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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


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



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.



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



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



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



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.



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



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



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



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.



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



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.



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


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



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.



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



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



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.



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


http://www.emd.horiba.com/

http://www.robortboshasa.com/


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.
