Gasoline Fuel-Injection System K-Jetronic
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Published by: © Robert Bosch GmbH, 2000 Postfach 30 02 20, D-70442 Stuttgart. Automotive Equipment Business Sector, Department for Automotive Services, Technical Publications (KH/PDI2). Editor-in-Chief: Dipl.-Ing. (FH) Horst Bauer. Editorial staff: Dipl.-Ing. Karl-Heinz Dietsche, Dipl.-Ing. (BA) Jürgen Crepin. Presentation: Dipl.-Ing. (FH) Ulrich Adler, Joachim Kaiser, Berthold Gauder, Leinfelden-Echterdingen. Translation: Peter Girling. Technical graphics: Bauer & Partner, Stuttgart. Unless otherwise stated, the above are all employees of Robert Bosch GmbH, Stuttgart. Reproduction, copying, or translation of this publication, including excerpts therefrom, is only to ensue with our previous written consent and with source credit. Illustrations, descriptions, schematic diagrams, and other data only serve for explanatory purposes and for presentation of the text. They cannot be used as the basis for design, installation, or scope of delivery. We assume no liability for conformity of the contents with national or local legal regulations. We are exempt from liability. We reserve the right to make changes at any time. Printed in Germany. Imprimé en Allemagne. 4th Edition, February 2000. English translation of the German edition dated: September 1998.
K-Jetronic Since its introduction, the K-Jetronic Combustion in the gasoline engine gasoline-injection system has pro- The spark-ignition or ved itself in millions of vehicles. Otto-cycle engine 2 This development was a direct result Gasoline-engine management of the advantages which are inherent Technical requirements 4 in the injection of gasoline with Cylinder charge 5 regard to demands for economy of Mixture formation 7 operation, high output power, and Gasoline-injection systems last but not least improvements to Overview 10 the quality of the exhaust gases K-Jetronic emitted by the vehicle. Whereas the System overview 13 call for higher engine output was the Fuel supply 14 foremost consideration at the start of Fuel metering 18 the development work on gasoline Adapting to operating conditions 24 injection, today the target is to Supplementary functions 30 achieve higher fuel economy and Exhaust-gas treatment 32 lower toxic emissions. Electrical circuitry 36 Between the years 1973 and 1995, Workshop testing techniques 38 the highly reliable, mechanical multi- point injection system K-Jetronic was installed as Original Equipment in series-production vehicles. Today, it has been superseded by gasoline injection systems which thanks to electronics have been vastly im- proved and expanded in their func- tions. Since this point, the K-Jetronic has now become particularly impor- tant with regard to maintenance and repair. This manual will describe the K-Jetronic’s function and its particu- lar features.
Combustion in the gasoline engine Combustion in the gasoline engine combustion process pressurizes the The spark-ignition cylinder, propelling the piston back down, or Otto-cycle engine exerting force against the crankshaft and performing work. After each combustion stroke the spent gases are expelled from Operating concept the cylinder in preparation for ingestion of The spark-ignition or Otto-cycle1) a fresh charge of air/fuel mixture. The powerplant is an internal-combustion (IC) primary design concept used to govern engine that relies on an externally- this gas transfer in powerplants for generated ignition spark to transform the automotive applications is the four-stroke chemical energy contained in fuel into principle, with two crankshaft revolutions kinetic energy. being required for each complete cycle. Today’s standard spark-ignition engines employ manifold injection for mixture formation outside the combustion The four-stroke principle chamber. The mixture formation system The four-stroke engine employs flow- produces an air/fuel mixture (based on control valves to govern gas transfer gasoline or a gaseous fuel), which is (charge control). These valves open and then drawn into the engine by the suction close the intake and exhaust tracts generated as the pistons descend. The leading to and from the cylinder: future will see increasing application of systems that inject the fuel directly into the 1st stroke: Induction, combustion chamber as an alternate 2nd stroke: Compression and ignition, concept. As the piston rises, it compresses 3rd stroke: Combustion and work, the mixture in preparation for the timed 4th stroke: Exhaust. ignition process, in which externally- generated energy initiates combustion via Induction stroke the spark plug. The heat released in the Intake valve: open, Fig. 1 Exhaust valve: closed, Reciprocating piston-engine design concept Piston travel: downward, OT = TDC (Top Dead Center); UT = BDC (Bottom Combustion: none. Dead Center), Vh Swept volume, VC Compressed volume, s Piston stroke. The piston’s downward motion increases VC OT the cylinder’s effective volume to draw fresh air/fuel mixture through the passage s exposed by the open intake valve. Vh UT Compression stroke Intake valve: closed, Exhaust valve: closed, OT Piston travel: upward, Combustion: initial ignition phase. UMM0001E 1) After Nikolaus August Otto (1832 –1891), who UT unveiled the first four-stroke gas-compression engine 2 at the Paris World Exhibition in 1876.
As the piston travels upward it reduces The ignition spark at the spark plug Otto cycle the cylinder’s effective volume to ignites the compressed air/fuel mixture, compress the air/fuel mixture. Just before thus initiating combustion and the the piston reaches top dead center (TDC) attendant temperature rise. the spark plug ignites the concentrated This raises pressure levels within the air/fuel mixture to initiate combustion. cylinder to propel the piston downward. Stroke volume Vh The piston, in turn, exerts force against and compression volume VC the crankshaft to perform work; this provide the basis for calculating the process is the source of the engine’s compression ratio power. ε = (Vh+VC)/VC. Power rises as a function of engine speed Compression ratios ε range from 7...13, and torque (P = M⋅ω). depending upon specific engine design. A transmission incorporating various Raising an IC engine’s compression ratio conversion ratios is required to adapt the increases its thermal efficiency, allowing combustion engine’s power and torque more efficient use of the fuel. As an curves to the demands of automotive example, increasing the compression ratio operation under real-world conditions. from 6:1 to 8:1 enhances thermal efficiency by a factor of 12 %. The latitude Exhaust stroke for increasing compression ratio is Intake valve: closed, restricted by knock. This term refers to Exhaust valve: open, uncontrolled mixture inflammation charac- Piston travel: upward, terized by radical pressure peaks. Combustion: none. Combustion knock leads to engine damage. Suitable fuels and favorable As the piston travels upward it forces the combustion-chamber configurations can spent gases (exhaust) out through the be applied to shift the knock threshold into passage exposed by the open exhaust higher compression ranges. valve. The entire cycle then recommences with a new intake stroke. The intake and Power stroke exhaust valves are open simultaneously Intake valve: closed, during part of the cycle. This overlap Exhaust valve: closed, exploits gas-flow and resonance patterns Piston travel: upward, to promote cylinder charging and Combustion: combustion/post-combus- scavenging. tion phase. Fig. 2 Operating cycle of the 4-stroke spark-ignition engine Stroke 1: Induction Stroke 2: Compression Stroke 3: Combustion Stroke 4: Exhaust UMM0011E 3
Gasoline- engine management Gasoline- engine management Technical requirements Primary engine- management functions The engine-management system’s first Spark-ignition (SI) and foremost task is to regulate the engine torque engine’s torque generation by controlling all of those functions and factors in the The power P furnished by the spark- various engine-management subsystems ignition engine is determined by the that determine how much torque is available net flywheel torque and the generated. engine speed. The net flywheel torque consists of the Cylinder-charge control force generated in the combustion In Bosch engine-management systems process minus frictional losses (internal featuring electronic throttle control (ETC), friction within the engine), the gas- the “cylinder-charge control” subsystem exchange losses and the torque required determines the required induction-air to drive the engine ancillaries (Figure 1). mass and adjusts the throttle-valve The combustion force is generated opening accordingly. The driver exercises during the power stroke and is defined by direct control over throttle-valve opening the following factors: on conventional injection systems via the – The mass of the air available for physical link with the accelerator pedal. combustion once the intake valves have closed, Mixture formation – The mass of the simultaneously The “mixture formation” subsystem cal- available fuel, and culates the instantaneous mass fuel – The point at which the ignition spark requirement as the basis for determining initiates combustion of the air/fuel the correct injection duration and optimal mixture. injection timing. Fig. 1 Driveline torque factors 1 Ancillary equipment 1 1 2 3 4 (alternator, a/c compressor, etc.), 2 Engine, 3 Clutch, 4 Transmission. Air mass (fresh induction charge) Combustion Engine Flywheel Drive Fuel mass output torque output torque torque Trans- force Engine Clutch – – – mission – Ignition angle (firing point) – – Gas-transfer and friction Ancillaries UMM0545-1E Clutch/converter losses and conversion ratios Transmission losses and conversion ratios 4
Ignition emissions control system (Figure 2). The Cylinder Finally, the “ignition” subsystem de- air entering through the throttle-valve and charge termines the crankshaft angle that remaining in the cylinder after intake- corresponds to precisely the ideal instant valve closure is the decisive factor for the spark to ignite the mixture. defining the amount of work transferred through the piston during combustion, The purpose of this closed-loop control and thus the prime determinant for the system is to provide the torque amount of torque generated by the demanded by the driver while at the engine. In consequence, modifications to same time satisfying strict criteria in the enhance maximum engine power and areas of torque almost always entail increasing – Exhaust emissions, the maximum possible cylinder charge. – Fuel consumption, The theoretical maximum charge is – Power, defined by the volumetric capacity. – Comfort and convenience, and – Safety. Residual gases The portion of the charge consisting of residual gases is composed of – The exhaust-gas mass that is not Cylinder charge discharged while the exhaust valve is open and thus remains in the cylinder, Elements and The gas mixture found in the cylinder – The mass of recirculated exhaust gas once the intake valve closes is referred to (on systems with exhaust-gas recircu- as the cylinder charge, and consists of lation, Figure 2). the inducted fresh air-fuel mixture along The proportion of residual gas is de- with residual gases. termined by the gas-exchange process. Although the residual gas does not Fresh gas participate directly in combustion, it does The fresh mixture drawn into the cylinder influence ignition patterns and the actual is a combination of fresh air and the fuel combustion sequence. The effects of this entrained with it. While most of the fresh residual-gas component may be thoroughly air enters through the throttle valve, desirable under part-throttle operation. supplementary fresh gas can also be Larger throttle-valve openings to com- drawn in through the evaporative- pensate for reductions in fresh-gas filling Fig. 2 Cylinder charge in the spark-ignition engine 1 Air and fuel vapor, 2 Purge valve with variable aperture, 2 3 3 Link to evaporative-emissions control system, 1 4 Exhaust gas, 5 EGR valve with α 4 5 variable aperture, 6 Mass airflow (barometric pressure pU), 11 12 7 Mass airflow (intake-manifold pressure ps), 6 7 10 8 Fresh air charge 8 (combustion-chamber pressure pB), 9 Residual gas charge 9 (combustion-chamber pressure pB), 10 Exhaust gas (back-pressure pA), UMM0544-1Y 11 Intake valve, 12 Exhaust valve, α Throttle-valve angle. 5
Gasoline- are needed to meet higher torque on a supplementary EGR valve linking engine demand. These higher angles reduce the the intake and exhaust manifolds. The management engine’s pumping losses, leading to engine ingests a mixture of fresh air and lower fuel consumption. Precisely reg- exhaust gas when this valve is open. ulated injection of residual gases can also modify the combustion process to Pressure charging reduce emissions of nitrous oxides (NOx) Because maximum possible torque is and unburned hydrocarbons (HC). proportional to fresh-air charge density, it is possible to raise power output by compressing the air before it enters the Control elements cylinder. Throttle valve Dynamic pressure charging The power produced by the spark- A supercharging (or boost) effect can be ignition engine is directly proportional to obtained by exploiting dynamics within the mass airflow entering it. Control of the intake manifold. The actual degree of engine output and the corresponding boost will depend upon the manifold’s torque at each engine speed is regulated configuration as well as the engine’s by governing the amount of air being instantaneous operating point inducted via the throttle valve. Leaving (essentially a function of the engine’s the throttle valve partially closed restricts speed, but also affected by load factor). the amount of air being drawn into the The option of varying intake-manifold engine and reduces torque generation. geometry while the vehicle is actually The extent of this throttling effect being driven, makes it possible to employ depends on the throttle valve’s position dynamic precharging to increase the and the size of the resulting aperture. maximum available charge mass through The engine produces maximum power a wide operational range. when the throttle valve is fully open (WOT, or wide open throttle). Mechanical supercharging Figure 3 illustrates the conceptual Further increases in air mass are correlation between fresh-air charge available through the agency of density and engine speed as a function Fig. 3 of throttle-valve aperture. Throttle-valve map for spark-ignition engine Throttle valve at intermediate aperture Gas exchange The intake and exhaust valves open and close at specific points to control the transfer of fresh and residual gases. The Throttle valve ramps on the camshaft lobes determine completely open both the points and the rates at which the valves open and close (valve timing) to define the gas-exchange process, and Fresh gas charge with it the amount of fresh gas available for combustion. Valve overlap defines the phase in which the intake and exhaust valves are open simultaneously, and is the prime factor in determining the amount of residual gas remaining in the cylinder. This process is known as "internal" exhaust-gas Throttle valve UMM0543-1E recirculation. The mass of residual gas completely closed can also be increased using "external" min. max. 6 exhaust-gas recirculation, which relies Idle RPM
mechanically driven compressors pow- ered by the engine’s crankshaft, with the Mixture formation Mixture formation two elements usually rotating at an in- variable relative ratio. Clutches are often used to control compressor activation. Parameters Exhaust-gas turbochargers Air-fuel mixture Here the energy employed to power the Operation of the spark-ignition engine is compressor is extracted from the exhaust contingent upon availability of a mixture gas. This process uses the energy that with a specific air/fuel (A/F) ratio. The naturally-aspirated engines cannot theoretical ideal for complete combustion exploit directly owing to the inherent is a mass ratio of 14.7:1, referred to as restrictions imposed by the gas ex- the stoichiometric ratio. In concrete terms pansion characteristics resulting from the this translates into a mass relationship of crankshaft concept. One disadvantage is 14.7 kg of air to burn 1 kg of fuel, while the higher back-pressure in the exhaust the corresponding volumetric ratio is gas exiting the engine. This back- roughly 9,500 litres of air for complete pressure stems from the force needed to combustion of 1 litre of fuel. maintain compressor output. The exhaust turbine converts the The air-fuel mixture is a major factor in exhaust-gas energy into mechanical determining the spark-ignition engine’s energy, making it possible to employ an rate of specific fuel consumption. impeller to precompress the incoming Genuine complete combustion and fresh air. The turbocharger is thus a absolutely minimal fuel consumption combination of the turbine in the exhaust- would be possible only with excess air, fas flow and the impeller that compresses but here limits are imposed by such the intake air. considerations as mixture flammability Figure 4 illustrates the differences in the and the time available for combustion. torque curves of a naturally-aspirated engine and a turbocharged engine. The air-fuel mixture is also vital in determining the efficiency of exhaust-gas Fig. 4 treatment system. The current state-of- Torque curves for turbocharged the-art features a 3-way catalytic and atmospheric-induction engines converter, a device which relies on a with equal power outputs stoichiometric A/F ratio to operate at 1 Engine with turbocharger, maximum efficiency and reduce un- 2 Atmospheric-induction engine. desirable exhaust-gas components by more than 98 %. Current engines therefore operate with a stoichiometric A/F ratio as soon as the 1 engine’s operating status permits Engine torque Md Certain engine operating conditions 2 make mixture adjustments to non- stoichiometric ratios essential. With a cold engine for instance, where specific adjustments to the A/F ratio are required. As this implies, the mixture-formation system must be capable of responding to UMM0459-1E 1 1 3 1 4 2 4 1 a range of variable requirements. Engine rpm nn 7
Gasoline- Excess-air factor deficiencies of 5...15 % (λ = 0.95...0.85), engine The designation l (lambda) has been but maximum fuel economy comes in at management selected to identify the excess-air factor 10...20 % excess air (λ = 1.1...1.2). (or air ratio) used to quantify the spread Figures 1 and 2 illustrate the effect of the between the actual current mass A/F ratio excess-air factor on power, specific fuel and the theoretical optimum (14.7:1): consumption and generation of toxic λ = Ratio of induction air mass to air emissions. As can be seen, there is no requirement for stoichiometric com- single excess-air factor which can bustion. simultaneously generate the most λ = 1: The inducted air mass corresponds favorable levels for all three factors. Air to the theoretical requirement. factors of λ = 0.9...1.1 produce λ < 1: Indicates an air deficiency, “conditionally optimal” fuel economy with producing a corresponding rich mixture. “conditionally optimal” power generation Maximum power is derived from λ = in actual practice. 0.85...0.95. Once the engine warms to its normal λ > 1: This range is characterized by operating temperature, precise and excess air and lean mixture, leading to consistent maintenance of λ = 1 is vital lower fuel consumption and reduced for the 3-way catalytic treatment of power. The potential maximum value for λ exhaust gases. Satisfying this re- – called the “lean-burn limit (LML)” – is quirement entails exact monitoring of essentially defined by the design of the induction-air mass and precise metering engine and of its mixture for- of fuel mass. mation/induction system. Beyond the Optimal combustion from current en- lean-burn limit the mixture ceases to be gines equipped with manifold injection ignitable and combustion miss sets in, relies on formation of a homogenous accompanied by substantial degener- mixture as well as precise metering of the ation of operating smoothness. injected fuel quantity. This makes In engines featuring systems to inject fuel effective atomization essential. Failure to directly into the chamber, these operate satisfy this requirement will foster the with substantially higher excess-air formation of large droplets of condensed factors (extending to λ = 4) since com- fuel on the walls of the intake tract and in bustion proceeds according to different the combustion chamber. These droplets laws. will fail to combust completely and the Spark-ignition engines with manifold ultimate result will be higher HC injection produce maximum power at air emissions. Fig. 1 Fig. 2 Effects of excess-air factor λ on power P and Effect of excess-air factor λ on untreated specific fuel consumption be. exhaust emissions a Rich mixture (air deficiency), b Lean mixture (excess air). HC NOX CO Specific fuel consumption be P Relative quantities of be CO; HC; NOX Power P , a b UMK0033E UMK0032E 0.8 1.0 1.2 0.6 0.8 1.0 1.2 1.4 Excess-air factor λ Excess-air factor λ 8
Adapting to specific Idle and part-load Mixture operating conditions Idle is defined as the operating status in formation which the torque generated by the engine Certain operating states cause fuel is just sufficient to compensate for friction requirements to deviate substantially from losses. The engine does not provide the steady-state requirements of an engine power to the flywheel at idle. Part-load (or warmed to its normal temperature, thus part-throttle) operation refers to the necessitating corrective adaptations in the range of running conditions between idle mixture-formation apparatus. The follow- and generation of maximum possible ing descriptions apply to the conditions torque. Today’s standard concepts rely found in engines with manifold injection. exclusively on stoichiometric mixtures for the operation of engines running at idle Cold starting and part-throttle once they have warmed During cold starts the relative quantity of to their normal operating temperatures. fuel in the inducted mixture decreases: the mixture “goes lean.” This lean-mixture Full load (WOT) phenomenon stems from inadequate At WOT (wide-open throttle) supple- blending of air and fuel, low rates of fuel mentary enrichment may be required. As vaporization, and condensation on the Figure 1 indicates, this enrichment walls of the inlet tract, all of which are furnishes maximum torque and/or power. promoted by low temperatures. To com- pensate for these negative factors, and to Acceleration and deceleration facilitate cold starting, supplementary fuel The fuel’s vaporization potential is strongly must be injected into the engine. affected by pressure levels inside the intake manifold. Sudden variations in Post-start phase manifold pressure of the kind encountered Following low-temperature starts, in response to rapid changes in throttle- supplementary fuel is required for a brief valve aperture cause fluctuations in the period, until the combustion chamber fuel layer on the walls of the intake tract. heats up and improves the internal Spirited acceleration leads to higher mixture formation. This richer mixture manifold pressures. The fuel responds also increases torque to furnish a with lower vaporization rates and the fuel smoother transition to the desired idle layer within the manifold runners expands. speed. A portion of the injected fuel is thus lost in wall condensation, and the engine goes Warm-up phase lean for a brief period, until the fuel layer The warm-up phase follows on the heels restabilizes. In an analogous, but inverted, of the starting and immediate post-start response pattern, sudden deceleration phases. At this point the engine still leads to rich mixtures. A temperature- requires an enriched mixture to offset the sensitive correction function (transition fuel condensation on the intake-manifold compensation) adapts the mixture to walls. Lower temperatures are synony- maintain optimal operational response mous with less efficient fuel proces- and ensure that the engine receives the sing (owing to factors such as poor mix- consistent air/fuel mixture needed for ing of air and fuel and reduced fuel va- efficient catalytic-converter performance. porization). This promotes fuel precip- itation within the intake manifold, with Trailing throttle (overrun) the formation of condensate fuel that will Fuel metering is interrupted during trailing only vaporize later, once temperatures throttle. Although this expedient saves have increased. These factors make it fuel on downhill stretches, its primary necessary to provide progressive mixture purpose is to guard the catalytic converter enrichment in response to decreasing against overheating stemming from poor temperatures. and incomplete combustion (misfiring). 9
Gasoline- injection systems Gasoline-injection systems Carburetors and gasoline-injection sys- Representative examples are the various tems are designed for a single purpose: versions of the KE and L-Jetronic systems To supply the engine with the optimal air- (Figure 1). fuel mixture for any given operating conditions. Gasoline injection systems, Mechanical injection systems and electronic systems in particular, are The K-Jetronic system operates by better at maintaining air-fuel mixtures injecting continually, without an exter- within precisely defined limits, which nal drive being necessary. Instead of translates into superior performance in being determined by the injection valve, the areas of fuel economy, comfort and fuel mass is regulated by the fuel convenience, and power. Increasingly distributor. stringent mandates governing exhaust emissions have led to a total eclipse of the Combined mechanical-electronic carburetor in favor of fuel injection. fuel injection Although current systems rely almost Although the K-Jetronic layout served as exclusively on mixture formation outside the mechanical basis for the KE-Jetronic the combustion chamber, concepts based system, the latter employs expanded on internal mixture formation – with fuel data-monitoring functions for more being injected directly into the combustion precise adaptation of injected fuel chamber – were actually the foundation quantity to specific engine operating for the first gasoline-injection systems. As conditions. these systems are superb instruments for achieving further reductions in fuel Electronic injection systems consumption, they are now becoming an Injection systems featuring electronic increasingly significant factor. control rely on solenoid-operated injection Fig. 1 Multipoint fuel injection (MPI) Overview 1 Fuel, 2 2 Air, 3 Throttle valve, Systems with 4 Intake manifold, 3 5 Injectors, external mixture formation 6 Engine. 4 The salient characteristic of this type of system is the fact that it forms the air-fuel mixture outside the combustion chamber, 1 inside the intake manifold. 5 Multipoint fuel injection Multipoint fuel injection forms the ideal basis for complying with the mixture- formation criteria described above. In this UMK0662-2Y type of system each cylinder has its own injector discharging fuel into the area 6 10 directly in front of the intake valve.
valves for intermittent fuel discharge. The combination of air and fuel common to Overview actual injected fuel quantity is regulated conventional injection systems. This is one by controlling the injector's opening time of the new system's prime advantages: It (with the pressure-loss gradient through banishes all potential for fuel condensation the valve being taken into account in within the runners of the intake manifold. calculations as a known quantity). External mixture formation usually Examples: L-Jetronic, LH-Jetronic, and provides a homogenous, stoichiometric air- Motronic as an integrated engine-manage- fuel mixture throughout the entire ment system. combustion chamber. In contrast, shifting the mixture-preparation process into the Single-point fuel injection combustion chamber provides for two Single-point (throttle-body injection (TBI)) distinctive operating modes: fuel injection is the concept behind this With stratified-charge operation, only the electronically-controlled injection system mixture directly adjacent to the spark plug in which a centrally located solenoid- needs to be ignitable. The remainder of the operated injection valve mounted air-fuel charge in the combustion chamber upstream from the throttle valve sprays can consist solely of fresh and residual fuel intermittently into the manifold. Mono- gases, without unburned fuel. This strategy Jetronic and Mono-Motronic are the furnishes an extremely lean overall mixture Bosch systems in this category (Figure 2). for idling and part-throttle operation, with commensurate reductions in fuel consumption. Systems for internal Homogenous operation reflects the mixture formation conditions encountered in external mixture Direct-injection (DI) systems rely on formation by employing uniform solenoid-operated injection valves to spray consistency for the entire air-fuel charge fuel directly into the combustion chamber; throughout the combustion chamber. the actual mixture-formation process takes Under these conditions all of the fresh air place within the cylinders, each of which within the chamber participates in the has its own injector (Figure 3). Perfect combustion process. This operational atomization of the fuel emerging from the mode is employed for WOT operation. injectors is vital for efficient combustion. MED-Motronic is used for closed-loop Under normal operating conditions, DI control of DI gasoline engines. engines draw in only air instead of the Fig. 2 Fig. 3 Throttle-body fuel injection (TBI) Direct fuel injection (DI) 1 Fuel, 2 1 Fuel, 2 Air, 2 Air, 3 Throttle valve, 3 Throttle valve 2 4 Intake manifold, 3 (ETC), 5 Injector, 4 Intake manifold, 6 Engine. 5 Injectors, 3 4 6 Engine. 4 1 1 5 5 UMK0663-2Y UMK1687-2Y 6 6 11
The story of fuel injection The story of fuel injection injection system: the intake-pressure- The story of fuel injection extends controlled D-Jetronic! back to cover a period of almost one In 1973 the air-flow-controlled L-Jetro- hundred years. nic appeared on the market, at the The Gasmotorenfabik Deutz was same time as the K-Jetronic, which fea- manufacturing plunger pumps for in- tured mechanical-hydraulic control and jecting fuel in a limited production was also an air-flow-controlled system. series as early as 1898. In 1976, the K-Jetronic was the first A short time later the uses of the ven- automotive system to incorporate a turi-effect for carburetor design were Lambda closed-loop control. discovered, and fuel-injection systems 1979 marked the introduction of a new based on the technology of the time system: Motronic, featuring digital pro- ceased to be competitive. cessing for numerous engine func- Bosch started research on gasoline- tions. This system combined L-Jetro- injection pumps in 1912. The first nic with electronic program-map con- aircraft engine featuring Bosch fuel in- trol for the ignition. The first automo- jection, a 1,200-hp unit, entered series tive microprocessor! production in 1937; problems with car- In 1982, the K-Jetronic model became buretor icing and fire hazards had lent available in an expanded configura- special impetus to fuel-injection devel- tion, the KE-Jetronic, including an opment work for the aeronautics field. electronic closed-loop control circuit This development marks the begin- and a Lambda oxygen sensor. ning of the era of fuel injection at These were joined by Bosch Mono- Bosch, but there was still a long path Jetronic in 1987: This particularly cost- to travel on the way to fuel injection for efficient single-point injection unit passenger cars. made it feasible to equip small vehicles 1951 saw a Bosch direct-injection unit with Jetronic, and once and for all made being featured as standard equipment the carburetor absolutely superfluous. on a small car for the first time. Sev- By the end of 1997, around 64 million eral years later a unit was installed in Bosch engine-management systems the 300 SL, the legendary production had been installed in countless types of sports car from Daimler-Benz. vehicles since the introduction of the In the years that followed, develop- D-Jetronic in 1967. In 1997 alone, the ment on mechanical injection pumps figure was 4.2 million, comprised of continued, and ... 1 million throttle-body injection (TBI) In 1967 fuel injection took another systems and 3.2 million multipoint fuel- giant step forward: The first electronic injection (MPI) systems. Bosch gasoline fuel injection from the year 1954 12
K-Jetronic Fuel supply An electrically driven fuel pump delivers K-Jetronic the fuel to the fuel distributor via a fuel System overview accumulator and a filter. The fuel distribu- tor allocates this fuel to the injection The K-Jetronic is a mechanically and valves of the individual cylinders. hydraulically controlled fuel-injection sys- tem which needs no form of drive and Air-flow measurement which meters the fuel as a function of the The amount of air drawn in by the engine intake air quantity and injects it contin- is controlled by a throttle valve and uously onto the engine intake valves. measured by an air-flow sensor. Specific operating conditions of the engine require corrective intervention in Fuel metering mixture formation and this is carried out The amount of air, corresponding to the by the K-Jetronic in order to optimize position of the throttle plate, drawn in by starting and driving performance, power the engine serves as the criterion for output and exhaust composition. Owing metering of the fuel to the individual to the direct air-flow sensing, the K-Je- cylinders. The amount of air drawn in by tronic system also allows for engine the engine is measured by the air-flow variations and permits the use of facilities sensor which, in turn, controls the fuel for exhaust-gas aftertreatment for which distributor. The air-flow sensor and the precise metering of the intake air quantity fuel distributor are assemblies which is a prerequisite. form part of the mixture control unit. The K-Jetronic was originally designed Injection occurs continuously, i.e. without as a purely mechanical injection system. regard to the position of the intake valve. Today, using auxiliary electronic equip- During the intake-valve closed phase, the ment, the system also permits the use of fuel is “stored”. Mixture enrichment is lambda closed-loop control. controlled in order to adapt to various The K-Jetronic fuel-injection system operating conditions such as start, warm- covers the following functional areas: up, idle and full load. In addition, supple- – Fuel supply, mentary functions such as overrun fuel – Air-flow measurement and cutoff, engine-speed limiting and closed- – Fuel metering. loop lambda control are possible. Fig. 1 Functional schematic of the K-Jetronic Electric Fuel fuel pump accumulator Fuel filter Fuel Air filter Air-flow Mixture Fuel Air sensor control unit distributor Throttle valve Injection valves Mixture Intake ports UMK0009E Combustion chamber 13
Gasoline- Fuel supply available. This avoids the formation of injection fuel-vapor bubbles and achieves good systems The fuel supply system comprises hot starting behavior. – Electric fuel pump, – Fuel accumulator, Electric fuel pump – Fine filter, The electric fuel pump is a roller-cell – Primary-pressure regulator and pump driven by a permanent-magnet – Injection valves. electric motor. An electrically driven roller-cell pump The rotor plate which is eccentrically pumps the fuel from the fuel tank at a mounted in the pump housing is fitted pressure of over 5 bar to a fuel accu- with metal rollers in notches around its mulator and through a filter to the fuel circumference which are pressed against distributor. From the fuel distributor the the pump housing by centrifugal force fuel flows to the injection valves. The and act as rolling seals. The fuel is car- injection valves inject the fuel con- ried in the cavities which form between tinuously into the intake ports of the the rollers. The pumping action takes engine. Thus the system designation K place when the rollers, after having (taken from the German for continuous). closed the inlet bore, force the trapped When the intake valves open, the mixture fuel in front of them until it can escape is drawn into the cylinder. from the pump through the outlet bore The fuel primary-pressure regulator (Figure 4). The fuel flows directly around maintains the supply pressure in the the electric motor. There is no danger of system constant and reroutes the excess explosion, however, because there is fuel back to the fuel tank. never an ignitable mixture in the pump Owing to continual scavenging of the fuel housing. supply system, there is always cool fuel Fig. 2 Schematic diagram of the K-Jetronic system with closed-loop lambda control 1 Fuel tank, 2 Electric fuel pump, 3 Fuel accumulator, 4 Fuel filter, 5 Warm-up regulator, 6 Injection valve, 7 Intake manifold, 8 Cold-start valve, 9 Fuel distributor, 10 Air-flow sensor, 11 Timing valve, 12 Lambda sensor, 13 Thermo-time switch, 14 Ignition distributor, 15 Auxiliary-air device, 16 Throttle-valve switch, 17 ECU, 18 Ignition and starting switch, 19 Battery. 1 3 5 2 4 11 6 8 7 9 13 14 12 10 15 16 17 BOSCH 18 19 UMK0077Y 14
The electric fuel pump delivers more fuel Electric fuel pump K-Jetronic than the maximum requirement of the 1 Suction side, 2 Pressure limiter, 3 Roller-cell engine so that compression in the fuel pump, 4 Motor armature, 5 Check valve, system can be maintained under all oper- 6 Pressure side. ating conditions. A check valve in the 2 3 4 5 pump decouples the fuel system from the fuel tank by preventing reverse flow of fuel to the fuel tank. 1 6 The electric fuel pump starts to operate UMK0121-2Y immediately when the ignition and start- ing switches are operated and remains switched on continuously after the engine Fig. 3 has started. A safety circuit is incorpor- Fig. 4 ated to stop the pump running and, thus, Operation of roller-cell pump to prevent fuel being delivered if the ig- 1 Suction side, 2 Rotor plate, 3 Roller, nition is switched on but the engine has 4 Roller race plate, 5 Pressure side. stopped turning (for instance in the case 2 3 4 of an accident). The fuel pump is located in the imme- diate vicinity of the fuel tank and requires 1 5 no maintenance. UMK0120-2Y Fuel accumulator The fuel accumulator maintains the pressure in the fuel system for a certain Fig. 5 time after the engine has been switched Fuel accumulator off in order to facilitate restarting, parti- a Empty, b Full. cularly when the engine is hot. The spe- 1 Spring chamber, 2 Spring, 3 Stop, 4 Diaphragm, cial design of the accumulator housing 5 Accumulator volume, 6 Fuel inlet or outlet, 7 Connection to the atmosphere. (Figure 5) deadens the sound of the fuel pump when the engine is running. a 1 2 3 4 5 The interior of the fuel accumulator is divided into two chambers by means of a diaphragm. One chamber serves as the accumulator for the fuel whilst the other represents the compensation volume 7 6 and is connected to the atmosphere or to the fuel tank by means of a vent fitting. During operation, the accumulator chamber is filled with fuel and the dia- phragm is caused to bend back against the force of the spring until it is halted by the stops in the spring chamber. The b diaphragm remains in this position, which corresponds to the maximum accumu- lator volume, as long as the engine is running. UMK1653Y 15
Gasoline- Fuel filter Fuel filter injection The fuel filter retains particles of dirt 1 Paper element, systems which are present in the fuel and which 2 Strainer, 3 Support 1 2 3 would otherwise have an adverse effect plate. on the functioning of the injection system. The fuel filter contains a paper element with a mean pore size of 10 µm backed up by a fluff trap. This combination UMK0119Y ensures a high degree of cleaning. The filter is held in place in the housing by means of a support plate. It is fitted in the fuel line downstream from the fuel Fig. 6 accumulator and its service life depends delivery drops slightly, the plunger is upon the amount of dirt in the fuel. It is shifted by the spring to a corresponding imperative that the arrow on the filter new position and in doing so closes off housing showing the direction of fuel flow the port slightly through which the excess through the filter is observed when the fuel returns to the tank. This means that filter is replaced. less fuel is diverted off at this point and the system pressure is controlled to its Primary-pressure regulator specified level. The primary-pressure regulator main- When the engine is switched off, the fuel tains the pressure in the fuel system pump also switches off and the primary constant. pressure drops below the opening pres- It is incorporated in the fuel distributor sure of the injection valves. The pressure and holds the delivery pressure (system regulator then closes the return-flow port pressure) at about 5 bar. The fuel pump and thus prevents the pressure in the fuel always delivers more fuel than is required system from sinking any further (Fig. 8). by the vehicle engine, and this causes a plunger to shift in the pressure regulator Fuel-injection valves and open a port through which excess The injection valves open at a given pres- fuel can return to the tank. sure and atomize the fuel through oscilla- The pressure in the fuel system and the tion of the valve needle. The injection force exerted by the spring on the valves inject the fuel metered to them into pressure-regulator plunger balance each the intake passages and onto the intake other out. If, for instance, fuel-pump valves. They are secured in special Fig. 7 Primary-pressure regulator fitted to fuel distributor a In rest position, b In actuated position. 1 System-pressure entry, 2 Seal, 3 Return to fuel tank, 4 Plunger, 5 Spring. a b 1 UMK1495Y 2 3 4 5 16
holders to insulate them against the heat Pressure curve after engine switchoff K-Jetronic radiated from the engine. The injection Firstly pressure falls from the normal system valves have no metering function them- pressure (1) to the pressure-regulator closing selves, and open of their own accord pressure (2). The fuel accumulator then causes it to increase to the level (3) which is below the when the opening pressure of e.g. 3.5 opening pressure (4) of the injection valves. bar is exceeded. They are fitted with a bar valve needle (Fig. 9) which oscillates 1 (“chatters”) audibly at high frequency when fuel is injected. This results in ex- cellent atomization of the fuel even with 4 Pressure p 3 the smallest of injection quantities. When the engine is switched off, the injection 2 valves close tightly when the pressure in UMK0018E the fuel-supply system drops below their opening pressure. This means that no ms more fuel can enter the intake passages Time t once the engine has stopped. Fig. 8 Fig. 9 Fuel-injection valve Air-shrouded fuel-injection valves a In rest position, Air-shrouded injection valves improve the b In actuated position. mixture formation particularly at idle. 1 Valve housing, 2 Filter, Using the pressure drop across the 3 Valve needle, throttle valve, a portion of the air inducted 4 Valve seat. 1 by the engine is drawn into the cylinder through the injection valve (Fig. 20): The result is excellent atomization of the fuel at the point of exit (Fig. 10). Air-shrouded injection valves reduce fuel consumption 2 and toxic emission constituents. UMK0069-2Y 3 4 a b Fig. 10 Spray pattern of an injection valve without air-shrouding (left) and with air-shrouding (right). UMK0042Y UMK0041Y 17
Gasoline- Fuel metering Principle of the air-flow sensor injection a Small amount of air drawn in: sensor plate only systems The task of the fuel-management system lifted slightly, b Large amount of air drawn in: is to meter a quantity of fuel corre- sensor plate is lifted considerably further. sponding to the intake air quantity. Basically, fuel metering is carried out a by the mixture control unit. This com- prises the air-flow sensor and the fuel distributor. In a number of operating modes however, h the amount of fuel required deviates greatly from the “standard” quantity and it becomes necessary to intervene in the b mixture formation system (see section “Adaptation to operating conditions”). h UMK0072Y Air-flow sensor The quantity of air drawn in by the engine is a precise measure of its operating Fig. 11 load. The air-flow sensor operates ac- cording to the suspended-body principle, air-fuel mixture. Since the air drawn in by and measures the amount of air drawn in the engine must pass through the air-flow by the engine. sensor before it reaches the engine, this The intake air quantity serves as the means that it has been measured and main actuating variable for determining the control signal generated before it the basic injection quantity. It is the actually enters the engine cylinders. The appropriate physical quantity for deriving result is that, in addition to other the fuel requirement, and changes in the measures described below, the correct induction characteristics of the engine mixture adaptation takes place at all have no effect upon the formation of the times. Fig. 12 Updraft 1 2 3 4 5 air-flow sensor a Sensor plate in its zero position, a b Sensor plate in its operating position. 1 Air funnel, 2 Sensor plate, 3 Relief cross-section, 4 Idle-mixture adjusting screw, 5 Pivot, 6 Lever, 7 Leaf spring. 7 6 b UMK1654Y 18
The air-flow sensor is located upstream Barrel with metering slits K-Jetronic of the throttle valve so that it measures all 1 Intake air, 2 Control pressure, 3 Fuel inlet, the air which enters the engine cylinders. 4 Metered quantity of fuel, 5 Control plunger, It comprises an air funnel in which the 6 Barrel with metering slits, 7 Fuel distributor. sensor plate (suspended body) is free to 7 pivot. The air flowing through the funnel 2 deflects the sensor plate by a given ,,,,, ,,,,, amount out of its zero position, and this 5 ,,,,, 6 4 ,,,, ,,,, 4 ,,,,,,,,,,,,,,,, movement is transmitted by a lever sys- ,,,, ,,,, ,,,, ,,,, ,,,, ,,,, , ,,,, ,,, ,,,,,,,,,,,,,,,, tem to a control plunger which deter- 3 ,,,, ,,,, , ,,, ,,,, ,,,,,,,,,,,,,,,, mines the basic injection quantity re- ,,,,,,,,,,,,,,,, quired for the basic functions. Consider- ,,,,,,,,,,,,,,,, able pressure shocks can occur in the ,,,,,,,,,,,,,,,, intake system if backfiring takes place in ,,,,,,,,,,,,,,,, the intake manifold. For this reason, the 1 ,,,,,,,,,,,,,,,, air-flow sensor is so designed that the UMK1496Y ,,,,,,,,,,,,,,,, sensor plate can swing back in the opposite direction in the event of misfire, and past its zero position to open a relief Fig. 13 cross-section in the funnel. A rubber buffer limits the downward stroke (the Fuel distributor upwards stroke on the downdraft air-flow Depending upon the position of the plate sensor). A counterweight compensates in the air-flow sensor, the fuel distributor for the weight of the sensor plate and meters the basic injection quantity to the lever system (this is carried out by an individual engine cylinders. The position extension spring on the downdraft air- of the sensor plate is a measure of the flow sensor). A leaf spring ensures the amount of air drawn in by the engine. The correct zero position in the switched-off position of the plate is transmitted to the phase. control plunger by a lever. Fig. 14 Barrel with metering slits and control plunger a Zero (inoperated position), b Part load, c Full load. 1 Control pressure, 2 Control plunger, 3 Metering slit in the barrel, 4 Control edge, 5 Fuel inlet, 6 Barrel with metering slits. ,,,,,, ,,,,,, ,,,,,, a ,,,,,, b ,,,,,, c ,,,,,, ,,,,,, 1 ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, ,,,,,, 2 ,,,,, , , ,,,,,,, ,,,,, ,,,,, , , , ,,,,,, ,,,,,, ,, ,,,, 3 ,,,,,,,,, ,,,,, ,,,, 4 , , , , , , , ,, ,,,,, , , , , ,,,,, ,,,, ,,,,, , ,,,,, , , , ,,,,,,,,,,,,, ,,,, , , , , ,,,, , , ,,,,,, ,,,,,, , , ,,,,, ,,,,, , , , ,,,, , , ,,,, ,,,, ,,,, ,,,, 5 6 UMK1497Y 19
Gasoline- Depending upon its position in the barrel Barrel with metering slits injection with metering slits, the control plunger The slits are shown enlarged (the actual slit is systems opens or closes the slits to a greater or about 0.2 mm wide). lesser extent. The fuel flows through the open section of the slits to the differential pressure valves and then to the fuel injection valves. If sensor-plate travel is only small, then the control plunger is lifted only slightly and, as a result, only a small section of the slit is opened for the passage of fuel. With larger plunger travel, the plunger opens a larger section of the slits and more fuel can flow. There is a linear relationship between sensor- plate travel and the slit section in the barrel which is opened for fuel flow. A hydraulic force generated by the so- called control pressure is applied to the control plunger. It opposes the movement UMK0044Y resulting from sensor-plate deflection. One of its functions is to ensure that the control plunger follows the sensor-plate Fig. 15 movement immediately and does not, for instance, stick in the upper end position the air drawn in by the engine can deflect when the sensor plate moves down again. the sensor plate further. This results in Further functions of the control pressure the control plunger opening the metering are discussed in the sections “Warm-up slits further and the engine being allo- enrichment” and “Full-load enrichment”. cated more fuel. On the other hand, if the control pressure is high, the air drawn in Control pressure by the engine cannot deflect the sensor The control pressure is tapped from the plate so far and, as a result, the engine primary pressure through a restriction receives less fuel. In order to fully seal off bore (Figure 16). This restriction bore the control-pressure circuit with absolute serves to decouple the control-pressure certainty when the engine has been circuit and the primary-pressure circuit switched off, and at the same time to from one another. A connection line joins maintain the pressure in the fuel circuit, the fuel distributor and the warm-up the return line of the warm-up regulator is regulator (control-pressure regulator). fitted with a check valve. This (push-up) When starting the cold engine, the valve is attached to the primary-pressure control pressure is about 0.5 bar. As the regulator and is held open during oper- engine warms up, the warm-up regulator ation by the pressure-regulator plunger. increases the control pressure to about When the engine is switched off and the 3.7 bar (Figure 26). plunger of the primary-pressure regulator The control pressure acts through a returns to its zero position, the check damping restriction on the control valve is closed by a spring (Figure 17). plunger and thereby develops the force which opposes the force of the air in the Differential-pressure valves air-flow sensor. In doing so, the restric- The differential-pressure valves in the tion dampens a possible oscillation of the fuel distributor result in a specific pres- sensor plate which could result due to sure drop at the metering slits. pulsating air-intake flow. The air-flow sensor has a linear charac- The control pressure influences the fuel teristic. This means that if double the 20 distribution. If the control pressure is low, quantity of air is drawn in, the sensor-
Primary pressure and control pressure 3 ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, K-Jetronic 1 Control-pressure 2 ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, effect (hydraulic ,,,,,,,,,,,,,,,,,,,,, force), 1 ,,,,,,,,,,,,,,,,,,,,, 2 Damping restriction, ,,,,,,,,,,,,,,,,,,,,, 3 Line to warm-up regulator, ,,,,,,,,,,,,,,,,,,,,, 4 Decoupling restric- ,,,,,,,,,,,,,,,,,,,,, tion bore, ,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, 5 Primary pressure (delivery pressure), 6 Effect of air pressure. ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,, , , , , , ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, , , , , , ,,,,,,,,, , , , , , , , , , , ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,, 4 UMK1498Y 6 5 Fig. 16 Fig. 17 Primary-pressure regulator with push- up valve in the a control-pressure circuit a In zero (inoperated) position, b In operating position. 1 Primary pressure intake, 2 Return (to fuel tank), 3 Plunger of the primary-pressure regulator, 4 Push-up valve, 5 Control-pressure b ,,,,, ,,,,, ,,,,, intake (from warm- up regulator). 1 5 ,,,,, ,,,,, UMK1499Y 2 3 4 plate travel is also doubled. If this travel is The differential-pressure valves main- to result in a change of delivered fuel in tain the differential pressure between the the same relationship, in this case double upper and lower chamber constant re- the travel equals double the quantity, gardless of fuel throughflow. The differ- then a constant drop in pressure must ential pressure is 0.1 bar. be guaranteed at the metering slits The differential-pressure valves achieve (Figure 14), regardless of the amount of a high metering accuracy and are of the fuel flowing through them. flat-seat type. They are fitted in the fuel 21
Gasoline- ,,, Differential-pressure valve injection ,,, systems a Diaphragm ,,, position with a low injected fuel quantity ,,,,,,,, ,, ,,,,,,,, , ,,,,,,,, ,,,,,,,, , ,,,,,,,, b Diaphragm position with a large injected fuel quantity ,,, ,,, ,,,,,,,, , ,,,,,,,, ,, ,,,,,,,, , ,,,,,,,, ,,,,,,,, UMK1656Y Fig. 18 distributor and one such valve is allo- is located in the upper chamber. Each cated to each metering slit. A diaphragm upper chamber is connected to a separates the upper and lower chambers metering slit and its corresponding con- of the valve (Figures 18 and 19). The nection to the fuel-injection line. The lower chambers of all the valves are con- upper chambers are completely sealed nected with one another by a ring main off from each other. The diaphragms are and are subjected to the primary pres- spring-loaded and it is this helical spring 22 sure (delivery pressure). The valve seat that produces the pressure differential.
Fuel distributor with differential-pressure valves K-Jetronic 1 Fuel intake (primary 2 3 4 5 6 pressure), 2 Upper chamber of the differential- ,,,, pressure valve, ,,,, 3 Line to the fuel- injection valve (injection pressure), 4 Control plunger, ,,,, 5 Control edge and metering slit, 6 Valve spring, ,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,, 7 Valve diaphragm, ,,,,,,,,,,,,,,,,,,,, 8 Lower chamber of the differential- pressure valve. 1 ,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,, UMK1602Y 8 7 Fig. 19 Fig. 20 If a large basic fuel quantity flows into the Mixture formation with air-shrouded fuel- upper chamber through the metering slit, injection valve the diaphragm is bent downwards and 1 Fuel-injection valve, 2 Air-supply line, enlarges the valve cross-section at the 3 Intake manifold, 4 Throttle valve. outlet leading to the injection valve until the set differential pressure once again prevails. 1 2 3 4 If the fuel quantity drops, the valve cross- section is reduced owing to the equilib- rium of forces at the diaphragm until the differential pressure of 0.1 bar is again present. ÀÀÀ ,,, @@@ This causes an equilibrium of forces to ,,, @@@ ÀÀÀ prevail at the diaphragm which can be ,, @@ ÀÀ ,, @@ ÀÀ maintained for every basic fuel quantity ,, @@ ÀÀ by controlling the valve cross-section. ,, @@ ÀÀ ,, @@ ÀÀ ,, @@ ÀÀ ,, @@ ÀÀ UMK0068Y Mixture formation ,, @@ ÀÀ The formation of the air-fuel mixture ,, @@ ÀÀ takes place in the intake ports and ,, @@ ÀÀ cylinders of the engine. The continually injected fuel coming from Air-shrouded fuel-injection valves favor the injection valves is “stored” in front of mixture formation since they atomize the intake valves. When the intake valve the fuel very well at the outlet point is opened, the air drawn in by the engine (Figures 10, 20). carries the waiting “cloud” of fuel with it into the cylinder. An ignitable air-fuel mixture is formed during the induction stroke due to the swirl effect. 23
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