Advanced Modeling and Control
Approaches for Engines with
Multiple Combustion Modes, 03-R9580
Principal Investigators
Junmin
Wang
Jayant V. Sarlashkar
Ryan Roecker
Inclusive Dates: 10/01/05 – 04/01/07
Background - Diesel engine emission regulations are becoming increasingly stringent. Of late, using multiple combustion modes in diesel engines has been considered as a means to maintain functionality of the exhaust treatment systems and significantly reduce emissions. More sophisticated alternative combustion modes, such as low-temperature combustion (LTC), homogeneous charge compression ignition (HCCI), and premixed charge compression ignition (PCCI), are being actively developed and implemented along with the conventional diesel combustion to achieve emission regulations and desired performances simultaneously. However, because the in-cylinder condition requirements of these combustion modes are quite different and some of the combustion modes are close to the edge of stability while very sensitive to the in-cylinder condition, it is challenging to achieve smooth, fast, and robust mode switching without sacrificing the performance with good drivability and low levels of emissions. As the engine system is multiple-variable and highly nonlinear, conventional calibration/mapping based and classical linear control approaches do not produce satisfactory and robust results during transient operations in vehicle applications. Advanced multiple-input-multiple-output (MIMO) nonlinear control modeling and design methods may offer great potential in meeting the real-world drivability and emission requirements simultaneously.
Approach - Control oriented engine intake/exhaust system dynamical models were to be developed and used for the design of control system. In this project, model-based MIMO nonlinear robust controllers (e.g., sliding mode control), organized by a finite state machine (FSM) based supervisory controller, were employed to achieve seamless transition among different combustion modes. The inherent singularity in turbocharged diesel engines was addressed using special techniques. Observers/estimators were designed to construct the necessary system states for the controllers based on the available measurement from the engine. The overall control structure is shown in Figure 1. The gas-handling devices were controlled by two paths. One was the feedforward terms, decided by desired torque and engine speed. Another was the feedback contributions, based on the desired and measured/estimated states through the robust nonlinear control laws.
Accomplishments - Important progress has been made in the project. Control-oriented engine intake/exhaust system dynamic models have been developed based on physical laws. Based on these models, different robust MIMO nonlinear controllers were designed for different combustion modes with respect to their characteristics and sensor measurement limitations. Figure 2 shows the engine transient test responses, engine torque, and exhaust gas air-to-fuel ratio (AFR), obtained on a modern light-duty diesel engine running LTC and conventional diesel combustion modes. Compared with the results of traditional calibration-based control approaches, the model-based MIMO robust nonlinear control approaches developed in this project provides much better performance in terms of seamless mode switching, robustness, and dramatically reduced calibration/mapping efforts.
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