Methodologies for modeling and feedback control of the nitrogen oxide-BSFC trade-off in high-speed, common-rail, direct-injection diesel engines.

摘要

Over the past decade, modern technologies such as Direct Injection (DI), Exhaust Gas Recirculation (EGR), Variable Geometry Turbocharging (VGT), and most recently, High Pressure Common Rail (HPCR) fuel injection have narrowed the gap between Diesel engines and Spark-Ignition (SI) engines in terms of environmental impact. These improvements in Diesel engine technology are accompanied by several challenges. The modern diesel engine is a complex nonlinear system that must be controlled optimally to ensure that it meets the environmental regulations while maintaining its performance. One-loop-at-a-time tuning is no longer effective due to the complexity of the system. Currently, a significant part of time is spent in the optimization of engine performance, a luxury industry cannot afford in the increasingly competitive scenario. For this reason, the automotive industry is realizing the significance of model based and multivariate control.; The CIDI engine can be thought of as being primarily composed of two subsystems---the air loop and the fuel path, that are eventually coupled at the combustion chamber. Multivariate control methods for the feedback control of the air loop have been extensively researched. Fuel path control on the other hand has mostly been of a feedforward nature due to lack of appropriate sensors. With sensors for emissions such as NOx beginning to become commercially viable, a need has arisen to formulate control paradigms that incorporate the emission optimization problem into the feedback control framework.; Methodologies for modeling and feedback control of the NOx- BSFC trade-off are explored. Two different types of subsystems of a common high-speed Diesel engine are modeled based on the chosen input parameters. Linear models for the open-loop torque and NOx dynamics are proposed for each subsystem based on models published in the literature. These models are identified and demonstrated to be capable of reproducing essential system properties.; A generic control paradigm is proposed that enables the explicit incorporation of the trade-offs between different output variables directly within the control framework. Two different instances of a constrained NOx- BSFC trade-off are demonstrated to exist in a Diesel engine. The first example relates to the existence of a NOx-BSFC trade-off in the context of torque control in the fuel path. The second example demonstrates the existence of a similar trade-off in the context of air flow control. The above control paradigm is applied to each example for the feedback control of the NOx-BSFC trade-off.; In summary, viable methodologies are demonstrated for the modeling of the Torque and NOx dynamics of a Diesel engine in response to both fuel path and air-loop inputs. A formal methodology for treatment of the constrained NOx-BSFC trade-off problem in a feedback control framework is developed. Application of this methodology is shown to ensure operation of the plant in a specified location of the NOx- BSFC Pareto surface.