MULTI POINT FUEL INJECTION SYSTEM PDF
In the Multipoint Injection System, we have one injector per cylinder; the injector injects the fuel into the admission valve which admits the fuel and air into the. How fuel injection is controlled & it's different types. Rear-mounted fuel tank, electric fuel pump, multi-point fuel injection system. System application: XU5J, XU5JA, XU5JA/K, XU51C/K, XU9JA, XU9JA/K.
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PDF | On Jan 2, , M A Vadivelu and others published Cooling System Optimisation of a Multi - Point Fuel Injection Engine. Fuel injection is a system for mixing fuel with air in an internal combustion engine . . Multipoint injection system. (sequential). Direct Injection. Fuel delivery. The Multi-Point Electronic Fuel Injection (EFI) system is an electronically controlled system which combines electronic sequential fuel injection and electronic.
Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top.
Multi Point Fuel Injection (MPFI) System | Types, Advantages, Disadvantages
This had the advantage of never flooding the engine, as any liquid fuel droplets would fall out of the carburetor instead of into the intake manifold; it also lent itself to use of an oil bath air cleaner, where a pool of oil below a mesh element below the carburetor is sucked up into the mesh and the air is drawn through the oil-covered mesh; this was an effective system in a time when paper air filters did not exist. Operation Fixed-Venturi in which the varying air velocity in the Venturi alters the fuel flow; this architecture is employed in most carburetors found on cars.
Variable-Venturi in which the fuel jet opening is varied by the slide which simultaneously alters air flow. In "constant depression" carburetors, this is done by a vacuum operated piston connected to a tapered needle which slides inside the fuel jet.
A simpler version exists, most commonly found on small motorcycles and dirt bikes, where the slide and needle is directly controlled by the throttle position.
The most common variable Venturi constant depression type carburetor is the sidedraft SU carburetor and similar models from Hitachi, Zenith-Stromberg and other makers. The UK location of the SU and Zenith-Stromberg companies helped these carburetors rise to a position of domination in the UK car market, though such carburetors were also very widely used on Volvos and other non-UK makes.
Other similar designs have been used on some European and a few Japanese automobiles. These carburetors are also referred to as "constant velocity" or "constant vacuum" carburetors. An interesting variation was Ford's VV Variable Venturi carburetor, which was essentially a fixed Venturi carburetor with one side of the Venturi hinged and movable to give a narrow throat at low rpm and a wider throat at high rpm.
This was designed to provide good mixing and airflow over a range of engine speeds, though the VV carburetor proved problematic in service. To function correctly under all these conditions, most carburetors contain a complex set of mechanisms to support several different operating modes, called circuits.
Basics A carburetor basically consists of an open pipe through which the air passes into the inlet manifold of the engine. The pipe is in the form of a Venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the Venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end- on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it almost completely blocks the flow of air.
The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent control on other vehicles or equipment. Fuel is introduced into the air stream through small holes at the narrowest part of the Venturi and at other places where pressure will be lowered when not running on full throttle.
Fuel flow is adjusted by means of precisely calibrated orifices, referred to as jets, in the fuel path. Main open-throttle circuit As the throttle is progressively opened, the manifold vacuum is lessened since there is less restriction on the airflow, reducing the flow through the idle and off-idle circuits.
This is where the Venturi shape of the carburetor throat comes into play, due to Bernoulli's principle i. The Venturi raises the air velocity, and this high speed and thus low pressure sucks fuel into the airstream through a nozzle or nozzles located in the center of the Venturi. Sometimes one or more additional booster Venturis are placed coaxially within the primary Venturi to increase the effect. As the throttle is closed, the airflow through the Venturi drops until the lowered pressure is insufficient to maintain this fuel flow, and the idle circuit takes over again, as described above.
Bernoulli's principle, which is a function of the velocity of the fluid, is a dominant effect for large openings and large flow rates, but since fluid flow at small scales and low speeds low Reynolds number is dominated by viscosity, Bernoulli's principle is ineffective at idle or slow running and in the very small carburetors of the smallest model engines. Small model engines have flow restrictions ahead of the jets to reduce the pressure enough to suck the fuel into the air flow.
Similarly the idle and slow running jets of large carburetors are placed after the throttle valve where the pressure is reduced partly by viscous drag, rather than by Bernoulli's principle. The most common rich mixture device for starting cold engines was the choke, which works on the same principle.
Accelerator pump Liquid gasoline, being denser than air, is slower than air to react to a force applied to it. When the throttle is rapidly opened, airflow through the carburetor increases immediately, faster than the fuel flow rate can increase.
This transient oversupply of air causes a lean mixture, which makes the engine misfire or "stumble" —an effect opposite what was demanded by opening the throttle. This is remedied by the use of a small piston or diaphragm pump which, when actuated by the throttle linkage, forces a small amount of gasoline through a jet into the carburetor throat.
This extra shot of fuel counteracts the transient lean condition on throttle tip-in. Eventually the seals around the moving parts of the pump wear such that pump output is reduced; this reduction of the accelerator pump shot causes stumbling under acceleration until the seals on the pump are renewed. The accelerator pump is also used to prime the engine with fuel prior to a cold start.
Excessive priming, like an improperly adjusted choke, can cause flooding. This is when too much fuel and not enough air are present to support combustion. For this reason, most carburetors are equipped with an unloader mechanism: The accelerator is held at wide open throttle while the engine is cranked, the unloader holds the choke open and admits extra air, and eventually the excess fuel is cleared out and the engine starts.
Choke When the engine is cold, fuel vaporizes less readily and tends to condense on the walls of the intake manifold, starving the cylinders of fuel and making the engine difficult to start; thus, a richer mixture more fuel to air is required to start and run the engine until it warms up.
A richer mixture is also easier to ignite. To provide the extra fuel, a choke is typically used; this is a device that restricts the flow of air at the entrance to the carburetor, before the Venturi. With this restriction in place, extra vacuum is developed in the carburetor barrel, which pulls extra fuel through the main metering system to supplement the fuel being pulled from the idle and off-idle circuits.
This provides the rich mixture required to sustain operation at low engine temperatures. In addition, the choke can be connected to a cam the fast idle cam or other such device which prevents the throttle plate from closing fully while the choke is in operation.
This causes the engine to idle at a higher speed. Fast idle serves as a way to help the engine warm up quickly, and give a more stable idle while cold by increasing airflow throughout the intake system which helps to better atomize the cold fuel. In many carbureted cars, the choke is controlled by a cable connected to a pull-knob on the dashboard operated by the driver. In some carbureted cars it is automatically controlled by a thermostat employing a bimetallic spring, which is exposed to engine heat, or to an electric heating element.
This heat may be transferred to the choke thermostat via simple convection, via engine coolant, or via air heated by the exhaust. More recent designs use the engine heat only indirectly: A sensor detects engine heat and varieselectric current to a small heating element, which acts upon the bimetallic spring to control its tension, thereby controlling the choke.
A choke unloader is a linkage arrangement that forces the choke open against its spring when the vehicle's accelerator is moved to the end of its travel.
This provision allows a "flooded" engine to be cleared out so that it will start. Some carburetors do not have a choke but instead use a mixture enrichment circuit, or enrichment. Typically used on small engines, notably motorcycles, enrichments work by opening a secondary fuel circuit below the throttle valves. This circuit works exactly like the idle circuit, and when engaged it simply supplies extra fuel when the throttle is closed. Classic British motorcycles, with side-draft slide throttle carburetors, used another type of "cold start device", called a "tickler".
History and Development
This is simply a spring-loaded rod that, when depressed, manually pushes the float down and allows excess fuel to fill the float bowl and flood the intake tract. If the "tickler" is held down too long it also floods the outside of the carburetor and the crankcase below, and is therefore a fire hazard.
Other elements The interactions between each circuit may also be affected by various mechanical or air pressure connections and also by temperature sensitive and electrical components. These are introduced for reasons such as response, fuel efficiency or automobile emissions control. Various air bleeds often chosen from a precisely calibrated range, similarly to the jets allow air into various portions of the fuel passages to enhance fuel delivery and vaporization.
A critical thing to understand about fueling an engine is the fact that peak torque occurs at the rpm at which an engine is achieving its best volumetric efficiency cylinder filling with air. Modern high-speed spark ignition engines usually make more horsepower at engine speeds exceeding this, but only because they are making more power pulses per unit of time. The cylinders are actually not filling as well with air. Therefore, fuel flow as a function of rpm no longer increases as steeply the elbow in the curve occurs at peak VE.
The problem with such constant-flow mechanical injection systems is that the mechanical fuel pump, driven by the engine, increases in speed with the engine.
Now a day, the digital revolution is taking place increasingly and
Assuming a linear increase in fuel pumped with pump speed fuel pumped doubles as pump speed doubles , the engine will begin to run rich as rpm increases beyond peak torque and fuel flow continues to increase at a constant rate while airflow into the engine increases more slowly as VE decreases.
The more precise fuel delivery cleans the exhaust and produces less toxic byproducts. Therefore, the engine and the air remain cleaner. MPFI system improves the engine performance. It atomizes the air in small tube instead additional air intake, and enhances the cylinder-to-cylinder fuel distribution that aid to the engine performance. It encourages distribution of more uniform air-fuel mixture to each cylinder that reduces the power difference developed in individual cylinder.
The MPFI automobile technology improves the engine response during sudden acceleration and deceleration. It improves functionality and durability of the engine components. The MPFI system encourages effective fuel utilization and distribution. Like this presentation?
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Why fuel system is required????? Another design of Port Type system 7. Air intake system 2. Fuel delivery system 3.
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electronic multipoint fuel injection system
Classic British motorcycles, with side-draft slide throttle carburetors, used another type of "cold start device", called a "tickler". Sahae Wang. With no Venturi effect or heated carburetor to help vaporize the gasoline AMC's EFI equipped engine breathed easier with denser cold air to pack more power sooner and it reached peak torque rpm quicker. On the other hand, older Opel-Astras had a 'single point' fuel injection system, which is in between an MPFI and the now obsolete SingleCarburetors systems.
All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. And for its effective working the very accurate control over the air-fuel ratio must be there. It improves functionality and durability of the engine components.
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