Journal of Energy Engineering

An experimental study has been conducted to investigate the effects of alcohol properties on dual-fuel (DF) combustion and unregulated emissions such as ${\mathrm{NO}}_2$, HCHO, and ${\mathrm{CH}}_3\mathrm{CHO}$ on a multicylinder turbocharged, intercooled, common-rail diesel engine with a diesel oxidation catalyst (DOC). Three alcohol fuels, i.e., methanol, ethanol, and hydrous ethanol, were injected in the intake port and diesel was directly injected into the cylinder to realize DF combustion modes called DM, DE, and DE70, respectively. Results show that under DF modes the starting point of combustion is delayed, and the proportion and rate of premixed heat release are increased as compared with diesel only. At full load, the premixed ethanol is compression ignited before diesel ignition. The ${\mathrm{NO}}_2$, HCHO, and ${\mathrm{CH}}_3\mathrm{CHO}$ emissions from DF combustion are significantly higher than those of diesel only and emissions increase with the rise in premixed alcohol ratio. DOC can effectively purify ${\mathrm{NO}}_2$, HCHO, and ${\mathrm{CH}}_3\mathrm{CHO}$ emissions of the DF mode with the average catalytic efficiencies of greater than 98%, 92%, and 91%, respectively. Research indicates that DF combustion could not cause excessive unregulated emissions with the DOC, or even lower than the original engine.

This work investigates the finite-element implementation of a piezoelectric energy harvester subjected to traffic-induced vibration of a railway bridge. To derive the electromechanical coupled framework, Hamilton’s variational principle is employed and the mechanical and electrical energy balance equations are considered in conjunction with suitable boundary conditions of the mechanical and electric fields. For the finite-element implementation, the output voltage is considered as an additional degree of freedom together with the displacement field. The developed finite-element model is then validated by comparison with the numerical results of the current finite-element model with closed-form solutions. The characteristics of the moving train load and corresponding train-induced vibration data measured on single- and double-span bridges are analyzed and the maximum vertical deflection is also evaluated for the safety assessment of the bridge. Lastly, the capability of the piezoelectric energy harvester as an energy-scavenging device on a railway bridge, the optimum location of the harvester, the optimum speed of the moving train, and the effect of resonance are discussed in terms of the generated output voltage and total energy.

The use of predried lignite as a factor to enhance flexibility of existing power plants is considered as a practically feasible step to ensure power supply and grid stability. In this work, the retrofit of a Greek lignite-firing power plant for the production of predried lignite through integration of drying systems has been investigated from a technical point of view through thermal cycle calculations and an economic one. The impact on efficiency and power output of the power plant and the predried lignite production cost are derived, respectively. The predried lignite is considered to be used in the plant or as an end product independently. The operation of the plant is simulated at 60%, 80%, and 100% load with drying systems integration. Three different technologies were integrated: a fluidized-bed dryer with internal waste heat utilization (WTA dryer), a tube dryer, and a drum dryer. The economic assessment is focused on the production cost of predried lignite as an end product. The drying plant’s operating hours and the electricity price are considered as highly influencing production cost factors and a parametric analysis was performed. Additionally, a parametric study, with respect to ${\mathrm{CO}}_2$ allowances, was performed for the utilization cost of raw and predried lignite. Results showed that among the three drying configurations, the WTA dryer has the least impact in terms of both power output loss and efficiency decrease on the thermal cycle of the unit for all three loads, with a net efficiency decrease in the range between 0.7% and 1.1%. Furthermore, the use of the WTA technology is also more favorable from an economic point of view, resulting in a predried lignite production cost only 8%–9.3% higher than the raw lignite production cost. The ${\mathrm{CO}}_2$ allowances cost as a parameter unveiled that the usage cost of predried and raw lignite has a break-even point, with respect to load operation, which varies in the area of $26.58–29.0€/{\mathrm{tCO}}_2$.

Using experimental (particle-image velocimetry and force measurement) and numerical tools [steady Reynolds-averaged Navier-Stokes (RANS) equations with the shear stress transport (SST) $k\text{-}\omega$ turbulence model], the overtaking maneuver between two identical vehicle models was examined. Considering the maneuver to be quasi-steady, one of the models (overtaken vehicle) was fixed while the other (overtaking vehicle) was set at various axial distances from the overtaken vehicle. The lateral clearance between the vehicles was constant and equal to 35% of the vehicles’ width. Due to the existence of an overpressure region upstream of the front of the overtaking vehicle, a side force was applied on the overtaken vehicle. Moreover, due to low pressures in the space between the two vehicles, a reduction in the base pressure of the overtaken vehicle caused an increase in its drag. Both forces and the yaw moment varied significantly when the front of the overtaking vehicle moved from the rear of the overtaken toward its front.

Through the use of a thermogravimetric analyzer and a fixed-bed reactor, the effects of ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ gasifications on oxy combustion and NO emission of pulverized coal at low oxygen concentrations were investigated by comparing the burning behaviors and NO release processes in ${\mathrm{O}}_2/{\mathrm{N}}_2$, ${\mathrm{O}}_2/{\mathrm{CO}}_2$, and ${\mathrm{O}}_2/{\mathrm{CO}}_2/{\mathrm{H}}_2\mathrm{O}$ mixtures (the latter two represented oxy-fuel combustion without and with steam addition, respectively). The thermogravimetric analyses show that at $5\%{\mathrm{O}}_2$ concentration, the burning rate of coal samples decreased in the order of $5\%{\mathrm{O}}_2/95\%{\mathrm{N}}_2$, $5\%{\mathrm{O}}_2/95\%{\mathrm{CO}}_2$, and $5\%{\mathrm{O}}_2/20\%{\mathrm{H}}_2\mathrm{O}/75\%{\mathrm{CO}}_2$ (molar concentration). As the oxygen concentration dropped to 2% because of the influence of ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ gasification, the overall reaction rate of coal samples increased in the same order at above 800°C. At 2% ${\mathrm{O}}_2$ concentration, because of the effect of ${\mathrm{CO}}_2$ gasification the overall reaction rate of char samples in the $2\%{\mathrm{O}}_2/98\%{\mathrm{CO}}_2$ mixture was accelerated and exceeded the burning rate in the $2\%{\mathrm{O}}_2/98\%{\mathrm{N}}_2$ mixture with increasing temperature. And the overall reaction rate of char samples in $2\%{\mathrm{O}}_2/20\%{\mathrm{H}}_2\mathrm{O}/78\%{\mathrm{CO}}_2$ further increased due to the enhanced ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$ co-gasification. The fixed-bed reactor tests showed that the NO emissions of pulverized coal in the ${\mathrm{O}}_2/{\mathrm{N}}_2$ mixture were always higher than those in the ${\mathrm{O}}_2/{\mathrm{CO}}_2$ mixture, regardless of temperature and ${\mathrm{O}}_2$ concentration. At 1,000°C and $2\%{\mathrm{O}}_2$ concentration, the NO emission in $2\%{\mathrm{O}}_2/20\%{\mathrm{H}}_2\mathrm{O}/78\%{\mathrm{CO}}_2$ ($5.64\mathrm{mg}/\mathrm{g}$) was higher than that in $2\%{\mathrm{O}}_2/98\%{\mathrm{CO}}_2$ ($5.13\mathrm{mg}/\mathrm{g}$) because the additional nitrogen precursors (HCN and ${\mathrm{NH}}_3$) generated by ${\mathrm{H}}_2\mathrm{O}$ gasification were oxidized to NO easily and quickly. However, increasing oxygen concentration to 5%, because of the weakened effect of ${\mathrm{H}}_2\mathrm{O}$ gasification, NO emission in $5\%{\mathrm{O}}_2/20\%{\mathrm{H}}_2\mathrm{O}/75\%{\mathrm{CO}}_2$ ($5.98\mathrm{mg}/\mathrm{g}$) decreased compared to that in $5\%{\mathrm{O}}_2/95\%{\mathrm{CO}}_2$ ($6.39\mathrm{mg}/\mathrm{g}$). In addition, because the effect of ${\mathrm{H}}_2\mathrm{O}$ gasification was enhanced at 1,200°C, regardless of the ${\mathrm{O}}_2$ concentration, the NO emissions in the ${\mathrm{O}}_2/{\mathrm{CO}}_2/{\mathrm{H}}_2\mathrm{O}$ mixture were always higher than those in the ${\mathrm{O}}_2/{\mathrm{CO}}_2$ mixture.

Wind turbine rotor failures have been reported that resulted in substantial damage and cost for maintenance and recovery. This work developed a wind turbine rotor blade design and optimization method to address a coupled energy generation efficiency and blade structural strength design issue, as a generic procedure applicable to both turbine rotors and propellers, in air and water. The optimization procedure was developed for optimum radial blade sectional thickness distribution with a prescribed constant safety factor across the span. While maintaining the required structural strength and integrity of the rotor blades, this procedure is to achieve the following objectives: (1) reduce material use to minimum and (2) obtain the optimum power generation efficiency with the optimum structural strength. A propeller-turbine rotor code coupling aerodynamic and structural properties was developed. For a given blade geometry and chosen material, performance prediction of the instantaneous loading acting on all blade sections and the strength of a local blade section was performed and optimized. A time-domain, three-dimensional unsteady panel method was implemented, developed, and used to perform the optimization. A wind turbine 10 m in diameter from the National Renewable Energy Laboratory (NREL) (Golden, Colorado) was used as a base design example and for optimization based on an extreme wind speed of $100\mathrm{km}/\mathrm{h}$. The final result achieved a total savings of 18.72% in blade material.