• Journal of the Korean Society of Combustion
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• v.7 no.2
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• pp.15-23
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• 2002

We measured emission indices for $NO_x$, CO, temperature and radical characteristics for partially premixied flames formed by suction & blow fans air condition. At sufficiently high levels of partial premixing a double flame structure consisting of a rich premixed inner flame and outer diffusion flame was established similar to that previously observed in premixed flames. $NO_x$, Temperature. CO concentration were experimented with approximately constant air flow rate and decreasing equivalence ratios. The reduction in $NO_x$, and temperature at suction condition as compared with that for blow condition was approximately 20%, but on the contrary, CO emission was increased. In addition, We measured temperature distributions and found that temperature increased continuously with increasing partial premixing. We also estimated CH, $C_2$ radical intensity. CH and $C_2$ radicals provide evidence that, for the present measurement, CH and $C_2$ radicals intensity was associsated with their premixed component. And we observed stronger $C_2$, CH radicals intensity at suction conditions than blow conditions.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.7-8
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• 2012

The effects of interaction between partially premixed and premixed swirl flames on CO and NOx emissions were experimentally investigated using a hybrid/dual swirl jet combustor for a micro-gas turbine. Under the condition of constant angle ($45^{\circ}$) for outer swirl vane, the angle and direction of inner swirl vane installed for a partially premixed flame were varied as main parameters with a constant fuel flow rate for each nozzle. It was found that for all conditions, CO and NOx emissions were measured below 4 ppm and 15 ppm at 15% $O_2$, respectively, in a wide range of equivalence ratio (0.6~0.9). For co-swirl flows, CO emission increased dramatically as the angle of inner swirl vane increased from $15^{\circ}$ to $45^{\circ}$ near lean-flammability limit (i.e. equivalence ratio of 0.5). On the other hand, the case of swirl $angle=45^{\circ}$ provided the lowest NOx emission at higher equivalence ratios than 0.6. For counter-swirl flows, the case of swirl $angle=45^{\circ}$ extended the lean-flammability limit but higher NOx emissions were found compared to those of co-swirl flows. These results could be inferred by interaction between (inner) partially premixed and (outer) premixed swirl flames. However, these estimations were not clear yet because there was insufficient data on turbulent flow structure and fuel-air mixing in the present experimental approach.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.77-84
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• 2001

Measurements of local CO, $CO_2$, $O_2$, $N_2$, $C_3$H$_{8}$, NOx concentrations and flame temperature are made for partially premixed flame with and without acoustic excitation. The CO, $CO_2$, $O_2$, $N_2$, and $C$_3$H_8$ concentrations are determined by thermal conductivity detection (Gas-chromatograph) and NOx concentrations are determined by chemiluminescent detection (NOx analyser). To measure local sample concentration, sampling probe was made by quartz with inlet diameter of 0.25mm. In the case of excitation, the visual shape of the flame is changed from laminar flame to turbulent-like flame. The flame length is also reduced, and the flame width becomes broad. In the observation of emission concentration without acoustic excitation, meanwhile, the $CO_2$ and NOx concentrations peak at flame front where the mixture meets with surrounding air, and the CO concentration is increasing at maximum position of CO2 concentration and peaks at the centerline of the burner. In the case of acoustic excitation, the $CO_2$ concentration is widely occurred at nozzle of the burner and is higher relative to unexcitation. The CO concentration is much reduced, but NOx concentration is more increasing. And flame temperature is higher relative to unexcitation. These are caused by enhancing of mixing with surrounding air due to excitation. However, in the case of acoustic excitation, the total NOx concentration is reduced because of the shortened flame length which affects residence time.e.

• 한국연소학회:학술대회논문집
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• 2002.06a
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• pp.24-32
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• 2002

The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (Representative Interactive Flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian Particle Flamelet Model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.81-89
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• 2002

The autoignition and subsequent flame propagation of initially nonpremixed turbulent system have been numerically analyzed. The unsteady flamelet modeling based on the RIF (representative interactive flamelet) concept has been employed to account for the influences of turbulence on these essentially transient combustion processes. In this RIF approach, the partially premixed burning, diffusive combustion and formation of pollutants(NOx, soot) can be consistently modeled by utilizing the comprehensive chemical mechanism. To treat the spatially distributed inhomogeneity of scalar dissipation rate, the multiple RIFs are employed in the framework of EPFM(Eulerian particle flamelet model) approach. Computations are made for the various initial conditions of pressure, temperature, and fuel composition. The present turbulent combustion model reasonably well predicts the essential features of autoignition process in the transient gaseous fuel jets injected into high pressure and temperature environment.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2977-2983
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• 2008

The combustion characteristics of a partially premixed flame in a dump combustor were studied to determine the effects of hydrogen enrichment in propane. Bluff-body was used for flame stabilization. Fuel mixtures containing a hydrogen mole fraction ranging from 0.1 to 0.5 were burnt at ambient pressure within a quartz chamber. Tests were carried out keeping the total reactant flow rate by adjusting the fuel and air flow rates. The fluctuations of pressure were measured by piezoelectric pressure sensor. The instantaneous flame structure and OH chemiluminescence images were described by High-speed Intensified Charged Coupled Device (HICCD) camera and Intensified Charged Coupled Device (ICCD) camera. The present results show that hydrogen enrichment in fuel changed the location of primary reaction zone from inner recirculation zone to turbulent shear layer and pressure signal. The reason is that chemical aspects take precedence over flow aspects in the hydrogen-enriched flame.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.265-266
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• 2015

The multi-environment PDF model coupled with flamelet generated manifolds(FGM) has been developed for a large eddy simulation of turbulent partially premixed lifted flame. This approach has a capability to realistically account for the transport and evolution of probability density function for mixture fraction and progress variable with the manageable computational burden. Using the tabulated chemistry, it is possible to track radical distributions which is important to predict autoignition process with the vitiated coflow environment. Numerical results indicate that the present yields the good agreement with experimental data in terms of mixture fraction, temperature, and species mass fractions.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.78-86
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• 2000

The objective of this research is to understand the characteristics of a nonpremixed, turbulent, hydrogen jet flame which is stabilized in Mach 1.8 coflowing air flows. In order to investigate the flame structure, flame lengths and fuel trajectories were measured by using direct photography, acetone PLIF, Mie scattering techniques, and numerical simulation. Effect of increasing air velocity was investigated when fuel velocity is fixed. The subsonic flame length was decreased drastically, however the supersonic flame length was increased slowly Then the change of flame blow out characteristics was observed as varying fuel nozzle lip thickness. The flame stability can be increased when fuel nozzle lip thickness was increased, which indicates that the minimum fuel lip thickness ratio is required for the stable supersonic flames. Also, it is found that fuel jet is blocked by high pressure zone and low scattering zone is made. Then the fuel that was moving along the recirculation zone had longer residence time within the supersonic flames, which made partially premixed zone.