Introduction to Modeling and Control of Internal Combustion Engine Systems
Internal combustion engines (ICE) still have potential for substantial improvements, particularly with regard to fuel efficiency and environmental compatibility. In order to fully exploit the remaining margins, increasingly sophisticated control systems h
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In this chapter, mean-value models (MVM) of the most important subsystems of SI and Diesel engines are introduced. In this book, the notion of MVM1 will be used for a specific set of models as defined below. First, a precise definition of the term MVM is given. This family of models is then compared to other models used in engine design and optimization. The main engine sub models are then discussed, namely the air system that determines how much air is inducted into the cylinder; the fuel system that determines how much fuel is inducted into the cylinder; the torque generation system that determines how much torque is produced by the air and fuel in the cylinder as determined by the first two parts; the engine inertial system that determines the engine speed; the engine thermal system that determines the dynamic thermal behavior of the engine; the pollution formation system that models the engine-out emission; and the pollution abatement system that models the behavior of the catalysts, the sensors, and other relevant equipment in the exhaust pipe. All these models are control oriented models (COM), i.e., they model the input-output behavior of the systems with reasonable precision but low computational complexity They include, explicitly, all relevant transient (dynamic) effects. Typically, these COM are represented by systems of nonlinear differential equations. Only physics-based COM will be discussed, i.e., models that are based on physical principles and on a few experiments necessary to identify some key parameters.
1
The terminology MVM was probably first introduced in [89]. One of the earliest papers proposing MVM for engine systems is [195]. A good overview of the first developments in the area of MVM of SI engine systems can be found in [167]. A more recent source of information on this topic is [44].
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2 Mean-Value Models
2.1 Introduction Reciprocating engines in passenger cars clearly differ in at least two aspects from continuously operating thermal engines such as gas turbines: • •
the combustion process itself is highly transient (Otto or Diesel cycle, with large and rapid temperature and pressure variations); and the thermodynamic boundary conditions that govern the combustion process (intake pressure, composition of the air/fuel mixture, etc.) are not constant.
The thermodynamic and kinetic processes in the first class of phenomena are very fast (a few milliseconds for a full Otto or Diesel cycle) and usually are not accessible for control purposes. Moreover, the models necessary to describe these phenomena are rather complex and are not useful for the design of real-time feedback control systems. Exceptions are models used to predict pollutant formation or analogous tasks. Appendix C describes the elementary ideas of engine thermodynamic cycle calculation. (See Sec. 2.5.3 for more details on engine test benches.) load torque Tl ("disturbance input") throttle uα
yω
speed
injection uϕ
yλ
air/fuel-ratio
yα
air mass-flow
ignition uζ EGR-valve uε etc. …
SI engine
y p manifold pressu
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