07-03-2011, 03:47 PM
report-Multi Point Fuel Injection-mpfi.doc (Size: 87 KB / Downloads: 140)
MPFI& Emission control system
1. INTRODUCTION
Petrol vehicles uses device called carburetor for supplying the air fuel mixture in correct ratio to cylinders in all rpm ranges. due to construction of the carburetor is relatively simple, it has been used almost exclusively on gasoline engines in the past. However in response to recent demands for cleaner exhaust emission, more economical fuel consumption, improved drivability, etc., the carburetor now must be equipped with various compensating devices, making it more complex system.
So In place of the carburetor, therefore, the MPFI (multi point fuel injection) system is used, assuring proper air fuel ratio to the engine by electrically injecting fuel in accordance with various driving conditions.
MPFI system injects fuel into individual cylinders, based on commands from the ‘on board engine management system computer’ – popularly known as the Engine Control Unit/ECU. These techniques result not only in better ‘power balance’ amongst the cylinders but also in higher output from each one of them, along with faster throttle response. The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions.
2. MAIN COMPONENTS OF MPFI SYSTEM
This system has four major components they are:
a) Air intake system
b) Fuel delivery system
c) Electronic control system
2.1. Air intake system
. The air (corresponding to the throttle valve opening) is filtered by the air cleaner, passes through the throttle body, and is distributed by the intake manifold and finally drawn into each combustion chamber. When the lAC valve is opened according to the signal from ECM, the air bypasses the1hrottle valve through bypass passage and is finally drawn into the intake manifold ¬
a. Throttle body
. The throttle body consists of the main bore, air bypass passage and the following parts. Throttle valve, which is interlocked with the accelerator pedal and controls the amount of the intake air. TP sensor which detects the throttle valve opening and sends a signal to ECM. lAC valve, which supplies the bypass, air depending on Engine condition.
b. Idle air control valve
The lAC valve controls opening of the bypass air passage. The air bypasses the throttle valve through bypass passage and is finally drawn into the intake manifold. Opening and closing of the valve itself is determined by
operation of the magnet, which is connected to it. The magnet operates according to electric current from ECM.
2.2. Fuel delivery system
The fuel in the fuel tank is pumped up by the fuel pump, filtered by fuel filter and fed under pressure to each injector through the delivery 'pipe. As the fuel pressure applied to the injector is always kept a certain amount higher than the pressure in the intake manifold by the fuel pressure regulator, the fuel is injected into the intake port of the cylinder head when the injector opens according to the injection signal form ECM. The fuel relieved by the fuel pressure regulator return through the fuel return to the fuel tank.
a. Fuel pump
The electrical fuel pump located on the fuel tank consists of armature, magnet, impeller, brush, check valve etc.The ECM controls its operation. When the power is supplied to the fuel pump, the motor in the pump runs and so does the impeller. This causes a pressure difference to occur between both sides of the impeller, as there are many grooves around it. Then the fuel is drawn through the inlet port, and with its pressure increases,
It is discharged through the outlet port, The fuel pump also has a check valve to keep some pressure in the fuel feed line even when the fuel pump is stopped.
b. Pressure regulator system
The fuel pressure regulator is diaphragm operated relief valve consisting of diaphragm, spring and valve. It keeps the fuel pressure applied to the injector 2.9Kglcm^2 higher than intake manifold at all times, The pressure applied to the upper chamber of the fuel pressure regulator intake manifold pressure and that to the lower chamber is fuel pressure. When the fuel pressure rises more than 2,9Kg/cm2 higher than the intake manifold pressure, the fuel pushes the valve in the regulator open and excess fuel return to the fuel tank through return line.
c. Injector
Each cylinder has one injector. Which is installed between the intake manifold delivery pipe. It is an electromagnetic type injection nozzle, which injects fuel into the intake port of the cylinder head according to the signal from ECM. When the solenoid coil of the injector is energised by ECM, it becomes an Electro magnet and attracts the plunger. At the same time, the ball valve which is incorporated with the plunger opens and the injector which is under the fuel pressure injects fuel. As the lift stroke of the ball valve of the injector is set constant, the amount of fuel injected at one time is determined by the length of the time during which the solenoid is energized
2.3. Electronic control system
The electronic control system consist of various sensors which detect the state of engine and driving conditions, ECM which controls various devices according to the signals from the sensors and Various controlled devices. The systems are
Fuel injection control system
Idle speed control system
Fuel pump control system,
Ignition control system,
Radiator fan control system,
Fuel injection control system
The electronic fuel injection system supplies the combustion chambers with air/fuel mixture of optimized ratio under widely varying driving conditions. It uses the sequential multi-port fuel injection system, which injects fuel into each intake port of the cylinder head. In this system ECM controls the time and timing of the fuel injection from the fuel injector into the cylinder head intake port according to the signals from the various sensors so that suitable air/fuel mixture is supplied to the engine in each driving condition. The factors to determine the injection time are the basic injection time which is calculated on the basis of the engine speed and the intake manifold pressure and various compensation which are determined according to the signals from various sensors that detect the state of the engine and driving conditions.