M. J. van Nieuwstadt

EGR-VGT control schemes: experimental comparison for a high-speed diesel engine

Variable-geometry turbochargers (VGTs) are employed in high-end diesel engines. These VGTs also help in controlling the trade-offs in emissions performance. Exhaust gas recirculation (EGR) is used to dilute the combustion mixture, resulting in lower peak combustion temperatures and a lower oxygen concentration and hence lower NOx emissions. In this article, we compare some of the control methodologies previously presented and some not yet presented to evaluate their benefits experimentally. We do not include any new theory. Rather we refer to other sources for the development of the controllers evaluated. We present an objective comparison of advanced control methodologies on a complex industrial problem with widespread applications. The control methodologies discussed are essentially system based, i.e., the initial controller is developed on an engine model.

Optimization of complex powertrain systems for fuel economy and emissions

Stringent emission regulations combined with customer demands for improved fuel economy and performance have forced the automotive industry to consider more advanced powertrain configurations than standard port-fuel injected gasoline engines. Modern state-of-the-art powertrain systems may combine several power sources (internal combustion engines, electric motors, fuel cells, etc.) and various exhaust aftertreatment devices (catalytic converters, lean NOx traps, particulate filters, etc.) in addition to conventional engine subsystems such as turbochargers and exhaust gas recirculation. The determination of the way in which these systems need to be operated to meet drivers torque demand, performance and fuel economy expectations while satisfying federal emission regulations is a complex and a multiobjective optimal control problem. This paper reviews some of the approaches to this problem in the context of two case studies.

Preserving stability/performance when facing an unknown time-delay

Abstract Embedded controllers executed in real-time are, frequently, subject to a time-varying delay induced by task prioritization or communication over prioritized communication networks. Depending on the microprocessor or network load the delay value may vary. The control design that is based on the worst case assumption with respect to the delay may be very conservative and fail to deliver the adequate performance. On the other hand, the price for not properly dealing with the delay is instability. In this paper some of these issues are discussed in more detail and a control scheme is proposed which combines an unknown input observer to estimate the delayed value of the input, an on-line estimation scheme for the delay and a controller that adjusts its gains as needed to preserve system stability. Some of the aspects of the proposed scheme are discussed and illustrated with simulations on an automotive example.

Decentralized and Multivariable Designs for EGR-VGT Control of a Diesel Engine

Abstract This paper is a study into the potential benefits of a coordinated EGRVGT control strategy for a high speed diesel engine equipped with EGR and a variable nozzle geometry turbocharger (VGT). Traditionally, control strategies for this problem use SISO techniques or use one actuator at a time. Since the effect of the EGR and VGT actuators is coupled through the pressure in the exhaust manifold, it can be expected that a coordinated approach will yield a performance benefit. We will investigate in this paper to what extent this claim holds true.

Charge control for direct injection spark ignition engines with EGR

Modern automotive engines rely increasingly on high performance estimation and control algorithms to deliver the expected performance benefits. This paper discusses a number of control problems and issues that arise in the design of a charge controller for a lean-burn direct injection spark ignition engine with exhaust gas recirculation (EGR). To deal with uncertainties and parameter variations that can significantly affect the engine performance, the use of feedback and adaptive controllers is shown to be essential.

Intake oxygen concentration estimation for DI diesel engines

In order to reduce emissions and improve performance of internal combustion engines, it is desirable to know the oxygen concentration of the gas inducted into the engine so that the appropriate amount of fuel can be injected. This is especially true for diesel engines in which up to 50% of the exhaust gas is recirculated back into the engine. This work presents an estimation algorithm for the oxygen concentration in the intake manifold of a turbocharged diesel engine. The only quantities needed for the estimation scheme are boost pressure, fueling rate, engine speed and EGR valve lift, all of which are generally known to the engine control unit. This estimator is a first order linear dynamic model (with time varying coefficients) and asymptotically stable. Due to the unobservability of the oxygen concentration model, the speed of convergence of the estimation scheme is fixed by engine parameters, but is as fast as the phenomenon of mixing of the exhaust gas recirculated with the air in the intake manifold. Simulation studies show the effectiveness of the proposed estimator.

Control Oriented Modeling of a Diesel Active Lean NOx Catalyst Aftertreatment System

The 2004 Federal Tier II and California LEV I emission standards for diesel light trucks mandate tailpipe NO x levels of 0.6 g/mi. Active lean NO x catalysts (ALNC or LNC) have been proposed as a means to achieve this standard. These catalysts require the delivery of supplemental hydrocarbons in order to reduce NO x in the lean environment typical of diesel exhaust. In the system studied here, these additional hydrocarbons are injected into the exhaust system downstream of the turbocharger. A control-oriented, gray-box mathematical model is developed for diesel active lean NO x catalysts. The model represents the phenomena relevant to NO x reduction and HC consumption, namely, the catalyst chemical reactions, HC storage in the ALNC, and heat transfer behavior on the basis of an individual exhaust element. As an illustration of how the model may be used, dynamic programing is applied to determine the optimal trade-off of NO x conversion efficiency versus quantity of injected hydrocarbons.

Robust Separation of Signal Domain From Single Channel Mixed Signal Output of Automotive Urea Based Selective Catalytic Reduction Systems

There is a class of sensor constrained, uncertain, chemical reactor systems that pose unique challenges with regard to the feedback signal. We refer specifically to the urea based selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the engine exhaust of diesel powertrains. These catalysts rely on adsorbed ammonia (NH3), produced from aqueous urea, for the catalytic reduction of NOx to N2. Typically, underinjection of urea will result in the slip of NOx, whereas overinjection will induce NH3 slip. The ideal control objective of such a plant is, therefore, to regulate urea injection such that the net slip over the catalyst is minimized. Meeting these control objectives is made difficult due to the presence of an output sensor that is cross sensitive to both NOx and NH3, thereby producing a mixed feedback signal. This signal confounding poses significant challenges with regard to the stability and robustness of both closed loop control as well as on board diagnostics. In the absence of a robust NH3 sensor, it becomes necessary to create alternate methods of signal disambiguation. However, so far in open literature, there has not been a detailed discussion of this problem nor has a concrete solution been proposed to robustly and continuously identify the nature of slip as NOx or NH3. In this paper, we discuss the systematic development of a new method that allows a robust and continuous determination of the slip regime from the mixed signal output of a standard NOx sensor. The full scope of the practical problem is discussed and the performance of the proposed method is shown via experimental data.

Modelling and dynamic control of an active lean NO/sub x/ catalyst

This paper presents a phenomenological model of an active lean NO/sub x/ catalyst for control purposes. It does not include a spatial dimension, but lumps the characteristics of the catalysts into a few parameters. It accounts for hydrocarbon combustion, storage and release, temperature rise and NO/sub x/ conversion.This paper presents a phenomenological model of an active lean NO/sub x/ catalyst for control purposes. It does not include a spatial dimension, but lumps the characteristics of the catalysts into a few parameters. It accounts for hydrocarbon combustion, storage and release, temperature rise and NO/sub x/ conversion.

Preserving Stability/Performance when Facing an Unknown Time-Delay

Abstract Embedded controllers executed in real-time are, frequently, subject to a time-varying delay induced by task prioritization or communication over prioritized communication networks. Depending on the microprocessor or network load the delay value may vary. The control design that is based on the worst case assumption with respect to the delay may be very conservative and fail to deliver the adequate performance. On the other hand, the price for not properly dealing with the delay is instability. In this paper we discuss some of these issues in more detail and propose a scheme which combines an unknown input observer to estimate the delayed value of the input, an on-line estimation scheme for the delay and a controller that adjusts its gains as needed to preserve system stability. Some of the aspects of the proposed scheme are discussed and illustrated with simulations on an example automotive application.