JOURNAL OF MECHANICAL ENGINEERING AMIRKABIR (AMIRKABIR)
Year:2011 | Volume:43 | Issue:1|Papers Count:11

Aim of this paper is to investigate mechanism of NO and soot reduction by using multiple injection as useful strategy for reducing DI diesel engines emissions. In this paper, we first studied the mechanism of NO and soot reduction by using double injection. Then after investigating different modes of injection, at last we introduce optimum mode of fuel injection for a DI diesel engine manufactured in our country.Experiments were induced at Motorsazan Tabriz to validate results of CFD simulation. Amount of fuel in each pulse and dwell time between injection pulses are essential parameters. Results showed that by using double injection soot and NO will reduce by 33% and 11% respectively.

In this research, for correction the combustion properties of biodiesel fuel, ethanol was added.Therefore, effect of using ethanol, biodiesel and diesel blend fuel on MT4-244 diesel engine performance pollutants emission parameters and emission were investigated. The biodiesel in this research produced from waste cooking oil that at (5, 10, 15, 20, 25 and 30% on volumetric basis) blended with Ethanol (2, 4 and 6%), and diesel fuel. So far, 18 samples including variable percent of three fuels were prepared which showed as BED forms. Engine testes were performed on ECE-R96 standard on full load and two engine rotations maximum torque (1300 RPM) and maximum power (2000 RPM). It was found increasing of biodiesel, decreased the pollutant emissions of CO, CO2, PM and HC in comparison to diesel fuel but BSFC and NOx emission increased. It also, Using biodiesel did not change the engine power and torque.

It is important to calculate the piston temperature distribution in order to control the thermal stresses and deformations within acceptable levels. In this study, the SI engine piston heat transfer is calculated and the piston is thermo-mechanically analyzed using finite element method. In order to calculate the heat transfer, a concise resistor model for wall temperature prediction is used. For each of the walls (piston, cylinder and cylinder head), the relevant heat transfer equations simultaneously with two zone combustion model is solved considering three unknown temperature. The simulations were done by a MATLAB code and the result validated with the experimental data of the EF7.TC engine. The above results have been curve fitted and imported by the commercial ANSYS code to loading the piston.To evaluate properly of results, stress analysis results is compared with real samples of damaged piston and it has been shown that Critical identified areas, match well with areas of failure in the real samples.

This paper discusses the simulation of the PV/T air systems with natural airflow operation for both glazed and unglazed types. Comparisons are made between the theoretical and experimental results and good agreement between these two values are obtained. Additionally, the influence of the glass cover on the different system parameters has been evaluated. Results show that setting glass cover on photovoltaic panels leads to an increase in thermal efficiency and decrease in electrical efficiency of these systems.

In this work a rectangular micro heat exchanger with constant hydraulic diameter at various aspect ratios was considered. The pressure drop and thermal parameters of the micro heat exchanger in laminar flow at different Reynolds numbers (25, 50, 100, 150, 225 and 300) at constant heat flux of 0.3 MWatt/m2 were analyzed and compared. Also, the effect of temperature-dependent fluid properties (viscosity, conductivity coefficient) on the pressure drop and the average and maximum temperature rise of fluid and thermal resistance of micro heat exchanger were investigated. Finally, a new criterion based on pumping power and transmitted heat per temperature gradient unit was proposed as a tool to evaluate micro heat exchangers' performance.

This article deals with numerical modeling of coupled heat conduction and radiation in glass wool and rock wool insulations in transient condition using semi-empirical parameters obtained from experimental results. In this research needed thermophysical and physical parameters for numerical model, such as: heat capacity, effective thermal conductivity, fiber's diameter, and apparent and solid density of these mineral wools are determined by experiments. Radiation heat transfer is modeled by direct simulation and applying Monte Carlo ray trace method, and the thermal conductivity due to air/solid conduction is determined by semi-empirical relation obtained by inverse parameter estimation method as well as experimental results. Radiation is coupled with conduction via heat source term in heat conduction equation. Code results are in a good agreement with experimental results.

In this paper, the effect of equivalence ratio, pore diameter and firing rate on flame stability in a SiC porous media has been studied experimentally. Based on the position of the flame, four regimes are observed as follows: Surface flame, submerged flame, under-surface and detached flame. The surface flame regime as a rich flame is one of the stability threshold and the detached flame as a lean flame is the other threshold of the flame stability. Change the pore diameter causes so little change in equivalence ratios corresponding to the detached flame threshold but increasing the pore diameter decreases the equivalence ratio changes for the surface flame. Also increasing the firing rate decreases flame stability range in the porous media. Flame position was estimated using axial temperature distribution in the sidewall of the burner. Temperature profiles versus equivalence ratio in a firing rate are approximately similar but the profiles are different for various firing rates. According to the results, flame is stable in near the upper surface or in the half bottom of the porous media.

During the course of expansion of steam in a Laval nozzle and a cascade of turbine, the state path crosses the saturation line; the steam first supercools and then reverts to equilibrium through the spontaneous formation of droplets or condensation shock, which causes aerodynamics and thermodynamics losses. In this way by formation of droplets and so reducing Gibbs energy, equilibrium is reached. This paper describes a two-phase model and provides an approach for including spontaneous homogeneous nucleation. In order to solve conservation equations, coupled with the equations of formation and growth of the droplets, a 2-D time-marching solution scheme with Baldwin-Lomax turbulence model, was used in this study. Pressure distribution and droplets size in a Laval nozzle and a turbine cascade are predicted and compared with empirical results. In the strength of validation, the effect of injection of water droplets into the steam flow in order to control the intensity and location of condensation shock is considered theoretically. A converging nozzle is used to producing droplets at inlet of turbine cascade. The results illustrate that wet steam at inlet of a turbine cascade weakens or delays the condensation shock in the passage of the blades.

In this paper, solar double-effect Ammonia-Water cooling cycle is simulated. Then, the effects of parameters on the cycle efficiency including temperature of generator and condenser, and pressure of evaporators have been analyzed. Also cooling load and COP of the cycle has been expressed as a function of the aforesaid parameters. Then cities of Iran has selected as a representative of different climates, and the performance of cycle for these cities has been analyzed using the environmental and geographical conditions such as solar radiation intensity, wet and dry bulb temperature for each city. The acceptable efficiency of the cycle for the southern cities of Iran which have the high radiant intensity is a result of this work.