سال:1392 | دوره:5 |تعداد مقالات:5

A NUMERICAL STUDY OF LAMINAR FLAME SPEEDS FOR PREMIXED H2 -NH3 -AIR JET FLAMES IS CARRIED OUT FOR 0 TO 80% NH3 IN H2 FOR DIFFERENT EQUIVALENCE RATIOS FROM LEAN TO RICH CONDITIONS. FLAME SPEED PREDICTIONS HAVE BEEN CONDUCTED BY CHEMKIN PACKAGE OVER A WIDE RANGE OF CONDITIONS. THESE DATA ARE THEN USED TO VALIDATE BY EXPERIMENTAL FLAME SPEEDS IN LITERATURE. THE RESULTS DEMONSTRATED THAT THESE MECHANISMS PERFORM WELL FOR H2 -AIR COMBUSTION. DIFFERENCES IN FLAME SPEEDS AND ASSOCIATED RADICAL SPECIES CONCENTRATIONS (H, O, AND OH) ARE FOUND TO BE LARGEST FOR HIGHER LEVELS OF NH3 AND WITH INCREASING EQUIVALENCE RATIO. IT IS ALSO REVEALED THAT OH IS THE KEY RADICAL LEADING TO NH3 DECOMPOSITION AND IS A LIKELY SOURCE OF DEVIATION BETWEEN MODEL PREDICTIONS. THE NUMERICAL DATA SHOW THAT GRI-MECH 3.0 MECHANISM IS THE CAPABLE OF ACCURATELY PROJECTING REDUCTIONS IN FLAME SPEED AS MUCH AS 90 TO 95% WITH NH3 ADDITION.

IN THE PRESENT WORK, COMBUSTION OF A QUIESCENT COAL DUST CLOUD HAS BEEN STUDIED IN THE MEDIA WITH SPATIALLY DISCRETE SOURCES BY MEANS OF NUMERICAL APPROACH. THE THERMAL MODEL HAS BEEN GENERATED TO ESTIMATE THE FLAME PROPAGATION SPEED WITH VARIOUS DUST CONCENTRATION IN AIR. OXYGEN AND NITROGEN HAVE BEEN CONSIDERED AS THE MAIN OXIDIZER AND THE INERT GAS, RESPECTIVELY. THE MODEL USES DISCRETE HEAT SOURCES TO ANALYZE DUST COMBUSTION OF COAL PARTICLES WITH THE DIAMETER OF 50 MM WITHOUT CONSIDERING THE VOLATILE MATTER. THE BURNING PROCESS IS SUPPOSED TO BE OF DIFFUSION TYPE FOR OBTAINING BURNING TIME. FLAME SPEED AS A FUNCTION OF PARTICLE DIAMETER HAS BEEN STUDIED. FURTHERMORE, MINIMUM IGNITION ENERGY AS A FUNCTION OF DUST CONCENTRATION FOR DIFFERENT PARTICLE SIZES HAS BEEN STUDIED. REASONABLE AGREEMENT BETWEEN THE NUMERICAL SOLUTION OF MICRON SIZED COAL DUST CLOUD COMBUSTION AND EXPERIMENTAL DATA WAS OBTAINED IN TERMS OF FLAME PROPAGATION SPEED AND MINIMUM IGNITION ENERGY.

THE INFLUENCES OF DIFFERENT DIESEL/BIODIESEL MIXTURES AND EGR RATES ON BRAKE SPECIFIC FUEL CONSUMPTION (BSFC), EXHAUST GAS TEMPERATURE AND NO, HC, CO EMISSIONS, IS STUDIED AND DEMONSTRATED. IN THIS PAPER, FOUR STROKES DIRECT INJECTION WATER COOLED DIESEL ENGINE WAS USED. THE COMBUSTION OF BIODIESEL AS AN ABSOLUTE FUEL OR MIXED WITH DIESEL IN AN UNCHANGED ENGINE CONSEQUENCES IN ADVANCED COMBUSTION, DECREASED IGNITION DELAY AND IMPROVED HEAT RELEASE RATE IN THE INITIAL UNCONTROLLED PREMIXED COMBUSTION PHASE THAT CAUSED, HIGHER CYLINDER PEAK PRESSURE AND TEMPERATURE THAT RESULT INCREASED NO. EXHAUST GAS RECIRCULATION (EGR) IS AN IMPRESSIVE TECHNIQUE FOR DECREASING NO EMISSIONS WHEN UTILIZING BIODIESEL-DIESEL FUEL MIXTURES. REDUCTIONS IN NO AND EXHAUST GAS TEMPERATURE WERE OBSERVED BUT EMISSIONS OF HC AND CO WERE FOUND TO HAVE INCREASED WITH USAGE OF EGR. THE ENGINE PERFORMANCE AND EFFICIENCY OBTAINED IN BIODIESEL CASE WERE LESS, WHICH COULD BE ATTRIBUTED TO LOWER CALORIFIC VALUE OF BIODIESEL. THE INCREASED OF BSFC OBTAINED WITH BIODIESEL ARE LOWER THAN THAT OF DIESEL FUEL WHEN APPLYING SAME EGR RATE. THUS, EGR HAS A LOWER NEGATIVE INFLUENCE ON ENGINE PERFORMANCE IN CASE OF BIODIESEL COMPARED TO DIESEL FUEL.

POROUS MEDIA HAS BENEFITS TO ENHANCE EVAPORATION OF DROPLETS IN LIQUID-FUEL BURNERS, REDUCE EMISSION OF POLLUTANTS AND MINIMIZE INSTABILITIES. THIS PAPER REPRESENTS THE NUMERICAL STUDY OF LIQUID-FUEL INJECTION AND COMBUSTION INSIDE CONSTANT-VOLUME CHEMICALLY INERT PM TO STABILIZE LEAN MIXTURE. 3D NUMERICAL RESULTS WERE OBTAINED BASED ON A MODIFIED KIVA-3V CODE. DIESEL IS DIRECTLY SPRAYED INSIDE HOT AND HIGH PRESSURE PM CHAMBER. COMPLETE EVAPORATION AND SELF-IGNITED WAS ACHIEVED DUE TO HIGH TEMPERATURE. THE RESULTS FOR AN ESPECIAL CONDITION HAVE COMPARED WITH AN EXPERIMENTAL DATA IN LITERATURE. CONTOURS OF DIESEL VAPOR, FLUID AND SOLID TEMPERATURE OF PM IN AZIMUTHALLY CROSS SECTION, WERE SHOWN. ALSO, EFFECTS OF MASS OF SPRAYED FUEL WERE STUDIED. THE RESULTS SHOW CONSIDERABLE REDUCTION IN CARBON MONOXIDE, NITROGEN MONOXIDE AND SOOT FORMATION.

IN THIS PAPER, A NUMERICAL SIMULATION OF METHANE/AIR COMBUSTION WITHIN A MODEL OF GAS TURBINE COMBUSTOR IS PRESENTED. THE EFFECT OF CO2 AS DILUENT IS INVESTIGATED IN PRIMARY AND SECONDARY ZONE. EDDY DISSIPATION MODEL FOR THE TURBULENCE AND FLAMELET MODEL FOR CHEMISTRY SIMULATION USED. TEMPERATURE DISTRIBUTION AND NO FRACTION IN FLOW AFFECTED DUE TODECREASED MOUNT OF O2 IN AIR FLOW. RESULTS SHOWED AS THE FRACTION OF CO2 INCREASED IN AIR FRACTION ESPECIALLY IN PRIMARY ZONE, THE AMOUNT OF NO REDUCED SIGNIFICANTLY AND FLAME LENGTH AND MAXIMUM TEMPERATURE DECREASED IN COMBUSTOR.