Diesel Exhaust Aftertreatment Systems Research Articles

Modelling the ammonia adsorption–desorption process over an Fe–zeolite catalyst for SCR automotive applications

The accurate description of NH3 adsorption/desorption from the catalyst surface is the basis for the correct description of the NH3–SCR catalytic chemistry. Currently, Temkin-type kinetics are widely and successfully used to describe the NH3 adsorption/desorption process over V-based and metal-promoted zeolite catalysts in the 200–600°C T-window: in this approach the heterogeneity of the catalytic surface is taken into account considering the activation energy of the desorption process as a linear function of the adsorbed species surface coverage. In the present work, carried out over a commercial Fe–zeolite SCR catalytic system, we show that this modelling approach fails when extended to lower temperatures (T≤150°C) and in the presence of water, conditions of growing interest for Diesel exhaust after-treatment systems. Based on literature evidence, an improved, physically consistent dual-site modelling approach is implemented, resulting in an accurate description of the ammonia adsorption/desorption process in the extended 50–550°C temperature window.

604 低温始動時におけるディーゼル後処理装置の効果(エンジンシステム)

604 低温始動時におけるディーゼル後処理装置の効果(エンジンシステム)

Diesel Exhaust Aftertreatment System Packaging and Flow Optimization on a Heavy-Duty Diesel Engine Powered Vehicle

Diesel Exhaust Aftertreatment System Packaging and Flow Optimization on a Heavy-Duty Diesel Engine Powered Vehicle

Modelling of soot oxidation by [formula omitted] in various types of diesel particulate filters

Diesel particulate filters (DPF) form significant part of the diesel exhaust aftertreatment systems. Collected soot particles can be burned off continuously at intermediate temperatures by nitrogen dioxide NO 2 (“passive regeneration”) or periodically at increased temperature by oxygen O 2 (“active regeneration”). NO 2 for passive regeneration of the DPF is generated from nitrogen monoxide (NO) and O 2 in the diesel oxidation catalyst (DOC) located upstream, or in the catalytic coating of DPF (CDPF), or by a combination of both. Two-dimensional nonstationary model of the filter, soot filtration and regeneration with detailed kinetics of soot combustion, and spatially 1D plug-flow model of the DOC are presented and utilized to compare various catalytic systems for soot oxidation by NO 2 and O 2 (DPF, CDPF, CRT®, CCRT®). Pressure drop, soot conversion and other properties of the systems during the passive and active regeneration are compared.

CO Emission Model for an Integrated Diesel Engine, Emissions, and Exhaust Aftertreatment System Level Model

CO Emission Model for an Integrated Diesel Engine, Emissions, and Exhaust Aftertreatment System Level Model

A novel 1D approach for the simulation of unsteady reacting flows in diesel exhaust after-treatment systems

A new one-dimensional approach, based on the solution of the governing equations for unsteady, reacting and compressible flows has been developed for the simulation of the hydrodynamics, the transient filtration/loading and the catalytic/NO2-assisted regeneration occurring in diesel particulate filters (DPF). The model is able to keep track of the chemical compounds, of the amount of soot transported by the flow, and it can estimate the increasing of back-pressure occurring in the exhaust system, due to the permeability variation of the porous wall and to the soot cake building up on the DPF porous surface. Further, a prediction of the oxidation of the deposited particulate induced by the Oxygen (collected in the exhaust gas), by the nitrogen dioxide (NO2), by the carbon oxide (CO) and by the hydrocarbons (HC) converted along the diesel oxidation catalysts (DOC) is given. A first validation of the code has been performed by the comparison with the results coming from computational fluid dynamics (CFD) and with experimental measurements published in literature. The proposed model has been included in an engine simulation code, in order to perform a simulation of a complete engine; results coming from an optimization work recently carried out on a 1.9 L JTD turbocharged diesel engine, equipped with a complex after-treatment system, are presented.

Optimisation of a dosing strategy for an HC-SCR diesel exhaust after-treatment system

Several principal aspects and components of an advanced catalytic exhaust after-treatment system for NO x reduction on a heavy-duty diesel truck engine have been systematically examined and evaluated. The after-treatment system consists of de-NO x catalysts, injection of a reducing agent (diesel fuel), and computer programs to model the engine and catalysts in real time. These models are combined with a third program, a strategy, to control the injection of reducing agent during transient operation. Evaluation of the system was performed using the standard European transient cycle (ETC). The benefits and disadvantages of an oxidation catalyst upstream the reductant injection are clarified. Whereas an increased NO 2/NO ratio is beneficial at larger reductant dosages, the effects of temperature levelling and delay are detrimental for system performance. The dynamic effect of introducing a strategy for distributing the reducing agent in time is elucidated. The strategy itself is presented and the process of its systematic optimisation is closely followed. Implications of the optimisation are that catalyst temperature is the most important variable in the strategy. Also, a considerable part of the reducing agent should be distributed at low and intermediate temperatures, for utilising an increased NO 2/NO ratio. Furthermore, results suggest that a smooth, rather than instantaneous, adjustment of reductant dosage to driving conditions is necessary. Finally, a set-up with two injectors is examined for its potential in the application. It is shown to be of disadvantage for the ETC as a whole, but may not be so at lower exhaust gas flows.

Computer aided engineering in diesel exhaust aftertreatment systems design

Computer aided engineering (CAE) methodologies are increasingly being applied to assist the design of spark-ignition (SI) engine exhaust aftertreatment systems in view of the stage III and IV emissions standards. Following this trend, the design of diesel exhaust aftertreatment systems is receiving more attention owing to the capabilities of recently developed mathematical models. The design of diesel exhaust systems must cope with three major aftertreatment categories: diesel oxidation catalysts, diesel particulate filters and de-NOx catalytic converters. An integrated CAE methodology that could assist the design of all these classes of systems is described in this paper. It employs the following computational tools: a computer code for modelling transient exhaust system heat transfer, a computer code for modelling the transient operation of a diesel oxidation or a de-NOx catalytic converter, a database containing chemical kinetics data for a variety of oxidation and de-NOx catalyst formulations and a computer code for modelling the loading and regeneration behaviour of a wall-flow filter, assisted by catalytic fuel additives. Application of the CAE methodology, which helps the exhaust aftertreatment system design engineer to meet the future emissions standards, is highlighted by referring to a number of representative case studies.