InTech-Gasoline_direct_injection.pdf

GASOLINE DIRECT INJECTION

MUSTAFA BAHATTIN ÇELIK * AND BÜLENT ÖZDALYAN **

*KARABUK UNIVERSITY, ENGINEERING FACULTY

** KARABUK UNIVERSITY, TECHNOLOGY FACULTY

TURKEY

1. INTRODUCTION

THE BASIC GOALS OF THE AUTOMOTIVE INDUSTRY; A HIGH POWER, LOW SPECIFIC FUEL CONSUMPTION,

LOW EMISSIONS, LOW NOISE AND BETTER DRIVE COMFORT. WITH INCREASING THE VEHICLE NUMBER, THE

ROLE OF THE VEHICLES IN AIR POLLUTION HAS BEEN INCREASING SIGNIFICANTLY DAY BY DAY. THE

ENVIRONMENT PROTECTION AGENCIES HAVE DRAWN DOWN THE EMISSION LIMITS ANNUALLY.

FURTHERMORE, CONTINUOUSLY INCREASING PRICE OF THE FUEL NECESSITATES IMPROVING THE ENGINE

EFFICIENCY. SINCE THE ENGINES WITH CARBURETOR DO NOT HOLD THE AIR FUEL RATIO CLOSE TO THE

STOICHIOMETRIC AT DIFFERENT WORKING CONDITIONS, CATALYTIC CONVERTER CANNOT BE USED IN THESE

ENGINES. THEREFORE THESE ENGINES HAVE HIGH EMISSION VALUES AND LOW EFFICIENCY. ELECTRONIC

CONTROLLED PORT FUEL INJECTION (PFI) SYSTEMS INSTEAD OF FUEL SYSTEM WITH CARBURETOR HAVE BEEN

USED SINCE 1980’S. IN FUEL INJECTION SYSTEMS, INDUCED AIR CAN BE METERED PRECISELY AND THE

FUEL IS INJECTED IN THE MANIFOLD TO AIR AMOUNT. BY USING THE LAMBDA SENSOR IN EXHAUST SYSTEM,

AIR/FUEL RATIO IS HELD OF STABLE VALUE. FUEL SYSTEMS WITHOUT ELECTRONIC CONTROLLED IT IS

IMPOSSIBLE TO COMPLY WITH THE INCREASINGLY EMISSIONS LEGISLATION.

IF PORT FUEL INJECTION SYSTEM IS COMPARED WITH CARBURETOR SYSTEM, IT IS SEEN THAT HAS SOME

ADVANTAGES. THESE ARE;

1. LOWER EXHAUST EMISSIONS.

2. INCREASED VOLUMETRIC EFFICIENCY AND THEREFORE INCREASED OUTPUT POWER AND TORQUE.

THE CARBURETOR VENTURI PREVENTS AIR AND, IN TURN, VOLUMETRIC EFFICIENCY DECREASE.

3. LOW SPECIFIC FUEL CONSUMPTION. IN THE ENGINE WITH CARBURETOR, FUEL CANNOT BE

DELIVERED THE SAME AMOUNT AND THE SAME AIR/FUEL RATIO PER CYCLE, FOR EACH CYLINDER.

4. THE MORE RAPID ENGINE RESPONSE TO CHANGES IN THROTTLE POSITION. THIS INCREASES THE

DRIVE COMFORT.

5. FOR LESS ROTATION COMPONENTS IN FUEL INJECTION SYSTEM, THE NOISE DECREASES

(HEYWOOD, 2000; FERGUSON, 1986).

THOUGH THE PORT FUEL INJECTION SYSTEM HAS SOME ADVANTAGES, IT CANNOT BE MEET CONTINUOUSLY

INCREASED THE DEMANDS ABOUT PERFORMANCE, EMISSION LEGISLATION AND FUEL ECONOMY, AT THE

PRESENT DAY (STONE, 1999). THE ELECTRONIC CONTROLLED GASOLINE DIRECT INJECTION SYSTEMS WERE

STARTED TO BE USED INSTEAD OF PORT FUEL INJECTION SYSTEM SINCE 1990’S.

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FUEL INJECTION

THE GASOLINE DIRECT INJECTION (GDI) ENGINES GIVE A NUMBER OF FEATURES, WHICH COULD NOT BE

REALIZED WITH PORT INJECTED ENGINES: AVOIDING FUEL WALL FILM IN THE MANIFOLD, IMPROVED

ACCURACY OF AIR/FUEL RATIO DURING DYNAMICS, REDUCING THROTTLING LOSSES OF THE GAS EXCHANGE BY

STRATIFIED AND HOMOGENEOUS LEAN OPERATION, HIGHER THERMAL EFFICIENCY BY STRATIFIED OPERATION

AND INCREASED COMPRESSION RATIO, DECREASING THE FUEL CONSUMPTION AND CO 2 EMISSIONS, LOWER

HEAT LOSSES, FAST HEATING OF THE CATALYST BY INJECTION DURING THE GAS EXPANSION PHASE,

INCREASED PERFORMANCE AND VOLUMETRIC EFFICIENCY DUE TO COOLING OF AIR CHARGE, BETTER COLD-

START PERFORMANCE AND BETTER THE DRIVE COMFORT (ZHAO ET AL., 1999; KARAMANGIL, 2004; SMITH ET

AL., 2006).

2. THE PERFORMANCE AND EXHAUST EMISSIONS OF THE GASOLINE DIRECT INJECTION

(GDI) ENGINE

2.1 PERFORMANCE OF THE GDI ENGINE

THE PARAMETERS THAT HAVE THE GREATEST INFLUENCE ON ENGINE EFFICIENCY ARE COMPRESSION RATIO

AND AIR/FUEL RATIO. THE EFFECT OF RAISING COMPRESSION RATIO IS TO INCREASE THE POWER OUTPUT

AND TO REDUCE THE FUEL CONSUMPTION. THE MAXIMUM EFFICIENCY (OR MINIMUM SPECIFIC FUEL

CONSUMPTION) OCCURS WITH A MIXTURE THAT IS WEAKER THAN STOICHIOMETRIC (ÇELIK, 2007).

BECAUSE THE PORT FUEL INJECTION ENGINES WORK AT STOICHIOMETRIC AIR/FUEL RATIO, IT IS IMPOSSIBLE

TO SEE MORE IMPROVEMENT IN THE FUEL ECONOMY. IN THESE ENGINES, THE COMPRESSION RATIO IS

ABOUT 9/1-10/1. TO PREVENT THE KNOCK, THE COMPRESSION RATIO CANNOT BE INCREASED MORE. FOR

THE SAME ENGINE VOLUME, THE INCREASING VOLUMETRIC EFFICIENCY ALSO RAISES THE ENGINE POWER

OUTPUT.

GDI ENGINE OPERATE WITH LEAN MIXTURE AND UNTHROTTLED AT PART LOADS, THIS OPERATION PROVIDE

SIGNIFICANTLY IMPROVEMENTS IN FUEL ECONOMY. AT FULL LOAD, AS THE GDI ENGINE OPERATES WITH

HOMOGENEOUS CHARGE AND STOICHIOMETRIC OR SLIGHTLY RICH MIXTURE, THIS ENGINE GIVES A BETTER

POWER OUTPUT (SPICHER ET AL., 2000). IN GDI ENGINE, FUEL IS INJECTED INTO CYLINDER BEFORE SPARK

PLUG IGNITES AT LOW AND MEDIUM LOADS. AT THIS CONDITION, AIR/FUEL (A/F) RATIO IN CYLINDER

VARY, THAT IS, MIXTURE IN FRONT OF SPARK PLUG IS RICH, IN OTHER PLACES IS LEAN. IN ALL CYLINDER A/F

RATIO IS LEAN AND A/F RATIO CAN ACCESS UNTIL 40/1. IN HOMOGENEOUS OPERATION, FUEL STARTS

INJECTING INTO CYLINDER AT INTAKE STROKE AT FULL LOADS (ALGER ET AL., 2000; ÇNAR, 2001). THE FUEL,

WHICH IS INJECTED IN THE INTAKE STOKE, EVAPORATES IN THE CYLINDER. THE EVAPORATION OF THE FUEL

COOLS THE INTAKE CHARGE. THE COOLING EFFECT PERMITS HIGHER COMPRESSION RATIOS AND INCREASING

OF THE VOLUMETRIC EFFICIENCY AND THUS HIGHER TORQUE IS OBTAINED (MUÑOZ ET AL., 2005). IN THE

GDI ENGINES, COMPRESSION RATIO CAN GAIN UNTIL 12/1 (KUME, 1996). THE KNOCK DOES NOT OCCUR

BECAUSE ONLY AIR IS COMPRESSED AT LOW AND MEDIUM LOADS. AT FULL LOAD, SINCE FUEL IS INJECTED

INTO CYLINDER, THE CHARGE AIR COOL AND THIS, IN TURN, DECREASES KNOCK TENDENCY.

SINCE THE VEHICLES ARE USED USUALLY IN URBAN TRAFFIC, STUDIES ON IMPROVING THE URBAN DRIVING

FUEL ECONOMY HAVE INCREASED. ENGINES HAVE RUN USUALLY AT PART LOADS (LOW AND MEDIUM

LOADS) IN URBAN DRIVING. VOLUMETRIC EFFICIENCY IS LOWER AT PART LOADS, SO ENGINE EFFECTIVE

COMPRESSION RATIO DECREASES (E.G. FROM 8/1 TO 3/1-4/1), ENGINE EFFICIENCY DECREASES AND FUEL

CONSUMPTION INCREASES. THE URBAN DRIVING FUEL ECONOMY OF THE VEHICLES IS VERY HIGH (ÇELIK,

1999). DISTINCTION BETWEEN THE HIGHWAY FUEL ECONOMIES OF VEHICLES IS VERY LITTLE. AS MAJORITY

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GASOLINE DIRECT INJECTION

OF THE LIFE TIME OF THE VEHICLES PASS IN THE URBAN DRIVING, THE OWNERS OF THE VEHICLES PREFER THE

VEHICLES OF WHICH THE URBAN DRIVING FUEL ECONOMY IS LOW.

AT FULL LOAD, AS THE GDI ENGINE OPERATE WITH THROTTLE, ONLY A SMALL REDUCTION OF FUEL

CONSUMPTION CAN BE OBTAINED TO THE PFI ENGINE. THERE IS THE MORE FUEL ECONOMY POTENTIAL AT

PART LOAD. AT COMPRESSION STROKE, SINCE AIR IS GIVEN THE CYLINDERS WITHOUT THROTTLE FOR

STRATIFIED CHARGE MODE, PUMPING LOSSES OF THE GDI ENGINE IS MINIMUM AT PART LOADS, FIG.1

(BAUMGARTEN, 2006). THE IMPROVEMENTS IN THERMAL EFFICIENCY HAVE BEEN OBTAINED AS A RESULT

OF REDUCED PUMPING LOSSES, HIGHER COMPRESSION RATIOS AND FURTHER EXTENSION OF THE LEAN

OPERATING LIMIT UNDER STRATIFIED COMBUSTION CONDITIONS AT LOW ENGINE LOADS. IN THE DI

GASOLINE ENGINES, FUEL CONSUMPTION CAN BE DECREASED BY UP TO 20%, AND A 10% POWER OUTPUT

IMPROVEMENT CAN BE ACHIEVED OVER TRADITIONAL PFI ENGINES (FAN ET AL., 1999).

FIG. 1. REDUCTION OF THROTTLE LOSSES IN THE STRATIFIED-CHARGE COMBUSTION (BAUMGARTEN, 2006).

THE CO 2 EMISSIONS, WHICH ARE ONE OF THE GASES, BRING ABOUT THE GLOBAL WARMING. TO DECREASE

CO 2 EMITTED FROM VEHICLES, IT IS REQUIRED TO DECREASE FUEL CONSUMPTION. DOWNSIZING

(REDUCTION OF THE ENGINE SIZE) IS SEEN AS A MAJOR WAY OF IMPROVING FUEL CONSUMPTION AND

REDUCING GREENHOUSE EMISSIONS OF SPARK IGNITED ENGINES. IN THE SAME WEIGHT AND SIZE,

SIGNIFICANT DECREASES IN CO 2 EMISSIONS, MORE POWER AND HIGHER BREAK MEAN EFFECTIVE

PRESSURE CAN BE OBTAINED. GDI ENGINES ARE VERY SUITABLE FOR TURBOCHARGER APPLICATIONS. THE

USE OF GDI ENGINE WITH TURBOCHARGER PROVIDES ALSO HIGH ENGINE KNOCK RESISTANCE ESPECIALLY

AT HIGH LOAD AND LOW ENGINE SPEED WHERE PFI TURBOCHARGED ENGINES ARE STILL LIMITED

(LECOINTE & MONNIER, 2003; STOFFELS, 2005). TURBOCHARGED GDI ENGINES HAVE SHOWED GREAT

POTENTIAL TO MEET THE CONTRADICTORY TARGETS OF LOWER FUEL CONSUMPTION AS WELL AS HIGH TORQUE

AND POWER OUTPUT (KLEEBERG, 2006).

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FUEL INJECTION

IN GDI ENGINE, BY USING TWIN CHARGING SYSTEM DRIVE COMFORT, ENGINE TORQUE AND POWER CAN

BE INCREASED FOR THE SAME ENGINE SIZE. FOR EXAMPLE, VOLKSWAGEN (VW) HAS USED THE DUAL

CHARGING SYSTEM IN TSI (TWIN CHARGED STRATIFIED INJECTION) ENGINE. THE SYSTEM INCLUDES A

ROOTS-TYPE SUPERCHARGER AS WELL AS A TURBOCHARGER. THE SUPERCHARGER IS BASICALLY AN AIR

COMPRESSOR. A MECHANICAL DEVICE DRIVEN OFF THE ENGINE'S CRANKSHAFT, IT EMPLOYS ROTATING

VANES WHICH SPIN IN OPPOSITE DIRECTIONS TO COMPRESS AIR IN THE ENGINE'S INTAKE SYSTEM. THE

HIGH AND CONSTANT TORQUE IS OBTAINED AT WIDE RANGE SPEED BY ACTIVATE SUPERCHARGER AT LOW

SPEEDS AND TURBO CHARGER AT HIGH SPEEDS (ANON, 2006).

IN TABLE 1, IT IS GIVEN SPECIFICATIONS OF THE TWO DIFFERENT ENGINES BELONGING TO THE 2009 MODEL

VW PASSAT VEHICLE, FOR EXAMPLE. TSI ENGINE URBAN DRIVING FUEL ECONOMY IS 18% LOWER THAN

THAT OF PFI ENGINE. CO 2 EMISSION IS 12% LOWER THAN THAT OF PFI ENGINE. ALTHOUGH TSI ENGINE

SWEPT VOLUME IS LOWER THAN PFI ENGINE, POWER AND TORQUE IS HIGHER BY 20% AND 35%,

RESPECTIVELY (TABLE 1). AS ENGINE TORQUE IS MAXIMUM AT INTERVAL 1500-4000 1/MIN, SHIFTING IS

NOT NECESSARY AT THE ACCELERATION AND THUS DRIVE COMFORT INCREASE (ANON, 2009).

FUEL ECONOMY

(HIGHWAY

DRIVING)

L/100KM

MIXTURE

FORMATION

SYSTEM

FUEL ECONOMY

(URBAN DRIVING)

L/100KM

CO 2

EMISSION

G/KM

ENGINE

TYPE

SWEPT

VOLUME

MAX.

TORQUE

MAX. POWER

GASOLINE

ENGINE

75 KW

5600 1/MIN

148 NM

3800 1/MIN

PFI (PORT FUEL

INJECTION)

1.6 L

10,5

6,0

179

TSI

GASOLINE

ENGINE

90 KW

5000 - 5500

1/MIN

200 NM

1500 - 4000

1/MIN

GDI (GASOLINE

DIRECT INJECTION)

1.4 L

8,6

5,5

157

TABLE 1. COMPARISON OF THE GDI AND PFI ENGINES (ANON, 2009).

2.2 EXHAUST EMISSIONS OF THE GDI ENGINE

CO EMISSION IS VERY LOW IN GDI ENGINE. CO VARIES DEPENDING ON AIR /FUEL RATIO. CO IS HIGH

AT RICH MIXTURES. SINCE GDI ENGINES OPERATE WITH LEAN MIXTURE AT PART LOADS AND

STOICHIOMETRIC MIXTURE AT FULL LOAD, CO IS NOT A PROBLEM FOR THESE ENGINES. IN GDI ENGINE,

DUE TO THE WETTING OF THE PISTON AND THE CYLINDER WALLS WITH LIQUID FUEL, HC EMISSION CAN

INCREASE. HYDROCARBON (HC) EMISSIONS ARE A FUNCTION OF ENGINE TEMPERATURE AND, THEREFORE IT

CAN RISE DURING COLD START. THE COLD STARTS CHARACTERISTICS VARY DEPENDING ON THE FUEL

DISTRIBUTION CHARACTERISTICS, THE IN-CYLINDER AIR MOTION, FUEL VAPORIZATION, AND FUEL-AIR MIXING

(GANDHI ET AL., 2006).

DURING COLD-START OF A GDI ENGINE, HOMOGENEOUS OPERATION CAN BE EMPLOYED DUE TO A HIGHER

EXHAUST GAS TEMPERATURE RESULTING IN A SHORTER TIME FOR CATALYST LIGHT-OFF, AND LOWER ENGINE

OUT HC EMISSIONS (GANDHI ET AL., 2006). GASOLINE ENGINES DO NOT EMIT SOOT EMISSION

NORMALLY. SOOT EMISSION CAN OCCUR AT VERY RICH MIXTURES. HOWEVER, THE GDI ENGINES EMIT

SOOT AT STRATIFIED-CHARGE OPERATION, AS IN–CYLINDER CAN BE AREAS WITH VERY RICH MIXTURES. IN

ADDITION, IN GDI ENGINE, IF MIXTURE FORMATION DO NOT REALIZE AT FULL LOADS DUE TO RICH MIXTURE,

THE SOOT EMISSION CAN INCREASE. NOX EMISSION IS MAXIMUM AT HIGH CYLINDER TEMPERATURES

AND AT Λ =1.1. AS TORQUE OUTPUT RISES, TEMPERATURES RISE AND, IN TURN, THE ENGINE-OUT NOX

EMISSIONS DISPLAY AN INCREASE. NOX EMISSIONS INCREASE ESPECIALLY AT FULL LOAD.

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GASOLINE DIRECT INJECTION

2.3 THE EMISSION CONTROL IN GDI ENGINE

ENVIRONMENTAL LEGISLATION DETERMINES THE LIMITS FOR EXHAUST EMISSIONS IN THE SPARK IGNITION

ENGINES. IT IS REQUIRED THE TREATMENT OF THE EXHAUST GASES TO MEET THESE LIMITS. THE THREE-WAY

CATALYTIC CONVERTER SHOW HIGH PERFORMANCE FOR CONVERTING THE CO, HC AND NOX IN THE

ENGINES WITH OPERATION AT Λ=1.0. BUT, NOX CANNOT BE COMPLETELY CONVERTED HARMLESS GASES AT

LEAN MIXTURE OPERATION. THEREFORE, ENGINES WITH LEAN MIXTURE ALSO REQUIRE A NOX STORAGE

TYPE CATALYTIC CONVERTER TO CONVERT THE NOX.

THE TWO CATALYTIC CONVERTERS ARE SUCCESSIVELY USED IN GDI ENGINE EXHAUST SYSTEM. THE ONE IS

PRE-CATALYTIC CONVERTER (THREE WAY CONVERTER -TWC). THIS CONVERTER HAS LITTLE VOLUME AND IS

CONNECTED CLOSE TO THE ENGINE. THE OTHER IS MAIN CATALYTIC CONVERTER WHICH COMBINES A NOX

CATALYST AND A TWC. THIS CONVERTER HAS HIGHER VOLUME THAN THE PRE-CATALYTIC CONVERTER AND

IS CONNECTED NOT CLOSE TO THE ENGINE. THE PRE-CATALYTIC CONVERTER CONVERT THE CO, HC AND

NOX TO HARMLESS GASES (CO 2 , H 2 O AND N 2 ) AT Λ=1.0. HOWEVER, WHEN ENGINE OPERATES AT

STRATIFIED MODE WITH LEAN MIXTURE, NOX CANNOT BE CONVERTED TO NITROGEN. IN SUCH CASES, NOX

IS SENT TO MAIN CATALYTIC CONVERTER (ANON, 2002).

IN THE NOX STORAGE TYPE CATALYTIC CONVERTER, THE COMPONENTS SUCH AS BA AND CA ARE USED FOR

NOX CONVERSION AT LEAN MIXTURES. THESE COMPONENTS PROVIDE NOX TO STORAGE. AT Λ=1.0, THE

OPERATION OF THE NOX CONVERTER RESEMBLES THREE WAY CONVERTER. AT LEAN MIXTURES, NOX

CONVERSION IS REALIZED IN THREE STAGES: NOX ACCUMULATION, NOX RELEASE AND CONVERSION.

NITROGEN OXIDES REACTS CHEMICALLY WITH BARIUM OXIDE (BAO) AND THUS BARIUM NITRATE

(BA(NO 3 ) 2 FORMS. (NOX STORAGE STAGE). THEN, TO CONVERT, ENGINE IS OPERATED MOMENTARILY IN

THE RICH HOMOGENEOUS MODE. THANKS TO RICH MIXTURE, THERE IS CO IN EXHAUST SYSTEM. THE

BARIUM NITRATE REACTS CHEMICALLY WITH CO AND, AS A RESULT OF THIS CO 2 , BAO AND NO ARISE

(NOX RELEASE STAGE). AND THEN, NO REACTS CHEMICALLY WITH CO AND, N 2 AND CO 2 FORM

(CONVERSION STAGE). NOX STORAGE CONVERTER CAN STORAGE THE NOX AT TEMPERATURES OF 250-500C

(ANON, 2002; BAUER, 2004). AN EXHAUST GAS RECIRCULATION SYSTEM IS NECESSARY, AS THE NOX

AFTERTREATMENT SYSTEMS DO NOT REACH THE CONVERSION RATES OF Λ = 1 CONCEPTS. WITH THE

EXCEPTION AT THE HIGHEST LOADS, EXHAUST GAS RECIRCULATION (EGR) IS USED EXTENSIVELY TO CONTROL

NOX EMISSIONS (ALKIDAS, 2007).

TO MEET THE VALID EMISSION LIMITS AND DIAGNOSE THE PRE AND MAIN CATALYST FAULTS, AND

PROVIDE OPTIMUM ENGINE OPERATION 4 SENSORS (3 LAMBDA SENSOR AND 1 EXHAUST GAS

TEMPERATURE SENSOR) ARE USED IN THE EXHAUST SYSTEM. THE WIDE BAND LAMBDA SENSOR

UPSTREAM OF PRE-CATALYST DETERMINES RESIDUAL OXYGEN VALUE IN EXHAUST GAS. THE REQUIRED Λ

FOR HOMOGENEOUS LEAN OPERATION CAN BE CONTROLLED BY THIS SENSOR. FOR EACH CATALYTIC

CONVERTER TWO LAMBDA SENSORS (UPSTREAM AND DOWNSTREAM SENSOR) ARE USED. THE FAULTS OF THE

PRE AND MAIN CONVERTERS CAN BE DIAGNOSED BY SIGNAL OF DUAL SENSORS. THE TEMPERATURE SENSOR

IS USED TO DETERMINE THE TEMPERATURE OF THE NOX CATALYST (KÜSELL ET AL., 1999).

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