فهرست مطالب محسن قاضی خانی

Numerous studies on using light fuels in compression ignition engines to reduce emission and increase efficiency have been done. The Reactivity Controlled Compression Ignition engines are one of these studies. Nevertheless, using heavy fuels vapor for achieving partially premixed combustion is not investigated. Using diesel fume (to upgrade conventional combustion to premixed combustion) resolves the need for a secondary fuel tank in a car. However, diesel fuel has heavy hydrocarbons and is a high reactivity fuel. So in this study, diesel has evaporated in a tank, and its vapor has injected into the intake air for studying a semi homogeneous combustion. The tests have performed at 2000 rpm (the speed of maximum torque). According to the achieved results, although diesel has heavy hydrocarbons and is a high reactivity fuel, adding diesel fumigation can reduce soot and NOx emissions up to 20% and 50%, respectively. Increasing load reduces the positive impact of adding diesel fumigation on soot and NOx emission reduction. However, the positive impact of adding diesel fumigation continues up to 80% of the full load. Adding diesel fumigation has no impact on cyclic variation and ringing intensity, but increases CO and HC emission. The evaporation of diesel averagely consumes 15% of brake power. Also on average, 5% of diesel evaporation energy can be supplied by recovering heat energy from the exhaust gas (warming up diesel from ambient temperature to the exhaust gas temperature).

Adsorption cycle has become one of most popular technologies in recent years which operates based upon the adsorption and desorption of an adsorptive material in an adsorbent material which is usually a porous solid. Thus, a four-bed adsorption cycle with silica gel-water as working pair is modeled by means of a computer code written in MATLAB software, and thermodynamic properties are obtained from REFPROP software. In this article, in order to consider the heat transfer process more accurately and the heat transfer to the environment from the tubes, the passing flow in the adsorbent beds, evaporator, condenser and the connecting pipes between the master and slave beds are discretized. The next step directs to investigate the effect of entrance flow temperature to the adsorbent bed during cooling and heating processes on the operating parameters of system and energy lost. The obtained results indicate that increasing the temperature of hot water and decreasing the temperature of cooling water will lead to the increase of COP and cooling capacity of system. Hence, the best choice based on the maximum available temperature for hot water and normal temperature range for cooling water are 75ᵒC and 25ᵒC, respectively. In these conditions, COP and cooling capacity of system will be 0.37 and 17.2Kw, respectively.

In this study, energy and exergy analysis of a two bed adsorption cooling system have been performed. Silica gel-water has been chosen as the adsorbent-refrigerant pair. Analysis is performed for evaluating the effect of operating conditions on the optimal timing and then on the maximum value of the SCP, COP, effectiveness and the minimum value of internal irreversibility and external irreversibility. A lumped parameter mathematical model and a global optimization method called the particle swarm optimization have been used to reach this purpose. In this model, internal and external irreversibility have been calculated with the new method without calculating irreversibility of the cycle internal component. Energy analysis showed that maximum of SCP increases with the increase of the mass flow rate and heat source temperature. Furthermore, an increase in the heat source temperature causes an increase in the COP, but an increase of the mass flow rate causes a decrease in the COP. Exergy analysis reviled that depending on the mass flow rate and heat source temperature, 65-90% of input exergy was expended by internal irreversibility, 1–20% were expended by external irreversibility and 8-14% is transferred to the cold reservoir in evaporator. It is concluded at the low-temperature heat source if the mass flow rate is chosen less than 0.6 kg/effectiveness at heat source temperature 75 is more than 65 and vice versa.

In this study, the relative humidity of the gases in the PEM fuel cell was changed and its effect on electro-osmotic flow was investigated. ýBy changing the humidity on both sides of the fuel cell and using the water balance equations, the values of the electro-osmotic flow, ýelectro-osmotic coefficient and net drag in different humidity levels were found. Results showed that variations of the electro-osmotic ýflow changed linearly by anode and cathode humidity to the special humidity and after that not much variation was seen. In addition, the ýresults revealed that humidity change at anode had more desirable effect than the cathode. For example, at 70% anode humidity and 35% ýcathode humidity with the current of 5A, the value of electro-osmotic flow was obtained as 2.66639E-06 mol/cm2.s, while in the former ýý35% and the latter 70% with the same current, this value was recorded as 2.56418E-06 mol/cm2.s. In addition, results showed that theýþ þvariations of the electro-osmotic coefficient changed linearly by humidity. It was determined the current change of fuel cell has not so ýeffect on the curves of electro-osmotic coefficient. The electro-osmotic coefficients varied between 0.636001 and 1.632476, which were ýin a good agreement with the values obtained in other related papers. In addition, the variations of the net drag in respect of humidity were ýinvestigated, too. It was determined that the net drag changed linearly by the cathode humidity with positive slope, but its variations by ýthe anode humidity were linearly with negative slope.ý

Low swirl burner provides an effective and low cost solution for stable lean premixed combustion. Several studies have been conducted on the performance of these burners in different pressures, temperatures, capacities, mixture velocities and equivalence ratios. The main design parameters of low swirl burners are the swirl number and the recess length. The objective of this paper is the investigation of recess length effects on the burner performance. A rig test has been established and utilized to study the effects of different equivalence ratios and recess lengths on the temperature distribution and flame regime of low swirl burners. Results revealed that increasing the recess length causes the increase in axial bulk velocity and hence the lifted flame would be stable in wider range of equivalence ratios. Observations also show the significant effect of the specific divergent flame regime of low swirl burners on result in uniform temperature distribution inside the combustion chamber and lower NOx production.

In this paper, numerical investigation was carried out for the sake of identifying optimum geometry for variable geometry ejector using in solar refrigeration system as the prerequisites to experimental tests. Variable geometry was made by using a movable primary nozzle and movable spindle in it. Vacuum tube collector was postulated as heat source and R600a used as working fluid. Condenser temperature based on Middle East area temperature and evaporator based on operative condition in HVAC system selected. Generator, condenser and evaporator operating temperatures have severe effects on the optimum geometry of ejector. Therefore, for maximum entrain ratio it is necessary to identify optimum geometry to cope with variations in operating condition. The results showed that using a variable geometry ejector is a requirement for cooling during the day.The following fluid structure was compared by entropy generation during mixing and shock phenomena. The results showed there is optimum back pressure to minimize fluid exit entropy. It coincides with critical back pressure. It was found that depending on back pressure maximum entropy generation happen by two reasons, mixing and shock phenomena.

Low swirl burners present an effective approach to increase stability in lean premixed combustion. Effects of swirl number as a key parameter in the performance of these burners have been investigated in several studies with different conditions of pressure, bulk velocity equivalence ratio and geometrical specifications. Swirler distance from the exit, called recess length is another key parameter, which affects the performance of the burner and there are a few studies about its effects on the performance of the burner. In this study by design and fabrication of a low swirl burner and setup a rig test, several combustion parameters include flame temperature; flow rate, pressure and temperature of the air and fuel, and analysis of combustion products have been measured. And the effects of recess length and equivalence ratio variations on the performance of the low swirl burner have been studied. In addition, the exergy analysis has been done in order to investigate the performance of these burners. Results reveal that increasing recess length would result in wider range of lifted flame for different equivalence ratios. In addition, results also show that although low swirl combustion is working on lean condition, it has about 17 percent lower irreversibility ratio in comparison with diffusion flame from second law of thermodynamic point of view. Besides, the heat transfer ratio has been increased about 14 percent in the lifted flame in comparison with the attached flame.

In this study، the theoretical design of a vapor ejector used in an air-conditioning system is performed and the designed ejector is then optimized via computational fluid dynamics. Based on the numerical simulations، two geometrical parameters، throat diameter and nozzle position، are optimized. Then، the effects of the operating parameters on the performance of the optimized ejector are investigated numerically. The optimized ejector geometry is used as a variable-geometry ejector by using a spindle in the primary throat and the performance of the system in various spindle positions is studied. The results show the importance of using a analytical design to obtain the overall geometry of the ejector and numerical simulation in order to achieve the optimal ejector performance. The variable-geometry ejector designed based on the proposed method in this study with using solar energy، in conjunction with a cold storage system، might be able to provide the necessary refrigeration for all day long.

In this study a fin-tube heat exchanger with different kinds of vortex generator has been studied experimentally، using exergy method. Three kinds of vortex generator have been employed: 1-Tetrahedral wedge shape 2-Rectangular block shape 3-Triangular winglet shape. In this research we used a wind tunnel to produce wind flow over heat exchanger. hot water was circulating with the steady volume flow rate and temperature range of 44 to 68 celsius in the system. The results shows that use of these VGs will decrease the air side irreversibility to heat transfer ratio (ASIHR) in the air region and for a heat exchanger with block shape VGs، this reduction is more than the other two types. This could be due to the irreversibility decline in the air region because of lower mean temperature difference of water and air and the heat transfer conditions improvement. To reveal the effects of various VGs on heat exchanger performance with respect to reducing ASIHR، a quantity is used namely performance of vortex generator (PVG). The results showed that PVG values are in the range of less than 5% for wedge-shaped VG''s to over 35% for block-shaped VG''s. Which represents the good effects of VGs especially block-shaped ones on the heat exchanger performance.

Controlling of the fuel injection، including the spray structure and injection timing has a significant impact on the engine performance، especially the formation of pollutants. In this study، a computational fluid dynamics software (AVL Fire) has been used to simulate the start time of the fuel injection in diesel engines and its effect on the soot formation rate. Results show that if the start angle of the fuel injection approaches the TDC، the maximum soot formed will be increased. Also، the amount of the remained soot is increased. Mixing of the fuel and the air cannot be completed as the start angle of the fuel injection gets closer to the TDC، because of increasing the combustion chamber pressure and so decreasing the ignition delay، as a consequent، the rich mixture volume increases and leads to more soot formations. Although that is better to the inject fuel earlier (far from the TDC)، but considering other effective parameters on the engine performance، like the ignition delay، produced power، it has been concluded that lower soot formation can not be an advantage by itself.

In this study is designed a heat exchanger for cooling exhaust gas and is carried out an experiment to investigate the effect of Exhaust Gas Recirculation (EGR) temperature on destruction of the fuel’s availability due to combustion processes in IDI diesel engine cylinder. To serve this aim an exergy analysis is conducted on the engine cylinder which provides all the availability terms by which the evaluation of in-cylinder irreversibilities is possible. The availability terms including heat transfer, inlet and exhaust gases and work output are presented during the engine operation at different load and speeds. To clarify the effect of using EGR in each case, EGR is introduced to the cylinder at various ratios and temperature during the tests. The results show about 60 to 70 % of fuel’s availability destroyed by irreversibilites. Also the results reveal that the increase of EGR temperature leads to reduce of combustion irreversibility. But On the other hand the increase of EGR temperature lead to heat and availability are dissipated of the wall and exhaust gas. So depend on the engine operation at different load and speeds, the increase of EGR temperature could be lead to a positive or negative effect on the engine performance

Current approaches to internal combustion engine analysis are no longer just from first law of thermodynamic's point of view. Evaluation of IC engines by second law of thermodynamics (concept of exergy) helps modifying different parts of engine that cause availability dissipation. EGR method is widely used as an effective method for decreasing NOx as a toxic pollutant in diesel engines. This teqnique decreases the in-cylinder peak temperature by lowering the oxygen concentration. In this experimental investigation is carried out in order to analyze different aspects of using EGR on in-cylinder irreversibility and second-law efficiency within the engine block. It was observed that use of EGR can generally decrease the second-law efficiency in various engine loads and speeds.

Exergy analysis is a method that can calculate thermodynamic losses by means of second law of thermodynamic. In this study، exergy analysis has been performed for the silencer of OM314 diesel engine. Irreversibility due to heat transfer from silencer to environment، silencer''s internal irreversibility and total irreversibility for different conditions of engine operation have been measured and calculated. For finding out the relation between irreversibility and exit sound intensity، simultaneously، exit sound intensity from the silencer has been measured. Results illustrate that by tripling of silencer irreversibility، exit sound intensity increases only 10 percent. Also the results shows that the irreversibility due to heat transfers have the most contribution in total irreversibility of silencer. So from the view point of second law of thermodynamics، it seems that cooling the silencer can be an effective method for sound reduction. Also results illustrate that، sound intensity of silencer is basically dependent to engine speed.

The role of ambient temperature in determining the performance of GE-F5 gas turbine is analysed by investigating the Shirvan gas turbine power plant, with 10MW, 15MW and 20MW power output. These parameters have been brought as a function of ambient temperature. The results show when ambient temperature increases 1oC, the compressor pressure decreases about 20kPa, compressor outlet temperature increases about 1.13oC and exhaust temperature increases about 2.5oC. It is revealed that variations are due to decreasing the efficiency of compressor and less due to mass flow rate of air reduction as ambient temperature increases at constant power output. The results shows cycle efficiency reduces 3% with increasing 50oC of ambient temperature, also the mof increases as ambient temperature increases for constant turbine work. These are also because of reducing the compressor efficiency as ambient temperature increases.