Dynamic Model of a Diesel Engine for Diagnosis and Balancing
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
To monitor and control the combustion in a diesel engine one can study the speed signal from the ﬂywheel. The idea is that if individual cylinders give different amount of torque this will lead to variations in the ﬂywheel speed. A model which describes the cylinder torque based on ﬂywheel speed can be used to estimate the torque from individual cylinders. With this new knowledge of the individual performance of each cylinder the engine can be balanced. The balancing aim at making the speed of the ﬂywheel more even but also required a model with estimated cylinder torque as input. This model may also be used for testing new control algorithms easily and gaining understanding of the dynamics.
In this thesis a time dissolved model is constructed to describe the cylinder pressure-, crankshaft-, ﬂywheel and damper dynamics. The model is based on a physical point of view by approximating the system into nodes containing mass, stiffness and friction. The inputs into the model are injection data from the engine management system (EMS) and a torque from a drive line. Ways to reduce the complexity of the model are investigated in order to invert the model to estimate the injection data based on ﬂywheel speed measurements. Measurementsare done in a test bed to receive data required for model simulation and validation.
The result is that the main behavior of the dynamics is caught. The self oscillation behaviors in some operating points are however not caught which indicates that the model can not explain all behaviors. A reduced model works almost as well but of course looses more of the non stiffness behavior. As expected, the model equations can not be solved in real time.
The result of the inverted reduced model depends on the ﬂywheel signal. When the signal contains little non stiffness behavior the result is good. An observer model based on the reduced model is suggested and tested in order to estimate the indicated torque from ﬂywheel data. The observer manages to detect errors in the injection.
Place, publisher, year, edition, pages
2005. , 45 p.
combustion supervision, cylinder balancing, physical model, engine model, cylinder pressure, ﬂywheel speed, crankshaft, observer, cylinder injection
IdentifiersURN: urn:nbn:se:kth:diva-107535OAI: oai:DiVA.org:kth-107535DiVA: diva2:576423
Subject / course
Master of Science in Engineering