McNair Scholars Research Journal
Volume 1 Article 6
2014
Applications of Lean Combustion to Reduce Emissions
Narhari Khanal Embry-Riddle Aeronautical University
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Recommended Citation Khanal, Narhari (2014) "Applications of Lean Combustion to Reduce Emissions," McNair Scholars Research Journal: Vol. 1 , Article 6. Available at: https://commons.erau.edu/mcnair/vol1/iss1/6
This Article is brought to you for free and open access by the Journals at Scholarly Commons. It has been accepted for inclusion in McNair Scholars Research Journal by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. Khanal: Applications of Lean Combustion to Reduce Emissions Khanal 1
Applications of Lean Combustion to Reduce Emissions Narhari Khanal Office of Mc-Nair Scholar Embry- Riddle Aeronautical University Daytona Beach, FL 12/02/2013
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Contents Acknowledgement:...... 3 Abstract: ...... 4 Applications of lean combustion to reduce emissions ...... 5 Introduction: ...... 5 Lean premixed combustion ...... 9 Flameless combustion...... 11 Catalytic combustion: ...... 16 Hydrogen Combustion:...... 18 Recommendations: ...... 21 Conclusion:...... Error! Bookmark not defined.24 References ...... 23
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Acknowledgement: I have been blessed to be a part of the MC-Nair Scholar program. I have gained so much knowledge and look forward to my future expectation of graduate and doctorate levels of study. I would like to thank the MC-Nair office members who encouraged me throughout the completion of this paper. I would like to give special thanks to my faculty mentor Dr. Narayanswami, Director of the MC-Nair office Dr. Camara, assistant director Ms. Reed and graduate student Mr. Matiko; all of whom assist me to conduct this research. Without their effort my research would be incomplete.
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Abstract: Environmental regulation has constricted over the last few decades as the hydrocarbon burning engines produce primarily large amount of nitrous oxides, carbon monoxide, unburned hydrocarbons and sulphur-oxides. For this reason, gas turbine manufacturers are working towards the design of combustion system that reduces the emission of these compounds. Numerous technologic attempts such as water injection combustion, lean pre-mixture combustion, ultra-lean premixed combustion, catalytic combustion, swirl premixed combustion system or the compartment combustion design along with many other concepts have been introduced. This research paper will introduce each combustion process in brief detail and compare the emission data available from each of them and then recommend the one that is suitable for emission controls.
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Applications of lean combustion to reduce emissions
Introduction: It is widely accepted that burning of hydrocarbon fuel has a negative impact on the environment.
A large number of engines used today emit environmental unfavorable substances such as Nox,
sulphur oxides, carbon monoxides or unburned hydrocarbons. These oxides have an adverse
effect on health, are responsible for acid rain, greenhouse effect, ozone layer depletion
photochemical smog, and can form toxic substances combining with other compounds in the air.
During the early 1980s, concern over these oxides emissions increased. As pollution went up,
environmental regulators tolerated these emissions less therefore more advanced technology was
required to address it. Most of the emissions are temperature and pressure dependent. Air
contains mostly nitrogen, carbon and oxygen by volume; therefore most of the Nox and CO is
produced when fuel is subjected to certain temperatures and pressures in the combustion process.
Nox forms in three mechanisms; thermal Nox, prompt Nox and fuel Nox. Thermal Nox formed
in applications of “high temperature”. Above 1200oC, thermal NOx formation increases in very
rate. Prompt NOx is formed by the fast reaction between nitrogen, oxygen and hydrocarbon
radicals (Baukal, C.). Fuel NOX is formed by direct oxidation of the nitrogen within the fuel
burn. Prompt and fuel Nox formation is relatively low compared to that of thermal Nox if high
quality gaseous fuels are used. The following figure shows the relation between the formations
of NOx at various temperatures presented by Baukal.
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Figure 1: NOx formation vs. temperature The graph shows that upon an increase in temperature above 2500oF, formation of NOx
increases exponentially. However, in the combustion and turbine energy extraction process,
higher temperature is preferred to meet the higher energy requirements. Therefore, gas turbine
engine manufacturers are facing the challenges to design combustion systems that not only
reduce the emissions, but also operate with higher energy extraction, flexibility in fuel, minimum
impact on component operation and component life. This research paper presents the various
lean combustion technologies invented in order to reduce the emissions from the gas turbine
engines and discusses their emission performance.
While lean combustion was introduced in the early 1920s, a practical contemplation
started only in the early1960s targeting to save fuel. Certain amount of atmospheric air is
required as an oxidizer during the combustion. The amount of air is different for different types
of fuel in order to burn fuel completely. The exact ratio of fuel to the air is known as
stoichiometric. The fuel-air ratio divided by its stoichiometric value is called the equivalence
ratio (Φ). The inverse of equivalence ratio is denoted by λ (Rankin, D. 2008). The Φ and λ are
the normalized quantities used to describe the amount of fuel to the air in combustion.
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