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### Research Papers: Energy Conversion/Systems

J. Energy Resour. Technol. 2016;138(5):051601-051601-8. doi:10.1115/1.4032521.

As demand for electricity in the U.S. continues to increase, it is necessary to explore the means through which the modern power supply system can accommodate both increasing affluence (which is accompanied by increased per-capita consumption) and the continually growing global population. Though there has been a great deal of research into the theoretical optimization of large-scale power systems, research into the use of an existing power system as a foundation for this growth has yet to be fully explored. Current successful and robust power generation systems that have significant renewable energy penetration—despite not having been optimized a priori—can be used to inform the advancement of modern power systems to accommodate the increasing demand for electricity. This work explores how an accurate and state-of-the-art computational model of a large, regional energy system can be employed as part of an overarching power systems optimization scheme that looks to inform the decision making process for next generation power supply systems. Research scenarios that explore an introductory multi-objective power flow analysis for a case study involving a regional portion of a large grid will be explored, along with a discussion of future research directions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):051602-051602-4. doi:10.1115/1.4033590.

Turbine blade surfaces are cooled by jet flow from expanded exit holes (EEHs) against the prevailing hot gas flow. The flow through EEH must be designed to form a film of cool air over the blade. Computational analyses are performed to examine the cooling effectiveness of flow from EEH over the suction side of a blade by solving conservation equations and the ideal gas equation of state for turbulent and compressible flow. For a sufficiently high coolant mass flow rate, the flow through EEH, which acts as a converging–diverging nozzle, is choked at the nozzle throat, resulting in a supersonic flow, a shock, and then a subsonic flow downstream. The location of the shock relative to the high-temperature gas flow determines the temperature distribution along the blade surface; which is analyzed in detail when the following conditions are varied: coolant mass flow rate, the temperature difference between gas-and coolant-flow, EEH location on the blade surface, EEH inclination angle to the blade surface, and exit-to-inlet area ratio (AR) of EEH. The film cooling effectiveness is calculated along the surface of the blade. The results show (1) increasing the coolant flow rate improves the effectiveness, (2) change in temperature difference between the mainstream and the coolant slightly affects the effectiveness, (3) inclination angle of EEH has a pronounced effect on film cooling and the corresponding effectiveness, (4) both the location of the EEH on a blade and the AR of the EEH slightly change the effectiveness.

Commentary by Dr. Valentin Fuster

### Research Papers: Energy From Biomass

J. Energy Resour. Technol. 2016;138(5):051801-051801-7. doi:10.1115/1.4032543.

In this work, the particles of two seaweeds, Enteromorpha clathrata (E. clathrata) (EN) and Sargassum natans (S. natans), were combusted in a fluidized bed. It was found that while combustion of EN particles was stable, there was a substantial slagging period during the combustion of S. natans particles. Seaweed and its bottom ash samples were collected, and their pore structures were determined with both mercury intrusion method and N2 adsorption–desorption method. The structural analysis revealed that the number of porosity, pore volume, and specific surface area was all increased and the internal pore in ash samples was expanded after combustion. Fractal analysis showed that while the surface of original seaweed was smooth, it became irregular and rough after combustion. This study has suggested that the ash of seaweeds with porous structure can be valuable for comprehensive utilization.

Commentary by Dr. Valentin Fuster

### Research Papers: Energy Systems Analysis

J. Energy Resour. Technol. 2016;138(5):052001-052001-10. doi:10.1115/1.4032727.

The multi-objective territorial particle swarm optimization (MOTPSO) technique is proposed in this work for the optimal design of steam surface condensers. The main objective of this work is to maximize the condensation rate in a condenser while the pressure loss is minimized. Various design parameters, such as the tube outside diameter, thickness, and pitch, are considered to find the optimal ones for shell and tube heat exchangers considered in this study. The two-dimensional computational fluid dynamics (CFD) analysis is performed to solve the fluid flow and heat transfer in the condenser to assess the performance of different designs.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052002-052002-9. doi:10.1115/1.4032792.

The effects of viscous dissipation on the entropy generation of water–alumina nanofluid convection in circular microchannels subjected to exponential wall heat flux are investigated. Closed-form solutions of the temperature distributions in the streamwise direction are obtained for the models with and without viscous dissipation term in the energy equation. The two models are compared by analyzing their relative deviations in entropy generation for different Reynolds numbers and nanoparticle volume fractions. The incorporation of viscous dissipation prominently affects the temperature distribution and consequently the entropy generation. When the viscous dissipation effect is neglected, the total entropy generation and the fluid friction irreversibility are nearly twofold overrated while the heat transfer irreversibility is underestimated significantly. By considering the viscous dissipation effect, the exergetic effectiveness for forced convection of nanofluid in microchannels attenuates with the increasing nanoparticle volume fraction and nanoparticle diameter. The increase in the entropy generation of nanofluid is mainly attributed to the intensification of fluid friction irreversibility. From the aspect of the second-law of thermodynamics, the widespread conjecture that nanofluids possess advantage over pure fluid associated with higher overall effectiveness is invalidated.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052003-052003-12. doi:10.1115/1.4032619.

Approximately, 55% of the energy produced from conventional vehicle resources is lost due to heat losses. An efficient waste heat recovery process will lead to improved fuel efficiency and greenhouse gas emissions. Thermoelectric generators (TEGs) are heat recovery devices that are being widely studied by a range of energy-intensive industries. Efficient solid-state thermoelectric devices are good candidates to reduce fuel consumption in an automobile. Thermoelectric materials have had limited automotive applications due to the automotive waste heat recovery temperature range, the rarity and toxicity of some materials, and the limited ability to mass manufacture thermoelectric devices from expensive TE materials. However, skutterudite is one class of material that has demonstrated significant promise in the transportation waste heat recovery temperature domain. Durability and reliability of the TEGs are the most significant concerns in the product development process. Cracking of the materials at hot-side interface is found to be a major failure mechanism of TEGs under thermal loading. Cracking affects not only the structural integrity but also the energy conversion and overall performance of the system. In this paper, cracking of thermoelectric material as observed in performance testing is analyzed using numerical simulations and analytic experiments. This paper shows, with the help of finite element analysis (FEA), the detailed distribution of stress, strain, and temperature is obtained for each design. Finite element (FE)-based simulations show the tensile stresses as the primary factor causing radial and circumferential cracks in the skutterudite. For a TEG design, loading conditions and closed-form analytical solutions of stress/strain distributions are derived. Scenarios with minimum tensile stresses are sought. These approaches yield the minimum of stress/strain fields which produce cracks. Finally, based on these analyses and computational fluid dynamics (CFD) studies, strategies in tensile stress reduction and failure prevention are proposed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052004-052004-11. doi:10.1115/1.4033425.

This paper proposes an ammonia–water Kalina cycle driven by low-grade waste energy released from the combustion reactions of mill's rejection which is coupled with 500 MWe coal-fired thermal power plant to quantify the additional electrical power. Energy of combustion for mill rejection is computed by combustion modeling equations. A thermodynamic property calculator for the binary mixture and a computer simulation program have been developed by MS-Excel and Visual Basic for Application (VBA) to calculate and optimize the Kalina cycle operating parameters based on thermodynamic modeling equations. Variation of key operating parameters, namely, turbine inlet pressure, mass flow rate of binary mixture, and ammonia mass fraction in mixture is studied and filters the optimum value accordingly to maximize the cycle efficiency. Techno-commercial feasibility is also done through economic analysis. The results show that about 562.745 kWe power generation can be added with total plant generation for organization profit. This will enhance the combined plant efficiency from 38.559% to 38.604%. Maximum net Kalina cycle efficiency of 24.74% can be achieved with ammonia mass fraction of 0.4 at condenser back pressure of 1.957 bar and turbine inlet pressure and temperature of 20 bar and 442.40 K, respectively. Ammonia mass fraction of 0.4 is the optimum choice for 20 bar turbine inlet pressure to get maximum output after maintaining minimum 50 K degree of superheat compared to ammonia mass fraction of 0.3. The cycle performance at ammonia mass fraction of 0.4 is better than 0.5 due to less condenser back pressure. Kalina cycle operating with less mass flow rate performs higher cycle efficiency when dryness fraction at turbine exhaust is less than 1 and performance deteriorates at above 1. This deterioration is due to higher condenser energy loss carried away by cooling water (CW) flow. The simple payback period of this system is around 5.5 years if the system is running with 80% plant availability factor and 100% plant load factor.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052005-052005-6. doi:10.1115/1.4033424.

Extraction–condensing steam turbines mix cold-condensing and cogeneration activities making the respective power and fuel flows not directly observable. A flawed assessment of the flows is causing confusion and bias. A steam expansion path on a Mollier diagram reveals the design characteristics of a thermal power plant and of its embedded combined heat and power (CHP) activities. State variable data on a unit mass of steam, entering the turboset as life steam and leaving it at one of the heat extraction exhausts, provide the roster of the power-heat production possibility set of the plant. The actual production possibilities are drawn from the roster by applying capacity data and constraints on the heat extraction points. Design power-to-heat ratios of CHP activities are univocally identified, allowing accurate assessments of cogenerated power. This information is needed for proper incentive regulation of CHP activities, pursuing maximization of CHP quality and quantity. Quality is gauged by the power-to-heat ratio, principally a design (investment) decision. Quantity is gauged by the operational amounts of recovered heat exhausts. Optimal regulatory specificity is attained through setting generic frameworks by technology, accommodating investment and operational decisions by plant owners. Our novel method is explained and applied with numerical data, also revealing the flaws in present regulations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052006-052006-7. doi:10.1115/1.4033503.

Thermal energy storage (TES) systems that store sensible heat in liquid media require the use of storage tanks. Spherical tanks require less building material and insulation, which might reduce the overall cost of a TES system while providing structural rigidity. The current study investigates an optimized plate diffuser in a thermocline spherical tank storage system to possibly increase the discharge flow rate without disrupting the thermocline region and without reducing the tank thermal efficiency. For low temperature (10–90 °C heat storage applications), such as heating, ventilation, and air conditioning (HVAC) and thermal water desalination, storing hot water in a thermocline system can increase the system thermal efficiency by up to 40% when compared to a fully mixed water tank and reduce the installation cost by 30% compared to a two-tank system. This study examines using a spherical tank in a thermocline system for such applications. A computational fluid dynamic (CFD) study simulated the discharge process from a spherical storage tank thermocline water system. Thermocline thickness and temperature profile in the tank were numerically determined for Reynolds number, Re = 600 and Froude number, Fr = 1.2; results were then experimentally validated. A CFD parametric study with (500 < Re < 7500) and (0.5 < Fr < 3.3): (i) determined the influence of tank flow dimensionless numbers (Reynolds, Froude, Richardson, and Archimedes) on thermal efficiency and thermocline thickness, (ii) produced an equation to predict the tank thermal efficiency using flow dimensionless numbers, and (iii) estimated the thermocline region volume occupation as a percentage of the total volume. The study of an optimized plate diffuser produced an equation for thermal efficiency based on Re and Fr numbers and estimated a thermocline volume equal to 15% of total tank volume. Flow rate ramp up by a factor of 3 was possible after the thermocline region was formed without losing tank thermal efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052007-052007-7. doi:10.1115/1.4033585.

This paper presents a comprehensive analysis of the heat transfer during the melting process of a high-temperature (>800 °C) phase-change material (PCM) encapsulated in a vertical cylindrical container. The energy contributions from radiation, natural convection, and conduction have been included in the mathematical model in order to capture most of the physics that describe and characterize the problem and quantify the role that each mechanism plays during the phase-change process. Numerical predictions based on the finite-volume method have been obtained by solving the mass, momentum, and energy conservation principles along with the enthalpy porosity method to track the liquid/solid interface. Experiments were conducted to obtain the temperature response of the thermal energy storage (TES) cell during the sensible heating and phase-change regions of the PCM. Continuous temperature measurements of porcelain crucibles filled with ACS grade NaCl were recorded. The temperature readings were recorded at the center of the sample and at the wall of the crucible as the samples were heated in a furnace over a temperature range of 700–850 °C. The numerical predictions have been validated by the experimental results, and the effect of the controlling parameters of the system on the melt fraction rate has been evaluated. The results showed that the natural convection is the dominant heat transfer mechanism. In all the experimental study cases, the measured temperature response captured the PCM melting trend with acceptable repeatability. The uncertainty analysis of the experimental data yielded an approximate error of ±5.81 °C.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052008-052008-10. doi:10.1115/1.4033586.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052009-052009-6. doi:10.1115/1.4033626.

Sustainable engineering brings about multidisciplinary solutions to environmental, sociocultural, and economic needs. Sustainable methods and technologies ensure the effectiveness of products, designs, and infrastructure, and minimize waste. Managing waste is critical in the successful practice of sustainable engineering. Success in the implementation of a waste management program must consider a very important strategy, namely, waste reduction which is highly dependent on social stewardship, education, and waste conversion. A sustainable program mix must include public policy, health management, and engineering. This paper presents a number of proven sources and techniques for wastes minimization and conversion and a discussion about the development of effective decision-making tools to implement the most feasible and cost-effective applications. Specifically, the conversion of waste as a resource is presented including the use of wastewater (greywater) for condenser cooling in a power plant; conversion of restaurant grease into biodiesel; the use of phosphate mine tailings as a road surface material; recycling and reuse of glass, metal, and plastics; reuse of rare metals from discarded computers; and the use of cattle waste as building materials. In all of these, the conservation of energy is realized practically. More emphasis has been focused on the use of greywater because it has direct impact on the energy–water nexus.

Commentary by Dr. Valentin Fuster

### Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2016;138(5):052201-052201-9. doi:10.1115/1.4032621.

The use of natural gas in compression ignition (CI) engines as a supplement to diesel under dual-fuel combustion mode is a promising technique to increase efficiency and reduce emissions. In this study, the effect of dual-fuel operating mode on combustion characteristics, engine performance and pollutant emissions of a diesel engine using natural gas as primary fuel and neat diesel as pilot fuel, has been examined. Natural gas (99% methane) was port injected into an AVL 5402 single cylinder diesel research engine under various engine operating conditions and up to 90% substitution was achieved. In addition, neat diesel was also tested as a baseline for comparison. The experiments were conducted at three different speeds—1200, 1500, and 2000 rpm, and at different diesel-equivalent loads (injection quantity)—15, 20 (7 bar IMEP), and 25 mg/cycle. Both performance and emissions data are presented and discussed. The performance was evaluated through measurements of in-cylinder pressure, power output and various exhaust emissions including unburned hydrocarbons (UHCs), carbon monoxide (CO), nitrogen oxides (NOx), and soot. The goal of these experiments was to maximize the efficiency. This was done as follows—the compressed natural gas (CNG) substitution rate (based on energy) was increased from 30% to 90% at fixed engine conditions, to identify the optimum CNG substitution rate. Then using that rate, a main injection timing sweep was performed. Under these optimized conditions, combustion behavior was also compared between single, double, and triple injections. Finally, a load and speed sweep at the optimum CNG rate and timings were performed. It was found that a 70% CNG substitution provided the highest indicated thermal efficiency (ITE). It appears that dual-fuel combustion has a maximum brake torque (MBT) diesel injection timing for different conditions which provides the highest torque. Based on multiple diesel injection tests, it was found that the conditions that favor pure diesel combustion, also favor dual-fuel combustion because better diesel combustion provides better ignition and combustion for the CNG-air mixture. For 70% CNG dual-fuel combustion, multiple diesel injections showed an increase in the efficiency. Based on the experiments conducted, diesel-CNG dual-fuel combustion is able to achieve similar efficiency and reduced emissions relative to pure diesel combustion. As such, CNG can be effectively used to substitute for diesel fuel in CI engines.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052202-052202-11. doi:10.1115/1.4032622.

Gasoline compression ignition (GCI), also known as partially premixed compression ignition (PPCI) and gasoline direct injection compression ignition (GDICI), engines have been considered an attractive alternative to traditional spark ignition (SI) engines. Lean-burn combustion with the direct injection of fuel eliminates throttle losses for higher thermodynamic efficiencies, and the precise control of the mixture compositions allows better emission performance such as NOx and particulate matter (PM). Recently, low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and lighter evaporation compared to gasoline fuel (Chang et al., 2012, “Enabling High Efficiency Direct Injection Engine With Naphtha Fuel Through Partially Premixed Charge Compression Ignition Combustion,” SAE Technical Paper No. 2012-01-0677). The feasibility of such a concept has been demonstrated by experimental investigations at Saudi Aramco (Chang et al., 2012, “Enabling High Efficiency Direct Injection Engine With Naphtha Fuel Through Partially Premixed Charge Compression Ignition Combustion,” SAE Technical Paper No. 2012-01-0677; Chang et al., 2013, “Fuel Economy Potential of Partially Premixed Compression Ignition (PPCI) Combustion With Naphtha Fuel,” SAE Technical Paper No. 2013-01-2701). The present study aims to develop predictive capabilities for low octane gasoline fuel compression ignition (CI) engines with accurate characterization of the spray dynamics and combustion processes. Full three-dimensional simulations were conducted using converge as a basic modeling framework, using Reynolds-averaged Navier–Stokes (RANS) turbulent mixing models. An outwardly opening hollow-cone spray injector was characterized and validated against existing and new experimental data. An emphasis was made on the spray penetration characteristics. Various spray breakup and collision models have been tested and compared with the experimental data. An optimum combination has been identified and applied in the combusting GCI simulations. Linear instability sheet atomization (LISA) breakup model and modified Kelvin–Helmholtz and Rayleigh–Taylor (KH-RT) break models proved to work the best for the investigated injector. Comparisons between various existing spray models and a parametric study have been carried out to study the effects of various spray parameters. The fuel effects have been tested by using three different primary reference fuel (PRF) and toluene primary reference fuel (TPRF) surrogates. The effects of fuel temperature and chemical kinetic mechanisms have also been studied. The heating and evaporative characteristics of the low octane gasoline fuel and its PRF and TPRF surrogates were examined.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052203-052203-11. doi:10.1115/1.4032623.

A closed-cycle gasoline compression ignition (GCI) engine simulation near top dead center (TDC) was used to profile the performance of a parallel commercial engine computational fluid dynamics (CFD) code, as it was scaled on up to 4096 cores of an IBM Blue Gene/Q (BG/Q) supercomputer. The test case has 9 × 106 cells near TDC, with a fixed mesh size of 0.15 mm, and was run on configurations ranging from 128 to 4096 cores. Profiling was done for a small duration of 0.11 crank angle degrees near TDC during ignition. Optimization of input/output (I/O) performance resulted in a significant speedup in reading restart files, and in an over 100-times speedup in writing restart files and files for postprocessing. Improvements to communication resulted in a 1400-times speedup in the mesh load balancing operation during initialization, on 4096 cores. An improved, “stiffness-based” algorithm for load balancing chemical kinetics calculations was developed, which results in an over three-times faster runtime near ignition on 4096 cores relative to the original load balancing scheme. With this improvement to load balancing, the code achieves over 78% scaling efficiency on 2048 cores, and over 65% scaling efficiency on 4096 cores, relative to 256 cores.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052204-052204-8. doi:10.1115/1.4032733.

A 2D model and heat transfer mechanism are proposed to analyze and study oxidative steam reforming of methane (OSRM) in a membrane reactor. The model describes mass and thermal dispersions for gas and solid phases. It also accounts for transport through the membrane. The effects of operating parameters on methane conversion and H2 yield are analyzed. The parameters considered are the bed temperature (800–1100 K), molar oxygen-to-carbon ratio (0.0–0.5), and steam-to-carbon ratio (1–4). The results show that our model prevents overestimation and provides valuable additional information about temperature and concentration gradients in membrane reactor which is not available in a simple one-dimensional approach. Simulation results show that large temperature and concentration gradients cannot be avoided. The particle properties and the bed diameter have a considerable effect on the extent of gas mixing. Effective gas mixing coefficient also increases with increasing gas and solid velocity. In membrane reactor, simulation results show that mixing which depends on operational and design parameters has a strong effect on the hydrogen conversion. Also, the removal of hydrogen with membranes breaks equilibrium barrier leading to efficient production of hydrogen, reduced reactor size, and tube lengths. The model can be used in real-time simulation of industrial reactors for control and optimization purposes.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052205-052205-11. doi:10.1115/1.4032729.

The present study was conducted to investigate the physicochemical properties and pyrolysis kinetics of sugarcane bagasse (SB). The physiochemical properties of SB were determined to examine its potential for pyrolysis. The physiochemical properties such as proximate analysis, ultimate analysis, heating values, lignocellulosic composition, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) of SB were investigated. The pyrolysis experiments were conducted in a nonisothermal thermogravimetric analyzer (TGA) to understand the thermal degradation behavior of SB. The activation energy $(Ea)$ of SB pyrolysis was calculated by model-free Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW) methods. Average values of activation energy determined through KAS and OFW methods are found as 91.64 kJ/mol and 104.43 kJ/mol, respectively. Variation in the activation energy with degree of conversion was observed, which shows that pyrolysis is a complex process composed of several reactions. Coats–Redfern method was used to calculate the pre-exponential factor and reaction order. Conversion of SB due to heat treatment computed by using the kinetic parameters is found to be in good agreement with the experimental conversion data, and the maximum error limit between the experimental and predicted conversions is 8.5% for 5 °C/min, 6.0% for 10 °C/min, and 11.6% for 20 °C/min. The current investigation proves the suitability of SB as a potential feedstock for pyrolysis.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052206-052206-7. doi:10.1115/1.4032941.

An experimental investigation was conducted to evaluate the suitability of hazelnut oil methyl ester (HOME) for engine performance and exhaust emissions responses of a turbocharged direct injection (TDI) diesel engine. HOME was tested at full load with various engine speeds by changing fuel injection timing (12, 15, and 18 deg CA) in a TDI diesel engine. Response surface methodology (RSM) and least-squares support vector machine (LSSVM) were used for modeling the relations between the engine performance and exhaust emission parameters, which are the measured responses and factors such as fuel injection timing (t) and engine speed (n) parameters as the controllable input variables. For this purpose, RSM and LSSVM models from experimental results were constructed for each response, namely, brake power, brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), exhaust gas temperature (EGT), oxides of nitrogen (NOx), carbon dioxide (CO2), carbon monoxide (CO), and smoke opacity (N), which are affected by the factors t and n. The results of RSM and LSSVM were compared with the observed experimental results. These results showed that RSM and LSSVM were effective modeling methods with high accuracy for these types of cases. Also, the prediction performance of LSSVM was slightly better than that of RSM.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052207-052207-7. doi:10.1115/1.4032942.

The use of exhaust gas recirculation (EGR) in internal combustion engines has significant impacts on engine combustion and emissions. EGR can be used to reduce in-cylinder NOx production, reduce fuel consumption, and enable advanced forms of combustion. To maximize the benefits of EGR, the exhaust gases are often cooled with liquid to gas heat exchangers. However, the build up of a fouling deposit layer from exhaust particulates and volatiles results in the decrease of heat exchanger efficiency, increasing the outlet temperature of the exhaust gases and decreasing the advantages of EGR. This paper presents an experimental data from a novel in situ measurement technique in a visualization rig during the development of a 378 μm thick deposit layer. Measurements were performed every 6 hrs for up to 24 hrs. The results show a nonlinear increase in deposit thickness with an increase in layer surface area as deposition continued. Deposit surface temperature and temperature difference across the thickness of the layer was shown to increase with deposit thickness while heat transfer decreased. The provided measurements combine to produce deposit thermal conductivity. A thorough uncertainty analysis of the in situ technique is presented and suggests higher measurement accuracy at thicker deposit layers and with larger temperature differences across the layer. The interface and wall temperature measurements are identified as the strongest contributors to the measurement uncertainty. Due to instrument uncertainty, the influence of deposit thickness and temperature could not be determined. At an average deposit thickness of 378 μm and at a temperature of 100 °C, the deposit thermal conductivity was determined to be 0.044 ± 0.0062 W/m K at a 90% confidence interval based on instrument accuracy.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052208-052208-11. doi:10.1115/1.4032979.

A numerical study of two-phase flow inside the nozzle holes and the issuing spray jets for a multihole direct injection gasoline injector has been presented in this work. The injector geometry is representative of the Spray G nozzle, an eight-hole counterbore injector, from the engine combustion network (ECN). Simulations have been carried out for a fixed needle lift. The effects of turbulence, compressibility, and noncondensable gases have been considered in this work. Standard k–ε turbulence model has been used to model the turbulence. Homogeneous relaxation model (HRM) coupled with volume of fluid (VOF) approach has been utilized to capture the phase-change phenomena inside and outside the injector nozzle. Three different boundary conditions for the outlet domain have been imposed to examine nonflashing and evaporative, nonflashing and nonevaporative, and flashing conditions. Noticeable hole-to-hole variations have been observed in terms of mass flow rates for all the holes under all the operating conditions considered in this study. Inside the nozzle holes mild cavitationlike and in the near-nozzle region flash-boiling phenomena have been predicted when liquid fuel is subjected to superheated ambiance. Under favorable conditions, considerable flashing has been observed in the near-nozzle regions. An enormous volume is occupied by the gasoline vapor, formed by the flash boiling of superheated liquid fuel. Large outlet domain connecting the exits of the holes and the pressure outlet boundary appeared to be necessary leading to substantial computational cost. Volume-averaging instead of mass-averaging is observed to be more effective, especially for finer mesh resolutions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052209-052209-8. doi:10.1115/1.4033107.

This paper presents the effects of the fuel lower heating value (LHV) of various syngas fuels on the performance and emissions of a two-after-body trapped vortex combustor (TVC). Optimizing the fuel composition will result in a higher LHV and will in turn produce a more efficient performance. On the other hand, the fuel composition has a direct effect on the emissions of the TVC. Computational fluid dynamics (CFD) simulations were conducted for various syngas fuels to determine the effects of the fuel constituents and heat of combustion on the TVC performance, and to optimize and accurately predict the performance of a syngas fuel that can meet the emissions requirements.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052210-052210-17. doi:10.1115/1.4033572.

This study was carried out with an objective to develop a 3D simulation methodology for rotary engine combustion study and to investigate the effect of recess shapes on flame travel within the rotating combustion chamber and its effects on engine performance. The relative location of spark plugs with respect to the combustion chamber has significant effect on flame travel, affecting the overall engine performance. The computations were carried out with three different recess shapes using iso-octane (C8H18) fuel, and flame front propagation was studied at different widths from spark location. Initially, a detailed leakage study was carried out and the flow fields were compared with available experimental results. The results for first recess with compression ratio 9.1 showed that the flow and vortex formations were similar to that of actual model. The capability of the 3D model to predict the combustion reaction rate precisely as that of practical engine is presented with comparison to experimental results. This study showed that the flame propagation is dominant toward the leading apex of the rotor chamber, and the air/fuel mixture region in the engine midplane, between the two spark plugs, has very low flame propagation compared to the region in the vicinity of spark. The air/fuel mixture in midplane toward the leading apex burns partially and most of the mixture toward the trailing apex is left unburnt. Recommendations have been made for optimal positioning of the spark plugs along the lateral axis of the engine. In the comparison study with different recess shapes, lesser cavity length corresponding to a higher compression ratio (CR) of 9.6 showed faster flame propagation toward leading side. Also, mass trapped in working chamber reduced and developed higher burn rate and peak pressure resulting in better fuel conversion efficiency. Third recess with lesser CR showed reduced burn rates and lower peak pressure.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052211-052211-8. doi:10.1115/1.4033588.

The in-cylinder pressure oscillations of a homogeneous charge compression ignition (HCCI)-DI engine fueled with dimethyl ether (DME) have been investigated using discrete wavelet transform (DWT) based on four different wavelet functions. The in-cylinder pressure is decomposed into three levels that contain three details D1, D2, and D3, and an approximation A1. In normal combustion, there are no obvious pressure impacts in three details due to smooth combustion process. The abnormal pressure oscillations occur in three details in knocking combustion, and the oscillation is most intense in D1. Its frequency band 5–10 kHz is the knock frequency band, and most high-frequency pressure oscillations and wavelet energy are in this frequency band. The pressure oscillations are located in the premixed combustion stage and diffusion combustion stage. Characteristics of in-cylinder pressure oscillations can be extracted using four wavelet functions “db4,” “db8,” “sym4,” and “sym8.” Extract abilities of four wavelet functions are different and wavelet db4 is suitable for pressure oscillation detection.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052212-052212-13. doi:10.1115/1.4033571.

Compression ignition (CI) engines are facing strong restrictive emission norms globally, which demand extremely low oxides of nitrogen (NOx) and particulate matter (PM) emissions. Homogeneous charge compression ignition (HCCI) engine is a very attractive solution to meet these stringent emission challenges due to its capability to simultaneously reduce NOx and PM. In this study, HCCI combustion was investigated using different test fuels such as diesoline (15% v/v gasoline with diesel), diesohol (15% v/v ethanol with diesel), and diesosene (15% v/v kerosene with diesel) vis-a-vis baseline mineral diesel. A dedicated fuel vaporizer was used for homogeneous fuel–air mixture preparation. The experiments were performed at constant intake charge temperature (180 °C), fixed exhaust gas recirculation (EGR) (15%) at different engine loads. Stable combustion characteristics were determined for diesosene at lower engine loads, however, diesoline and diesohol yielded improved emissions compared to baseline diesel HCCI combustion. At higher loads, diesoline and diesosene showed higher knocking tendency compared to baseline diesel and diesohol. Diesohol showed lower NOx and smoke opacity, however, diesoline and diesosene showed slightly lower hydrocarbon (HC) and carbon monoxide (CO) emissions compared to baseline diesel HCCI combustion. Performance results of diesohol and diesosene were slightly inferior compared to diesel and diesoline HCCI combustion. Physical characterization of exhaust particulates was done for these test fuels using engine exhaust particle sizer (EEPS). Particle number-size distribution showed that most particles emitted from diesoline and diesohol were in ultrafine size range and baseline diesel and diesosene emitted relatively larger particles. Reduction in total particle number concentration with addition of volatile fuel components in mineral diesel was another important observation of this study.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052213-052213-8. doi:10.1115/1.4033627.

This work investigates the laminar flame speed, SN, of gas-to-liquid (GTL) fuel and its 50–50% by volume blends with conventional diesel, in a cylindrical bomb capable of measuring SN at different initial temperatures and equivalence ratios at ambient pressure. SN was measured by analysing the pressure signals after combustion detected by a pressure transducer mounted on the bomb. Direct visualization has also been conducted to observe the ignition and flame propagation. It was found that pure GTL fuel has the highest SN near stoichiometric conditions, which is about 88.3 cm/s. However, at lean and rich mixtures, SN of GTL is slightly lower than that of the conventional diesel. The blended fuel has the lowest SN at lean and rich mixture conditions comparing with those of GTL and diesel fuels. Studying the effect of increasing the initial temperature on SN revealed that SN of the three tested fuels increases with the increase in the initial temperature almost linearly. However, the blended fuel has the lowest SN at the highest temperature, about 89.7 cm/s at 250 °C.

Commentary by Dr. Valentin Fuster

### Research Papers: Petroleum Engineering

J. Energy Resour. Technol. 2016;138(5):052901-052901-9. doi:10.1115/1.4032237.

This study presents an integrated approach to evaluate the efficiency of fracturing stimulation and predict well production performance. As the pressure disturbance propagates throughout the reservoir during long-time transient flow regimes, it will shape an expanding drainage volume. A macroscopic “compressible tank model (CTM)” using weak (integral) form of mass balance equation is derived to relate dynamic drainage volume (DDV) and average reservoir pressure to production history in extremely shale reservoirs. Fluids and rock compressibility, desorption parameters (for shale or coal gas), and production rates control the speed at which the boundaries advance. After the changes of average reservoir pressure within the expanding drainage volume are obtained, a new empirical inflow performance relationship (transient IPR) correlation is proposed to describe well performance during long transient flow periods in shale reservoirs. This new empirical correlation shows better match performance with field data than that of conventional Vogel-type IPR curves. The integrated approach of both CTM model and transient IPR correlation is used to determine and predict the optimal fracturing spacing and the size of horizontal section for few wells from one of shale oil plays in U.S. The results suggest the existence of optimal fracture spacing and horizontal well length for multistage fractured horizontal wells in shale oil reservoirs. In practice, this paper not only provides an insight in understanding the long transient flow production characteristics of shale reservoirs using concept of expanding drainage volume. Neither methods require comprehensive inputs for the strong form (differential) nor any prior knowledge about the sophisticated shale reservoir features (shape, size, etc.), the ultimate drainage volume, the ultimate recovery, optimal fracture spacing, and the length of horizontal section for each well can also be easily obtained by this new integrated analytical method.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052902-052902-7. doi:10.1115/1.4032618.

Recently developed laboratory and numerical techniques reveal that the very thin, near-wall (assumed) “laminar” fluid layer, an essential feature of all turbulent flow conditions, houses a world of identifiable jetlike structures including bursts generated from the near-wall regions and lumps of fluids projected back onto the wall zones. This activity, identified as “coherent structures” (CS), is recognized as an important mechanism for radial mass transport and energy dissipation, particularly in near-wall or fluid–bed zones. Buoyancy-, adhesion-, hydrodynamic-, and CS-related updraft forces act on particles positioned in the fluid–bed interface zone. Depending on the particle nature, bulk fluid properties, and transport velocity, three pairs of forces were identified corresponding to the equilibrium condition of deposit particles in each of the three size ranges with respect to the onset of entrainment into the bulk flow. This mechanistic approach using a set of force equilibrium equations to assess the potential entrainment of particles was first suggested in 1980 by Phillips and was later (2006) applied by Toma and a research team from ARC and PETRONAS to explain the aging of wall-deposit layer occurring during waxy crude transportation as an effect of size-selective removal of paraffin crystals formed from a mixture of crystalized alkanes. The merit of this paper, regarded as an extension of the 2006 publication, is to introduce a more general selective extraction rate function that enables calculations of both the rate of paraffin aging and size alteration of any fine, polydisperse particulate matter exposed to bulk turbulent flow, gas or liquid. Without any adjustment of the process or physical constants, the modeling results presented in this paper compared satisfactorily with the experimental results obtained independently by the Texaco Research (aging of waxy crude) and laboratory data from the University of Alberta on the effect of size-selective extraction of fine sand or glass beads (GB) initially deposited on the bottom of a pipe and exposed to a turbulent bulk flow of water. An overarching objective of this paper is to stir interest in mechanistic modeling and prediction of size-selective radial transport and separation for a broad range of industrial and environmental applications and studies and specifically in the recognition and use of burst-sweep CS structures for calculating radial transport of small particle sizes, particularly in near-interface zones exposed to turbulent flow conditions.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052903-052903-9. doi:10.1115/1.4032547.

One of the main reservoir development plans is to find optimal locations for drilling new wells in order to optimize cumulative oil recovery. Reservoir simulation is a necessary tool to study different configurations of well locations to investigate the future of the reservoir and determine the optimal places for well drilling. Conventional well-known numerical methods require modern hardware for the simulation and optimization of large reservoirs. Simulation of such heterogeneous reservoirs with complex geological structures with the streamline-based simulation method is more efficient than the common simulation techniques. Also, this method by calculation of a new parameter called “time-of-flight” (TOF) offers a very useful tool to engineers. In the present study, TOF and distribution of streamlines are used to define a novel function which can be used as the objective function in an optimization problem to determine the optimal locations of injectors and producers in waterflooding projects. This new function which is called “well location assessment based on TOF” (WATOF) has this advantage that can be computed without full time simulation, in contrast with the cumulative oil production (COP) function. WATOF is employed for optimal well placement using the particle swarm optimization (PSO) approach, and its results are compared with those of the same problem with COP function, which leads to satisfactory outcomes. Then, WATOF function is used in a hybrid approach to initialize PSO algorithm to maximize COP in order to find optimal locations of water injectors and oil producers. This method is tested and validated in different 2D problems, and finally, the 3D heterogeneous SPE-10 reservoir model is considered to search locations of wells. By using the new objective function and employing the hybrid method with the streamline simulator, optimal well placement projects can be improved remarkably.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052904-052904-10. doi:10.1115/1.4032831.

Prediction of differential pipe sticking (DPS) prior to occurrence, and taking preventive measures, is one of the best approaches to minimize the risk of DPS. In this paper, probabilistic artificial neural network (ANN) has been introduced. Moreover, conventional ANNs through multilayer perceptron (MLP) and radial basis function (RBF) have been used to compare with probabilistic ANN. Furthermore, to determine the most important parameters, forward selection sensitivity analysis has been applied. By predicting DPS and performing sensitivity analysis, it is possible to improve well planning process. The results from the analyses have shown the better potentiality of the probabilistic ANN in this area.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052905-052905-13. doi:10.1115/1.4032728.

Carbonate matrix acidizing is widely used in oil fields as a simple and easy method of production enhancement. However, the dissolution pattern created due to the reaction between the acid and the carbonates is a complex phenomenon. Several experimental and modeling studies have been carried out to simplify this process and design the optimum conditions for acidizing. One approach is to develop continuum models to simulate the dissolution process in the core scale. Conventional modeling approaches typically do not consider the effects of spent acid in the models. However, there are a few studies and observations on the solubility of CO2 in the CaCl2-H2O-CO2 system, which shows the possibility of formation of a separate CO2 phase during acidizing. The presence of CO2 as a separate phase affects the dominant wormhole propagation and also the dissolution regime. Moreover, the acid/rock reaction leads to the change of physical properties of the flowing fluid. Hence, neglecting the alterations in the physical properties of the moving fluid, such as density and viscosity, affects the accuracy of the models. In this study, a basic model previously introduced in the Darcy scale is developed to consider the effect of reaction products on the overall acidizing performance. A thermodynamic model is used to estimate the CO2 solubility in the spent acid. The insoluble CO2 may change the relative permeability of the reactants and influence on the optimum conditions. Furthermore, the physical properties of the fluid are estimated and updated at each step of the modeling. Consideration of the spent acid effects in the modeling can improve the modeling accuracy. The developed model has the ability to consider the effect of pressure and temperature of the medium on the optimum conditions. In addition, the developed model has shown better predictions by considering the physical changes during the dissolution.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052906-052906-8. doi:10.1115/1.4033400.

Reinjection is one of the most important methods to dispose fluid associated with oil and natural gas production. Disposed fluids include produced water, hydraulic fracture flow back fluids, and drilling mud fluids. Several formation damage mechanisms are associated with the injection including damage due to filter cake formed at the formation face, bacteria activity, fluid incompatibility, free gas content, and clay activation. Fractured injection is typically preferred over matrix injection because a hydraulic fracture will enhance the well injectivity and extend the well life. In a given formation, the fracture dimensions change with different injection flow rates due to the change in injection pressures. Also, for a given flow rate, the skin factor varies with time due to the fracture propagation. In this study, well test and injection history data of a class II disposal well in south Texas were used to develop an equation that correlates the skin factor to the injection flow rate and injection time. The results show that the skin factor decreases with time logarithmically as the fracture propagates. At higher injection flow rates, the skin factor achieved is lower due to the larger fracture dimensions that are developed at higher injection flow rates. The equations developed in this study can be applied for any water injector after calibrating the required coefficients using injection step rate test (SRT) data.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052907-052907-6. doi:10.1115/1.4033304.

Materials such as added clays, weight materials, drill solids, and metallic wear products in the drilling fluid are known to distort the geomagnetic field at the location of the measurement while drilling (MWD) tool magnetometers that are used to measure the direction of well path. This distortion contributes to substantial errors in determination of azimuth while drilling deviated wells. These errors may result in missing the target of a long deviated 12 ¼ in. section in the range of 1–200 m, representing a significant cost to be mitigated. The error becomes even more pronounced if drilling occurs in arctic regions close to the magnetic north pole (or south pole). The effect on the magnetometer readings is obviously linked to the kinds and amounts of magnetic materials in the drilling fluid. The problem has recently been studied by laboratory experiments and analyses of downhole survey data. A series of experiments has been carried out to understand how some drilling fluid additives relate to the magnetic distortion. Experiments with free iron ions show that presence of iron ions does not contribute to magnetic distortion, while experiments with bentonite-based fluids show a strong effect of bentonite on magnetic shielding. Albeit earlier measurements showing a strong dependency of the content of organophilic clay, clean laboratory prepared oil-based drilling fluids show no increased shielding when adding organophilic hectorite clays. The anticipated difference between these two cases is outlined in the paper. When eroded steel from an offshore drilling site is added into the oil-based drilling fluid, it is found that these swarf and steel fines significantly increase the magnetic shielding of the drilling fluid. The paper outlines how the drilling direction may be distorted by the presence of these additives and contaminants and how this relates to the rheological properties of the drilling fluid.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2016;138(5):052908-052908-8. doi:10.1115/1.4033401.

Commentary by Dr. Valentin Fuster

### Expert View

J. Energy Resour. Technol. 2016;138(5):054701-054701-3. doi:10.1115/1.4032624.

The U.S. Government determines the guidelines for daily diet of humans in their various life stages. The current guidelines for caloric intake are about 2800 cal daily for the adult male, and about 600 cal less for the adult female. This work brings up the point that with the growing diversity of the population, these caloric intake guidelines need to consider the effect of temperature at the time the food is consumed. The motivation of this study is diversity; it is recognized that the Chinese and South Korean cuisines typically have high temperatures when served, whereas much of standard American food is consumed at room temperature. The thermal capacity of the food consumed has not been taken into consideration. It is likely that the “empty” calories related to consumption of hot foods are helpful, in keeping the body warm without the risk of weight gain. They may also be used judiciously to lose weight.

Commentary by Dr. Valentin Fuster