2 IntroductionA modern gasoline injection system uses pressure from an electric fuel pump to spray fuel into the engine intake manifold. Like a carburetor, it must provide the engine with the correct air-fuel mixture for specific operating conditions. Unlike a carburetor, however, PRESSURE, not engine vacuum, is used to feed fuel into the engine. This makes the gasoline injection system very efficient
3 A gasoline injection system has several possible advantages over a carburetor type of fuel system. Some advantages are as follows:* Improved atomization. Fuel is forced into the intake manifold under pressure that helps break fuel droplets into a fine mist.* Better fuel distribution. Equal flow of fuel vapors into each cylinder.* Smoother idle. Lean fuel mixture can be used without rough idle because of better fuel distribution and low-speed atomization.
4 * Lower emissions. Lean efficient air-fuel mixture reduces exhaust pollution. * Better cold weather drivability. Injection provides better control of mixture enrichment than a carburetor. * Increased engine power. Precise metering of fuel to each cylinder and increased air flow can result in more horsepower output. * Fewer parts. Simpler, late model, electronic fuel injection system have fewer parts than modern computer-controlled carburetors.
5 There are many types of gasoline injection systems There are many types of gasoline injection systems. Before studying the most common ones, you should have : A basic knowledge of the different classifications : * single- or multi-point injection * indirect or direct injection
6 The point or location of fuel injection is one way to classify a gasoline injection system. A single-point injection system, also call throttle body injection (TBI), has the injector nozzles in a throttle body assembly on top of the engine. Fuel is sprayed into the top center of the intake manifold .
7 A multi-point injection system, also called port injection, has an injector in the port (air-fuel passage) going to each cylinder. Gasoline is sprayed into each intake port and toward each intake valve. Thereby, the term multipoint (more than one location) fuel injection is used.
9 System component : Fuel tank Electric fuel pump Fuel filter Electronic control unitCommon rail and Pressure sensorElectronic Injectorsfuel line
10 Fuel tankis safe container for flammable liquids and typically part of an engine system in which the fuel is stored and propelled (fuel pump) or released (pressurized gas) into an engine.Typically, a fuel tank must allow or provide the following:* Safe (UL Approved) fuel storage, there is some concern that UL (Underwriters Laboratories) is not the final arbiter of safety.* Filling (the fuel tank must be filled in a secure way) No Sparks.* Storage of fuel (the system must contain a given quantity of fuel and must avoid leakage and limit evaporative emissions)
11 * Provide a method for determining level of fuel in tank, Gauging (the remaining quantity of fuel in the tank must be measured or evaluated) * Venting (if over-pressure is not allowed, the fuel vapors must be managed through valves) * Feeding of the engine (through a pump) * Anticipate potentials for damage and provide safe survival potential.
12 Electric fuel pumpAn electric fuel pump is used on engines with fuel injection to pump fuel from the tank to the injectors. The pump must deliver the fuel under high pressure (typically 30 to 85 psi depending on the application) so the injectors can spray the fuel into the engine.Electric fuel pumps are usually mounted inside the fuel tank,Some vehicles may even have two fuel pumps (a transfer pump inside the tank, and a main fuel pump outside).
13 Electric fuel pumps come in a variety of designs Electric fuel pumps come in a variety of designs. Some older applications use a positive displacement "roller cell" pump. This type uses rollers mounted on an offset disc that rotates inside a steel ring. Fuel is drawn into the spaces (cells) between the rollers and pushed along from the pump inlet to the outlet. This type of pump can generate very high pressure, and the flow rate tends to be constant. But the output comes in pulses, so a muffler is often mounted in the fuel line after the pump to dampen pressure pulses. A roller cell pump may also be mounted outside the fuel tank, and used with a second low pressure supply pump mounted inside the fuel tank.
14 Most newer vehicles use a "turbine" style fuel pump Most newer vehicles use a "turbine" style fuel pump. A turbine pump has an impeller ring attached to the motor. The blades in the impeller push the fuel through the pump as the impeller spins. This type of pump is not a positive-displacement pump, so it produces no pulsations, runs very smoothly and quietly. It is also less complicated to manufacture and is very durable. Some aftermarket pump supplies use this type of pump to replace the older designs.
15 Fuel filterThe fuel filter is the fuel system's primary line of defense against dirt, debris and small particles of rust that flake off the inside of the fuel tank .many filters for fuel injected engines trap particles as small as 10 to 40 microns in size.fuel filter normally made intocartridges containing a filter paper.
16 Electronic control unit In automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle.An engine control unit (ECU), also known as power-train control module (PCM), or engine control module (ECM) is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.
17 Working of ECUControl of fuel injection: ECU will determine the quantity of fuel to inject based on a number of parameters. If the throttle pedal is pressed further down, this will open the throttle body and allow more air to be pulled into the engine. The ECU will inject more fuel according to how much air is passing into the engine. If the engine has not warmed up yet, more fuel will be injected .Control of ignition timing : A spark ignition engine requires a spark to initiate combustion in the combustion chamber. An ECU can adjust the exact timing of the spark (called ignition timing) to provide better power and economy.
18 Control of idle speed : Most engine systems have idle speed control built into the ECU. The engine RPM is monitored by the crankshaft position sensor which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor.
19 Common rail and Pressure sensor The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high pressure fuel.
21 Electronic InjectorsThe injectors can survive the excessive temperature and pressure of combustion by using the fuel that passes through it as a coolant
22 The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as electricity is applied to the injector's solenoid coil.When the injector is turned on, it opens, spraying atomized fuel at the combustion chamber .Depending on engine operating condition ,injection quantity will vary .
23 fuel lineFuel line hoses carry gasoline from the tank to the fuel pump, to the fuel filter, and to the fuel injection system. While much of the fuel lines are rigid tube, sections of it are made of rubber hose, which absorb engine and road vibrations.There are two basic types of fuel hose: Fuel and oil hoses that meet the SAE 30R7 standard, and fuel injection hose that meets the requirements of SAE 30R9.
24 Gasoline direct injection In internal combustion engines, gasoline direct injection is a variant of fuel injection employed in modern two- and four- stroke petrol engines. The petrol/gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.
26 When the driver turns the ignition key on, the power train control module (PCM) energizes a relay that supplies voltage to the fuel pump. The motor inside the pump starts to spin and runs for a few seconds to build pressure in the fuel system. A timer in the PCM limits how long the pump will run until the engine starts.Fuel is drawn into the pump through an inlet tube and mesh filter sockThe fuel then exits the pump through a one-way check valve and is pushed toward the engine through the fuel line and filter.
27 The fuel filter traps any rust, dirt or other solid contaminants that may have passed through the pump to prevent such particles from clogging the fuel injectors.The fuel then flows to the fuel supply rail on the engine and is routed to the individual fuel injectors. A fuel pressure regulator on the fuel rail maintains fuel pressure, and recirculates excess fuel back to the tank.The fuel pump runs continuously once the engine starts, and continues to run as long as the engine is running and the ignition key is on. If the engine stalls, the (PCM) will detect the loss of the RPM signal and turn the pump off.
28 Finally :what is Fuel Injection? it describes the way the fuel (usually a liquid fuel) is injected (pumped under pressure) into some part of the engine where it can combine with the air charge in the cylinders and combustion can take place, releasing energy to propel the vehicle.What’s different about diesel [CI] engine injection?Diesel (compression ignition or CI ) and petrol/gasoline (spark ignition or SI ) engines go about the task of releasing energy from their fuels in quite different ways.
29 In fuel-injected spark ignition [SI] engines, fuel is always injected into the air charge well before ignition takes place. This necessary because the liquid or gaseous fuel must be thoroughly mixed together with air into a combustible mixture, able to be ignited by the electrical arc generated by the sparkplug. If the ratio of air to fuel is not reasonably close to 15:1 in the vicinity of the sparkplug, the mixture will not ignite at all and a miss-fire results.
30 Compression ignition [CI] engines always inject the fuel charge directly into a combustion chamber in the engine. Fuel injection and ignition are inextricably tied together in compression ignition [CI] engines. Recall that CI engines only work because they compress the air charge so that it is hot enough to instantly ignite the fuel charge as it is being injected. The combustion of the fuel begins at the instant it begins being injected (well, within a couple of milliseconds, if you want to split hairs) into the combustion chamber full of very hot air (more than 400 ºC, often over 700 ºC).This means the timing of ignition is intimately tied to the fuel injection process. So, the fuel injection system of a CI engine is responsible for regulating both the quantity of fuel to be injected and timing of the beginning of combustion. Many ingenious techniques have been developed to achieve both these tasks with admirable accuracy, long before the advent of sophisticated electronic controls.
31 How much fuel are we injecting here? let’s do a few simple sums based on 1997 Land Rover Discovery. It has a 4 cylinder 2.5 liter engine. At 100 km/h in 5th gear it’s doing very close to 2400 rpm or 2400/60 = 40 revolutions per second. Because it’s a 4 cylinder 4 stroke engine, it will be producing 2 power strokes every revolution, so that’s 80 power strokes per second. At a steady cruising speed of 100 km/h, it is likely to be covering 10 km/liter or, in other words, using 10 litres/100 km. Therefore, our fuel burn rate is 10 liters per hour or 10/3600 = liters per second = 2.78 mL/sec. Now, this 2.78 mL is shared between the 80 power strokes of the engine per second. So, for each power stroke of the engine while we are cruising at 100 km/h, the fuel injection system is delivering 2.78/80 = mL into each cylinder. Not much is it? And the injection system delivers precisely this quantity of fuel to one of the cylinders of the engine, 80 times per second and at the exact instant the cylinder needs to fire. Not bad for a completely mechanical system with no electronic “smarts” at all, is it?
32 How much pressure?SI engine (petrol/gasoline) injection systems typically run at pressure of 2 to 3 bar (30 to 40 psi). In contrast CI (diesel) engines employ injection pressures of at least 350 bar (~5000 psi) and possibly in excess of 2000 bar (>29,000 psi) – quite a bit different to petrol/gasoline systems! This explains why CI injection systems are so solidly built and piped-up with strong steel tubing, etc.Petrol/gasoline readily vaporizes in the air stream entering the engine’s cylinders and in contact with the hot cylinder head surfaces, to form an easily ignitable air/vapor mixture. On the other hand, to instantly ignite the much less volatile diesel fuel in the hot air charge of a CI engine it is necessary to spray it into the combustion chamber in extremely small droplets. And to achieve this, extremely high injection pressures are required – the higher the better, in general.