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Overview
Introduction Principle Working Features Scope for further development Conclusion
Introduction
The country among other things has seen an enormous development in engines used in cars also.
The Diesel engines have also undergone a sea change from the time Rudolf Diesel invented it way back in 1892.
Today Common Rail Direct Injection (CRDI) is the order of the day.
CRDI Engine
Principle Unlike in conventional diesel engines,
the fuel is fed into the common tube or rail and high pressure is maintained.
This allows fuel to combine with air much more efficiently.
It features high-pressure fuel rail feeding individual solenoid valves as opposed to low-pressure fuel pump feeding injectors.
Layout of a CRDI Engine
Low –pressure circuit comprises of:Fuel tank ,Pre-supply pump, Fuel filter, And the
respective connection lines.
The Common Rail Sub functions
Low –pressure circuitThe low –pressure circuit is responsible for
transporting the fuel to the high –pressure circuit
High –pressure circuit comprises: High – pressure pump with pressure – control valve The high – pressure accumulator (Rail )with the
rail –pressure sensor Injectors, and The respective high – pressure connection lines.
The Common Rail Sub functions
The high – pressure circuit
It is the responsibility of the highpressure circuit to generate a constantunvarying high pressure in the highpressure accumulator (the rail) and toinject the fuel through the injectors
intothe engine’s combustion chambers.
ECU and sensorsThe common rail ECU evaluates the signals from
the following sensors. Crankshaft – speed sensor, Camshaft sensor, Accelerator-pedal travel sensor
The Common Rail Sub functions
The common rail ECU evaluates the signals from the following sensors:
Boost – pressure sensor, Air temperature sensor, Air – mass meter, and Rail pressure sensor.
The Common Rail Sub functions
The Common Rail Sub functionsECU and sensorsThe sensor are responsible for measuring important
physical quantities. The ECU calculates injected fuel quantity, start of injection, duration of injection, and rate of discharge curve, as well supervises the correct functioning of the injection system as a whole.
PRE SUPPLY PUMP Transports fuel from the fuel tank to the high
pressure pump. An electric fuel pump is used for this purpose
in the CRFIS. When the electric fuel pump is switched off,
the supply of fuel is interrupted and the engine stops.
COMMON RAIL FUEL INJECTION SYSTEM
DESIGN
PRE SUPPLY PUMP
The electric fuel pump comprises of:1.Electric Motor2.Roller-Cell Pump3.Non Return Valve
The roller cell is driven by an electric motor.
Its rotor is mounted eccentrically and provided with slots in which movable rollers are free to travel.
PRE SUPPLY PUMP
The rollers are forced against the base plate by rotation and by fuel pressure .
The fuel is transported to the outlet openings on the pump’s pressure side.
PRE SUPPLY PUMP
Gear type fuel pump The drive gear
wheel is driven by the engine .
Delivery quantity is directly proportional to engine speed .
Shut off is by means of an electromagnet..
PRE SUPPLY PUMPvariants
High- pressure pump The pump plunger moves downwards The inlet valve opens The fuel is drawn in to the pumping
element chamber(suction stroke)
At BDC, the inlet valve closes The fuel in the chamber can be compressed
by the upward moving plunger.
High- pressure pump
An electromagnet is used for pumping element switch-off.
High- pressure pump
High- pressure accumulator (Rail) Store fuel Prevent pressure fluctuations
Rail is a forged-steel tube. ID is approx.. 10mm Length is between 280 and 600mm The volume must be “ as small as
possible, as large as necessary”
High- pressure accumulator (Rail)
Pressure-control valve (DRV)
Responsible for maintaining the pressure in the rail at a constant level.
Rail-pressure sensor (RDS)
Measures the pressure in the rail
inputs the information to the ECU
RDS should provide extremely precise measured values.
RDS is mounted directly on the rail.
Injector Injects exactly the correct amount of
fuel in to the combustion chamber at precisely the right moment in time
The injector is equipped with: 2/2 electromagnetic servo valve Nozzle Valve control chamber Return line
Injector
The essential forces for correct functioning are:
Nozzle-spring force Valve spring force Electromagnet force Force due to the pressure in the valve-
control chamber Force due to the pressure in the nozzle
needle
Injector
ECU with sensors
Common Rail is an EDC controlled injection system
The ECU controls & monitors the complete injection process
The sensors delivers all the measured values which are required in the process
SummaryComponents of CRFIS
are: Pre-supply pump High-pressure pump High-pressure
accumulator(rail) Pressure-control valve
Rail-pressure sensor
Injectors ECU with sensors
COMMON RAIL FUEL INJECTION SYSTEM
Working Solenoid valves make possible fine
electronic control over the injection time and amount, and the higher pressure that the common rail technology makes available provides better fuel atomization. In order to lower engine noise, the engine's electronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimizing injection timing and the process continues
Features Direct injector Spiral-shaped intake port Integrated port Air flow metering Multiple Pilot injection and
Post injection Powerful Microcomputer Newly-developed catalytic
converters Reduced noise levels
Direct injector
A fuel injector is nothing but an electronically controlled valve.
Spiral-shaped Intake port
Provides optimum swirl and even distribution of fuel.
Integrated port
Integrated port is used for exhaust gas recycling. There are three advantages to this system
• eliminates external pipes which are subject to vibration
• quicker engine warm-up• better combustion.
Air flow metering
It gives exact analysis of the air-mass that is being taken in.
Due to this metering system, the microcomputer that controls engine timing receives precise data.
Multiple Pilot injection and Post injection
Pilot injections is small doses of fuel made prior to the main injection which help to smoothen the sharp combustion character.
Post injection is a similarly small dose of fuel injected after the main injection to reduce particulates.
Powerful Microcomputer
The microcomputer regulates the amount of time the valves stay open and thus the amount of fuel injected, depending on operating conditions and how much output is needed.
Newly-developed catalytic converters
Besides electronically-controlled exhaust-gas recycling which contributes to lower nitrous oxide emissions, CRDI engines are equipped with catalytic converters near the motor and emission control devices on the underbody. These vouch for a high degree of efficiency.
Reduced Noise levels
The Electronic control and multiple injections reduced noise to a great extent
Scope for further development
Use of different fuels for zero emissions and better engine performance
By using different fuels and cetane improvers, maximum torque can be obtained
Lowering the cost Closed-loop control injection with ion
sensing technology
Conclusion
CRDI technology revolutionized diesel engines. It has changed the way one looks as diesel cars by providing the above said advantages.
Advantages-More power is developed-Increased fuel efficiency-More stability-Pollutants are reduced-Particulates of exhaust are reduced-Exhaust gas recirculation is enhanced-Precise injection timing is obtained-Pilot and post injection increase the
combustion quality-The powerful microcomputer makes the
whole system more perfect
Manufacturers of CRDI engine
The car makers refer to their common rail engines by their own brand names. Some of them are
BMW's D-engines Mahindra's CRDe Tata's DICOR Honda's i-CTDi Hyundai-Kia's CRDi etc
References
International Journal of Automotive Technology
Approaches to Automotive Emissions Control
Magazines: Auto week, Automobile India
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