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Internal Combustion Emission Presntation
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• EMISSION FROM ENGINES
•
EMISSIONS
• EMISSION ARE UNWANTED CHEMICALS, PRODUCED BY CERTAIN CHEMICAL REACTIONS/ PROCESSES ETC. WHICH ARE HEATH HAZARD, DESTROYS ENVIRONMENTAL CONDITIONS, OZONE LAYER, AND HORTICULTURES ETC.
• THESE MAY IN SOLID, LIQUID AND GASSES PHASES.
• IN ENGINES, GENERALLY GASSES AS POLLUTANTS ARE EMITTED.
THE POLLUTANT EMISSIONS ARE RESPONSIBLE FOR
SKIN DISEASES, RESPIRATORY, NERVOUS AND CIRCULATORY SYSTEMS.
MUTAGENIC AND CANCER
HEART ATTACKS
GLOBAL WARMING
GREEN HOUSE EFFECT ETC
EMISSIONSCOMBUSTION GENERATED EMISSION FROM ENGINES INCLUDE:
• UHCS (FROM GASOLINE, DIESEL & GAS TURBINE)
• CO (FROM GASOLINE, DIESEL & GAS TURBINE)
• NOX ( FROM GASOLINE, DIESEL & GAS TURBINE)
• SOX (FROM DIESEL & GAS TURBINE)
• PARTICULAR MATTER (FROM GASOLINE, DIESEL & GAS TURBINE)
• SMOKE (FROM DIESEL & GAS TURBINE)
• CO2 (FROM GASOLINE, DIESEL & GAS TURBINE)
SOME AUTHORITIES DO NOT CATEGORIZE CO2 AS POLLUTANT, BUT IT PRODUCES
GLOBAL WARMING
LOW COMBUSTION EFFICIENCY IS CHARACTERIZED BY OCCURRENCE OF UHCS & CO IN THE EXHAUST
* GAS TURBINE ENGINES USED IN COMMERCIAL AIRLINES
RECOGNITION OF THE THREAT THE MENACE OF VEHICULAR EMISSION WAS FIRST
RECOGNIZED AS SERIOUS THREAT IN 1950S, WHEN CALIFORNIANS ENCOUNTERED WITH PHOTOCHEMICAL SMOG BY KNOWING THE CAUSE OF DETERIORATION OF THE AUTOMOBILES TIRES BY HIGH CONCENTRATIONS OF GROUND LEVEL OZONE. PHOTOCHEMICAL SMOG, A SECONDARY POLLUTANT FROM VEHICLE EXHAUST, IS PRODUCED BY THE REACTION OF VOLATILE ORGANIC COMPOUND (VOC) AND NITROGEN OXIDE IN THE PRESENT OF SUNLIGHT.
EFFECTSPollutants EffectsSOx (oxides of sulfur) Toxic & Corrosive
COUHCs (unburned hydrocarbons)
Toxic: CO has stronger adherence to hemoglobinCarcinogenic: HCs with nitric oxide (NO), lead to the formation of ground level ozone, which can cause lung tissue damage and respiratory illness
NOx (oxides of nitrogen)
Toxic , Depletion of ozone within stratosphere, Increase in ground level ozone, culprit of producing photochemical SMOG with UHC in sunlight
CO2 Green house gas, produces global warming
Particulate matter /Soot (C)
Visibility Effects
Lead oxides (gasoline with lead additives)
Lead is a commutative poison, and can cause adverse effects in mental development in children
CO-HARMFUL EFFECTS• WHEN INHALED, CO PASSES THROUGH THE LUNGS &
DIFFUSES DIRECTLY IN TO THE BLOOD STREAM WHERE IT COMBINES WITH THE RED BLOOD PIGMENT CALLED HEMOGLOBIN FORMING CARBOXY HEMOGLOBIN (COHB). THE AFFINITY OF CO FOR HEMOGLOBIN IS 250 TIMES GREATER THAN OXYGEN & AS A RESULT THE AMOUNT OF HEMOGLOBIN AVAILABLE FOR CARRYING OXYGEN FOR BODY TISSUES ARE THUS DEPRIVED OF THE OXYGEN SUPPLY AND DEATH COULD RESULT BY LACK OF OXYGEN.
• EXPOSURE (LOW CONCENTRATION) CAN CAUSE HEADACHE AND NAUSEA, DISCOMFORT & ULTIMATELY BECOMES LETHAL
CAUSES OF CO EMISSION
• THE MOST IMPORTANT ENGINE PARAMETER THAT AFFECTS CO EMISSION IS FUEL-AIR EQUIVALENCE RATIO.
• MAXIMUM CO IS GENERATED WHEN ENGINE RUNS RICHER THAN STOICHIOMETRIC LEVEL AND FUEL COMPONENTS DO NOT FIND ENOUGH OXYGEN TO REACT. THIS CONDITION OCCURS DURING ENGINE TRANSIENTS SUCH AS START UP AND RAPID ACCELERATION UNDER LOAD.
• HIGH RPM
• DISASSOCIATION
EXHAUST CO CONCENTRATION IN DIESEL ENGINE
Exhaust CO concentrations from diesel engine, in mole fractions, on a dry basis as a function of equivalence ratios
UHCs
Hydrocarbon emissions result from the presence of unburned fuel in the engine exhaust. However, some of the exhaust hydrocarbons are not found in the fuel, but are hydrocarbons derived from the fuel whose structure was altered due to chemical reaction that did not go to completion. For example: acetaldehyde, formaldehyde, 1,3 butadiene, and benzene all classified as toxic emissions. About 9% of the fuel supplied to the engine is not burn stroke. Only during the normal combustion phase of the expansion 2% ends up in the exhaust.As a consequence hydrocarbon emissions cause a decrease in the thermal efficiency, as well as being an air pollutant.
UHCS- HARMFUL EFFECTS
• THESE POLLUTANTS MAY BE EITHER INHALED OR ABSORBED THROUGH THE SKIN & CAN QUICKLY POISON THE BODY BY AFFECTING THE CENTRAL NERVOUS SYSTEM
• PROLONGED BREATHING, CAUSES DIGESTIVE DISTURBANCES, HEADACHE, NERVOUS DISORDERS , SKIN ERUPTION, EYES & RESPIRATORY IRRITATION.
• GASOLINE & OTHER FUELS CONTAIN TOXIC CHEMICALS SUCH AS BENZENE, THAT CAN CAUSE A WIDE RANGE OF ADVERSE HEALTH EFFECTS INCLUDING CANCER
CAUSES OF UHCS EMISSIONS (S.I ENGINE)
• THE MAIN CAUSES OF HC EMISSIONS FROM S.I ENGINES ARE OPERATION OF ENGINE AT NON- STOICHIOMETRIC AIR-FUEL RATIO, INCOMPLETE COMBUSTION, AND CREVICE VOLUME, LEAKAGE PAST THE EXHAUST VALVE, VALVE OVERLAP, AND DEPOSITS ON COMBUSTION CHAMBER WALLS AND OIL ON COMBUSTION CHAMBER WALLS
• IF AIR-FUEL RATIO IS TOO LEAN POORER COMBUSTION OCCURS, RESULTING IN LARGE AMOUNTS OF HC EMISSIONS, THE EXTREME IS TOTAL MISFIRE AT LEANER AIR-FUEL RATIOS. ONE MISFIRE OUT OF 1000 CYCLES GIVES EXHAUST EMISSIONS OF 1GM/KG OF FUEL USED
UHCs Emission Sources for SI Engines-summary
There are six primary mechanisms believed to be responsible for hydrocarbon emissions:
% fuel escaping Source normal combustion % HC emissions
Crevices 5.2 38Oil layers 1.0 16Deposits 1.0 16Liquid fuel 1.2 20Flame quench 0.5 5Exhaust valve leakage 0.1 5
Total 9.0 100
UHCs Emission SourcesCrevices – these are narrow regions in the combustion chamber into whichthe flame cannot propagate.
Crevices are located around the piston, head gasket, spark plug and valve seats and represent about 1 to 2% of the clearance volume.
The crevice around the piston is by far the largest, during compression the fuelair mixture is forced into the crevice (density higher than cylinder gas since gas is cooler near walls) and released during expansion.
Crevice Piston ring
Oil layers - Since the piston ring is not 100% effective in preventing oil migration into the cylinder above the piston, an oil layer exists within the combustion chamber that traps fuel.
Deposits – Carbon deposits build up on the valves, cylinder and piston crown. These deposits are porous with pore sizes smaller than the quenching distance so trapped fuel cannot burn.
Liquid fuel – For some fuel injection systems there is a possibility that liquid fuel is introduced into the cylinder past an open intake valve. The less volatilefuel constituents may not vaporize (especially during engine warm-up) and be absorbed by the crevices or carbon deposits.
Flame quenching – It has been shown that the flame does not burn completely to the internal surfaces, the flame extinguishes at a small but finite distance from the wall.
UHCs Emission Sources
UHCs Exhaust ProcessWhen the exhaust valve opens the large rush of gas escaping the cylinder
drags with it some of the hydrocarbons released from the crevices, oil layer and deposits.
During the exhaust stroke the piston rolls the hydrocarbons distributed alongthe walls into a large vortex that ultimately becomes large enough that a portion of it is exhausted.
Blowdown(near BC)
ExhaustStroke
CAUSES OF UHCS EMISSIONS (DIESEL ENGINE)
THE FIVE MAIN SOURCES OF HYDROCARBON IN DIESEL ENGINES ARE:
• OVER MIXING OF FUEL & AIR BEYOND LEAN FLAMMABILITY LIMIT
• UNDER MIXING OF FUEL-AIR RATIOS (TOO RICH FOR COMPLETE COMBUSTION)
• IMPINGEMENT OF FUEL SPRAY ON WALLS I.E. SPRAY OVER PENETRATION
• BULK QUENCHING OF COMBUSTION REACTIONS DUE TO MIXING WITH COOLER AIR OR EXPANSION.
• POORLY ATOMIZED FUEL FROM THE NOZZLE SAC VOLUME AND NOZZLE HOLES AFTER THE END OF INJECTION.
19
Hydrocarbon Emission Sources for CI EnginesCrevices - Fuel trapped along the wall by crevices, deposits, or oil due to
impingement by the fuel spray (not as important as in SI engines).
Under-mixing of fuel and air - Fuel leaving the injector nozzle at low velocity, at the end of the injection process cannot completely mix with air and burn.
Over-mixing of fuel and air - During the ignition delay period evaporated fuel mixes with the air, regions of fuel-air mixture are produced that are too lean to burn. Some of this fuel makes its way out the exhaust. Longer ignition delay more fuel becomes over mixed.
Exh
aust
HC
, pp
m C
air
a b
Schematic representation of diesel hydrocarbon formation mechanisms:(a) for fuel injected during delay period; (b) for fuel injected while combustion occurring
Hydrocarbon formation mechanism for CI Engines
Hydrocarbon formation mechanism for CI Engines
NOX HARMFUL EFFECTS• NO2 IS IRRITATING AND UPON INHALATION CAN CAUSE
DAMAGE TO THE LUNG TISSUES.
• LONG TERM EXPOSURE TO CONCENTRATION OF THE ORDER OF 1PPM COULD LEAD TO SYMPTOMS RESEMBLING EMPHYSEMA AND BIOMEDICAL ALTERNATION IN THE BLOOD.
• SMALLER EXPOSURE WITH LONGER EXPOSURE TIME CAN CAUSE RESPIRATORY DISEASE WHILE HIGH CONCENTRATION LIKE 90PPM IN 30 MINUTES CAN CAUSE PULMONARY EDEMA
• IN THE PRESENCE OF SUNLIGHT NOX REACT WITH
HYDROCARBON TO PRODUCE PHOTOCHEMICAL SMOG (INCLUDING OZONE) AND SOME FORM OF ACID
PRECIPITATION.
SOURCES OF NOX FORMATION
THERMAL NOX :
THERMAL NOX IS PRODUCED WHEN NITROGEN AND AIR WITH EXCESS OXYGEN ARE PRESENT AT HIGHER TEMPERATURE (GREATER THAN 1800 K) IN THE COMBUSTION PROCESS. TWO OF THE MAIN REACTIONS FOR THE FORMATION OF THERMAL NOX ARE DESCRIBED
AN ADDITIONAL REACTION AT NEAR STOICHIOMETRIC AND FUEL RICH MIXTURE IS
THERMAL NOX CONTRIBUTES THE LARGEST PORTION TO THE TOTAL NOX PRODUCED
NONNO 22
NOOON 2
NOHOHN
SOURCES OF NOX FORMATION
FUEL NOX :
FUEL NOX IS FORMED IN THE COMBUSTION SYSTEM REACTION FROM CHEMICALLY BOUND NITROGEN IN FUEL; PRIOR TO ENTERING THE COMBUSTION ZONE, THE NITROGEN COMPOUNDS IN FUEL DECOMPOSE TO LOW MOLECULAR WEIGHT NITROGEN CONTAINING COMPOUNDS OR RADICALS SUCH AS NH3, NH2, NH, CN ETC. THIS WILL FURTHER FACILITATE OXIDATION OF FUEL BOUND NITROGEN COMPOUND TO FORM NITRIC OXIDE RAPIDLY
PROMPT NOX
PROMPT NOX FORMS IN THE FLAME ZONE, THE BREAKDOWN OF HYDROCARBON FRAGMENTS ( C, CH, CH2) MAY REACT WITH ATMOSPHERIC NITROGEN AND THEIR SUBSEQUENT COMBINATION TO PRODUCE OTHER NITROGEN SPECIES SUCH AS (CN, HCN, H2CN AND NH) UNDER FUEL RICH CONDITION. IN PROMPT NOX FORMATION, THE FOCUS AREA IS FLAME FRONT AND THE REGIONS NEAR IT.
SMOG
• SMOG IS A NICK NAME GIVEN TO A VISIBLE CLOUD OF AIR- BORNE
PARTICLES (UHCS +NOX). SMOG IS DERIVED FROM THE WORDS “SMOKE”
AND “FOG”.
• SMOG IS COMMON IN LARGE CITIES. IF DENSE ENOUGH, SMOG CAN BE HARMFUL TO HUMANS, ANIMALS & VEGETATION, EVEN PAINT, RUBBER, AND OTHER MATERIALS.
• IN MORE TECHNICAL LANGUAGE, SMOG IS PROPERLY TERMED PHOTOCHEMICAL SMOG. PHOTOCHEMICAL MEANS THAT AIR-BORNE PARTICLES REACT WITH SUNLIGHT, FORMING A DIRTY BROWN COLORED SMOG.
UHCS +NOX +SUNLIGHT → PHOTOCHEMICAL SMOG
NOX FORMATION IN DIESEL ENGINE
NOX FORMATION IN DIESEL ENGINE
• AT HIGH LOADS WHEN THE PEAK PRESSURE AND TEMPERATURE IS HIGH AND LARGER REGION OF COMBUSTION CHAMBER IS COMPOSED OF CLOSE TO STOICHIOMETRIC BURNED GAS, NO LEVEL INCREASES. WITH A DECREASING OVER-ALL-EQUIVALENCE RATIO, NO LEVEL DECREASES BUT LESS RAPIDLY THAN S.I ENGINES DO DUE TO NON-UNIFORM FUEL DISTRIBUTION IN DIESEL ENGINES.
• THE HIGH TEMPERATURE & PRESSURE DURING PRE-MIXED COMBUSTION PHASE IS IMPORTANT IN CONNECTION WITH THE FORMATION OF NO. THE NO FORMATION INCREASES AS COMBUSTION PROCEEDS AND CYLINDER PRESSURE INCREASES. AFTERWARD DURING THE EXPANSION PROCESS, THE NO FORMING DECLINES BECAUSE OF DECREASE IN CHARGE TEMPERATURE & PRESSURE.
SOX
• SULFUR DIOXIDE IS DIESEL/JET ENGINE EMISSION WHICH ORIGINATE FROM FUEL SULFUR
• SO2 IS A COLORLESS GAS WITH A CHARACTERISTICS IRRITATING ODOR.
• SULFUR DIOXIDE(SO2) CAN BE OXIDIZED TO SULFUR TRIOXIDE (SO3 ),
WHICH IS THE PRECURSOR OF SULFURIC ACID RESPONSIBLE FOR SULFATE PARTICULATE EMISSION
• THE MAJORITY OF SULFUR IN RAW DIESEL EXHAUSTS EXISTS AS SO2 .
ONLY APPROXIMATELY 2~4% OF FUEL SULFUR IS EMITTED AS SO3 FROM
THE ENGINE
• SULFUR OXIDES ARE ONE OF THE MAJOR CAUSES OF ACID RAIN.
PARTICULATE MATTER
• THE EXHAUST OF DIESEL ENGINE CONTAINS SOLID CARBON SOOT PARTICLES THAT ARE GENERATED IN FUEL-RICH ZONES WITHIN THE CYLINDER DURING COMBUSTION
• THESE ARE SEEN AS EXHAUST SMOKE AND ARE AN UNDESIRABLE ODOROUS POLLUTION
• SOOT PARTICLES ARE CLUSTERS OF SOLID CARBON SPHERES HAVING DIAMETERS FROM 10NM TO 80NM, WITH MOST WITHIN THE RANGE OF 15~30NM.
PARTICULATE MATTER
• DIESEL ENGINES CONTAIN PARTICULATE MATTER AND SMOKE IN THE EXHAUST, WHICH IS COMPOSED OF CARBONACEOUS MATERIAL OR SOOT PRODUCED DURING FUEL-RICH COMBUSTION. IN CHEMICAL TERMS TOTAL PARTICULATE MATTER (TPM) IS DIVIDED IN TO THREE FRACTIONS.
• 1-SOLID FRACTION (SOL)-ELEMENTAL CARBON OR SOOT FORMED DURING COMBUSTION
• 2-SOLUBLE ORGANIC FRACTION (SOF)-ORGANIC MATERIAL DERIVED FROM FUEL AND LUBE OIL.
• 3- SULPHATE PARTICULATES (SO4) - HYDRATED SULPHURIC ACID
INCOMPLETE COMBUSTION PRODUCES MOST OF THE PARTICULATE MATERIALS (PM); HOWEVER SOME OF THESE ARE CONTRIBUTED FROM LUBRICATING OIL
OXIDES OF LEAD (LEAD CONTAINING FUEL)• LEAD DAMAGES THE NERVES CAUSING DEADENING OF THE
NERVE SENSE RECEPTORS.
• IT ALSO CAUSES ANEMIA WHICH IS A DEFICIENCY OF RED BLOOD CELLS ALSO CAUSES HYPERTENSION & LOSS OF HEARING.
• LEAD COMPOUNDS CAN BE INHALED, ABSORBED THROUGH THE SKIN AND BY INGESTION.
• INHALED LEAD IS MORE SERIOUS THAN INGESTED LEAD
• THE FINE PARTICLES EMITTED BY AUTOMOBILES ARE RETAINED WITHIN THE LUNGS AND ARE ABSORBED BY THE BODY.
• EFFECTS THE BRAIN DEVELOPMENT OF CHILDREN IN TERMS OF INTELLIGENCE & BEHAVIOR.
• ALSO POISONS CATALYTIC CONVERTERS
LeadLead is the second worse pollutant in terms of its health affects. At fairly low levels it causes birth defects, low IQ and mental retardation. At higher levels it can kill. In the USA ~15,000 children per year are still treated for lead poisoning mostly from ingesting lead paints that were widely used up until the 1950’s. About 200 children die per year of lead poisoning.Lead pollution in the air used to come from automobiles as a result of lead additives in gasoline. These were phased out in the 70’s and early 80’s and as a result lead pollution in the air has decreased by over 95% to levels that can be hard to measure. As a result 22,000 lives are saved per year and the average IQ of children born today is 3 points higher than 30 years ago.
EMISSIONS FROM GASOLINE ENGINES
SOURCES OF EMISSION
• EVAPORATION FROM THE FUEL TANK ( 5%)
• BLOW-BY GASES WHICH ESCAPE FROM THE CRANKCASE. (20-25%)
• TAIL PIPE EMISSIONS. (60-75%)
• CARBURETOR EVAPORATION FROM THE FLOAT BOWL ON OLD CARS.
WHY 14.7:1 (STOICHIOMETRIC A/RATIO)
CO EMISSION VERSUS A/F RATIO
EMISSION FORMING BEHAVIOR• Spark-ignited gasoline
engine emissions of CO, NO and hydrocarbons (expressed as hexane) as a function of intake air-to-fuel ratio in grams of air per gram of fuel.
• HC and CO emissions decline with increasing O2 injection.
• Conditions that maximize the flame temperature will generate high NO levels.– Need to consider fuel
economy as well as pollution abatement.
SUMMARY IN S.I ENGINES MAXIMUM BURNED GAS TEMPERATURES OCCUR AT Ø ≈1.1, BUT
AT THIS EQUIVALENCE RATIO OXYGEN CONCENTRATION IS LOW , HOWEVER AT SLIGHTLY LEAN MIXTURE CONDITION I.E AT Ø≈0.9; NO EMISSION LEVEL IS AT ITS PEAK. UNDER VARIOUS DRIVING MODES DIFFERENT AMOUNTS OF POLLUTANTS ARE GENERATED. TYPICALLY AT ENGINE WARM UP AND IDLING CONDITIONS WHEN THE MIXTURE IS RICH (A/F RATIO 12:1) ENGINE EXHAUST CONTAINS GREATER
CONCENTRATION OF CO & HC, WHILE THE CONCENTRATION OF NOX DECREASES
TO MINIMUM DUE TO FALL IN COMBUSTION TEMPERATURE. AT LOW AND MINIMUM SPEEDS CONDITIONS THE AIR-FUEL RATIO IS BIT LEANER (A/RATIO 16:1~18:1) THAN THEORETICAL AIR-FUEL RATIO THERE BY PRODUCING LOWER CO & HC
EMISSIONS BUT THE AMOUNT OF NOX PRODUCTION IS HIGH. AT HIGH SPEED
CONDITION THE MIXTURE IS RICH (A/F RATIO13: 1~14:1) AND THE CONCENTRATION OF CO &HC IS HIGH IN THE EXHAUST. DURING ACCELERATION THE CONCENTRATION OF CO & HC INCREASES SHARPLY DUE TO VERY RICH MIXTURE CONDITION (A/F RATIO 8:1) AND AS THE ENGINE SPEED RISES, THE SPEED OF COMBUSTION ALSO INCREASES, CAUSING COMBUSTION TEMPERATURE
AND NOX TO RISE. DURING DECELERATION CO & HC INCREASES DUE TO OVER
RICH MIXTURE AND ERRATIC COMBUSTION. THE PRODUCTION OF NOX IS LOW AT
THIS MODE.
EMISSION CONTROL IN
GASOLINE ENGINES
EMISSION CONTROL STRATEGIES
• PRE-COMBUSTION
• IN-CYLINDER (COMBUSTION CHAMBER DESIGN MODS)
• POST COMBUSTION
• LEAN BURN OPERATION
PRE-COMBUSTION MEASURES
• BETTER MIXTURE PREPARATION , DISTRIBUTION & FUEL METERING• INTRODUCTION OF TUNED INTAKE MANIFOLD
• INTAKE MANIFOLD HEATING
• REPLACEMENT OF CARBURETOR WITH MPFI (MULTI POINT ELECTRONIC FUEL INJECTION)
• GASOLINE REFORMULATION
• INTRODUCTION OF ALTERNATIVE FUELS• NATURAL GAS (CNG & LNG)
• LIQUEFIED PETROLEUM GAS (LPG)
• ETHANOL
• METHANOL
• HYDROGEN
IN-CYLINDER MEASURES
• REDUCTION IN COMPRESSION RATIO
• MODIFICATION IN COMBUSTION CHAMBER GEOMETRY• SMALLER COMBUSTION CHAMBER SURFACE VOLUME
• REDUCTION IN CREVICE VOLUME
• REDUCE QUENCH AREAS IN COMBUSTION CHAMBER
• CENTRALLY LOCATION OF SPARK PLUG
* HEMISPHERICAL COMBUSTION CHAMBER IS BEST IN THIS REGARD
• VARIABLE VALVE TIMING
• EMPLOYING HIGH ENERGY/DUAL IGNITION SYSTEM
• RETARDATION OF IGNITION TIMING
• INCREASE IN IDLING SPEED
POST COMBUSTION/ADD-ON SYSTEM
• PCV (POSITIVE CRANK CASE VENTILATION SYSTEM)
• EGR (EXHAUST GAS RECIRCULATION SYSTEM)
• CATALYTIC CONVERTER
• AIR INJECTION SYSTEM
LEAN BURN OPERATION(GASOLINE DIRECT
INJECTION) WITH THE RISING EMPHASIS ON CONTROLLING CO2 EMISSIONS
(WHICH IS A GREEN HOUSE GAS) AND ON FUEL ECONOMY, IT IS ESSENTIAL TO OPERATE THE ENGINES ON FUEL LEAN MIXTURES. GASOLINE DIRECT INJECTION (GDI) ENGINES HAVE BEEN DEVELOPED BY DIFFERENT MANUFACTURES WHICH WORK ON THE PRINCIPLE OF CHARGE STRATIFICATION (LEAN MIXTURE OPERATION). IN THESE ENGINES, THE FUEL BURNS MORE
EFFICIENTLY WITH LESS POLLUTANT EMISSION OF CO, HC AND CO2
AND WITH LOWER FUEL CONSUMPTION. THE FUEL CONSUMPTION IS LOWERED UP TO 30% COMPARED TO THE STOICHIOMETRIC COMBUSTION . THESE ENGINES CAN OPERATE VERY LEAN OVERALL; THE AIR-FUEL RATIO NEAR THE SPARK PLUG IS NEARLY STOICHIOMETRIC OR SLIGHTLY FUEL RICH WHILE THE OTHER PARTS OF THE COMBUSTION CHAMBER ARE PROVIDED WITH VERY LEAN AIR-FUEL RATIOS.
EMISSION CONTROL IN GASOLINE ENGINES
Positive Crankshaft Ventilation (PCV)
Combustion gases leak past piston rings, into crankcase - blowby.
Modern vehicles use a PCV system to remove gases to be burnt in the inlet manifold.
Older vehicles vented gases into atmosphere.
PCV system operation is regulated by a PCV valve.
Fresh air enters through the air cleaner
Vapours pass into the inlet manifold
Air flow
Blowby
Fresh air mixes with blowby gases in the crankcase
PCV valve
POSITIVE CRANKCASE VENTILATION
• USES MANIFOLD VACUUM TO CLEAN BLOW-BY GASES FROM CRANKCASE.
• NEEDS A BREATHER TUBE FOR FRESH AIR.
• NEEDS A PCV VALVE TO REGULATE THE AMOUNT OF GASES ENTERING THE INTAKE MANIFOLD.
PCV OPERATION
• THE PCV VALVE HAS TWO FUNCTIONS:
1. TO REGULATE THE AMOUNT OF VAPOR ENTERING THE
INTAKE MANIFOLD AT
VARIOUS ENGINE SPEEDS. 2. PREVENT DAMAGE FROM BACKFIRE.
PCV Valve
Spring loaded valve that is shut when engine is off.At idle, maximum vacuum defeats spring pressure and minimal crankcase vapours flow.
At normal engine speeds, plunger moves to a central position and maximum vapours flow.
Spring
To manifold
Valve
Seal seat From crankcase
= Vapour
REGULATING THE PCV VAPOR FLOWAmount
ConditionManifoldVacuum
Blow-byGases
Idle HighVacuum
Small Volume
High Speed Low Vacuum Large Volume
Catalytic ConverterAll catalytic converters are built in a honeycomb or pellet geometry to expose
the exhaust gases to a large surface made of one or more noble metals: platinum, palladium and rhodium.
Rhodium used to remove NO and platinum used to remove HC and CO.
Lead and sulfur in the exhaust gas severely inhibit the operation of a catalytic converter (poison).
Steel shell
Catalytic Converter
Removes harmful gases that exit exhaust.Contains honeycomb coated with platinum and palladium (oxidation converter) and rhodium (reduction converter).
Inlet
Outlet
Catalyst honeycomb
Reduction converter
Oxidization converter
Oxidization converter changes HC and CO into H2O and CO2 (carbon dioxide).
Reduction converter changes NOX into N2 (nitrogen) and O2.
(oxygen).Conversion temperatures up to 900°C (1600°F).
56
Three-way Catalytic ConverterA catalyst forces a reaction at a temperature lower than normally occurs.
As the exhaust gases flow through the catalyst, the NO reacts with the CO,HC and H2 via a reduction reaction on the catalyst surface.e.g., NO+CO→½N2+CO2 , NO+H2 → ½N2+H2O, and others
The remaining CO and HC are removed through an oxidation reaction formingCO2 and H2O products (air added to exhaust after exhaust valve).
A three-way catalysts will function correctly only if the exhaust gas compositioncorresponds to nearly (±1%) stoichiometric combustion.
If the exhaust is too lean – NO are not destroyedIf the exhaust is too rich – CO and HC are not destroyed
A closed-loop control system with an oxygen sensor in the exhaust is used to determine the actual A/F ratio and used to adjust the fuel injector so that theA/F ratio is near stoichiometric.
Since thermal efficiency is highest for slightly lean conditions it may seem that the use of a catalytic converter is a rather severe constraint.
The same high efficiency can be achieved using a near stoichiometric mixtureand diluting by EGR
Effect of Mixture Composition
Effect of TemperatureThe temperature at which the converter becomes 50% efficient is referred to as the light-off temperature.
The converter is not very effective during the warm up period of the engine
TYPES OF CATALYTIC CONVERTERS
• TWO-WAY CATALYST; CHANGES HC AND CO INTO CO2 AND H2O
• THREE-WAY CATALYTIC CONVERTER: USED WITH OXYGEN SENSOR
• REDUCES NOX AND OXIDIZES HC AND CO
• SINGLE OR DUAL BED DESIGN
• DUAL BED CATALYTIC CONVERTERS INCLUDE AIR SWITCHING VALVE AND DIVERTER
• USE RHODIUM AS A CATALYST
• NEEDS HEAT AND REGULATED AIR-FUEL MIXTURE
Catalytic Converter for Diesels
For Diesel engines catalytic converters are used to control HC and CO, but reduction of NO emissions is poor because the engine runs lean in order to avoid excess smoke.
The NO is controlled by retarding the fuel injection from 20o to 5o before TDC in order to reduce the peak combustion temperature.
This has a slight negative impact, increases the fuel consumption by about 15%.
Air Injection System
Forces air into exhaust ports to burn excess hydrocarbons.
Air pump provides a supply of pressurized air, via air injection manifold.
Diverter valve stops air flow under deceleration.
Check valve stops hot exhaust gases coming back up air hose.
Diverter valveto air injection
hose
Air injection manifold
Check valve
Air pump to
diverter valve hose
Vacuum source and line
Diverter valve
Air pump
Exhaust Gas Recirculation (EGR) System
EGR valve can be vacuum and/or electronically controlled.
Reduces NOX by feeding inert exhaust gases into inlet manifold, therefore lowering combustion temperature.
Early EGR valves operated by ported vacuum.
(Closed) Exhaust gasInlet
manifold
EGR valve
Throttle valve
Vacuum
Temperature switch (TVV)
(Open)
Ported vacuum
Exhaust gas flow
EVAPORATIVE CONTROLS• CONTROL EMISSION OF GASOLINE VAPORS FROM TANK
• ACTIVATED CHARCOAL STORE GASOLINE VAPORS UNTIL THEY ARE DRAWN INTO THE ENGINE AND BURNED
• EMISSION OF FUEL VAPORS IS CONTROLLED BY SEALING THE FUEL SYSTEM
• GASOLINE TANKS ALLOW FOR FUEL EXPANSION OF 10%
• EXPANSION DOME AND LIQUID/VAPOR SEPARATOR
• EXPANSION TANK
• FILLER NECK DESIGN
• GAS CAPS SEALED OR HAVE PRESSURE VACUUM VALVE
Evaporative Controls
Electronic Evaporative Emissions ControlFuel stored in a container (fuel tank) produces vapours.
Fuel tank is fitted with sealed cap and air dome for fuel expansion.
Modern vehicles have sealed fuel system.
Older vehicles had vented fuel system, allowing vapours into atmosphere.
High pressurerelease cap
Air dome
Fuel outlet
Vent line
Electronic Evaporative Emissions ControlVent line connects to charcoal canister, via roll over/vapour separator valve.
Purge valve controls vapour removal into inlet manifold, via purge line.Purge valve operated by vacuum (shown) and/or ECU.
Charcoal canister stores fuel vapours.
Vacuum
Fuel vapourAir
Purge line
Fuel tank Charcoal canister
Non-vented cap
Inlet manifold
Throttle valveRoll over valve/ vapour separator
Purge valveVent line
Vacuum line
•Diesel exhaust particulates will comprise carbon (20-50%), sulfates (5- 5%), unburned fuel (10-30%), unburned lubricant (1 0-20%), and unknown (- 10%). The composition will depend on the engine, its operating point, and the fuel being used (sulfur and other inorganic content).
• THE NOX EMISSIONS INCREASE WITH LOAD BECAUSE OF THE INCREASE IN COMBUSTION TEMPERATURE AND THIS INCREASE IN COMBUSTION TEMPERATURE IS WHY THE HYDROCARBON EMISSIONS FALL. SIMILARLY, RETARDING THE INJECTION TIMING IN ALL CASES LEADS TO LOWER COMBUSTION TEMPERATURES. THIS LOWERS THE NOX EMISSIONS BUT INCREASES THE HYDROCARBON EMISSIONS. THE DI DIESEL HAS LOWER NOX EMISSIONS THAN THE IDI ENGINE BECAUSE THE LOWER COMPRESSION RATIO GIVES LOWER IN-CYLINDER TEMPERATURES. THE HYDROCARBON EMISSIONS ARE HIGHER FROM THE DL ENGINE BECAUSE THERE IS A LONGER IGNITION DELAY PERIOD, RESULTING IN MORE OVER-DILUTION AT THE FRINGES OF THE SPRAY. THE IGNITION DELAY PERIOD INCREASES WITH A REDUCED LOAD IN THE DL ENGINE BECAUSE THE COMBUSTION CHAMBER SURFACE TEMPERATURES ARE LOWER, AND THERE WILL BE MORE COOLING OF THE CHARGE DURING COMPRESSION. IN CONTRAST, THE PRE-CHAMBER INSERT IN THE IDI ENGINE IS ALWAYS HOT ENOUGH TO ENSURE A SHORT IGNITION DELAY PERIOD.
Summary of pollutant formation mechanism in a direct injection diesel engine during “pre-mixed” and ‘mixing controlled combustion phases
Diesel Emissions: Summary
DIESEL EMISSION CONTROL STRATEGY
• DIESEL REFORMULATION (REMOVING SULFUR ETC)• INJECTION SYSTEM OPTIMIZATION
• VARIABLE GEOMETRY TURBO-CHARGING
• AFTER TREATMENT• EGR
• SCR (SELECTIVE CATALYTIC CONVERTER)
• SNCR (SELECTIVE NON- CATALYTIC CONVERTER)
• PARTICULATE/SOOT TRAPS
DİESEL ENGİNE EMİSSİONS CONTROL
EXHAUST GAS RECİRCULATİON (EGR)
SCR• IN SELECTIVE CATALYTIC REDUCTION (SCR), AMMONIA (NH3) OR UREA (NH2CO
NH2) IS ADDED TO EXHAUST GASES TO EFFECT CHEMICAL REDUCTION OF NO
TO N2. CONVERSION EFFICIENCIES UP TO 80% HAVE BEEN REPORTED [35] WITH
THIS TECHNIQUE. IN PASSIVE DENOX, HYDROCARBON PRESENT IN THE EXHAUST
GASES HAS BEEN USED TO REDUCE NO CHEMICALLY. A NARROW TEMPERATURE
WINDOW OF 160˚C TO 220˚C IS REQUIRED FOR PLATINUM CATALYST FOR NOX
REDUCTION . A PEAK NOX CONVERSION EFFICIENCY OF 40% HAS BEEN
REPORTED AT 400C AND 62.32% AT 450˚C WITH COPPER-EXCHANGED
ZEOLITE CATALYST WITH PASSIVE DENOX TECHNIQUE. IN ACTIVE DENOX
TECHNIQUE HYDROCARBON FUEL IS INJECTED IN TO THE EXHAUST STREAM FOR
NOX REDUCTION. UP TO 20% NOX REDUCTION IN DIESEL ENGINES HAVE BEEN
REPORTED WITH 1.5% INCREASE IN FUEL CONSUMPTION. IN NOX TRAP
TECHNOLOGY; A 3-WAY CATALYST IN CONJUNCTION WITH NOX ABSORBING
MATERIAL IS UTILIZED. UNDER FUEL-RICH CONDITION THE STORED NOX IS
RELEASED WHICH IS THEN REDUCED TO N2 BY HC, CO AND H2 OVER NOBLE
METAL CATALYST (3-WAY CATALYST) .
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