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Research Papers: Fuel Combustion

J. Energy Resour. Technol. 2009;131(1):012201-012201-9. doi:10.1115/1.3066345.

This paper presents the experimental testing of relatively cost-effective expanders in an organic Rankine cycle (ORC) to produce power from low-grade energy. Gerotor and scroll expanders were the two types of expanders tested to determine their applicability in producing power from low-grade energy. The results of the experimental testing showed that both types of expanders were good candidates to be used in an ORC. The gerotor and scroll expanders tested produced 2.07 kW and 2.96 kW, and had isentropic efficiencies of 0.85 and 0.83, respectively. Also the paper presents results of an analytical model produced that predicted improved cycle efficiency with certain changes. One change was the flow rate of the working fluid in the cycle was properly matched with the inlet pocket volume and rotational speed of the expander. Also, the volumetric expansion ratio of the expander was matched to the specific volume ratio of the working fluid (R-123) across the expander. The model incorporated the efficiencies of the expanders and pump obtained during experimental testing, and combined two expanders in series to match the specific volume ratio of the working fluid. The model determined the power produced by the expanders, and subtracted the power required by the working fluid pump and the condenser fan. From that, the model calculated the net power produced to be 6271 W and the overall energy efficiency of the cycle to be 7.7%. When the ORC was simulated to be integrated with the exhaust of a stationary engine, the exergetic efficiency, exergy destroyed, and reduction in diesel fuel while still producing the same amount of power during 2500 h of operation were 22.1%, 22,169 W, and 4,012 L (1060 U.S. gal), respectively. Consequently, the model presents a very realistic design based on results from experimental testing to cost-effectively use low-grade energy.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2009;131(1):012202-012202-9. doi:10.1115/1.3068345.

As a result of decreasing petroleum supplies, new fuel sources, such as transesterified biofeedstock based oils and their blends with petroleum diesel fuels, have emerged with potential to partially replace conventional diesel and gasoline fuels. Although these fuels have shown some promising results in engine studies, their basic combustion properties have not been well documented. Also, research is underway to develop new fuels from other sources or by altering their molecular structure to be fungible with conventional fuels. Thus, there is a need for tests to characterize the combustion and emission properties of these new liquids, which are available only in small quantities at the research and development stage. This paper deals with a technique that meets those goals. The fuel was prevaporized and mixed with air and burnt in a tubular burner (9.5 mm inner diameter) at atmospheric pressure under laminar conditions. A pilot methane/air flame was used as the ignition source. The test conditions were so chosen that the measured properties could be attributed primarily to the fuel chemical structure. Several liquid fuels were tested, including commercially available petroleum-based No. 2 diesel fuel, canola methyl ester (CME B100) biodiesel, kerosene, methanol, toluene, and selected alkanes. The radiative heat flux from the flames was measured using a wide-angle pyrheliometer; the emissions from the flames were sampled to measure the concentration of CO, $CO2$, and NO. The measured radiant heat fraction values and the emission indices of NO and CO of both petroleum-derived and biofuels agreed well with those found in literature; thus, the feasibility of this method to rapidly characterize the combustion and emission properties of new liquids, such as biofuels, is demonstrated.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2009;131(1):012203-012203-4. doi:10.1115/1.3068347.

Performance and emission testing for a single cylinder four-stroke diesel engine have been experimentally performed to determine the optimum operation conditions for this engine when it is used as a hybrid power unit. The studied operation parameters included brake specific fuel consumption (BSFC), exhaust emission ($NOx$, CO, $CO2$, and $O2$), and engine life. The results indicate that the lowest BSFC of the engine was found when the engine runs around 1 kW charging load at speed ranged between 1900 rpm and 2700 rpm. As the speed of the engine is maintained constant, the minimum level of BSFC is below $300 g/kW h$ at around 1900 rpm. The best engine operation conditions, for low emission, are found at engine speed around 2500 rpm. It was found that the oxides of nitrogen remain within the acceptable level (below 180 ppm) for such a diesel engine. The battery charge has been conducted at constant speeds, where the lubricant oil temperature was constant and always below maximum temperature; this is a good indication for longer engine life.

Commentary by Dr. Valentin Fuster

Research Papers: Heat Energy Generation/Storage/Transfer

J. Energy Resour. Technol. 2009;131(1):012401-012401-8. doi:10.1115/1.3066392.

It is a difficult technical challenge to design thermoelectric power generation systems that work optimally over a broad dynamic range of thermal input power. Conventional systems are designed to work optimally for a nominal operating condition, while maintaining the ability to operate at off nominal and extreme operating conditions without damage to the system. For systems that operate in a narrow range of thermal power conditions, thermoelectric waste heat recovery system design is simplified. However, for applications that do have a wide range of operating conditions, designs typically exhibit overall average efficiencies that are reduced by approximately 20% or more compared with that achievable for the thermoelectric material operating at peak efficiency. Both cars and trucks consume significant fuel at low mass flow rates. Since the ultimate goal of waste heat recovery systems is to minimize fuel consumption, it is critical that the recovery system be designed to operate near peak efficiency over the range of mass flow rates that make a significant contribution to overall power recovery. Such performance capability is especially important in city driving, and in hybrid vehicle applications. This paper describes a design concept that maximizes the performance for thermoelectric power generation systems in which the thermal power to be recovered is from a fluid stream (e.g., exhaust gas) subject to varying temperatures and a broad range of exhaust flow rates. The device is constructed in several parts, with each part optimized for a specific range of operating conditions. The thermoelectric system characteristics, inlet mass flow rates and fluid temperatures, and load and internal electrical resistances are monitored and generator operation is controlled to maximize performance. With this design, the system operates near optimal efficiency for a much wider range of operating conditions. Application of the design concept to an automobile is used to show the benefits to overall system performance.

Commentary by Dr. Valentin Fuster

Research Papers: Hydrates/Coal Bed Methane/Heavy Oil/Oil Sands/Tight Gas

J. Energy Resour. Technol. 2009;131(1):012501-012501-4. doi:10.1115/1.3068338.

Oil shale samples from the Ellajjun area south of Jordan were pyrolyzed in different conditions and environments. Sulfur of shale oil was determined using x-ray fluorescence (XRF). Generated products swept from the retort by several sweeping media; they include nitrogen, water vapor, hydrogen, and mixture of nitrogen and water vapor. Other conditions are 2–11 mm particle size, 1 atm operating pressure, and $410–550°C$ temperature range. The sulfur content of shale oil was found to be $12 wt %$ for hydrogen pyrolysis, while water vapor at 1 atm decreased this value to $7 wt %$. Hydrogenation of oil shale resulted in $12 wt %$. the sulfur content of shale oil being at $420°C$, and then reduced to $10.3 wt %$ at temperatures higher than $470°C$. When water vapor is added to nitrogen, the sulfur in the oil shale is increased by $4 wt %$. Water vapor sweeping gas increased the sulfur of the shale oil from $6.5 wt %$ to $8.1 wt %$ compared with a nitrogen pyrolyzing medium. Retorted shale analysis showed $44 wt %$, and $31 wt %$ is left in the retorted shale of the original $4.5 wt %$. Sulfur found in the raw oil shale is unretorted for nitrogen and hydrogen sweeping gases. On the other hand, increasing particle size from 2 mm to 11 mm did not have any significant influence on the sulfur content of the produced shale oil.

Commentary by Dr. Valentin Fuster

Research Papers: Hydrogen Energy

J. Energy Resour. Technol. 2009;131(1):012601-012601-10. doi:10.1115/1.3068336.

In this paper, a novel approach of middle-temperature solar hydrogen production using methanol steam reforming is proposed. It can be carried out at around $200–300°C$, much lower than the temperatures of other solar thermochemical hydrogen production. For the realization of the proposed solar hydrogen production, solar experiments are investigated in a modified 5 kW solar receiver/reactor with one-tracking parabolic trough concentrators. The feature of significantly upgrading the energy level from lower-grade solar thermal energy to higher-grade chemical energy is experimentally identified. The interaction between the hydrogen yield and the energy-level upgrade of solar thermal energy is clarified. Also, this kind of solar hydrogen production is experimentally compared with methanol decomposition. The preliminarily economic evaluation of the hydrogen production is identified. As a result, in the solar-driven steam reforming, the thermochemical efficiency of solar thermal energy converted into chemical energy reached up to 40–50% under a mean solar flux of $550–700 W/m2$, and exceeding 90% of hydrogen production is achieved, with about 70% higher than that of methanol decomposition. The thermochemical performance of solar-driven methanol steam reforming experimentally examined at around $200–300°C$ for hydrogen production may be competitive with conventional methane reforming. The promising results obtained here indicate that the proposed solar hydrogen production may provide the possibility of a synergetic process of both high production of hydrogen and effective utilization of solar thermal energy at around $200–300°C$.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Wells-Drilling/Production/Construction

J. Energy Resour. Technol. 2009;131(1):013101-013101-7. doi:10.1115/1.3066412.

The expansion process subjects a solid tubular to large plastic deformations leading to variations in tubular thickness and length, which may result in premature and unexpected failures. It was noticed that the expansion process induces wall thickness imperfections due to excessive local plastic deformation as a result of mandrel sticking and slipping relative to the expanded tubular; such irregularities increase the probability of failure. Mandrel sticking may be the result of lack of enough lubrication, tubular surface irregularities, and the presence of welded and/or threaded connections, which require higher drawing force to push the mandrel forward. When the drawing force required to overcoming the maximum static friction and the mandrel forward motion is assured, the mandrel slips relative to the expanded tubular. This “stick-slip” phenomenon results in mandrel oscillations that affect the tubular response in terms of further reduction in thickness and may jeopardize the tubular capacity under normal operating field conditions. Therefore, the present work studies the mandrel dynamics and their effect on the tubular structural response. A mathematical model, which is an extension of the quasistatic tubular expansion analysis, has been developed to describe the dynamic friction effects of the stick-slip phenomenon. A special case of tubular expansion consisting of 25% expansion ratio of a 4/12 in. (114.3 mm) liner hanger was considered. It was found that the level of mandrel oscillations is in the order of 1–2 mm around its equilibrium position resulting in tubular thickness reduction of approximately 9% on top of its variation caused by the steady state expansion process. This increase in thickness reduction may affect the postexpansion collapse strength of the tubular.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2009;131(1):013102-013102-6. doi:10.1115/1.3066429.

This paper presents steady state productivity equations for a fully penetrating vertical well in the following three anisotropic systems: (a) sector fault, (b) channel, and (c) rectangular reservoir using a uniform line sink model. The new equations, which are based on conformal mapping method, are simple, accurate, and easy to use in field practice. If the well is in a sector fault reservoir, the productivity is a function of the angle of the sector, wellbore location angle, off-vertex distance, and drainage radius. If the well is in a channel reservoir with two parallel impermeable lateral boundaries, well flow rate reaches a maximum value when the well is located in the middle of the channel width. If the well is in a rectangular reservoir with constant pressure lateral boundaries, a new equation is provided to calculate the productivity of the well arbitrarily located in the anisotropic reservoir for the case where the flow rate of an off-center well is bigger than that of a centered well. It is concluded that, for a vertical well, different steady state productivity equations should be used in different reservoir geometries.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2009;131(1):013103-013103-10. doi:10.1115/1.3066367.

Ester-based drilling fluids based on aliphatic esters were introduced in 1990. Esters can be synthesized from fatty acids and alcohols. Previous studies indicated that ester hydrolysis in drilling fluids happens only under certain conditions. In order for ester hydrolysis to occur, two primary conditions must be present: high temperature and excessive hydroxyl. When the temperature exceeds $300°F$, ester hydrolysis can occur under the presence of excessive hydroxyl. Hydrolysis breaks down the ester component into its parent carboxylic acid and alcohol. The current study shows that the stability of ester-based drilling fluids at high temperature conditions depends on the composition so that the selection of proper components and additives such as emulsifiers, stabilizers, copolymers, viscosifiers, and rheological modifiers can increase the temperature stability of the fluid. Hereby, the application of an ester-based drilling fluid is improved up to $350°F$. The composition of the provided fluid is unique in the view point of its higher thermal stability against the previous formulations provided in literature. Furthermore, the experimental results of this study show the favorable effect of hot-rolling pressure on barite sag and electrical stability of the mud, i.e., increasing the pressure at three particular temperatures of $300°F$, $325°F$, and $350°F$ reduced the barite sag and at some instances increased the electrical stability.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2009;131(1):013104-013104-9. doi:10.1115/1.3000100.

Although the microhole coiled tubing drilling rigs have been used extensively in Canada, their application in the U.S. has been very limited. In an effort to introduce this technology to the U.S. operators, GTI, with the support of DOE∕NETL, has completed a successful field testing of the coiled tubing microhole drilling technology. In this paper we report results of field testing of the system in 25 wells drilled in the Niobrara unconventional gas play of Kansas and Colorado. The objective of the field test was to measure and document the rig performance under actual drilling conditions. In these tests, a coiled tubing drilling rig (designed and built by T Gipson with Advanced Drilling Technologies Inc.) was utilized. The rig operations have continued to improve to the point where it now drills a $3100ft$ well in a single day. Well cost savings of approximately 30% over conventional rotary well drilling have been documented. A description of the rig and a summary of its performance in the Niobrara unconventional gas play are included. In addition, an estimate of economic advantages of widespread application of microhole drilling technology in the lower 48 states is presented.

Topics: Drilling , Tubing
Commentary by Dr. Valentin Fuster

Discussions

J. Energy Resour. Technol. 2009;131(1):015501-015501-2. doi:10.1115/1.3068348.
FREE TO VIEW

For readers wanting to know how computational fluid dynamics (CFD) modeling might help the Stirling engine realize its full potential as a source of sustainable energy, the “closure” from Mahkamov in the December 2007 issue (1), may have proved somewhat disappointing.

Commentary by Dr. Valentin Fuster

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