Heat transfer in wall-flow monoliths has gained in interest because of the widespread adoption of these systems by automotive industry to fulfil soot emission regulations and the importance of heat exchange on the regeneration process control to avoid damaging the monolith. This paper presents a heat transfer model for wall-flow diesel particulate filters coupled with an unsteady compressible flow solver. The heat exchange between the gas and the solid phase is based on a bi-dimensional discretisation of the porous medium both in axial and tangential directions. The monolith can be discretised in the radial direction to account for the heat fluxes towards the environment through the monolith and the canister, which is also coupled with the inlet and outlet ducts of the filter. The model is validated against experimental data obtained in a flow test rig. A test campaign under non-reacting conditions has been conducted to show the capability for thermal response prediction. Tests cover clean and soot loaded monolith, continuous flow under steady and transient thermal conditions, and pulsating flow. In this case, the characteristics of the pressure waves in amplitude and frequency are similar to those that the monolith can undergo depending on its location along the exhaust line.

The combination of more strict regulation for pollutant and CO2 emissions and the new testing cycles, covering a wider range of transient conditions, makes very interesting the development of predictive tools for engine design and pre-calibration. This paper describes a new integrated Virtual Engine Model (VEMOD) that has been developed as a standalone tool to simulate new standard testing cycles. The VEMOD is based on a wave-action model that carries out the thermo-and fluid dynamics calculation of the gas in each part of the engine. In the model, the engine is represented by means of 1D ducts, while the volumes, such as cylinders and reservoirs, are considered as 0D elements. Different sub-models are included in the VEMOD to take into account all the relevant phenomena. Thus, the combustion process is calculated by the Apparent Combustion Time (ACT) 1D model, responsible for the prediction of the rate of heat release and NOx formation. Experimental correlations are used to determine the rest of pollutants. In order to predict tailpipe pollutant emissions to the ambient, different sub-models have been developed to reproduce the behavior of the aftertreatment devices (DOC and DPF) placed in the exhaust system. Dedicated friction and auxiliaries sub-models allow obtaining the brake power. The turbocharger consists of 0D compressor and turbine sub-models capable of extrapolating the available maps of both devices. The VEMOD includes coolant and lubricant circuits linked, on the one hand, with the engine block and the turbocharger through heat transfer lumped models; and on the other hand with the engine heat exchangers. A control system emulating the ECU along with vehicle and driver submodels allow completing the engine simulation. The Virtual Engine Model has been validated with experimental tests in a 1.6 L Diesel engine using steady and transient tests in both hot and cold conditions. Engine torque was predicted with a mean error of 3 Nm and an error below 14 Nm for 90 % of the cycle duration. CO2 presented a mean error of 0.04 g/s, while during 80 % of the cycle, error was below 0.44 g/s.

Elsevier Luján, JM.; Bermúdez, V.; Piqueras, P.; Garcia Afonso, O. (2015). Experimental assessment of pre-turbo aftertreatment configurations in a single stage turbocharged diesel engine. AbstractDiesel oxidation catalysts and diesel particulate filters are standard aftertreatment systems in Diesel engines which are traditionally placed downstream of the turbine. However, pre-turbo aftertreatment configurations are being approached as a way to improve the aftertreatment performance in terms of light-off and passive regeneration. This exhaust line architecture can also benefit fuel economy. The objective of this work is to analyse experimentally how the pre-turbo aftertreatment placement impacts on the performance of a single stage turbocharged Diesel engine.The work has been divided into two parts focused on steady-state and transient engine operation separately. The first part comprises the analysis of the experimental results corresponding to steady-state operating conditions. The range of operation covers different engine loads and speeds. The engine response with pre-turbo aftertreatment placement is mainly affected by the change in the pumping work caused by the aftertreatment pressure drop reduction and its new location, which avoids the multiplicative effect of the turbine expansion ratio when setting the engine back-pressure. These effects become more significant as the engine load increases benefiting fuel consumption from low to high loads. Concerning aftertreatment performance, the results evidence noticeable benefits in DPF passive regeneration and CO/HC emissions reduction at low engine load.

Reactivity controlled compression ignition is a promising combustion strategy due to the combination of excellent thermal efficiency with ultra-low nitrogen oxides and particulate matter raw emissions. However, very high levels of unburned hydrocarbons and carbon monoxide emissions are found. It limits the reactivity controlled compression ignition use at very low loads and presents an additional challenge for the diesel oxidation catalyst. The low exhaust temperature and high carbon monoxide and hydrocarbon concentration can penalise the catalyst conversion efficiency.The objective of this work is to evaluate the response of an automotive diesel oxidation catalyst when used for reactivity controlled compression ignition combustion combining experimental and modelling approaches. For this purpose, dedicated tests have been done using diesel-gasoline as fuel combination in a single-cylinder engine. This way, the catalyst conversion efficiency has been determined within a wide operating range covering hydrocarbon adsorption conditions and the pollutants abatement dependence on the mass flow and temperature. The experimental results in the full-size catalyst has been analysed by modelling. A lumped diesel oxidation catalyst model has been applied to extend the results to multi-cylinder engine conditions and to determine the light-off curves for both carbon monoxide and hydrocarbons. These tests evidence the penalty in light-off temperature due to high pollutants mass fraction, which promotes inhibition limitations to the reaction rate.

The increasingly restrictive legislation on pollutant emissions is involving new homologation procedures driven to be representative of real driving emissions. This context demands an update of the modelling tools leading to an accurate assessment of the engine and aftertreatment systems performance at the same time as these complex systems are understood as a single element. In addition, virtual engine models must retain the accuracy while reducing the computational effort to get closer to real-time computation. It makes them useful for pre-design and calibration but also potentially applicable to on-board diagnostics purposes. This paper responds to these requirements presenting a lumped modelling approach for the simulation of aftertreament systems. The basic principles of operation of flow-through and wall-flow monoliths are covered leading the focus to the modelling of gaseous emissions conversion efficiency and particulate matter abatement, i.e. filtration and regeneration processes. The model concept is completed with the solution of pressure drop and heat transfer processes. The lumped approach hypotheses and the solution of the governing equations for every submodel are detailed. While inertial pressure drop contributions are computed from the characteristic pressure drop coefficient, the porous medium effects in wall-flow monoliths are considered separately. Heat transfer sub-model applies a nodal approach to account for heat exchange and thermal inertia of the monolith substrate and the external canning. In wall-flow monoliths, the filtration and porous media properties are computed as a function of soot load applying a spherical packed bed approach. The soot oxidation mechanism including adsorption reactant phase is presented. Concerning gaseous emissions, the general scheme to solve the chemical species transport in the bulk gas and washcoat regions is also described. In particular, it is finally applied to the modelling of CO and HC abatement in a DOC and DPF brick. The model calibration steps against a set of steady-state in-engine experiments allowing separate certain phenomena are discussed. As a final step, the model performance is assessed against a transient test during which all modelled processes are taking place simultaneously under highly dynamic driving conditions. This test is simulated imposing different integration time-steps to demonstrate the model´s potential for real-time applications.

Internal combustion engines (ICE) are the main propulsion systems in road transport [...]

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ElsevierBermúdez Tamarit, VR.; Serrano Cruz, JR.; Piqueras Cabrera, P.; Garcia Afonso, O. (2015 AbstractWall-flow type diesel particulate filter (DPF) is a required aftertreatment system for particle emission abatement and standards fulfilment in Diesel engines. However, the DPF use involves an important flow restriction, especially as the substrate gets soot and ash loaded. It gives as a result the increase of the exhaust back-pressure and hence a fuel consumption penalty. The increasing damage of fuel consumption with DPF soot loading leads to the need of the regeneration process. Usually based on active strategies, this process involves an additional fuel penalty but prevents from excessive DPF pressure drop and ensures secure soot burnt out.Under this context, new solutions are required to improve the state of the art DPF soot loading to pressure drop ratio. This paper presents a novel technique based on pre-DPF water injection to reduce the DPF pressure drop under soot loading conditions by disrupting its dependence on soot/ash loading. It provides benefits to engine fuel economy and also higher flexibility for DPF regeneration and maintenance. The work covers a test campaign performed in a passenger car turbocharged Diesel engine equipped with a wall-flow DPF. The main objective is to describe the technique, to provide a figure of its potential for pressure drop control and fuel consumption reduction. The results of the experiments also confirm soot and ash loading capacity increase and demonstrate the lack of negative effects on filtration efficiency and active and passive regeneration.