FUEL AND COMBUSTION CONFERENCE OF IRAN | Year:2008 | دوره:2 |Papers Count:15

ENGINE WITH THE HOMOGENEOUS CHARGE COMPRESSION IGNITION, HCCI, OFFERS A NUMBER OF BENEFITS OVER CONVENTIONAL SI AND CI, SUCH AS MUCH LOWER NOX EMISSION AND PARTICULATE MATTER EMISSION. IN THIS PAPER, THE EFFECTS OF INTAKE TEMPERATURE AND PRESSURE, EQUIVALENCE RATIO, ENGINE SPEED AND COMPRESSION RATIO ON THE AUTO IGNITION OF THE NATURAL-GAS HCCI ENGINE HAVE BEEN INVESTIGATED. THE CHEMICAL KINETIC MECHANISM INCORPORATED THE GRI-3. 0 MECHANISM THAT CONSIDERS 53 SPECIES AND 325 REACTIONS TOGETHER. TO SIMULATE HCCI ENGINE CYCLES, A VARIABLE VOLUME COMPUTATION HAS BEEN PERFORMED BY INCLUDING THE PISTON MOTION INTO THE CHEMICAL REACTION DESIGN, CHEMKIN, CODE. THE SENKIN CODE USED IN ORDER TO SIMULATE THE IN-CYLINDER COMBUSTION. IT WAS FOUND THAT INCREASING THE INTAKE TEMPERATURE AND PRESSURE WOULD RESULT IN ADVANCE IGNITION AND HIGH PEAK TEMPERATURE. IT WAS ALSO FOUND THAT ADDITION A SMALL PERCENT OF ETHAN AND INCREASING THE EQUIVALENCE RATIO WOULD RESULT IN ADVANCE IGNITION, IN CONTRAST, INCREASING THE EQUIVALENCE RATIO AND ENGINE SPEED RETARDED THE IGNITION TIMING.

FLUID MECHANICAL OR CFD SIMULATION IS PLAYING AN INCREASINGLY IMPORTANT ROLE IN THE SIMULATION OF ENGINE PROCESSES, AS IT MAKES POSSIBLE THE MOST DETAILED PHYSICAL DESCRIPTION OF THE RELEVANT PROCESSES. THE OBJECTIVE OF THIS WORK IS TO SIMULATE SPRAY FLOW WITH DIFFERENT BREAK-UP MODELS AND INVESTIGATE THE EFFECT OF THESE MODELS ON DI DIESEL ENGINE COMBUSTION AND PERFORMANCE. IN THIS SIMULATION, THE 3 -DIMENSIONAL NAIVER-STOKES EQUATION IS SOLVED WITH SIMPLEC ALGORITHM. AN EDDY BREAK-UP COMBUSTION MODEL AND A DIESEL AUTO-IGNITION MODEL WERE IMPLEMENTED TO SIMULATE THE IGNITION AND COMBUSTION PROCESS IN A DIESEL ENGINE. ALL THE SIMULATIONS WERE CARRIED OUT BY THE USE OF FIRE CFD TOOL. RESULTS WERE VALIDATED WITH AVAILABLE EXPERIMENTAL DATA FOR OM_355 DI DIESEL ENGINE FOR MEAN CYLINDER PRESSURE. THE RESULTS SHOW THAT THERE HAVE BEEN GOOD AGREEMENTS BETWEEN EXPERIMENTS AND THE CFD CALCULATIONS. THE RESEARCH DEMONSTRATED THAT MULTIDIMENSIONAL MODELING IS USEFUL FOR DIESEL ENGINE SPRAY MODELING AND OPTIMIZATION.

NATURAL GAS RESOURCES IN IRAN ARE LOCATED IN WIDE RANGE OF AREA. WE DIVIDED NATURAL GAS RESOURCES IN IRAN INTO 3 CATEGORIES ACCORDING TO THE ZONE OF EXTRACTION THE QUALITY OF NATURAL GAS IN EACH OF THESE ZONES DIFFERS FROM EACH OTHER. IT’S BETTER TO KNOW WHICH ZONE OF OUR COUNTRY HAS THE MOST APPROPRIATE OF NATURAL GAS IN QUALITY FOR INTERNAL COMBUSTION ENGINES AND OTHER ZONES WITH LESS QUALITY FOR DOMESTIC USES AND EXPORT. ALSO IT’S USEFUL TO KNOW THE COMBUSTION CHARACTERISTICS OF NATURAL GAS FROM EACH ZONE OF OUR COUNTRY AND RATE OF ITS AIR POLLUTION IN INTERNAL COMBUSTION ENGINES AT DIFFERENT CONDITIONS. IN THIS PAPER, THE NATURAL GASES OF IRAN ARE CLASSIFIED UPON THEIR CHEMICAL PROPERTIES AND HEAT RATE AND AIR POLLUTION LEVEL IN INTERNAL COMBUSTION ENGINES WITH THE AID OF GOVERNING EQUATION AND COMPUTER SIMULATION FROM REFERENCE (8), WE OBTAINED MEAN OCTANT NUMBER AND HEATING VALUE PER UNIT VOLUME OF NATURAL GAS EXTRACTED IN EACH ZONE. NEXT WE CALCULATED HEATING VALUE OF NATURAL GAS PER UNIT MASS IN EACH ZONE. IT IS FOUND THAT THE QUALITY OF NATURAL GAS FROM NORTHERN AND EAST-NORTHERN ZONE OF OUR COUNTRY (CALLED ZONE 3) HAS ADVANTAGES FOR APPLICATION IN INTERNAL COMBUSTION ENGINES.

THE PERFORMANCE OF A SOLID ROCKET MOTOR DEPENDS HEAVILY ON THE FLOW CHARACTERISTICS, THE CHEMICAL COMPOSITION OF THE GRAIN, COMBUSTION PRODUCTS AND THE BURNING RATE. IN THIS STUDY THE START-UP TRANSIENT INTERNAL BALLISTICS OF A TYPICAL SOLID ROCKET MOTOR (SRM) IS NUMERICALLY SIMULATED. TWO BURNING RATE LAWS ARE USED TO MODEL SIMPLE AND EROSIVE BURNING. GOVERNING EQUATIONS OF 2 -DIMENSIONAL IN VISCID FLOW ARE SOLVED USING AN EXPLICIT MACCORMACK FINITE DIFFERENCE TECHNIQUE IN WHICH THE LOCATIONS OF SHOCK WAVES ARE CAPTURED BY THE SOLUTION SCHEME. EROSIVE BURNING INCREASES THE CHAMBER PRESSURE AND THRUST DURING THE EARLY PORTION OF BURNING FOR A PARTICULAR MOTOR.

AN EXPERIMENTAL INVESTIGATION OF PREMIXED METHANE/AIR COMBUSTION WITHIN A NOVEL POROUS CERAMIC BURNER IS DESCRIBED IN THIS PAPER. THE BURNER IS COMPOSED OF THREE RECTANGULAR POROUS CERAMIC LAYERS STACKED ON EACH OTHER AND INSULATED AROUND THE CIRCUMFERENCE. THE UPSTREAM LAYER IS ASSUMED TO BE THE PREHEAT ZONE, WHILE THE OTHERS ARE SERVED AS THE COMBUSTION ZONES. THE OPERATING PARAMETERS INCLUDE FUEL/AIR MIXTURE FLOW RATE AND EQUIVALENCE RATIO. THE MAIN OBJECTIVES OF THIS STUDY ARE DOCUMENTING THE FLAME STABILIZATION WITHIN THE BURNER AND DETERMINATION OF OPERATING RANGE. THE BURNER IS TESTED OVER THE RANGE OF LEAN LIMIT (F£0.65). THE EXPERIMENTAL DATA DEMONSTRATES THE ADVANTAGES OF BURNING A COMBUSTIBLE GAS INSIDE THE POROUS CERAMIC BURNER. THE BURNER SHOWS A GREAT ABILITY TO EXTEND THE BLOW OFF LIMIT AT EACH EQUIVALENCE RATIO.

THE THERMAL BALANCE OF A FOUR STROKE, FOUR-CYLINDER SI ENGINE OPERATING ON ETHANOL -GASOLINE BLENDS (0, 5, 10, 15 AND 20%) WAS ESTABLISHED. THE THERMAL BALANCE WAS RESPECT OF USEFUL WORK, HEAT LOST THROUGH EXHAUST, HEAT LOST TO THE COOLING WATER AND UNACCOUNTED LOSSES (HEAT LOST BY LUBRICATING OIL AND RADIATION). THE RESULTS INDICATE THAT AS THE PERCENTAGE OF ETHANOL IN THE ETHANOL-GASOLINE BLENDS INCREASED, THE PERCENTAGE OF USEFUL WORK INCREASED, WHILE THE OTHER LOSSES DECREASED AS COMPARED TO NEAT GASOLINE FUEL. THE MAXIMUM USEFUL WORK AND MINIMUM HEAT LOSSES WERE OBTAINED AT 20% ETHANOL-GASOLINE BLEND (E20). IT CAN BE CONCLUDED THAT AN ETHANOL-GASOLINE BLEND RATIO OF 20:80 IS AN OPTIMUM BLEND AS FAR AS THERMAL BALANCE IS CONCERN LEAVING THE OTHER PARAMETERS INTACT.

IN THE SIMULATION OF THE SPARK IGNITION ENGINE CYCLES, MODELING OF THE TURBULENT FLAME PROPAGATION PRESENTS PARTICULAR PROBLEMS. GENERALLY, TURBULENT FLAME PROPAGATION MODELS ARE BASED ON LAMINAR BURNING VELOCITY, TURBULENT INTENSITY AND ONE OR MORE SCALE PARAMETERS OF TURBULENCE. AN EMPIRICAL MODEL IS PRESENTED FOR LAMINAR BURNING VELOCITY AS A FUNCTION OF MIXTURE STRENGTH, UNBURNED MIXTURE TEMPERATURE, PRESSURE, AND RESIDUAL GAS FRACTION. FUELS CONSIDERED INCLUDE METHANE, ETHANOL, METHANOL, ALCOHOL/WATER BLENDS, ISOOCTANE/ALCOHOL BLENDS, PROPANE AND ISOOCTANE. PUBLISHED DATA OF OTHER WORKERS AND THE PREDICTIONS OF THEORETICAL THERMO-KINETIC MODELS HAVE ALSO BEEN CONSIDERED. IT WAS NOTICED THAT IN A CONSTANT UNBURNED MIXTURE TEMPERATURE AND EQUIVALENCE RATIO, ARRANGEMENT FOR BURNING VELOCITY OF ISOOCTANE-METHANOL BLENDS IS METHANOL, ISOOCTANE, 90%ISOOCTANE/10%METHANOL AND 80%ISOOCTANE/20%METHANOL. IN ISOOCTANE-ETHANOL BLENDS, RESULTS OF SIMULATION INDICATES WHICH MAXIMUM BURNING VELOCITY OF ETHANOL IS HIGHER THAN 80%ISOOCTANE/20%ETHANOL, 90%ISOOCTANE/10%ETHANOL AND ISOOCTANE. IN CONSTANT CIRCUMSTANCES MAXIMUM LAMINAR BURNING VELOCITY FOR EQUIVALENCE RATIO OF 0.7-1.1 BELONG TO BLEND OF 80%ISOOCTANE (GASOLINE) AND 20%ETHANOL WHILE IN EQUIVALENCE RATIO OF 1.1-1.4 IT BELONGS TO ETHANOL.

IN THIS PAPER, A THERMOCHEMICAL EQUILIBRIUM MODEL IS USED TO PREDICT THE PERFORMANCE OF A DOWNDRAFT GASIFIER. NUMERICAL RESULTS ARE SHOWN TO BE IN GOOD AGREEMENT WITH THOSE OF THE EXPERIMENTS. DIFFERENT BIOMASS MATERIALS ARE TESTED USING THE MODEL AND FOREST RESIDUAL IS SHOWN TO BE THE MOST ENERGETIC ONE. FOR THIS MATERIAL, THE GASIFICATION TEMPERATURE, SYNGAS COMPOSITION AND CALORIFIC VALUE ARE CALCULATED. THE EFFECTS OF MOISTURE CONTENT, AIR/FUEL RATIO, AIR INLET TEMPERATURE AND STEAM/FUEL RATIO ARE ALSO INVESTIGATED. THE AIR INLET TEMPERATURE IS FOUND TO BE THE ONLY WAY TO INCREASE THE GAS CALORIFIC VALUE AND COLD GAS EFFICIENCY. THE STEAM/FUEL RATIO, ON THE OTHER HAND, PLAYS A KEY RULE IN CONTROLLING THE GASIFICATION TEMPERATURE AND H2/CO RATIO.

THE COMBUSTION PROCESS OF POLYMER IS A COMPLEX COUPLING OF ENERGY FEEDBACK FROM A FLAME TO THE POLYMER SURFACE WITH GASIFICATION OF THE POLYMER TO GENERATE COMBUSTIBLE DEGRADATION PRODUCTS. IN THIS PAPER THE EFFECT OF THE DIMENSION OF THE POLYMER SHEETS UPON THE DOWNWARD FLAME SPREAD IS STUDIED BY THEORETICAL AND EXPERIMENTAL METHODS. IN THE THEORETICAL METHOD THE EFFECT OF THE DIMENSIONS OF THE SOLID FUEL ON THE ENERGY BALANCE IN THE SOLID PHASE IS STUDIED BY SCALE UP METHOD. THIS STUDY SHOW THAT THE FLAME SPREAD OVER THE SOLID FUEL IS INDEPENDENT OF THE WIDTH OF THE SAMPLE IF THE RATIO OF THE WIDTH TO THE THICKNESS OF THE SOLID IS HIGHER THAN TEN. THE EXPERIMENTAL RESULTS CONFIRM THE THEORETICAL RESULTS.

MODIFIED PEROVSKITE-TYPE OXIDES WERE SYNTHESIZED BASED ON TWO DIFFERENT METHODS, NAMELY CO-PRECIPITATION AND CONVENTIONAL CITRATE. THE SYNTHESIZED PEROVSKITE MATERIALS HAD THE NOMINAL COMPOSITIONS OF LACOO3, LACO0.8CU0.2O3, LA0.8SR0.2CO0.8CU0.2O3, LA0.8M0.2FE0.8O3 (WHERE M=CE AND SR). THE CATALYTIC ACTIVITY OF PEROVSKITE SAMPLES TOWARD CO COMBUSTION WERE MEASURED USING A GAS MIXTURE CONTAINING N2/O2/CO IN THE FOLLOWING PROPORTIONS 97/1/2. THE PREPARED PEROVSKITE SAMPLES WERE CHARACTERIZED BY SEM, NITROGEN ADSORPTION (BET), XRF AND XRD ANALYSES. ALL THE CATALYSTS DISPLAYED GOOD STABILITY ABOVE 600°C AND A HIGH ACTIVITY TOWARD CO COMBUSTION. OUR NOVEL PROPOSED PEROVSKITE COMPOSITION, NAMELY LA0.8SR0.2CO0.8CU0.2O3 SHOWED THE HIGHEST ACTIVITY FOR ACHIEVING CO CONVERSION ABOVE 80%. WHILE HOMOGENEOUS GAS-PHASE COMBUSTION OF CO REQUIRES TEMPERATURES IN EXCESS OF 700°C TO ACHIEVE FAIR KINETICS, OUR NOVEL CATALYST SAMPLE ACHIEVED 100%CO COMBUSTION AT 355°C.

THERMAL SPRAYING BY HIGH-VELOCITY OXYGEN-FUEL (HVOF) PROCESS IS BEING USED IN AN INCREASING VARIETY OF COATING APPLICATIONS. IN THIS STUDY A COMPUTATIONAL FLUID DYNAMICS (CFD) MODEL IS DEVELOPED TO PREDICT GAS DYNAMIC BEHAVIOR IN A HIGH-VELOCITY OXYGEN-FUEL (HVOF) THERMAL SPRAY GUN IN WHICH PREMIXED OXYGEN AND PROPANE ARE BURNT IN A COMBUSTION CHAMBER LINKED TO A PARALLEL -SIDED NOZZLE. THE CFD ANALYSIS IS APPLIED TO INVESTIGATE AXISYMMETRIC, STEADY-STATE, TURBULENT, COMPRESSIBLE, CHEMICALLY REACTING, SUBSONIC AND SUPERSONIC FLOW WITHIN THE GUN. A SEGREGATED, FINITE VOLUME NUMERICAL TECHNIQUE IS USED TO SOLVE THE COUPLED CONSERVATION OF MASS, MOMENTUM, AND ENERGY EQUATIONS FOR THE GAS IN A SEQUENTIAL MANNER. A STANDARD, TWO -EQUATION, REALIZABLE K-E TURBULENCE MODEL IS EMPLOYED FOR THE TURBULENT FLOW FIELD. AN EDDY DISSIPATION MODEL IS USED TO SOLVE THE GLOBAL REACTION. THIS APPROACH IS BASED ON THE SOLUTION OF TRANSPORT EQUATIONS FOR SPECIES MASS FRACTIONS. THE REACTION RATES ARE ASSUMED TO BE CONTROLLED BY THE TURBUL ENCE INSTEAD OF THE CALCULATION OF ARRHENIUS CHEMICAL KINETICS. RESULTS DESCRIBE THE GENERAL GAS DYNAMIC FEATURES OF HVOF SPRAYING AND THEN GIVE A DETAILED DISCUSSION OF THE COMPUTATIONAL PREDICTIONS OF THE PRESENT ANALYSIS. THE GAS VELOCITY, TEMPERATURE, PRESSURE AND MACH NUMBER DISTRIBUTIONS ARE PRESENTED FOR VARIOUS LOCATIONS INSIDE THE GUN. THE GAS MACH NUMBER INCREASES THROUGH THE GUN AND REACHES A MAXIMUM VALUE OF APPROXIMATELY 2.3 OUT OF THE NOZZLE EXIT. IN ADDITION, THE RESULTS REPORTED IN THIS PAPER ILLUSTRATE THAT THE NUMERICAL SIMULATION CAN BE ONE OF THE MOST POWERFUL AND BENEFICIAL TOOLS FOR THE HVOF SYSTEM DESIGN, OPTIMIZATION AND PERFORMANCE ANALYSIS.

THE LAMINAR BURNING VELOCITIES OF HYDROGEN-AIR AND HYDROGEN-METHANE-AIR MIXTURES ARE VERY IMPORTANT IN DESIGNING AND PREDICTING THE PROCESS OF COMBUSTION AND PERFORMANCE OF COMBUSTION SYSTEMS WHERE HYDROGEN IS USED AS FUEL. IN THIS STUDY LAMINAR BURNING VELOCITIES OF HYDROGEN -AIR AND DIFFERENT COMPOSITIONS OF HYDROGEN METHANE AIR MIXTURES (FROM 100%METHANE TO 100%HYDROGEN) HAVE BEEN PREDICTED USING CHEMKIN, PREMIX CODE EMPLOYING GRI-MECH 3.0 REACTION MECHANISM FOR METHANE OXIDATION AT AMBIENT TEMPERATURE FOR VARIABLE EQUIVALENCE RATIOS (F=0.5-1.5). THE RESULTS SHOW THAT INCREASING THE HYDROGEN PERCENTAGE IN THE HYDROGEN-METHANE MIXTURE INCREASES THE BURNING VELOCITY WHICH IS CONSISTENT WITH THE PUBLISHED EXPERIMENTAL DATA.

UNDER TIME DOMAIN ANALYSIS VARIOUS OPERATIONS ARE PERFORMED ON DIGITAL TIME HISTORY RECORDS OF THE SIGNALS IN THE TIME DOMAIN ITSELF TO YIELD INFORMATION ON RATES, COMMENCEMENT, DURATION AND END OF EVENTS, AND IDENTIFICATION OF DIFFERENT PHASES OF ANY PROCESS. THIS KIND OF ANALYSIS OFTEN REQUIRED SOME INTERMEDIATE STAGES OF DATA PROCESSING. IN THIS PAPER, ANALYSIS OF COMBUSTION PARAMETERS IN A DI DIESEL ENGINE WHICH HAS BEEN PERFORMED IN THE TIME DOMAIN YIELDED THE FOLLOWINGS: ESTIMATES OF CYLINDER PRESSURE DERIVATIVES, ESTIMATES FOR START OF INJECTION AND IGNITION DELAY, ESTIMATES OF THE DURATION OF FUEL INJECTION ALONG WITH THE START OF DYNAMIC FUEL INJECTION, ESTIMATES OF THE HEAT RELEASE DESCRIPTORS, IDENTIFICATION OF THE PHASES OF COMBUSTION AND ESTIMATES OF THEIR DURATION, IDENTIFICATION OF THE PHASES OF LINER VIBRATIONS VIS-À-VIS THEIR ORIGIN. THE ANALYSIS PROCEDURE RELATING TO THESE PARAMETERS HAS BEEN DISCUSSED IN THIS PAPER. BESIDES THE DIRECTLY CONTROLLED PARAMETERS OF ENGINE SPEED (N), LOAD TORQUE (TR) OR ENGINE POWER AND FUEL INJECTION TIMING, THE DERIVED PARAMETERS IDENTIFIED COMBUSTION PARAMETERS ARE PEAK CYLINDER PRESSURE [PC]MAX, MAXIMUM RATE OF CYLINDER PRESSURE RISE [P·C]MAX, MAXIMUM ACCELERATION OF CYLINDER PRESSURE [P··C]MAX, PEAK RATE OF HEAT RELEASE [Q·]MAX WHICH HAVE BEEN INVESTIGATED IN THIS PAPER.

THE ALGORITHM OF DIRECTED RELATION GRAPH (DRG) RECENTLY DEVELOPED FOR SKELETAL MECHANISM REDUCTION IS EXTENDED TO OVERALL LINEAR TIME OPERATION, THEREBY GREATLY FACILITATING THE COMPUTATIONAL EFFORT IN MECHANISM REDUCTION, PARTICULARLY FOR THOSE INVOLVING LARGE MECHANISMS. THIS ALGORITHM IS APPLIED TO A SPATIALLY HOMOGENEOUS CONSTANT-PRESSURE AUTO IGNITION OF METHANE COMBUSTION AND RESULT ARE COMPARED WITH CSP METHOD. IT IS OBSERVED THAT THE ACCURACY OF SKELETAL MECHANISMS IS EQUIVALENTLY BOUNDED BY THE USER-SPECIFIED ERROR THRESHOLD VALUE. DRG METHOD BECAUSE OF DIRECTLY ELIMINATE UNIMPORTANT SPECIES INSTEAD OF ELEMENTARY REACTIONS, COMPUTATIONAL IS MORE EFFICIENT.

HOMOGENEOUS CHARGE COMPRESSION IGNITION (HCCI) IS ONE OF THE ALTERNATIVES TO REDUCE SIGNIFICANTLY ENGINE EMISSIONS FOR FUTURE REGULATIONS. THIS NEW ALTERNATIVE COMBUSTION PROCESS IS MAINLY CONTROLLED BY CHEMICAL KINETICS IN COMPARISON WITH THE CONVENTIONAL COMBUSTION IN INTERNAL COMBUSTION ENGINES. IN THIS PAPER, THE EFFECT OF H2 ADDITION ON IGNITION TIMING OF A NATURAL -GAS HCCI ENGINES HAVE BEEN INVESTIGATED NUMERICALLY BY ADOPTING A SINGLE-ZONE ZERO-DIMENSIONAL MODEL. THE CHEMICAL KINETIC MECHANISM INCORPORATED THE GRI-3.0 MECHANISM THAT CONSIDERS 53 SPECIES AND 325 REACTIONS TOGETHER. TO SIMULATE HCCI ENGINE CYCLES, A VARIABLE VOLUME COMPUTATION HAS BEEN PERFORMED BY INCLUDING THE PISTON MOTION INTO THE CHEMICAL REACTION DESIGN, CHEMKIN, CODE. THE SENKIN CODE USED IN ORDER TO SIMULATE THE IN-CYLINDER COMBUSTION. IT WAS FOUND THAT AN ADDITIVE-FREE MIXTURE DID NOT IGNITE FOR THE INTAKE TEMPERATURE OF 500 K.A MIXTURES CONTAINING A SMALL QUANTITY OF ADDITIVES AT THE SAME TEMPERATURE WAS IGNITED. FOR A FIXED QUANTITY OF ADDITIVE, IT WAS FOUND THAT H2 ADDITION WAS EFFECTIVE IN ADVANCING THE IGNITION TIMING. IT WAS ALSO FOUND THAT THE PERCENTAGE OF ADDITIVE REQUIRED TO ACHIEVE A NEAR TDC IGNITION TIMING INCREASES LINEARLY WITH THE INCREASE IN THE ENGINE SPEED WHILE DECREASES WITH THE INCREASE IN THE EQUIVALENCE RATIO. FURTHERMORE, THE ADDITION OF 24% MASS OF H2 COULD IGNITE A MIXTURE AT AN INTAKE TEMPERATURE OF 450 K.