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research-article  
Russell Prater and Yongsheng Lian
J. Eng. Gas Turbines Power   doi: 10.1115/1.4037128
Recent experiments have shown that the lateral motion of a high pressure injector needle can lead to significant asymmetrical flow in the sac and asymmetric spray pattern in the combustor, which in turn degrades the combustion efficiency and results in spray hole damage. However, the underlying cause of the lateral needle motion is not understood. In this paper we numerically studied the complex transient flow in a high pressure diesel injector using the detached eddy simulation to understand the cause of the lateral needle motion. The flow field was described by solving the compressible Navier-Stokes equations. The mass transfer between the liquid and vapor phases of the fuel was modeled using the Zwart-Gerber-Belamri equations. Our study revealed the vortical flow structures in the sac are responsible for the lateral needle motion and the hole-to-hole flow variation. The transient motion of the vortical structure also affected vapor formation variations in spray holes. Further analysis showed that the rotational speed of the vortical flow structure is proportional to the lateral force magnitude on the lower needle surfaces.
TOPICS: Flow (Dynamics), Simulation, High pressure (Physics), Ejectors, Diesel, needles, Sprays, Vortex flow, Vapors, Fuels, Eddies (Fluid dynamics), Mass transfer, Combustion, Transients (Dynamics), Combustion chambers, Navier-Stokes equations, Damage, Unsteady flow
research-article  
W.F. Fuls
J. Eng. Gas Turbines Power   doi: 10.1115/1.4037097
This paper studies the origin and applicability of the traditional Stodola ellipse law, and demonstrates it deficiencies when applied in certain conditions. It extends the equation by Cooke and Traupel through the definition a semi-ellipse law. This new law produces more accurate results as compared to the ellipse law, especially for turbines with a low number of stages. It does however require knowledge of the choking behavior of the turbine, as well as an appropriate pressure ratio exponent. Through numerical studies and the careful application of nozzle flow equations, correlations were developed to predict the critical pressure ratio of a multi-stage turbine, taking nozzle and blade efficiency into account. Correlations are also presented to obtain an appropriate pressure ratio exponent to use in the semi-ellipse law. A methodology is proposed through which the necessary semi-ellipse law terms can be calculated using only design base conditions, and estimates of efficiencies. This was successfully validated on a steam turbine. The semi-ellipse law is believed to be the most accurate way of modelling an axial-flow multi-stage steam or gas turbine from design base conditions, without requiring a stage-by-stage analysis.
TOPICS: Turbines, Modeling, Pressure, Design, Nozzles, Gas turbines, Flow (Dynamics), Axial flow, Blades, Steam, Steam turbines
research-article  
Svilen S. Savov, Nicholas. R. Atkins and Sumiu Uchida
J. Eng. Gas Turbines Power   doi: 10.1115/1.4037027
The effect of purge flow, engine-like blade pressure field and mainstream flow coefficient are studied experimentally for a single and double lip rim seal. Compared to the single lip, the double lip seal requires less purge flow for similar levels of cavity seal effectiveness. Unlike the double lip seal, the single lip seal is sensitive to overall Reynolds number, the addition of a simulated blade pressure field and large scale non-uniform ingestion. In the case of both seals, unsteady pressure variations attributed to shear layer interaction between the mainstream and rim seal flows appear to be important for ingestion at off-design flow coefficients. The double lip seal has both a weaker vane pressure field in the rim seal cavity and a smaller difference in seal effectiveness across the lower lip than the single lip seal. As a result, the double lip seal is less sensitive in the rotor-stator cavity to changes in shear layer interaction and the effects of large scale circumferentially non-uniform ingestion. However, the reduced flow rate through the double lip seal means that the outer lip has increased sensitivity to shear layer interactions. Overall, it is shown that seal performance is driven by both the vane/blade pressure field and the gradient in seal effectiveness across the inner lip. This implies that accurate representation of both, the pressure field and the mixing due to shear layer interaction would be necessary for more reliable modelling.
TOPICS: Pressure, Flow (Dynamics), Seals, Engines, Reynolds number, Shear (Mechanics), Design, Modeling, Rotors, Blades, Cavities, Stators
research-article  
Ivan Gogolev and James S. Wallace
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036968
Natural gas direct injection and glow plug ignition assist technologies were implemented in a single-cylinder, compression-ignition optical research engine. Initial experiments studied the effects of injector and glow plug shield geometry on ignition quality. Injector and shield geometric effects were found to be significant, with only two of 20 tested geometric combinations resulting in reproducible ignition. Of the two successful combinations, the combination with 0 degree injector angle and 60 degree shield angle was found to result in shorter ignition delay and was selected for further testing. Further experiments explored the effects of the overall equivalence ratio (controlled by injection duration) and intake pressure on ignition delay and combustion performance. Ignition delay was measured to be in the range of 1.6 to 2.0 ms. Equivalence ratio was found to have little to no effect on the ignition delay. Higher intake pressure was shown to increase ignition delay due to the effect of swirl momentum on fuel jet development, air entrainment and jet deflection away from optimal contact with the glow plug ignition source. Analysis of combustion was carried out by examination of the rate of heat release (ROHR) profiles. ROHR profiles were consistent with two distinct modes of combustion: premixed mode at all test conditions, and a mixing-controlled mode that only appeared at higher equivalence ratios following premixed combustion.
TOPICS: Compression, Ignition, Gas engines, Ignition delay, Combustion, Luminescence, Ejectors, Pressure, Momentum, Heat, Fuels, Engines, Optical research, Natural gas, Testing, Air entrainment, Cylinders, Deflection, Geometry
research-article  
David Coghlan and Dara Childs
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036969
Static and thermal characteristics (measured and predicted) are presented for a 4-pad, spherical-seat, TPJB with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The LEG, SBB, and SB are all considered methods of “directed lubrication”. These methods rely on lubrication injected directly to the pad/rotor interface. The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa respectively. Static data includes rotor-bearing eccentricities, and attitude angles. Thermal data include measured temperatures from sixteen bearing thermocouples. Twelve of the bearing thermocouples are embedded in the babbitt layer of the pads while the remaining four are oriented at the leading and trailing edge of the loaded pads exposed to the lubricant. Bearing thermocouples provide a circumferential and axial temperature gradient. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.
TOPICS: Lubrication, Bearings, Thermocouples, Stress, Rotors, Sprays, Shells, Stiffness, Temperature, Babbitt metal, Manufacturing, Lubricants, Clearances (Engineering), Temperature gradient
research-article  
David Coghlan and Dara Childs
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036970
Measured and predicted rotordynamic characteristics are presented for a 4-pad, spherical-seat, TPJB with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa respectively. Dynamic data includes four sets (one set for each bearing configuration) of direct and cross-coupled rotordynamic coefficients derived from measurements and fit to a frequency independent KCM model. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.
TOPICS: Lubrication, Bearings, Sprays, Stress, Clearances (Engineering), Manufacturing, Shells, Stiffness
research-article  
Kyuho Sim and Dong-Jun Kim
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036967
This paper presents the development and performance measurements of a beta-type free-piston Stirling engine (FPSE) along with dynamic model predictions. The FPSE is modeled as a two-degree-of-freedom (2-DOF) vibration system with the equations of motion for displacer and piston masses, which are connected to the spring and damping elements and coupled by working pressure. A test FPSE is designed from root locus analyses, and developed with flexure springs and a dashpot load. The stiffness of the test springs and the damping characteristics of the dashpot are identified through experiments. An experimental test rig is developed with an electric heater and a water cooler, operating under the atmospheric air. The piston dynamic behavior, including the operating frequency, piston stroke, and phase angle, and engine output performance are measured at various heater temperatures and external loads. The experimental results are compared to dynamic model predictions. The test FPSE is also compared to a conventional kinematic engine in terms of engine output performance and dynamic adaptation to environments. Incidentally, nonlinear dynamic behaviors are observed during the experiments and discussed in detail.
TOPICS: Stirling engines, Pistons, Dynamic models, Springs, Engines, Stress, Shock absorbers, Damping, Stiffness, Water, Kinematics, Pressure, Temperature, Vibration equipment, Equations of motion, Bending (Stress)
Technical Brief  
Hossein Balaghi Enalou, Eshagh Abbasi Soreshjani, Mohamed Rashed, Seang Shen Yeoh and Serhiy Bozhko
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036947
Multiple spool gas turbines are usually utilized for power supply in aircrafts, ships and terrestrial electric utility plants. As a result, having a reliable model of them can aid with the control design process and stability analysis. Since several interconnected components are coupled both thermodynamically and through shafts, these engines cannot be modelled linearly as single shaft gas turbines. In this paper, inter component volume method (ICV) has been implemented for turbine modelling. A switched feedback control system incorporating bump-less transfer and anti-windup functionality is employed as governor for the engine. Validation with test results from a three spool gas turbine highlights high accuracy of turbine-governor model in various maneuvers. Results show that over-speed after load rejection is considerable due to the fact that in this arrangement, the power turbine is not coupled with the compressor which acts like a damper for single shaft gas turbines. To address this problem, bleed valves (mainly before combustion chamber) are used to arrest the over-speed by 20 per cent. In addition, a switch is employed into the governor system to rapidly shift fuel to permissible minimum flow.
TOPICS: Governors, Turbines, Gas turbines, Engines, Compressors, Stress, Stability, Flow (Dynamics), Fuels, Combustion chambers, Dampers, Design, Modeling, Valves, Aircraft, Feedback, Ships, Switches
research-article  
Guohui Zhu, Jingping Liu, Jianqin Fu and Shuqian Wang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036955
A combined ORC was proposed for both engine coolant energy recovery (CER) and exhaust energy recovery (EER), and it was applied to a gasoline direct injection (GDI) engine to verify its waste heat recovery (WHR) potential. After several kinds of organic working medium were compared, R123 was selected as the working fluid of this ORC. Two cycle modes, low-temperature cycle and high-temperature cycle were designed according to the evaporation way of working fluid. The working fluid is evaporated by coolant heat in low-temperature cycle but by exhaust heat in high-temperature cycle. The influence factors of cycle performance and recovery potential of engine waste heat energy were investigated by cycle simulation and parametric analysis. The results show that recovery efficiency of waste heat energy is influenced by both engine operating conditions and cycle parameters. At 2000 r/min, the maximum recovery efficiency of waste heat energy is 7.3% under 0.2 MPa BMEP but 10.7% under 1.4 MPa BMEP. With the combined ORC employed, the fuel efficiency improvement of engine comes up to 4.7 percent points under the operations of 2000 r/min and 0.2 MPa BMEP, while it further increases to 5.8 percent points under the operations of 2000 r/min and 1.4 MPa BMEP. All these indicate the combined ORC is suitable for IC engine WHR.
TOPICS: Heat recovery, Internal combustion engines, Organic Rankine cycle, Cycles, Engines, Waste heat, Fluids, Heat, Low temperature, Coolants, Energy recovery, Exhaust systems, High temperature, Gasoline, Fuel efficiency, Evaporation, Simulation
research-article  
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
research-article  
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
research-article  
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
research-article  
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
research-article  
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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