Gas Turbine Exhaust Research Articles

Benchmarking of a micro gas turbine model integrated with post-combustion CO2 capture

The deployment of post-combustion CO2 capture on large-scale gas-fired power plants is currently progressing, hence the integration of the power and capture plants requires a good understanding of operational requirements and limitations to support this effort. This article aims to assist research in this area, by studying a micro gas turbine (MGT) integrated with an amine-based post-combustion CO2 capture unit. Both processes were simulated using two different software tools –IPSEpro and Aspen Hysys, and validated against experimental tests. The two MGT models were benchmarked at the nominal condition, and then extended to part-loads (50 and 80 kWe), prior to their integration with the capture plant at flue gas CO2 concentrations between 5 and 10 mol%. Further, the performance of the MGT and capture plant when gas turbine exhaust gases were recirculated was assessed. Exhaust gas recirculation increases the CO2 concentration, and reduces the exhaust gas flowrate and specific reboiler duty. The benchmarking of the two models revealed that the IPSEpro model can be easily adapted to new MGT cycle modifications since turbine temperatures and rotational speeds respond to reaching temperature limits; whilst a detailed rate-based approach for the capture plant in Hysys resulted in closely aligned simulation results with experimental data.

Cold-Air Bypass Characterization for Thermal Management of Fuel Cell Gas Turbine Hybrids

The effect of cathode airflow variation on the dynamics of a fuel cell gas turbine hybrid system was evaluated using a cyber-physical emulator. The coupling between cathode airflow and other parameters, such as turbine speed or pressure, was analyzed comparing the results at fixed and variable speed. In particular, attention was focused on fuel cell temperatures and gradients: cathode airflow, which is generally employed for thermal management of the stack, was varied by manipulating a cold-air bypass. A significant difference was observed in the two cases in terms of turbine inlet, exhaust gas, cathode inlet, and average cell temperatures. When the turbine speed was held constant, a change in cathode airflow resulted in a strong variation in cathode inlet temperature, while average cell temperature was not significantly affected. The opposite behavior was observed at variable speed. The system dynamics were analyzed in detail in order to explain this difference. Open-loop response was analyzed in this work for its essential role in system identification. However, a significant difference was observed between fixed and variable speed cases, because of the high coupling between turbine speed and cathode airflow. These results can give a helpful insight of system dynamics and control requirements. Cold-air valve bypass position also showed a strong effect on surge margin and pressure dynamics in both cases.

Structural integrity analyses of two gas turbines exhaust systems used for naval propulsion

Heating and cooling cycles, as well as accelerations and decelerations, to which naval gas turbine's exhaust systems under study are submitted to, could lead to the nucleation and propagation of cracks, and result in the reduction of its expected fatigue life. The paper herein presented refers to the numerical simulations of the mechanical and thermal behaviours of two different gas turbine's exhaust systems used in naval propulsion. In addition, some experimental values that were collected, namely temperature and pressure, served as input values for the finite element analyses carried out. The analyses made to the exhaust systems revealed the existence of high stresses near the lower support flanges, which are mainly caused by the non-uniform thermal expansion that the exhaust systems are subjected to. Additionally, redesigned exhaust systems were studied in order to enhance the thermal behaviour of the exhaust systems and, therefore, increasing its fatigue life. The modifications introduced in the exhaust systems resulted in the reduction of the induced stresses. However, frequent surveys should be performed to the critical welds of the exhaust systems, in order to prevent crack propagation from the weld toes. Moreover, high quality fabrication is required in order to avoid the presence of initial defects in the structure.

Cycle analysis of MCFC/gas turbine system

High temperature fuel cells such as the solid oxide fuel cell (SOFC) and the molten carbonate fuel cell (MCFC) are considered extremely suitable for electrical power plant application. The molten carbonate fuel cell (MCFC) performances is evaluated using validated model for the internally reformed (IR) fuel cell. This model is integrated in Aspen Plus™. Therefore, several MCFC/Gas Turbine systems are introduced and investigated. One of this a new cycle is called a heat recovery (HR) cycle. In the HR cycle, a regenerator is used to preheat water by outlet air compressor. So the waste heat of the outlet air compressor and the exhaust gases of turbine are recovered and used to produce steam. This steam is injected in the gas turbine, resulting in a high specific power and a high thermal efficiency. The cycles are simulated in order to evaluate and compare their performances. Moreover, the effects of an important parameters such as the ambient air temperature on the cycle performance are evaluated. The simulation results show that the HR cycle has high efficiency.

Analysis of the start-up and variable load operation of a combined cycle power plant for off-grid mines

Mining is an economic activity that intensively uses energy in the extraction and processing of raw minerals. This means that large amounts of greenhouse gas (GHG) emissions are released into the atmosphere. Natural gas in conjunction with combined cycle power plants (CCPP) could replace other more contaminant sources of energy, such as diesel, which is the fuel traditionally preferred in mining to generate power in remote sites. Today, however, the operation of CCPP in stand-alone power systems under frequent load variations and plant start-ups remains challenging. During start-up operations of CCPP, high thermal and mechanical stresses negatively affect the components of the heat recovery steam generator (HRSG). Special off-grid CCPP applications require additional considerations regarding design and operation. Motivated by the challenges associated with using CCPPs in off-grid mines as a main source of electrical power, a CCPP mathematical model was developed to evaluate load changes during start-up and shut-down operations. Two strategies were investigated to minimise consumption of steam: bypass of gas turbine (GT) exhaust gases during a time interval and GT warm-up hold. Results demonstrated that these strategies reduced stresses on the steam drum and lifetime consumption, but could also induce additional fatigue cycles during start-up operations.

Моделирование энергосберегающих промышленных установок с термохимической регенерацией

The article explains importance of elaborating scientific and technical solutions aimed at creating energy-saving and environmentally friendly technologies based on thermochemical recovery (TCR) of the heat of natural gas combustion products. To address this challenge, the authors propose to use the SCAN (Steam Conversion Analyzer) software package, a computation system based on the results from numerical investigation of the processes that occur during thermochemical heat recovery and intended for providing the necessary information support to specialists in charge for developing process flow diagrams involving the use of TCR. A characteristic feature of the above-mentioned software system is that it combines mathematical models intended for calculating process flow diagrams (represented by lumped-parameter or system models) and models for calculating hydrodynamic and heat-and-mass transfer processes accompanied by chemical reactions in the apparatuses included in the composition of process flow diagrams (represented by distributed-parameter or detailed models). The SCAN package allows the user to select packages and subroutines that make it possible to minimize the computation time and resources required to perform the computation. In addition, the system includes features for tracking how the values of sought characteristics depend on the degree of detail (accuracy) of the model describing the process under study. The SCAN software system includes a library module containing the process flow diagrams of installations and individual apparatuses within their composition. Each example is supplemented with recommendations for modeling and arranging the processes, which were obtained as a result of numerical calculations. Two examples of using the SCAN software system for elaborating circuit solutions and simulating the processes involving TCR are given. The first example is devoted to the scheme for analyzing the TCR of the heat of gas turbine exhaust gases, and the second one is devoted to modeling the processes according to an algorithm combining system and detailed calculations. It is pointed out that the SCAN software system offers the possibility to study the effect the design features of apparatuses (including the design of reaction elements that make up the conversion reactor) and the process operating parameters have on the conversion completeness degree. It also allows the user to evaluate the saving of fuel in a production process or in generating electricity.

Development of an exhaust air turbine engine

The article discusses ways of utilizing exhaust gas heat to improve the power efficiency of heat engines. The concept of an air turbine engine is chosen to make a generator drive with the capacity of 150 kW intended to produce energy for a gas-pumping unit. In an air turbine engine atmospheric air heated by the exhaust gases of the gas turbine drive of a gas pumping unit serves as the working fluid. Three thermodynamic cycle schematics for an air turbine engine (ATE) are analyzed. The optimal design of an ATE comprising a two-stage axial compressor, a recuperative air heater (RAH), an ejector and a single-stage axial turbine is determined on the basis of thermodynamic calculations. Compressed air from the ATE compressor unit is used in the ejector as the active flow, while the combustion products of the NK-16ST engine are used as the passive flow. The recuperative air heater and ejector are located in the exhaust line of the gas pumping unit. The chosen design concept of the air turbine engine corresponds to the technical requirements of gas transmission enterprises.

Transient Simulation of a Waste Heat Recovery from Gas Turbine Exhaust

Transient Simulation of a Waste Heat Recovery from Gas Turbine Exhaust

Exergy analysis of the dual pressure HRSG for varying physical parameters

Heat recovery steam generator (HRSG) is used to capture the heat of gas turbine exhaust gases for generating steam to run the steam turbine in gas/steam combined cycle power plant (CCPP). The performance of HRSG affects the steam turbine output and thus the overall combined cycle performance. The present study considers operating conditions of a 663MW, combined cycle power plant at Auraiya (U.P.), India for carrying out the exergy based investigation of a dual pressure HRSG. Different physical parameters of HRSG such as fin height, fin density and fin thickness are varied for analyzing exergy loss and exergy efficiency at different steam generation pressures. The exergy analysis shows how the exergy losses get lowered for LP evaporator and the exergy efficiency improves in LP economizer for higher fin heights and fin densities.

Thermodynamic assessment of integrated biogas-based micro-power generation system

In this paper, a thermodynamic modelling of an integrated biogas (60%CH4+40%CO2) micro-power generation system for electricity generation is reported. This system involves a gas turbine cycle and organic Rankine cycle (ORC) where the wasted heat of gas turbine cycle is recovered by closed ORC. The net output power of the micro-power generation system is fixed at 1.4MW includes 1MW power generated by GT and 0.4MW by ORC. Energy and exergy assessments and related parametric studies are carried out, and parameters that influence on energy and exergy efficiency are evaluated. The performance of the system with respect to variation of design parameters such as combustion air inlet temperature, turbine inlet temperature, compressor pressure ratio, gas turbine isentropic efficiency and compressor isentropic efficiency (from the top cycle) and steam turbine inlet pressure, and condenser pressure (from bottoming cycle) is evaluated. The results reveal that by the increase of gas turbine isentropic efficiency, the outlet temperature of gas turbine decreases which incurs negative impacts on the performance of air preheater and heat exchanger, however the energy and exergy efficiency increases in the whole system. By the increase of air compressor pressure ratio, the energy and exergy of the combined cycle decreases. The exergy efficiency of ORC alters by the variation of gas turbine parameters which can be attributed to the variation of temperature discrepancy between gas turbine exhaust temperature and ORC working fluid. Both first and second law efficiency of the combined cycle increases with the enhancement of inlet pressure of ORC turbine due to the mitigation of exergy destruction in heat exchanger. The rate of power generation in ORC increases by the enhancement of ORC turbine inlet pressure, however overall exergy destruction of the cycle decreases slightly.

Design of a hybrid power plant integrated with a residential area

Power generation with high efficiency and low CO2 emission is a crucial issue for power production industry. In this research, a retrofit design for a power plant was proposed to use of solar irradiation before combustion section of gas turbine cycle. To do so, a solar tower with heliostat field was employed for compressed air preheating. A steady-state modeling of all parts of the proposed hybrid power plant was performed. Then, a coupled method of Particle Swarm Optimization and Genetic Algorithm was applied for a multi-objective optimization on the power plant performance. Based on the results, with %62 solar share factor, fuel efficiency was increased to %85 and about 400 kg reductions in CO2 emissions were occurred. Finally, for heat recovery of exhaust gases of solar gas turbine, a CCHP system was designed to supply cooling, heating and power for more than 15,000 households in a residential area near the studied power plant. Therefore, along with effective utilization of thermal content of turbine discharging gases and according to local energy consumption pattern, 4000 MWhe per year of electricity was obtained. Moreover, 31 million cubic meters saving in natural gas consumption were approximately achieved as a result of solar-heat integration.

Thermodynamic analysis of combined cycle under design/off-design conditions for its efficient design and operation

To achieve a highly efficient design and operation of combined cycles, this study analyzed in detail the off-design characteristics of the main components of three combined cycles with different compressor pressure ratios (PRs) based on real units. The off-design model of combined cycle was built consisting of a compressor, a combustor, a gas turbine, and a heat recovery steam generator (HRSG). The PG9351FA unit is selected as the benchmark unit, on the basis of which the compressor is redesigned with two different PRs. Then, the design/off-design characteristics of the three units with different design PRs and the interactive relations between topping and bottoming cycles are analyzed with the same turbine inlet temperature (TIT). The results show that the off-design characteristics of the topping cycle affect dramatically the combined cycle performance. The variation range of the exergy efficiency of the topping cycle for the three units is between 11.9% and 12.4% under the design/off-design conditions. This range is larger than that of the bottoming cycle (between 9.2% and 9.5%). The HRSG can effectively recycle the heat/heat exergy of the gas turbine exhaust. Comparison among the three units shows that for a traditional gas-steam combined cycle, a high design efficiency results in a high off-design efficiency in the usual PR range. The combined cycle design efficiency of higher pressure ratio is almost equal to that of the PG9351FA, but its off-design efficiency is higher (maximum 0.42%) and the specific power decreases. As for the combined cycle with a design PR of 12.73, the decrement of the efficiency under the design/off-design conditions is in the range of 0.20–0.39%, however, its specific power increases. Thus, for the efficient design of a combined cycle, its optimal efficiency and maximum specific power, instead of that of the topping cycle, should be considered. For the operation strategy, the performance of the topping cycle should be kept at a high level first (the turbine inlet temperature should be as high as possible), followed by the high setting of the turbine exhaust temperature.

Failure Mechanisms of Fiber Optic Temperature Sensors in High Temperature and Vibration Environments

ABSTRACTFiber optic temperature sensors are used in a variety of harsh environment applications. We have explored use of such temperature sensors in commercial gas turbines to measure the temperature at various regions of interest within the turbine system. More specifically, fiber optic temperature rakes were designed and installed on a commercial gas turbine under full load conditions. This work will focus on failure mechanisms observed at multiple length scales that impact the performance of high temperature optical fiber sensors. It was found that Au-coated silica fibers, which are a standard in the industry, undergo various failure modes when subjected to combinations of high temperature and high vibration. More specifically, the Au coating became soft/ductile as the temperature is increased. We also observed that the Au coating was not well bonded to the silica fiber, as expected since there were no adhesion layers present. These effects led to significant damage of the fiber optic under high vibrations. We also found that vibrations from the gas turbine coupled into fundamental modes of the fiber optic probe assembly, which were analyzed by detailed dynamic mechanical analysis. This led to the fiber impacting the internal wall of the probe assembly, which caused further damage and failure of the fiber and the Au coating. The silica fibers returned from the field also exhibited significant twisting throughout most of their length. This suggests the fibers reached temperatures above their strain point (about 1000 C for pure silica glass), which is explained by either a) the strain point had been significantly reduced by the presence of the Ge dopant, or b) the temperature was higher than expected in the gas turbine exhaust region. It was also hypothesized that complex anelastic effects may play a role under the high temperature, high vibration environment experienced by the probes. Detailed structural analysis of the fiber optic temperature sensors by scanning electron microscopy, ToF-SIMS, and X-ray microscopy will be presented to corroborate the above simulations and proposed damage mechanisms. Finally, we note that the fiber Bragg gratings (FBG) present within the temperature probes provided promising temperature data, and were in fact not damaged/erased by the high temperature environment.

Sequential supplementary firing in natural gas combined cycle with carbon capture: A technology option for Mexico for low-carbon electricity generation and CO2 enhanced oil recovery

Combined cycle gas turbine power plants with sequential supplementary firing in the heat recovery steam generator could be an attractive alternative for markets with access to competitive natural gas prices, with an emphasis on capital cost reduction, and where supply of carbon dioxide for Enhanced Oil Recovery (EOR) is important. Sequential combustion makes use of the excess oxygen in gas turbine exhaust gas to generate additional CO2, but, unlike in conventional supplementary firing, allows keeping gas temperatures in the heat recovery steam generator below 820°C, avoiding a step change in capital costs. It marginally decreases relative energy requirements for solvent regeneration and amine degradation. Power plant models integrated with capture and compression process models of Sequential Supplementary Firing Combined Cycle (SSFCC) gas-fired units show that the efficiency penalty is 8.2% points LHV compared to a conventional natural gas combined cycle power plant with the same capture technology. The marginal thermal efficiency of natural gas firing in the heat recovery steam generator can increase with supercritical steam generation to reduce the efficiency penalty to 5.7% points LHV. Although the efficiency is lower than the conventional configuration, the increment in the power output of the combined steam cycle leads a reduction of the number of gas turbines, at a similar power output to that of a conventional natural gas combined cycle. This has a positive impact on the number of absorbers and the capital costs of the post combustion capture plant by reducing the total volume of flue gas by half on a normalised basis. The relative reduction of overall capital costs is, respectively, 15.3% and 9.1% for the subcritical and the supercritical combined cycle configurations with capture compared to a conventional configuration. For a gas price of $2/MMBTU, the Total Revenue Requirement (TRR) – a metric combining levelised cost of electricity and revenue from EOR – of subcritical and supercritical sequential supplementary firing is consistently lower than that of a conventional NGCC by, respectively, 2.2 and 5.7 $/MWh at 0 $/t CO2 and by 4.9 and 6.7 $/MWh at $50/t CO2. At a gas price of $4/MMBTU and $6/MMBTU, the TRR of a subcritical configuration is consistently lower for any carbon selling price higher than 2.5 $/t CO2 and 37 $/t CO2 respectively.

Dual frequency comb laser absorption spectroscopy in a 16 MW gas turbine exhaust

We demonstrate the first frequency comb laser absorption spectroscopy in an industrial environment. Recent advancements in robust frequency comb design enabled installation of the sensor in an operating power plant, where we simultaneously measured temperature, H2O and CO2 concentration in the exhaust of a 16 MW stationary gas turbine. The frequency comb laser spectrometer probed 16,000 individual wavelengths of light spaced by 0.007 cm−1 (0.0014 nm) near 1440 nm, spanning 279 absorption features of H2O and 43 features of CO2. Fits to the measured absorption spectra yield simultaneous temperature, H2O and CO2 concentrations with between 10 and 60 second time resolution. Measurements over a 5 hour period tracked variations in the exhaust consistent with various changes to the gas turbine operation. Much larger wavelength ranges (200+ nm) and different time resolutions are possible depending on the desired precision by changing various settings on the same spectrometer. Overall, this work demonstrates the potential for frequency comb laser absorption spectroscopy in industrial combustion environments.

Thermodynamic performance simulation and concise formulas for triple-pressure reheat HRSG of gas–steam combined cycle under off-design condition

Concise semi-theoretical, semi-empirical formulas are developed in this study to predict the off-design performance of the bottoming cycle of the gas–steam turbine combined cycle. The formulas merely refer to the key thermodynamic design parameters (full load parameters) of the bottoming cycle and off-design gas turbine exhaust temperature and flow, which are convenient in determining the overall performance of the bottoming cycle. First, a triple-pressure reheat heat recovery steam generator (HRSG) is modeled, and thermodynamic analysis is performed. Second, concise semi-theoretical, semi-empirical performance prediction formulas for the bottoming cycle are proposed through a comprehensive analysis of the heat transfer characteristics of the HRSG and the energy conversion characteristics of the steam turbine under the off-design condition. The concise formulas are found to be effective, i.e., fast, simple, and precise in obtaining the thermodynamic parameters for bottoming cycle efficiency, HRSG heat transfer capacity, HRSG efficiency, steam turbine power output, and steam turbine efficiency under the off-design condition. Accuracy is verified by comparing the concise formulas’ calculation results with the simulation results and practical operation data under different load control strategies. The calculation errors are within 1.5% (mainly less than 1% for both simulation and actual operation data) under combined cycle load (gas turbine load) ranging from 50% to 100%. However, accuracy declines sharply when the turbine exhaust temperature seriously deviates from the design value and several specific operation strategies are employed when the units operate at ultra-low load (50% less combined cycle load/gas turbine load). The prediction results can be utilized as a relative reference. To improve prediction accuracy, a corresponding correction factor can be introduced for modification based on operating experience.

Thermo-economic optimization of heat recovery steam generator for a range of gas turbine exhaust temperatures

This paper illustrates the effect of selling price on the optimum design parameters of a heat recovery steam generator (HRSG) and the selection of its ideal configuration for an outlet temperature range of 350–650°C. The Particle Swarm Optimization (PSO) method was used, considering the steam cycle specific work as an objective to be maximized, the net present value as another objective to be maximized for the economic optimization and a combination of both. Three configurations of heat recovery steam generators are considered with one, two and three pressure levels and a reheat. The results show that, the three pressure level system is the best configuration from a thermodynamic point of view, but with respect to the economical aspect the two pressure levels is the best configuration for the low and medium selling prices (0.04$/kWh, 0.08$/kWh and 0.2$/kWh), whereas the three pressure level configuration would only be interesting for a high selling price of 0.3$/kWh and a temperature range 450–600°C. For a temperature of 650°C, the high cost of the three level system leads to a decrease in the net present value. As the selling price increases the optimized design parameters of the three pressure level HRSG based on economic or thermodynamic optimization are similar. The obtained results are used to elaborate a new correlation relating the net present value with the gas turbine outlet temperature, gas mass flow rate, number of levels of HRSG and selling price.

Ariane 5 Performance Optimization Using Dual-Bell Nozzle Extension

To evaluate the impact of dual-bell nozzles on the payload mass delivered into geostationary transfer orbit by Ariane 5 Evolution Cryotechnique Type A (ECA), detailed studies were conducted. For this purpose, a multitude of Vulcain 2 extension contours were designed. The two variation parameters were the starting point and the inflection angle of the nozzle extension. As the most upstream starting point, the position of the turbine exhaust gas injection was chosen. Geometrical restrictions were imposed by the launch pad ELA 3. Considering these parameters, an analytical and a numerical method were applied to predict the impact of the dual-bell nozzle on the payload mass. The analytical approach yields a correlation between specific impulse, nozzle mass, and payload mass increment. The numerical approach was conducted applying German Aerospace Research Center’s trajectory simulation code Trajectory Optimization and Simulation of Conventional and Advanced Transport Systems. Both calculation procedures yield good agreement, and the payload gain into geostationary transfer orbit was evaluated to be up to 490 kg. The study revealed the potential of a new class of dual-bell nozzles whose mode transitions already occur during engine startup, under sea-level conditions. A payload gain up to 200 kg was found. These nozzles were designated as “sea-level transitional dual-bell.”

Pressure model based coordinated control of VGT and dual-loop EGR in a diesel engine air-path system

This paper describes a pressure-model-based coordinated control method of a variable geometry turbine (VGT) and dual-loop exhaust gas recirculation (EGR) in a diesel engine air-path system. Conventionally, air fraction or burnt gas fraction states are controlled for the control of dual-loop EGR systems, but fraction control is not practical since sensors for fractions are not available on production engines. In fact, there is still great controversy over how best to select control outputs for dual-loop EGR systems. In this paper, pressure and mass flow states are chosen as control outputs without fraction states considering the availability and reliability of sensors. A coordinated controller based on the simple control-oriented model is designed with practical aspects, which is applicable for simultaneous operations of high pressure (HP) EGR, low pressure (LP) EGR, and VGT. In addition, the controller adopts the method of input-output linearization using back-stepping to solve the chronic problems of conventional pressure-based controllers such as coupling effects between operations of HP EGR, and VGT. The control performance is verified by simulation based on the proven GT-POWER model of a heavy-duty 6000cc diesel engine air-path.

An Experimental Investigation of the Performance Impact of Swirl on a Turbine Exhaust Diffuser/Collector for a Series of Diffuser Strut Geometries

A comprehensive experimental investigation was initiated to evaluate the aerodynamic performance of a gas turbine exhaust diffuser/collector for various strut geometries over a range of inlet angle. The test was conducted on a 1/12th scale rig developed for rapid and accurate evaluation of multiple test configurations. The facility was designed to run continuously at an inlet Mach number of 0.40 and an inlet hydraulic diameter-based Reynolds number of 3.4 × 105. Multihole pneumatic pressure probes and surface oil flow visualization were deployed to ascertain the effects of inlet flow angle and strut geometry. Initial baseline diffuser-only tests with struts omitted showed a weakly increasing trend in pressure recovery with increasing swirl, peaking at 14 deg before rapidly dropping. Tests on profiled struts showed a similar trend with reduced recovery across the range of swirl and increased recovery drop beyond the peak. Subsequent tests for a full diffuser/collector configuration with profiled struts revealed a rising trend at lower swirl when compared to diffuser-only results, albeit with a reduction in recovery. When tested without struts, the addition of the collector to the diffuser not only reduced the pressure recovery at all angles but also resulted in a shift of the overall characteristic to a peak recovery at a lower value of swirl. The increased operation range associated with the implementation of struts in the full configuration is attributed to the deswirling effects of the profiled struts. In this case, the decreased swirl reduces the flow asymmetry responsible for the reduction in pressure recovery attributed to the formation of a localized reverse-flow vortex near the bottom of the collector. This research indicates that strut setting angle and, to a lesser extent, strut shape can be optimized to provide peak engine performance over a wide range of operation.