Laminar burning speed and ignition delay time behavior of iso-octane at the presence of two different biofuels, ethanol and 2,5 dimethyl furan (DMF), was studied in this work. Biofuels are considered as a better alternative source of fossil fuels. There is a potentiality that combustion characteristics of iso-octane can be improved using biofuels as an oxygenated additive. In this study, three different blending ratios of 5%, 25%, and 50% of ethanol/iso-octane and DMF/iso-octane were investigated. For laminar burning speed calculation, equivalence ratio of 0.6–1.4 was considered. Ignition delay time was measured under temperature ranges from 650 K to 1100 K. Two different mechanisms were considered in numerical calculation. These mechanisms were validated by comparing the results of pure fuels with wide range of experimental and numerical data. The characteristic change of iso-octane with the presence of additives was observed by comparing the results with pure fuel. Significant change was observed on behavior of iso-octane at 50% blending ratio. A comparison was also done on the effect of two different additives. It has found that addition of DMF brings significant changes on iso-octane characteristics comparing to ethanol.
Ethanol is considered one of the most attractive renewable energy sources in the modern days. A chemical mechanism on ethanol is generated in this work to predict the performance of this fuel in engine-relevant operating conditions. To build this mechanism, a reaction mechanism generator (RMG) is utilized. The generated mechanism is compared against experimental results to find its accuracy. Important reactions responsible for the results are selected through sensitivity and path flux analysis. The rate parameter of important reactions is further adjusted from available literature data. The final mechanism is named PCRL-Mech1 and consists of 67 species and 1016 reactions. This mechanism shows an excellent agreement with experimental results of laminar burning speed and ignition delay time (using a shock tube and rapid compression machine). The mechanism is validated at temperatures, pressures, and equivalence ratios of 300−600 K, 1−10 atm, and 0.6−1.4 for laminar burning speed, respectively. For ignition delay time verification, temperatures of 820−1450 K, pressures of 3.3−80 atm, and equivalence ratios of 0.3−2 are considered. The newly developed mechanism is also validated for species concentration through a flow reactor, a jet stirred reactor, and a partially premixed counter flow flame. Finally, the PCRL-Mech1 mechanism is compared with six-top mechanisms available in literature. A normalized ratio of accuracy and computational time for other mechanisms with respect to PCRL-Mech1 is generated. It is found that PCRL-Mech1 has better combination of accuracy and time throughout all the varied operating conditions.
Abstract-This paper presents the pointed tip effects on the aerodynamic load of NREL Phase VI wind blade rotor. The aerodynamic loads around flow field are evaluated using 3D CFD simulation. The commercial ANSYS Fluent and parameterized 3D cad models of NREL Phase VI are used for the analyses. The simple Spalart-Allmaras turbulence model and 0-degree yaw angle condition are adopted for CFD analysis. The pointed tip shape was made by reducing the original NREL chord length gradually near the tip region. To find out the 3D pointed tip effects on aerodynamic load, the pressure coefficient and integrated drag force and torque about primary axis are calculated. The numerical difference of Cp on wind blade surface between original and modified pointed tip models is negligible except near tip region, and also shown good agreement with experimental result in low wind speed case, however there is more deviation between the experimental data and CFD for high wind speed case, especially on the blade upper surface. Because the flow is highly unsteady, and the massive separation occurred due to the high angle of attack created by the higher wind speed while the rotational speed of the wind blade is kept constant for all cases.
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