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Study and Development of Techniques to Improve Engine Stability and Reduce Emissions from Natural Gas Engines

Einewall, Patrik LU (2003)
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling beskriver olika metoder att förbättra motorstabilitet och minska skadliga avgasutsläpp från naturgasmotorer. Gasflöden inuti cylindern mättes med laserdiagnostik, även cylindertryck och avgassammansättning mättes. Sex olika förbränningsrum utvärderades med ovan angivna metoder. Ett högturbulent (brinner snabbt) förbränningsrum visade sig fungera bäst med avseende på motorstabilitet och avgasutsläpp. Ett förbränningsrum med snabb förbränning är bättre lämpat, än ett långsamt, om motorn skall använda EGR (återföring av avgaser till cylindrarna). Med EGR kan de skadliga avgasutsläppen minska och verkningsgraden för motorn öka. Väldigt låga avgasutsläpp kunde påvisas med EGR och en... (More)
Popular Abstract in Swedish

Denna avhandling beskriver olika metoder att förbättra motorstabilitet och minska skadliga avgasutsläpp från naturgasmotorer. Gasflöden inuti cylindern mättes med laserdiagnostik, även cylindertryck och avgassammansättning mättes. Sex olika förbränningsrum utvärderades med ovan angivna metoder. Ett högturbulent (brinner snabbt) förbränningsrum visade sig fungera bäst med avseende på motorstabilitet och avgasutsläpp. Ett förbränningsrum med snabb förbränning är bättre lämpat, än ett långsamt, om motorn skall använda EGR (återföring av avgaser till cylindrarna). Med EGR kan de skadliga avgasutsläppen minska och verkningsgraden för motorn öka. Väldigt låga avgasutsläpp kunde påvisas med EGR och en trevägskatalysator av liknande typ som sitter i bilar. (Less)
Abstract
The objective of this thesis was to find ways to improve combustion and reduce emissions from supercharged natural gas engines. In-cylinder flow measurements were made with laser doppler velocimetry, LDV, heat release was calculated from cylinder pressures and emissions were measured at various locations. The original combustion chamber was a low turbulence-generating geometry, resulting in an overall slow combustion. Four new combustion chambers were designed, to generate high turbulence and hence a fast combustion. The piston-geometry with the highest turbulence was more tolerant for highly diluted mixtures in terms of engine stability, which is favorable for lean burn operation or high amounts of EGR at stoichiometric operation. The... (More)
The objective of this thesis was to find ways to improve combustion and reduce emissions from supercharged natural gas engines. In-cylinder flow measurements were made with laser doppler velocimetry, LDV, heat release was calculated from cylinder pressures and emissions were measured at various locations. The original combustion chamber was a low turbulence-generating geometry, resulting in an overall slow combustion. Four new combustion chambers were designed, to generate high turbulence and hence a fast combustion. The piston-geometry with the highest turbulence was more tolerant for highly diluted mixtures in terms of engine stability, which is favorable for lean burn operation or high amounts of EGR at stoichiometric operation. The flow-measuring tests were made on a single-cylinder engine. Base-engine performance measurements were conducted on a multi-cylinder version of the engine. The results show that pulse-width fuel-injection close to the cylinders (at the throttle) resulted in variations in air/fuel ratio between the cylinders. Cycle-to-cycle variations were high in cylinders with leaner mixtures, and NOX emissions were high from cylinders with richer mixtures. Late ignition timing, high boost pressure and lean mixture led to the need for a small spark gap in order to avoid misfires with the original ignition system. A larger gap results in higher spark energy, but the ignition system must be powerful enough not to cause misfires. The original ignition settings were retarded to suppress NOX formation. The HC and CO emissions were also lower than at maximum brake torque ignition (MBT) due to higher temperatures during expansion and exhaust, leading to more post-oxidation. Load and efficiency were reduced with the retarded ignition timing. A new engine control system was installed with high power ignition modules, enabling a larger spark gap. Idle quality was improved and maximum load was increased with this new system. Cylinder-individual control of fuel injection and ion-current measurements in all six cylinders made it possible to adapt port fuel-injection and cylinder balancing. Both cycle-to-cycle and cylinder-to-cylinder variations were reduced with cylinder balancing at lean operation. The ion-current integral and variations in the integral were used to perform the cylinder balancing. Lean burn operation was compared to stoichiometric operation diluted with EGR. The raw emissions of NOX and HC were higher at lean burn operation than for the EGR case. NOX emissions after a three-way catalyst were up to 700 times higher at lean operation (29.5 g/kWh vs. 0.042 g/kWh), and HC emissions approximately 20 times higher (2.7 g/kWh vs. 0.13 g/kWh). The early flame period (ignition to 5% burned) was much longer for the EGR case, since EGR has a stronger influence on laminar flame speed than excess air. The main combustion duration (10% to 90% burned) was similar for both cases. The ion-current signal was very weak for the lean burn cases, but a strong signal was found for the EGR case. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Agama, Rey, Senior Engine Specialist, Caterpillar, USA
organization
publishing date
type
Thesis
publication status
published
subject
keywords
framdrivningssystem, Motorer, Motors and propulsion systems, "Low Emissions", "Natural Gas Engines", "EGR"
pages
317 pages
publisher
Combustion Engines, Box 118, 22100 LUND,
defense location
M-building, room M:B, Lund Institute of Technology.
defense date
2003-12-19 10:15
ISSN
0282-1990
ISBN
91-628-5885-8
language
English
LU publication?
yes
id
11a38f60-997c-48ba-8ef9-34fba6fdc5ee (old id 466514)
date added to LUP
2007-09-06 14:13:43
date last changed
2018-05-29 09:49:00
@phdthesis{11a38f60-997c-48ba-8ef9-34fba6fdc5ee,
  abstract     = {The objective of this thesis was to find ways to improve combustion and reduce emissions from supercharged natural gas engines. In-cylinder flow measurements were made with laser doppler velocimetry, LDV, heat release was calculated from cylinder pressures and emissions were measured at various locations. The original combustion chamber was a low turbulence-generating geometry, resulting in an overall slow combustion. Four new combustion chambers were designed, to generate high turbulence and hence a fast combustion. The piston-geometry with the highest turbulence was more tolerant for highly diluted mixtures in terms of engine stability, which is favorable for lean burn operation or high amounts of EGR at stoichiometric operation. The flow-measuring tests were made on a single-cylinder engine. Base-engine performance measurements were conducted on a multi-cylinder version of the engine. The results show that pulse-width fuel-injection close to the cylinders (at the throttle) resulted in variations in air/fuel ratio between the cylinders. Cycle-to-cycle variations were high in cylinders with leaner mixtures, and NOX emissions were high from cylinders with richer mixtures. Late ignition timing, high boost pressure and lean mixture led to the need for a small spark gap in order to avoid misfires with the original ignition system. A larger gap results in higher spark energy, but the ignition system must be powerful enough not to cause misfires. The original ignition settings were retarded to suppress NOX formation. The HC and CO emissions were also lower than at maximum brake torque ignition (MBT) due to higher temperatures during expansion and exhaust, leading to more post-oxidation. Load and efficiency were reduced with the retarded ignition timing. A new engine control system was installed with high power ignition modules, enabling a larger spark gap. Idle quality was improved and maximum load was increased with this new system. Cylinder-individual control of fuel injection and ion-current measurements in all six cylinders made it possible to adapt port fuel-injection and cylinder balancing. Both cycle-to-cycle and cylinder-to-cylinder variations were reduced with cylinder balancing at lean operation. The ion-current integral and variations in the integral were used to perform the cylinder balancing. Lean burn operation was compared to stoichiometric operation diluted with EGR. The raw emissions of NOX and HC were higher at lean burn operation than for the EGR case. NOX emissions after a three-way catalyst were up to 700 times higher at lean operation (29.5 g/kWh vs. 0.042 g/kWh), and HC emissions approximately 20 times higher (2.7 g/kWh vs. 0.13 g/kWh). The early flame period (ignition to 5% burned) was much longer for the EGR case, since EGR has a stronger influence on laminar flame speed than excess air. The main combustion duration (10% to 90% burned) was similar for both cases. The ion-current signal was very weak for the lean burn cases, but a strong signal was found for the EGR case.},
  author       = {Einewall, Patrik},
  isbn         = {91-628-5885-8},
  issn         = {0282-1990},
  keyword      = {framdrivningssystem,Motorer,Motors and propulsion systems,"Low Emissions","Natural Gas Engines","EGR"},
  language     = {eng},
  pages        = {317},
  publisher    = {Combustion Engines, Box 118, 22100 LUND,},
  school       = {Lund University},
  title        = {Study and Development of Techniques to Improve Engine Stability and Reduce Emissions from Natural Gas Engines},
  year         = {2003},
}