Internal Combustion Lec 5 M.Omar (Diesel Fuel Injection Systems)-2.pdf

Internal Combustion Engines Lecture 5 Diesel Injection Systems By, Dr. Mahmoud Omar Amer Internal Combustion Engines-Dr. Mahmoud Omar Amer 1  Lecture workflow Introduction...

Internal Combustion Engines Lecture 5 Diesel Injection Systems By, Dr. Mahmoud Omar Amer Internal Combustion Engines-Dr. Mahmoud Omar Amer 1  Lecture workflow Introduction Inline Unit Diesel Injection Injector Mechanical Fuel tank Distributor Common Pump system Injector and Supply Injection rail (Low pump system Pressure) system Internal Combustion Engines-Dr. Mahmoud Omar Amer 2 Introduction Internal Combustion Engines-Dr. Mahmoud Omar Amer 3  Objectives of Diesel fuel Injection systems Meter the correct amount of fuel and distribute it equally among the cylinders. Inject the fuel at the correct time in the cycle. Inject the fuel at the correct rate. Inject the fuel with high pressure enough to form the spray pattern and atomization demanded by the design of the combustion chamber. Injection pressure 300 → 900 bar in IDI Injection pressure 1000 → 3000 in DI Begin and end the injection sharply without dribbling or after injection. Internal Combustion Engines-Dr. Mahmoud Omar Amer 4  Main Elements of fuel injection systems Mixing control: Metering elements: Distributing elements: Timing control: to to atomize and Pumping elements: To measure and to divide the metered adjust the start distribute fuel to move fuel from supply fuel as per fuel equally among and end of within tank to cylinder load and speed. cylinders. injection. combustion chamber. Main Components of fuel injection systems Low Pressure Pump Injector: it is High pressure (Fuel supply High pressure Pump: mechanically, lines: they system): transfers generates the high or solenoid connect between Fuel Tank fuel from tank to injection pressure to actuated valve the high-pressure the high-pressure ensure good air/fuel contains one or pump and the system via filters mixing. more holes for injector. and pipes. atomization. Internal Combustion Engines-Dr. Mahmoud Omar Amer 5  Fuel injection systems Fuel injection systems consist mainly of 2 stages; low pressure stage high pressure stage. The main differences between fuel-injection systems are in the high-pressure generation system, and in the control of start of injection and injection duration. The control of fuel quantity and injection timing is either mechanical or electronically. Types of fuel injection systems: In-line fuel-injection pumps Distributor injection pumps Individual injection pumps type PF (pump with external drive) Unit Injector System (UIS) Unit Pump System (UPS) Internal Combustion Engines-Dr. Mahmoud Omar Amer 6 Common-Rail system (CR) Fuel injection system components Internal Combustion Engines-Dr. Mahmoud Omar Amer 7 Fuel tank and Supply (Low Pressure) system Internal Combustion Engines-Dr. Mahmoud Omar Amer 8  Fuel Tank The fuel tank stores the fuel. It must be corrosion- resistant and leak-proof at double the operating pressure, but at least at 0.3 bar. Any gauge pressure must be relieved automatically by suitable vents or safety valves. When the vehicle is negotiating corners, inclines or bumps, fuel must not escape past the filler cap or leak out of the pressure- relief vents or valves. The fuel tank must be separated from the engine to prevent the fuel from igniting in case of an accident. Fuel Lines (Low pressure lines) Flexible, flame-retardant tubes reinforced with braided-steel armoring can be used in the low-pressure stage. They must be routed so as to avoid contact with moving components that might damage them and in such a way that any leak fuel or evaporation cannot collect or ignite. The function of the fuel lines must not be impaired by twisting of the chassis, movement of the engine or any other similar effects. Internal Combustion Engines-Dr. Mahmoud Omar Amer 9  Fuel Filter The fuel filter has the following functions: Reduce particulate impurities to avoid particulate erosion Separate un-dissolved water from free water to avoid corrosion damage 2 stages filtration are usually used. Water trap/sedimenter is used to remove water from the fuel. Fuel supply pump (Low pressure Pump) To deliver fuel from tank to pass through the filter and water separator till it reaches the high-pressure pump at the engine. It could be mechanically-driven (mounted on the engine or inside the high pressure pump itself) Diaphragm → usually mounted on the engine Plunger → mainly used with inline injection pump and driven by a cam inside the pump body Vane → mainly used with distributor type pump and number of lots is equal to number of injectors Electrically driven (vane or roller Pump) Internal Combustion Engines-Dr. Mahmoud Omar Amer 10  Electrical fuel pump The electric fuel pump is only fitted to passenger cars and light-duty trucks. They are installed either in-line of the fuel suction line → easily accessed in-tank → inside the tank itself (most common) [cooled with the fuel itself] Starting with the engine cranking process, the electric fuel pump runs continuously, irrespective of engine speed. This means that it permanently delivers fuel from the fuel tank through a fuel filter to the fuel- injection system. The pump always draws more fuel than the engine could ever use to ensure that under all conditions the engine gets the required fuel, excess fuel flows back to the tank through an overflow or pressure limiter valve. Internal Combustion Engines-Dr. Mahmoud Omar Amer 11  Priming pump Priming pump is used to remove air from fuel system. Air can enter the fuel system during any maintenance in the fuel system such as replacement of fuel filter or disconnecting fuel lines. The air removal can be done either by: Using a mechanical priming pump which is either a priming lever in the fuel supply pump or a separate priming pump. Starting the engine many times so the fuel supply pump will keep pumping fuel inside all the components of the fuel system until all air exit from the injectors but that may lead to discharge the battery. Internal Combustion Engines-Dr. Mahmoud Omar Amer 12 Inline Injection Pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 13 Inline Injection Pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 14  Inline Injection Pump Delivery Valve In inline injection pump: Fuel input from No. of barrels and plungers = supply system the number of cylinders = no. of cams Its camshaft’s speed is half the crankshaft's speed (4- stroke engine) Control Rack All the inside of the inline pump is filled with diesel fuel which performs two functions: Cooling Lubrication for moving parts Connection to the throttle valve Pump camshaft Barrel with Plunger driven by the engine Internal Combustion Engines-Dr. Mahmoud Omar Amer 15 Inline Injection Pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 16 Inline Injection Pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 17  Inline Injection Pump The plunger has 2 motions: Reciprocating motion determining the plunger’s stroke which is always constant according to the cam’s travel, the plunger returns by a spring. Rotary motion of the helix determining the effective stroke controlling amount of injected fuel, and it is controlled by the control rack which is controlled by the accelerator’s pedal. Plunger operating sequence When the plunger is at the bottom position the fuel enters from the inlet port and fills the compartment above the plunger plunger moves up, inlet and spill ports are closed so fuel pressure increases, and the nozzle opens (Delivery valve), and fuel is injected into the combustion chamber. When the plunger’s helix (3) clears the inlet port, fuel escapes, and pressure is lost. The nozzle closes and fuel injection ceases. As rotation angle increases → spill port opening delayed → effective stroke increases → injected quantity increases Some inline pump’s designs have: Designated intake and spill ports (both are connected to the fuel inside the pump’s body from the fuel delivery system) (Left image) A single port used for intake and spill (rightInternal image) Combustion Engines-Dr. Mahmoud Omar Amer 18  Inline Injection Pump 1 Effective stroke → the distance the plunger moves from the closure of the inlet port (start of fuel injection) until the opening of the spill port (end of injection) There are three different helix configurations 1. The helix starts from the top and its bottom part is variable → constant start of injection & variable end of injection 2. The helix starts and the bottom and its top part is variable → variable start of injection and 2 constant end of injection 3 3. The helix is both variable at top and bottom → both the start and end of injection can be varied. Internal Combustion Engines-Dr. Mahmoud Omar Amer 19 Distributor Injection Pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 20  Distributor fuel injection pump Distributor pump has only one plunger that meters, distributes and injects the fuel into all engine cylinders. It can only be used with a maximum of 6 cylinders. Why????? It is used with small, high-speed diesel engines. They are mainly used with passenger cars and light trucks. Internal Combustion Engines-Dr. Mahmoud Omar Amer 21 Distributor fuel injection pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 22 Distributor fuel injection pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 23 Distributor fuel injection pump Internal Combustion Engines-Dr. Mahmoud Omar Amer 24  Distributor fuel injection pump 1. Vane-type fuel supply pump with pressure regulating valve Draws in the fuel and generates pressure inside the pump 2. High pressure pump with distributor Generates injection pressure, delivers and distributes fuel 3. Mechanical (flyweight) governor Controls the pump speed and varies the delivery quantity within the control range 4. Electromagnetic fuel shutoff valve Interrupts the fuel supply when the engine is shut off 5. Timing device Adjusts the start of delivery (port closing) as a function of the pump speed and in part as a function of the load Internal Combustion Engines-Dr. Mahmoud Omar Amer 25  Operating Principle of Distributor fuel injection pump An integrated vane pump draws the fuel from the tank into the whole pump and to the high-pressure chamber (6). The plunger performs two motions Rotary motion by being connected to the camshaft → performs fuel intake and distribution to the injectors of the individual cylinders by opening and closing metering slots and spill ports (8) Reciprocating motion by sliding the camplate (3) over the rollers (2) → generates the high injection pressure by the axial piston (4) and delivers the metered amount of fuel to the injectors. The injection duration and injected fuel quantity is controlled by a control collar (5) which is connected mechanically to the accelerator pedal which determines the effective stroke of the plunger. The timing device (1) can vary the pump’s start of delivery by turning the roller ring. The number of cam lobes on the bottom of the cam plate is equal to the number of engine cylinders. For each rotation of the plunger, it completes a number of strokes equal to the number of engine cylinders to be supplied. Internal Combustion Engines-Dr. Mahmoud Omar Amer 26  Operating Principle of Distributor fuel injection pump The plunger rotates and reciprocates at the same time For a 4-cylinder engine → the pump plunger reciprocates every 90° Internal Combustion Engines-Dr. Mahmoud Omar Amer 27 Metering and distribution of the fuel Internal Combustion Engines-Dr. Mahmoud Omar Amer 28  Injection Lag When the pump plunger moves with high speed during the compression phase, the fuel close to the plunger is highly compressed locally The compressed fuel now generates a pressure wave which runs through the delivery valve and the pipe to open the injector The speed of this pressure wave is equal to the speed of sound, which is approximately 1500 m/s in diesel fuel The pressure wave’s propagation time is determined by the length of the high- pressure pipe (Δt=L/v=L/1500) The time between the generation of pressure wave at the pump and the start of fuel injection into the cylinder is called injection lag The length of the high-pressure pipes connecting between the pump and the injectors must be kept as short as possible in order to reduce the injection lag All injection pipes must have the same length in order to equalize the injection performance for all cylinders Internal Combustion Engines-Dr. Mahmoud Omar Amer 29  Injection and ignition Lag with engine speed The injection lag in terms of crank angle degrees can be calculated from: ΔƟ=ωΔt, where ω represents the crankshaft speed As engine speed increases, the injection lag in terms of crankshaft degrees increases Also, it was found experimentally that the ignition lag (delay period) in terms of crank angle degrees increases with the increase of engine speed Therefore, the start of delivery timing (the start of generating the pressure wave at the pump) must be advanced with the increase of engine speed This allows the combustion to end at the suitable time and the maximum pressure to occur at the suitable time required for optimum engine performance Internal Combustion Engines-Dr. Mahmoud Omar Amer 30  Controlling injection timing (Timing device) There is a passage in one end of the timing device piston through which the fuel can enter, while at the other end the piston is held by a compression spring The piston is connected to the roller ring through a sliding block and a pin so that piston movement can be converted to rotational movement of the roller ring The speed of fuel supply pump is proportional to engine speed. As a result, the fuel pressure inside the high-pressure pump is proportional to engine speed The fuel pressure is applied to the end of the timing-device piston opposite to the spring Starting from 300 rpm, the fuel pressure starts to overcome the piston spring and shifts the piston to the left The roller ring is rotated relative to the cam plate by the movement of the piston and the injection timing changes As engine speed increases, the fuel pressure increases, the angle of rotation of the roller ring increases , and the injection timing is more advanced Internal Combustion Engines-Dr. Mahmoud Omar Amer 31 Inline vs Distributor Internal Combustion Engines-Dr. Mahmoud Omar Amer 32  Electronically controlled distributor fuel injection pump The electronic control is divided into: Sensors: they register operating conditions and convert physical quantities into electrical signals ECU: it receives the information from all sensors and generates electrical signals to the actuators Actuators: they convert the ECU’s electrical signals into mechanical motion The electronic control of the injection quantity and timing: A solenoid actuator engages with the control collar through a shaft in order to open or close the cutoff port in order to determine the amount of injected fuel The fuel pressure which is applied to the timing device piston is controlled by a solenoid valve in order to control the start of injection timing Internal Combustion Engines-Dr. Mahmoud Omar Amer 33 Unit injector system Internal Combustion Engines-Dr. Mahmoud Omar Amer 34  Unit injector system In a Unit Injector System, UIS, the fuel-injection pump and the injection nozzle form a single unit. There is a unit injector fitted in the cylinder head for each cylinder. The maximum injection pressure is presently about 2,200 bar. The fuel is delivered to the unit injector system via passages in the cylinder head An electronic control unit calculates start of injection and injection duration, which are controlled by a high-pressure solenoid valve. Advantages The long high-pressure pipes are eliminated. That results in the hydraulic delays to be greatly reduced. The injection rate diagram more closely follows the cam profile which facilitates the optimization of the injection system performance The fast end of injection eliminates the need of using a delivery valve. This greatly limits the pressure waves effect, and consequently, problems such as after-injection and cavitation are greatly avoided. That increases the nozzle life Disadvantages The injectors tend to be bulky, and therefore, difficult to accommodate in the cylinder heads of small engines as they demand more space More complex cylinder head designs and higher cylinder head loads are needed. In large engines, they are bulky and difficult to handle. Internal Combustion Engines-Dr. Mahmoud Omar Amer 35 Unit injector system (UIS) Vs Unit Pump System (UPS) Internal Combustion Engines-Dr. Mahmoud Omar Amer 36 Common rail system Internal Combustion Engines-Dr. Mahmoud Omar Amer 37  Common Rail system It is one of the advanced fuel-injection systems. The main advantage of the CR system is its ability to vary injection pressure and timing over a broad scale. This was achieved by separating pressure generation (high-pressure pump) from the fuel-injection system (injectors). The rail acts as a pressure accumulator to separate pump and injectors. Pressures range up to 1600 bar (passenger cars) and 1800 bar (commercial vehicles). The Electronic Diesel Control (EDC) calculates the injection point and injected fuel quantity dependent on engine operating state, ambient conditions, and rail pressure. Fuel is metered by controlling injection time and injection pressure. Pressure is controlled by the pressure-control valve which returns excess fuel to the fuel tank. This system is able to deliver the same injection pressure at all speeds from rated speed to idling The common-rail system consists of the following main component groups. The low-pressure stage, comprising the fuel supply system components. The high-pressure system, comprising components such as the high-pressure pump, fuel rail, injectors, and high-pressure fuel lines. The electronic diesel control (EDC), consisting of system modules, such as sensors, the electronic control unit, and actuators. The common rail system permits multiple-stage injection. Internal Combustion Engines-Dr. Mahmoud Omar Amer 38  Multistage injection Multiple-stage injection means injecting the overall fuel quantity in two or more stages The common rail system permits multiple-stage injection by simply causing the ECU to send signals to open and close the injector twice or more during the overall injection process For example, injecting only a small fuel quantity at the beginning of injection process (before the main injection), which is called pilot injection. This ensures that the amount of fuel which burns immediately after the delay period is small enough which reduces engine knock and noise Another example is injecting a small fuel quantity after the main injection, which is called post injection, in order to control the exhaust gas temperature which makes the exhaust processing in the engine’s aftertreatment process more effective Internal Combustion Engines-Dr. Mahmoud Omar Amer 39  Common Rail system operating concept Injection pressure control A pressure control valve is used to control injection pressure, which allows ECU to decide mainly injection timing. The pressure-control valve is mounted preferably on the fuel rail. Extra fuel is returned to the tank. The engine control unit detects the accelerator-pedal position and the current operating states of the engine and vehicle by means of sensors. The data collected includes: Crankshaft speed and angle Fuel-rail pressure Charge-air pressure Intake air Coolant temperature Fuel temperature Air-mass intake Road speed The ECU evaluates the input signals. It calculates the triggering signals for the pressure control valve, the injectors, and the other actuators (the EGR valve. Exhaust gas turbocharger actuators) Internal Combustion Engines-Dr. Mahmoud Omar Amer 40 Diesel Mechanical Injector Internal Combustion Engines-Dr. Mahmoud Omar Amer 41  Diesel Injector The diesel injector is a valve which opens and closes to start and end the fuel injection It must be capable of atomizing the fuel It is a determining factor in the efficiency of mixture formation and combustion and, therefore has a fundamental effect on engine performance, exhaust-gas behavior, and noise. The nozzle plays a major role in: Shaping the rate-of-discharge curve (precise progression of pressure and fuel distribution relative to crankshaft rotation) Optimum atomization and distribution of fuel in the combustion chamber Sealing off the fuel-injection system from the combustion chamber The smaller the fuel droplet exiting the injector, the faster it will vaporize and ignite The size of the fuel droplets depends on the nozzle orifice size and the injection pressure The nozzle valve is held closed by the injector spring and when the fuel pressure sufficiently increases, it overcomes the spring causing the injector to open and inject the fuel Internal Combustion Engines-Dr. Mahmoud Omar Amer 42  Diesel Injector Diesel injector consists of a nozzle holder and an injection nozzle Internal Combustion Engines-Dr. Mahmoud Omar Amer 43  Types of injection nozzles Pintle nozzles (used with IDI diesel engines) which can be classified into: Standard pintle nozzle Throttling pintle nozzle Flatted pintle nozzle Hole-type nozzles (used with DI diesel engines), which can be classified into: Seat hole nozzle Sac-hole nozzle The fundamental design of all pintle nozzles is virtually identical. The differences between them are to be found in the geometry of the pintle. Internal Combustion Engines-Dr. Mahmoud Omar Amer 44  Pintle Nozzles The fundamental design of all pintle nozzles is virtually identical. The differences between them are to be found in the geometry of the pintle. On the standard pintle nozzle, the nozzle needle is provided with a pintle which extends into the injection orifice of the nozzle body The opening pressure of this nozzle is relatively low compared to the hole nozzle This nozzle is used with indirect injection diesel engines, which depends mainly on the air motion rather than the injection pressure to improve the air-fuel mixing The fuel is injected in the pre-chamber where the fuel has a relatively short distance to travel, and the air pressure is not as high as the pressure in the main chamber Internal Combustion Engines-Dr. Mahmoud Omar Amer 45  Hole Nozzles The hole nozzles are commonly used in direct injection engines, and they can be single hole or multi-hole The number and size of holes depends on the amount of injected fuel, the combustion chamber geometry and the air motion (swirl) inside the cylinder They operate at very high injection pressure and give a hard fuel spray which is necessary to penetrate the highly compressed air in the combustion chamber The fuel spray has a high velocity and good atomization Seat hole nozzle The needle covers the nozzle holes The radial motion of the needle tip can influence the mass flow through the different holes and the fuel spray symmetry Sac-hole nozzle This nozzle has an additional volume below the needle seat to prevent the effect of the needle radial motion on the fuel spray However, some of the fuel in this volume can enter the cylinder after the end of injection with poor atomization, which increases the HC and soot emissions it is important to keep this volume as small as possible Internal Combustion Engines-Dr. Mahmoud Omar Amer 46  Characteristics of the nozzle-end line pressure and needle lift When the pressure in the nozzle pressure chamber is greater than the mechanical force of the spring, the nozzle needle lifts, and injection starts The injection pulse continues as long as the needle valve remains open The injection ends when the pressure in the nozzle pressure chamber collapses so that the mechanical spring force pushes the needle down on its seat This closing pressure will be lower than the opening pressure by about 10% to 20% It takes more pressure to open the nozzle valve than the pressure required to keep it open!! To open the injector needle, the fuel pressure affects only the annulus area showed in (1) which generates F1 = P1 * A1 = Needle force After the needle is lifted, the fuel pressure affects the annulus area in (1) and (2) generating force F2 = P2 * A2 (1) As A2 > A1 → F2> F1 but needle force is constant, so we don’t need more than F1 to open it then P2 < P1 Internal Combustion Engines-Dr. Mahmoud Omar Amer 47 (2)  Dribble Dribble → When the injector is about to close by the end of main injection, the fuel pressure is greatly reduced causing the fuel to continue to emerge from the nozzle at very low pressures resulting in poor fuel atomization Injecting the fuel with poor atomization (dribble) causes engine smoke The injection period must end sharply to ovoid dribble. That means the injector closure time must be very short To end the injection duration very quickly, a delivery valve (check or non-return valve) is used The delivery valve separates the pump from the high-pressure pipe which connects between the pump and injector Internal Combustion Engines-Dr. Mahmoud Omar Amer 48  The function of the delivery valve The delivery valve is opened by the injection pressure and closes by its return spring During delivery, the pressure generated in the pump causes the delivery valve to open and Fuel then flows via the high-pressure pipe to the injector As soon as the pressure in the pump sufficiently drops, the delivery valve spring forces the valve back on its seat This results in a sudden increase in the volume of the injection line. The pressure now at the nozzle is higher than the pressure at the other end of injection line As a result, a pressure wave is created and transmits from the injector to the delivery valve causing the injector to close very quickly When the pressure wave reaches the delivery valve, it is reflected back to the injector. This pressure wave is reflected backwards and forwards along the pipe If this pressure wave is reflected back to the injector with a pressure that equals to or exceeds the injector opening pressure, the injector will open again, and some fuel will be injected in the cylinder. This phenomena is called after injection (or secondary injection) The fuel injected during the secondary injection will be poorly atomized due to the low injection pressure and will be injected late in the combustion process As a result, after injection increases engine smoke and HC emissions The pressure waves following the sudden closure of the nozzle needle can also cause cavitation which causes erosion in the pipes and injectors Internal Combustion Engines-Dr. Mahmoud Omar Amer 49  Diesel Spray Structure Under diesel injection conditions, the fuel jet usually forms a cone-shaped spray at the nozzle exit The liquid column leaving the nozzle disintegrates within the cylinder over a finite length called the break up length into drops of different sizes As one moves away from the nozzle, the mass of air within the spray increases, the spray width increases, and the droplet velocity decreases The droplets on the outer edge of the spray evaporate first creating a fuel vapor mixture around the fuel spray cone The equivalence ratio is highest on the centerline of spray cone (fuel rich zone) The equivalence ratio decreases along the spray radial direction till it reaches to zero at the spray boundary (air only zone) Ɵ=cone angle S=spray tip penetration Lbreak up=break up length Internal Combustion Engines-Dr. Mahmoud Omar Amer 50  Diesel Spray Tip Penetration The spray penetration has an important influence on engine emissions: The spray penetration is limited by the distance between the nozzle and piston Over penetration may result in the impingement of fuel on cool cylinder wall surfaces forming a liquid wall film The wall film evaporates slowly and could be partially burned which results in an increase in HC and soot emissions Under penetration results in poor air utilization since the air on the periphery of the chamber does not contact the fuel. This also can lead to an increase in HC and soot emissions The spray penetration depends on time Because of the small needle lift and the mass flow at the beginning of injection, the injection velocity is small leading to a small penetration and inefficient atomization Internal Combustion Engines-Dr. Mahmoud Omar Amer 51  Thank you Internal Combustion Engines-Dr. Mahmoud Omar Amer 52