Upload
olivia-hopkins
View
214
Download
1
Embed Size (px)
Citation preview
Emissions
Air is made up of :
21%O2
78%N 1% other gasses (mostly argon)
Fuel is primarily made up of :
HC
Perfect combustion =
HC, O2, N2 in
Heat, H2O, CO2 and N2 out
Imperfect combustion
Adds HC, CO, NOx and O2 to exhaust
Stoichiometric
Much of our emissions are related directly to A/F mixtures
Theoretical best a/f ratio for emissions, economy, performance is 14.7:1
14.7 pounds of air to 1 pound of fuel
Think about it
Gasoline weighs 6 pounds per gallon Air weighs 1 pound per 100 gallons At 15:1 it takes 9000 gallons of air to
burn 1 gallon of fuel– 9000 Gallons of air is equal to a single
car garage
HC - Hydrocarbons
Unburned fuel Currently measured in parts per
million (ppm)
Common causes of high HC
Misfiring will cause HCs– Ignition –Mechanical – Lean
A/f ratios off either way Timing too advanced
Not so common causes of HC
Quench areas in combustion chamber– Carbon – Poor combustion chamber design
Cam profiles too aggressive
CO - Carbon monoxide
Currently measured in % EXTREMELY deadly gas!!! Partially burned fuel Too much fuel or too little O2
– Combustion process ran out of air CO directly related to a/f ratios
Causes of high CO
Rich AFR - (Over fueling) Lack of O2
Inverse to level of O2
O2 - Oxygen
Currently measured in % Unused air in exhaust O2 directly related to A/F Can also come from dilution– Air pump, exhaust leaks
Misfires will raise O2
CO2 - Carbon dioxide
Currently measured in % Byproduct of complete combustion Peak indicates good A/F Any problems pull CO2 away from
peak
NOx - Oxides of nitrogen
Created when peak combustion temps. exceed 2500F
Causes of high NOx
Advanced timing Inoperative EGR Carbon build up Anything that overheats combustion
chamber TAC stuck in ‘hot’ position
Emission Controls
PCV systems
Purpose of PCV
Control of blow by gasses (HC) Reducing moisture and acids
extending oil life
PCV system problems
Plugged system causes:– High CO at idle
Stuck open PCV causes:– lean fuel– high idle speed
Evaporative emissions system
Evap system purpose To control HC during fuel
evaporation
Evap system components
Gas cap Vapor liquid separator Canister Vapor line(s) from tank(s)– Electronic solenoids– Switching with purge valve– Pressure or flow sensor/switch
Evap system operation (purging)
Purges stored fuel vapors in canister Typical purge warm engine at cruise Some systems purge at idle & cruise,
cold & hot engine Computer controls OBDII diagnostics
Early fuel evaporation systems
EFE system purpose
Helps a/f mixture vaporize on cold engine
Provide good cold driveability (cold air too dense and leans out mixture)
Improve cold emissions
EFE system purpose
Warms intake to prevent condensation of fuel
Prevents icing in carbs (temps can drop 66°f when fuel vaporizes)
Four types of EFE
1. T.A.C. (thermostatic air cleaner) 2. EFE grid 3. Coolant heated intakes and
throttle bodies 4. Heat riser valve
T.A.C. components
Mode door– Cold air position for warm eng.–Warm air position for cold eng.
Uses manifold vacuum and vacuum motor to move mode door
Heat stove and pipe– Primary failure of emission tests
T.A.C. problems
Stuck in hot air position will cause ping / NOx– Often caused by a plugged bleed off
hole Any missing piece can cause cold
driveability problems
EFE grid components
Electrical heater – Usually only, on carburetors and only
on primary bore(s) Commonly ceramic
EFE grid operation
Heats and mixes a/f mixture Controlled by switches or relay– Usually powered up cold only
EFE grid problems
Grids melt Switches stick on Heater element opens
Coolant passages
Primarily icing controls Also helps warm intakes
Heat riser valve purpose
Directs exhaust to underside of intake manifold
Prevents condensation Improves vaporization Not necessary on PFI engines
Heat riser valve components
Vacuum with rod– Uses TVS
Bimetal spring On V engines valve will plug off one
side of exhaust when cold
Heat riser problems
Binding on shaft Stuck in cold mode causing ping and
NOx by overheating incoming a/f mixture
Valve disintegrating
Air pump system
Air systems purpose
To pump or allow air to be sucked into exhaust system– Completes combustion– Dilutes exhaust gasses– Gives O2 to cats– Heats O2 sensor
Two types - air pump and air suction (pulseair)
Air pump
Belt driven vane and rotor pump Some use electric air pumps Some means of filtered air intake– Often using a centrifugal filter
1/2 Hp draw on engine
Diverter and gulp valves
Purpose: divert AIR away from exhaust on decel to prevent backfire
Gulp dumps AIR to intake– Similar to a decel valve / mixture control
valve Vacuum or electric controlled
Check valve
Purpose: to prevent exhaust from coming up into AIR system
Failed valves can cause melted hoses and diverter valves
Air manifolds and pipes
Rotting out causing backfire / exhaust leaks
Pulseair system
No pump Uses negative exhaust pulses Reed valves Can still divert or block off AIR Can be computer controlled Often mounted to air cleaner
Pulseair system problems
Back firing on decel if reed valves leak
Melted stuff is melted if valves leak Can stick upstream
EGR systems
Purpose : flows exhaust gas into intake to lower combustion
temps which lowers NOx
EGR details
Exhaust supports no combustion Dilutes a/f mix and slows
combustion slightly First used on Buicks in 1972,
common in 1973 Does not affect a/f ratios
Three methods to obtain EGR
Floor jets– Egr at all times
Cam grinds – Egr at all times
Egr valves VCT –variable cam timing
Control of EGR needed for three reasons
Idle; can not support dilution and little NOx
Cold; poor driveability, no NOx, not all engines
WOT; limits power and less NOx due to richer a/f
Backpressure Transducer
Limits with exhaust pressures Exhaust pressures good load
indicator Can modulate valve Many valves have built in
transducers– Positive valves vs. Negative valves
Electronic controls
Can use vsv’s to control EGR via ECU Electric valves– Using solenoids to control operation
Sensors– Position (EVP)– Exhaust pressure (PFE)– Temperature switch
Problems
Inop valves cause high combustion temps = pinging =NOx
Plugged EGR passages common Too much EGR = lack of power,
surge Stuck open at idle causes rough idle
due to excessive dilution
EGR testing
Egr movement under load– Some need to see VSS input
Vacuum present at valve Lift up at idle to check passages
Catalytic converters
Two types of converters
Oxidizing Reducing
Oxidizing
Converts HC and CO to H2O, CO2 and heat
Monolith construction (honeycomb)
Ceramic coated with p&p Lots of surface area
Pellet construction
Aluminum oxide pellets coated with p&p
Not as much surface area
Oxidizing operation
Needs O2 to convert HC and CO to H2O AND CO2
– Gets O2 from lean a/f ratios, AIR systems, missfires
Light off at 500°f, average temps 1400°f inside, 700°f outside
Reducing cat
Converts NOX into N2, CO2, O2
Needs lack of oxygen and some CO to work– Likes richer mix
Uses rhodium
Three way or dual bed
First part (bed) reducing
Gives off O2 to help second bed Needs CO which second bed
eliminates
Second part oxidizing bed
Uses O2 from first part Can use air into cat behind first bed
Needs to be close to stoichiometric to work
TWC is Only found on cars with closed loop fuel
Problems
Plugging– Abuse– If not abuse must find cause before
replacing Rich Leaded fuel Misfire Air system
Symptoms of plugging:
Lack of power No start in extreme cases
Testing backpressure
Vacuum test not always accurate Back pressure reading of > 3psi is
excessive Test at back pressure transducer, O2
sensor, AIR fitting, EGR
Efficiency loss
Loss can be due to lead, coolant, oil, miles
Aftermarket not as effective
Symptoms:
Excessive HC or CO or both
OBDII efficiency monitor
Efficiency testing
Temps 100-200°f increase across cat Intrusive method– Egr, AIR pipes (must seal), drilling hole– Need thin probe– Rivet holes up
– Not at O2 sensor
Using the underhood decal to ID major components