Post on 19-Nov-2014
description
Common Rail Direct Injection
1. INTRODUCTION
Today IC engine playing a dominant role in vehicles and still has
prospers future.
The fuel injection is a key component of engine and it’s playing
important role in meeting the emission challenges and improving performance of
engine. So, injection system has a following feature:
High mean effective injection pressure.
Flexible injection pressure control.
Flexible control of fuel quantity and injection timing.
Less engine noise.
Low manufacturing cost despite of high technical requirement.
The common rail injection system has high pressure pump which
operates continuously and charges a high pressure rail or reservoir or accumulator.
Fuel is led from this rail to the injector mounted on the cylinder head through lines.
The injector is solenoid operated. It receives pulses from the ECU to open the same.
The injection occurs when the solenoid is energised. The quality of
fuel injected is directly dependant on the duration on pulse when the injection
pressure is constant. Sensors on crankshaft indicate its position and speed and so the
timing of injection and its frequency can be controlled.
The conventional DI engine ignites all the fuel at same time, leading to
rapid increase in pressure and temperature. One of the big benefits using CR is that it
allows injection of minute quantity of fuel just before the main injection.
B. N. College of Engineering, Pusad1
Common Rail Direct Injection
2. TRADITIONAL INJECTION SYSTEM
In the basic injection system which is use before CR injection system
having individual pump a separating metering and compression is use for each
cylinder. An auxiliary cam on the engine camshaft drives a single-cylinder injection
pump. Early in the stroke of the plunger, the inlet port is closed and the fuel trapped
above the plunger is forced through a check valve into the injection line. The injection
nozzle has several holes through which the fuel sprays into the cylinder. A spring-
loaded injection needle keeps the injection valve closed until the pressure in the
injector volume, acting on parts of the needle surface, overcomes the spring force and
opens the valve. Thus, the phase of the pump camshaft relative to the engine
crankshaft controls the start of injection, while the force given by the initial
displacement of the spring gives the opening pressure. The pressure on spring size is
released and the delivery valves falls back to its seat and supply of fuel is stop. The
injection pump cam design and the position of the helical groove determine the
amount of fuel injected into the cylinder. Thus for a given cam design, the rotating
plunger and its helical groove controls the load.
Fig. 1 – Traditional cam-driven fuel injection system
B. N. College of Engineering, Pusad2
Common Rail Direct Injection
3. NEED OF COMMON RAIL DIRECT INJECTION
The image of diesel engine had been on an upward trend since
introduction of direct injection (DI) which has higher fuel efficiency. Beside all the
positive aspect of diesel engine one must not disregard endangering factors like
pollutants which traffic brings along it. The major pollutants in exhaust gas are
unburned hydrocarbon (HC), oxide of nitrogen (NOx), carbon monoxide (CO) and
particular matter (PM).
Scientists and engineers thinking about pollutant emission because
further reduction of emission with optimum performance will be more difficult
problem for them as worlds population grows, emission std. have become more
stringent out of necessity the strictest laws are generally initiate in California, with the
rest of U.S. and world following. All though air pollution is global problem. Including
India have started following euro-I, euro-II and euro-III std. Details of euro norms as
shown in table
Emission norms-Diesel Passenger car
Emission norms Euro-I Euro-II Euro-III Euro-IV
Carbon monoxide (g/Km) 2 .72 1.0 0.64 0.3
HC + NOx (g/Km) 0.97 0.7 0.56 0.56
Particular matter (g/Km) 0.14 0.08 0.05 0.02
Conventional diesel engine beneficial up to euro-II and euro-III but it
will not meet euro-IV and euro-V. That is why we had to move for common rail
diesel injection technology.
B. N. College of Engineering, Pusad3
Common Rail Direct Injection
4. COMMON RAIL CONCEPT DESIGN
The common rail composed of following components.
1. High pressure pump with pressure regulator and inject metering valve
2. Rail for fuel storage
3. Electro hydraulic injector
4. Electronic control unit (ECU)
Fig. 2 -Block dia. of CRDI components
Figure shows the common rail hydraulic circuit. Electrical or
mechanical pump raises the pressure of fuel flowing from the tank via the filter to the
of the high pressure pump. A solenoid operated metering valve mounted on the pump
inlet circuit controls the high-pressure fuel delivery. The high-pressure pump is driven
by the engine and delivers fuel at a constant pressure via the pressure regulator to the
rail. A pressure sensor mounted on the rail detects the fuel pressure. The signal is used
by the ECU to adjust the rail pressure to the desired value by acting on both the
B. N. College of Engineering, Pusad4
Common Rail Direct Injection
pressure regulator and the inlet metering valve. The injection pressure can be
controlled at each engine operating condition within the range of 150 to 1400 bar for
first generation.
The rail supplied fuel at constant pressure to the injector via high-
pressure pipes. It has the role of fuel accumulator and pressure pulsating damper. This
adjustment enables high pressure injection even at a low engine speed, and allows fuel
to be atomized sufficiently at any engine speed range. The current pulse generated by
the ECU energizes each injector solenoid valve in sequence and defines the start and
the end of each injection event per engine cycle. The common rail can generates more
than one injection and gives more flexible control of the rate of injection that
conventional rotary pump system
B. N. College of Engineering, Pusad5
Common Rail Direct Injection
5. SYSTEM OVERVIEW
1. High pressure pump:
The high pressure pump pumps the fuel delivered from the feed pump
(HP) into he high pressure accumulator Rail. An in line pump is used in heavy duty
vehicles like trucks. And radial piston pump with cam rings in cars. The pump
operates at low maximum torque and thus substantially reduces drive power
requirements.
A) In line fuel injection pump with electronic governor (activators) and integral
timing devices. In this pump system a number of pumping elements (also know as
plunger and barrel assemblies) corresponding to number of engine cylinders are
accommodates in a housing and operated by means of common cam shaft.
B) The common rail system high pressure pump utilizes redial pump as shown in
figure.
Fig. 3 – LDCR High pressure pump
B. N. College of Engineering, Pusad6
Common Rail Direct Injection
The two section of high pressure pump are shown as below:-
This high pressure pump has a cam which is stationary and a rotating
hydraulic head which houses two plungers. These plungers touch the cam and are
push in four times a rotation. Thus fuel is pumped four times per rotation. A non
return valve is used to send the fuel to the rail. The inlet of the pump is controlled to
maintain the needed delivery. It may be noted that any excess delivery is ultimately
returned back from the rail pressure regulator after it is throttle down to tank pressure.
This amounts to fuel heating and also loss of work takes place to pump the fuel.
Hence, controlling the delivery at the pump is a good idea. A high pressure pump is
also used. Both these valves are solenoid operated and are controlled by the ECU.
In the rail pressure regulator the spring force and the electromagnetic
force generated by the coil regulate the pressure. The pressure is controlled by ECU.
2. Rail for fuel storage:
The rail is connected to the injectors through high pressure pipes. The
rail acts as a reservoir for the fuel trapped between the check valves of the high
pressure pump and the injector. The injectors provides with the fuel at the required
injection pressure. The volume for a four- cylinder passenger car with 2 liter
displacement is around 20-25 ccs. The stored volume is also used as a damper for any
pressure fluctuations that occur due to the pulsating supply of fuel from the high
pressure pump and the brief, large fuel withdrawal during injection through the
injectors.
B. N. College of Engineering, Pusad7
Common Rail Direct Injection
Hence the rail volume should be carefully optimized Smaller volume
otherwise results in unnecessarily large pulsation in fuel pressure and a large volume
increases the response time of the pressure during transient and start conditions.
3. Electro hydraulic injector:
High pressure generation and control of the injection quantity occurs
independent of each other. Thus the injection pressure at start of injection can be
freely selected within relatively wide limits. The core of the system is the solenoid
valve controlled injector for each individual cylinder of the engine. A pulse from ECV
to the solenoid valves in the injector initiate the injection process. Opening duration of
solenoid valve and fuel pressure in the common rail system determines fuel quantity.
The injector consist of
A multi hole nozzle with a spring pressing the nozzle needle to its seating seat.
A control piston
An orifice feeding fuel to control piston
Solenoid assembly.
Fig. 4 - Injector
B. N. College of Engineering, Pusad8
Common Rail Direct Injection
The high pressure fuel fills the cavity around the injector nozzle. When
the solenoid valve is deactivated the orifice top of the control piston is close the high
pressure fuel flows on top of the control piston through orifice The resulting pressure
on the control piston in addition to the injector nozzle spring pressure keeps the
injector nozzle closed. When the solenoid valve is energized it opens orifice and the
fuel on top of the control piston flows back into the tank via return line. One of the
strength of the common rail system is multiple injection. This is possible because the
rail pressure is always available at the injector nozzle.
A solenoid injector have improved respond properties thereby
shortening the injection time and realizing multiple injection at one fuel intervals and
realizing multiple injections at one fuel combustion.
The five multiple injections as named
1. Pilot
2. Pre
3. Main
4. After post
The pilot injection, which occurs well before ignition provides time for the fuel
and air to mix... A large fuel injected during pilot injection increases particulate
matter emission. Hence pilot injection must take place at the right interval the
main injection and quantity has to be controlled precisely.
Pre injection shortens ignition delay in the main injection and there by reduces
generation of NOx noise and vibration
B. N. College of Engineering, Pusad9
Common Rail Direct Injection
The after injection, which occur a split second after the main injection, reburns the
any remaining PM.
The ultimate injection. Post injection helps manger the exhaust gas temperature
which makes the exhaust processing in the after treatment system more effective.
4. Electronic control unit (ECU):
The software in the ECU uses the sensor signals as inputs. And with
the help of the stored characteristic maps. Calculates the fuel quantity to be injected,
pressure at which it is to be injected and the time of injection (in degrees before
TDC). The quantity of fuel to be injected determines the duration of injection
(opening of the solenoid valve in the injector). The specified accuracy and the
engine’s high dynamic response demand high levels of computing power.
Fig. – 5- ECU
B. N. College of Engineering, Pusad10
Common Rail Direct Injection
The ECU supports high speed communication between other ECU on
the vehicle. It is used for information exchange over a dedicated network called the
Controller and network (CAN). The ECU stores the faults occur in the system along
with other environment information.
Sensors:-
Sensors act as set point generator for registrations of the operating
conditions. They convert a variety of physical parameters into electrical signals.
These signals are conditioned and processed by the ECU and used for calculation of
the fuel quantity, pressure and timing. Some of the important sensors present in the
EDC (Electronic Diesel Control) system are:
Boost pressure sensor:
The boost pressure sensor is connected to the intake manifold and
measures absolute pressure at the intake manifold.
Air mass sensor:
This sensor precisely registers the air mass flow into the intake
manifold.
Actuator:
Special injectors with hydraulic servo and electrical triggering element
(solenoid vale) are used to achieve efficient start of injector and precise injection fuel
quantity. At start of injection a high pickup current results in quick opening of the
solenoid valve. As soon as the nozzle needle has traveled its complete stroke and the
nozzle has opened completely. The energizing current is reduced to a lower holding
value. The injector opening time and the rail pressure define the injected fuel quantity.
As soon as the energizing current is removed the nozzle closes.
B. N. College of Engineering, Pusad11
Common Rail Direct Injection
6. SPRAY CHARACTERISTIC
The full forced through the nozzles under high pressure it is
disintegrated in to the fine droplets due to air resistance dense air present in the
combustion chamber. The disintegration of the fuel in to fine droplets depends on the
characteristics of the fuel and air the nozzles VCO type and has a six hole each having
a diameter of 0.15 to MM and length of 1mm (L/D=6.579) results in turbulent
velocity for mixing and evaporation less than 5 micro in size due to pressurize fuel to
1400 bar and produce fast and uniformity of atomization.
Fig. 6 - Spray Characteristic
Variation of parameter with time under injection pressure of 600 bar
and 400 bar respectively the tip penetration under lower chamber pressure longer than
under a higher chamber pressure for same injection pressure. A higher injection
B. N. College of Engineering, Pusad12
Common Rail Direct Injection
pressure provide less fuel momentum and hence spray travel faster and faster mixing
and better mixture towards homogeneous type with achieving Complete combustion
(burning) process. As the atomization by friction up to the 1400 bar more in the
atomization thus it is supported by the figure which illustrates the decrease in the
mean droplet diameter with increasing injection pressure.
B. N. College of Engineering, Pusad13
Common Rail Direct Injection
7. EFFECT OF INJECTION PARAMETERS
7.1 EFFECT OF INJECTION PRESSURE ON ENGINE
PERFORMANCE
With common rail systems, it is possible to keep injection pressure
almost constant throughout the injection period. It enables the injection pressure to be
taken as a varying parameter. The effect of injection pressure on engine performance
(break specific fuel consumption and mean indicated pressure were taken as
representative of specific and indicated results) are only significant in the range
between 300 and 700bar, and mainly for delayed combustion processes (figure).
Advancing injection is always beneficial in terms of engine performance, but
especially so for low injection pressure. Finally hole diameter of 0.23 mm presents
slightly better results than the other tested
Fig. 7-Injection pressure V/s BSFC Fig. 8- Injection pressure V/s mean
indicated pressure
7.2 EFFECT OF INJECTION PRESSURE ON EMISSION
As expected, more appreciable effects were found in terms of
emissions in figure Rising the injection pressure leads to noticeable increases on NOx
emissions and to different tendencies on smoke opacity. The effect of the injection
hole diameter is also noticeable: that of 0.23 mm presents the best smoke and CO B. N. College of Engineering, Pusad14
Common Rail Direct Injection
results but slightly higher NOx emissions than the others. The expected increases of
NOx with advanced combustion are compensated by smoke reductions only when the
injection pressure is very high as shown in fig.
Fig.9- Injection pressure Vs. CO Fig.10- Injection pressure Vs. smoke opacity
Fig. 11-Injection pressure Vs. NOx
B. N. College of Engineering, Pusad15
Common Rail Direct Injection
7.3 BREAK THERMAL EFFICIENCY
Figure show the variation in break thermal efficiency as a function of
load for the injection pressure 1400 bar and 2000 bar. It is clearly shown that the
engine performance very good perform at higher pressure and poor performance on
reduce injection pressure for poor distribution automation fuel in to air mixing due to
low pressure result in improper combustion, reducing thermal efficiency of the engine
full load efficiency up to 42.5% for 1400 bar while at to 200 bar 33.1%.
Fig. 12 – Figure shows the variation in thermal efficiency as a function of load for
the injection of 1400 bar and 2000 bar.
B. N. College of Engineering, Pusad16
Common Rail Direct Injection
8. FEATURES AND BENEFITS
FEATURES
Injection pressure and injection event are independent of engine speed or position
Injection pressure and injection event can be optimized independently
Multiple injection event capability
Alignment of pilot and post injection event to emission or after treatment system
requirement
Suction metered pumping principle for improved fuel consumption
Applicable to light, medium and heavy duty vehicles
BENEFITS
Delivers high torque at low engine speed
Applicable to variety of cylinder configurations
Potential solution to the future emission challenge
Flexible design can be easily integrated into diesel engine
Excellent application flexibility relative to injection pressure ,timing pilot and
post-event control
Proven application and manufacturing experience. Bosch was first market with
common rail for passenger car application
Delivers quiet, high-torque, low-emission and efficient diesel engine performance
to the consumer
B. N. College of Engineering, Pusad17
Common Rail Direct Injection
9. CRDI IN INDIAN MARKET
The next few year will see a marked change in Indian automobile
scene MICO is gearing itself up to introduce common rail technology to the Indian
market in the near future with corporation of Robert Bosch Gimbh. While considering
change to an electronically controlled injection system like the sophisticated common
rail system. One should keep in mind the following aspects.
The introduction of electronics requires a major shift in thinking in
may respects with more complex systems. The development and application time is
going to incasing when designed tested, built, assembled and traded with experience
and electronic system can be more reliable than mechanical system as they generally
don’t wear out fast
B. N. College of Engineering, Pusad18
Common Rail Direct Injection
10. CONCLUSION
An innovative common rail injection system for diesel power vehicle
with high pressure generation and control of the injection during can be freely
selected within relative wide limit
Compare to the unit injection system (UIS) and unit pumps system
(UPS) the CRS can reduce the emission level, also reduce the noise.
The electronic control unit controls the rail pressure, solenoid valve in
injector and injection pressure which help in reduction in noise, particulate matter and
NOx with increase break thermal efficiency.
Scientists always try to optimize the performance and emission
level .The CRDI with electronic control unit embodies additional strength, which
improves engine stability and reduces emission for clear environment.
The CRDI is only technology which will meet the Euro-IV and Euro-v
norms with better performance.
B. N. College of Engineering, Pusad19
Common Rail Direct Injection
REFERENCES
1. N. Gurrassi and P. Dupraz : ”A Common Rail Injection System For High Speed
Injection Engine” SAE Technical paper series 98803 internal Congress and
Exposition detoil Michigan Feb 23-26, 1998
2. O. Bunes and P. M. Einang : “MARINTEK paper at Ensus 2000 international
conference on marine science and technology for environment sustainability
Newcastle, September 2000
3. Magín Lapuerta, Octavio Armas and Juan Jose Hernandez :Universidad de
Castilla-La Mancha “Effect of the Injection Parameter of a CRI System “
4. L. M. Naik (MICO Banglor), Arun Bhat (Robert Bosh India) : “Common
Rail technology” for diesel passenger car.
5. Engine technology International: Issue 4/03 January 2003 Journal
6. Ganeshan, “Internal Combustion Engine” Ignition in CI engine / common rail
injection / page no. 349-355, Engine emission / Air pollution / page no. 495-498.
7. Ramalingam, “Internal Combustion Engine”
8. R. K. Rajput, “Internal Combustion Engine”
9. www.robortboshasa.com
10. www. fedral-mogal.com
11. www.emd.horiba.com
B. N. College of Engineering, Pusad20
Common Rail Direct Injection
ABSTRACT
The day of diesel engine is just about dawn in India ! To improve
power output fuel economy, reduce engine noise and vibration, simultaneously to
maintain the increasingly stringent requirement of the Euro-III and coming soon
Euro-IV legislation that common rail diesel injection technology for vehicle has proud
to be significant breakthrough. The biggest difference of technology when compare to
other diesel system is, its ability to generate high pressure independence of engine
speed and load As the result this system can be flexible in allowing splitting of fuel
quantity into pilot pre, main post injections.
A feed pump transport the fuel from tank to high pressure fuel pumps.
The high pressure fuel pump delivers the compressed fuel to high pressure rail. The
pressure sensor on rail allows an exact close loop rail pressure governing. The injector
with solenoid control is directly connected to rail and have same pressure as the rail.
The silent features of the rail technology injection pressure and timing can be control
and injection pressure is constant during injection.
B. N. College of Engineering, Pusad21