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

Abstract

The 2004 Federal Tier II and California LEV I emission standards for diesel light trucks mandate tailpipe NOx levels of 0.6g∕mi. Active lean NOx 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 NOx 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 NOx catalysts. The model represents the phenomena relevant to NOx 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 NOx conversion efficiency versus quantity of injected hydrocarbons.

Automotive Powertrain Control - A Survey

“…The complicating factors are the hydrocarbon storage phenomenon in the catalyst and the interactions between hydrocarbon storage and temperature. A control oriented model for the ALNC is developed and extended in [94,95]. Dynamic programming is applied in [94] to generate a control law that minimizes the weighted sum of tailpipe NO x and spent fuel.…”

An Integrated Software Environment For Powertrain Feasibility Assessment Using Optimization And Optimal Control

“…Our second example is an application of the software to a diesel engine case study treated in [11]. The engine is equipped with an Active Lean NOx Catalyst (ALNC) as well as with a hydrocarbon (HC) injector upstream of ALNC in the exhaust system.…”

“…The trade-off variables in this problem are the fuel consumption by the HC injector and the post-ALNC NOx emissions. The key dynamic states in this problem [11] are the temperature of the ALNC and the amount of HC stored in the ALNC.…”

“…In the original problem formulation, the total flow rate through the ALNC, the concentrations of NOx, HC, and oxygen at the inlet of the ALNC, as well as pressure and temperature at the inlet of the ALNC are prescribed as functions of time [11]. The hydrocarbon injection rate is the quantity being optimized.…”

“…The introduction of energy and storage elements, such as the battery for hybrid vehicles and lean NOx trap for lean burn engines, has however necessitated a new optimization paradigm, where the dynamics optimization is essential to address the performance trade-offs over various driving cycles. Several recent publications have demonstrated the successful applications of deterministic and stochastic dynamic programming [9][10][11][12][13], linear programming [14], and computational game theory [15]. These efforts have laid the foundation for establishing a model-based and optimization-enabled software environment for carrying out powertrain feasibility assessment.…”