Hossein Ajam

In this work, the first and second laws of thermodynamics are employed to evaluate exergetic parameters of a diesel engine at different speed and load ranges. Various blends of waste cooking oil biodiesel with diesel fuel were tested in a direct injection diesel engine at different speeds (1300, 1600, and 2000 rpm) and loads (25%, 50%, and 75% of the rated load). Combustion reactions were determined using emission data and then exergetic parameters of the engine such as fuel exergy, heat loss exergy, exhaust loss exergy, and exergy destruction were calculated and analyzed. Results showed that fuel and heat losses as well as exhaust exergies increase by increasing engine speed and load. Exergy destruction result indicated an opposite trend. It was found that the exergy destruction is the major part of exergy losses by about 45–50% for fuel blends. The maximum exergetic efficiency was found 38.77% at engine speed of 1300 rpm and engine load of 75% rated load. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 534–541, 2019

In recent years, numerous studies have been carried out on the effect of biodiesel fuels on engine performance and exhaust emissions. But in those studies, no attention has been paid to the thermo-economic analysis of engines while using biodiesel and its blends with diesel fuel. For this aim, various blends of waste cooking oil biodiesel with diesel fuel were tested in a four-cylinder direct-injection diesel engine. The experiments were carried out at a constant engine speed and load and four different biodiesel–diesel blends. The combustion reactions were determined using experimental data and, finally, the thermo-economic analysis was performed for steady-state control volume of the engine by using and solving energy, exergy and economic balances. First law, second law and combustion efficiencies, specific fuel consumption and the rate of exergy destruction were the results of thermodynamic analysis. The economic analysis also leads to some results such as the cost rates of power generation, fuel consumption and losses. The results showed that the best thermodynamic condition of the engine was achieved when using pure diesel. The most economical and costly operating conditions occurred when using 50% and 10% biodiesel–diesel by volume.

An experimental and numerical study of supercavitating flows tric cavitators

Biodiesel is a renewable, clean-burning Diesel replacement. Biodiesel is made from vegetable oils or animal fats. It can be used as a fuel for vehicles in its pure form, but it is usually used as a Diesel additive to reduce exhaust emissions. Numerous studies have been performed on effects of various biodiesels on engine performance and emissions; however, in those studies, less attention has been paid to the availability (exergy) of engine processes. In this investigation, various biodiesel blends have been tested experimentally on a four-cylinder turbocharged Diesel engine. Engine energy, exergy and economic analysis have been performed using the experimental data. The results showed that the structural oxygen content of biodiesel improves the combustion efficiency. However, the engine’s thermal efficiency decreases due to the lower heating value of the biodiesel. Also, destruction of exergy increases when using biodiesel. Among various biodiesel blends, the 15% biodiesel–Diesel blend shows an optimum condition. In this case, the engine power slightly decreases, and both the thermal efficiency and the exergetic efficiency increase. Also, the highest combustion efficiency was observed. The results of emissions economic analysis showed that all biodiesel blends were more affordable than Diesel fuel. The results of full economic analysis (emissions, fuel cost, fuel consumption and engine power loss) showed that only the 5% biodiesel–Diesel blend was more affordable compared to Diesel.

In this paper, a 3D forward curved (FC) centrifugal fan is simulated numerically to predict the turbulent flow and pressure field of the fan. Through this numerical simulation, the various turbulent models are compared and the influence of blade shapes on the fan performance is examined. For this means, four turbulence models (k-ε, k-ω, RSM, Spallart Allmaras) are applied to choose the most suitable one. Also for three kinds of blade shapes (flat blade, circular blade and NACA4412 airfoil blade), the flow fields are simulated separately to determine the most efficient blade shape. In numerical analysis, FVM (finite volume method) is used to solve the governing equations. Steady state conditions and multiple reference frames, including a MRF (moving reference frame) for the rotor region and a stationary reference frame for stator region, are used for numerical modeling. The numerical results are validated with experimental data. It is observed that k- ε is the most suitable turbulence model and the circular blade is the most efficient shape for this type of fan.

In the present study, a numerical simulation is performed for the detailed prediction of heat transfer, phase change and fluid flow in welding process with moving heat source. This process may be considered steady with respect to the reference frame attached to the heat source for a long metal block. The problem is formulated by considering the three-dimensional equations of continuity, momentum and energy based on enthalpy model. The equations is solved using a fully implicit, control-volume-based computational method for fixed grids. The calculation domain including solid and liquid phases is solved together as a continuous region. Solid phase velocity is corrected using suitable source terms in the momentum equations. Phase change is considered based on the latent heat of evolution as a source term in the energy equation.The effects of thermal buoyancy and Marangoni flow on melting process are analyzed.