Lecture 22 - Overarching Questions: Next Generation...

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CEE 260: Environmental and Sustainable Engineering Principles Lecture#22 Next Generation Vehicles Rubin Ch 3. (Pg. 109-123). Sections 3.3-3.5 ICP #21: Shifting Environmental Burdens in the Vehicle Life Cycle. Overarching Questions: Next Generation Vehicles Have vehicles changed over the past 20 years? What vehicle emissions control strategies have become common over this time period? What is a diesel vehicle (as opposed to a gas one)? What are alternative approaches that are under consideration to reduce fuel consumption and vehicle emissions? What trade-offs exist environmentally when switching to electric cars? What is a hybrid vehicle? A hypercar? How do fuel cells work? Where does the hydrogen come from? Are fuel cell vehicles really less polluting? Exhaust System Controls: Thermal Reactor A thermal reactor is an afterburner that encourages the continued oxidation of CO and HC after they have left the combustion chamber. Since the reactor is outside the engine, enough unburned fuel must be present to sustain combustion, run engine rich! This lowers NO x in addition to HC and CO, but also wastes gas. φ > 1 φ < 1 Exhaust System Controls: Exhaust Gas Recirculation By recirculating the exhaust gas, some of the heat generated during combustion is absorbed, and thus the chamber temperature is lowered without impacting A/F. This lowers NO X … and performance too a bit. The coupling of EGR and thermal reactor reduces all three major pollutants, CO, HC, and NO x regulated by EPA, but at some expense of performance and fuel economy. Three Way Catalytic Converter Oxidize HC and CO to CO 2 while reducing NO X to N 2 . A separate stage is required for reduction since oxidation of NO X would result in NO 2 . Highly effective, and permit the engine to operate at near stoichiometric conditions, where engine performance and efficiency are higher. – In fact, catalytic converters must run near these conditions, or else the efficiency drops off. – This requires active control of the air fuel mixture. Reduction Catalyst Oxidation Catalyst Control System CO 2 N 2 O Diesel No spark plugs! (Higher compression) – Lean mixtures = More fuel efficient. – Lean mixtures = Low HC and CO – High compression ratios = High NO X emissions. Fuel is burned with extra O 2 , conventional exhaust system controls requiring anoxic conditions are ineffective. Diesel engines also emit large quantities of carbonaceous soot particles, and diesel engine exhaust has been characterized as a probable human carcinogen. The difficulty in controlling NO
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This note was uploaded on 04/17/2008 for the course CEE 260 taught by Professor Kimf.hayes during the Fall '06 term at University of Michigan.

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Lecture 22 - Overarching Questions: Next Generation...

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