In the next years, the upcoming emission legislations are expected to introduce further restrictions on the admittable level of pollutants from vehicles measured on homologation cycles and real drive tests. In this context, the strict control of pollutant emissions at the cold start will become a crucial point to comply with the new regulation standards. This will necessarily require the implementation of novel strategies to speed-up the light-off of the reactions occurring in the after-treatment system, since the cold start conditions are the most critical one for cumulative emissions. Among the different possible technological solutions, this paper focuses on the evaluation of the potential of a burner system, which is activated before the engine start. The hypothetical burner exploits the lean combustion of an air-gasoline mixture to generate a high temperature gas stream which is directed to the catalyst section promoting a fast heating of the substrate. In this work, an experimental test bench has been adopted to characterize the thermal transient of the after-treatment system when the burner-like system is activated, monitoring the temperature of the gas flow and the temperature of the metallic walls at different locations. Moreover, a CFD model has been developed to investigate the light-off of the reactions during the initial operation of the burner and the subsequent start of the engine. The model, developed on the basis of the OpenFOAM code, resorts to a multi-region approach, where different meshes are employed to describe the fluid domain and the solid regions, namely the catalytic porous substrates and the metallic walls constituting pipes and canning. Specific submodels are implemented to consider flow resistance, heat transfer, mass transfer and catalytic reactions occurring in the catalyst region. The CFD framework has been initially validated on the experimental data acquired on the test bench. The methodology has been then applied to the preliminary analysis of the catalyst light-off at engine cold start, considering a full exhaust line equipped with burner-like system.

The thermal transient of the after-treatment system (ATS) during the cold start and the typical urban drive low load engine operations is a crucial point for the conversion efficiency. In this context, the adoption of electrical heating is regarded as an effective solution to promote the catalytic activity and the pollutants abatement. This paper focuses on the evaluation of the radiative heat transfer affecting the operation of an electrical heated catalyst employed to increase the abatement efficiency of a standard catalyst. The modeling methodology relies on a CFD framework based on a Conjugate Heat Transfer (CHT) approach in OpenFOAM, so that a detailed characterization of the thermal transient of the different components of the exhaust line can be achieved. The electrical heating device under investigation is based on a metallic support and it is heated by the Joule effect. The distribution of the heat and its subsequent interaction with the gas flow significantly influence the catalyst operations. In this context, the CFD modeling framework has been further developed so that it is possible to accurately evaluate the radiative heat transfer in correspondence of the porous regions. The description of such features is mandatory for an accurate prediction of the maximum electrical heating device temperatures, resulting in a reliable estimation of the gas flow temperature and its subsequent interaction with the catalyst. The simulation methodology has been applied at first excluding the radiative heat transfer. Then, the developed radiation modeling is applied, so that its influence on the ATS performance can be fully evaluated.

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In the last decade, additive manufacturing (AM) techniques have been progressively applied to the manufacturing of many mechanical components. Compared to traditional techniques, this technology is characterized by disruptive potential in terms of the complexity of the objects that can be produced. This opens new frontiers in terms of design flexibility, making it possible to create new components with optimized performances in terms of mechanical properties and weight. In this work, the focus is on a specific field of application: the development of novel porous media structures which can be the basis of advanced after-treatment systems for internal combustion engines. In particular, the possibility to design periodic open cellular structures (POCSs) that can be applied as catalytic substrates opens new perspectives in terms of flexibility and integrated functionalities. The present study investigates an innovative solution where the catalytic substrates are located in the pipes of the exhaust manifolds of a high-performance engine. A preliminary characterization of the pressure drop induced by the POCS structure is carried out, with a particular focus on the impact of the backpressure on the engine performances. Moreover, each POCS integrates an electrical circuit which is used to promote the heating of the device, with beneficial effects on the light-off of the catalytic reactions. An advanced CFD model is applied to evaluate the potential of the solution, comparing the pollutant conversion with that of the baseline configuration equipped with a standard after-treatment system solution.

<div class="section abstract"><div class="htmlview paragraph">The reduction of the catalyst light-off time at the engine cold start represents a key factor for the pollutant emissions control from vehicles tested on homologation cycles and real drive conditions. The adoption of heating strategies to increase the temperature of the catalytic substrate in the early phase of the engine start is regarded as a promising solution. The present study focuses on the application of electrical heated catalyst (EHC) in an after-treatment line for a spark-ignition gasoline engine. The analysis is carried out by means of an advanced CFD framework, which includes the modeling of catalytic reactions in the substrates and accounts for the thermal evolution of all the components included in the after-treatment system. In this work the model has been extended with: a) the solution of the electrical circuit of the EHC to provide an accurate description of the non-uniform temperature distribution of the coils heated by Joule effect and b) a specific model for the radiative heat transfer from the porous EHC, which plays a significant role in the thermal balance of the device. The simulation model is validated considering an experimental test configuration, suitably instrumented to provide temperature measurements at different locations under different operating conditions. Then, a complete exhaust line has been simulated, analyzing the thermal transient of the catalytic substrate during the different phases of the EHC activation. The reaction light-off in the catalyst is monitored, assessing the benefits in terms of reduction of the overall emissions with respect to the base case.</div></div>