Lean Combustion

Technology and Control

Derek Dunn-Rankin, Peter Therkelsen

• Publisher: Academic Press
• Year: 2016
• ISBN:
  9780128005774
• Edition: 2
• Topic: Ciencias físicas
• Subtopic: Termodinámica

Lean Combustion: Technology and Control, Second Edition outlines and explains the latest advances in lean combustion technology and systems. Combustion under sufficiently fuel-lean conditions can have the desirable attributes of high efficiency and low emissions. The book offers readers both the fundamentals and latest developments in how lean burn (broadly defined) can increase fuel economy and decrease emissions, while still achieving desired power output and performance. This volume brings together research and design of lean combustion systems across the technology spectrum in order to explore the state-of-the-art in lean combustion.

Readers will learn about advances in the understanding of ultra-lean fuel mixtures and how new types of burners and approaches to managing heat flow can reduce problems often found with lean combustion (such as slow, difficult ignition and frequent flame extinction).

This book offers abundant references and examples of real-world applications. New to this edition are significantly revised chapters on IC engines and stability/oscillations, and new case studies and examples. Written by a team of experts, this contributed reference book aims to teach its reader to maximize efficiency and minimize both economic and environmental costs.

• Presents a comprehensive collection of lean burn technology across potential applications, allowing readers to compare and contrast similarities and differences
• Provides an extensive update on IC engines including compression ignition (diesel), spark ignition, and homogeneous charge compression ignition (HCCI)
• Includes an extensive revision to the Stability/Oscillations chapter
• Includes use of alternative fuels such as biogas and hydrogen for relevant technologies
• Covers new developments in lean combustion using high levels of pre-heat and heat recirculating burners, as well as the active control of lean combustion instabilities

1

Introduction and Perspectives

D. Dunn-Rankin¹, M.M. Miyasato², and T.K. Pham^{3 1}University of California, Irvine, CA, United States ²South Coast Air Quality Management District, Diamond Bar, CA, United States ³California State University, Los Angeles, CA, United States

Abstract

Combustion processes operating under fuel lean conditions can have very low emissions and very high efficiency. Pollutant emissions are reduced because flame temperatures are low. In addition, for hydrocarbon combustion, when leaning is accomplished with excess air, complete burnout of fuel generally results, reducing hydrocarbon and carbon monoxide emissions. Achieving these improvements and meeting the demands of practical combustion systems are complicated by low reaction rates, extinction, instabilities, mild heat release, and sensitivity to mixing. This first and introductory chapter introduces the concept of lean conditions broadly; it provides specific examples from mobile and stationary sources on how lean combustion technology is driven by regulatory concerns, and it provides a highlight preview of the remaining chapters of the volume. With the complexity, breadth, and dynamic nature of the lean combustion field, it is impossible for any book to claim a complete state-of-the-art representation. Rather, we have tried to provide a foundation for lean combustion discussion and understanding across a range of technologies.

Keywords

Air quality; Dilute combustion; Emission regulations; Fuel lean combustion; High preheat; Lean burn; Lean combustion history; Mobile sources; NO_x reduction; Stationary sources; Technology drivers

Nomenclature

BACT Best available control technology

EGR Exhaust gas recirculation

FGR Flue gas recirculation

HC Hydrocarbons

HCCI Homogeneous charge compression ignition

IC Internal combustion

ICE Internal combustion engine

LNB Low NO_x burner

PCV Positive crankcase ventilation

RQL Rich-quench-lean

SCAQMD South Coast Air Quality Management District

SCR Selective catalytic reduction

VOC Volatile organic compounds

λ Relative air–fuel ratio

ϕ Equivalence ratio

1. Introduction

Lean combustion is employed in nearly all combustion technology sectors, including gas turbines, boilers, furnaces, and internal combustion (IC) engines. This wide range of applications attempts to take advantage of the fact that combustion processes operating under fuel lean conditions can have very low emissions and very high efficiency. Pollutant emissions are reduced because flame temperatures are typically low, reducing thermal nitric oxide formation. In addition, for hydrocarbon combustion, when leaning is accomplished with excess air, complete burnout of fuel generally results, reducing hydrocarbon and carbon monoxide emissions. Unfortunately, achieving these improvements and meeting the demands of practical combustion systems is complicated by low reaction rates, extinction, instabilities, mild heat release, and sensitivity to mixing. Details regarding these advantages and challenges appear in various chapters in this book. As a whole, therefore, the volume explores broadly the state of the art and technology in lean combustion and its role in meeting current and future demands on combustion system performance. Beyond the fundamentals of lean combustion, topics to be examined include lean combustion with high levels of preheat (mild combustion) and heat recirculating burners; novel IC engine lean operating modes; gas turbine engines, burners, and sources of instability; and the potential role of hydrogen and other alternative fuels on lean combustion.

This book is a continuation of a first volume, which was an outgrowth of two international workshops on the topic of lean combustion. The first workshop, held in Santa Fe, New Mexico, in November of 2000, identified the range of applications in which lean combustion could be and is used, along with the tools available to help design the combustion processes for these systems. The second conference, held in Tomar, Portugal, in April of 2004, focused on the role of lean combustion technology in an energy future that is increasingly constrained by concerns over emissions (both criteria pollutants and greenhouse gases) and excessive fossil fuel use. This second conference focused discussions on the applications of lean combustion that are likely to be the most effective contributors to rational energy utilization and power generation. Both of these conferences included participants with backgrounds in a wide range of industries, as well as combustion researchers, focused on different aspects of lean combustion fundamentals. One goal of the workshops was to identify fundamentals, processes, design tools, and technologies associated with lean combustion that could be used across application boundaries. This book is created in that same spirit.

2. Brief Historical Perspective

Studies of lean combustion are among the oldest in the combustion literature because its extreme represents the lean limit of inflammability, which was a well-recognized hazard marker from the inception of combustion science. In fact, Parker (1914) argues that the first useful estimates for the lean limit of methane/air mixtures were reported by Davy (1816) in his efforts to prevent explosions of methane gas (called “firedamp”) in coal mines (incidentally, this is the same paper where Davy published his famous explosion-safe lantern design that used wire gauze walls to allow air and light to pass but prevent flame propagation). Davy reported limits of inflammability between 6.2% and 6.7% methane in air by volume. In modern terminology, this represents an equivalence ratio range for methane between 0.65 and 0.70. Parker also reports a threefold variation in the limits reported by the early literature (with Davy's near the upper end), which he attributes to the fact that the limit of inflammability depends on the vessel used for the test, among other experimental variations. This recognition led eventually to standard inflammability measurements based on the upward propagation of a flame through a mixture indefinitely. However, Parker further complicated the concept of the lower limit of inflammability by examining mixtures of oxygen and nitrogen rather than using the standard ratio of these molecules in air. His findings are shown in Fig. 1.1, with a minimum at 5.77% methane using a 25% oxygen mixture. The exact values are not that important but these results show clearly that the limits of lean combustion depend not simply on an equivalence ratio, but on the oxidizer and diluent composition. For example, if the 5.77% methane is considered relative to a stoichiometric mixture of methane and normal air, the equivalence ratio would be ϕ = 0.61, but if the stoichiometry is taken relative to the slightly oxygen enriched mixture reported, the equivalence ratio at the lean limit is 0.52. In 1918, Mason and Wheeler also complicated the picture of lean limits by demonstrating conclusively that the temperature of the mixture affected dramatically the limits of inflammability, as illustrated by Fig. 1.2. Their finding was not surprising, even to them, but it showed that combustion limits ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Dedication
• Copyright
• List of Contributors
• Preface
• 1. Introduction and Perspectives
• 2. Fundamentals of Lean Combustion
• 3. Highly Preheated Lean Combustion
• 4. Lean-Burn Internal Combustion Engines
• 5. Lean Combustion in Gas Turbines
• 6. Lean Premixed Burners
• 7. Combustion Instabilities in Lean Premixed Systems
• Index