Fakultet inzenjerskih nauka u Kragujevcu
SEMINAR from English Language
By Dejan Matic 831/2013
CONTENTS 1. Introduction to Common Rail 2. Structure of Common Rail Direct Injection System 3. Common Rail Injection System 4. Operating Principle 5. Advantages 6. An insight to Cdi Engine 7. Conclusion 8. Reference
COMMON RAIL DIESEL INJECTION INTRODUCTION Diesels known for their power handling capabilities acquired the title workhorse engines. Diesels may reside in heavy-duty trucks, buses, tractors, and trains, not to mention large ships, bulldozers, cranes, and other construction equipment. Gasoline engines might dwell in the typical passenger vehicle, lawn equipment and recreational vehicles. There are basically 2 types of popular engines used in the world today: 1. Petrol engines 2. Diesel engines Petrol fuel is injected as an air/fuel mixture into the combustion chamber and ignited by the spark from spark plugs. Diesel fuel is pressurized and injected into the combustion chamber through a fuel injector nozzle, just when the air in the chamber has been subjected to high pressure that it is hot enough to ignite the fuel spontaneously. Traditional fuel injection systems for diesel engines are designed with the objective to secure acceptable fuel spray characteristics during the combustion process at all load conditions. Incorrect injection causes reduced efficiency and increased emission of harmful species.. Among the advantages claimed with respect to the common rail concept are injection rate shaping, variable timing and duration of the injection, in addition to variable injection pressure, enabling high injection pressure even at low engine loads. Medium speed diesel engines are different from the automotive diesel engines, especially in that the majority of them operate at constant load and speed most of the time, and the advantages of the more complicated common rail system may not be justified. The common rail injection system is not capable of supplying all possible rate shapes, and rate shaping is mostly restricted to delivering a pre injection prior to the main injection. When the rate of injection is the key to an effective combustion process, it is vital to determine how the 4 rate of injection from the common rail system compares to the rate of injection from a traditional injection system.
STRUCTURE OF COMMON RAIL DIRECT INJECTION SYSTEM The Common Rail Direct Diesel Injection system consists of the following parts:
Injection nozzle: Injects fuel into the combustion chamber (for direct injection) or pre-combustion (for indirect injection).
Fuel Supply Pump : The fuel supply pump in low pressure stage is responsible for maintaining an adequate supply of fuel to the high pressure components. This applies: 1. Irrespective of operating state. 2. With a minimum of noise. 3. at necessary pressure. 4. Throughout the vehicle’s service life.
The fuel supply pump draws fuel out of the fuel tank and conveys it continuously in the required quantity to the high pressure fuel injection installation. Many pumps leed themselves automatically so that starting is possible even when fuel tank has run dry. There are three designs: 1. electric fuel pump 2. Mechanically driven gear pump 3. Tandem fuel pumps. In axial-piston and radial-piston distributor pumps, a vane type supply pump is used as pre-supply pump and is integrated directly in the fuel injection pump.
Fuel Filter : The service life design of the fuel injection system depends on a specific minimum purity of the fuel. Functions of fuel filter are: 1. Particulate filtration:. 2. Water Separation: Two filters can also be fitted in parallel, resulting in greater particulate storage capacity. Connecting the filter in series produces a higher filtration efficiency. Pre-filter is fitted on the suction or pressure side if requirements are particularly high with a filter fineness matched to the main filter.
The Rail of Common Rail Injection System: The common rail is a modular system, and can therefore be easily adapted for different engines. Besides acting as fuel accumulator, the fuel rail also distributes fuel to the injectors. The function of the high pressure accumulator is to maintain the fuel at high pressure. In so doing accumulator volume has to dampen pressure fluctuations caused by fuel pulses delivered by the fuel pump and the fuel injection cycles. This ensures that, when the injector opens the injection pressure remains constant.
High-pressure Line: In common rail systems, they serve as the connection between the high pressure pump and the rail and from rail to the injector. The pipe is made of steel as it has to withstand high pressures. The following types of fittings are used: 1. Sealing cone and union nut 2. Heavy duty insert fittings 3. Perpendicular connection fittings. The high pressure fuel lines must withstand the systems maximum pressure as well as pressure variations that can attain very high fluctuations. The lines are seamless precision made steel tubing in killed cast steel which has particularly consistent microstructure.
Fuel injection pumps : Diesel fuel injection pumps are generally divided into two categories: 1.
2.
3.
Mechanically controlled fuel injection pumps are available as: 1.In-line type 2. Distributor type Electronically controlled fuel injection pumps are available as: 1. In-line type 2. Distributor type Common Rail type
Mechanically controlled fuel injection pumps: In-line Fuel Injection pumps have the same number of plungers as cylinders in the engine. They have been around the longest and include Camshaft-Less (PFR) types.
Electronically controlled fuel injection pump: An electronically controlled fuel injection pump utilizes a microcomputer to control fuel injection quantity and injection timing according to running conditions of the engine. Unlike conventional mechanical control, fuel injection quantity and injection timing are controlled electronically, thereby resulting in fine and accurate control. It can be referred to as Electronic Control Diesel or ECD.
Electronically controlled fuel injection pump: An electronically controlled fuel injection pump utilizes a microcomputer to control fuel injection quantity and injection timing according to running conditions of the engine. Unlike conventional mechanical control, fuel injection quantity and injection timing are controlled electronically, thereby resulting in fine and accurate control. It can be referred to as Electronic Control Diesel or ECD.
High-pressure stage of the radial-piston distributor injection pump:
Radial-piston
high-pressure
pumps
produce
higher
injection
pressures than Axial-piston high-pressure pumps. Consequently, they also require more power to drive themThe radial-piston high-pressure pump is driven directly by the distributor Pump driveshaft. The main pump components are
the cam ring
the roller supports
rollers
the delivery plungers
the drive plate
the front section (head) of the distributor shaft The drive shaft drives the drive plate by means of radially positioned guide slots. The guide slots simultaneously act as the locating slots for the roller supports. The roller supports and the rollers held by They run around the inner cam profile of the cam ring that surrounds the drive shaft. The number of cams corresponds to the number of cylinders in the engine. The drive plate drives the distributor shaft. The head of the distributor shaft holds the delivery lungers which are aligned radially to the drive-shaft axis (hence the name “radial-piston high-pressure pump”). The delivery plungers rest against the roller supports. As the roller supports are forced outwards by centrifugal force, the delivery plungers follow the profile of the cam ring and describe a cyclical reciprocating motion.
Injector: A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car, and it is capable of opening and closing many times per second. Different types of injectors are
Solenoid Valve Injector: When
the
injector
is
energized,
an
electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel to make as fine am mist as possible so that it can burn easily.
Piezo-Inline Injector: The nozzle needle on piezo-inline injector is controlled indirectly by servo valve. The required injected fuel quantity is then controlled by the valve triggering period. The nozzle is kept closed by the rail pressure
exerted in the control chamber. When the piezo actuator is triggered, the serve valve opens and closes the bypass passage. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU.
Electronic Control Unit: An Engine Control Unit (ECU), also known as Engine Management
System
(EMS)
is
an
electronic
device,
fundamentally a computer, that is part of an internal combustion engine, which reads several sensors in the engine and uses the information to control the ignition systems of the engine.
An electronic control unit contains the hardware and software (firmware). The hardware consists of electronic components on a printed circuit board (PCB). The main component on this circuit board is a microcontroller chip (CPU). The software is stored in the microcontroller or other chips on the PCB, typically in EPROMs or flash memory so the CPU can be re-programmed by uploading updated code. This is also referred to as an (electronic) Engine Management System (EMS). There are two main types of control for multi-port systems
The fuel injectors can all open at the same time,
Each one can open just before the intake valve for its cylinder opens (this is called
sequential multi-port fuel injection). The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The range of tasks performed by the engine control unit includes the following functions:
Common-rail injection
Delivery control of the high-pressure pump
Engine speed limitation
Deceleration fuel cut-off
Fuel pump
Air
supply
Drive control
Diagnosis
A separate data network links the engine management system with the generator and the glow control unit, which lies at the heart of an innovative quick-start low system. This shortens the preheating time for the engine to just a moment, so hat the diesel is now also the equal of a petrol engine in this respect.
Nothing ‘COMMON’ About It. More Torque, Less Emission and Less Noise. While the Japanese are leading in petrol direct injection technology, Germany's Bosch, working in conjunction with several European car makers, pioneered Common Rail Direct Injection for diesel engines. Compare with petrol, diesel is the lower quality ingredient of petroleum family. Diesel particles are larger and heavier
than
difficult
to
petrol,
thus
pulverise.
more
Imperfect
pulverisation leads to more unburnt particles, hence more pollutant, lower fuel
efficiency
and
less
power.
Common-rail technology is intended to improve the pulverisation process. The rail assembly used in CRDi is as shown in figure. The main components on the rail assembly are: 1. Common pressure accumulator (the “rail”) 2. High pressure regulator (option) 3. Inlet metered high-pressure supply pump with integrated lift pump 4. Injectors 5. Electronic control unit (ECU) 6. Filter unit To improve pulverisation, the fuel must be injected at a very high pressure, so high that normal fuel injectors cannot achieve. In common-rail system, the fuel pressure is implemented by a strong pump instead of fuel injectors. The high-pressure fuel is fed to
individual fuel injectors via a common rigid pipe (hence the name of "common-rail"). In the current first generation design, the pipe withstand the pressure as high as 1,350 bar or 20,000 psi. Fuel always remains under such pressure even in stand-by state. Therefore whenever the injector (which acts as a valve rather than a pressure generator) opens, the high-pressure fuel can be injected into combustion chamber quickly. As a result, not only pulverisation is improved by the higher fuel pressure, but the duration of fuel injection can be shortened and the timing can be precisely controlled. Benefited by the precise timing, common-rail injection system can introduce a "postcombustion", which injects small amount of fuel during the expansion phase thus create a small scale combustion before the normal combustion takes place.
OPERATING PRINCIPLE A feed pump delivers the fuel through a filter unit to the high pressure pump through feed pipe. The high-pressure pump delivers fuel to the high-pressure accumulator (the rail). The electronically controlled injectors inject fuel into the combustion chamber when the solenoid valve is actuated. Because the injection pressure is independent of engine speed and load, the actual start of injection, the injection pressure, and the duration of injection can be freely chosen from a wide range.The introduction of pilot injection, which is adjusted depending on engine needs, results in significant engine noise reduction, together with a reduction in NOx emissions. The pressure in the system is controlled by the actuator. The figure shows all the components in a common rail system for a fully equipped, 4 cylinder, passenger car diesel engine. Depending on the type of vehicle and its application, some of the components may not be fitted. The sensors and setpoint generators are not depicted in their real installation position to simplify presentation. Exceptions are the exhaust-gas treatment sensors and the rail pressure sensor as their installation positions are required to understand the system. Data exchange between the various sections takes place via the CAN bus in the interfaces suction: • Starter Motor • Alternator • Electronic Immobilizer
• Transmission control • Traction Control System • Electronic Stability Program
System Diagram For Passenger Cars
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
AN INSIGHT INTO THE CDI ENGINE
Pilot Injection Feature: The high combustion pressure of up to 145 bar (2130 psi) in the CDI engine, and the rate at which this pressure rises during the combustion process normally produce higher noise levels in direct injection engines than in their pre-chamber (indirect injection) counterparts.
CONCLUSION CRDI technology revolutionized diesel engines. It has changed the way one looks as diesel cars by providing the above said advantages.
REFERENCES: http/www.crdi.technolog.co.in www.google.com
