Parametric Effects on Exergetic Efficiency During H2-O2 Combustion Including Singlet Oxygen

2014 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Ignition Temperature ◽  
Equivalence Ratio ◽  
Flow Reactor ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Inlet Concentration ◽  
Optimal Range

Previous work conducted by the authors showed that for a stoichiometric inlet fuel-oxidizer ratio at 1 atm and 1200 K, an optimal range of exergetic efficiency exists for H2 combustion when singlet oxygen composes 0–20% of the oxidizer; with the maximum occurring at approximately 10%. Additionally, in the optimal range, 60% of the total exergy destruction occurs before ignition. These results provide encouraging evidence that it is possible to improve the exergetic efficiency of combustion inherently and thereby reduce fuel usage for a desired energy transfer. The focus of this study is to determine if the exergetic efficiency of combustion can be further optimized by varying other combustion parameters in addition to the inlet concentration of singlet oxygen. The chemical kinetics simulation was accomplished by developing an adiabatic plug flow reactor model in CHEMKIN-PRO® and employing the Moscow State University H2-O2 mechanism. The ranges of parameters considered were: equivalence ratio 0.7–1.3, inlet temperature 1100–1300 K, inlet concentration of singlet oxygen 0–20%, and diluent type (Ar, N2, no dilution). Pressure was held fixed at 1 atm. The calculated quantities were: exergetic efficiency, exergy destruction before ignition, molar conversion of H2, exit temperature, ignition temperature, and ignition distance. Results of the study show that over the optimum range the maximum exergetic efficiency occurs for an equivalence ratio of 1.3, with no dilution at 1300 K. Furthermore, the data show that for 20% inlet singlet oxygen there is significant variability in exergy destruction before ignition, ignition temperature, and ignition distance. Understanding how varying traditional combustion parameters impacts the enhancing effect that singlet oxygen has on the exergetic efficiency of H2 combustion provides a framework for directing future research efforts for hydrocarbon combustion under a broader range of operating conditions of practical engineering interest.

A Phenomenological Analysis of Exergy Destruction During Hydrogen Combustion With Electronically Excited Oxygen

2013 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Flow Reactor ◽  
Hydrogen Oxidation ◽  
Combustion Process ◽  
Hydrogen Combustion ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Optimal Range ◽  
Electronically Excited ◽  
Excited Oxygen

This study investigates the effects of introducing electronically excited oxygen on trends in exergy destruction during hydrogen combustion. Electronically excited oxygen enhances many properties of combustion. By understanding how it alters the chemical kinetics, and hence the destruction of exergy, it may be possible to improve the overall exergetic efficiency of combustion thereby reducing fuel use to achieve desired energy conversion. A numerical model was developed of an adiabatic plug flow reactor using CHEMKIN-PRO; in conjunction with a hydrogen oxidation mechanism that includes explicit reaction pathways for various electronically excited species. Exergy destruction was calculated for cases where singlet oxygen composed 0%–100% of the oxidizer while maintaining a stoichiometric oxidizer-fuel ratio; all other inlet conditions were held fixed. Results show that an optimal range of exergetic combustion efficiency exists between 0%–20%, with the maximum occurring at approximately 10%. A detailed assessment of the total exergy destruction reveals that, for the optimal range of exergetic combustion efficiencies, as much as 60% of the total exergy destruction occurs prior to ignition. For inlet percentages of singlet oxygen greater than 20%, the majority of the total exergy destruction occurs after ignition. This paper examines the phenomenological events taking place in the reaction mechanism that give rise to the destruction of exergy during combustion. Understanding these mechanisms and the effects of introducing excited oxygen into the combustion process, sheds light on how we might use excited oxygen to increase the exergetic efficiency of combustion.

Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

2013 ◽  
Author(s):  
Fan Gong ◽  
Yong Huang
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Heat Conducting ◽  
Inlet Velocity ◽  
The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

Optimisation of CO Turndown for an Axially Staged Gas Turbine Combustor

2020 ◽  
Author(s):  
Jacob E. Rivera ◽  
Robert L. Gordon ◽  
Mohsen Talei ◽  
Gilles Bourque
Keyword(s):  
Residence Time ◽  
Parametric Study ◽  
Gas Turbines ◽  
Flow Reactor ◽  
Operating Conditions ◽  
Independent Effect ◽  
Inlet Temperature ◽  
Operating Characteristics ◽  
Two Stage ◽  
The Impact

Abstract This paper reports on an optimisation study of the CO turndown behaviour of an axially staged combustor, in the context of industrial gas turbines (GT). The aim of this work is to assess the optimally achievable CO turndown behaviour limit given system and operating characteristics, without considering flow-induced behaviours such as mixing quality and flame spatial characteristics. To that end, chemical reactor network modelling is used to investigate the impact of various system and operating conditions on the exhaust CO emissions of each combustion stage, as well as at the combustor exit. Different combustor residence time combinations are explored to determine their contribution to the exhaust CO emissions. The two-stage combustor modelled in this study consists of a primary (Py) and a secondary (Sy) combustion stage, followed by a discharge nozzle (DN), which distributes the exhaust to the turbines. The Py is modelled using a freely propagating flame (FPF), with the exhaust gas extracted downstream of the flame front at a specific location corresponding to a specified residence time (tr). These exhaust gases are then mixed and combusted with fresh gases in the Sy, modelled by a perfectly stirred reactor (PSR) operating within a set tr. These combined gases then flow into the DN, which is modelled by a plug flow reactor (PFR) that cools the gas to varying combustor exit temperatures within a constrained tr. Together, these form a simplified CRN model of a two-stage, dry-low emissions (DLE) combustion system. Using this CRN model, the impact of the tr distribution between the Py, Sy and DN is explored. A parametric study is conducted to determine how inlet pressure (Pin), inlet temperature (Tin), equivalence ratio (ϕ) and Py-Sy fuel split (FS), individually impact indicative CO turndown behaviour. Their coupling throughout engine load is then investigated using a model combustor, and its effect on CO turndown is explored. Thus, this aims to deduce the fundamental, chemically-driven parameters considered to be most important for identifying the optimal CO turndown of GT combustors. In this work, a parametric study and a model combustor study are presented. The parametric study consists of changing a single parameter at a time, to observe the independent effect of this change and determine its contribution to CO turndown behaviour. The model combustor study uses the same CRN, and varies the parameters simultaneously to mimic their change as an engine moves through its steady-state power curve. The latter study thus elucidates the difference in CO turndown behaviour when all operating conditions are coupled, as they are in practical engines. The results of this study aim to demonstrate the parameters that are key for optimising and improving CO turndown.

Exergetic Efficiency: A Detailed Reaction Mechanism Analysis of Hydrogen Combustion With Singlet Oxygen

2015 ◽  
Author(s):  
DeVon A. Washington ◽  
Howard N. Shapiro
Keyword(s):  
Singlet Oxygen ◽  
Reaction Pathways ◽  
Combustion Mechanism ◽  
Mechanism Analysis ◽  
Exergy Destruction ◽  
Exergetic Efficiency ◽  
Chemical Induction ◽  
Fuel Use ◽  
Detailed Reaction Mechanism ◽  
Thermal Induction

In previous work the authors have demonstrated that when hydrogen is combusted in stoichiometric proportions at 1 atm and 1200 K, and singlet oxygen comprises 0–20% of the oxidizer, an optimal range of exergetic efficiency exists. The maximum exergetic efficiency occurs at approximately 10%. Over this range, roughly 60% of the total exergy destruction occurs prior to ignition. This is a significant result because it suggests that the exergetic efficiency of combustion might be improved at a fundamental level by chemical means, thereby inherently increasing the efficiency of fuel use for a desired energy application. The objective of the study presented in this paper is to analyze the reaction mechanisms for combustion with varying percentages of singlet oxygen, to determine which reaction pathways most influence the observed trends in exergy destruction and exergetic efficiency. This was accomplished by performing both sensitivity and rate-of-production analyses of the hydrogen-oxygen combustion mechanism. The results of the analysis show that the presence of singlet oxygen governs the rate of production of hydroxyl and other key radicals. These key radicals directly affect the phenomenological processes associated with chemical induction and thermal induction during ignition. Therefore, the observed optimum exergetic efficiency correlates to the quantity of singlet oxygen in the inlet charge that minimizes exergy destruction by fostering chemical reactions due to radical formation to a greater extent than thermal heat release. The results of this analysis are noteworthy and provide new insight regarding how the exergetic efficiency of combustion may be optimized by introducing singlet oxygen, thereby altering the reaction pathways to enhance energy conversion in a fundamental way that could have important implications for improved fuel use.

Behavior Prediction Model in Gas Fueled Spark Ignition Internal Combustion Engines Turbocharged for Genset Application

2013 ◽  
Author(s):  
Jorge Duarte Forero ◽  
German Amador Diaz ◽  
Fabio Blanco Castillo ◽  
Lesme Corredor Martinez ◽  
Ricardo Vasquez Padilla
Keyword(s):  
Equivalence Ratio ◽  
Internal Combustion Engines ◽  
Combustion Engine ◽  
Internal Combustion ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Combustion Engines ◽  
Gaseous Fuels ◽  
Methane Number

In this paper, a mathematical model is performed in order to analyze the effect of the methane number (MN) on knock tendency when spark ignition internal combustion engine operate with gaseous fuels produced from different thermochemical processes. The model was validated with experimental data reported in literature and the results were satisfactory. A general correlation for estimating the autoignition time of gaseous fuels in function of cylinder temperature, and pressure, equivalence ratio and methane number of the fuel was carried out. Livengood and Wu correlation is used to predict autoignition in function of the crank angle. This criterium is a way to predict the autoignition tendency of a fuel/air mixture under engine conditions and consider the ignition delay. A chemical equilibrium model which considers 98 chemical species was used in this research in order to simulate the combustion of the gaseous fuels at differents engine operating conditions. The effect of spark advance, equivalence ratio, methane number (MN), charge (inlet pressure) and inlet temperature (manifold temperature) on engine knocking is evaluated. This work, explore the feasibility of using syngas with low methane number as fuel for commercial internal combustion engines.

Random Behavior of Kerosene Spray Autoignition in Crossflow

2016 ◽  
Author(s):  
Yongsheng Zhao ◽  
Chi Zhang ◽  
Yuzhen Lin
Keyword(s):  
High Speed ◽  
Flow Reactor ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
High Speed Photography ◽  
Primary Analysis ◽  
Photoelectric Detection ◽  
Random Behavior ◽  
Gauss Distribution ◽  
Autoignition Delay

Based on the flow reactor with rectangle cross-section, this paper studies the spray autoignition characteristics of liquid kerosene injected into air crossflow under high temperature and high pressure conditions. Millisecond-level kerosene injection, millisecond-level photoelectric detection, and high speed photography record experiment techniques are adopted in this research. The operating conditions of this research are as follows: 2.3MPa inlet pressure, 917K inlet temperature, fuel/ air momentum ratio of 52, and Weber number of 355. Photoelectric sensor and photomultiplier equipped with CH filter are used to get the autoignition delay time (ADT). A total of 320 experiments are conducted under the same operating conditions in order to obtain the random ADT probability distribution. The high speed photography is utilized to observe and record the developing process of spray autoignition of kerosene. The results show that the ADT varies from 2.5–5.5millisecond (ms) in the above operating conditions, and confirm the existence of the random behavior of kerosene spray autoignition in the crossflow. These random behaviors of ADT can be correlated well with Gauss distribution. The primary analysis shows that the random behavior stems from the random distributions in the diameter and dispersion due to intrinsic turbulence breakup and transportation which dominate the characteristics of spray autoignition.

The Effects of Fuel Composition on Flame Structure and Combustion Dynamics in a Lean Premixed Combustor

2007 ◽  
Author(s):  
Lorenzo Figura ◽  
Jong Guen Lee ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Fuel Composition ◽  
Two Dimensional ◽  
Inlet Velocity ◽  
Unstable Combustion ◽  
Fuel Mixtures

The stability characteristics of a laboratory-scale lean premixed combustor operating on natural gas - hydrogen fuel mixtures have been studied in a variable length combustor facility. The fuel and air were mixed upstream of the choked inlet to the combustor to eliminate equivalence ratio fluctuations and thereby ensure that the dominant instability driving mechanism was flame-vortex interaction. The inlet velocity, inlet temperature, equivalence ratio and percent hydrogen in the fuel were systematically varied, and at each operating condition the combustor pressure fluctuations were measured as a function of the combustor length. The results are presented in the form of two-dimensional stability maps, which are plots of the normalized rms pressure fluctuation versus the equivalence ratio and the combustor length, for a given inlet temperature, inlet velocity, and fuel mixture. In order to understand the effects of operating conditions and fuel composition on the observed stability characteristics, two-dimensional chemiluminescence images of the flame structure were recorded at all operating conditions and for all fuel mixtures under stable conditions. Changes in the stable flame structure, as characterized by the location of the flame’s “center of heat release”, were found to be consistent with the observed instability characteristics. The location of the flame’s “center of heat release” was found to lie along a single path for all operating conditions and fuel mixtures. It was also observed that there were regions of stable and unstable combustion as one moved along this path. Furthermore it was found that flames having the same “center of heat release” location, but different operating conditions and fuel composition, have very nearly the same flame shape. These results will be useful for developing phenomenological models for predicting unstable combustion.

Measuring Ignition Temperature and the Rate of Energy Generation From Canola Methyl Ester and Soy Methyl Ester in Oxygen-Nitrogen Mixtures on Platinum-Rhodium

2011 ◽  
Author(s):  
Bradley McGary ◽  
Judi Steciak ◽  
Ralph Budwig ◽  
Steve Beyerlein
Keyword(s):  
Methyl Ester ◽  
Ignition Temperature ◽  
Equivalence Ratio ◽  
Flow Reactor ◽  
Volume Fraction ◽  
Surface Reactions ◽  
Energy Generation ◽  
Fuel Vapor ◽  
Vapor Flow ◽  
Soy Methyl Ester

A heated plug flow reactor was used to study the reactions of nonflammable mixtures of canola methyl ester-oxygen and soybean methyl ester-oxygen diluted with nitrogen over a coiled 90%:10% platinum:rhodium wire catalyst. The temperature the catalyst needed to reach to initiate surface reactions (ignition temperature) and the subsequent rate of energy generation were determined. The absolute volume fraction of fuel was varied from 0.238% to 0.445% and the relative fuel-oxygen equivalence ratio, φ, was varied between 0.4 and 1.0. The 127 micrometer diameter Pt-Rh wire was coiled and suspended crosswise in the quartz tube of the reactor. Evaporated biodiesel was delivered by heated nitrogen into the apparatus and blended with oxygen in a mixing nozzle. The wire catalyst was electrically heated and acted as a resistance thermometer to measure its average temperature. Ignition temperatures increased with increasing equivalence ratio and volumetric fuel vapor percentage, thus indicating initial fuel coverage of the catalyst surface. Temperatures as low as 912 K at φ = 0.4 for 0.268% Soy Methyl Ester (SME) and as high as 991 K at φ = 1.0 for 0.445% Canola Methyl Ester (CME) were recorded. The rate of energy generated due to surface reactions for both biodiesels decreased with increasing equivalence ratio and generated less energy as fuel percentages decreased. The lowest and highest rates of energy generation were both obtained from experiments with CME with 6.9 W/cm2 at φ = 1 for 0.268% fuel and 25.3 W/cm2 at φ = 0.4 for 0.445% fuel. The extremes of the rate of heat generated from SME reactions were 5.1 W/cm2 and 28.6 W/cm2, both at φ = 0.4, with 0.238% and 0.417% fuel, respectively. Another outcome of this work was achieving steady evaporation of microliter/hour heavy fuel vapor flow rates. This was aided by thermogravimetric analysis (TGA) to determine thin-film vaporization temperatures. CME and SME had the lowest evaporation temperatures of 188 K and 186 K, respectively.

Exergy Analysis of a Solar-Driven Dual Parallel-Connected Ejector Refrigeration System

2016 ◽  
Vol 839 ◽  
pp. 100-106
Author(s):  
Yahya Gaafar Abdella Mohammed ◽  
Tawat Suriwong ◽  
Sakda Somkun ◽  
Timeyo Mkamanga Maroyi
Keyword(s):  
Solar Collector ◽  
Exergy Analysis ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Saturated Steam ◽  
Working Fluid ◽  
Electric Heater ◽  
Exergy Destruction ◽  
Refrigeration System ◽  
Exergetic Efficiency

Nowadays, developing solar cooling technologies, especially ejector refrigeration system, has become preferable to scientific researchers. Exergy analysis is a technique in which the basis of evaluation of thermodynamic losses follows the second law rather than the first law of thermodynamics. An experimental exergy analysis of a solar-driven dual parallel-connected ejector (DPE) refrigeration system was conducted using water as working fluid. Saturated steam with 2 bar and 120oC was provided by heat–pipe evacuated tube solar collector with an assistant of an electric heater. The saturated stream was used as a motive flow for the ejectors. The exergy destruction and exergetic efficiency of the main components of the DPE refrigeration system were determined and compared with those when using a single ejector (SE) under same operating conditions. It was found that the most irreversibilities of both systems occurred at the solar collector, electric boiler and ejectors, respectively. Also, the total irreversibility (Exergy destruction) of the system when using DPE was lower than using a SE. In additions, the exergetic efficiency of the ejector, evaporator, and overall system when using DPE were increased by 21%, 10%, and 27%, respectively. The system thermal ratio (STR) and coefficient of performance (COP) of the system using DPE compared with SE were increased by 20% and 23%, respectively.

scholarly journals Exergetic analysis of a dual-fuel engine, PEM electrolyzer and thermoelectric generator integrated system

DYNA ◽  
2020 ◽  
Vol 87 (215) ◽  
pp. 66-75
Author(s):  
Nelly De Armas Calderón ◽  
Cristina Lizarazo Bohórquez ◽  
Jorge Duarte Forero
Keyword(s):  
Thermoelectric Generator ◽  
Combustion Engine ◽  
Integrated System ◽  
Operating Conditions ◽  
Dual Fuel ◽  
Inlet Temperature ◽  
Exergetic Efficiency ◽  
Pem Electrolyzer ◽  
Exergetic Analysis ◽  
A Current

In this research, the implementation of an integrated system composed of a dual-fuel engine (Diesel-Hydrogen), a PEM electrolyzer and a thermoelectric generator is envisioned. In order to know the optimal operating conditions of each sub-system, the exergetic efficiency and destroyed exergy were studied. It was estimated that for the dual combustion engine, the destroyed exergy would increase as a function of the concentration of methane in its mixture. By varying the electrical input to the electrolyzer, it was found that when the input current was 2A, the exergetic efficiency would go up to 92.59%, while for a current of 5A, the efficiency decreased in 51.80%. Finally, the exergetic efficiency of TEG decreased by increasing the hot flow temperature; 86.68% of the decrease in efficiency occurred for temperatures between 470K and 510K. On the other hand, the destroyed exergy increased linearly with an increase in the inlet temperature of exhaust gases.

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