Journal of Energy Engineering

This paper deals with the enhancement of performance and emission characteristics of a diesel engine operated on Pongamia biodiesel–diesel blend with the addition of 5% $n$-butanol and diethyl ether by volume. Engine trials were performed on a variable speed (1,000–3,000 rpm), four-cylinder Indica car engine. Engine performance parameters such as brake thermal efficiency, brake-specific fuel consumption, brake-specific energy consumption, and engine emissions such as carbon monoxide, unburned hydrocarbons, nitrogen oxide, and smoke opacity were measured. Performance and emissions characteristics of the modified blends (blends with additives) were compared with baseline fuel (Pongamia biodiesel–diesel blend) for the assessment of the enhancement. The analysis revealed that the modified blends had remarkable enhancement in performance and emission characteristics.

This study proposes a supercritical ${\mathrm{CO}}_2$ recompression cycle based on external oxy-coal combustion. It aims to evaluate and improve the performance of the system guided by energetic and exergetic analyses. The influence of the heat integration of the air separation unit (ASU) on performance is initially assessed and sensitivity analyses of cycle variables are then conducted. The system parameters are thermodynamically optimized using a genetic algorithm. Results show that the net efficiency of the base case is 42.13%. If ASU heat integration is considered, then the net efficiency increases to 45.1%, showing an efficiency increment of 2.97%. The comparison of the layouts reveals that the intercooled reheat cycle has the maximum net efficiency that can reach 47.73% when the optimal inlet and outlet pressures are 40 and 7.6 MPa, respectively. Finally, the proposed optimized system is compared with an ultra-supercritical pulverized coal (USC-PC) plant, and the economic performance is evaluated. Results show that the proposed optimized system is economically suitable, the net efficiency is comparable to that of the USC-PC plant, and the net efficiency with carbon capture is 4.27% higher than that of the USC-PC plant.

The effect of blending on the combustion behavior of a Turkish lignite blended with biomass or magnesite dust using a thermogravimetric analyzer (TGA) coupled with a Fourier transform infrared spectrometer (FTIR) under air atmosphere has been investigated. The lignite used in this study is Tunçbilek lignite (TL), which is blended with two biomasses, olive residue (OR) and almond shell (AS), and the inorganic industrial waste, magnesite dust (MD). The blends are composed of various weight fractions of fuels, with a constant weight fraction of molasses (10% by weight) as a binding agent. TGA weight loss trends are used to obtain characteristic temperatures and to define weight conversion stages. Experimental results show three distinct stages of conversion during combustion of biomass fuels and two stages for lignite. Burnout temperature increases and the combustibility index decreases for lignite when blended with molasses. On the other hand, blending of biomass with lignite results in approximately 40°C lower ignition temperatures and an increase in combustibility index and reactivity. FTIR results of biomass blend combustion indicate a positive effect in reducing the CO and ${\mathrm{SO}}_{\mathrm{x}}$ emissions when blended with lignite. Magnesite dust addition causes a decrease in gaseous emissions for all blending ratios having the maximum reduction at 10% by weight of magnesite. Moreover, kinetic parameters (apparent activation energy, pre-exponential factor) for each fuel are obtained using a model-fitting method (Coats-Redfern). Addition of biomass/magnesite dust to the lignite caused a decrease in apparent activation energy. Specifically, apparent activation energy of lignite decreases from 105.6 to $81.6\mathrm{kJ}·{\mathrm{mol}}^{-1}$ by adding molasses and reaches approximately $20\mathrm{kJ}·{\mathrm{mol}}^{-1}$ by adding 70% by weight of olive residue and almond shell, respectively.

Many researchers have studied different horizontal-axis and vertical-axis wind turbines (VAWTs) by conducting the experimental and numerical simulations. However, the vertical-axis wind turbine has currently attracted attention because of its simpler geometry and lower manufacturing costs compared with the horizontal-axis wind turbine. This study investigates the effects of steady and quasi-unsteady upstream winds on the aerodynamic performance of vertical axis wind turbines with a symmetric (NACA 4415) and an asymmetric (RISØ-A1-24) airfoil using the double multiple stream tube (DMST) method. To verify the developed MATLAB code, the experimental results of tangential force are compared with the present result for the NACA 0012 airfoil. The results also are compared with another numerical simulation using the same method (DMST) for the NACA 4415 airfoil, which shows good agreement for all comparisons. In order to generate the quasi-unsteady wind, although some past simulations have used computational fluid dynamics (CFD) and experimental approaches, this study applies a new approach using a random function with a turbulence intensity of 20% and a random wind with a wide range of frequencies. The main aim of this research is to study the effect of steady and quasi-unsteady wind on a symmetric and an asymmetric airfoil as well as the capability of the DMST method to predict quasi-unsteady loads. According to the results, both symmetric and asymmetric airfoils result in similar power coefficients. Furthermore, comparison of the results in steady and quasi-unsteady flow shows that the highest amplitude of the fluctuation occurs when each blade passes an azimuth angle of $-40°$ to 40°. Results of this study reveal the capability of the DMST method to predict quasi-unsteady results due to unsteady wind. Therefore, predicting the aerodynamic performance of VAWT using wind inputs that represent the typical turbulence spectrum is feasible.

A large amount of wind energy curtailment is observed during the winter off-peak period in northern China. Because heat demand is high but electric demand is low, combined heat and power (CHP) units have to generate power to supply heat, leaving no load for wind farms to serve. To solve this problem, this paper proposes an energy management method to take advantage of the flexibility in different heating resources in a CHP-based microgrid to relieve wind power curtailment. A novel two-layer coordinated strategy (a schedule layer and a real-time layer) is proposed to control all the components including distributed generation (DG) units, different heating sources, and electrical energy storage (EES). In the schedule layer, a centralized optimization model based on forecasting data is implemented. The real-time layer calculates control signals based on metrical data and received reference values from the upper layer. Flexible control of EES and electric heater scheme (FCEE) is developed to further increase grid integration of wind generation. A 14-bus test system is designed to illustrate the performance of the proposed approach. Results show that the presented method is able to significantly reduce wind curtailment and ensure promising operation efficiency of the studied CHP-based microgrid.

Geothermal heat pumps are characterized as environmentally friendly, cost-effective, and reliable, and a thermoelectric generator is a sustainable, scalable energy-harvesting technique. In this paper, an innovative and multifunctional design for a snow melting system is proposed that combines a geothermal heat pump system with a thermoelectric generator (i.e., geothermoelectrical system) to promote sustainable and intelligent transportation infrastructure development. The performance of the geothermal heat exchanger (GHE) and thermoelectric harvester were predicted using holistic computational models. Based on this, energy balance analyses were conducted to determine the amount of extracted heat by GHE and the extent its use for pavement snow melting as well as to estimate the total amount of electricity that can be produced by converting the extracted heat from the GHE via thermoelectric harvesting. The results show that the heat extracted by GHE from underground provided reasonable coverage areas for snow melting, particularly when real-time melting is not required, whereas its capability is limited for real-time snow melting. The amount of electricity that can be harvested is also limited due to the low efficiency of thermoelectric conversion. The stored energy, however, can provide supplement energy for snow melting or be used to supply electricity for utilities. As a source of green energy, the potential of geothermal and geothermoelectrical energy for transportation applications is promising but remains to be further explored.