Sharif Digital Repository

Exhaust gas emissions from mobile sources and its importance in urban pollution have currently attracted lots of interests towards studying on alternative fuel systems for road vehicles usage. One of the best replacements is the natural gas/diesel dual fuel, which offers an alternative to standard compression-ignition diesel engines. In the dual fuel system the primary fuel is natural gas, which may replace as much as 90% of the diesel fuel with a small amount of diesel fuel required ensuring effective ignition. Methane, the main constituent of natural gas, has high combustion efficiency. Dual fuel engines produce lower NOx emissions and fewer particulates. However, at moderate engine loads,... 

Using natural gas combined with diesel fuel in diesel engines provides a considerable contribution to modern industrial societies in order to control air pollution and, also, generalize and facilitate the use of public vehicles. In spite of the attractive features of this idea, including reduction of NO(X) and particulates, there is an important burden imposed upon the system at low to intermediate torques, namely high concentration of CO and unburned total hydrocarbons (THC), mostly composed of methane. In this work, based upon the oxidation of CO and unburned HCs and through experimental results, application of a monolithic oxidizing bifunctional catalytic converter as a novel... 

The monolithic catalytic converter still is the main pollution control device for modern vehicles in order to reach the ever-increasing legislative demands for low emission standards. The catalytic converters require a large expansion from the exhaust pipe to the front face of the monolith. Unfortunately, packaging constraints often do not permit the use of long diffusers. Hence, flow separation within the diffuser leads to a non-uniform flow distribution across the monolith. A uniform flow distribution at the inlet monolith face is favorable for the conversion efficiency as well as the durability of the catalytic converter. Therefore the main problem is to optimize the flow distribution at... 

This article presents the research results on production and performance of palladium-only catalytic converters. Monolith is used as catalyst carrier and gamma alumina as substrate. Dipping method is used for monolith washcoating. Palladium as the active metal is impregnated on gamma alumina using wet impregnation to produce catalyst samples. The effects of factors such as percent solid in slurry, milling time, calcination time and temperature, pH and existence of Al(NO3)3 on wash-coat characteristics were studied experimentally. SEM, XRD, and BET tests were carried out on the samples. Catalyst performance was tested in an experimental reactor that was designed for this research. The results... 

Reduction of cold start hydrocarbon (HC) emission requires a proper compromise between low engine-out HC emission and fast light-off of the three way catalytic converter (TWC). In this paper a model based approach is used to design and optimize a hybrid switching system for reducing HC emission of a mid-sized passenger car during the cold start phase of FTP-75. This hybrid system takes the benefit of increasing TWC temperature during the early stages of the driving cycle by switching between different operational modes. The switching times are optimized to reduce the cumulative tailpipe HC emission of an experimentally validated automotive emission model. It is shown that the new hybrid... 

Modified perovskite-type oxides were synthesized through co-precipitation and conventional citrate methods. The synthesized perovskite materials had the nominal compositions of LaCoO3, LaCo0.8Cu0.2O3, La0.8Sr0.2Co0.8Cu0.2O 3, and La0.8M0.2FeO3 (where M = Ce and Sr). The catalytic activity of the perovskite samples (for low-temperature CO oxidation) was measured using a quartz reactor with an inlet gas mixture containing 97% N2, 1% O2, and 2% CO. The prepared perovskite samples were characterized by SEM, nitrogen adsorption (BET), XRF, and XRD analyses. The perovskite catalysts showed good structural and chemical stability up to 600 °C and high activity for the catalytic CO oxidation... 

Reduction of cold start hydrocarbon (HC) emissions requires a proper compromise between low engine-out HC emission and fast light-off of the three way catalytic converter (TWC). In this paper, a hybrid switching system is designed and optimized for reducing HC emissions of a mid-sized passenger car during the cold start phase of FTP-75 (Federal Test Procedure). This hybrid system has the benefit of increasing TWC temperature during the early stages of the driving cycle by switching between different operational modes. The switching times are optimized to reduce the cumulative tailpipe HC of an experimentally validated automotive emission model. The designed hybrid system is tested in...