Computer Aided Assessment of Catalyst Ageing Cycles

Topics in Catalysis, 2000

There are no general accepted models for CO and HC oxidation and NO x reduction in automotive catalysis. Many factors affect the observed kinetics e.g. the catalyst preparation method and conditioning, the composition of the exhaust gases, mass and heat transfer, and all the reaction conditions that the catalyst has been exposed to prior to an experiment. However, most experiments are done under idealized conditions with a fresh catalyst and without water, SO 2 , etc. Simple models will only describe the individual experiments and more complex models require determination of the parameters from independent measurements under realistic conditions. The kinetic models available in the literature are only reliable for the exact catalyst and reaction conditions for which they have been developed.

Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2001

The application of computer simulation in the development of catalytic exhaust aftertreatment systems for cars is over thirty years old. However, ever-increasingly stringent exhaust emissions legislation requires an ever-increasing degree of accuracy and complexity in the mathematical models applied. Traditionally, the Langmuir-Hinshelwood kinetics were applied in the majority of the models available, with a small number of representative chemical reactions. In this paper it is proved, by means of typical case studies, that the above modelling approach, with the necessary re ning, can be brought to the level of accurately predicting the behaviour of advanced catalyst systems employed in EURO-3 and EURO-4 emissions homologation. An essential characteristic that was introduced to this end is the computer-aided selection ( best t) of the tunable parameters representing the apparent chemical kinetics and oxygen storage and release properties of each diVerent catalystwashcoat combination. Other modelling improvements are also discussed in the present paper, setting the scene for high accuracy simulations in view of the current and future emissions standards for spark-ignited, diesel and gasoline direct injection (GDI )-engined vehicles. These include the modelling of the aged catalyst, as well as taking into account the eVect of precious metal loading variation on the apparent kinetics.

Emission Control Science and Technology, 2019

Our previously developed model of NO x chemistry over a commercially used diesel oxidation catalyst has been extended by adding CO and HC chemistry. Synthetic gas bench experiments were conducted in order to elucidate mechanisms and provide the experimental foundation necessary for model calibration. Reactions tested and folded into the model include pure gas-phase CO oxidation, water-gas shift, and surface oxidation reactions for CO and HC. The majority of the experiments were performed at a space velocity corresponding to medium load in terms of driving conditions. The complete model was validated against engine test data. For that, it was necessary to assess the aging of the catalyst (in modeling terms translated to precious metal dispersion) used in the engine tests. After assuming a reasonable dispersion using engineering judgment, model validation against engine test data was performed. This showed the ability of the model to predict both trends and time resolved details.

Frontiers in Mechanical Engineering, 2019

Today restrictions on pollutant emissions require the use of catalyst-based after-treatment systems as a standard both in SI and in Diesel engines. The application of monolith cores with a honeycomb structure is an established practice: however, to overcome drawbacks such as weak mass transfer from the bulk flow to the catalytic walls as well as poor flow homogenization, the use of ceramic foams has been recently investigated as an alternative showing better conversion efficiencies (even accepting higher flow through losses). The scope of this paper is to analyse the effects of foam substrates characteristics on engine performance. To this purpose a 0D "crank-angle" real-time mathematical model of an I.C. Engine developed by the authors has been enhanced improving the heat exchange model of the exhaust manifold to take account of thermal transients and adding an original 0D model of the catalytic converter to describe mass flows and thermal processes. The model has been used to simulate a 1.6l turbocharged Diesel engine during a driving cycle (EUDC). Effects of honeycomb and foam substrates on fuel consumption and on variations of catalyst temperatures and pressures are compared in the paper.

Industrial & Engineering Chemistry Research, 2011

One of the critical needs of a Three Way Catalyst (TWC) model is to be able to predict light-off. This is crucial for application studies and vehicle architectural studies because most of the emissions from a TWC occur before light-off (called coldstart emissions). Laboratory experiments give detailed insights to the reaction mechanism and analytical forms of the rate expressions as they are well-controlled and well-behaved as compared to vehicle tests. However, to predict emissions on a vehicle test, the laboratory-estimated kinetic parameters are not entirely capable because of the various uncertainties in the vehicle tests. In this work, six different vehicle data sets are used to calibrate and validate the TWC global kinetic model. Our emphasis in this work is restricted to predicting the light-off (cold-start emissions) in TWC. The kinetic model is calibrated using 4 vehicle data sets (which use the FTP drive cycle) using iSIGHT software package. The kinetic parameters of the various reactions occurring in the TWC are estimated to match the experimental data through exploratory and local optimization methods. A systematic approach (with increasing complexity) is used to estimate the kinetic parameters. The estimated parameters are then used to validate the model on two different vehicle data sets (one NEDC drive cycle and one FTP drive cycle) with different catalyst compositions and engine power (and hence different engine out exhaust compositions). The model with estimated kinetic parameters predicts the light-off reasonably well for the new data sets. The parameter estimation approach in this work is kept as generic as possible to exhaust aftertreatment devices, and a set of guidelines for parameter estimation (specifically for use in exhaust aftertreatment devices) is presented (in the Appendix).

Applied Catalysis B: Environmental, 1996

Steady state kinetics data from a commercial Pt-based lean NO, catalyst have been used to formulate a kinetic model to describe the performance of the catalyst. It is clear from this analysis that steady state kinetics in isolation are not sufficient to provide a full picture of the operational performance of such a catalyst. However, when this kinetic analysis is combined with mechanistic information obtained over the catalyst, the resulting model is extremely powerful. Within this paper, the development of the kinetic model is described, and the requirement for both accurate mechanistic information and detailed kinetic measurements is clearly demonstrated. The use of the model to predict the performance of a light-duty diesel vehicle under light-off conditions is described, and the power and flexibility of the model, and indeed of the modelling approach within the lean NO, area, are emphasised.

Industrial & Engineering Chemistry Research, 2009

A modeling approach to predict the performance of commercial diesel oxidation catalyst (DOC) is presented in this study. Prior to completing this prediction, the conversion behavior of DOC as previously published was re-evaluated with a verification of the present numerical model. To calibrate and validate the model adopted in this study, steady-state experiments with DOC mounted on a light duty 4-cylinder 2.0 liter turbocharged diesel engine were performed using an enginedynamometer system. The reaction rates for CO, HC, and NO oxidations over a Pt/Al 2 O 3 catalyst were determined in conjunction with a fully transient two-phase 1D+1D monolith channel model with diesel exhaust gas temperature ranges from 150 to 450˚C and space velocity ranges from 10 5 to 5×10 5 h-1. To determine the kinetic parameters which best fit the experimental data, a two-step optimization procedure is introduced. First, the results from the conjugated gradient method (CGM) with individual temperatures for each species are plotted in an Arrhenius plot to generate proper intermediate guesses from initial guesses for all pre-exponential factors and activation energies. Then, kinetic parameters for all species are obtained simultaneously by searching the best fits to experimental data using the CGM from the intermediate guesses for all species. The prediction accuracy of the model was improved by the optimization procedure employed in this study, and the optimized kinetic parameters were validated against experimental data obtained at both 1500 and 2000 rpm.

Catal Today, 1997

Automotive catalytic converters show highly transient operation due to fluctuating exhaust gas conditions in real application. Local ignition of the reactions with very steep temperature gradients as well as moving reaction fronts can occur in the monolithic catalyst. Theoretical investigations are presented based upon detailed simulation studies with a onedimensional two-phase model for the catalytic converter. The simulation of the heat-up of the automotive catalyst during the cold-start shows a highly transient behavior for different cold-start concepts. Also, hot spot phenomena can be observed in the simulation under specific exhaust gas conditions.

Chemical Engineering Communications, 2004

The application of mathematical models to the prediction of the performance of automotive catalytic converters is gaining increasing interest, both for gasoline and diesel engined-vehicles. This article addresses converter modeling in the transient state under realistic experimental conditions. The model employed in this study relies on Langmuir-Hinshelwood kinetics, and a number of apparent kinetic parameters must be tuned to match the behavior of each different catalyst formulation. The previously applied procedure of manually tuning kinetics parameters requires significant manpower. This article presents a methodology for kinetic parameter estimation that is based on standard optimization methods. The methodology is being applied in the exploitation of synthetic gas experiments and legislated driving cycle tests and the assessment of the quality of information contained in the test results. Although the optimization technique employed for parameter estimation is well known, the development of the specific parameter estimation methodology that employs the results of the available types of experiments is novel and required significant development. Application of this refined tuning methodology increases the quality and reliability of prediction and also greatly reduces the required manpower, which is important in the specific engineering design process. The parameter estimation procedure is applied to the example of modeling of a diesel catalytic converter with adsorption capabilities, based on laboratory experiments and vehicle driving cycle tests.

IntechOpen eBooks, 2022

Use of detailed chemistry augments the combustion model of a three-dimensional unsteady compressible turbulent Navier-Stokes solver with liquid spray injection when coupled with fluid mechanics solution with detailed kinetic reactions. Reduced chemical reaction mechanisms help in the reducing the simulations time to study of the engine performance parameters, such as, in-cylinder pressure in spark ignition engines. Sensitivity analysis must be performed to reduce the reaction mechanism for the compression and power strokes utilizing computational singular perturbation (CSP) method. To study a suitable well-established surrogate fuel, an interface between fluid dynamics and chemical kinetics codes must be used. A mesh independent study must be followed to validate results obtained from numerical simulations against the experimental data. To obtain comprehensive results, a detailed study should be performed for all ranges of equivalence ratios as well as stoichiometric condition. This gives rise to the development of a reduced mechanism that has the capability to validate engine performance parameters from stoichiometric to rich mixtures in a spark ignition engine. The above-mentioned detailed methodology was developed and implemented in the present study for premixed and direct injection spark ignition engines which resulted in a single reduced reaction mechanism that validated the engine performance parameters for both engine configurations.