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Estimation of the In-Cylinder Air/Fuel Ratio of an Internal Combustion Engine by the Use of Pressure Sensors

Tunestål, Per LU (2001) In Department of Heat and Power Engineering, Lund Institute of Technology 1025.
Abstract (Swedish)
Popular Abstract in Swedish

Rätt förhållande mellan mängden bränsle och luft är viktigt i dagens förbränningsmotorer för att den katalytiska avgasreningen skall fungera. Motorer i serieproduktion mäter syrehalten i avgaserna för att få en uppfattning om blandningsförhållandet. Denna utvecklar en metod att skatta blandningsförhållandet genom mätning av cylindertrycket. Man kan på så sätt få snabbare information om blandningsförhållandet, såväl som individuell information för varje cylinder.



Cylindertryckgivare ger ett flytande mätvärde som saknar absolutreferens. För att cylindertryckmätningar skall kunna användas för termodynamisk analys av förbränningsförloppet i motorn måste en absolutreferens erhållas.... (More)
Popular Abstract in Swedish

Rätt förhållande mellan mängden bränsle och luft är viktigt i dagens förbränningsmotorer för att den katalytiska avgasreningen skall fungera. Motorer i serieproduktion mäter syrehalten i avgaserna för att få en uppfattning om blandningsförhållandet. Denna utvecklar en metod att skatta blandningsförhållandet genom mätning av cylindertrycket. Man kan på så sätt få snabbare information om blandningsförhållandet, såväl som individuell information för varje cylinder.



Cylindertryckgivare ger ett flytande mätvärde som saknar absolutreferens. För att cylindertryckmätningar skall kunna användas för termodynamisk analys av förbränningsförloppet i motorn måste en absolutreferens erhållas. Det normala förhållandet är att ha en separat tryckgivare i insuget. Avhandlingen presenterar en metod att skatta denna absolutreferens genom att analysera kompressionstakten. (Less)
Abstract
This thesis investigates the use of cylinder pressure measurements for estimation of the in-cylinder air/fuel ratio in a spark ignited internal combustion engine.



An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust.



A... (More)
This thesis investigates the use of cylinder pressure measurements for estimation of the in-cylinder air/fuel ratio in a spark ignited internal combustion engine.



An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust.



A thermochemical model of the combustion process in an internal combustion engine is developed. It uses a simple chemical combustion reaction, polynomial fits of internal energy as function of temperature, and the first law of thermodynamics to derive a relationship between measured cylinder pressure and the progress of the combustion process. Simplifying assumptions are made to arrive at an equation which relates the net heat release to the cylinder pressure.



Two methods for estimating the sensor offset of a cylinder pressure transducer are developed. Both methods fit the pressure data during the pre-combustion phase of the compression stroke to a polytropic curve. The first method assumes a known polytropic exponent, and the other estimates the polytropic exponent. The first method results in a linear least-squares problem, and the second method results in a nonlinear least-squares problem. The nonlinear least-squares problem is solved by separating out the nonlinear dependence and solving the single-variable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear least-squares problem is only slightly higher than solving the linear least-squares problem. Both methods show good statistical behavior. Estimation error variances are inversely proportional to the number of pressure samples used for the estimation as predicted by the central limit theorem. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Stefanopoulou, Anna, University of Michigan, Ann-Arbor MI
organization
publishing date
type
Thesis
publication status
published
subject
keywords
vakuumteknik, hydraulik, Maskinteknik, nonlinear, cylinder pressure, engine, least-squares, Mechanical engineering, estimation, hydraulics, vibration and acoustic engineering, vacuum technology, vibrationer, akustik, Motors and propulsion systems, Motorer, framdrivningssystem
in
Department of Heat and Power Engineering, Lund Institute of Technology
volume
1025
pages
118 pages
publisher
Department of Heat and Power Engineering, Lund university
defense location
Maskinhuset, Lunds Tekniska Högskola, room M:B
defense date
2001-04-06 10:15
ISSN
0282-1990
language
English
LU publication?
yes
id
d7c69d47-fe7b-4673-96a0-15c670590a78 (old id 20361)
date added to LUP
2007-05-28 08:30:32
date last changed
2018-05-29 11:51:13
@phdthesis{d7c69d47-fe7b-4673-96a0-15c670590a78,
  abstract     = {This thesis investigates the use of cylinder pressure measurements for estimation of the in-cylinder air/fuel ratio in a spark ignited internal combustion engine.<br/><br>
<br/><br>
An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust.<br/><br>
<br/><br>
A thermochemical model of the combustion process in an internal combustion engine is developed. It uses a simple chemical combustion reaction, polynomial fits of internal energy as function of temperature, and the first law of thermodynamics to derive a relationship between measured cylinder pressure and the progress of the combustion process. Simplifying assumptions are made to arrive at an equation which relates the net heat release to the cylinder pressure.<br/><br>
<br/><br>
Two methods for estimating the sensor offset of a cylinder pressure transducer are developed. Both methods fit the pressure data during the pre-combustion phase of the compression stroke to a polytropic curve. The first method assumes a known polytropic exponent, and the other estimates the polytropic exponent. The first method results in a linear least-squares problem, and the second method results in a nonlinear least-squares problem. The nonlinear least-squares problem is solved by separating out the nonlinear dependence and solving the single-variable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear least-squares problem is only slightly higher than solving the linear least-squares problem. Both methods show good statistical behavior. Estimation error variances are inversely proportional to the number of pressure samples used for the estimation as predicted by the central limit theorem.},
  author       = {Tunestål, Per},
  issn         = {0282-1990},
  keyword      = {vakuumteknik,hydraulik,Maskinteknik,nonlinear,cylinder pressure,engine,least-squares,Mechanical engineering,estimation,hydraulics,vibration and acoustic engineering,vacuum technology,vibrationer,akustik,Motors and propulsion systems,Motorer,framdrivningssystem},
  language     = {eng},
  pages        = {118},
  publisher    = {Department of Heat and Power Engineering, Lund university},
  school       = {Lund University},
  series       = {Department of Heat and Power Engineering, Lund Institute of Technology},
  title        = {Estimation of the In-Cylinder Air/Fuel Ratio of an Internal Combustion Engine by the Use of Pressure Sensors},
  volume       = {1025},
  year         = {2001},
}