Common-Rail Direct Injection (CRDI) System:

In this system the fuel from the tank is first supplied to common header called accumulator with the help of high pressure pump.

Fuel from accumulator is led into the engine cylinders through tubing to the injectors. A spring loaded high pressure relief valve maintains a constant pressure in the system and it returns the excess fuel of the header to the fuel tank.

The fuel is spread into the cylinders through a nozzle whose opening and closing is the controlled by needle valve. The upward and downward motion of needle valve is controlled by the motion of the cam.

When the cam is during its swell period, the spring forces the needle valve into the nozzle passages and prevents the admission of fuel into the cylinder. The lift of a cam pushes the push rod upwards and this motion is transmitted to the needle valve thought the valve through the rocker arm and lever.

The fuel is always kept in the space above the valve seat from the header and sealed from top through the packing gland. When the needle valve lifts, the high pressure fuel is passed through the nozzle to the cylinder.

The wedge is operated either manually or by a governor which controls the amount of fuel to be injected in accordance to the power requirement of the engine since the duration of its opening depends upon its position.

The fuel pressure in the accumulator can be varied by adjusting the spring pressure in high pressure relief valve.

Multi Point Fuel Injection system

It is one in which each cylinder has a separate fuel injector to supply/spray fuel into cylinder. Whereas, in a single point fuel injection (S.P.F.I.) system, only one centrally located fuel injector is used to supply/spray fuel to all cylinders.

M.P.F.I. system is the ultra-modern technology which is used in modern automobile engines. In the beginning, this system was developed only for aeroplane engines, but now this system is widely used in light vehicles. This system is the combination of electrical, electronics, computer and mechanical science.

Daewoo Matiz is the first vehicle equipped with M.P.F.I. system in Indian automobile industry.

M.P.F.I. system uses pressure from an electric fuel pump to spray fuel into engine intake manifold. It provides correct A.F. ration at all operating conditions of the engine. The suction pressure of that engine is used to spray fuel into engine in this system unlike carburettors in which engine vacuum is used to feed the fuel.

M.P.F.I. system has following main components:

A computer called Electronic Control unit (ECU): It controls the ignition timing and quality of fuel to be injected.

A set of sensors to monitor ambient, coolant and exhaust gas temperatures, exhaust content, intake pressure, throttle position, speed etc.

A solenoid injector:

The general layout of M.P.F.I. is shown in Fig.

In the fig., a single injector is mounted on the intake port pf each cylinder. Fuel is sent under pressure by the fuel tank. The fuel is distributed to each of the injectors. Fuel injection is carried our simultaneously in each injector once in every rotation. This is shown in fig. by various stages i.e. stages (1) to (4).