Preheat Limits in Practical Combustor Design: Experiments and Simulations

2018 ◽  
Author(s):  
Aleksandr Fridlyand ◽  
Brian Sutherland ◽  
Paul Glanville
Keyword(s):  
Natural Gas ◽  
A Priori ◽  
Effective Means ◽  
External Source ◽  
Chemical Kinetic ◽  
Residual Energy ◽  
Spontaneous Ignition ◽  
Autoignition Temperature ◽  
Air Stream ◽  
Experimental Apparatus

Autoignition in commercial and residential gas appliances is typically a phenomenon to be avoided. The autoignition temperature for a particular fuel, defined as the minimum temperature at which spontaneous ignition will occur without an external source of energy, is often used to characterize this phenomenon. In the design of combustion systems, it is used to demarcate conditions where autoignition may occur. In an emerging class of residential and commercial heating, cooling, and power generation appliances, preheating air and fuel can provide an effective means of boosting the overall energy efficiency by recuperating residual energy in the exhaust and reinvesting it back into the thermodynamic process. In such applications, the design question to answer is: How much can the air and fuel be preheated without autoignition? The autoignition temperature, often determined experimentally and can vary as much as 100°C for methane, may not be the most useful metric in this context. This work describes the results of a recent experimental investigation into the preheat limits for autoignition of air and natural gas with the aim of recuperating as much heat as possible in a heat pump. The experimental apparatus consisted of an air-fuel mixer supplying preheated mixture to a radiant burner. The air was first heated in excess of 750°C, cool natural gas was injected into and mixed with the hot-air stream, and all while avoiding autoignition. The current capability to predict autoignition in such applications a priori was also assessed using available chemical kinetic models and numerical simulations.

scholarly journals Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3731
Author(s):  
Maik Bertke ◽  
Ina Kirsch ◽  
Erik Uhde ◽  
Erwin Peiner
Keyword(s):  
Mass Concentration ◽  
Limit Of Detection ◽  
A Priori ◽  
Micro Electro Mechanical System ◽  
Single Chip ◽  
Air Stream ◽  
Mems Technology ◽  
Clean Air ◽  
Particle Sizer ◽  
Ultrafine Aerosol

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air.

Semi–Empirical Predictions and Correlations of NOx Emissions From Utility Combustion Turbines

1995 ◽  
Author(s):  
Donald M. Newburry ◽  
Arthur M. Mellor
Keyword(s):  
Natural Gas ◽  
A Priori ◽  
Fuel Oil ◽  
Pollutant Emissions ◽  
Nox Emissions ◽  
Time Model ◽  
Heterogeneous Effects ◽  
Inlet Conditions ◽  
Thermal Nox ◽  
Semi Empirical

Semi–empirical equations model the dominant subprocesses involved in pollutant emissions by assigning specific times to the fuel evaporation, chemistry, and turbulent mixing. They then employ linear ratios of these times with model constants established by correlating data from combustors with different geometries, inlet conditions, fuels, and fuel injectors to make a priori predictions. In this work, thermal NOx emissions from two heavy–duty, dual fuel (natural gas and fuel oil #2) diffusion flame combustors designated A and B operating without inert injection are first predicted, and then correlated using three existing semi–empirical approaches termed the Lefebvre (AHL) model, the Rizk–Mongia (RM) model, and the characteristic time model (CTM). Heterogeneous effects were found to be significant, as fuel droplet evaporation times were required to align the natural gas and fuel oil data. Only the RM model and CTM were employed to study this phenomenon. The CTM achieved the best overall prediction and correlation, as the data from both combustors fell within one standard deviation of the predicted line. The AHL and RM models were not able to account for the geometries of the two combustors. For Combustor A the CTM parameter correlated the data in a highly linear manner, as expected, but for Combustor B there was significant curvature. Using the CTM this was shown to be a residence time effect.

scholarly journals Pyrolysis and spontaneous ignition of wood under transient irradiation: Experiments and a-priori predictions

2017 ◽  
Vol 91 ◽  
pp. 218-225 ◽  
Author(s):  
Izabella Vermesi ◽  
Matthew J. DiDomizio ◽  
Franz Richter ◽  
Elizabeth J. Weckman ◽  
Guillermo Rein
Keyword(s):  
A Priori ◽  
Spontaneous Ignition

Experimental Investigation of Absorption and Desorption of Gas in Riser During MPD Well Control

2019 ◽  
Author(s):  
Mahendra Kunju ◽  
James L. Nielsen ◽  
Yuanhang Chen ◽  
Ting Sun
Keyword(s):  
Mass Transfer ◽  
Natural Gas ◽  
Large Scale ◽  
Drilling Fluid ◽  
Laboratory Scale ◽  
Initial Time ◽  
Dissolution Behavior ◽  
Transfer Model ◽  
Drilling Fluids ◽  
Experimental Apparatus

Abstract In this experimental work, the absorption and desorption of CO2 (Carbon Dioxide) in oil using a laboratory scale low-pressure experimental apparatus was conducted to study the dissolution behavior of gas in the oil. Estimating the concentration and rate of CO2 transfer from/to a non-aqueous column of static fluid is very important to understand the dissolution of natural gas in an oil-based mud within a well. Studying how natural gas dissolves in an oil-based drilling fluid is of great significance due to risks that a gas kick in an oil-based mud poses to equipment and workers’ health and safety once it is in the riser. By understanding the variables associated with this phenomena, better field practices can be developed and implemented to predict the dynamics of an influx and determine the best course of action when handling the influx. A laboratory scale experimental apparatus was designed and built to inject CO2 at the bottom of a seven-foot static column of VO. The apparatus has five test chambers that can be closed individually to isolate and measure the concentration of dissolved CO2 in oil in each of the sections. As a part of the experiment, the the backpressure applied to the column of oil was varied to observe how pressure affects the mass transfer due to absorption and desorption within the oil column. The amount of gas injected was 1.0 liter per minute of CO2 with a back pressure of the apparatus ranging from 40 to 80 psi. The results of this study will influence further experiments and testing using larger scale equipment involving the dissolution of natural gas within various oil-based drilling fluids at higher pressures. This study also allows for the development of an initial time-dependent mass transfer model which will also be used for predicting dissolution dynamics of Methane in diesel for future large-scale testing.

Anaerobic 35°C and 55°C Treatment of a BCTMP/TMP Effluent: Sulphur Management Strategies

1994 ◽  
Vol 29 (5-6) ◽  
pp. 433-445 ◽  
Author(s):  
R. J. Stephenson ◽  
R. M. R. Branion ◽  
K. L. Pinder
Keyword(s):  
Hydrogen Sulphide ◽  
Effective Means ◽  
Management Strategies ◽  
Sulphate Reduction ◽  
Anaerobic Sludge ◽  
Thermomechanical Pulp ◽  
Treatment Efficiency ◽  
Sulphur Compounds ◽  
Experimental Apparatus ◽  
Molybdenum Addition

Pulp manufacture uses sulphur in a variety of forms and these sulphur compounds ultimately end up in the effluent. Under anaerobic conditions, sulphite and sulphate are reduced to sulphide, presenting problems of toxicity, odour, corrosion, and reduced methane yields and treatment efficiencies. The fate of these inorganic sulphur compounds in a bleached chemi-thermomechanical pulp/thermomechanical pulp (BCTMP/TMP) effluent mixture was examined in two phase anaerobic reactors at 35°C and 55°C. The following sulphur management strategies were investigated: 1) controlling the pH of the acidogenic reactor, 2) inhibiting the sulphur reducing bacteria via molybdenum addition to the feed tank, and 3) stripping the hydrogen sulphide dissolved in the methane phase reactor liquor by recycling hydrogen sulphide-free off gas. The laboratory scale experimental apparatus consisted of upflow anaerobic sludge bed pre-treatment or acidogenic reactors followed by hybrid upflow anaerobic sludge bed/fixed film methanogenic reactors. At 35°C, controlling the pH of the acidogenic reactors with sodium carbonate from 5.5 (uncontrolled) to 8.0 in order to shift the formed sulphide species to the less toxic ionic form appeared to be ineffective in promoting wastewater treatment efficiency. Molybdenum addition to the wastewater at levels from 0.1 to 1.0 mM was effective at 1.0 mM in retarding sulphate reduction or sulphide formation. Hydrogen sulphide stripping, using ferric chloride scrubbed and recycled off gas, appeared to be the most effective means of sulphur management for this type of wastewater under these conditions. Tbermophilic 55°C anaerobic treatment was also studied using the same effluent, inocula and sulphur management strategies. Overall, both the treatment efficiency and the sulphate reduction were lower for the thermophilic runs compared to the mesophilic runs. Raising the acidogenic phase reactor pH from 7.0 to 7.5 to 8.0 appeared to have no significant effect on organic carbon removal efficiency or on sulphate reduction. Molybdenum inhibition of sulphur reduction was not as marked as for the 1.0 mM level at 35°C, perhaps due to the already low baseline sulphate reduction efficiency at 55°C. Stripping hydrogen sulphide from the reactor liquor helped to promote the treatment efficiency and lowered the sulphide and sulphate levels. Similar to the 35°C study, sulphide removal by gas stripping appeared to be the most effective means of sulphur management

Modeling of Ignition and Combustion for Glow Plug Assisted Direct Injection Natural Gas Engines

2012 ◽  
Author(s):  
Stewart Xu Cheng ◽  
James S. Wallace
Keyword(s):  
Natural Gas ◽  
Heated Surface ◽  
Direct Injection ◽  
Cfd Modeling ◽  
Spontaneous Ignition ◽  
Layer Model ◽  
Glow Plug ◽  
Natural Gas Engines ◽  
Gas Ignition ◽  
Ignition And Combustion

Direct injection natural gas (DING) engines offer the advantages of high thermal efficiency and high power output compared to spark ignition natural gas engines. Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist. Simple experiments show that the thickness of the heat penetration layer of a glow plug is very small (≈10−5 m) within the time scale of the ignition preparation period (1–2 ms). Meanwhile, the theoretical analyses reveal that only a very thin layer of the surrounding gases (in micrometer scale) can be heated to high temperature to achieve spontaneous ignition. A discretized glow plug model and virtual gas sub-layer model have been developed for CFD modeling of glow plug ignition and combustion for DING diesel engines. In this paper, CFD modeling results are presented. The results were obtained using a KIVA3 code modified to include the above mentioned new developed models. Natural gas ignition over a bare glow plug was simulated. The results were validated against experiments. Simulation of natural gas ignition over a shielded glow plug was also carried out and the results illustrate the necessity of using a shield. This paper shows the success of the discretized glow plug model working together with the virtual gas sub-layer model for modeling glow plug assisted natural gas direct injection engines. The modeling can aid in the design of injection and ignition systems for glow plug assisted DING engines.

scholarly journals Alternative Fuels Based on Biomass: An Experimental and Modeling Study of Ethanol Cofiring to Natural Gas

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Marina Braun-Unkhoff ◽  
Jens Dembowski ◽  
Jürgen Herzler ◽  
Jürgen Karle ◽  
Clemens Naumann ◽  
...  
Keyword(s):  
Power Generation ◽  
Natural Gas ◽  
Gas Turbine ◽  
Kinetic Modeling ◽  
Ignition Delay ◽  
Chemical Kinetic ◽  
Parameter Range ◽  
Ignition Delay Times ◽  
Combustion Properties ◽  
Delay Times

In response to the limited resources of fossil fuels as well as to their combustion contributing to global warming through CO2 emissions, it is currently discussed to which extent future energy demands can be satisfied by using biomass and biogenic by-products, e.g., by cofiring. However, new concepts and new unconventional fuels for electric power generation require a re-investigation of at least the gas turbine burner if not the gas turbine itself to ensure a safe operation and a maximum range in tolerating fuel variations and combustion conditions. Within this context, alcohols, in particular, ethanol, are of high interest as alternative fuel. Presently, the use of ethanol for power generation—in decentralized (microgas turbines) or centralized gas turbine units, neat, or cofired with gaseous fuels like natural gas (NG) and biogas—is discussed. Chemical kinetic modeling has become an important tool for interpreting and understanding the combustion phenomena observed, for example, focusing on heat release (burning velocities) and reactivity (ignition delay times). Furthermore, a chemical kinetic reaction model validated by relevant experiments performed within a large parameter range allows a more sophisticated computer assisted design of burners as well as of combustion chambers, when used within computational fluid dynamics (CFD) codes. Therefore, a detailed experimental and modeling study of ethanol cofiring to NG will be presented focusing on two major combustion properties within a relevant parameter range: (i) ignition delay times measured in a shock tube device, at ambient (p = 1 bar) and elevated (p = 4 bar) pressures, for lean (φ = 0.5) and stoichiometric fuel–air mixtures, and (ii) laminar flame speed data at several preheat temperatures, also for ambient and elevated pressure, gathered from literature. Chemical kinetic modeling will be used for an in-depth characterization of ignition delays and flame speeds at technical relevant conditions. An extensive database will be presented identifying the characteristic differences of the combustion properties of NG, ethanol, and ethanol cofired to NG.

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