Release of Nanoparticles in the Environment and Catalytic Converters Ageing

A Three-Way Catalyst (TWC) contains a cordierite ceramic monolith coated with a layer of Al2O3, CexZr1−xO2 and platinoids mixture. Under standard operation, the platinoid concentration decreases, exposing the remaining washcoat structure. After that particle release stage, the sintering process follows where the crystalline CexZr1−xO2 solution is broken and begins to separate into ZrO2 and CeO2 phases. ZrO2 is released to the environment as micro and nanoparticles, while a small amount of CeO2 generates a new AlxCe1−xO2 composite. The main effect of Ce capture is the growth in the size of the polycrystal structure from 86.13 ± 16.58 nm to 225.35 ± 69.51 nm. Moreover, a transformation of cordierite to mullite was identified by XRD analysis. Raman spectra showed that the oxygen vacancies (Vö) concentration decreased as CexZr1−xO2 phases separation occurred. The SEM-EDS revealed the incorporation of new spurious elements and microfractures favouring the detachment of the TWC support structure. The release of ultrafine particles is a consequence of catalytic devices overusing. The emission of refractory micro to nanocrystals to the atmosphere may represent an emerging public health issue underlining the importance of implementing strict worldwide regulations on regular TWCs replacement.

Cold-Start Modeling and On-Line Optimal Control of the Three-Way Catalyst

We present a three-way catalyst (TWC) cold-start model, calibrate the model based on experimental data from multiple operating points, and use the model to generate a Pareto-optimalcold-start controller suitable for implementation in standard engine control unit hardware. The TWC model is an extension of a previously presented physics-based model that predicts carbon monoxide, hydrocarbon, and nitrogen oxides tailpipe emissions. The model axially and radially resolves the temperatures in the monolith using very few state variables, thus allowing for use with control-policy based optimal control methods. In this paper, we extend the model to allow for variable axial discretization lengths, include the heat of reaction from hydrogen gas generated from the combustion engine, and reformulate the model parameters to be expressed in conventional units. We experimentally measured the temperature and emission evolution for cold-starts with ten different engine load points, which was subsequently used to tune the model parameters (e.g. chemical reaction rates, specific heats, and thermal resistances). The simulated cumulative tailpipe emission modeling error was found to be typically − 20% to + 80% of the measured emissions. We have constructed and simulated the performance of a Pareto-optimal controller using this model that balances fuel efficiency and the cumulative emissions of each individual species. A benchmark of the optimal controller with a conventional cold-start strategy shows the potential for reducing the cold-start emissions.

Analysis of the aftertreatment performance in HD-SI engine fueled with LPG

This research/article aimed to analyze the influence of an after-treatment system (ATS) on emissions of a heavy-duty spark-ignition (HD-SI) engine fueled with liquified petroleum gas (LPG), in the context of current Euro VI emissions requirements. The ATS is composed by a three-way catalyst (TWC) in series with a diesel particle filter (DPF). Emissions testing were carried out on an engine test bench according to homologation procedures, performing both world harmonized stationary cycle (WHSC) and world harmonized transient cycle (WHTC), to study the effects of the engine operating parameters on pollutant emissions behavior and ATS performance during steady and dynamic states, respectively. Instruments used were a gas analyzer Horiba MEXA ONE to measure gaseous emissions, HORIBA OBS ONE PN to measure particle matter (PM) concentration, and spectrometer TSI EEPS 3090 to measure PM concentration and particle size distribution (PSD). The results showed some important aspects such as the effects of engine speed and load on pollutant emissions formation and ATS performance, the influence of the three-way catalyst (TWC) on particulate matter (PM) reduction due to the relationship between volatile unburned hydrocarbons (UHC) and the emergence of nucleation-mode particles, stressing that ATS implementation is mandatory to meet the current emissions requirements.