Fuel inlet Intake port Fuel sump Spill port Plunger 20 10 0. Control rack Toothed control sleeve. Lug attached to plunger Housing Plunger return spring.
Plungers Fig. Fuel inlet Transfer pump Delivery port. Cam ring Roller and shoe. Quantity of fuel delivered increases with load causing excessive carbon deposits and high exhaust temperature. Drastic reduction in load will cause over speeding to dangerous values. It is the duty of an injection pump governor to take care of the above limitations.
Governors are generally of two types,. The working principle of mechanical governor is illustrated in Fig. This causes the bell crank levers to raise the sleeve and operate the control lever in down- ward direction. This actuates the control rack on the fuel-injection pump in a direction which reduces the amount of fuel delivered. Fulcrum Sleeve Lever. Lever to operate Governor shaft control rack Fig. The details of a pneumatic governor is shown in Fig.
A diaphragm is con- nected to the fuel pump control rack. Therefore, position of the accelerator pedal also determines the position of the pump control rack and hence the amount of fuel injected. Quick and complete combustion is ensured by a well designed fuel injector. The injector assembly consists of. A cross sectional view of a typical Bosch fuel injector is shown in Fig. Venturi control unit Vacuum pipe. Fuel to injector Control rack Idling spring Diaphragm unit.
Fuel injection pump Idling spring adjuster Diaphragm spring Diaphragm Fig. After, fuel from the delivery pump gets exhausted, the spring pressure pushes the nozzle valve back on its seat. The spring tension and hence the valve opening pressure is controlled by adjusting the screw provided at the top.
Nozzle is that part of an injector through which the liquid fuel is sprayed into the combustion chamber. End cap Adjusting screw Lock nut. Nozzle valve Fuel passage Nozzle body. This is necessary because fuel striking the walls decomposes and produces carbon deposits.
This causes smoky exhaust as well as increase in fuel consumption. The fuel must then be properly distributed, or dispersed, in the desired areas of the chamber. In this phase, the injection pressure, the density of the air in the cylinder and the physical qualities of the fuel in use, as well as the nozzle design, become important factors.
Higher injection pressure results in better dispersion as well as greater penetration of the fuel into all locations in the chamber where is presence is desired. The physical qualities of the fuel itself, such as viscosity, surface tension, etc. The nozzle must spray the fuel into the chamber in such a manner as to minimize the quantity of fuel reaching the surrounding walls. Any fuel striking the walls tends to decompose, producing carbon deposits, unpleasant odour and a smoky exhaust, as well as an increase in fuel consumption.
The design of the nozzle is closely interrelated to the type of combustion chamber used. The non-turbulent type of combustion chamber, on the other hand, depends almost entirely on both the nozzle design and injection pressure to secure the desired mixing in the combustion chamber; consequently, with this type of chamber, the nozzle must accomplish the ad- ditional function of mixing the fuel and air.
Various types of nozzles are used in CI engines. These types are shown in Fig. The most common types are: i the pintle nozzle, ii the single hole nozzle iii the multi-hole nozzle, iv pintaux nozzle i Pintle Nozzle : The stem of the nozzle valve is extended to form a pin or pintle which protrudes through the mouth of the nozzle [Fig. The size and shape of the pintle can be varied according to the require- ment.
It provides a spray operating at low injection pressures of MPa. Advantage of this nozzle is that it avoids weak injection and dribbling. It prevents the carbon deposition on the nozzle hole. The size of the hole is usually of the order of 0. Major disadvantage with such nozzle is that they tend to dribble. Besides, their spray angle is too narrow to facilitate good mixing unless higher velocities are used.
These nozzles operate at high injection pressures of the order of 18 MPa. Their advantage lies in the ability to distribute the fuel properly even with lower air motion available in open combustion chambers. Auxiliary hole d Pintaux. It injects a small amount of fuel through this additional hole which is called pilot injection in the upstream direction slightly before the main injection.
The needle valve does not lift fully at low speeds and most of the fuel is injected through the auxiliary hole.
Main advantage of this nozzle is better cold starting performance. A major drawback of this nozzle is that its injection characteristics are poorer than the multihole nozzle. Therefore single droplets are formed as in Fig. It is given by the following equation.
Larger droplets provide a higher penetration into the chamber but smaller droplets are required for quick mixing and evaporation of the fuel. The diameter of most of the droplets in a fuel spray is less than 5 microns. The droplet sizes depends on various factors which are listed below:.
The volume of the fuel injected per second, Q, is given by. Increasing the rate of injection decreases the duration of injection for a given fuel input and subsequently introduces a change in injection timing. A higher rate of injection may permit injection timing to be retarded from optimum value. This helps in maintaining fuel economy without excessive smoke emission.
However, an increase in injection rate requires an increased injection pressure and increases the load on the injector push rod and the cam. Fuel-injection systems are commonly used in CI engines. Presently gasoline injection system is coming into vogue in SI engines because of the following drawbacks of the carburetion.
A gasoline injection system eliminates all these drawbacks. The injection of fuel into an SI engine can be done by employing any of the following methods which are shown in Fig.
There are two types of gasoline injection systems, viz. It is adopted when manifold injection is contemplated. Injection timing is not a critical factor in SI engines.
It is believed that the petrol injection has a promising future compared to carburetion and may replace carburetor in the near future. Calculate the quantity of fuel to be injected per cycle per cylinder. The pressure in the combustion chamber is 40 bar. The bsf c is 0. At the beginning of injec- tion pressure is 30 bar and the maximum cylinder pressure is 50 bar. The injection is expected to be at bar and maximum pressure at the injector is set to be about bar. The injection pressure is bar and the average pressure of charge during injection is 25 bar, when the needle cone is fully lifted up.
If an injection pressure of bar had been used, what would have been the time taken to penetrate the same dis- tance. The combustion chamber pressure is 25 bar. Each cylinder has a separate fuel pump, injector and pipe line. If the average injector pressure is bar and average pressure of charge during injection is 40 bar, calculate the displacement volume of one plunger per cycle and power lost in pumping fuel to the engine for all cylinders.
Power lost for pumping the fuel 6. The diameter and the length of the fuel line from pump to injector is 2. The fuel in the injection valve is 2 cc. Assume a pump inlet pressure of 1 bar. Why the air injection system is not used nowadays?
With a neat sketch explain the various components of a fuel feed system of a CI engine. What are two types of injection pump that are commonly used? What are the two major type of governors?
Mention the various parts of a injector assembly. With sketches explain the various types of nozzles. The pressure in the combustion chamber is 38 bar.
At the beginning of in- jection, pressure is 35 bar and the maximum cylinder pressure is 55 bar. The injection is expected to be at bar and maximum pres- sure at the injector is set to be about bar. The combustion chamber pressure is 30 bar. If the average injector pressure is bar and average pressure of charge during injection is 30 bar, calculate the displacement volume of one plunger per cycle and power lost in pumping fuel to the engine for all cylinders. Ans: i Disp. The diameter of the fuel line from pump to injector is 3 mm and is mm long.
The fuel in the injection valve is 3 cc. Injection system in which the pump and the injector nozzle is combined in one housing is known as.
Ans: 1. The year is a memorable year in the history of IC engine development. Therefore, the injection system for gasoline engines is not a new proposition.
In case of automotive engines a continuous metered quantity of the gasoline- air mixture must be ensured to make the engine run smoothly. In a gasoline injection system, the fuel is injected into the intake manifold or near the intake port through an injector. Compared to carburetion the mixing of gasoline with the air stream is better in this case. Nowadays, gasoline injection is employed in a number of automobiles. Figure 9. As may be noticed that the intake valve is open in cylinder 2.
As can also be observed the gasoline moves to the end of the manifold and accumulates there. This enriches the mixture going to the end cylinders. However, the central cylin- ders, which are very close to the carburettor, get the leanest mixture. Thus the various cylinders receive the air-gasoline mixture in varying quantities and richness. This problem is called the maldistribution and can be solved by the port injection system by having the same amount of gasoline injected at each intake manifold.
Therefore, there is an urgent need to develop injection systems for gasoline engines. By adopting gasoline injection each cylinder can get the same richness of the air-gasoline mixture and the maldistribution can be avoided to a great extent. Accumulation of Large gasoline droplets Air gasoline mixture liquid gasoline.
As already mentioned, some of the recent automotive engines are equipped with gasoline injection system, instead of a carburetion for one or more of the following reasons:. The above fuel injection systems can be grouped under two heads, viz.
In the single point injection system, one or two injectors are mounted inside the throttle body assembly. Fuel sprays are directed at one point or at the center of the intake manifold. Another name of the single point injection is throttle body injection. Multipoint injection has one injector for each engine cylinder. In this system, fuel is injected in more than one location. This is more common and is often called port injection system.
As already mentioned the gasoline fuel injection system used in a spark- ignition engine can be either of continuous injection or timed injection. Electronic Injection Systems The pump maintains a fuel line gauge pressure of about 0. The system injects the fuel through a nozzle located in the manifold immediately downstream of the throttle plate. In a supercharged engine, fuel is injected at the entrance of the supercharger.
The timing and duration of the fuel injection is determined by Electronic Control Unit ECU depending upon the load and speed. A fuel metering or injection pump and a nozzle are the other parts of the system. The nozzle injects the fuel in the manifold or the cylinder head port at about 6. Timed injection system injects fuel usually during the early part of the suction stroke.
During maximum power operation injection begins after the closure of the exhaust valve and ends usually after BDC. Direct in-cylinder injection is superior and always desirable and better compared to manifold injection.
However, it was noticed that direct injection caused oil dilution in the frequent warm up phases if the car is used for daily transportation. Typical fuel injection methods used in four stroke and two stroke gasoline engines are shown in Fig. At the same time it must maintain the required air-fuel ratio as per the load and speed requirement of the engine.
To achieve all the above tasks, a number of components are required in the fuel injection system, the functions of which are mentioned below. Low pressure Low pressure intake Low pressure direct injection manifold injection semi-direct injection. High pressure Low pressure Low pressure intake direct injection semi-direct injection manifold injection. Low pressure transfer port injection b Fuel injection in two-stroke engines. Modern gasoline injection systems use engine sensors, a computer, and solenoid operated fuel injectors to meter and inject the right amount of fuel into the engine cylinders.
These systems called electronic fuel injection EFI use elec- trical and electronic devices to monitor and control engine-operation.
An electronic control unit ECU or the computer receives electrical signals in the form of current or voltage from various sensors. It then uses the stored data to operate the injectors, ignition system and other engine related devices. As a result, less unburned fuel leaves the engine as emissions, and the vehicle gives better mileage. Typical sensors for an electronic fuel injection system includes the following:. Sensor output voltage changes in proportion to air-fuel ratio.
The fuel injector in an EFI is nothing but a fuel valve. When it is not energized, spring pressure makes the injector to remain closed and no fuel will enter the engine. Fuel then spurts into the intake manifold. The injector pulse width is an indication of the period for which each injector is energized and kept open. The computer decides and controls the injector pulse width based on the signals received from the various sensors. The ECU will then increase the injector pulse width to enrich the mixture which will enable the engine to produce higher power.
Under low load and idling conditions, the ECU will shorten the pulse width by which the injectors are kept in the closed position over a longer period of time. Because of this, air-fuel mixture will become leaner and will result in better fuel economy.
Electronic fuel injection system has a cold start injector too. This is an extra injector that sprays fuel into the center of the engine intake manifold, when the engine is cold.
It serves the same purpose as the carburettor choke. The cold start injector ensures easy engine startup in very cold weather. It eliminates majority of carburettor pressure losses and almost eliminates the requirement of manifold heating. These systems function under two basic arrangements, namely. The gasoline mixes with the air in a reasonably uniform manner. This mixture of gasoline and air then passes through the intake valve and enters into the cylinder. If there are six cylinders, there will be six injectors.
This throttle body is similar to the carburettor throt- tle body, with the throttle valve controlling the amount of air entering the intake manifold.
An injector is placed slightly above the throat of the throttle body. The injector sprays gasoline into the air in the intake manifold where the gasoline mixes with air.
This mixture then passes through the throttle valve and enters into the intake manifold. As already mentioned, fuel-injection systems can be either timed or con- tinuous. In the timed injection system, gasoline is sprayed from the injectors in pulses. In the continuous injection system, gasoline is sprayed continuously from the injectors. The port injection system and the throttle-body injection system may be either pulsed systems or continuous systems.
In both systems, the amount of gasoline injected depends upon the engine speed and power demands. In addition, it senses the vol- ume of air by its density. As air enters into the intake manifold, the manifold pressure sensor detects the intake manifold vacuum and sends the information to the ECU. The speed sensor also sends information about the rpm of the engine to the ECU.
The ECU in turn sends commands to the injector to regulate the amount of gasoline supply for injection. When the injector sprays fuel in the intake manifold the gasoline mixes with the air and the mixture enters the cylinder.
In this type the fuel metering is regulated by the engine speed and the amount of air that actually enters the engine. Similarly, the speed sensor sends information about the speed of the engine to the ECU.
The ECU processes the information received and sends appropriate commands to the injector, in order to regulate the amount of gasoline supply for injection. When injection takes place, the gasoline mixes with the air and the mixture enters the cylinder. The MPFI system can be functionally divided into i electronic control system, ii fuel system, and iii air induction system.
These functional divisions are described in the following sections. The sensors that monitor intake air temperature, the oxygen, the water temperature, the starter signal and the throttle position send signals to the ECU. The ignition sensor sends information about the engine speed. The ECU processes all these signals and sends appropriate commands to the injectors, to control the volume of the fuel for injection.
In this system, fuel is supplied by the fuel pump. At the time of starting, the cold start injector is operated by the cold start injector time switch. The cold start injector injects fuel into the air intake chamber, thus enriching the air-fuel mixture. The pressure regulator regulates the pressure of the fuel. The injectors receive signals from the ECU and inject the fuel into the intake manifold. The quantity of air supplied is just what is necessary for complete combustion.
Air flow sensor Gasoline. To injectors Sensors Input To cold start injector Output. Cold start injector Electronic control unit ECU time switch. To air intake Cold start injector chamber. Injection signal from Injection to intake manifold ECU controlling fuel injection volume.
The electronic control system consists of mainly the Electronic Control Unit ECU , which determines the duration of operation of the injectors. In addi- tion to this, there is a starter timing switch, which controls the operation of the cold start injector during engine starting. There is a circuit opening relay to control fuel pump operation.
There is also a resistor, which stabilizes the injector operation. When a cold engine is started, it requires a richer mixture. The cold start injector serves the purpose of supplying more fuel at the time of starting. In Fig. The cold start injector is a type of solenoid valve to which power is supplied from a battery for the opening and closing of the valve inside, thus for injecting the fuel. The fuel injected should not be excessive. Therefore the duration of injection time is controlled by a timing switch.
The timing switch is composed of a bimetal element and an electric heater coil. When the engine is cold, the starter motor cranks the engine. At this time, the cold start injector injects fuel to enrich the mixture. The main injector also injects fuel during the same time. The injection by both the injectors is shown in Fig. When the engine is hot, the cold start injector will stop injection and only the main injector will inject the fuel to the cylinder.
Battery Ignition switch. Cold start injector Air flow meter time switch Cold start injector. When the engine is cold, the throttle plate will be in the closed position. As can be seen in Fig. When the temperature is low, the air valve opens completely. Thus a large volume of air passes through the air valve to the intake manifold.
As the temperature rises, the air valve closes gradually. A thermo wax valve operates depending on the temperature of the engine coolant. This valve controls the opening and closing of the air valve. Consider a cylinder of a four cylinder engine. The timing at which the injection of the fuel takes place inside the inlet manifold is called injection timing. The injection timing for one cylinder of this four cylinder engine is de- scribed below.
This injected fuel mixes with the air in the air intake chamber. At the beginning of the suction stroke, intake valve opens and the air-fuel mixture is sucked into the cylinder during the suction stroke. In this four cylinder engine, the ECU calculates the appropriate injection timing for each cylinder and the air fuel-mixture is made available at each suction stroke. In order to meet the operating conditions, the injection valve is kept open for a longer time by ECU. For example, if the vehicle is accelerating, the injection valve will be opened for longer time, in order to supply additional fuel to the engine.
In an engine having group gasoline injection system, the injectors are not activated individually, but are activated in groups. In a four-cylinder engine also there are two groups, each group having two injectors.
In a six-cylinder engine, there are two groups, each group having 3 injectors. Sensors for detecting pressure in the manifold, engine speed in rpm, throttle position, intake manifold air temperature and the coolant temperature send information to the ECU.
With this information, the ECU computes the amount of gasoline that the engine needs. The ECU then sends signals to the injectors and other parts of the system. The timing of the injectors is decided by the engine-speed sensor. Intake manifold Group I injectors air temperature. Based on the signals from the speed sensor, the ECU activates one group of injectors.
For example, the injector grouping for a six-cylinder engine is shown in Fig. Injectors for cylinders 1, 3 and 5 open at the same time and inject gasoline into the intake manifold.
After these injectors close, the injectors for the cylinders 2, 4 and 6 open and inject gasoline. Eight injectors are connected to a fuel sys- tem and are divided into two groups, each group having four injectors. Each group of injectors is alternately turned on by the ECU. When the crankshaft makes two revolutions, the injectors are turned on once. Intake boost pump Fuel going to the injectors.
Fuel filter Fuel pump Injector. It may be noted that meeting future emission and other norms puts a large stress on the fuel injection system of a diesel engine. A conventional fuel injection pump with variable delivery capability is already seen in Fig. All parameters related to the injection process like, timing, rate of injection, end of injection, quantity of injected fuel etc.
Mechanical systems only sense a few parameters and meter the fuel quantity or adjust the injection timing. They seldom change the injection rate or the injection pressure. Subsequently the main injection takes place into gases, which are already hot. Thus the amount of fuel taking part in the premixed or the uncontrolled combustion phase is minimized and this leads to a reduction in noise and NOx levels. By means of EFI systems one can achieve the precise control of:. There are various versions of electronically controlled diesel injection systems.
Some of the important ones are discussed below:. Electronically controlled diesel fuel injection systems may use the following as inputs:. The frequency of injection depends on the engine speed and number of cylinders. The timing of injection has to be advanced as the speed increases. The accelerator pedal position indicates the load on the engine. Intake air temperature and pressure indicate atmospheric conditions based on which the injection quantity and timing may have to be altered.
The lubricating oil and coolant temperatures indicate the engine condition. This input can be used to detect cold start and warm up conditions, which will need the injection timing to be retarded and the fuel quantity to be momentarily increased. Various electronically controlled injection systems are discussed below in some detail.
Unit in- jectors can be combination of high-pressure pumps and injectors in one unit. They do not have high-pressure lines and hence the injection lag is low.
The main high-pressure pump is situated above the injector. Fuel is fed into the high-pressure pump by a supply gear pump at low pressure. The plunger of the high-pressure pump is pushed down at the appropriate time by a cam, and rocker mechanism. The fuel pushed down by the injector just bypasses the injection nozzle till the solenoid controlled spill valve closes the spill port. The closure of the spill port initiates the injection process.
The injection stops when the solenoid valve opens the spill port. The timing and duration of the square pulse given to the solenoid can thus control the fuel timing and injection quantity. The solenoid can also be opened and closed more than once to have a pilot injection spray followed by the main spray. The pressure of injection is however controlled by the rate of displacement of the fuel and the size of the hole in the nozzle.
The ECU generates the pulses to operate the solenoid controlled spill valve. The start of injection in the conventional inline element is determined by the instant when the top of the plunger covers the bypass or the spill ports.
The end of delivery occurs when the helical slot or groove on the plunger uncovers these ports. In the case of the electronically controlled system there will be a control sleeve which can be moved up and down by an actuator which is controlled by the ECU Electronic Control Unit.
The ECU determines the amount of fuel to be injected depending on the throttle position, engine speed, and other parameters. Once this is obtained the control sleeve is positioned so that the required quantity of fuel can be injected.
The timing of injection is still done mechanically. Distributor pumps use control sleeves for metering the injected quantity. Thus they can be easily be made to work with an electronically controlled solenoid actuator. The principle of operation is similar to the one explained above. Inline pump governors in mechanical systems are quite complex. These basically alter the injected fuel quantity of the pump so that the engine speed can be maintained.
In addition to the speed the governor also puts a limit on the maximum fuel delivery depending on engine operating and ambient conditions. It also has to supply excess fuel just for starting. The fuel delivery has to be controlled based on the turbocharger outlet conditions. The governor has to also limit the maximum speed and ensure stable idling operation. The schematic of an electronically controlled inline fuel injection system is given in the Fig.
The ECU determines the correct quantity of the fuel to be injected based on the inputs and the data in the look up table. The fuel input de- pends on the rack position and thus the ECU controls the rack position using a solenoid.
The position of the rack is measured and used for feedback. The accelerator pedal position is the input from the driver and a potentiometer is used to sense it.
The ECU can also regulate the fuel quantity depending on other con- ditions like braking. The ECU also protects the engine against overheating by regulating the maximum quantity of fuel delivered. Charge-air Injected fuel quantity pressure sensor Fuel injection pump Temperature sensors Stop coolant, air, fuel. Vehicle speed sensor Vehicle ECU option. Desired-value generators Fuel quantity override Accelerator pedal sensor. Operator panel Data maps vechicle speed, characteristic intermediate speed Variant programming curves Programming device only for data Switches for brakes, program exhaust brake, clutch.
This system provides control of many important parameters linked to the in- jection system refer Chapter It has a wide range of application, from small to heavy duty engines.
Some important features are:. The common rail injection system has a high pressure pump which oper- ates continuously and charges a high pressure rail or reservoir or accumulator. Fuel is led from this rail to the injector mounted on the cylinder head through lines. The injector is solenoid operated.
It received pulses from the ECU to open the same. The engine directly drives the pump of the common rail system. It is generally of the multi-cylinder radial piston type. The generated pressure is independent of the injection process unlike conventional injection systems. The rail pressure pump is generally much smaller than conventional pumps and also is subjected to lesser pressure pulsations. The injection occurs when the solenoid is energized.
The quantity of fuel injected is directly dependent on the duration of the pulse when the injection pressure is constant. Sensors on the crankshaft indicate its position and speed and so the timing of injection and its frequency can be controlled. A typical layout of the common rail fuel injection system is indicated in Fig. The main pumping element can be a conventional gear pump or of the roller cell type. The roller cell pump has a rotor with radial slots.
These slots house rollers which are always in contact with the inner surface of the housing due to fuel pressure and centrifugal forces. The space between the rotor and the housing varies as the rotor turns and this is responsible for the suction and delivery.
Lucas diesel systems is of a high pressure pump which is seen in Fig. This pump has a cam which is stationary and a rotating hydraulic head which houses two plungers. These plungers touch the cam and are pushed in four times a rotation. Thus fuel is pumped four times per rotation. Author: V. Pages: Size: 39 Mb. Share this:. One comment. Download Psychiatry as a Neuroscience ». One comment Salawu Themithorpe Harbhioye. Mar 17, at am. Comment Cancel reply.
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