25-04-2012, 10:56 AM
Fuel Injection
Fuel Injection.pptx (Size: 103.17 KB / Downloads: 60)
MPFI is the most precise way of delivering the correct fuel mixture to each cylinder. Because the injectors are located at the cylinder head's intake port, there is no cylinder to cylinder variation. Custom intake manifolds can be fabricated for any engine because the manifolds are simply air delivery devices. The disadvantage of MPFI is that it is more expensive and complex to install than a TBI system.MPFI systems come in three varieties. Batch systems are those which fire all of the injectors simultaneously with every crankshaft rotation. Bank to bank systems fire half the injectors, alternating between halves, with every crankshaft rotation. Sequential systems fire each injector prior to the opening of its intake valve.
Operational benefits to the driver of a fuel-injected car include smoother and more dependable engine response during quick throttle transitions, easier and more dependable engine starting, better operation at extremely high or low ambient temperatures, increased maintenance intervals, and increased fuel efficiency. On a more basic level, fuel injection does away with the choke which on carburetor-equipped vehicles must be operated when starting the engine from cold and then adjusted as the engine warms up.
An engine’s air/fuel ratio must be accurately controlled under all operating conditions to achieve the desired engine performance, emissions, driveability, and fuel economy. Modern electronic fuel-injection systems meter fuel very accurately and precisely, and use closed loop fuel-injection quantity-control based on feedback from an oxygen sensor (or “O2 sensor”). This enables fuel-injected engines to produce less air pollution than comparable carbureted engines. Properly-designed fuel injection systems can react rapidly to changing inputs such as sudden throttle movements, and will control the amount of fuel injected to match the engine’s needs across a wide range of operating conditions such as engine load, ambient air temperature, engine temperature, fuel octane level, and prevailing barometric pressure.
A multipoint fuel injection system generally delivers a more accurate and equal mass of fuel to each cylinder than can a carburetor, thus improving the cylinder-to-cylinder distribution. Exhaust emissions are cleaner because the more precise and accurate fuel metering reduces the concentration of toxic combustion byproducts leaving the engine, and because exhaust cleanup devices such as the catalytic converter can be optimized to operate more efficiently since the exhaust is of consistent and predictable composition.
Fuel injection generally increases engine fuel efficiency. With the improved cylinder-to-cylinder fuel distribution, less fuel is needed for the same power output. When cylinder-to-cylinder distribution is less than ideal, as is always the case to some degree with a carburetor or throttle body fuel injection, some cylinders receive excess fuel as a side effect of ensuring that all cylinders receive sufficient fuel. Power output is asymmetrical with respect to air/fuel ratio; burning extra fuel in the rich cylinders does not reduce power nearly as quickly as burning too little fuel in the lean cylinders. However, rich-running cylinders are undesirable from the standpoint of exhaust emissions, fuel efficiency, engine wear, and engine oil contamination. Deviations from perfect air/fuel distribution, however subtle, affect the emissions, by not letting the combustion events be at the chemically ideal (stoichiometric) air/fuel ratio. Grosser distribution problems eventually begin to reduce efficiency, and the grossest distribution issues finally affect power. Increasingly poorer air/fuel distribution affects emissions, efficiency, and power, in that order. By optimizing the homogeneity of cylinder-to-cylinder mixture distribution, all the cylinders approach their maximum power potential and the engine’s overall power output improves.
A fuel-injected engine often produces more power than an equivalent carbureted engine. Fuel injection alone does not necessarily increase an engine’s maximum potential output. Increased airflow is needed to burn more fuel, which in turn releases more energy and produces more power. The combustion process converts the fuel’s chemical energy into heat energy, whether the fuel is supplied by fuel injectors or a carburetor. However, airflow is often improved with fuel injection, the components of which allow more design freedom to improve the air’s path into the engine. In contrast, a carburetor’s mounting options are limited because it is larger, it must be carefully oriented with respect to gravity, and it must be equidistant from each of the engine’s cylinders to the maximum practicable degree. These design constraints generally compromise airflow into the engine. Furthermore, a carburetor relies on a restrictive venturi to create a local air pressure difference, which forces the fuel into the air stream. The flow loss caused by the venturi, however, is small compared to other flow losses in the induction system. In a well-designed carburetor induction system, the venturi is not a significant airflow restriction.
Fuel is saved while the car is coasting because the car’s movement is helping to keep the engine rotating, so less fuel is used for this purpose. Control units on modern cars react to this and reduce or stop fuel flow to the engine reducing wear on the brakes.
Advantage of M. P. F. I.
(1) More uniform A/F mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this the life of engine components is improved. (2) No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system. (3) Immediate response, in case of sudden acceleration / deceleration. (4) Since the engine is controlled by ECM* (Engine Control Module), more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level. (5) The mileage of the vehicle will be improved. ECM ( Engine Control Module) and its function The function of ECM is to receive signal from various sensors, manipulate the signals and send control signals to the actuators. Sensors; Sensing different parameters (Temperature, Pressure, Engine Speed etc.) of the engine and send signal to ECM. Actuators; Receives control signal from ECM and does function accordingly (ISCA, PCSV, Injectors, Power Transistor etc.) Case I: If ECM fails to send control signal to all actuators then the engine won't get started. Case II: If ECM fails to service from all sensors then also the engine won't get started.
Fuel Injection systems are now almost universal on road cars. The biggest reason for this is the law requiring very tight emission control that usually needs a Catalytic Converter (catatonic diverter, catastrophic inverter or whatever!). These things are rapidly ruined and become ineffective if used with a normal carb system. A carb cannot keep the fuel mixture so "exact" as fuel injection can. A slightly rich mixture ruins the Catalytic converter! The advent of computers makes modern electronic fuel injection possible at a sensible price. Advantages:Better mixture controlNo "choke" needed for cold startsReliabilityless "flat spots" than carb systemHigher peak power possible due to no restriction caused by carb venturiDisadvantages: ComplexityLess flexible to modification of motorRe-jetting is impossible and remapping more complex than swapping jetsweight, battery, computer,