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Module 7

Module 7. Mobile Sources. Preliminaries. Design night Thursday 7:30? How many will come? Pizza party at the Sink, Tues May 2 6pm Conference on World Affairs - 5 HW pts per session, can go to 2 sessions (turn in write ups) Seminar Thursday 3:30 DLC - 5 HW pts (turn in write ups).

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Module 7

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  1. Module 7 Mobile Sources

  2. MCEN 4131/5131 Preliminaries • Design night Thursday 7:30? How many will come? • Pizza party at the Sink, Tues May 2 6pm • Conference on World Affairs - 5 HW pts per session, can go to 2 sessions (turn in write ups) • Seminar Thursday 3:30 DLC - 5 HW pts (turn in write ups)

  3. MCEN 4131/5131 LearningObjectivesfor Today Module 7 Educational Objectives • Impact of mobile sources • Equivalence ratio ER • pollutant emissions under different combustion conditions • Fuel rich and fuel lean • ER • crank angle • The IC engine • Add-on technologies that control emissions • catalytic converter • carbon canister • Non-combustion related emissions

  4. MCEN 4131/5131 LearningObjectives Clicker Question? Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions The rise of mobile sources has altered the field of air pollution control around the world. There are several reasons for this change. Which of the following is NOT a reason discussed in the text? • Millions of small sources that move around are more difficult to control than fewer stationary sources • The sources of the pollutants are very close to people living and working in urban areas • Many vehicles are equipped with 2-stroke engines and these engines are a necessity and difficult to control

  5. MCEN 4131/5131 (F/A)actual f = (F/A)stoichiometric LearningObjectives Equivalence Ratio Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions The equivalence ratio,, is defined as: • A = mass rate of air, F = mass rate of fuel The Air equivalence ratio, ER, is defined as: (A/F)actual ER = (A/F)stoichiometric

  6. MCEN 4131/5131 (1.5 moles O2 x 32 g/mole) + (5.64 moles N2 x 28 g/mole) (1 mole CH2 x 14 g/mole) LearningObjectives ER Example Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions CH2 + (1.5) O2 + (1.5)(3.76)N2 CO2 + H2O + (1.5)(3.76)N2 What is (A/F)stoichiometric? = 14.7 g air / g CH2

  7. MCEN 4131/5131 LearningObjectives Group Clicker Question? Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions Will the AFR for a gasoline-burning engine decrease or increase if it is driven in Mexico City and what pollutant emissions will be increased? • decrease, NOx • increase, NOx • decrease, CO • increase, CO

  8. MCEN 4131/5131 LearningObjectives Fuel Lean vs. Fuel Rich Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • What if the system is fuel rich (ER < 1)? • Not all of the fuel is combusted completely • There will probably be some CO, H2, and other products of incomplete combustion in the exhaust • Not all of the chemical energy has been released as heat • The final adiabatic temperature will be lower than if ER=1 • What if the system is fuel lean (ER > 1)? • There will be extra oxygen left over after the combustion • All of the chemical energy available in the fuel is definitely released • However, that energy has to heat up more mass in the form of the extra O2 and N2 • Thus, the temperature is also lower

  9. MCEN 4131/5131 LearningObjectives Effects of AFR on HC, CO, and NOx exhaust emissions Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

  10. MCEN 4131/5131 LearningObjectives Crank Angle influences emissions! Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions a is the angle Before top dead center For the purposes ofcontrolling emissions, Some engines are Operated so that Ignition takes place Slightly after TDC

  11. MCEN 4131/5131 LearningObjectives Clicker question? Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions Why is the combustion in an IC gasoline-burning engine not 100% complete? • spark ignition timing is off • cylinder walls cool combustion reactions • gasoline is contaminated with sulfur

  12. MCEN 4131/5131 LearningObjectives Add-On Technologies Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • Catalytic converter • Carbon canister • Carbon bed adsorber that collects evaporative emissions of VOCs from hot engine. If carbon is spent, breakthrough will occur and VOCs are not collected (happens if you let your car sit for a long time) • Positive crankcase ventilation valve

  13. MCEN 4131/5131 LearningObjectives 1st Catalytic converter Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • Original catalyst fully oxidized CO and HCs left over from incomplete combustion in the cylinders • The reactions taking place in the catalyst are (where CH2 represents some generic hydrocarbon) • CO + 1/2 O2 CO2 • CH2 + 3/2 O2 CO2 + H2O

  14. MCEN 4131/5131 LearningObjectives 2nd Catalytic Converter Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • Realized this didn’t remove NOx • New 2-stage system used HC, H2, and CO to reduce NOx to N2 • Reduction by CO NO + CO  1/2N2 + CO2 2NO + CO  N2O + CO2 • Reduction by H2 NO + H2 1/2 N2 + H2O 2NO + H2 N2O + H2O 2NO + 5H2 2NH3 + 2H2O • Reduction by hydrocarbons 3 NO + CH2 3/2 N2 + CO2 + H2O

  15. MCEN 4131/5131 LearningObjectives 3-Way Catalyst Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • Introduced in 1979 • Combines chemistry of the 2 stage system into a single catalyst • Requires very tight control over the A/F mixture, must be very near stoichiometric

  16. MCEN 4131/5131 LearningObjectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions Single bed oxidation catalyst Dual bed catalyst Single bed 3 way catalyst

  17. MCEN 4131/5131 LearningObjectives Non-combustion related emissions from mobile sources Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions • Breathing emissions • Refueling emissions • Running losses • Hot soak losses

  18. MCEN 4131/5131 LearningObjectives Clicker question? Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions Why are oxygenated fuels of high interest? • NOx emissions are reduced • CO emissions are reduced

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