Module 7 Mobile Sources

MCEN 4131/ 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)

MCEN 4131/ Learning Objectives for 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

MCEN 4131/ Clicker Question? 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? a. Millions of small sources that move around are more difficult to control than fewer stationary sources b. The sources of the pollutants are very close to people living and working in urban areas c. Many vehicles are equipped with 2-stroke engines and these engines are a necessity and difficult to control Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

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

MCEN 4131/ ER Example CH 2 + (1.5) O 2 + (1.5)(3.76)N 2  CO 2 + H 2 O + (1.5)(3.76)N 2 What is (A/F) stoichiometric ? (1.5 moles O 2 x 32 g/mole) + (5.64 moles N 2 x 28 g/mole) (1 mole CH 2 x 14 g/mole) = 14.7 g air / g CH 2 Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

MCEN 4131/ Group Clicker Question? 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? a. decrease, NOx b. increase, NOx c. decrease, CO d. increase, CO Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

MCEN 4131/ Fuel Lean vs. Fuel Rich What if the system is fuel rich (ER < 1)? –Not all of the fuel is combusted completely –There will probably be some CO, H 2, 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 O 2 and N 2 –Thus, the temperature is also lower Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

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

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

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

MCEN 4131/ Add-On Technologies 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 Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

MCEN 4131/ st Catalytic converter Original catalyst fully oxidized CO and HCs left over from incomplete combustion in the cylinders The reactions taking place in the catalyst are (where CH 2 represents some generic hydrocarbon) –CO + 1/2 O 2  CO 2 –CH 2 + 3/2 O 2  CO 2 + H 2 O Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

MCEN 4131/ nd Catalytic Converter Realized this didn’t remove NOx New 2-stage system used HC, H 2, and CO to reduce NOx to N 2 –Reduction by CO NO + CO  1/2N 2 + CO 2 2NO + CO  N 2 O + CO 2 –Reduction by H 2 NO + H 2  1/2 N 2 + H 2 O 2NO + H 2  N 2 O + H 2 O 2NO + 5H 2  2NH 3 + 2H 2 O –Reduction by hydrocarbons 3 NO + CH 2  3/2 N 2 + CO 2 + H 2 O Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

MCEN 4131/ Way Catalyst 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 Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

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

MCEN 4131/ Non-combustion related emissions from mobile sources Breathing emissions Refueling emissions Running losses Hot soak losses Learning Objectives Impact of mobile sources Equivalence ratio Combustion conditions IC engine Add-ons Non-combustion emissions

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