous,liquid and solid fuels).It is suggested that the application of the MILD combustion can be expanded significantly.The present review summarizes the progress and recent trend made in the R&D of this combustion and recommends further fundamental studies for improving our knowledge and widening its applications.展开更多
The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of...The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of the high-temperature preheated fuel(coal gas&coal char)has been achieved in all experimental cases.Through fire-observation windows,the combustion zone was transparent and no flame fronts were seen.Additionally,differentλ_(2)in this study were basically within the common range of self-preheating combustion technology.The results manifested that the rapid ignition of coal gas and the recirculation of high-temperature flue gas resulted in relatively high combustion temperatures close to the secondary air nozzle exit.With the increase of.12,the unburned carbon content of fly ash increased slightly and combustion efficiencies of all experiments exceeded98%.Moreover,the exit NO_(x)emission was not reduced linearly,which was dissimilar from conventional air staging combustion.The main reason was that the volatile-N was released in the self-preheating device,and the air staging method could not effectively reduce the char-NO_(x).In the course of the experiments,the lowest NO_(x)emission was 64.35 mg/m3(@6%O2)whenλ_(2)was 0.40.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.50706054)
文摘Flameless combustion is a new technology with the following advantages:1)Ultra-low emissions of both NOX and CO;2)fuel flexibility,from liquid fuels,natural gas to hydrogen-rich syngas;3)lower possibility of flashback and thermoacoustic oscillations.In this paper,we focus on the dynamic characteristics of a flameless model combustor.Experimental results show that flameless combustion can lower emissions while maintaining combustion stability.However,combining a pilot flame with flameless combustion may excite thermoacoustic instability.
文摘This paper presents the experimental and numerical results for a two stagecombustor capable of achieving flameless combustion with liquid fuels for different thermalheat inputs of 20,30,40 and 60 kW and heat release density of 5-15 MW/m^(3).Combustioncharacteristics and pollutant emissions are studied for three different fuels,kerosene,diesel andgasoline.The influence of droplet diameter on pollutant emissions at all conditions is studied.The fuel and oxidizer are supplied at ambient conditions.The concept of high swirl flows hasbeen adopted to achieve high intemal recirculation rates,residence time and increased dilutionof the fresh reactants in the primary combustion zone,resulting in flameless combustion mode.Air is injected through four tangential injection ports located near the bottom of the combustorand liquid fuel is injected through a centrally mounted pressure swirl injector.Computationalanalysis of the flow features shows that decrease in the exit port diameter of the primarychamber increases the recirculation rate of combustion products and helps in achieving theflameless combustion mode.Based on preliminary computational studies,a 30 mm primarychamber exit pont diameter is chosen for experimental studies.Detailed experimentalinvestigations show that flameless combustion mode was achieved with evenly distributedcombustion reaction zone and unifom temperature distribution in the combustor.Pollutant emissions of CO, NO_(x),C_(x)H_(y) are measured and compared for all operating conditions ofdifferent fuels and different thermal inputs. The acoustic emission levels are reduced by6-8 dB as combustion mode shifts from conventional mode to flameless combustion mode.
基金supported by the National Natural Science Foundation of China(Grant No.11072005,50936001)the Open Foundation of State Key Laboratory of Coal Combustion(Grant No.FSKLCC0801)
文摘Moderate or intense low oxygen dilution(MILD)combustion plays a significant role in the mitigation of combustion-generated pollutants and greenhouse gases whilst meeting thermal efficiency needs.However,due to the lack of the fundamental knowledge on this combustion,there is a misconception that MILD combustion should be established by high preheating of the air,which has limited its application.Our research and development on this combustion has been performed for several years. We have found that the requirements for establishing the MILD combustion are more relaxed than previously.It is also revealed that this combustion of different type,i.e.,non-premixed,partially premixed and fully premixed,can be achieved by firing various fuels(i.e.,gaseous,liquid and solid fuels).It is suggested that the application of the MILD combustion can be expanded significantly.The present review summarizes the progress and recent trend made in the R&D of this combustion and recommends further fundamental studies for improving our knowledge and widening its applications.
基金supported by Strategic Priority Research Program of the CAS(XDA29010200)CAS Project for Young Scientists in Basic Research(YSBR-028)Youth Innovation Promotion Association of the CAS(2019148)。
文摘The effects of the secondary air excess ratio(λ_(2))on the self-preheating combustion characteristics and NO_(x)emission of semi-coke have been experimentally studied on a bench-scale test rig.Flameless combustion of the high-temperature preheated fuel(coal gas&coal char)has been achieved in all experimental cases.Through fire-observation windows,the combustion zone was transparent and no flame fronts were seen.Additionally,differentλ_(2)in this study were basically within the common range of self-preheating combustion technology.The results manifested that the rapid ignition of coal gas and the recirculation of high-temperature flue gas resulted in relatively high combustion temperatures close to the secondary air nozzle exit.With the increase of.12,the unburned carbon content of fly ash increased slightly and combustion efficiencies of all experiments exceeded98%.Moreover,the exit NO_(x)emission was not reduced linearly,which was dissimilar from conventional air staging combustion.The main reason was that the volatile-N was released in the self-preheating device,and the air staging method could not effectively reduce the char-NO_(x).In the course of the experiments,the lowest NO_(x)emission was 64.35 mg/m3(@6%O2)whenλ_(2)was 0.40.
