Advanced Catalysts for HC Control - Engine Combustion - Lecture Notes, Study notes of Sustainability Management

Download Advanced Catalysts for HC Control - Engine Combustion - Lecture Notes and more Study notes Sustainability Management in PDF only on Docsity! Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture23/23_1.htm[6/15/2012 3:05:10 PM] Module 5:Emission Control for SI Engines Lecture23:Advanced Catalysts for HC Control The Lecture Contains: Catalytic Converters for Cold Start HC Emission Control Electrically Heated Catalysts Close-Coupled Catalysts Hydrocarbon Adsorber /Trap Systems Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture23/23_6.htm[6/15/2012 3:05:10 PM] Module 5:Emission Control for SI Engines Lecture23:Advanced Catalysts for HC Control ADVANCED CATALYTIC EXHAUST AFTERTREATMERNT Catalytic Converters for Cold Start HC Emission Control Figure 5.19 shows HC emissions on US EPA cycle beginning from the instant when the engine is started from cold. Also, the LEV and ULEV HC limits are shown on this figure. Figure 5.19 HC emissions during cold start in US FTP cycle. LEV and ULEV emission limits are alsoshown. From this figure it is observed that; About 60 to 80% of total US FTP cycle HC emissions are produced during the first 2 minutes of vehicle operation after cold start. To meet LEV standards catalyst should become functional within 80 seconds For ULEV limts the catalyst should become functional within 50 seconds • Electrically heated catalysts (EHC) • Close-coupled catalysts • Hydrocarbon traps Electrically Heated Catalysts The converters can be electrically heated before the engine started. In the metallic monoliths, metal honeycomb itself has been used as a heating element. Use of thin steel foils reduces thermal capacity of the catalyst. However, electrical heating still requires considerable energy to be drawn from the battery particularly in cold climates. Under cold ambient conditions the batteries are subjected to very high power drain. This becomes more difficult proposition as at the low ambient temperatures the battery activity is low and a high amount of energy is also required to crank and start the engine. Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture23/23_8.htm[6/15/2012 3:05:11 PM] Module 5:Emission Control for SI Engines Lecture23:Advanced Catalysts for HC Control contd... Hydrocarbon Adsorber /Trap Systems A closed coupled catalyst needs up to 40 seconds to become operational after cold start and hence, considerable portion of the engine out emissions escapes the closed –coupled catalyst. A more advanced system has been developed that adsorbs and stores HC on an adsorbent which are released once the catalyst downstream reaches the light off temperature. A typical HC adsorption-release cycle is shown on Fig 5.21. Figure 5.21 HC adsorption and release cycle for a HC trap Typical layouts of the hydrocarbon adsorber/trap and main catalysts are shown in Fig 5.22 . Figure 5.22 A schematic layout of exhaust system with hydrocarbon trap and main catalyst. In another design, the hydrocarbon adsorber and the oxidation catalyst are integrated in one unit. This Objectives_template file:///C|/...%20and%20Settings/iitkrana1/My%20Documents/Google%20Talk%20Received%20Files/engine_combustion/lecture23/23_8.htm[6/15/2012 3:05:11 PM] is followed downstream by the main catalytic converter for reduction of emissions under normal engine operation. In another advanced configuration of the integrated adsorber-catalyst system, double layered catalyst structure is coated on a cordierite substrate. The catalyst structure is shown schematically in Fig 5.23. The HC adsorbent is coated as the bottom layer close to the substrate and the normal 3-way catalyst as the upper layer. Under low temperatures the HC are adsorbed and released and get oxidized as the catalyst gets heated. However, under normal operation the adsorber being at higher temperature it does not absorb HC and all the emissions are converted in the main 3-way catalyst system. Figure 5.23 A two layer configuration of HC adsorbent and 3-waycatalyst loaded on the same ceramic substrate.