RESUMO
This work presented the influence of metal oxides as the support for silver-supported catalysts on the catalytic oxidation of diesel particulate matter (DPM). The supports selected to be used in this work were CeO2 (reducible), ZnO (semiconductor), TiO2 (reducible and semiconductor), and Al2O3 (acidic). The properties of the synthesized catalysts were investigated using XRD, TEM, H2-TPR, and XPS techniques. The DPM oxidation activity was performed using the TGA method. Different states of silver (e.g., Ag° and Ag+) were formed with different concentrations and affected the performance of the DPM oxidation. Ag2O and lattice oxygen, which were mainly generated by Ag/ZnO and Ag/CeO2, were responsible for combusting the VOCs. The metallic silver (Ag°) formed primarily on Ag/Al2O3 and Ag/TiO2 was the main component promoting soot combustion. Contact between the catalyst and DPM had a minor effect on VOC oxidation but significantly affected the soot oxidation activity.
RESUMO
This work presented the kinetic analysis of devolatilized diesel-soot combustion accelerated by Ag/Al2O3 and Ag/CeO2 catalysts. Isoconversional and master-plots techniques were employed to estimate activation energy and identify the reaction model. The apparent activation energy of uncatalyzed soot oxidation was 101.85 kJ/mol, and it was reduced to 61.85 and 82.78 kJ/mol for the combustion catalyzed by Ag/Al2O3 and Ag/CeO2, respectively. The reaction-order model, f(α) = (1- α)n, with n of 1.4, 1, and 1 showed the best fit for the uncatalyzed soot oxidation and soot oxidation catalyzed by Ag/Al2O3 and Ag/CeO2, respectively. The proposed single-step reaction models were quite capable of reproducing experiments for the uncatalyzed soot oxidation and soot oxidation catalyzed by Ag/CeO2. In the presence of Ag/Al2O3, the oxidation rate at the first 20% of conversion was faster than the 1st-order reaction reflecting that the soot was rapidly oxidized by highly active species generated by Ag/Al2O3. The oxidation of the remaining soot closely followed the 1st-order reaction mechanism.
RESUMO
The effects of ethanol on combustion and emission were investigated on a single-cylinder unmodified diesel engine. The ethanol content of 10-50 vol % was chosen to blend with diesel and biodiesel fuels. Selective catalytic reduction (SCR) of nitrogen oxides (NO x ) in the passive mode was also studied under real engine conditions. Silver/alumina (Ag/Al2O3) was selected as the active catalyst, and H2 (3000-10000 ppm) was added to assist the ethanol-SCR. The low cetane number of ethanol resulted in longer ignition delay. The diesel-biodiesel-ethanol fuel blends caused an increase in fuel consumption due to their low calorific value. The brake thermal efficiency of the engine fuelled with relatively low ethanol fraction blends was higher than that of diesel fuel. Unburned hydrocarbons (HC) and carbon monoxide (CO) increased, while NO x decreased with ethanol quantity. The higher ethanol quantity led to increases in the HC/NO x ratio which directly affected the performance of NO x -SCR. Addition of H2 considerably improved the activity of Ag/Al2O3 for NO x reduction. The proper amount of H2 added to promote the ethanol-SCR depended strongly on the temperature of the exhaust where a high fraction of H2 was required at a low exhaust temperature. The maximum NO x conversion of 74% was obtained at a low engine load (25% of maximum load), an ethanol content of 50 vol %, and H2 addition of 10000 ppm.
RESUMO
Diesel particulate matter (DPM) and oxides of nitrogen (NOx) are the emissions from diesel engines (compression ignition engines) of the most concern and are currently strictly regulated. In this work, we present an alternative diesel emission control technique to assist in further emission reduction. An experiment-oriented study on diesel engine emission abatement using low-power, low-frequency, high-voltage discharge (HVD) treatment was carried out in a laboratory-scale reactor with whole diesel engine exhaust gas. A dielectric barrier discharge (DBD) reactor was used in direct contact with diesel exhaust gas at atmospheric temperature with an input energy density between 200 and 400 J/L. An investigation of the direct effect of the high-voltage discharge reactor on the diesel exhaust gas treatment was carried out to characterize both diesel particle and gaseous emissions. The proposed HVD system demonstrated up to 95% particulate matter reduction by mass or 64% reduction by number, and 63% reduction of the diesel soot particle geometrical mean diameter by HVD-generated O3 oxidation. Thermogravimetric analysis revealed the significant change in the diesel soot compositions and oxidation characteristics. HVD-treated particulate matter demonstrated a lower reactivity in comparison to untreated soot. Gas composition analysis indicated the generation of free radicals (e, O, OH, O3, and N) by the HVD system, as mainly indicated by the increase of the NO2/NO ratio and concentration of CO and O2. The pattern of CO2 reduction while CO and O2 increased indicated the dissociation of CO2 by HVD. Free radicals generated by HVD directly affected DeNO, DeNOx, NO2/NO ratio, and CO and CO2 selectivities.
