TECHNICAL PAPERS: Gas Turbines: Controls, Diagnostics, and Instrumentation

J. Eng. Gas Turbines Power. 2002;124(3):510-516. doi:10.1115/1.1473150.

A simulation program for transient analysis of the startup procedure of heavy duty gas turbines for power generation has been constructed. Unsteady one-dimensional conservation equations are employed and equation sets are solved numerically using a fully implicit method. A modified stage-stacking method has been adopted to estimate the operation of the compressor. Compressor stages are grouped into three categories (front, middle, rear), to which three different stage characteristic curves are applied in order to consider the different low-speed operating characteristics. Representative startup sequences were adopted. The dynamic behavior of a representative heavy duty gas turbine was simulated for a full startup procedure from zero to full speed. Simulated results matched the field data and confirmed unique characteristics such as the self-sustaining and the possibility of rear-stage choking at low speeds. Effects of the estimated schedules on the startup characteristics were also investigated. Special attention was paid to the effects of modulating the variable inlet guide vane on startup characteristics, which play a key role in the stable operation of gas turbines.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):517-527. doi:10.1115/1.1456092.

This paper introduces the methodology of rolling element bearing defect detection using high-gain displacement transducers. The nature of defect influence on the outer race deflection in the vicinity of the transducer tip in time base has been established. Inner race, outer race, and rolling element (ball/roller) defects, which often occur sequentially, can be clearly identified according to spike signals on the time-varying outer race deflection curve along with known bearing frequencies. The developed techniques are fully corroborated by experimental data. Spike-to-deflection amplitude ratio, which is almost independent of changes in speed and load for a given defect, is used to judge the defect severity. Spectral characteristics due to these defects have also been found. It is shown that this direct measurement by using displacement transducers without casing influence, which would be inevitable by using accelerometers mounted on the casing, is a reliable approach to detect bearing defects as well as their severity and locations.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics

J. Eng. Gas Turbines Power. 2002;124(3):586-597. doi:10.1115/1.1451753.

A new method for the dynamic analysis of mistuned bladed disks is presented. The method is based on exact calculation of the response of a mistuned system using response levels for the tuned assembly together with a modification matrix constructed from the frequency response function (FRF) matrix of the tuned system and a matrix describing the mistuning. The main advantages of the method are its efficiency and accuracy, which allow the use of large finite element models of practical bladed disk assemblies in parametric studies of mistuning effects on vibration amplitudes. A new method of calculating the FRF matrix of the tuned system using a sector model is also developed so as to improve the efficiency of the method even further, making the proposed method a very attractive tool for mistuning studies. Various numerical aspects of the proposed method are addressed and its accuracy and efficiency are demonstrated using representative test cases.

Topics: Disks , Manufacturing
Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Turbomachinery

J. Eng. Gas Turbines Power. 2002;124(3):608-616. doi:10.1115/1.1454113.

Compressor fouling is generally accepted to be an important factor when monitoring the efficiency of an engine’s operation. However, there are not many studies related to the local fouling behavior of the individual components of the compressor. In the present paper, the CFD-ACE software package is used for the flow field calculation and the results are utilized to calculate the deposition rates on the blade surfaces of a conventional compressor stator and rotor. The deposition model takes into account the particle and surface material properties and the energy balance at the point of impact. A discussion is presented regarding the various mechanisms that produce the final deposition rate distribution and how the flow field and blade geometry affect it.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Nuclear Engineering

J. Eng. Gas Turbines Power. 2002;124(3):725-733. doi:10.1115/1.1426086.

The high-temperature gas-cooled reactor is a promising concept for inherently safe nuclear power generation. This article deals with dynamic modeling of a combined heat and power plant, based on a helium-cooled reactor in combination with a closed-cycle gas turbine system. A one-dimensional flow model describing the helium flow and the two-phase water flow is used through the whole plant, with different source terms in different pieces of equipment. A stage-by-stage model is produced for the radial compressor and axial turbine. Other models include the recuperator, water/helium heat exchangers, a natural convection evaporator, valves, etc. In Part II the model will be used to analyze the dynamic behavior and to design a control system.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):734-743. doi:10.1115/1.1426087.

Using the dynamic model of the cogenerating nuclear gas turbine plant developed in Part I of this article, the dynamic behavior of this plant is analyzed and a control structure is designed. First it is determined how several design choices affect the system dynamics. Then the requirements and options for a control system design are investigated. A number of possible control valve positions in the flowsheet are tested with transients in order to make an argued choice. The model is subsequently used to determine the optimal working conditions for different heat and power demands, these are used as set-points for the control system. Then the interaction between manipulated and controlled variables is mapped and based on this information a choice for coupling them in decentralized feedback control loops is made. This control structure is then tuned and tested. It can be concluded that both heat and power demand can be followed with acceptable performance over a wide range.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Aircraft Engine

J. Eng. Gas Turbines Power. 2002;124(3):447-458. doi:10.1115/1.1391279.

The current high-performance aircraft development programs, and the trends in research and development activities suggest a rapidly increasing level of aircraft subsystem integration, particularly between the airframe/inlet and the propulsion system. Traditionally these subsystems have been designed, analyzed, and tested as isolated systems. The interaction between the subsystems is modeled primarily through evaluating inlet distortion in an inlet test and simulating this distortion in engine tests via screens or similar devices. In the current paper, an overview of current techniques for inlet performance and distortion characterization and engine distortion testing is presented. A review of the current state of the art in inlet analysis is also presented along with a discussion of current engine analysis techniques, from a semi-empirical approach to high-fidelity full Navier-Stokes simulations. Finally, a proposal to coordinate the existing test techniques and analysis capabilities to provide a truly integrated inlet-engine test and evaluation capability is outlined.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels

J. Eng. Gas Turbines Power. 2002;124(3):471-480. doi:10.1115/1.1377871.

To help understand how methane ignition occurs in gas turbines, dual-fuel diesel engines, and other combustion devices, the present study addresses reaction mechanisms with the objective of predicting autoignition times for temperatures between 1000 K and 2000 K, pressures between 1 bar and 150 bar, and equivalence ratio between 0.4 and 3. It extends our previous methane flame chemistry and refines earlier methane ignition work. In addition to a detailed mechanism, short mechanisms are presented that retain essential features of the detailed mechanism. The detailed mechanism consists of 127 elementary reactions among 31 species and results in nine intermediate species being most important in autoignition, namely, CH3, OH, HO2,H2O2,CH2O,CHO, CH3O, H, O. Below 1300 K the last three of these are unimportant, but above 1400 K all are significant. To further simplify the computation, systematically reduced chemistry is developed, and an analytical solution for ignition delay times is obtained in the low-temperature range. For most fuels, a single Arrhenius fit for the ignition delay is adequate, but for hydrogen the temperature sensitivity becomes stronger at low temperatures. The present study predicts that, contrary to hydrogen, for methane the temperature sensitivity of the autoignition delay becomes stronger at high temperatures, above 1400 K, and weaker at low temperatures, below 1300 K. Predictions are in good agreement with shock-tube experiments. The results may be employed to estimate ignition delay times in practical combustors.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):481-488. doi:10.1115/1.1473153.

Polydisperse sprays in complex three-dimensional flow systems are important in many technical applications. Numerical descriptions of sprays are used to achieve a fast and accurate prediction of complex two-phase flows. The Eulerian and Lagrangian methods are two essentially different approaches for the modeling of disperse two-phase flows. Both methods have been implemented into the same computational fluid dynamics package which is based on a three-dimensional body-fitted finite volume method. Considering sprays represented by a small number of droplet starting conditions, the Eulerian method is clearly superior in terms of computational efficiency. However, with respect to complex polydisperse sprays, the Lagrangian technique gives a higher accuracy. In addition, Lagrangian modeling of secondary effects such as spray-wall interaction enhances the physical description of the two-phase flow. Therefore, in the present approach the Eulerian and the Lagrangian methods have been combined in a hybrid method. The Eulerian method is used to determine a preliminary solution of the two-phase flow field. Subsequently, the Lagrangian method is employed to improve the accuracy of the first solution using detailed sets of initial conditions. Consequently, this combined approach improves the overall convergence behavior of the simulation. In the final section, the advantages of each method are discussed when predicting an evaporating spray in an intake manifold of an internal combustion engine.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):489-495. doi:10.1115/1.1451755.

The effect of water injection in the combustion chamber of an industrial gas turbine is studied by means of analytic relations. Equations for the estimation of changes in the main performance parameters are provided. The relations are derived on the basis of an order of magnitude analysis and taking into account variation of gas properties due to water injection as well as changes in the interrelation of component performance parameters. It is shown that water/fuel ratio is the main parameter on which performance deviations depend. Data from the performance testing of an industrial gas turbine are used to check the validity of the proposed relations. The comparison of the predictions to the test data shows that the mechanisms of performance deviations are well modeled by the analysis presented.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):496-502. doi:10.1115/1.1473156.

Computational and experimental studies are performed to investigate the effect of swirl flow of gas turbine exhaust gas (GTEG) in an inlet duct of a heat recovery steam generator (HRSG). A supplemental-fired HRSG is chosen as the model studied because the uniformity of the GTEG at the inlet plane of the duct burner is essential in such applications. Both velocity and oxygen distributions are investigated at the inlet plane of the duct burner installed in the middle of the HRSG transition duct. Two important parameters, the swirl angle of GTEG and the momentum ratio of additional air to GTEG, are chosen for the investigation of mixing between the two streams. It has been found that a flow correction device (FCD) is essential to provide a uniform gas flow distribution at the inlet plane of the duct burner.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Combustion and Fuels, and Cycle Innovations

J. Eng. Gas Turbines Power. 2002;124(3):503-509. doi:10.1115/1.1413462.

The emergence of fuel cell systems and hybrid fuel cell systems requires the evolution of analysis strategies for evaluating thermodynamic performance and directing design and development. A description and application of the recently developed tool for analyzing tubular SOFC based systems is presented. The capabilities of this tool include an analytical model for the tubular SOFC derived from first principles and the secondary equipment required to analyze hybrid power plants. Examples of such secondary equipment are gas turbine, reformer, partial oxidation reactor, shift reactor, humidifier, steam turbines, compressor, gas expander, heat exchanger, and pump. A “controller” is included which is essential for modeling systems to automatically iterate in order to meet the desired process or system design criteria. Another important capability that is included is to be able to arrange the various components or modules as defined by the user in order to configure different hybrid systems. Analysis of the hybrid cycle as originally proposed by Westinghouse (SureCell TM) indicates that the thermal efficiency of the cycle is quite insensitive to the pressure ratio, increasing from 65.5 percent to 66.6 percent on a lower calorific value of the fuel as the pressure ratio decreases from 15 to 6.5.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Controls, Diagnostics and Instrumentation, and Aircraft Engines

J. Eng. Gas Turbines Power. 2002;124(3):528-533. doi:10.1115/1.1473822.

Advanced thermal barrier coatings (TBCs) are increasingly being used in high-performance turbine engines. For optimized use of the coatings, accurate surface temperature measurements are required in the combustion environment. Current on-engine pyrometers, which use short infrared wavelengths to accurately measure the temperatures of metal surfaces, show increased uncertainties when used on TBCs. Studies have suggested that long infrared wavelengths are a suitable alternative. Therefore, to evaluate the response of both wavelength regions, simultaneous measurements with short and long wavelength infrared pyrometers have been accomplished in the first stage turbine of a Siemens V84.3A 60 Hz 180 MW engine at the Berlin Gas Turbine Development and Manufacturing Center.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Vehicular and Small Turbomachines, and Ceramics

J. Eng. Gas Turbines Power. 2002;124(3):617-626. doi:10.1115/1.1417983.

Honeywell Engines, Systems & Services has successfully addressed critical concerns that are slowing commercialization of structural ceramics in gas turbines. The U.S. Department of Energy (DoE) sponsored Ceramic Turbine Engine Demonstration Project (CTEDP) had the mission of advancing ceramic gas turbine component technology toward commercialization. The thrust of the program was to “bridge the gap” between ceramics in the laboratory and near-term commercial heat engine applications. Most of this mission has been achieved. The 331-200[CT] auxiliary power unit (APU) test bed featured ceramic first-stage nozzles and blades. Fabrication of ceramic components provided manufacturing process demonstration scale-up to the minimum levels needed for commercial viability. Through this program, design methods refinement and the development of new design methods unique to ceramic turbine components have been supported and validated in rig and development engine testing. Over 6800 hours of on-site endurance tests demonstrated component reliability. Additional field testing in APUs onboard commercial aircraft and stationary industrial engines has been initiated and will continue beyond completion of this program.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):627-635. doi:10.1115/1.1451704.

The Japanese ceramic gas turbine (CGT) research and development program (FY1988-1998) as a part of the New Sunshine Project funded by the Ministry of International Trade and Industry (MITI) was completed in March 1999. Kawasaki Heavy Industries, Ltd. (KHI) participated in this research program from the beginning and developed a twin-shaft CGT with a recuperator, designated as the “CGT302.” The purposes of this program were (1) to achieve both a high efficiency and low pollutant emissions level using ceramic components, (2) to prove a multifuel capability to be used in cogeneration systems, and (3) to demonstrate long-term operation. The targets of this program were (i) to achieve a thermal efficiency of over 42 percent at a turbine inlet temperature (TIT) of 1350°C, (ii) to keep its emissions within the regulated value by the law, and (iii) to demonstrate continuous operation for more than a thousand hours at 1200°C TIT. The CGT302 has successfully attained its targets. In March 1999 the CGT302 recorded 42.1 percent thermal efficiency, and 31.7 ppm NOx emissions (O2=16 percent) at 1350°C TIT. At this time it had also accumulated over 2000 hours operation at 1200°C. In this paper, we summarize the development of the CGT302.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Electric Power

J. Eng. Gas Turbines Power. 2002;124(3):534-541. doi:10.1115/1.1447240.

This paper presents the O&M experience at the Kalaeloa Cogeneration Plant. Performance issues and other problems related to firing heavy oil in a combustion turbine are presented together with their long-term solutions leading to the current successful operation of the IPP power station in Hawaii, USA.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):542-549. doi:10.1115/1.1470484.

During more than 100 years engineers of the Swiss development center of A.-G. BBC Brown, Boveri & Cie., from 1988 onwards ABB Asea Brown Boveri Ltd., in 1999 ABB ALSTOM POWER Ltd., and now ALSTOM Power Ltd. in Baden, Switzerland, have significantly contributed to the achievement of today’s advanced gas turbine concept. Numerous “firsts” are highlighted in this paper—ranging from the first realization of the industrial, heavy-duty gas turbine in the 1930s to today’s high-technology gas turbine (GT) products, combining excellent performance, extraordinary low environmental impact with commercial attractiveness for global power generation. Interesting connections could be unveiled for the early parallel development of industrial and areo gas turbines.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Heat Transfer

J. Eng. Gas Turbines Power. 2002;124(3):550-560. doi:10.1115/1.1456093.

To achieve high thermal efficiencies, 30 percent and higher, for small gas turbines a recuperator is mandatory. As the recuperator represents 25–30 percent of the overall machine cost, efforts are now being focused on establishing new low-cost recuperator concepts for gas turbine engines. In this paper the cross corrugated (CC), also called chevron pattern, heat transfer surface is reviewed to assess its thermal and hydraulic performance and compare it to some other candidate surfaces for a 50 kW microturbine. The surfaces may be categorized into three primary surface types and one plate-fin type. Design calculations of a recuperator heat transfer matrix using these surfaces enable direct comparison of the recuperator matrix volumes, weights and dimensions. It is concluded that the CC surface has great potential for use in recuperators of the future.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Industrial and Cogeneration

J. Eng. Gas Turbines Power. 2002;124(3):561-565. doi:10.1115/1.1447237.
Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Structures and Dynamics, and Controls, Diagnostics, and Instrumentation

J. Eng. Gas Turbines Power. 2002;124(3):598-607. doi:10.1115/1.1421058.

The hybrid squeeze film damper (HSFD) has proven itself to be an effective controlling device of vibration in rotating machinery. The critical stage in the development of the HSFD as an active vibration suppressant, is the development of the control algorithms for active control of rotor vibrations. This paper summarizes, evaluates, and compares the control algorithms for HSFD-supported rotors. Quantitative as well as qualitative measures of the effectiveness of the control algorithms are presented. The study includes the PID-type controllers, LQR, gain scheduling, adaptive and bang-bang controllers. The adaptive, gain scheduling, and nonlinear proportional controllers have proved to be quite effective in the active control of HSFD supported rotors, with impressive results.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Advanced Energy Systems

J. Eng. Gas Turbines Power. 2002;124(3):441-446. doi:10.1115/1.1451843.

An alternative configuration for a regenerative gas turbine engine cycle is presented that yields higher cycle efficiencies than either simple or conventional regenerative cycles operating under the same conditions. The essence of the scheme is to preheat compressor discharge air with high-temperature combustion gases before the latter are fully expanded across the turbine. The efficiency is improved because air enters the combustor at a higher temperature, and hence heat addition in the combustor occurs at a higher average temperature. The heat exchanger operating conditions are more demanding than for a conventional regeneration configuration, but well within the capability of modern heat exchangers. Models of cycle performance exhibit several percentage points of improvement relative to either simple cycles or conventional regeneration schemes. The peak efficiencies of the alternative regeneration configuration occur at optimum pressure ratios that are significantly lower than those required for the simple cycle. For example, at a turbine inlet temperature of 1300°C (2370°F), the alternative regeneration scheme results in cycle efficiencies of 50 percent for overall pressure ratios of 22, whereas simple cycles operating at the same temperature would yield efficiencies of only 43.8 percent at optimum pressure ratios of 50, which are not feasible with current compressor designs. Model calculations for a wide range of parameters are presented, as are comparisons with simple and conventional regeneration cycles.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Ceramics

J. Eng. Gas Turbines Power. 2002;124(3):459-464. doi:10.1115/1.1455637.

General Electric has developed SiC fiber-reinforced SiC-Si matrix composites produced by silicon melt infiltration for use in gas turbine engine applications. High temperature, high-pressure combustion rig testing, and engine testing has been performed on combustor liners and turbine shrouds made from such MI composites. Frame 5 sized combustor liners were rig tested under lean head end diffusion flame conditions for 150 hours, including 20 thermal trip cycles, with no observed damage to the ceramic liners. Similarly, 46-cm diameter, single-piece turbine shroud rings were fabricated and tested in a GE-2 gas turbine engine. The fabrication and testing of both components are described.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):465-470. doi:10.1115/1.1470480.

There exists today considerable interest in developing continuous fiber-reinforced ceramic matrix composites (CMC) that can operate as hot-section components in advanced gas turbine engines. The objective of this paper is to present simple analytical and empirical models for predicting the effects of time and temperature on CMC tensile rupture under various composite and engine conditions. These models are based on the average rupture behavior measured in air for oxide and SiC-based fibers of current technical interest. For example, assuming a cracked matrix and Larson-Miller rupture curves for single fibers, it is shown that model predictions agree quite well with high-temperature stress-rupture data for SiC/SiC CMC. Rupture models, yet to be validated, are also presented for three other relevant conditions: (a) SiC fibers become oxidatively bonded to each other in a cracked CMC, (b) applied CMC stresses are low enough to avoid matrix cracking, and (c) Si-based CMC are subjected to surface recession in high-temperature combustion gases. The practical implications of the modeling results are discussed, particularly in regard to the optimum fibers and matrices for CMC engine applications and the thermostructural capability of SiC/SiC CMC in comparison to nickel-based superalloys, monolithic ceramics, and oxide/oxide CMC.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Manufacturing, Materials, and Metallurgy

J. Eng. Gas Turbines Power. 2002;124(3):571-579. doi:10.1115/1.1455638.

Metallurgical analysis of rotating blades operating in advanced gas turbine engines is important in establishing actual operating conditions, degradation modes, remaining life, and most importantly, the proper repair and rejuvenation techniques to be used in developing optimum component life strategies. The elevated firing temperatures used in the latest engine designs result not only in very high metal surface temperatures but also in very high temperature gradients and concommitant thermal strains induced in part by the complex and efficient cooling systems. This has changed the primary function of today’s superalloy-coating systems from one of hot corrosion protection to moderating high temperature oxidation reactions. Furthermore, as a result of the high thermal strains induced by the cooling systems, long-term metallurgical structural stability issues now revolve around optimizing both thermal mechanical fatigue (TMF) resistance and creep life. Thus the gradual change to directionally solidified (DS) and single crystal (SC) alloys throughout the industry. The use of DS and SC alloys coated with state of the art TBC, platinum modified aluminide and MCrAlY coatings with or without subsequent aluminizing applied by vacuum plasma spray (VPS), high velocity oxygen fuel (HVOF), physical vapor deposition (PVD), air plasma spray (APS), and by chemical vapor deposition (CVD) methods along with the widespread use of internal aluminide coatings have made today’s rotating components prohibitively expensive to replace after only one cycle of operation. It is therefore, or should now be a high priority for all cost conscious gas turbine users to help develop reliable repair and rejuvenation strategies and techniques to minimize their operating cost. Traditional metallurgical considerations required for life assessment and the reliable refurbishment and requalification of gas turbine blades are reviewed along with some new exciting techniques. Examples of component degradation modes are presented. Appropriate attention to metallurgical issues allows turbine users to more successfully and economically operate their turbines.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Industrial and Cogeneration and Control Diagnostics and Instrumentation

J. Eng. Gas Turbines Power. 2002;124(3):566-570. doi:10.1115/1.1417484.

Many important industrial problems in the control of rotating machinery with active magnetic bearings concern the minimization of the rotor vibration response to poorly characterized disturbances at a single or several shaft locations, these typically not corresponding to those of a sensor or actuator. Herein, we examine experimental results of a multivariable controller obtained via μ synthesis with a laboratory test rig. These indicate that a significant improvement in performance can be obtained with a multivariable μ controller over that achieved with an optimal decentralized PD controller.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Gas Turbines: Marine

J. Eng. Gas Turbines Power. 2002;124(3):580-585. doi:10.1115/1.1451716.

From an operational availability stand point, the U.S. Navy is interested in the short term reliability of its ship based LM2500 gas turbine engines. That is the likelihood that an engine will operate successfully through a six-month deployment (usually 1500 to 2000 operational hours). From a maintenance and cost of ownership standpoint both the short-term and long-term reliability are of concern. Long-term reliability is a measure in time (in operating hours) between engine removals. To address these requirements U.S. Navy Fleet support maintenance activities employ a system of tests and evaluations to determine the likelihood that an LM2500 will meet its short and long-term goals. The lowest level inspection is the predeployment inspection, which attempts to identify primarily mechanical faults with the engine. Gas Turbine Bulletin inspections are used to determine if predefined wear out modes exists. Performance evaluations can be performed which determine the ability of the LM2500 and its control system to meet expected power requirements. Lube oil system data can be analyzed to determine if excessive leakage or excessive scavenge temperatures exist. Engine vibration characteristics can be reviewed to identify the source of both synchronous and nonsynchronous vibration and determine if corrective measures need to be taken. This paper will discuss how the lowest level inspections feed the more sophisticated analysis and how these inspections and evaluations work to provide a systematic method of insuring both short and long-term LM2500 reliability.

Commentary by Dr. Valentin Fuster

TECHNICAL PAPERS: Internal Combustion Engines

J. Eng. Gas Turbines Power. 2002;124(3):636-644. doi:10.1115/1.1456460.

To fulfill the commitments of future pollutant regulations, current development of direct injection (DI) Diesel engines requires to improve knowledge on the injection/combustion process and the effect of the injection parameters and engine operation conditions upon the spray and flame characteristics and how they affect engine performance and pollutant emissions. In order to improve comprehension of the phenomena inherent to Diesel combustion, a deep experimental study has been performed in a single-cylinder engine with the main characteristics of a six-cylinder engine passing the EURO III legislation. Some representative points of the 13-mode engine test cycle have been considered modifying the nominal values of injection pressure, injection load, intake pressure, engine speed, and injection timing. The study combines performance and emissions experimental measurements together with heat release law (HRL) analysis and high-speed visualization. Controlling parameters for BSFC, NOx, and soot emissions are identified in the last part of the paper.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):645-649. doi:10.1115/1.1455639.

An analysis procedure, using the time-frequency distribution, has been developed for the analysis of internal combustion engine noise signals. It provides an approach making use of advantages of both the linear time-frequency distribution and the bilinear time-frequency distribution but avoiding their disadvantages. In order to identify requirements on the time-frequency analysis and also correlate a time-frequency analysis result with noise sources, the composition of the noise signal is discussed first. With this discussion, a mathematical model has been suggested for the noise signal. An example of identifying noise sources and detecting the abnormal condition of an injector with the noise signal time-frequency distribution for a diesel engine is also provided.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):650-659. doi:10.1115/1.1470486.

Engine knocking and misfire cause a negative effect on the engine power and the exhaust emissions such as HC, CO and NOx. They also cause permanent damages to the three way catalyst (TWC) system. And a heavy knock can cause severe damages to the engine itself, which gives more reason why it must be detected and corrected. This study introduces a new system concept for detecting combustion misfire and knocking using breakdown voltage (BDV) characteristics between spark plug electrodes. This system detects and evaluates the degree of combustion by measuring the breakdown voltage which predicts that the breakdown voltage depends on the pressure and the temperature.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):660-667. doi:10.1115/1.1473157.

The objective of this study was to experimentally clarify the effect of two-stage split and early injection on the combustion and emission characteristics of a direct-injection (DI) diesel engine. Engine tests were carried out using a single-cylinder high-speed DI diesel engine and an injection system, combining an ordinary jerk pump and an electronically controlled high-pressure injection system, KD-3. In these experiments to compare the combustion and exhaust emission characteristics with two-stage split and early injection, a single-stage and early injection was tested. The FT-IR exhaust-gas analyzer simultaneously measured the exhaust emissions of 26 components. The results showed that HCHO, CH3CHO, and CH3COOH were emitted during the very early stage of both single injection and two-stage injection. These concentrations were higher than those from diesel combustion with ordinary fuel injection timings. These exhaust emissions are characteristic components of combustion by premixed compression ignition with extremely early injection. In particular, the HCHO concentration in exhaust was reduced with an increase in the maximum rate of heat release after cool flame due to pre-reaction of pre-mixture. At extremely early injection, the NOx concentration was extremely low; however, the indicated specific fuel consumption (ISFC) was higher than that of ordinary diesel combustion. In the case of two-stage injection, the degree of constant volume is increased, so that ISFC is improved. These results also demonstrated the possibility of reducing HCHO, NOx, and smoke emissions by means of two-stage split and early injection.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):668-677. doi:10.1115/1.1454115.

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):678-685. doi:10.1115/1.1454116.
Topics: Gas engines
Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):686-694. doi:10.1115/1.1454117.

In this work the tracer gas method using nitrous oxide as the tracer gas is implemented on a stationary two-stroke cycle, four-cylinder, fuel-injected large-bore natural gas engine. The engine is manufactured by Cooper-Bessemer, model number GMV-4TF. It is representative of the large bore natural gas stationary engine fleet currently in use by the natural gas industry for natural gas compression and power generation. Trapping efficiency measurements are carried out with the tracer gas method at various engine operating conditions, and used to evaluate the scavenging efficiency and trapped A/F ratio. Scavenging efficiency directly affects engine power and trapped A/F ratio has a dramatic impact on pollutant emissions. Engine operating conditions are altered through variations in boost pressure, speed, back pressure, and intake port restriction.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):695-701. doi:10.1115/1.1455640.

A multicode approach, based on the simultaneous use of zero-dimensional, one-dimensional, and three-dimensional models, has been developed and tested, and is here applied to predict the thermodynamic and fluid dynamic phenomena that characterize the unsteady gas flow propagation along the exhaust system of a turbocharged four-cylinder engine. The investigation is carried out by applying each model in a different region of the geometry, allowing to obtain detailed information of the flow behavior in complex elements, such as junctions, avoiding the significant limitations that a one-dimensional scheme always introduces, as well as fast processing typical of one-dimensional and zero-dimensional models, devoted to the analysis of ducts and volumes. The effect of the influence of different configurations of the exhaust system on the engine performance is analyzed.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):702-707. doi:10.1115/1.1413766.

Detailed chemical kinetics was used in an engine CFD code to study the combustion process in HCCI engines. The CHEMKIN code was implemented in KIVA such that the chemistry and flow solutions were coupled. The reaction mechanism consists of hundreds of reactions and species and is derived from fundamental flame chemistry. Effects of turbulent mixing on the reaction rates were also considered. The results show that the present KIVA/CHEMKIN model is able to simulate the ignition and combustion process in three different HCCI engines including a CFR engine and two modified heavy-duty diesel engines. Ignition timings were predicted correctly over a wide range of engine conditions without the need to adjust any kinetic constants. However, it was found that the use of chemical kinetics alone was not sufficient to accurately simulate the overall combustion rate. The effects of turbulent mixing on the reaction rates need to be considered to correctly simulate the combustion and heat release rates.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):708-716. doi:10.1115/1.1456091.

Hydrocarbon (HC) emissions from direct injection (DI) diesel engines are mainly due to fuel injected and mixed beyond the lean combustion limit during ignition delay and fuel effusing from the nozzle sac at low pressure. In the present paper, the concept has been developed to provide an elegant model to predict the HC emissions considering slow burning. Eight medium speed engines differing widely in bores, strokes, rated speeds, and power were studied for applying the model. The engines were naturally aspirated, turbocharged, or turbocharged with intercooling. The model has been validated by collecting data on HC emission, and pressures in the cylinder and in the fuel injection system from the experimental engines. New coefficients for the correlation of HC with operating parameters were obtained and these are different from the values published earlier, based on single-engine experiments.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2002;124(3):717-724. doi:10.1115/1.1456094.

A multicomponent droplet vaporization model including both gas and liquid phase transport processes was developed for multidimensional spray computations. This paper focuses on two effects altering vaporization in a high-pressure and high-temperature environment. One effect is on droplet surface regression caused by a higher vaporization rate. This effect is well characterized by the Lewis number and the Peclet number with the regression velocity. Formulas based on the two numbers were included to improve model accuracy. The other effect is on the nonideal behavior and was covered in the model by using the Peng-Robinson equation of state to determine phase equilibrium at the droplet surface. The model was validated by the results from an accurate simplified vortex model and experimental measurements, and excellent agreements were demonstrated. Further comparisons against the model without the two effects and an infinite diffusion model show that significant improvement was achieved by the model for single-droplet and spray computations.

Commentary by Dr. Valentin Fuster

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