Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2011;133(2):022201-022201-6. doi:10.1115/1.4003881.

Thermodynamic properties of ionized gases at high temperatures have been calculated by a new model based on local equilibrium conditions. Calculations have been done for nitrogen, oxygen, air, argon, and helium. The temperature range is 300–100,000 K. Thermodynamic properties include specific heat capacity, density, mole fraction of particles, and enthalpy. The model has been developed using statistical thermodynamics methods. Results have been compared with other researchers and the agreement is good.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;133(2):022202-022202-5. doi:10.1115/1.4003806.

Presented are the results of experiments designed to investigate flame lift-off behavior in the hysteresis regime for low Reynolds number turbulent flows. The hysteresis regime refers to the situation where the jet flame has dual positions favorable to flame stabilization: attached and lifted. Typically, a jet flame is lifted off of a burner and stabilized at some downstream location at a pair of fuel and coflow velocities that is unique to a flame at that position. Since the direction from which that condition is arrived at is important, there is an inherent hysteretic behavior. To supplement previous research on hysteretic behavior in the presence of no coflow and low coflow velocities, the current research focuses on flames that are lifted and reattached at higher coflow velocities, where the flame behavior includes an unexpected downstream recession at low fuel velocities. Observations on the flame behavior related to nozzle exit velocity and coflow velocity are made using video imaging of flame sequences. The results show that a flame can stabilize at a location downstream despite a decrease in the local excess jet velocity and assist in determining the effect of coflow velocity magnitude on hysteretic behavior. These observations are of utility in designing maximum turndown burners in air coflow, especially for determining stability criteria in low fuel-flow applications.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;133(2):022203-022203-6. doi:10.1115/1.4003808.

Methyl and ethyl esters of vegetable oils have become an important source of renewable energy with convenient applications in compression-ignition (CI) engines. While the use of biofuels results in a reduction of CO, particulate matter, and unburned hydrocarbons in the emissions, the main disadvantage is the increase of nitrogen oxides (NOx ) emissions. The increase in NOx emissions is attributed to differences in chemical composition and physical properties of the biofuel, which in turn affect engine operational parameters such as injection delay and ignition characteristics. The effects of fuel injection timing, which can compensate for these changes, on the performance and emissions in a single cylinder air-cooled diesel engine at partial loads using canola methyl ester and its blends with diesel are presented in this study. The engine is a single cylinder, four stroke, naturally aspirated, CI engine with a displacement volume of 280 cm3 rated at 5 HP at 3600 rpm under a dynamometer load. It was equipped with a pressure sensor in the combustion chamber, a needle lift sensor in the fuel injector, and a crank angle sensor attached to the crankshaft. Additionally, the temperature of the exhaust gases was monitored using a thermocouple inside the exhaust pipe. Pollutant emissions were measured using an automotive exhaust gas analyzer. Advanced, manufacturer-specified standard, and delayed injection settings were applied by placing shims of different thicknesses under the injection pump, thus, altering the time at which the high-pressure fuel reached the combustion chamber. The start of injection was found to be insensitive to the use of biofuels in the engine. The late injection timing of the engine provided advantages in the CO and NO emissions with a small penalty in fuel consumption and thermal efficiency.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;133(2):022204-022204-6. doi:10.1115/1.4003999.

This study aims at carrying out an emission/performance experimental analysis to evaluate and compare the use of pure Biodiesel obtained from different sources: castor, soybean, and palm oil, in a 30 kW regenerative Diesel one shaft gas microturbine engine installed in the laboratories of the Federal University of Itajubá—UNIFEI, Brazil, at steady state condition and at different level loads. A comparison study with the obtained results for Biodiesel and Diesel was carried out for all cases. There were no significant changes in the performance of the microturbine that reached thermal efficiency levels of about 26%. The minimum heat rate obtained at full load was for the Biodiesel fuel from palm oil and the maximum was for castor oil, with a value 8.38% higher than the Diesel fuel. In addition, a slight rise in CO and a reduction in the NOx concentrations were observed.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Transport/Pipelines/Multiphase Flow

J. Energy Resour. Technol. 2011;133(2):023001-023001-10. doi:10.1115/1.4004264.

Predicting erosion resulting from the impact of solid particles such as sand is a difficult task, since it is dependent on so many factors. The difficulty is compounded if the particles are entrained in multiphase flow. Researchers have developed models to predict erosion resulting from solid particles in multiphase flow that account for a variety of factors. However, no model currently accounts for the flow orientation on the severity of erosion. This work provides three sets of experimental results that demonstrate pipe orientation can have a significant impact on the amount of erosion for annular flow. A semimechanistic model to predict erosion in annular flow is also outlined that accounts for the upstream flow orientation.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Wells-Drilling/Production/Construction

J. Energy Resour. Technol. 2011;133(2):023101-023101-9. doi:10.1115/1.4004027.

Recent laboratory and field studies indicated that polymer-based in situ gelled acids can cause formation damage. Coreflood experiments using single-stage and multistage acids were conducted at 250 °F. 15 wt. % regular HCl and 5 wt. % in situ gelled acid-based on Fe(III) as a crosslinker were the acids that were used in this study. Propagation of acids and crosslinker inside 20 in. long cores was examined for the first time in detail. Stage volume and injection rate, which were the parameters that affect the propagating of various chemical species, were examined. Samples of the core effluent were collected and the concentrations of calcium, crosslinker, and acid were measured. Material balance was conducted to determine the amount of cross-liker that retained in the core. The results show that in situ gelled acid should be pumped at low injection rates. In situ gelled acid at low injection rate instantaneously plugged the tip of the wormhole and did not create additional wormholes inside the core. Therefore, when the final regular acid stage bypassed the gel, it started to propagate from nearly the last point that the first stage ended. In site gelled acid stage volume should not exceed 0.5 PV. No benefits were gained by increasing the volume of in situ gelled acids. Retention of total iron in the core increased in multistage acid treatments, especially at low acid injection rates.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;133(2):023102-023102-10. doi:10.1115/1.4004026.

Barite Sag is the settling of barite particles in the wellbore (or other weighting materials), which results in undesirable fluctuations in drilling fluid density. A variety of major drilling problems including lost circulation, well control difficulties, poor cement jobs, and stuck pipe can result from uncontrolled barite sag. Study of this phenomenon and how to mitigate its effects has long been of interest. This paper describes a fundamental mathematical approach to analyze the settling of barite particles in shear flow of Newtonian fluids. A set of four coupled partial differential equations to describe dynamic barite sag in Newtonian fluids in pipe flow is obtained by applying mass and momentum conservation for solid and liquid phase. Solid concentration in axial and radial directions as a function of time is calculated by using an explicit numerical method to solve these equations. A number of experiments in a flow loop were conducted to verify the mathematical model. Two mass flow meters were installed at the inlet and outlet of the flow loop’s test section. Differences in the density measurements over time were converted to the solid accumulation, which was compared with results from the modeling. In addition, based on the experimental results, three different stages of barite accumulation due to the settling and bed pickup of barite particles during circulation will be presented. The proposed methodology and results of this study will help drillers have a better understanding in terms of undesirable density fluctuations and barite bed characteristics.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;133(2):023103-023103-10. doi:10.1115/1.4004265.

The mechanism of atomization of part of the liquid film to form drops in annular two-phase flow is not entirely understood. It has been observed that drop creation only occurs when there are large disturbance waves present on the film interface. (Woodmansee and Harrantty, 1969, “Mechanisms for the Removal of Droplets From a Liquid Surface by a Parallel Air Flow,” Chem. Eng. Sci., 24 , pp. 299–307) observed that ripples on these waves were precursors to drops. Though it has been reported that drops occur in bursts by (Azzopardi, Gas-Liquid Flows Begell House Inc., New York, 2006), all previous drop size or concentration measurements have always been time integrated to simplify data analysis. Dynamic time averaged drop size measurements are reported for the first time in annular flow. Experiments were carried out on a 19 mm internal diameter vertical pipe with air and water as fluids. Spraytec, a laser diffraction-based, drop size measurement instrument, was used in the drop related data acquisition. Simultaneous time-resolved measurements were carried out for drop, film thickness, and pressure drop. Film thickness has been measured using the conductance probes employing a pair of flush mounted rings as electrodes. Pressure drop was logged using differential pressure cell connected to two pressure taps located within the test section. The gas superficial velocity was varied systematically from 13 to 43 m/s at fixed liquid superficial velocities of 0.05 and 0.15 m/s, respectively. Additional tests were carried out with the gas velocity fixed at 14 m/s while the liquid superficial velocity was varied from 0.03 to 0.18 m/s. Signal acquired are presented in form of time series to permit data analysis at different levels. Based on signal analysis, interrelationships between liquid film where the drops are sourced and the contribution of the entrained liquid droplets to the overall pressure drop in the system has been elucidated. Though structures are not clearly visible in the signals acquired, the time series have been analyzed in amplitude space to yield probability density function (Pdf). Beyond gas superficial velocity of 30 m/s, Pdf of drop size distribution becomes monomodal or single-peaked marking transition to mist annular flow.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Energy Resour. Technol. 2011;133(2):024501-024501-3. doi:10.1115/1.4003882.

A boiler or steam generator is a device used to create steam by applying heat energy to water. Compact boilers are specially designed to generate unlimited amount of steam in short time span for home appliance applications. The main objective of the present work is to analyze pressure behavior of a compact boiler when heat energy is applied under closed-open-closed system conditions (saturation pressure condition) and to study the characteristic behavior of water during the transition between liquid and vapor phases. This experiment investigates the pressure-temperature relationship at constant volume when the system reaches saturation point. This experiment also investigates the effect of suction pressure (saturation pressure at room temperature) on the system during the cold start condition and possible solutions to overcome the undesired final effect. Also, experiments are conducted on a small scale of the equipment and used as a base line values for the current experiments.

Commentary by Dr. Valentin Fuster

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