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Typical diesel engine-out emissions consist of hydrocarbons (HC), carbon monoxide (CO), particulate matter (PM) & oxides of nitrogen (NOx). The HC and CO emissions are oxidized by a diesel oxidation catalyst (DOC), placed upstream, closer to the exhaust manifold. The DOC is often followed by a diesel particulate filter (DPF), which entraps and combusts PM. The NOx is often controlled by a selective catalytic reduction (SCR) catalyst. An SCR catalyst commonly uses NH3 to reduce the NOx to N2. Vanadium-based SCR catalysts have been widely used for many years. More recently, Cu-Zeolite based SCR (CuZ-SCR) is gaining much attention primarily due to the potential environmental hazards of vanadium and a wider temperature window of effective operation. The SCR reaction is facilitated by the presence of NO2 at lower exhaust gas temperatures by means of the so-called “fast” reaction. However, this is only advantageous up to about 300°C.

Pollutants emitted from an internal combustion engine need to be controlled to improve quality of air. The pollutants emitted from a diesel engine are carbon monoxide (CO), unburnt hydrocarbons (HCs), oxides of nitrogen (NOx) and particulate matter (PM). These pollutants can be controlled using after treatment systems which comprise of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF) and a selective catalytic reduction (SCR) unit. With increasing vehicle density and lower speed driving scenarios, there is a need to improve the rate of oxidation and reduction in after treatment systems at lower exhaust gas temperatures for effectively decreasing pollutant emissions. There is a need to lower the light off temperature (LOT or T50, the temperature at which 50% conversion is achieved) for unburnt hydrocarbons (HCs) to improve quality of exhaust air during cold start conditions.

Kinetic modelling of exhaust aftertreatment systems is a topic of extensive research in the automobile sector. This study represents the modelling of catalytic reactions on the surface of platinum dispersed diesel oxidation catalysts. In addition to oxidation reactions in the catalytic converter, a model for hydrocarbon adsorption/desorption on zeolite was adopted and validated with experimental results. The model was further used to simulate the experimental results at two different Pt loadings on the catalyst surface. The simulated results were observed to fit reasonably well with the experimental results at each Pt loading on the catalyst. The adsorption/desorption behaviour on the catalyst surface was found to be affected by Pt loading. The simulation results have shown that Pt atoms might have occupied the active site of zeolite which resulted in the reduction of adsorption/desorption rates.

The purification efficiency of exhaust gas catalysts depends on several factors. One of the most important factors is the diffusivity of the exhaust gases in the catalytic coating layer, especially at moderate to high temperature and space velocity conditions. Porous silica, γ-alumina, zirconia, carbons and many other porous crystalline materials that are commonly used as catalysts and catalyst supports are traversed by a labyrinth of tortuous micro and mesopores. If the connectivity is very low, the labyrinth of pores becomes more difficult to penetrate, increasing the overall “tortuosity” and slowing down the transportation of gas molecules within catalyst layers. A new approach to overcome these diffusion and transport limitations in an exhaust gas catalyst is to create a continuous interconnected network of mesopores and macropores via increase in void fractions within the washcoat components and layers.

From the recent past, automotive exhaust emission management strategies has been progressing towards an alternative for vanadia based selective catalytic reduction (V-SCR) of NOx in diesel powered vehicles. Some of the major inadequacies of existing V-SCR technology were as follows: poor thermal endurance (deteriorates at 550°-600°C), volatilization of harmful vanadium into environment and inadequate NO2 conversion. Metal incorporated zeolite systems, (the metals being preferably selected from transition metal elements), has gained momentum for commercial DeNOx applications. However, the major challenge with this zeolite SCR (Z-SCR) was its low thermal/hydrothermal stability. In the current study, it has been attempted to overcome this by various zeolites and metals combinations. Various combinations of metallic Z-SCR were extensively studied for their low and high temperature activities.

Current restrictions on environmental pollution worldwide has created the need for new methodologies and technology development which should not only ensure ultra-low emission level from different categories of engine but should also use less fuel resulting in lower carbon dioxide (CO2) emissions. The state-of-art technology to achieve ultra-low emissions placed after engine in exhaust line is a ‘catalytic converter’. Catalytic converter is an after treatment device which typically oxidizes or reduces the toxic pollutants emitted by any engine to carbon dioxide (CO2), nitrogen (N2) and water (H2O). Catalytic converters used in Gasoline / CNG operated vehicles contains oxygen storage component as a key component for supplying oxygen in rich mode of operation and the oxygen concentration release rate is function of gas concentration and air to fuel ratio (A/F) or lambda (λ).

Light Duty Vehicles (LDVs), typically with engine displacement volume of less than 1.5L are an integral part of the India’s automobile sector as they are one of the most preferred means of transportation in rural as well as urban India. This market has always been on the rise as a result of rising population, growing commercialization, increasing commercial activities, etc. which are all contributing to the increased demand for intra city transportation. The passenger LDVs such as the three wheeler segment dominates the market as the need for affordable passenger commutation is higher than the need for goods carriage within a city. With BS VI norms slated to be implemented in 2020, it becomes imperative to understand, plan and work out strategies to meet these norms effectively on the Indian roads & actual Indian driving behavior, especially for these LDVs.

BS III norms (BS IV in 13+26 cities) have been implemented in India for a long time. There have been discussions over further country wide implementation of BS IV norms. All the engine categories (on-road & off-road) will be required to comply with stringent norms in future sooner or later. The Original Equipment Manufacturers (OEMs) have been working to comply with the norms. There has been a lot of work in the field of power train, transmission, aerodynamics etc. in order to make application better in all possible ways. However it has been largely focused on engine optimization and vehicle improvisation. The time has come when industry is staring on implementation of stringent emission norms and it will be vital to look at it in a whole perspective. It would not be incorrect to say there have been little work been done specifically on after-treatment systems which has been built for Indian market and driving conditions.