High Back Pressure Research Articles

Impact of Active Control Turbocharging on the Fuel Economy and Emissions of a Light-Duty Reactivity Controlled Compression Ignition Engine: A Simulation Study

While forced induction strategies such as turbocharging can increase the power output and extend the load limit of engines operating on low temperature combustion strategies such as reactivity controlled compression ignition, the low exhaust enthalpy prevalent in these strategies requires the use of high backpressures to attain high turbocharger efficiencies, leading to high pumping losses and in turn poor fuel economy. Hence, there is a need to improve the exhaust energy utilization by the turbocharger such that the negative effects of the high backpressure requirements are offset. One turbocharger operating strategy that has the potential to enhance exhaust enthalpy conversion by the turbine is active control turbocharging (ACT), in which the rack position of a variable geometry turbocharger (VGT) is actuated using a continuously varying sinusoidal signal whose frequency is proportional to engine speed. In this study, the impact of ACT on turbocharger performance and fuel economy of a light-duty reactivity controlled compression ignition engine equipped with a VGT is investigated through coupled GT-POWER/KIVA-3V simulations at a medium-load cruise operating condition. A design of experiments study was executed in which the rack position amplitude and phase angle were independently varied, and the turbine efficiency, compressor efficiency, crankshaft torque, and brake specific fuel consumption were tracked for each run. The results show that ACT operation significantly increased the torque output while improving fuel economy over baseline VGT operation, but the range of actuation signal amplitude ratio was limited to 40% of the maximum amplitude possible due to peak cylinder pressure and peak pressure rise rate constraints. It is also shown that the impact of signal phase angle on turbocharger efficiency and overall system performance is not as significant as the amplitude ratio. The best fuel economy improvement over the baseline VGT operation at cruise conditions was observed at 40% amplitude ratio and 0° phase angle, and this value was 2.8%.

Study of Debris Filter Valve Opening Angle Adjustment for NPHR Improvement in Kaltim Teluk CFPP

Many things can affect the Net Plant Heat Rate (NPHR) value, including operating parameters, fuel and equipment’s condition. The performance target of NPHR for Kaltim Teluk CFB CFPP based on specifications is 3430 kCal / kWh. Operational data shows that the NPHR of Unit #1 and Unit #2 is higher then the performance target. Analysis of operation and maintenance data showed that the low average net load and high condenser back pressure are the dominant problems that caused heat loss. One way to minimize heat loss and improve NPHR performance can be done by maximizing debris filter cleaning process through adjusting valve opening angle which can reduce differential pressure and finally reduce the backpressure at the condenser. With the flow simulation inside the debris filter, in order to achieve maximum flow rate with acceptable erosion rate, the optimum cleaning reached at valve opening angle 75°-60° and with this cleaning method, heat loss can be reduced 14.96 kCal/kWh and 50.09 kCal/kWh for unit #1 and unit #2 respectively.

Harmonic Forcing from Distortion in a Boundary Layer Ingesting Fan

Integrating a fan with a boundary layer ingestion (BLI) configuration into an aircraft fuselage can improve propulsion efficiency by utilizing the lower momentum airflow in the boundary layer developed due to the surface drag of the fuselage. As a consequence, velocity and total pressure variations distort the flow field entering the fan in both the circumferential and radial directions. Such variations can negatively affect fan aerodynamics and give rise to vibration issues. A fan configuration to benefit from BLI needs to allow for distortion without large penalties. Full annulus unsteady computational fluid dynamics (CFD) with all blades and vanes is used to evaluate the effects on aerodynamic loading and forcing on a fan designed to be mounted on an adapted rear fuselage of a Fokker 100 aircraft, i.e., a tail cone thruster. The distortion pattern used as a boundary condition on the fan is taken from a CFD analysis of the whole aircraft with a simplified model of the installed fan. Detailed simulations of the fan are conducted to better understand the relation between ingested distortion and the harmonic forcing. The results suggest that the normalized harmonic forcing spectrum is primarily correlated to the circumferential variation of inlet total pressure. In this study, the evaluated harmonic forces correlate with the total pressure variation at the inlet for the first 12 engine orders, with some exceptions where the response is very low. At higher harmonics, the distortion content as well as the response become very low, with amplitudes in the order of magnitude lower than the principal disturbances. The change in harmonic forcing resulting from raising the working line, thus, increasing the incidence on the fan rotor, increases the forcing moderately. The distortion transfers through the fan resulting in a non-axisymmetric aerodynamic loading of the outlet guide vane (OGV) that has a clear effect on the aerodynamics. The time average aerodynamic load and also the harmonic forcing of the OGV vary strongly around the circumference. In particular, this is the case for some of the vanes at higher back pressure, most likely due to an interaction with separations starting to occur on vanes operating in unfavorable conditions.

Experimental and numerical investigation on inner flow and spray characteristics of elliptical GDI injectors with large aspect ratio

The application of non-circular elliptical orifice is recognized to increase the fuel spray and mixing quality, which has potential ability for modern gasoline direct injection (GDI) engines. In this research work, a single-hole elliptical GDI injector with aspect ratio of 4 was adopted. Numerical simulation and experimental spray test are both introduced to study the inner flow patterns and spray characteristics. The results indicated that the cavitation is mainly distributed on the minor axial plane of the elliptical GDI injector, and the cavitation domain decreases gradually with the increase of back pressure. Additionally, the unique swallowtail-like spray structure discharging from the elliptical GDI injector with aspect ratio of 4 was captured for the first time, and the swallowtail-like spray structure only appeared on the major view plane of the elliptic spray. Moreover, the GDI elliptical spray tip branching length reduced with the increase of the back pressure, and the high back pressure can inhibit the formation of swallowtail-like spray structure. Finally, the branching angle at the spray tip increased with the increase of back pressure, because high back pressure will enhance the effect of high aerodynamic force.

An Improved Calculation Method of Coal Consumption Index for Heating in CHP with a High Back Pressure Turbine

CHP (combined heating and power) system is playing an important role for district heating, meanwhile, the latent heat of exhausted steam at the thermal power plant is discharged to atmosphere directly, which is often more than 30%. Waste heat recovery is of great significance for reducing coal consumption indicators for heating in CHP system. The method by replacing different rotors of the LP (low pressure) cylinder is presented and experimented with a 140MW turbine, whose exhausted steam could be recovered completely. Besides, an improved calculation method of coal consumption index for heating is discussed. The improved mathematical model is used to calculate the influence of exhaust pressure on steam turbine power generation efficiency, which improves the accuracy of heating coal consumption. This experimented coal consumption index for heating is 12.7 kgce/GJ, which is much lower than the traditional CHP system (20 kgce/GJ).

Operation strategies of axial flow fans in a direct dry cooling system under various meteorological conditions

AbstractFor a direct dry cooling system, the turbine back pressure fluctuates with the meteorological conditions. Moreover, the operation of axial flow fans plays an important role in the cooling performance of air‐cooled condensers (ACC). It is of significant use to study the operation strategies of axial flow fans under various ambient conditions. Based on typical 2 × 660 MW direct dry cooling power generating units, the ACC model coupled with the turbine thermodynamic characteristics is developed, by which the thermo‐flow performances of the ACC are predicted in the dominant wind direction, and then the standard coal consumption is calculated. The results show that the increased ambient temperature and wind speed, or the reduced fan rotational speed leads to the high turbine back pressure. At the low ambient temperature and wind speed, the standard coal consumption rate of the unit can be reduced by reducing the speed of axial flow fans appropriately, with the maximum drop in coal consumption rate reached 0.734 g/(kWh) when the ambient temperature is 10°C without wind. If the wind speed exceeds 12 m/s or the ambient temperature reaches 25°C, 110% of the rated fan rotational speed is recommended.

Thermal performance of an absorption-assisted two-stage ejector air-to-water heat pump

A gas-fired air-to-water ejector heat pump (EHP) for domestic hot water production is proposed and analyzed thermodynamically. The COP of the EHP is improved by using binary fluids (HFE7500 and water), and the high backpressure in the primary ejector (first-stage) is actively controlled by either a second-stage ejector and/or a LiBr-H2O absorption subsystem. A thermodynamic model is established for analysis and performance evaluation. A case study shows the backpressure of the first-stage ejector is reduced by 53.5%, and the backpressure control using the second-stage ejector increases the system COP by 21.0% compared with that using LiBr-H2O absorption. Parametric studies are conducted to investigate the roles of the first-stage ejector, the second-stage ejector, and the LiBr-H2O absorption subsystem. The first-stage ejector plays a dominant role in the EHP system performance. The EHP’s heating COP can reach 2.0 with an entrainment ratio of 0.12 in the first-stage ejector. EHP performance can be improved with a high entrainment ratio and a low-temperature primary working fluid in the first-stage and second-stage ejectors, a low condensation temperature in the first-stage ejector, and a high generating temperature and a low concentration of the LiBr-H2O solution.

Modeliranje i evaluacija efekata visokog povratnog pritiska na sistemima baklji u rafineriji

Safety and reliability of the flare system are often affected by High Back-Pressure (HBP). The primary aim of this study is to simulate a steady-state model of flare system using Aspen Flare System Analyzer and with the aid of real plant data generated from Kaduna Refining and Petrochemical Company (KRPC) Ltd, Nigeria. Three credible scenarios (normal operation/surplus fuel, cooling water failure and power failure) were considered. The results showed that the steady-state model of flare system for normal operation (Surplus Fuel), cooling failure and power failure scenario and the flare system meet performance requirements at a system back pressure of 1.01325 bar, except for cooling water failure scenario which showed the occurrence of high fluid velocity and momentum (rhoV 2). Also, flare operation at normal back pressure, for all three scenarios does not exceed design and operational limits. The work recommends that KRPC managers should review options for reducing HBP particularly for cooling failure and power failure scenarios such that the back pressure would not exceed 10% of set pressure for the conventional valves.

Spatial and Time Distributions of Energy Consumption of High Back Pressure District Heating by Combined Heat and Power Generation

Spatial and Time Distributions of Energy Consumption of High Back Pressure District Heating by Combined Heat and Power Generation

Numerical analysis of a novel two-phase turbine using thermal non-equilibrium, homogeneous nucleation phase change

A total flow geothermal system with objective to co-generate fresh water from the expelled flash is being investigated for well heads located in the east African rift countries. Numerical analysis using two-phase models has been used to design the two-phase turbine of the power plant. A base turbine configuration of a curved rotating nozzle was evaluated against available test data at 400 kPa feedwater pressure, temperature of 117 °C and a back-pressure condition of 6 kPa in a water-cooled condenser operated at near vacuum. Along with the sensitivity of modelling factors on turbine performance, analysis indicated that the channel cross section, curvature, torque characteristics and pumping effect in the nozzle were required to be improved for obtaining a higher power output and efficiency. A novel two-phase turbine configuration has been proposed in this article that consists of a rotor–stator arrangement which facilitates reduction in the pumping effect at the inlet and transports the feedwater to a throat located at a larger radius of the disk. The new nozzle channel curvature is designed such that the suction surface produces negligible opposing torque, and the pressure surface produces a uniformly increasing torque. The new turbine is estimated to produce a 2.3 kW power output at 4623 rpm and although the feedwater flow increased by 34%, a 40% higher specific power output is obtained at an isentropic efficiency of 24%. Fresh water recovery was estimated to be around 12% for these working conditions. Two-phase flow evolution in the turbine has been presented as local variation of pressure, thermal non-equilibrium, and vapour distribution with varying operating speed. The proposed turbine is also capable of producing work output at high back pressure, close to atmospheric conditions so that it can be used in combined power and freshwater generation thermal plants.

Chiral metal-organic framework [Co2(d-cam)2(TMDPy)]@SiO2 core-shell microspheres for HPLC separation

Chiral metal-organic frameworks (MOFs), an emerging class of chiral porous materials, possess many excellent characteristics such as uniform and adjustable cavities, abundant chiral active sites and excellent chemical stability, which make them a promising candidate as new chiral stationary phases (CSPs) for usage in HPLC. Up to now, there are some homochiral MOFs that have been applied as CSPs for HPLC enantioseparations. Nevertheless, the irregular morphology of most prepared MOF crystals with wide size distribution often cause high column backpressure and low column efficiency for MOF packed columns, which is the main impediment for the practical applications of chiral MOFs in chiral separation. In this article, we adopted an in-situ growth method to prepare monodisperse homochiral MOF [Co2(d-cam)2(TMDPy)]@SiO2 core-shell composites as chiral selector for HPLC enantioseparation. The fabricated [Co2(d-cam)2(TMDPy)]@SiO2 column (column A) exhibited excellent chiral resolution ability toward various racemates. In addition, some positional isomers can be well separated on column A. Compared with the resolution ability of [Co2(d-cam)2(TMDPy)] packed column (column B), the column A shows higher column efficiency (e.g., 17,000 plates/m for trans-stilbene oxide) and lower background pressure (column pressure = 27 bar) than those of column B. The results indicated that the monodisperse chiral MOF [Co2(d-cam)2(TMDPy)]@SiO2 core-shell composites as CSP greatly improve the column efficiency and chiral resolution ability of the chiral MOF columns, providing a promising platform for chiral MOFs widely used in chiral separation.

Fundamental Study on Injector Flow Characteristics of Self-Pressurizing Fluid for Small Rocket Engines

Abstract Nitrous oxide is a suitable propellant for rocket engines and has been widely used in various countries, given its high saturated vapor pressure, which enables self-pressurization. Because nitrous oxide is in a state of vapor–liquid equilibrium in tanks, it is easy to form a gas–liquid two-phase flow by cavitation in feed line. Since accurately estimating the performance of rocket engines requires evaluating the characteristics of propellant flows, tests reported in this paper were conducted using hybrid rocket engines under three conditions: cold flow test, hot firing test at low back pressure, and hot firing test at high back pressure. With consideration to the subcooling degrees, nitrous oxide may be in an unsteady superheated state in the upstream flow of the injector. In a comparison of the pressure ratios between the injector in each test condition, it is observed that a critical two-phase flow was formed in the injector in the cold flow test and in the low backpressure firing test. In the high backpressure hot firing test, the injector flow may be choked, but the large oscillations were observed in chamber pressure and thrust. According to the FFT analysis results, these oscillations were caused by chugging and acoustic oscillation. In light of these experimental results, it is suggested that when the chamber pressure fluctuates due to combustion instability such as chugging and acoustic oscillation, it may affect the injector flow characteristics and the critical two-phase flow.

The role of fines on internal instability and its impact on undrained mechanical response of gap-graded soils

This study presents an experimental investigation of the contribution of non-plastic fines to the development of seepage-induced internal instability and its impact on the undrained mechanical response of gap-graded sands. The purpose of the laboratory tests is to observe the internal instability of two key microstructures: (1) an underfilled microstructure in which the coarser particles control the stress transfer and (2) an overfilled microstructure in which the finer particles play a primary role in the stress transfer. Tests on medium dense sands with seven different fines contents are conducted using a pressure-controlled triaxial erosion device. The device enables internal erosion tests with high back pressure under a pressure-controlled condition. The results indicate that the initial fines content significantly affects the initiation and progress of internal instability. The phenomena of self-filtering and suffusion, evident for underfilled soil, can occur at relatively small hydraulic gradients. Depending on the initial fines content, overfilled soil is vulnerable to suffosion, seepage-induced failure, or an internally stable state, which can occur at large hydraulic gradients. Undrained compression tests on eroded soils reveal that suffusion makes the soil looser and more contractive, while suffosion makes the soil more dilative at large strain levels. As suffusion may create an unstable structure in the soils, sudden drops in deviator stress and sharp increases in pore water pressure and radial strain with axial straining are detected in all the post-suffusion soils at small strain levels. Finally, the identificaton of internal instability is illustrated in terms of the void ratio and the fines content, for assessing the initiation and progress of instability phenomena, as well as the possible soil microstructures.

Thermodynamic, operational, and techno-economic analysis of the cascade heating system with a double-unit

High back-pressure technology is an efficient way to recover waste heat and improve the energy utilization efficiency and heating capacity of cogeneration systems. In this study, a coal-fired cogeneration system with a double-unit (2 × 300 MW) was selected as the reference system and modeled in the EBSILON professional system. Then, a detailed comparative analysis of cogeneration systems with double-units was conducted from the perspective of thermodynamic, operational, and techno-economic analyses. The results show that with the high back pressure technology, the gross thermal and generation efficiencies of the novel system increased by 8.82% and 14.28%, respectively, while the standard coal consumption rate for generation was reduced by 43.47 g/kWh. Besides, the average energy quality coefficient of the novel system was reduced by 0.12. The temperatures of the exhaust steam, supplied and returned water changed the operational characteristics, including the maximum heating capacity and feasible operational region. Moreover, with the decrease in the maximum temperature rise ratio in the heating condenser, the feasible operational region of the novel system was reduced. The techno-economic analysis shows that under the given conditions, the net annual revenue of the novel system is 3.55 × 106 CNY/year, and the discounted payback period of the novel system is 10.55 years.

Performance improvement of low-pressure cylinder in high back pressure steam turbine for direct heating

It is the general retrofit to remove the last stages in the low-pressure cylinder of steam turbine for high back pressure direct heating, which can avoid the exergy loss caused by the traditional extracting steam heating mode of combined heat and power. However, the flow field of low-pressure cylinder will change. In this study, the last stage flow field of low pressure cylinder of such high back pressure turbine, as well as the temperature distribution, is analyzed and optimized by setting the diversion ring. Low-pressure cylinder of the 300 MW steam turbine is selected as the research object. The optimal scheme is obtained after analyzing vortex distribution, static pressure recover coefficient and total pressure loss coefficient in flow field under different heating conditions. The results show that adding appropriate diversion ring bringing about vortex effectively reduced, leading to a sharp increase of 7.84% in efficiency of low-pressure cylinder and 0.63in statistic pressure recover efficient. It is also contributing to an apparently decrease of 0.95 in total pressure loss efficient. All results indicate that the aerodynamic performance of low-pressure cylinder has obvious promotion. Under high back pressure heating condition, the structure of low-pressure cylinder of steam turbine changed.

Analysis on thermal characteristics of high back pressure heating retrofit for large-scale steam turbine units

High back pressure heating with large-scale steam turbine units boasts preponderant heating capacity and preferable integrated utilization of energy while suffering high operation and maintenance cost and low operation flexibility. First, the high back pressure heating retrofit technology is introduced. Then, a model to analyze off-design performance of turbine and condenser for a 350MW heating unit was established using EBSILON software, by which quantitative calculation was performed of the influence of the key factors, so as to attain thermal characteristics of high back pressure heating. Finally, the paper was ended with multivariate analysis of the key factors in a combination of the theoretical analysis, the calculation results and the actual operating environment of the 350MW heating unit, in a bid to outline a change range of each factor. It thereby provided reference for selection of key parameters, feasibility analysis and operation economic analysis in high back pressure heating retrofit.

How Can Active Exhaust Systems Contribute to the Reduction of CO <sub>2</sub> Emission and Comply with Future Pass-By Noise Limits?

<div class="section abstract"><div class="htmlview paragraph">The pass-by noise limits of passenger vehicles according to ISO 362 / R51.03 [<span class="xref">1</span>, <span class="xref">2</span>] will be further reduced by 2 dB in 2024 in Europe. Since the pass-by noise is substantially influenced by exhaust noise, the effort for the exhaust system needs to be increased substantially. This results in systems with larger mufflers or higher backpressure. However, the more stringent CO<sub>2</sub>-emission targets require ever more efficient powertrains, which calls for rather lower backpressure to optimize the engine design.</div><div class="htmlview paragraph">This paper describes how compact active exhaust lines can support a design for low backpressure and high acoustic attenuation at the same time. For two passenger vehicles with gasoline engines active exhaust lines are investigated in detail and the results are compared to the series production exhaust lines. Thus, in one exemplary case, the pass-by noise of a limousine could be reduced from 70 dB(A) to 68 dB(A) without any change in the vehicle design except the improved exhaust system. In a second example, the backpressure of a passenger vehicle was reduced by > 100 mbar and at the same time a lower tailpipe noise could be achieved with essentially the package space.</div></div>

Numerical studies and validation of combustor and annular isolator interactions of hydrocarbon based axisymmetric dual combustion ramjet

Combustor Intake interactions study is very important for design of Ramjet/Scramjet propulsion systems. High Combustion-induced back pressures make the shock train propagate upstream further and interfere the flow of inlet and the scramjet would unstart. The study has more relevance especially for the propulsion systems like Dual Combustion Ramjet (DCR) due to its wider range operation of Mach number. In this paper, numerical simulation of flow field in an axisymmetric scramjet/ramjet combustor with annular isolator is carried out. Configuration chosen for simulation is Dual Combustion Ramjet, which has a dump subsonic combustor, main supersonic Combustor and an annular isolator. Objective of the work is to evolve a CFD procedure for combustor-isolator interaction and validation of the model with experimental data. Geometry of model DCR is taken from literature for simulations and studies are carried out for Isolator inlet Mach No. 1.79 and 2.23. Favre Averaged equations are solved using Commercial code–ANSYS FLUENT. Premixed composition of air and Kerosene is introduced into dump combustor. Reactive flow is modelled using 7 species and 4 step chemistry. Numerical simulations have been carried out with various turbulence models namely k–ε (Standard), (RNG) k–ε, kω-Standard, kω-SST and combustor wall pressures were compared with experimental results. Error in estimation of starting location of Shock train, Maximum Pressure, Average pressure in combustor is compared. (RNG) k–ε predicted shock train location with an error difference of 5% compared to k–ε (Standard). Further, effect on shock train position in isolator with change in gas generator equivalence ratio is also studied for free stream Mach numbers 4 and 5. Shock train moves upstream in Isolator with increase in gas generator equivalence ratio. Various parameters such as Wall static Pressure, Shock train location, length and static pressure along shock train centre, Velocity profile and Combustion efficiency are compared for reactive flow turbulence models.

Energy and Exergy Evaluations of a Combined Heat and Power System with a High Back-Pressure Turbine under Full Operating Conditions

High back-pressure technology is a promising method for the waste heat recovery of exhaust steams in combined heat and power systems. In this research, a 300 MW coal-fired subcritical combined heat and power system was selected as the reference system, and modeled in EBSILON professional. Then, energy-based and exergy-based performances of the high back-pressure system and traditional combined heat and power system were compared under full operating conditions. Moreover, a novel exergy-based evaluation method, which considers the energy level of the heating supply, was proposed and applied to evaluate the two systems. Results show that: In design conditions, both the heating capacity and power output of the high back-pressure system were higher than those of the extraction condensing system, which led to 17.67% and 33.21% increments of the gross thermal efficiency and generation efficiency, respectively. Compared with the extraction condensing system, the exergy efficiencies of the high back-pressure system were 7.04–8.21% higher. According to the novel exergy-based evaluation, the exergy efficiencies for the generation of the high back-pressure system and extraction condensing system were 46.48% and 41.22%, respectively. This paper provides references for the thermodynamic performance evaluation of the combined heat and power system.

Turbine vane endwall partition film cooling based on the passage vortex core line

The aerodynamic and cooling characteristics of the endwall were studied by numerical and experimental methods. Two film-hole configurations, i.e. conventional film-hole arrangement and partitioned film-hole arrangement, were taken into consideration. The partitioned film-hole arrangement is proposed based on the analysis of the heat load and the near wall flow field of the endwall. The results show that the high heat transfer coefficient region on the endwall pressure side is consistent with the passage vortex core line, but independent of the pressure side separation line of the horseshoe vortex. Accordingly, the endwall is divided into five regions based on the suction side separation line of the horseshoe vortex and the passage vortex core line. The five regions include upstream-passage wedge region, leading edge region, pressure side region, downstream region of the pressure side and downstream region of the suction side. Compared with the conventional film-hole arrangement, the partitioned film-hole arrangement weakens the mixing of the coolant jet and the mainstream, thus reducing the energy loss and the total pressure loss at the outlet of the cascade. More importantly, the partitioned film-hole arrangement provides much uniform film coverage and a significant increase of the area-averaged film-cooling effectiveness by using less cooling air. This is derived from the fact that the partitioned film-hole arrangement has more film holes in the pressure side of the endwall with high back pressure, which improves the distribution of coolant on the endwall.