Research Papers: Air Emissions From Fossil Fuel Combustion

J. Energy Resour. Technol. 2011;134(1):011101-011101-9. doi:10.1115/1.4005243.

This paper presents the oxides of nitrogen (NOx ) and nitrous oxide (N2 O) emission characteristics of a Cooperative Fuel Research (CFR) engine modified to operate in homogeneous charge compression ignition (HCCI) combustion mode. N-heptane was used as the fuel in this research. Several parameters were varied, including intake air temperature and pressure, air/fuel ratio (AFR), compression ratio (CR), and exhaust gas recirculation (EGR) rate, to alter the HCCI combustion phasing from an overly advanced condition where knocking occurred to an overly retarded condition where incomplete combustion occurred with excessive emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO). NOx emissions below 5 ppm were obtained over a fairly wide range of operating conditions, except when knocking or incomplete combustion occurred. The NOx emissions were relatively constant when the combustion phasing was within the acceptable range. NOx emissions increased substantially when the HCCI combustion phasing was retarded beyond the optimal phasing even though lower combustion temperatures were expected. The increased N2 O and UHC emissions observed with retarded combustion phasing may contribute to this unexpected increase in NOx emissions. N2 O emissions were generally less than 0.5 ppm; however, they increased substantially with excessively retarded and incomplete combustion. The highest measured N2 O emissions were 1.7 ppm, which occurred when the combustion efficiency was approximately 70%.

Commentary by Dr. Valentin Fuster

Research Papers: Co-generation/Systems

J. Energy Resour. Technol. 2011;134(1):011301-011301-8. doi:10.1115/1.4005082.

This paper presents an analytic approach for defining optimal operation decisions for a power generation unit (PGU) in combined heating and power (CHP) systems. The system is optimized with respect to cost, and the independent variables are the thermal load and the electric load. Linear programming is a common tool used to find the optimal PGU operation for a given combination of thermal and electric loads, but these methods are more computationally intensive than the analytical approach proposed in this paper. The analytic process introduced in this paper shows that the optimal PGU operation for all possible thermal and electric loads can be decided by simple and explicit equations even when the efficiency of the PGU is allowed to vary with PGU loading. Moreover, the analysis reveals that for all possible load conditions, the optimal CHP system operation is based on either following the electric load (FEL) or following the thermal load (FTL) strategies. The cost ratio, i.e., the ratio of the electricity price to the fuel price, is introduced as the key parameter used for making optimal decisions. Cost ratios in Chicago, IL and Philadelphia, PA are used as case studies to show the effect that different cost ratios have on the optimal operation decisions for each possible input load.

Commentary by Dr. Valentin Fuster

Research Papers: Energy From Biomass

J. Energy Resour. Technol. 2011;134(1):011801-011801-6. doi:10.1115/1.4005245.

Most of the current production cost in algae biodiesel plants utilizing photobioreactors comes from the high energy required for pumping, CO2 transfer, mixing, and harvesting. Since pumping affects the mixing and CO2 transfer, which are the main factors in algae productivities, solutions to reduce the required energy for pumps can significantly make algae biodiesel production more economically feasible. An investigation on the effect of Scenedesmus obliquus’s growth from low to high biomass concentration inside a horizontal tubular photobioreactor to determine the impact that it has on hydrodynamic performances, which will affect cost and production efficiency, was performed. As the biomass concentration increased, the algal culture was found to remain Newtonian. Additionally, the biomass concentration (expressed in cell density) was found to have lower viscosity even at the highest concentrations evaluated at 2.48 × 108 cell/ml (1.372 × 10−3  ± 1.32 × 10−4 Pa s) compared to the Modified Bold’s 3N medium (1.408 × 10−3  ± 9.41 × 10−5 Pa s). Furthermore, the total energy consumption does not appear to depend on the S. obliquus biomass concentrations, but rather on the medium the algae grows in. The rheological properties of autotrophic algae will not have significant impact on energy requirements until technology improves so that the concentrations reach those of heterotrophic algae.

Commentary by Dr. Valentin Fuster

Research Papers: Hydrogen Energy

J. Energy Resour. Technol. 2012;134(1):012601-012601-15. doi:10.1115/1.4005246.

With emission legislations getting more stringent in order to comply with the responsibilities of environmental obligations, engine manufacturers are turning to explore new avenues to meet the paradox of curtailing particulate matter (PM) and NOx emissions on one hand and maintaining consumer expectations of reduced fuel consumption and increased thermal efficiency on the other. Studies dedicated in mitigating such paradoxical objectives have established novel emission reduction systems such as the diesel particulate filter (DPF) and selective catalytic reduction (SCR) after treatment systems but at the expense of increased complexity of deployment and cost. The present work explores the emission and performance characteristics of an existing four stroke single cylinder engine operating with a predefined flow rate of hydrogen as a dual fuel. The hydrogen was premixed with the incoming air and inducted during the duration of intake valve opening by means of an indigenously developed cam actuated electromechanical timed manifold injection technique. exhaust gas recirculation (EGR) (hot and cooled) technique has been implemented in the present work to reduce NOx emissions which were enriched with the same amount of hydrogen. Research studies carried out on the efficacy of EGR techniques have reported the inherent penalty of increasing the common diesel pollutants of smoke and particulate matter and fuel consumption at the expense of reducing NOx emissions. Trade-off studies in the present work revealed contrary results, where 20% cooled EGR under hydrogen enrichment registered a decrease of 9.2% and 12.3% in NOx emissions at 60% and 80% load as compared to diesel operation while simultaneously retaining a reduction of 4.6% and 1.9% in brake specific energy consumption (BSEC) along with 10% and 8.33% corresponding decrease in smoke emissions and a reduction of 11.30% and 12.31% in total unburnt hydrocarbon (TUHC) emissions. CO emissions were simultaneously decreased by 26.6% and 20.0% while CO2 emissions decreased by 24.5% and 29.1%, respectively, while maintaining 4.8% and 2% increase in brake thermal efficiency and a reduction of 23.3% and 18.95% in specific fuel consumption (SFC) (diesel) simultaneously at the respective loads. Similar trade-off potential, as was evident in the 10% EGR strategies, provide a strong motivation to explore the role of hydrogen as in situ dual fuel solution to counter the conflicting emission and performance requirements of contemporary diesel engines made to operate under EGR.

Commentary by Dr. Valentin Fuster

Research Papers: Petroleum Wells-Drilling/Production/Construction

J. Energy Resour. Technol. 2011;134(1):013101-013101-9. doi:10.1115/1.4005239.

Sand control by hydraulic fracturing in high permeable gas formation is becoming an increasingly popular completion option. This improves the well’s productivity as well as manages the sand production. So, optimizing the treatment parameters for hydraulic fracturing, which can prevent most unfavorable effects, one of them being sand production, is now a critical process to be programmed systematically with all realistic design constraints. This paper describes the development of an integrated program with global optimization algorithms that optimize all treatment parameters simultaneously; maximizing objective function (net present value) and satisfying newly modeled design constraints. These constraints are formulated as functions of treatment parameters, fracture geometry, and mechanical and petrophysical properties of the reservoir, so that the critical conditions that induce sand production and other unfavorable effects do not become active. One of the important constraints is the critical drawdown pressure (CDP) relating to sand production. A genetic-evolutionary computing algorithm is integrated to solve the constrained treatment design problem that it finds optimum values for treatment parameters and fracture geometry that are formation compatible. The capability of the integrated model is demonstrated by application to a hypothetical gas reservoir and predicting the production and CDP over a number of years, helping sand control. When compared with the proposed model, the traditional model violates some important constraints.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;134(1):013102-013102-6. doi:10.1115/1.4005284.

Liquid loading has been a problem in natural gas wells for several decades. With gas fields becoming mature and gas production rates dropping below the critical rate, deliquification becomes more and more critical for continuous productivity and profitability of gas wells. Current methods for solving liquid loading in the wellbore include plunger lift, velocity string, surfactant, foam, well cycling, pumps, compression, swabbing, and gas lift. All these methods are to optimize the lifting of liquid up to surface, which increases the operating cost, onshore, and offshore. However, the near-wellbore liquid loading is critical but not well understood. Through numerical reservoir simulation studies, effect of liquid loading on gas productivity and recovery has been quantified in two aspects: backup pressure and near-wellbore liquid blocking by considering variable reservoir permeability, reservoir pressure, formation thickness, liquid production rate, and geology. Based on the new knowledge, we have developed well completion methods for effective deliquifications. These lead to better field operations and increased ultimate gas recovery.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 2011;134(1):013103-013103-7. doi:10.1115/1.4005324.

There have been papers that analyze the relationship between bit design and a bit’s vibrational characteristics. These papers typically are based on the analysis of three-axis near-bit down-hole vibration sensors. In this paper, the authors take a simpler approach. Using a standard microphone literally pointed at the bit, they record the noise of the bit/rock interaction while drilling and analyze the resulting noise for these bit vibrational characteristics. The data were gathered at the Colorado School of Mines in Golden, CO. The noise of a PDC core, roller cone, and diamond core bits were recorded under various weight and rotary speeds using a microphone and a vertically mounted uniaxial geophone (used for confirming the data recorded on the microphones). Using a Fast Fourier Transform, the frequency spectra were extracted from the recorded data and analyzed. The data were normalized for rotational speed. The results of the frequency analysis of the roller cone, the PDC, and the natural diamond bits are presented in this paper. The major differences in the three bit frequency characteristics could be detected and furthermore, for drag bits, the frequency characteristics could be related to the bit’s design. The frequency spectra of the roller cone bit can best be described with a general high amplitude level that is relatively evenly distributed over the whole frequency spectrum. The drag bit data showed a strong relationship between the number and arrangement of cutting elements and frequency peaks on a plot of amplitude versus cycles per revolution. Frequency peaks were observed at multiples of the number of cutting elements. In general this relationship was strongly visible on the PDC bit data but not as strongly visible on the diamond bit data. The conclusion is that bit characteristics can be determined using only the noise of a bit. Potential applications of this research include detecting and diagnosing bit problems (e.g., broken teeth and bit balling) in real time using simple microphone based acoustic data.

Commentary by Dr. Valentin Fuster

Technical Briefs

J. Energy Resour. Technol. 2011;134(1):014501-014501-6. doi:10.1115/1.4005244.

The idea of pushing the limits of drilling oil and gas wells by improving drilling fluids for undemanding and cost efficient drilling operations by extracting advantage from the wonders of nanotechnology forms the basis of the work presented here. Foremost, in order to highlight the significance of reducing the size distribution of particles, new clay ATR which has a chain like structure and offers enormous surface area and increased reactivity was tested in different sizes that were chemically and mechanically milled. Bentonite which is a commonly used drilling fluid additive was also tested in different particle size distribution (PSD) and rheological properties were tested. Significant reduction in viscosity with small sized particles was recorded. The tested material called ATR throughout this paper is shown to offer better functionality than bentonite without the requirement of other expensive additives. Experiments were performed with different size distributions and compositions and drastic changes in rheological properties are observed. A detailed investigation of the shear thinning behavior was also carried out with ATR samples in order to confirm its functionality for eliminating the problem of mechanical and differential pipe sticking, while retaining suitable viscosity and density for avoidance of problems like lost circulation, poor hole cleaning and inappropriate operating hydrostatic pressures.

Commentary by Dr. Valentin Fuster

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