Estimation of the InCylinder Air/Fuel Ratio of an Internal Combustion Engine by the Use of Pressure Sensors
Research output: Thesis › Doctoral Thesis (monograph)
Abstract
This thesis investigates the use of cylinder pressure measurements for estimation of the incylinder 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. Cycleaveraged 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 precombustion 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 leastsquares problem, and the second method results in a nonlinear leastsquares problem. The nonlinear leastsquares problem is solved by separating out the nonlinear dependence and solving the singlevariable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear leastsquares problem is only slightly higher than solving the linear leastsquares 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.
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. Cycleaveraged 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 precombustion 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 leastsquares problem, and the second method results in a nonlinear leastsquares problem. The nonlinear leastsquares problem is solved by separating out the nonlinear dependence and solving the singlevariable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear leastsquares problem is only slightly higher than solving the linear leastsquares 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.
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Organisations  
Research areas and keywords  Subject classification (UKÄ) – MANDATORY
Keywords

Original language  English 

Qualification  Doctor 
Awarding Institution  
Supervisors/Assistant supervisor 

Award date  2001 Apr 6 
Publisher 

Publication status  Published  2001 
Publication category  Research 
Bibliographic note
Defence details
Date: 20010406
Time: 10:15
Place: Maskinhuset, Lunds Tekniska Högskola, room M:B
External reviewer(s)
Name: Stefanopoulou, Anna
Title: Professor
Affiliation: University of Michigan, AnnArbor MI

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