Pressure Dependence of the Stability Limits and the NOX Exhaust Gas Concentrations in Case of Swirl-Stabilized, Diffusion Flames Burning in a Lift-Off Regime

2009 ◽  
Author(s):  
Plamen Kasabov ◽  
Nikolaos Zarzalis
Keyword(s):  
Reaction Zone ◽  
Diffusion Flames ◽  
Sudden Change ◽  
Measurement Data ◽  
Exhaust Gas ◽  
Stabilization Mechanism ◽  
Lifted Flames ◽  
Lift Off ◽  
Stability Limits ◽  
The Impact

The present study deals with confined, swirl-stabilized, diffusion flames burning in a lift-off regime and is meant to be a meaningful extension of our previous work [1]. The unique features of these hybrid flames originate from the presence of the so called lift-off zone located between the burner exit and the reaction zone. In the lift-off zone, surrounded by hot recirculating exhaust gases, the liquid fuel heats up and will reach a certain degree of prevaporation and premixing before entering the reaction zone. For that reason lifted flames posses some of the advantages of the premixed flames, for example in respect of emissions, but lack their major drawbacks, such as susceptibility to flashback and combustion noise. The investigations were motivated by the high NOX reduction potential of the lifted flames and the scarce information about their emission characteristics, flame behaviour and stability limits for gas turbine typical conditions especially when operated with liquid fuels. In order to gain a deeper understanding of the stabilization mechanism of lifted flames, several process parameters were varied within this study. The impact of the pressure (up to 18bar), of the air preheating and of the stoichiometry on the NOX emissions and on the lean blowout limits was investigated and discussed. The lift-off burning mode was achieved by utilizing a modified airblast nozzle and kerosene serving as a fuel. To acquire measurement data for a set of Reynolds numbers and residence times, four nozzles with similar geometries, but different scaling factors were employed. All main components of the exhaust gas were detected by means of conventional gas analysis. The NOX concentrations for the whole measured pressure range and for adiabatic flame temperatures up to 1800K does not exceed 20ppm normalized for 15% O2. The carbon monoxide concentration served as indicator for the presence of flame instabilities. The evaluation of the gathered data revealed some interesting phenomena. For example a sudden change in the nitrogen oxides concentration plotted over the equivalence ratio allows to distinguish between two burning modes: lift-off and detached flame. Another interesting finding is a maximum in the profile of the LBO limits as a function of the operational pressure, signifying a change in the predominant stabilization mechanism.

Effects of Flame Lift-Off on the Differences Between the Diffusion Flames From Circular and Elliptic Burners

1998 ◽  
Vol 120 (2) ◽  
pp. 161-166 ◽  
Author(s):  
S. R. Gollahalli
Keyword(s):  
Experimental Study ◽  
Combustion Product ◽  
Axial Velocity ◽  
Diffusion Flames ◽  
Air Entrainment ◽  
Lifted Flames ◽  
The Mean ◽  
Lift Off ◽  
Product Species

An experimental study conducted to determine the effects of lifting the flame base off the burner rim on the differences between the flame characteristics of diffusion flames from circular and elliptic burners is presented. The in-flame profiles of temperature, concentrations of fuel and combustion product species, and the mean and fluctuating components of axial velocity are presented. This study has shown that the effects of burner geometry in turbulent lifted flames are considerable only in the near-burner region. In the midflame and far-burner regions, the effects traceable to burner geometry are much weaker, contrary to those observed in the attached flame configuration. The observations are attributed to the turbulence and additional air entrainment into the jet prior to the flame base accompanying the lift-off process, which mitigate the effects of burner geometry.

Influence of Liquid and Gaseous Fuel on Lifted Flames at Elevated Pressure Stabilized by Outer Recirculation

2014 ◽  
Author(s):  
Julia Sedlmaier ◽  
Peter Habisreuther ◽  
Nikolaos Zarzalis ◽  
Peter Jansohn
Keyword(s):  
Elevated Pressure ◽  
Operating Conditions ◽  
Liquid Fuels ◽  
Reacting Flow ◽  
Ratio Distribution ◽  
Wide Range ◽  
Lifted Flames ◽  
Lift Off ◽  
Safety Considerations ◽  
The Impact

Lifting a flame from the flow generating nozzle to some distance apart has a wide variety of effects on the properties of the resulting combustion phenomenon. The reason of this influence is the generation of a non-reacting flow domain where mixing takes place prior to the combustion reaction. It is obvious that the quality of premixing that can be achieved strongly depends on the time that is given to flow and the intensity of the turbulence that is mixing fuel and air. The most important parameter that is characterizing this time is the size of the premixing zone quantified by the so called lift-off height (LOH). Additionally, when employing liquid fuel the lift-off of a flame provides time to achieve better pre-evaporation of the fuel. As a consequence, better mixing of fuel and air helps to avoid high temperature regions that may be a result from an inhomogeneous equivalence ratio distribution. From safety considerations a major advantage of this method compared to the application of a premixing duct is that the risk of hardware destruction by flame flash back can be eliminated. The current work extents the knowledge on lifted flames by the investigation of flames that are generated with an airblast atomizing nozzle that was designed to resemble systems close to application. Lifting of the flame is achieved applying a combination of swirling and non-swirling inflow ducts. A wide range of operating conditions as well as gaseous and liquid fuels are used to investigate their influence on the lift-off height. The lift-off height and location of the reaction zone was determined by means of chemiluminescence of OH* and it is shown, that the impact of pressure drop and preheating temperature on the LOH is different for gaseous and liquid fuels.

Lift-Off, Reattachment and Blowout Limits of Co-Flow Jet Diffusion Flames

2002 ◽  
Author(s):  
M. Karbasi ◽  
I. Wierzba
Keyword(s):  
Diffusion Flames ◽  
Flame Stabilization ◽  
Nozzle Geometry ◽  
Stream Velocity ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Lifted Flames ◽  
Lift Off ◽  
The Stability ◽  
Flowing Stream

The stability behaviour of jet diffusion flames in a co-flowing stream of air was examined. Their lift-off, reattachment and blowout limits were established for methane, propane, ethylene and hydrogen. The co-flowing air stream velocity affected significantly the mechanism of flame stabilization. Different flow regimes where the blowout of lifted flames or attached flames can occur were recognized. A transition region in which both the blowout of lifted flames as well as that of attached flames was observed and identified with respect to the value of the air stream velocity. It was found that the blowout limits for lifted flames in this region were much smaller than for the attached flames. The effects of changes in the nozzle geometry and co-flowing stream composition were also considered.

Three-Stream Flamelet Model for Industrial Applications

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Dirk Riechelmann ◽  
Masahiro Uchida
Keyword(s):  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Mixture Fraction ◽  
Industrial Applications ◽  
Exhaust Gas ◽  
Water Steam ◽  
Flamelet Model ◽  
Jet Diffusion Flames ◽  
Key Points ◽  
Lift Off

Efficient turbulent combustion models are typically designed for the numerical simulation of two-stream problems, namely, the combustion of fuel in air. There are applications, however, where large amounts of a diluent such as water steam or recirculated exhaust gas is supplied to the combustor independent of fuel and air supplies. In such cases, classical approaches become quite time-consuming. In the present paper, a new three-stream flamelet model is presented, which is essentially an extension of the two-stream flamelet model for diffusion flames. Key points of the approach are the introduction of a second mixture fraction variable and the efficient establishment of the flamelet library. After presentation of the theory, the applicability of the new model is demonstrated by comparison with experimental results for the lift-off height of jet diffusion flames.

scholarly journals A global analysis of the impact of COVID-19 stay-at-home restrictions on crime

2021 ◽  
Author(s):  
Amy E. Nivette ◽  
Renee Zahnow ◽  
Raul Aguilar ◽  
Andri Ahven ◽  
Shai Amram ◽  
...  
Keyword(s):  
Public Space ◽  
Global Analysis ◽  
Sudden Change ◽  
Interrupted Time Series ◽  
Urban Crime ◽  
Substantial Variation ◽  
Different Types ◽  
Time Series Analyses ◽  
The Impact ◽  
At Home

AbstractThe stay-at-home restrictions to control the spread of COVID-19 led to unparalleled sudden change in daily life, but it is unclear how they affected urban crime globally. We collected data on daily counts of crime in 27 cities across 23 countries in the Americas, Europe, the Middle East and Asia. We conducted interrupted time series analyses to assess the impact of stay-at-home restrictions on different types of crime in each city. Our findings show that the stay-at-home policies were associated with a considerable drop in urban crime, but with substantial variation across cities and types of crime. Meta-regression results showed that more stringent restrictions over movement in public space were predictive of larger declines in crime.

scholarly journals Quantification of Non-Exhaust Particulate Matter Traffic Emissions and the Impact of COVID-19 Lockdown at London Marylebone Road

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 190
Author(s):  
William Hicks ◽  
Sean Beevers ◽  
Anja H. Tremper ◽  
Gregor Stewart ◽  
Max Priestman ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Measurement Data ◽  
Emission Factors ◽  
Meteorological Conditions ◽  
Traffic Emissions ◽  
Atmospheric Particulate Matter ◽  
Exhaust Emission ◽  
Brake Wear ◽  
The Impact ◽  
Exhaust Particulate

This research quantifies current sources of non-exhaust particulate matter traffic emissions in London using simultaneous, highly time-resolved, atmospheric particulate matter mass and chemical composition measurements. The measurement campaign ran at Marylebone Road (roadside) and Honor Oak Park (background) urban monitoring sites over a 12-month period between 1 September 2019 and 31 August 2020. The measurement data were used to determine the traffic increment (roadside–background) and covered a range of meteorological conditions, seasons, and driving styles, as well as the influence of the COVID-19 “lockdown” on non-exhaust concentrations. Non-exhaust particulate matter (PM)10 concentrations were calculated using chemical tracer scaling factors for brake wear (barium), tyre wear (zinc), and resuspension (silicon) and as average vehicle fleet non-exhaust emission factors, using a CO2 “dilution approach”. The effect of lockdown, which saw a 32% reduction in traffic volume and a 15% increase in average speed on Marylebone Road, resulted in lower PM10 and PM2.5 traffic increments and brake wear concentrations but similar tyre and resuspension concentrations, confirming that factors that determine non-exhaust emissions are complex. Brake wear was found to be the highest average non-exhaust emission source. In addition, results indicate that non-exhaust emission factors were dependent upon speed and road surface wetness conditions. Further statistical analysis incorporating a wider variability in vehicle mix, speeds, and meteorological conditions, as well as advanced source apportionment of the PM measurement data, were undertaken to enhance our understanding of these important vehicle sources.

Waterflooding in Carbonate Reservoirs: Does the Salinity Matter?

2014 ◽  
Vol 17 (03) ◽  
pp. 304-313 ◽  
Author(s):  
A.M.. M. Shehata ◽  
M.B.. B. Alotaibi ◽  
H.A.. A. Nasr-El-Din
Keyword(s):  
Oil Recovery ◽  
Sudden Change ◽  
Oil Production ◽  
Deionized Water ◽  
Production Performance ◽  
Shallow Aquifer ◽  
Secondary Recovery ◽  
Tertiary Recovery ◽  
The Impact ◽  
Indiana Limestone

Summary Waterflooding has been used for decades as a secondary oil-recovery mode to support oil-reservoir pressure and to drive oil into producing wells. Recently, the tuning of the salinity of the injected water in sandstone reservoirs was used to enhance oil recovery at different injection modes. Several possible low-salinity-waterflooding mechanisms in sandstone formations were studied. Also, modified seawater was tested in chalk reservoirs as a tertiary recovery mode and consequently reduced the residual oil saturation (ROS). In carbonate formations, the effect of the ionic strength of the injected brine on oil recovery has remained questionable. In this paper, coreflood studies were conducted on Indiana limestone rock samples at 195°F. The main objective of this study was to investigate the impact of the salinity of the injected brine on the oil recovery during secondary and tertiary recovery modes. Various brines were tested including deionized water, shallow-aquifer water, seawater, and as diluted seawater. Also, ions (Na+, Ca2+, Mg2+, and SO42−) were particularly excluded from seawater to determine their individual impact on fluid/rock interactions and hence on oil recovery. Oil recovery, pressure drop across the core, and core-effluent samples were analyzed for each coreflood experiment. The oil recovery using seawater, as in the secondary recovery mode, was, on the average, 50% of original oil in place (OOIP). A sudden change in the salinity of the injected brine from seawater in the secondary recovery mode to deionized water in the tertiary mode or vice versa had a significant effect on the oil-production performance. A solution of 20% diluted seawater did not reduce the ROS in the tertiary recovery mode after the injection of seawater as a secondary recovery mode for the Indiana limestone reservoir. On the other hand, 50% diluted seawater showed a slight change in the oil production after the injection of seawater and deionized water slugs. The Ca2+, Mg2+, and SO42− ions play a key role in oil mobilization in limestone rocks. Changing the ion composition of the injected brine between the different slugs of secondary and tertiary recovery modes showed a measurable increase in the oil production.

The impact of stabilization mechanism on the aggregation kinetics of silver nanoparticles

2012 ◽  
Vol 429 ◽  
pp. 325-331 ◽  
Author(s):  
Amro M. El Badawy ◽  
Kirk G. Scheckel ◽  
Makram Suidan ◽  
Thabet Tolaymat
Keyword(s):  
Silver Nanoparticles ◽  
Aggregation Kinetics ◽  
Stabilization Mechanism ◽  
The Impact ◽  
Kinetics Of

A New Calculation Approach to the Energy Balance of a Gas Turbine Including a Study of the Impact of the Uncertainty of Measured Parameters

2005 ◽  
Author(s):  
Helmer G. Andersen ◽  
Pen-Chung Chen
Keyword(s):  
Energy Balance ◽  
Gas Turbine ◽  
Control Volume ◽  
Ambient Air ◽  
Energy Balance Equation ◽  
Inlet Temperature ◽  
Exhaust Gas ◽  
Gas Composition ◽  
Intake Flow ◽  
The Impact

Computing the solution to the energy balance around a gas turbine in order to calculate the intake mass flow and the turbine inlet temperature requires several iterations. This makes hand calculations very difficult and, depending on the software used, even causes significant calculation times on PCs. While this may not seem all that important considering the power of today’s personal computers, the approach described in this paper presents a new way of looking at the gas turbine process and the resulting simplifications in the calculations. This paper offers a new approach to compute the energy balance around a gas turbine. The energy balance requires that all energy flows going into and out of the control volume be accounted for. The difficulty of the energy balance equation around a gas turbine lies in the fact that the exhaust gas composition is unknown as long as the intake flow is unknown. Thus, a composition needs to be assumed when computing the exhaust gas enthalpy. This allows the calculation of the intake flow, which in turn provides a new exhaust gas composition, and so forth. By viewing the exhaust gas as a flow consisting of ambient air and combusted fuel, the described iteration can be avoided. The study presents the formulation of the energy balance applying this approach and looks at the accuracy of the result as a function of the inaccuracy of the input parameters. Furthermore, solutions of the energy balance are presented for various process scenarios, and the impact of the uncertainty of key process parameter is analyzed.

scholarly journals A Statistical Modeling Methodology for Long-Term Wind Generation and Power Ramp Simulations in New Generation Locations

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2442 ◽  
Author(s):  
Jussi Ekström ◽  
Matti Koivisto ◽  
Ilkka Mellin ◽  
Robert Millar ◽  
Matti Lehtonen
Keyword(s):  
Power Generation ◽  
Wind Power ◽  
Statistical Modeling ◽  
Renewable Energy Sources ◽  
Measurement Data ◽  
Wind Power Generation ◽  
System Level ◽  
Wind Generation ◽  
The Impact

In future power systems, a large share of the energy will be generated with wind power plants (WPPs) and other renewable energy sources. With the increasing wind power penetration, the variability of the net generation in the system increases. Consequently, it is imperative to be able to assess and model the behavior of the WPP generation in detail. This paper presents an improved methodology for the detailed statistical modeling of wind power generation from multiple new WPPs without measurement data. A vector autoregressive based methodology, which can be applied to long-term Monte Carlo simulations of existing and new WPPs, is proposed. The proposed model improves the performance of the existing methodology and can more accurately analyze the temporal correlation structure of aggregated wind generation at the system level. This enables the model to assess the impact of new WPPs on the wind power ramp rates in a power system. To evaluate the performance of the proposed methodology, it is verified against hourly wind speed measurements from six locations in Finland and the aggregated wind power generation from Finland in 2015. Furthermore, a case study analyzing the impact of the geographical distribution of WPPs on wind power ramps is included.

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