Accepted Manuscripts

Qiang Zhang, Ryan M. Ogren and Song-Charng Kong
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036766
Modern diesel engines are charged with the difficult problem of balancing emissions and efficiency. For this work, a variant of the Artificial Bee Colony algorithm was applied for the first time to the experimental optimization of diesel engine combustion and emissions. In this study, the employed and onlooker bee phases were modified to balance both the exploration and exploitation of the algorithm. The improved algorithm was successfully trialed against Particle Swarm Optimization (PSO), Genetic Algorithm (GA) and a recently proposed PSO-GA hybrid with three standard benchmark functions. For the engine experiments, six variables were changed throughout the optimization process, including exhaust gas recirculation rate, intake temperature, quantity and timing of pilot fuel injections, main injection timing, and fuel pressure. Low sulfur diesel fuel was used for all tests. In total, sixty-five engine runs were completed in order to reduce a five-dimensional objective function. In order to reduce nitrogen oxide emissions while keeping PM below 0.09 g/kW-h, solutions call for 43% exhaust gas recirculation, with a late main fuel injection near top-dead-center. Results show that early pilot injections can be used with high exhaust gas recirculation to improve the combustion process without a large nitrogen oxide penalty when main injection is timed near top-dead center. The emission reductions in this work show the improved ABC algorithm presented here to be an effective new tool in engine optimization.
TOPICS: Fuels, Algorithms, Optimization, Diesel engines, Emissions, Exhaust gas recirculation, Particle swarm optimization, Engines, Combustion, Nitrogen oxides, Sulfur, Pressure, Temperature, Genetic algorithms, Diesel
Jose Eugenio Torres Carmona
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036685
The present study analysed the potential re-utilization and integration of the Heat Recovery Steam Generator (HRSG) blow-down into the evaporative cooling system. The Ras Al Khair Power and Desalination plant owned and operated by the Saline Water Conversion Corporation, located in the Eastern Province of the Kingdom of Saudi Arabia, was used as case study. The results indicates that during the summer season recycling the HRSG water blowdown into the gas turbine evaporative cooling systems would result on the internal water consumption for the gas turbine evaporative coolers decreasing by 545 ton/day , or 23.79%, compared with the original plant design which does not contemplate blowdown re-use. At the same time, by means of using the saved blowdown water on the evaporative cooling system of the plant, there is an overall gain of 186 MW, or 10.27 %, on gross power output, compared with the case on which the evaporative cooling system is not in operation. At the same time, and because of the reduction in fuel consumption resulting from the use of evaporative cooling, the CO2 emissions decrease by 46.8 t CO2/h which represents an 13.8 % reduction, if compared with the additional extra fuel needed to generate the equivalent power produced without evaporative cooling. Cost analysis demonstrated that implementation of the changes results in a negligible increase of the operational expenses (OPEX) of the plant, i.e. implementation of the suggested modification has no impact on the Cost of Electricity (CoE).
TOPICS: Evaporative cooling, Water reuse, Power stations, Heat recovery steam generators, Water, Gas turbines, Carbon dioxide, Coolers, Recycling, Fuels, Fuel consumption, Plant design, Emissions
Bader Almansour, Subith Vasu, Sreenath B. Gupta, Qing Wang, Robert Van Leeuwen and Chuni Ghosh
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036621
Market demands for lower fueling costs and higher specific powers in stationary natural gas engines has engine designs trending towards higher in-cylinder pressures and leaner combustion operation. However, Ignition remains as the main limiting factor in achieving further performance improvements in these engines. Addressing this concern, while incorporating various recent advances in optics and laser technologies, laser igniters were designed and developed through numerous iterations. Final designs incorporated water-cooled, passively Q-switched, Nd:YAG micro-lasers that were optimized for stable operation under harsh engine conditions. Subsequently, the micro-lasers were installed in the individual cylinders of a lean-burn, 350 kW, inline 6-cylinder, open-chamber, spark ignited engine and tests were conducted. The engine was operated at high-load (298 kW) and rated speed (1800 rpm) conditions. Ignition timing sweeps and excess-air ratio (Lambda) sweeps were performed while keeping the NOx emissions below the USEPA regulated value (BSNOx < 1.34 g/kW-hr), and while maintaining ignition stability at industry acceptable values (COV_IMEP <5 %). Through such engine tests, the relative merits of (i) standard electrical ignition system, and (ii) laser ignition system were determined. A rigorous combustion data analysis was performed and the main reasons leading to improved performance in the case of laser ignition were identified.
TOPICS: Lasers, Cylinders, Gas engines, Engines, Ignition, Combustion, Ignition systems, Emissions, Engine design, Q-switching, Water, Nitrogen oxides, Stress, Stability, Optics
Qilun Zhu, Robert Prucka, Michael Prucka and Hussein Dourra
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036622
The need for cost-effective fuel economy improvements has driven the introduction of automatic transmissions with an increasing number of gear ratios. Incorporation of interlocking dog clutches in these transmissions decreases package space and increases efficiency, as compared to conventional dry or wet clutches. Unlike friction based clutches, interlocking dog clutches require very precise rotational speed matching prior to engagement. Precise engine speed control is therefore critical to maintaining high shift quality. This research focuses on controlling the engine speed during a gearshift period by manipulating throttle position and combustion phasing. Model predictive control (MPC) is advantageous in this application since the speed profile of a future prediction horizon is known with relatively high confidence. The MPC can find the optimal control actions to achieve the designated speed target without invoking unnecessary actuator manipulation and violating hardware and combustion constraints. This research utilizes linear parameter varying (LPV) MPC to control the engine speed during the gearshift period. Combustion stability constraints are considered with a control oriented covariance of indicated mean effective pressure model (COV of IMEP). The proposed MPC engine speed controller is validated with a high-fidelity 0-dimensional engine model with crank angle resolution. Four case studies, based on simulation, investigate the impact of different MPC design parameters. They also demonstrate that the proposed MPC engine controller successfully achieves the speed reference tracking objective while considering combustion variation constraints.
TOPICS: Engines, Combustion, Control equipment, Pressure, Stability, Friction, Corporate average fuel economy, Simulation, Hardware, Resolution (Optics), Actuators, Design, Gears, Optimal control, Predictive control, Fuel efficiency
Shuonan Xu, Hirotaka Yamakawa, Keiya Nishida and Zoran Filipi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036575
Diesel engines dominate the heavy duty market and significant segments of the global light duty market due to their intrinsically high thermal efficiency. Predictive simulation tools significantly reduce the time and cost associated with optimization of engine controls, and enable investigation over a broad operating space. Quasi-D models offer a balance between predictiveness and computational effort, thus making them very suitable for enhancing the fidelity of engine system simulation tools. A most widely used approach for diesel engine applications is a multi-zone spray and combustion model pioneered by Hiroyasu and his group. It divides diesel spray into packets and tracks fuel evaporation, air entrainment, gas properties and ignition delay (induction time) individually during the injection and combustion event. However, original sub-models are not well suited for modern diesel engines, and the main objective of this work is to develop a multi-zonal simulation capable of capturing the impact of high-injection pressures and Exhaust Gas Recirculation (EGR). In particular, a new spray tip penetration sub-model is developed based on measurements obtained in a high-pressure, high-temperature constant volume combustion vessel. Next, ignition delay correlation is modified to capture the effect of reduced oxygen concentration in engines with EGR, and an algorithm considering the chemical reaction rate of hydrocarbon-oxygen mixture improves prediction of the heat release rates. Spray and combustion predictions were validated with experiments on a single-cylinder diesel engine with common rail fuel injection, charge boosting, and EGR.
TOPICS: Heat, Combustion, Modeling, Sprays, Diesel, Diesel engines, Ignition delay, Exhaust gas recirculation, Engines, Simulation, Fuels, Oxygen, Vessels, Cylinders, Optimization, Electromagnetic induction, Chemical kinetics, High pressure (Physics), Algorithms, Evaporation, High temperature, Air entrainment, Common rail fuel injectors, Thermal efficiency
Daniele Massini, Emanuele Burberi, Carlo Carcasci, Lorenzo Cocchi, Bruno Facchini, Alessandro Armellini, Luca Casarsa and Luca Furlani
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036576
A detailed aerothermal characterization of an advanced leading edge cooling system has been performed by means of experimental measurements. Heat transfer coefficient distribution has been evaluated exploiting a steady-state technique using Thermocromic Liquid Crystals (TLC), while flow field has been investigated by means of Particle Image Velocimetry (PIV). The geometry key features are the multiple impinging jets and the four rows of coolant extraction holes, which mass flow rate distribution is representative of real engine working conditions. Tests have been performed in both static and rotating conditions, replicating a typical range of jet Reynolds number (Rej), from 10000 to 40000, and Rotation number (Roj) up to 0.05. Different cross-flow conditions (CR) have been used to simulate the three main blade regions (i.e. tip, mid and hub). The aerothermal field turned out to be rather complex, but a good agreement between heat transfer coefficient and flow field measurement has been found. In particular, jet bending strongly depends on crossflow intensity, while rotation has a weak effect on both jet velocity core and area-averaged Nusselt number. Rotational effects increase for the lower cross-flow tests. Heat transfer pattern shape has been found to be substantially Reynolds-independent.
TOPICS: Rotation, Cooling systems, Gas turbines, Blades, Flow (Dynamics), Heat transfer coefficients, Cross-flow, Geometry, Shapes, Steady state, Heat transfer, Liquid crystals, Particulate matter, Engines, Reynolds number, Coolants, Jets
Thomas R. Powell, Ryan O'Donnell, Mark A. Hoffman and Zoran Filipi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036577
In-cylinder surface temperature has significant impacts on the thermo-kinetics governing the Homogeneous Charge Compression Ignition (HCCI) process. Thermal Barrier Coatings (TBCs) enable selective manipulation of combustion chamber surface temperature profiles throughout a fired cycle. In this way, TBCs enable a dynamic surface temperature swing, which prevents charge heating during intake while minimizing heat rejection during combustion. This preserves volumetric efficiency while fostering more complete combustion and reducing emissions. This study investigates the effect of a Yttria-Stabilized Zirconia (YSZ) coating on Low Temperature Combustion (LTC) engine combustion, efficiency, and emissions. This is an initial step in a systematic effort to engineer coatings best suited for LTC concepts. A YSZ coating was applied to the top of the aluminum piston using a powder Air Plasma Spray process, Final thickness of the coatings was approximately 150 microns. The coated piston was subsequently evaluated in the single-cylinder HCCI engine with exhaust re-induction. Engine tests indicated significant advancement of the autoignition point and reduced combustion durations with the YSZ coating. Hydrocarbon and carbon monoxide emissions were reduced, thereby increasing combustion efficiency. The combination of higher combustion efficiency and decreased heat loss during combustion produced tangible improvements in thermal efficiency. When the effects of combustion advance were removed, the overall improvements in emissions and efficiency were lower, but still significant. Overall, the results encourage continued efforts to devise novel coatings for LTC.
TOPICS: Combustion, Thermal barrier coatings, Homogeneous charge compression ignition engines, Emissions, Coatings, Cylinders, Pistons, Temperature, Engines, Plasmas (Ionized gases), Combustion chambers, Carbon, Low temperature, Sprays, Cycles, Electromagnetic induction, Aluminum, Temperature profiles, Heating, Exhaust systems, Heat losses, Engineers, Thermal efficiency, Heat
Andrew Marshall, Julia Lundrigan, Prabhakar Venkateswaran, Jerry Seitzman and Tim Lieuwen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4035819
Fuel composition has a strong influence on the turbulent flame speed, even at very high turbulence intensities. An important implication of this result is that the turbulent flame speed cannot be extrapolated from one fuel to the next using only the laminar flame speed and turbulence intensity as scaling variables. This paper presents curvature and tangential strain rate statistics of premixed turbulent flames for high hydrogen content fuels. Global (unconditioned) stretch statistics are presented as well as measurements conditioned on the leading points of the flame front. These measurements are motivated by previous experimental and theoretical work that suggests the turbulent flame speed is controlled by the flame front characteristics at these points. The data were acquired with high speed particle image velocimetry (PIV) in a low swirl burner (LSB). We attained measurements for several H2:CO mixtures over a range of mean flow velocities and turbulence intensities. The results show that fuel composition has a systematic, yet weak effect on curvatures and tangential strain rates at the leading points. Instead, stretch statistics at the leading points are more strongly influenced by mean flow velocity and turbulence level. It has been argued that the increased turbulent flame speeds seen with increasing hydrogen content are the result of increasing flame stretch rates, and therefore SL,max values, at the flame leading points. However, the differences observed with changing fuel compositions are not significant enough to support this hypothesis. Additional analysis is needed to understand the physical mechanisms through which the turbulent flame speed is altered by fuel composition effects.
TOPICS: Fuels, Flames, Hydrogen, Statistics as topic, Turbulence, Flow (Dynamics), Particulate matter
Klaus Brun, Rainer Kurz and Sarah Simons
J. Eng. Gas Turbines Power   doi: 10.1115/1.4034314
Pressure pulsations into a centrifugal compressor can move its operating point into surge. This is concerning in pipeline stations where centrifugal compressors operate in series/parallel with reciprocating compressors. Sparks (1983), Kurz et al., (2006), and Brun et al., (2014) provided predictions on the impact of periodic pressure pulsation on the behavior of a centrifugal compressor. This interaction is known as the “Compressor Dynamic Response” (CDR) theory. Although the CDR describes the impact of the nearby piping system on the compressor surge and pulsation amplification, it has limited usefulness as a quantitative analysis tool, due to the lack of prediction tools and test data for comparison. Testing of compressor mixed operation was performed in an air loop to quantify the impact of periodic pressure pulsation from a reciprocating compressor on the surge margin of a centrifugal compressor. This data was utilized to validate predictions from Sparks' CDR theory and Brun's numerical approach. A 50 hp single-stage, double-acting reciprocating compressor provided inlet pulsations into a two-stage 700 hp centrifugal compressor. Tests were performed over a range of pulsation excitation amplitudes, frequencies, and pipe geometry variations to determine the impact of piping impedance and resonance responses. Results provided clear evidence that pulsations can reduce the surge margin of centrifugal compressors and that geometry of the piping system immediately upstream and downstream of a centrifugal compressor will have an impact on the surge margin reduction. Surge margin reductions of <30% were observed for high centrifugal compressor inlet suction pulsation.
TOPICS: Compressors, Surges, Pressure, Pipes, Geometry, Piping systems, Testing, Dynamic response, Suction, Pipelines, Excitation, Resonance
shilpi agarwal, Puneet Rana and B. S. Bhadauria
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028491
In this paper, we study the effect of local thermal non-equilibrium on the linear thermal instability in a horizontal layer of a Newtonian nanofluid. The nanofluid layer incorporates the effect of Brownian motion along with thermophoresis. A two-temperature model has been used for the effect of local thermal non-equilibrium among the particle and fluid phases. The linear stability is based on normal mode technique and for nonlinear analysis, a minimal representation of the truncated Fourier series analysis involving only two terms has been used. We observe that for linear instability, the value of Rayleigh number can be increased by a substantial amount on considering a bottom heavy suspension of nano particles. The effect of various parameters on Rayleigh number has been presented graphically. A weak nonlinear theory based on the truncated representation of Fourier series method has been used to find the concentration and the thermal Nusselt numbers. The behavior of the concentration and thermal Nusselt numbers is also investigated by solving the finite amplitude equations using a numerical method.
TOPICS: Equilibrium (Physics), Nanofluids, Rayleigh-Benard convection, Fourier series, Rayleigh number, Nanoparticles, Numerical analysis, Stability, Temperature, Fluids, Particulate matter, Brownian motion
Corey E. Clifford and Mark Kimber
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028492
Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for free cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this study, a numerical model of a heated horizontal cylinder confined between two, vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the pseudo-unconfined cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.
TOPICS: Heat, Natural convection, Cylinders, Storage, Heat transfer, Rayleigh number, Heat flux, Fuels, Safety, Computer simulation, Cooling, Temperature, Flow (Dynamics), Buoyancy, Spent nuclear fuels, Convection, Boundary-value problems

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