Accepted Manuscripts

Marco Pietropaoli, Richard Ahlfeld, Francesco Montomoli, Alessandro Ciani and Michele D'Ercole
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036358
The new possibilities offered by Additive Manufacturing (AM) can be exploited in gas turbines to produce a new generation of complex and efficient internal coolant systems. The flexibility offered by this new manufacturing method needs a paradigm shift in the design approach and a possible solution is offered by Topology Optimization. The overall goal of this work is to propose an innovative method to design internal channels in gas turbines that that fully exploit AM capabilities. The present work contains a new application of a Fluid Topology sedimentation method to optimize the internal coolant geometries with minimal pressure losses while maximizing the heat exchange. The domain is considered as a porous medium with variable porosity: the solution is represented by the final solid distribution that constitutes the optimised structure. In this work the governing equations for an incompressible flow in a porous medium are considered together with a conjugate heat transfer equation that includes porosity dependent thermal diffusivity. An adjoint optimisation approach with steepest descent method is used to build the optimisation algorithm. The simulations are carried out on two different geometries: a U-Bend and a straight duct. For the U-Bend a series of splitter is automatically generated by the code, minimizing the stagnation pressure losses. In the straight duct the impact of different porosity dependant thermal diffusivity is analysed to achieve high thermal exchange. The results show “rib like” structures that enhance the heat transfer
Muthuvel Murugan, Anindya Ghoshal, Fei Xu, Ming-Chen Hsu, Yuri Bazilevs, Luis G. Bravo and Kevin Kerner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036359
Gas turbine engines are generally optimized to operate at nearly a fixed speed with fixed blade geometries for the design operating condition. When the operating condition of the engine changes, the flow incidence angles may not be optimum with the blade geometry resulting in reduced off-design performance. Articulating the pitch angle of turbine blades in coordination with adjustable nozzle vanes can improve performance by maintaining flow incidence angles within the optimum range at all operating conditions of a gas turbine engine. Maintaining flow incidence angles within the optimum range can prevent the likelihood of flow separation in the blade passage and also reduce the thermal stresses developed due to aerothermal loads for variable speed gas turbine engine applications. U.S. Army Research Laboratory has partnered with University of California San Diego and Iowa State University Collaborators to conduct high fidelity stator-rotor interaction analysis for evaluating the aerodynamic efficiency benefits of articulating turbine blade concept. The flow patterns are compared between the baseline fixed geometry blades and articulating conceptual blades. The computational fluid dynamics studies were performed using a stabilized finite element method developed by the Iowa State University and University of California San Diego researchers. The results from the simulations together with viable smart material based technologies for turbine blade actuations are presented in this paper.
Zhe Wang, Qilun Zhu, Robert Prucka, Michael Prucka and Hussein Dourra
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036360
Spark ignition engine in-cylinder air charge estimation is important for air-to-fuel ratio control, maintaining high after-treatment efficiency, and determination of current engine torque. Current cylinder air charge estimation methodologies generally depend upon either a mass air flow (MAF) sensor or a manifold absolute pressure (MAP) sensor individually. Methods based on either sensor have their own advantages and disadvantages. Some production vehicles are equipped with both MAF and MAP sensors to offer air charge estimation and other benefits. This research proposes several observer based cylinder air charge estimation methods that take advantage of both MAF and MAP sensors to potentially reduce calibration work while providing acceptable transient and steady-state accuracy with low computational load. This research also compares several common air estimation methods with the proposed observer based algorithms using steady-state and transient dynamometer tests and a rapid-prototype engine controller. With appropriate tuning the proposed observer based methods are able to estimate cylinder air charge mass under different engine operating conditions based on the manifold model and available sensors. Methods are validated and compared based on a continuous tip-in tip-out operating condition.
Xueying Li, Jing Ren and Hongde Jiang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036361
The switch from diffusive combustion to premixed combustion in a modern gas turbine will change the combustor exit temperature profile to a more uniform one. This will directly affect the cooling of the first stage vane especially the endwall region. A typical endwall configuration with matched non-dimensional parameters to the engine condition was investigated experimentally in this study. Two endwall cooling arrangements at four different coolant to mainstream mass flow ratios (MFR) were tested in a linear cascade. Detailed measurements of pressure distribution, heat transfer coefficient, adiabatic film cooling effectiveness and overall effectiveness of the endwall were performed. The temperature sensitive paint (TSP) and pressure sensitive paint (PSP) were used to acquire these parameters. The conjugate heat transfer characteristic of endwall with film cooling and impingement cooling was discussed. Moreover the influence of coolant mass flow rate on conjugate heat transfer of endwall was analyzed. 1D and 2D method for overall effectiveness prediction based on experimental data for separate parameters and correlations were also studied.
Luke Hagen, George Lavoie, Margaret Wooldridge and Dennis Assanis
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036319
A new experimental method was developed which isolated charge composition effects for wide levels of internal EGR (iEGR) at constant total EGR (tEGR) for homogeneous charge compression ignition (HCCI) combustion. The effect of changing iEGR was examined for both gasoline (RON = 90.5) and PRF40 at constant charge composition. For this study, the charge composition was defined as the total mass of fresh air, fuel and tEGR. From the experimental results, for a given iEGR level, PRF40 was found to have a reduced burn duration and higher maximum heat release rate (HRR) compared with gasoline. PRF40 was found to have a nearly constant burn duration and HRR for a given load and CA50, largely independent of engine speed and iEGR level. Gasoline, for equivalent conditions, showed an increased burn duration at higher iEGR levels. When comparing PRF40 to gasoline at fixed combustion phasing and iEGR level, the increase in HRR was correlated with reduced intake valve closing (IVC) temperatures for the PRF40. To examine the impact of thermal gradients (due to IVC temperature differences) relative to fuel chemistry, a multi-zone ``balloon model'' was used to evaluate experimental conditions. The model results demonstrated that when the in-cylinder temperature profiles between fuels were matched by adjusting wall temperature, the heat release rates were nearly identical. This result suggested the observed differences in burn rates between gasoline and PRF40 were influenced to a large degree by differences in thermal stratification, and to a lesser extent by differences in fuel chemistry.
TOPICS: Combustion, Fuels, Thermal stratification, Homogeneous charge compression ignition engines, Gasoline, Heat, Temperature, Exhaust gas recirculation, Chemistry, Cylinders, Temperature profiles, Wall temperature, Engines, Stress, Valves, Temperature gradient
Ming ZHANG, Jun ZHONG, Stefano CAPELLI and Luigi LUBRANO
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036301
The development process of a down-sized turbo-charged GDI engine/vehicle (Euro 6c-oriented) was partially introduced. Combined numerical and experimental analyses were made to compare the characteristics of upgraded prototype injectors for injector selection. Effect of injection control parameters (injection pressure, start of injection timing, number of injection pulses etc.) on the engine-out emission, especially the particulate matter, was illustrated. The number of fuel injection and start of injection timing were found playing the leading role in terms of the particle mass (PM) / particle number (PN) emission suppression. With single injection strategy, a fine combination of injection timing and injection pressure is generally able to decrease upto 50% of PM emission on a wide range of the engine map; while with multiple injection, upto an order of magnitude PM emission is achieved. Several NEDC emission cycles were arranged on a demo vehicle to evaluate the effect of the injection system upgrade and adjusted calibration. This work will provide a guide for the emission control of GDI engines/vehicles fulfilling future emission legislation.
TOPICS: Particulate matter, Engines, Turbochargers, Emissions, Gasoline, Vehicles, Pressure, Direct injection spark ignition engines, Ejectors, Engineering prototypes, Air pollution control, Fuels, Calibration, Cycles, Experimental analysis
Bader Almansour, Subith Vasu, Sreenath B. Gupta, Qing Wang, Robert Van Leeuwen and Chuni Ghosh
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036291
Lean-burn operation of stationary natural gas engines offers lower NOx emissions and improved efficiency. A proven pathway to extend lean-burn operation has been to use laser ignition instead of standard spark ignition. However, under lean conditions, flame speed reduces thereby offsetting any efficiency gains resulting from the higher ratio of specific heats, ?. The reduced flame speeds, in turn, can be compensated with the use of a prechamber to result in volumetric ignition, and thereby lead to faster combustion. In this study, the optimal geometry of PCLI was identified through several tests in a single-cylinder engine as a compromise between autoignition, NOx and soot formation within the prechamber. Subsequently, tests were conducted in a single-cylinder natural gas engine comparing the performance of three ignition systems: standard electrical spark ignition (SI), single-point laser ignition (LI), and prechamber equipped laser ignition (PCLI). Out of the three, the performance of PCLI was far superior compared to the other two. Efficiency gain of 2.1% points could be achieved while complying with EPA regulation (BSNOx < 1.34 kW-hr) and the industry standard for ignition stability (COV_IMEP < 5%). Test results and data analysis are presented identifying the combustion mechanisms leading to the improved performance.
TOPICS: Lasers, Ignition, Gas engines, Nitrogen oxides, Flames, Combustion, Stability, Engineering standards, Cylinders, Geometry, Soot, Single-cylinder engines, Emissions, Ignition systems
Wei Jing, Zengyang Wu, William Roberts and Tiegang Fang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036292
Soot formation process was investigated for biomass-based renewable diesel fuel, such as biomass to liquid (BTL), and conventional diesel combustion under varied fuel quantities injected into a constant volume combustion chamber. Soot measurement was implemented by two-color pyrometry under quiescent type diesel engine conditions (1000 K and 21% O2 concentration). Different fuel quantities, which correspond to different injection widths from 0.5 ms to 2 ms under constant injection pressure (1000 bar), were used to simulate different loads in engines. For a given fuel, soot temperature and KL factor show a different trend at initial stage for different fuel quantities, where a higher soot temperature can be found in a small fuel quantity case but a higher KL factor is observed in a large fuel quantity case generally. Another difference occurs at the end of combustion due to the termination of fuel injection. Additionally, BTL flame has a lower soot temperature, especially under a larger fuel quantity (2 ms injection width). Meanwhile, average soot level is lower for BTL flame, especially under a lower fuel quantity (0.5 ms injection width). BTL shows an overall low sooting behavior with low soot temperature compared to diesel, however, trade-off between soot level and soot temperature needs to be carefully selected when different loads are used.
TOPICS: Combustion, Fuels, Biomass, Diesel, Soot, Temperature, Stress, Flames, Tradeoffs, Combustion chambers, Diesel engines, Pressure, Engines
Kang Pan and James S. Wallace
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036293
This paper presents a numerical study on fuel injection, ignition and combustion in a direct-injection natural gas (DING) engine with ignition assisted by a shielded glow plug (GP). The shield geometry is investigated by employing different sizes of elliptical shield opening and changing the position of the shield opening. The results simulated by KIVA-3V indicated that fuel ignition and combustion is very sensitive to the relative angle between the fuel injection and the shield opening, and the use of an elliptical opening for the glow plug shield can reduce ignition delay by 0.1~0.2ms for several specific combinations of the injection angle and shield opening size, compared to a circular shield opening. In addition, the numerical results also revealed that the natural gas ignition and flame propagation will be delayed by lowering a circular shield opening from the fuel jet center plane, due to the blocking effect of the shield to the fuel mixture, and hence it will reduce the DING performance by causing a longer ignition delay.
TOPICS: Luminescence, Natural gas, Diesel engines, Ignition, Fuels, Combustion, Ignition delay, Engines, Flames, Geometry
Dorrin Jarrahbashi, Sayop Kim and Caroline L. Genzale
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036294
Recent experimental observations show that lifted diesel flames tend to propagate back towards the injector after the end of injection under conventional high-temperature conditions. The term “combustion recession” has been adopted to reflect this process. This phenomenon is closely linked to the end-of-injection entrainment and its impact on the transient mixture-chemistry evolution upstream of the lift-off length. A few studies have explored the physics of combustion recession with experiments and simplified modeling, but the details of the chemical kinetics and convective-diffusive transport of scalars and the capability of engine CFD simulations to accurately capture them are mainly unexplored. In this study, highly-resolved numerical simulations have been employed to explore the mixing and combustion of a diesel spray after the end of injection and the influence of modeling choices on the prediction of these phenomena. The simulations are centered on a temperature sweep around the Engine Combustion Network (ECN) Spray-A conditions, from 800 – 1000 K, where different combustion recession behaviors are observed experimentally. Reacting spray simulations are performed via OpenFOAM, using a RANS with a Lagrangian-Eulerian framework. Two reduced chemical kinetics models for n-dodecane are used to evaluate the impact of low-temperature chemistry and mechanism formulation on predictions of combustion recession. Observations from the simulations are consistent with recent findings that a two-stage auto-ignition sequence drives the combustion recession process. Simulations with two different chemical mechanisms indicate that low-temperature chemistry reactions drive the likelihood of combustion recession.
TOPICS: Combustion, Simulation, Diesel engines, Engineering simulation, Sprays, Chemistry, Diesel, Low temperature, Modeling, Chemical kinetics, Engines, Flames, Ignition, Reynolds-averaged Navier–Stokes equations, High temperature, Transients (Dynamics), Computational fluid dynamics, Ejectors, Computer simulation, Scalars, Physics, Temperature
Amin Reihani, Brent Patterson, John Hoard, Galen B. Fisher, Joseph R. Theis and Christine K. Lambert
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036295
Lean NOx Traps (LNTs) are often used to reduce NOx on smaller diesel passenger cars where urea-based Selective Catalytic Reduction (SCR) systems may be difficult to package. However, the performance of LNTs at temperatures above 400°C needs to be improved. Rapidly Pulsed Reductants (RPR) is a process in which hydrocarbons are injected in rapid pulses ahead of the LNT in to improve its performance at higher temperatures and space velocities. This approach was developed by Toyota and was originally called Di-Air [1]. Four important parameters were identified to maximize NOx conversion while minimizing fuel penalty associated with hydrocarbon injections in RPR operation: (1) flow field and reductant mixing uniformity; (2) pulsing parameters including the pulse frequency, duty cycle, and magnitude; (3) reductant type; (4) catalyst composition, including the type and loading of precious metal and NOx storage material, and the amount of oxygen storage capacity (OSC). In this study, RPR performance was assessed between 150°C and 650°C with several reductants including dodecane, propane, ethylene, propylene, H2, and CO. Under RPR conditions, H2, CO, C12H26, and C2H4 provided approximately 80% NOx conversion at 500°C; however, at 600°C the conversions were significantly lower. The NOx conversion with C3H8 was low across the entire temperature range. In contrast, C3H6 provided greater than 90% NOx conversion over a broad range of 280°C to 630°C. This suggested that the high temperature NOx conversion with RPR improves as the reactivity of the hydrocarbon increases.
TOPICS: Diesel, Nitrogen oxides, Temperature, Storage, Flow (Dynamics), Oxygen, Selective catalytic reduction, Metals, Fuels, Ethylene-propylene rubber, Automobiles, Catalysts, Cycles, High temperature
Technical Brief  
Rui-lin Liu, Zhongjie Zhang, Surong Dong and Guangmeng Zhou
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036283
To improve engine power at high altitude, the regulated two-stage turbocharger (RTST) was developed by authors. The working process model of heavy-duty common-rail diesel engine matched with RTST was built to study the regulating characteristic of VGT vane and both turbine by-pass valves, and also matching performance of RTST with engine at different altitudes. The control scheme of RTST at different altitudes and engine operating conditions was put forward, and the optimal opening MAPs of VGT vane and both turbine by-pass valves at different altitudes and engine operating conditions were obtained. The results show that the optimal openings of VGT vane and both turbine by-pass valves decrease with increase of altitude, and the optimal opening range of VGT vane becomes narrower with increase of altitude. The operating points of both high and low compressors locate at high efficiency region of each compressor map respectively and compressor efficiency exceeds 70% at altitude of 5500m. The total boost pressure ratio increases with altitude and reach the maximum value of 5.1 at altitude of 5500m. Compared with single-stage turbocharged engine the rated power, maximum torque and torques at lower engine speed at altitude of 5500m increase by 48.2%, 51% and 65%~121% separately, and the minimum fuel consumption decreases by 12.6%.
TOPICS: Diesel engines, Turbochargers, Engines, Compressors, Turbines, Valves, Torque, Pressure, Turbocharged engines, Fuel consumption, Common rail fuel injectors
Marius C. Banica, Peter Limacher, Heinz-Juergen Feld and Carsten Spinder
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036284
In large modern turbochargers, transonic compressors often constitute the main source of noise, with a frequency spectrum typically dominated by tonal noise at the blade passing frequency (BPF) and its harmonics. Inflow BPF noise is mainly generated by rotor locked shock fronts. Outflow noise, while also dominated by BPF tones, is linked to more complex source mechanisms. Its modal structure and the relationships between sources and modal sound pressure levels (SPL) are less well understood and its numerical analysis is, in general, significantly more complex than for compressor inflows. To shed some light on the outflow acoustic characteristics of radial machines, transient simulations of a 360° model of a radial compressor stage, including its vaned diffuser and volute, were carried out. Four increasingly finer grids were used for this purpose. On all grids, numerical damping had detrimental effects on prediction quality. A simple and mathematically sound method is proposed to account for this damping. With it, the global outflow acoustic power level (PWLg) is predicted to within an accuracy of 2dB of the experimental result on the finest grid. This shows that satisfactory accuracy can be obtained with state-of-the-art CFD codes if care is taken with the simulation setup. The simulations are further validated with experimental data from 17 transient wall pressure sensors.
TOPICS: Acoustics, Compressors, Outflow, Noise (Sound), Simulation, Transients (Dynamics), Inflow, Damping, Numerical analysis, Rotors, Blades, Machinery, Computational fluid dynamics, Diffusers, Shock waves, Turbochargers, Pressure sensors, Sound pressure
Eiji Ishii, Kazuki Yoshimura, Yoshihito Yasukawa and Hideharu Ehara
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036285
Lower engine emissions like CO2, particulate matter (PM) and NOx have recently become more necessary in automobile engines to protect the earth’s environment. Keeping uniformity of air/fuel mixture and decreasing fuel adhesion on walls of cylinder and piston are effective in order to reduce the engine emissions. In order to achieve the target fuel-spray, fuel injectors for gasoline direct injection engines need to be designed to deal with multiple injections. One of difficulties in the multiple injections is to control fuel spray behaviors during opening and closing valve; flow rate and spray penetration which are changed due to slow velocity of fluid during opening and closing valve, cause non-uniformity of air/fuel mixture that results in increase of PM. In this study, we developed an air/fuel mixture simulation that is connected with an inner-flow simulation with a valve opening and closing function. The simulation results were validated by comparing the simulated fuel breakup near the nozzle outlets and the air/fuel mixtures in the air region with the measured ones, revealing good agreement between them. It was found that the opening and closing of the valve affected the front and rear behaviors of the air/fuel mixture and also affected spray penetrations. It was also found that the magnetic circuit with the solenoid needs to be designed to achieve high speed valve-motion, and also keeps same valve motion in each injection, especially during opening and closing valve.
TOPICS: Fuels, Valves, Fuel injectors, Sprays, Emissions, Engines, Simulation, Flow (Dynamics), Fluids, Adhesion, Particulate matter, Nozzles, Carbon dioxide, Circuits, Cylinders, Pistons, Simulation results, Solenoids, Automotive engines, Direct injection spark ignition engines, Nitrogen oxides
Gen Fu and Alexandrina Untaroiu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036188
Textured thrust bearings are capable of providing higher load capacity and lower friction torque compared to non-textured bearings. However, most previous optimization efforts for texturing geometry were focused on rectangular dimples and employed Reynolds equation. Limited studies have been done to investigate the effects of partially textured thrust bearings with elliptical dimples. This study proposes a new optimization approach to find the optimal partially texture geometry with elliptical dimples, which maximize the loading capacity and minimize the friction torque. In this study, a 3D-CFD model for a parallel sector-pad thrust bearing is built using ANSYS-CFX. Mass conserving cavitation model is used to simulate the cavitation regions. Energy equation for Newtonian flow is also solved. The results of the model are validated by the experimental data from the literature. Based on this model, the flow pattern and pressure distribution inside the dimples are analyzed. The geometry of elliptical dimple is parameterized and analyzed using design of experiments. The selected geometry parameters include the length of major and minor axis, dimple depth, radial and circumferential space between two dimples, the radial and circumferential extend. A multi-objective optimization scheme is used to find the optimal texture structure with the load force and friction torque set as objective functions. The results show that the shape of dimples has a crucial effect on the performance of the textured thrust bearings. This optimization approach proposed is expected to be useful in typical texture design process of thrust bearing.
TOPICS: Computational fluid dynamics, Design, Cavitation, Shapes, Thrust bearings, Geometry, Texture (Materials), Optimization, Torque, Friction, Stress, Flow (Dynamics), Bearings, Pareto optimization, Pressure, Experimental design
Brian T. Fisher, Jim S. Cowart, Michael R. Weismiller, Zachary J. Huba and Albert Epshteyn
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036189
Energetic nanoparticles are promising fuel additives due to their high specific surface area, high energy content, and catalytic capability. Novel amorphous reactive mixed-metal nanopowders (RMNPs) containing Ti, Al, and B, synthesized via a sonochemical reaction, have been developed at the Naval Research Laboratory. These materials have higher energy content than commercial nano-aluminum (nano-Al), making them potentially useful as energy-boosting fuel components. This work examines combustion of RMNPs in a single-cylinder diesel engine (Yanmar L48V). Fuel formulations included up to 4 wt. % RMNPs suspended in JP-5, and equivalent nano-Al suspensions for comparison. Although the effects were small, both nano-Al and RMNPs resulted in shorter ignition delays, retarded peak pressure locations, decreased maximum heat release rates, and increased burn durations. A similar but larger engine (Yanmar L100V) was used to examine fuel consumption and emissions for a suspension of 8 wt. % RMNPs in JP-5 (and 8 wt. % nano-Al for comparison). The engine was operated as a genset under constant load with nominal gross indicated mean effective pressure of 6.5 bar. Unfortunately, the RMNP suspension led to deposits on the injector tip around the orifices, while nano-Al suspensions led to clogging in the fuel reservoir and subsequent engine stall. Nevertheless, fuel consumption rate was 17 % lower for the nano-Al suspension compared to baseline JP-5 for the time period prior to stall, which demonstrates the potential value of reactive metal powder additives in boosting volumetric energy density of hydrocarbon fuels.
TOPICS: Combustion, Cylinders, Diesel engines, Fuels, Engines, Pressure, Fuel consumption, Emissions, Ignition delay, Density, Orifices, Stall behavior, Heat, Metals, Aluminum, Reservoirs, Metal powders, Stress, Nanoparticles, Ejectors
Peter G. Dowell, Sam Akehurst and Richard D. Burke
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036101
Hardware-in-the-Loop (HiL) approaches are becoming popular when the engine system is represented as a real-time capable model to allow development of the controller hardware and software without the need for the real engine system. A number of semi-physical, zero-dimensional combustion modelling techniques are enhanced and combined into a complete model, these include- ignition delay, pre-mixed and diffusion combustion and wall impingement. A fuel injection model was used to provide fuel injection rate from solenoid energizing signals. The model was parameterized using a small set of experimental data and validated against a complete data set covering the full engine speed and torque range. The model was shown to characterize Rate of Heat Release (RoHR) well. Critically the wall impingement model improved R2 value for maximum RoHR from 0.89 to 0.96. This reflected in the model’s ability to match both pilot and main combustion phasing, and peak heat release rates derived from measured data. The model predicted indicated mean effective pressure and maximum pressure with R2 values of 0.99 across the engine map. The results demonstrate the predictive ability of the model, with only a small set of empirical data for training - this is a key advantage over conventional methods. The fuel injection model yielded good results for predicted injection quantity (R2=0.99), and enables the use of the RoHR model without the need for measured rate of injection.
TOPICS: Heat, Diesel engines, Engines, Combustion, Fuels, Hardware, Pressure, Torque, Diffusion (Physics), Modeling, Computer software, Control equipment, Signals, Solenoids, Ignition delay
Jerald Caton
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036102
During the last several decades, investigations of the operation of internal combustion engines utilizing exhaust gas recirculation (EGR) has increased. This increased interest has been driven by the advantages of the use of EGR with respect to emissions and, in some cases, thermal efficiency. The current study uses a thermodynamic engine cycle simulation to explore the fundamental reasons for the changes of thermal efficiency as functions of EGR. EGR with various levels of cooling are studied. Both a conventional (throttled) operating condition and a high efficiency operating condition are examined. With no EGR, the net indicated thermal efficiencies were 32.1% and 44.6% for the conventional and high efficiency engines, respectively. For the conditions examined, the cylinder heat transfer is a function of the gas temperatures and convective heat transfer coefficient. For increasing EGR, the gas temperatures generally decrease due to the lower combustion temperatures. For increasing EGR, however, the convective heat transfer coefficient generally increases due to increasing cylinder pressures and decreasing gas temperatures. Whether the cylinder heat transfer increases or decreases with increasing EGR is the net result of the gas temperature decreases and the heat transfer coefficient increases. For significantly cooled EGR, the efficiency increases partly due to decreases of the heat transfer. On the other hand, for less cooled EGR, the efficiency decreases due at least partly to the increasing heat transfer. Two other considerations to explain the efficiency changes include the changes of the pumping work, and the specific heats during combustion.
TOPICS: Engines, Exhaust gas recirculation, Temperature, Heat transfer, Cylinders, Thermal efficiency, Combustion, Convection, Internal combustion engines, Cycles, Cooling, Simulation, Emissions, Heat transfer coefficients
Lars Seidel, Corinna Netzer, Martin Hilbig, Fabian Mauss, Christian Klauer, Michal Pasternak and Andrea Matrisciano
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036093
In this work we apply a sequence of concepts for mechanism reduction on one reaction mechanism including novel quality control. We introduce a moment based accuracy rating method for species profiles. The concept is used for a necessity based mechanism reduction utilizing 0D reactors. Thereafter a stochastic reactor model (SRM) for internal combustion engines is applied to control the quality of the reduced reaction mechanism during the expansion phase of the engine. This phase is sensitive on engine out emissions, and is often not considered in mechanism reduction work. The proposed process allows to compile highly reduced reaction schemes for CFD application for internal combustion engine simulations. It is demonstrated that the resulting reduced mechanisms predict combustion and emission formation in engines with accuracies comparable to the original detailed scheme.
TOPICS: Engines, Chemical reactions, Internal combustion engines, Emissions, Combustion, Quality control, Simulation, Computational fluid dynamics, Engineering simulation
Stacie M. Tibos, Christos Georgakis, Kevin Harvey and Joao A. Teixeira
J. Eng. Gas Turbines Power   doi: 10.1115/1.4036058
In the application of film-riding sealing technology there are various groove features that can be used to induce hydrodynamic lift, however, there is little guidance in selecting the relative parameter settings in order to maximise hydrodynamic load and fluid stiffness. In this study two groove types are investigated; Rayleigh step and inclined groove. The study uses a design of experiments approach and a Reynolds equation method to explore the design space. Key parameters have been identified that can be used to optimise seal designs. Results show that the relationship between parameters is likely to be very non-linear. It was also found that higher pressure drops hinder the hydrodynamic load and stiffness of the seal suggesting an advantage for using hydrostatic load support in such conditions.
TOPICS: Stress, Experimental design, Stiffness, Pressure drop, Design, Hydrostatics, Fluids, Lift (Fluid dynamics), Sealing (Process)

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