Crdi COMMON RAIL DIRECT INJECTION full report
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Compared with petrol, diesel is the lower quality product of petroleum family. Diesel particles are larger and heavier than petrol, thus more difficult to pulverize. Imperfect pulverization leads to more unburnt particles, hence more pollutant, lower fuel efficiency
and less power.
Common-rail technology is intended to improve the pulverization process. Conventional direct injection diesel engines must repeatedly generate fuel pressure for each injection. But in the CRDI engines the pressure is built up independently of the injection sequence and remains permanently available in the fuel line. CRDI system that uses an ion sensor to provide real-time combustion data for each cylinder. The common rail upstream of the cylinders acts as an accumulator, distributing the fuel to the injectors at a constant pressure of up to 1600 bar. Here high-speed solenoid valves, regulated by the electronic engine management, separately control the injection timing and the amount of fuel injected for each cylinder as a function of the cylinder's actual need.
In other words, pressure generation and fuel injection are independent of each other. This is an important advantage of common-rail injection over conventional fuel injection systems as CRDI increases the controllability of the individual injection processes and further refines fuel atomization, saving fuel and reducing emissions. Fuel economy of 25 to 35 % is obtained over a standard diesel engine and a substantial noise reduction is achieved due to a more synchronized timing operation. The principle of CRDi is also used in petrol engines as dealt with the GDI (Gasoline Direct Injection) , which removes to a great extent the draw backs of the conventional carburetors and the MPFI systems.
Submitted By:Junet Babu
CRDi stands for Common Rail Direct Injection meaning, direct injection of the fuel into the cylinders of a diesel engine via a single, common line, called the common rail which is connected to all the fuel injectors.
Whereas ordinary diesel direct fuel-injection systems have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence. This pressure then remains permanently available throughout the fuel line. The engine's electronic timing regulates injection pressure according to engine speed and load. The electronic control unit (ECU) modifies injection pressure precisely and as needed, based on data obtained from sensors on the cam and crankshafts. In other words, compression and injection occur independently of each other. This technique allows fuel to be injected as needed, saving fuel and lowering emissions.
More accurately measured and timed mixture spray in the combustion chamber significantly reducing unburned fuel gives CRDi the potential to meet future emission guidelines such as Euro V. CRDi engines are now being used in almost all Mercedes-Benz, Toyota, Hyundai, Ford and many other diesel automobiles.
2. PRINCIPLE OF CRDi IN GASOLINE ENGINES.
Gasoline or petrol engines were using carburetors for supply of air-fuel mixture before the introduction of MPFI system .but even now carburetors are in use for its simplicity and low cost. Now a days the new technology named Gasoline Direct Injection (GDI) is in use for petrol engines. The GDI is using the principle of CRDi system. Now let us examine the various factors that lead to introduction of GDI technology.
2.1.The fall of carburettor.
For most of the existence of the internal combustion engine, the carburetor has been the device that supplied fuel to the engine. On many other machines, such as lawnmowers and chainsaws, it still is. But as the automobile evolved, the carburetor got more and more complicated trying to handle all of the operating requirements. For instance, to handle some of these tasks, carburetors had five different circuits:
2.1.1 : Main circuit Provides just enough fuel for fuel-efficient cruising
2.1.2 : Idle circuit Provides just enough fuel to keep the engine idling
2.1.3 : Accelerator pump Provides an extra burst of fuel when the accelerator pedal is first depressed, reducing hesitation before the engine speeds up
2.1.4 : Power enrichment Provides extra fuel when the car is going up a hill or
circuit towing a trailer
2.1.5 : Choke Provides extra fuel when the engine is cold so that it will start effortlessly
In order to meet stricter emissions requirements, catalytic converters were introduced. Very careful control of the air-to-fuel ratio was required for the catalytic converter to be effective. Oxygen sensors monitor the amount of oxygen in the exhaust, and the engine control unit (ECU) uses this information to adjust the air-to-fuel ratio in real-time. This is called closed loop controlâ€it was not feasible to achieve this control with carburetors. There was a brief period of electrically controlled carburetors before fuel injection systems took over, but these electrical carburetors were even more complicated than the purely mechanical ones.
At first, carburetors were replaced with throttle body fuel injection systems (also known as single point or central fuel injection systems) that incorporated electrically controlled fuel-injector valves into the throttle body. These were almost a bolt-in replacement for the carburetor, so the automakers didn't have to make any drastic changes to their engine designs.
Gradually, as new engines were designed, throttle body fuel injection was replaced by multi-port fuel injection (also known as port, multi-point or sequential fuel injection). These systems have a fuel injector for each cylinder, usually located so that they spray right at the intake valve. These systems provide more accurate fuel metering and quicker response.
3.DIRECT INJECTION SYSTEMS.
Direct injection means injecting the fuel directly into the cylinder instead of premixing it with air in separate intake ports. That allows for controlling combustion and emissions more precisely, but demands advanced engine
Unlike petrol engines, diesel engines donâ„¢t need ignition system. Due to the inherent property of diesel, combustion will be automatically effective under a certain pressure and temperature combination during the compression phase of Otto cycle. Normally this requires a high compression ratio around 22 : 1 for normally aspirated engines. A strong thus heavy block and head is required to cope with the pressure. Therefore diesel engines are always much heavier than petrol equivalent.
The lack of ignition system simplifies repair and maintenance, the absence of throttle also help. The output of a diesel engine is controlled simply by the amount of fuel injected. This makes the injection system very decisive to fuel economy. Even without direct injection, diesel inherently delivers superior fuel economy because of leaner mixture of fuel and air. Unlike petrol, it can combust under very lean mixture. This inevitably reduces power output but under light load or partial load where power is not much an important consideration, its superior fuel economy shines.
Another explanation for the inferior power output is the extra high compression ratio. On one hand the high pressure and the heavy pistons prevent it from revving as high as petrol engine (most diesel engine deliver peak power at lower than 4500 rpm.), on the other hand the long stroke dimension required by high compression ratio favors torque instead of power. This is why diesel engines always low on power but strong on torque.
To solve this problem, diesel makers prefer to add turbocharger. It is a device to input extra air into the cylinder while intake to boost up the power output of the engine. Turbochargerâ„¢s top end power suits the torque curve of diesel very much, unlike petrol. Therefore turbocharged diesel engines output similar power to a petrol engine with similar capacity, while delivering superior low end torque and fuel economy.
4.COMMON RAIL DIRECT INJECTION: FEATURES:
Simply explained, common rail refers to the single fuel injection line on the CRDi engines. Whereas conventional direct injection diesel engines must repeatedly generate fuel pressure for each injection, in CRDi engines the pressure is built up independently of the injection sequence and remains permanently available in the fuel line.
In the CRDi system developed jointly by Mercedes-Benz and Bosch, the electronic engine management system continually adjusts the peak fuel pressure according to engine speed and throttle position. Sensor data from the camshaft and crankshaft provide the foundation for the electronic control unit to adapt the injection pressure precisely to demand.
Common Rail Direct Injection is different from the conventional Diesel engines. Without being introduced to an antechamber the fuel is supplied directly to a common rail from where it is injected directly onto the pistons which ensures the onset of the combustion in
the whole fuel mixture at the same time. There is no glow plug since the injection pressure is high. The fact that there is no glow plug lowers the maintenance costs and the fuel consumption.
Compared with petrol, diesel is the lower quality fuel from petroleum family. Diesel particles are larger and heavier than petrol, thus more difficult to pulverize. Imperfect pulverization leads to more unburned particles, hence more pollutant, lower fuel efficiency and less power. Common-rail technology is intended to improve the pulverization process.
To improve pulverization, the fuel must be injected at a very high pressure, so high that normal fuel injectors cannot achieve it.
In common-rail system, the fuel pressure is implemented by a very 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 withstands pressures as high as 1,600 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 pulverization is improved by the higher fuel pressure, but the duration of fuel injection can be shortened and the timing can be more precisely controlled. Precise timing reduces the characteristic Diesel Knock common to all diesel engines, direct injection or not.
Benefited by the precise timing, common-rail injection system can introduce a "post-combustion", which injects small amount of fuel during the expansion phase thus creating small scale combustion after the normal combustion takes place. This further eliminates the unburned particles and also increases the exhaust flow temperature thus reducing the pre-heat time of the catalytic converter. In short, "post-combustion" cuts pollutants. The drive torque and pulsation inside the high-pressure lines are minimal, since the pump supplies only as much fuel as the engine actually requires. The high-pressure injectors are available with different nozzles for different spray configurations. Swirler nozzle to produce a cone-shaped spray and a slit nozzle for a fan-shaped spray.
The new common-rail engine (in addition to other improvements) cuts fuel consumption by 20%, doubles torque at low engine speeds and increases power by 25%. It also brings a significant reduction in the noise and vibrations of conventional diesel engines. In emission, greenhouse gases (CO2) is reduced by 20%. At a constant level of NOx, carbon monoxide (CO) emissions are reduced by 40%, unburnt hydrocarbons (HC) by 50%, and particle emissions by 60%.
CRDI principle not only lowers fuel consumption and emissions possible; it also offers improved comfort and is quieter than modern pre-combustion engines. Common-rail engines are thus clearly superior to ordinary motors using either direct or indirect fuel-injection systems.
This division of labor necessitates a special chamber to maintain the high injection pressure of up to 1,600 bar. That is where the common fuel line (rail) comes in. It is connected to the injection nozzles (injectors) at the end of which are rapid solenoid valves to take care of the timing and amount of the injection.
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. When the timing shuts the solenoid valves, fuel injection ends immediately.
With the state-of-the-art common-rail direct fuel injection used an ideal compromise can be attained between economy, torque, ride comfort and long life.
A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump, and it is capable of opening and closing many times per second. 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 a mist as possible so that it can burn easily. 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 injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors. Each injector is complete and self-contained with nozzle, hydraulic intensifier, and electronic digital valve. At the end of each injector, a rapid-acting solenoid valve adjusts both the injection timing and the amount of fuel injected. A microcomputer controls each valve's opening and closing sequence.
4.2 Spiral-Shaped Intake Port For Optimum Swirl:
The aluminum cylinder head for the CRDI engines is a new development. Among its distinguishing features are two spiral-shaped intake ports. One serves as a swirl port while the other serves as a charge port. Both ports are paired with the symmetrical combustion chamber, rapidly swirling the intake air before it enters the cylinders. The result is an optimum mixture, especially under partial throttle. The newly-designed injector nozzles (injectors) located in the middle of the cylinders provide for even distribution of fuel inside the combustion chambers
4.3 Integrated Port For Exhaust Gas Recycling:
Another novelty is the integrated port for exhaust gas recycling (EGR) in the cylinder head. Whereas older diesel engines lead exhaust gases outside around the engine the new CRDi engines are incorporated with a cast port for the direct injection motor which conducts the gases within the cylinder head itself. The exhaust gases recirculate directly from the exhaust side to the intake side. There are three advantages to this system. For one, it eliminates external pipes which are subject to vibration. Then, integrating EGR into the cylinder head means that part of the exhaust heat is transferred to the coolant, resulting in quicker engine warm-up. Finally, this new technique allows cooler exhaust gases and that means better combustion.
4.4 Precise Timing Courtesy Air Flow Metering:
The hot-film mass air-flow meter is located in front of the turbocharger's compressor permitting an exact analysis of the air-mass that is being taken in. This mass will alter depending on temperature or atmospheric pressure. Due to this metering system, the microcomputer that controls engine timing receives precise data. It is thus able to regulate exhaust-gas recycling according to engine load and speed in the interest of lowering nitrous oxide and particle emissions.
The compressed air from the turbocharger then flows through the intercooler which cools it down to 70 degrees centigrade. Since cool air has less volume than warm air, more air is taken inside the combustion chamber, thus amplifying the effect of the turbocharger. In the subordinate mixing chamber, fresh air and exhaust gas mingle in a computer-determined ratio to match engine load at the moment. The mixing chamber is outfitted with a special exhaust-gas recycling valve and a butterfly valve controlled by a electro-pneumatic converter. The throttle increases the pressure gradient between the intake and outlet sides, thus increasing the recycled exhaust gases' effect on performance
4.5 Swirl-Control Valves In The Intake Manifolds:
Pneumatically guided swirl valves in the intake system help bring the fuel-air mixture to a high swirl rate at low rpm. This leads to efficient combustion and high torque. At high rpm the swirl is reduced and this in turn improves power output.
On the way to the combustion chambers the compressed fresh air mixed with exhaust gases passes through swing manifolds. The intake area just before the cylinder head is single-channel, later becoming dual-channel. These two channels have different tasks. One acts as a spiral channel, swirling the mixture while the other serves as a charge channel which closes with the aid of electro-pneumatically activated valves under partial-load operation. The advantage of this arrangement is that de-energizing increases the rate of swirl in the cylinders so that combustion produces less particle emissions than older direct-injection engines.
4.6 Multiple Pilot Injection And Post Injection:
The high combustion pressure of up to 145 bar (2130 psi) 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. However, the CRDi system employs a piece of technical wizardry known as pilot injection' to overcome this problem: A few nanoseconds before the main fuel injection, a small amount of diesel is injected into the cylinder and ignites, thereby establishing the combustion process and setting the ideal conditions for the main combustion process. Consequently, the fuel ignites faster with the result that the rise in pressure and temperature is less sudden.
The system utilizes multiple pilot injections - small doses of fuel made prior to the main injection of fuel in each cylinder's firing, which help to smooth the sharp combustion character of the diesel engine to gasoline-like smoothness. The end effect, however, is not only a reduction in combustion noise but also a reduction in nitrogen oxide (NOx) emissions.
Post injection is a similarly small dose of fuel injected after the main injection. Common rail technology's potential to lower particulate emissions is profound in this area. The small post injection is inserted with precise timing at the moment that is ideal for lower particulate discharge.
Other methods to reduce noise are providing special cover for the cylinder head and the intercooler, and bracing on the oil pan, the timing-gear case and crankcase. The bottom line is that the noise produced by the new CRDI engines is lower than for comparable pre-combustion engines
4.7 Powerful Microcomputer:
The new direct-injection motors are regulated by a powerful microcomputer linked via CAN (Controller Area Network) data bus to other control devices on board. These devices exchange data. The engine's electrical controls are a central element of the common rail system because regulation of injection pressure and control of the solenoid valves for each cylinder - both indispensable for variable control of the motor - would be unthinkable without them.
This electronic engine management network is a critical element of the common rail system because only the speed and spontaneity of electronics can ensure immediate pressure injection adjustment and cylinder-specific control of the injector solenoid valves.
4.8 Newly-Developed Catalytic Converters With Zeolith Coating:
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. Emissions conform for the German "D3" norms which are 50 percent tighter than the maximum values prescribed in the EURO-2 guidelines. A new coating for the catalytic converters consisting of platinum, aluminum oxide and Zeolith crystals has been devised that besides oxidizing hydrocarbons and carbon monoxide, also converters diminish nitrous oxide. The converter near the engine is equipped with a bypass channel via which a residual amount of hydrocarbons are passed on to the emission control devices on the underbody.
4.9 High Rigidity Cylinder Block And Dual Mass Flywheel
To complement the new-generation common-rail system's unprecedented smoothness and low noise several enhancements have been added to its structure. Cylinder- block rigidity is increased by ribs in the water jacket and the crankshaft bearing cap is integrated into the lower block to greatly reduce engine vibration. A dual-mass flywheel is fitted to the engines to compensate for the harmonic effect of diesel engine on the powertrain elements, eliminating the characteristic rattle often associated with diesels.
4.10 Unique Intake And Exhaust Ports:
The CRDi engine uses an aluminium cylinder head with two spiral intake ports, one for swirling the fuel/air mixture and the other for filling the combustion chamber.
Both ports are tuned to the symmetrically shaped combustion chambers and are designed to set the air into rapid swirling motion even before it reaches the cylinders. This ensures an optimal fuel/air mixture, especially in the part throttle range.
Inside the combustion chambers, newly developed injectors are positioned in the middle of the cylinder to promote uniform fuel distribution.
Another new feature of the CRDi engine is the integration of a port in the cylinder head for the exhaust gas recirculation (EGR) system. In most diesel engines this system is routed around the outside of the engine but in the CRDI system an EGR port has been cast into the cylinder head to channel gas from the exhaust side of the engine to the intake side.
This design has three distinct benefits: It dispenses with external EGR lines, transfers exhaust heat to the coolant for quicker engine warm-up, and at the same time cools exhaust gases to further enhance combustion.
4.11 Reduced Noise Levels:
Diesel engines are known to be noisy. But the introduction of the CRDi engines has made many attributes of the old Diesel engines have become something of the past. One of these is noise. The noisy side of the old Diesel engines which was a cause of inconvenience has given way largely to a quietness in the CRDi technology, because many functions executed by mechanical systems in the old Diesel engines are carried out electronically in the CRDi technology. This in turn enables the engine to run with much less noise. Moreover the carrying out of the injection via multiple injections instead of single is one of the causes which ensures the quietness of the engine. In the CRDi technology it is ensured that all the parts of the engine work in harmony, thereby minimizing the engine noise. Besides that, a high efficiency is achieved now even at low engine speeds. If the unequalled noise insulation is added to this it is almost impossible to hear any engine noise, especially inside the car.
5 CRDi â€œ FUTURE TRENDS :
5.1 Ulra-High Pressure Common â€œRail Injection:
Newer CRDi engines feature maximum pressures of 1800 bar. This pressure is up to 33% higher than that of first-generation systems, many of which are in the 1600-bar range. This technology generates an ideal swirl in the combustion chamber which, coupled with the common-rail injectorsâ„¢ superior fuel-spray pattern and optimized piston head design, allows the air/fuel mixture to form a perfect vertical vortex resulting in uniform combustion and greatly reduced NOx (nitrogen oxide) emissions. The system realizes high output and torque, superb fuel economy, emissions low enough to achieve Euro Stage IV designation and noise levels the same as a gasoline engines. In particular, exhaust emissions and Nox are reduced by some 50% over the current generation of diesel engines.
5.2 CRDi And Particle Filter:
Particle emission is always the biggest problem of diesel engines. While diesel engines emit considerably less pollutant CO and Nox as well as green house gas CO2, the only shortcoming is excessive level of particles. These particles are mainly composed of carbon and hydrocarbons. They lead to dark smoke and smog which is very crucial to air quality of urban area, if not to the ecology system of our planet.
Basically, particle filter is a porous silicon carbide unit; comprising passageways which has a property of easily trapping and retaining particles from the exhaust gas flow. Before the filter surface is fully occupied, these carbon / hydrocarbon particles should be burnt up, becoming CO2 and water and leave the filter accompany with exhaust gas flow. The process is called regeneration.
Normally regeneration takes place at 550Ã‚Â° C. However, the main problem is: this temperature is not obtainable under normal conditions. Normally the temperature varies between 150Ã‚Â° and 200Ã‚Â°C when the driving in town, as the exhaust gas is not in full flow.
The new common-rail injection technology helps solving this problem. By its high-pressure, precise injection during a very short period, the common-rail system can introduce a "post-combustion" by injecting small amount of fuel during expansion phase. This increases the exhaust flow temperature to around 350Ã‚Â°C.
Then, a specially designed oxidizing catalyst converter locating near the entrance of the particle filter unit will combust the remaining unburnt fuel come from the "post-combustion". This raises the temperature further to 450Ã‚Â° C.
The last 100Ã‚Â°C required is fulfilled by adding an addictive called Eolys to the fuel. Eolys lowers the operating temperature of particle burning to 450Ã‚Â° C, now regeneration occurs. The liquid-state additive is store in a small tank and added to the fuel by pump. The PF unit needs to be cleaned up every 80,000 km by high-pressure water, to get rid of the deposits resulting from the additive.
5.3 CRDi And Closed-Loop Control Injection:
One feature of diesel-engine management had been holding back diesel's technical advance: the lack of true, closed-loop control of the injection system. This is significant because an open-loop system cannot accurately compensate for factors such as wear, manufacturing tolerances in the fuel injectors, or for variations in temperature and fuel quality. Gasoline-injection systems have been closed loop for years, and many of the advances in power, refinement, economy, and emissions seen today have been possible because of the real-time feedback that this provides.
Its solution to this problem is an all-new common-rail, direct-injection system that uses an ion sensor to provide real-time combustion data for each cylinder. It is said to provide closed-loop control at a cost that will be roughly equivalent to today's best production systems. High-speed, common-rail direct-injection diesel engines are theoretically capable of excellent performance, economy, and emissions, but to achieve this they will require a much higher level of control than is possible with today's technology. With closed-loop systems and ion-sensing technology, the potential of diesel engines for automotive applications can be unlocked.
The ion-sensing system creates an electrical field in the region where combustion starts by introducing a positive dc voltage at the tip of the glow plug. The field attracts the negatively charged particles created during combustion, producing a small current from the sensor to the piston and cylinder walls, which provide a ground. The current is measured by the engine control module (ECM) and processed to provide a signal that is proportional to the applied sensor voltage and to the level of ionization in the vicinity of the sensor. The difference in ionization before and after the start of combustion is quite pronounced, allowing the ion-sensing system to provide precise start-of-combustion (SOC) data that can be compared with a table of required SOC timings held by the ECM. The fuel control strategy can therefore be changed from open loop to closed loop, allowing the desired SOC to be maintained for all engine speeds, loads, temperatures, and fuel qualities; and to accommodate production tolerances and wear in each injector. Because the sensing function is combined with the glow plug, no engine modifications are required, and the sensor is in a near ideal location. One significant feature of the location is that soot build-up, which can reduce the resistance between the sensor and ground, can be easily detected and burnt off through a simple, automated routine.
To reduce audible noise and NOx, a current production high-pressure common-rail system will typically inject a pilot pulse of around 3-5 mm3 of fuel before the main injection event. Pilot injection can reduce noise by 3-5 dB, but too large a pulse will compromise fuel consumption and emissions. Existing technology can reduce the pilot injection volume to around 1-2 mm3 but only at low injection pressures. Most engine designers would prefer higher pressures because this allows cylinders to be fueled more quickly and for the spray pattern to be improved, leading to increased torque and less smoke.
Closed-loop system allows a pilot volume of around 0.5-1.0 mm3 under high pressures using standard injectors, and is said to reduce particulates by around 10-20%. The precise volume of the pilot injection can be balanced between cylinders, leading to a further reduction in noise. The adaptively learned injector calibrations can also be applied to post-injection pulses, which provide a more complete combustion. 2-3% improvement in fuel consumption can be achieved compared with today's high-pressure systems by
incorporating closed loop control.
The seminar and presentation that I had taken is CRDi system from which we reached to the conclusion that CRDi technology revolutionized diesel engines and also petrol engines(by introduction of GDI technology).
By introduction of CRDi a lot of advantages are obtained ,some of them are
Â¢ More power is developed.
Â¢ Increased fuel efficiency.
Â¢ Reduced noise.
Â¢ More stability.
Â¢ Pollutants are reduced.
Â¢ Particulates of exhaust are reduced.
Â¢ Exhaust gas recirculation is enhanced.
Â¢ Precise injection timing is obtained.
Â¢ Pilot and post injection increase the combustion quality.
Â¢ More pulverization of fuel is obtained.
Â¢ A very high injection pressure can be achieved.
Â¢ The powerful microcomputer make the whole system more perfect.
Â¢ It doubles the torque at lower engine speeds.
The main disadvantage is that this technology increase the cost of the engine.Also this technology cant be employed to ordinary engines.
1. Automotive Mechanics by S Srinivasan.
2. I C Engines By M.L.Malthur & Sharma.
3. I C Engines By V . Ganesan.
4. Automotive Engines by S Srinivasan.
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In older diesel engines , a distributor-type injection pump ,regulated by the engine ,supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine’s combustion chamber. In common rail system the distributor injection pump is eliminated. Instead, a high-pressure pump pressurizes fuel at up to 1500 bar in a ‘common rail’. The common rail is a tube that branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid valve piezoelectric actuators. These systems are capable of high pressures. One of the function of the CRDI system is to decouple noises by keeping the pressure inside the injection pipes constant and adjustable. Injection pressure and timing can be regulated independently of each other by control unit.
CRDI- 24 report.doc (Size: 589 KB / Downloads: 430)
passwordeminar and presentationproject and implimentations
TABLE OF CONTENTS
CHAPTER TITLE PAGE NO:
1 INTRODUCTION 5
2 WHAT IS A COMMON RAIL SYSTEM ? 6
3 FUNCTIONS 7
4 FEATURES 8
5 INJECTION 9
6 INJECTION SYSTEMS 12
7 PRINCIPLES 15
8 COMPONENTS OF CRDI SYSTEM 17
9 WORKING 22
10 EMISSIONS 24
11 APPLICATIONS 27
12 CONCLUSION 28
13 REFRENCES 29
TABLE OF FIGURES
FIGURE NO: NAME OF FIGURE PAGE NO
2.1 Common Rail System 6
5.1 CRDI System 9
5.2 ECU, COMMON RAIL WITH INJECTORS, HIGH PRESSURE PUMP 10
6.1 DIRECT & INDIRECT INJECTION 12
6.2 Common Rail Injection System 13
7.1 Solenoid Valve 15
8.1 Parts Of CRDI System 17
8.2 CRDI System 18
8.3 High Pressure Pump 19
8.4 Pressure Control Valve 20
8.5 Common Rail 20
8.6 Fuel Injector 21
9.1 CRDI System 22
10.1 Catalystic Converter 25
10.2 Particulate Filter 26
The common rail system prototype was developed in the late 1960’s by Robert Huber of Switzerland. After that the technology was further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (estb. 1995) in Oberageri. The CRDI systems are capable of high pressures. One of the function of CRDI systems is to decouple injection noises by keeping the pressure inside the injection pipes constant and adjustable. Maximum pressure is available from the beginning. The injection pressure and timing can be regulated independently of each other by the control unit. This system is applicable to the passenger car Diesel Engines with direct injection, also truck engines.
WHAT IS A COMMON RAIL SYSTEM ?
FIGURE2.1 COMMON RAIL SYSTEM
Common rail refers to a small accumulation tank called Rail where the pressure of the fuel remains almost constant and always available in order to supply the electronic injectors and therefore for an optimum injection. The protection of the environment, the need to reduce the consumption of fuel and to make the diesel engines more silent and better performing are the key factors that determined the study and development of the Unijet common rail system. Born as a project and implimentation from Marelli in 1987, it was afterwards acquired by Fiat’s research centre in Bari who set it up and tested it on a vehicle in 1992. The project and implimentation was transferred to Bosch Group for the final industrialisation process in 1994. The first vehicles with Unijet Common Rail installation were introduced into the market in 1997.
A pump inhales the fuel from the tank (ELECTRONIC PUMP) and continuously sends the quantity of requested fuel towards a second pump (HIGH PRESSURE PUMP) by making it pass first through the fuel filter that purifies it from any impurity which would cause a premature wear of its components. The high-pressure pump compresses the fuel at a pressure of 1350 bar and transfers it through a connection pipe to the high-pressure accumulation duct (Rail). This tank develops the function of mitigating the pressure oscillations caused by the opening and closing of the injectors and by the continuous discharges of the pump. The fuel is then transferred from the Rail through some connection pipes to the electronic injectors, which - instructed by an electromagnetic valve –inject the correct amount of fuel directly into the combustion chamber of the engine.
The fuel in excess, required for the opening of the nozzles, is sent back to the tank along with the leakages of fuel coming from the pressure regulation valve and from the high pressure pump itself. In this type of system, the quantity of injection is being established by the driver through the accelerator pedal while the initial stage and the pressure of injection are calculated and controlled by the electronic control unit (EDC). Through the accelerator pedal’s sensor, the electronic control unit registers the driver’s intention while, thanks to other sensors, it registers the exercising conditions of the engine and vehicle and – according to the information acquired – it carries out the intervention for the engine regulation.
The power supply of the fuel is divided into low-pressure circuit and high-pressure circuit. The low-pressure circuit is made of:
- auxiliary immersed electronic pump
- diesel filter;
- leakage manifold
The high-pressure circuit is made of:
- repair collector
1. Very high injection pressures of the order of 1500 bar
2. Complete control over start , and end of injection
3. Injection pressure is independent of engine speed
4. Ability to have pilot, main and post injection
5. Variable injection pressure
Diesel engines are not throttled. Instead, the combustion behaviour is affected by these variables:
• Timing of start of injection
• Injection duration
• Injector discharge curve
Since the use of electronically controlled common rail injection allows these variables to be individually controlled, we’ll briefly look at each.
FIGURE5.1 CRDI SYSTEM
5.1 TIMING OF START OF INJECTION
The timing of the injection of fuel has a major affect on emission levels, fuel consumption and combustion noise. The optimal timing of the start of injection varies with engine load. In car engines, optimal injection at no load is within the window of 2 crankshaft degrees Before Top Dead Centre (BTDC) to 4 degrees After Top Dead Centre (ATDC). At part load this alters to 6 degrees BTDC to 4 degrees ATDC, while at full load the start of injection should occur from 6 – 15 degrees BTDC. The duration of combustion at full load is 40 – 60 degrees of crankshaft rotatio Too early an injection initiates combustion when the piston is still rising, reducing efficiency and so increasing fuel consumption. The sharp rise in cylinder pressure also increases noise. Too late an injection reduces torque and can result in incomplete combustion, increasing the emissions of unburned hydrocarbons
FIGURE5.2 ECU, COMMON RAIL WITH INJECTORS, HIGH PRESSURE PUMP
5.2 INJECTION DURATION
Unlike a conventional port fuel injected petrol engine, where the amount of fuel injected can be considered to be directly proportional to the injector opening time, a diesel injector will vary in mass flow depending on the difference between the injection and combustion chamber pressures, the density of the fuel (which is temperature dependent), and the dynamic compressibility of the fuel. The specified injector duration must therefore take these factors into account.
5.3 DISCHARGE CURVE
Diesel fuel injectors do not add the fuel for a combustion cycle in one event, instead they operate in up to four different modes. The first is pre-injection, a short duration pulse which reduces combustion noise and Oxides of Nitrogen (NOx) emissions. The bulk of the fuel is then added in the main injection phase, before the injector is turned off momentarily before then adding a post-injection amount of fuel. This post-injection reduces soot emissions. Finally, at up to 180 crankshaft degrees later, a retarded post-injection can occur. The latter acts as a reducing agent for an NOx accumulator-type catalytic converter and/or raises the exhaust gas temperature for the regeneration of a particulate filter.
The injection amounts vary between 1 cubic millimetre for pre-injection to 50 cubic millimetres for full-load delivery. The injection duration is 1-2 milliseconds.
The CR system is an injection system used in Direct-Injection (DI) engines. It is common to differentiate between Direct-Injection (DI) engines and Indirect-Injection (IDI) engines. In IDI the fuel is injected into a prechamber in which the combustion is initiated. In DI engines the fuel is injected directly into the cylinders combustion chamber. DI engines feature fuel savings of up to 20 percent compared with IDI engines, but the latter generates less noise than the former. The advantage of the CR System is the high pressure in the rail, which makes it possible to use precise and highly flexible injection processes.
FIGURE6.1 DIRECT & INDIRECT INJECTION
The CR System system can be divided into three different functional groups
• The high pressure circuit
• The low pressure circuit
• The ECU (Engine Control Unit) with sensors
6.1 THE HIGH PRESSURE CIRCUIT
The high pressure circuit contains a high pressure pump, a pressure-control valve, a high pressure accumulator (the rail) with a rail pressure sensor, high pressure connection lines and injectors. This part of the CR system is responsible for generating a stable high pressure level in the rail and for injecting the fuel into the engines combustion chambers. The high pressure pump forces the fuel into the rail and generates a maximum pressure . There is one injector for each cylinder and injectors contain a solenoid valve which receives a current signal as an ‘open’ command from ECU at the time for injection. Every time an injection occurs, fuel is taken from the rail. The pressure control valve attempts to keep the pressure at the desired level. This control is based on measurements from the rail pressure sensor.
6.2 THE LAW PRESSURE CIRCUIT
The low pressure circuit provides the high pressure part with fuel. The fuel is drawn out of the tank by a pre-supply pump and forced through the lines and through a fuel filter to the high pressure pump in the high pressure circuit. Uninjected fuel from the rail is led back to the tank through the pressure control valve
6.3 THE ECU WITH SENSORS
The ECU evaluates signals from different sensors and supervises the correct functioning of the injection system as a whole. The main tasks for the ECU in the CR systems are to keep the pressure in the rail at a desired level by controlling the pressure control valve, and to start and terminate the actual injection processes. Some of the quantities that the ECU calculates from the sensor measurments (e.g. rail pressure, engine speed, accelerator-pedal position and air temperature) are the correct quantities for the fuel injections and the optimal start and duration of injections .
Solenoid or piezoelectric 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 atomisation. 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 optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.
FIGURE7.1 SOLENOID VALVE
ommon rail engines require no heating up time, and produce lower engine noise and lower emissions than older systems.
In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber. As the fuel is at low pressure and there cannot be precise control of fuel delivery, the spray is relatively coarse and the combustion process is relatively crude and inefficient.
In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure up to 2,000 bar (200 MPa) in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Driven by a computer (which also controls the amount of fuel to the pump), the valves, rather than pump timing, control the precise moment when the fuel injection into the cylinder occurs and also allow the pressure at which the fuel is injected into the cylinders to be increased. As a result, the fuel that is injected atomizes easily and burns cleanly, reducing exhaust emissions and increasing efficiency.
Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Isuzu, Toyota, Nissan and recently Honda, have also developed common rail diesel engines. Some Indian companies have also successfully implemented this technology, notably Mahindra & Mahindra for their 'Scorpio-CRDe' and Tata Motors for their 'Safari-DICOR'.
COMPONENTS OF CRDI SYSTEM
FIGURE8.1 PARTS OF CRDI SYSTEM
1. fuel tank
2. overall immersed pump complete with level indicator command
3.fuel introduction pipe
4. multifunctional valve
5. cartridge for diesel filter
6. pressure pump
7. high pressure connecting pipe
8. allotment collector 9. electronic injectors
10. electronic injectors recycle
11. return collector (low pressure)
12. pressure regulator
13. fuel temperature sensor
14. fuel pressure sensor
15. diesel heater
16. heat switch
FIGURE8.2 CRDI SYSTEM
This figure indicates various flows. The light arrows indicate diesel at high pressure (discharges). The dark arrows indicate diesel at low pressure (return to tank and discharges from primer pump).
8.1 ELECTRONIC PUMP TANK
The main trigger pump of fuel is situated in the tank inside a sump containing a filter with and a sensor for the level of fuel. It is a volumetrically type with a roller impeller and its function is to fill up the circuit and to supply the high-pressure pump. It has two valves: a non-return one in order to prevent the emptying of the circuit and a safety one which limits the pressure to a maximum value of 5 bar in case of obstruction of the diesel circuit. The electronic pump is feeded at 12V from the special relay, which is instructed – at its turn – from the EDC control unit. It guarantees a minimum flow of 0.5 litres/minute and with lot pressure of about 0.5 bar.
8.2 HIGH PRESSURE MECHANICAL PUMP
The high pressure is obtained from the action of three small pistons being arranged in radial position (radialjet) at an angular distance of 120° and thanks to their action; they generate a pressure from a minimum of 150 bar to 1350 bar and even more among the pumps of latest generation.
The pump is dragged by the engine through the toothed distribution belt at about half speed. The pump does not require the phasing since the instant and time of injection are being entrusted to the control unit, which manages the opening of the injectors. The alterning movement of the three small pistons is assured by a triangular cam connected to the pump’s shaft and every pumping group is characterised by a suction valve and by a discharging one, the first having a clay shape and thesecondasphericalone.
FIGURE8.3 HIGH PRESSURE PUMP
8.3 FUEL FILTERS
The fuel could contain impurities or combined water (emulsion) or non-combined water (for example: condensation formation due to an change of temperature), which may cause corrosion and wear damages to the components of the pumps and injectors. For this reason, the system needs a fuel filter with a water-collecting compartment, which must be periodically emptied.
8.4 PRESSURE CONTROL VALVE
The fuel pressure control valve comprises a fuel-cooled solenoid valve. The valve opening is varied by its solenoid coil being pulse width modulated at a frequency of 1 KHz. When the pressure control valve is not activated, its internal spring maintains a fuel pressure of about 100 Bar. When the valve is activated, the force of the electromagnet aids the spring, reducing the opening of the valve and so increasing fuel pressure. The fuel pressure control valve also acts as a mechanical pressure damper, smoothing the high frequency pressure pulses emanating from the radial piston pump when less than three pistons are activated.
FIGURE8.4 PRESSURE CONTROL VALVE
8.5 FUEL RAIL
The fuel rail feeds each injector. It is made sufficiently large that the internal pressure is relatively unaffected by fuel being released from the injectors. As indicated earlier, the rail is fitted with a fuel pressure sensor. To guard against dangerously high fuel pressure, a fuel pressure relief valve is also fitted.
FIGURE8.5 FUEL RAIL
8.6 FUEL INJECTORS
The fuel injectors superficially look like the injectors used in conventional petrol injection systems but in fact differ significantly. This diagram shows a common rail injector. Because of the very high fuel rail pressure, the injectors use a hydraulic servo system to operate. In this design, the solenoid armature controls not the pintle but instead the movement of a small ball which regulates the flow of fuel from a valve control chamber within the injector.
FIGURE8.6 FUEL INJECTOR
The life of a common rail diesel fuel injector is certainly a hard one. Bosch estimates a commercial vehicle injector will open and close more than a billion times in its service life.
FIGURE 9.1 CRDI SYSTEM
1. High pressure pump
3. Common rail
4. Fuel rail control valve
6. Fuel filter
7. Fuel tank
9. Engine speed sensor
10. Camshaft position sensor
11. Accelerator pedal travel sensor
12. Boost pressure sensor
13. Intake air temperature sensor
14. Engine coolant temperature sensor
The common rail injection system has a high pressnre 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 received pulses from the ECU to open the same.
The engine directly drives the pump of the common rail system. It is generally of the multi-cylinder radial piston type. The generated pressure is independent of the injection process unlike conventional injection systems. The rail pressure pump is generally much smaller that conventional pumps and also is subjected to lesser pressure pulsations. The injection occurs when the solenoid is energized. The quantity of fuel injected is directly dependent on the duration of the pulse when the injection pressure is constant. Sensors on the crankshaft indicate its position and speed and so the timing of injection and its frequency can be controlled. A typical layout of the common rail fuel injection system is indicated in Fig.10.18. Fuel from the tank is lifted by a low pressure pump and passed through a filter. The pump is generally run by an electric motor independent of the engine speed. The maiu pumping element can be a conventional gear pump or of the roller cell type. The roller cell pump has a rotor with radial slots. These slots house rollers which are always in contact with the inner surface of the housing due to fuel pressure arid centrifugal forces. The space between the rotor and the housing varies as the rotor turn and this is responsible for the suction and delivery.
Five major approaches are taken to reducing diesel exhaust emissions
Within the engine itself, the design of the combustion chamber, the placement of the injection nozzle and the use of small droplets all help reduce the production of emissions at their source. Accurate control of engine speed, injection mass, injection timing, pressures, temperatures and the air/fuel ratio are used to decrease emissions of oxides of nitrogen, particulates, hydrocarbons and carbon monoxide.
10.2 EXHAUST GAS RECIRCULATION
Exhaust gas recirculation, where a proportion of the exhaust gas is mixed with the intake charge, is also used to reduce oxides of nitrogen emissions. It does this by reducing the oxygen concentration in the combustion chamber, the amount of exhaust gas passing into the atmosphere, and the exhaust gas temperature. Recirculation rates can as high as 50 per cent
10.3 CATALYTIC CONVERTER
Diesel oxidation-type catalytic converters can be used to reduce hydrocarbon and carbon monoxide emissions, converting these to water and carbon dioxide. So they rapidly reach their operating temperature, this type of catalytic converter is fitted close to the engine
NOx accumulator-type catalytic converters are also used. This type of design breaks down the NOx by storing it over periods from 30 seconds to several minutes. The nitrogen oxides combine with metal oxides on the surface of the NOx accumulator to form nitrates, with this process occurring when the air/fuel ratio is lean (ie there is excess oxygen). However, the storage can only be short-term and when the ability to bind nitrogen oxides decreases, the catalytic converter needs to be regenerated by having the stored NOx released and converted into nitrogen. In order that this takes place, the engine is briefly run at a rich mixture (eg an air/fuel ratio of 13.8:1)
FIGURE10.1 CATALYTIC CONVERTER
Detecting when regeneration needs to occur, and then when it has been fully completed, is complex. The need for regeneration can be assessed by the use of a model that calculates the quantity of stored nitrogen oxides on the basis of catalytic converter temperature. Alternatively, a specific NOx sensor can be located downstream of the accumulator catalytic converter to detect when the efficiency of the device is decreasing. Assessing when regeneration is complete is done by either a model-based approach or an oxygen sensor located downstream of the cat; a change in signal from high oxygen to low oxygen indicates the end of the regeneration phase.
In order that the NOx storage cat works effectively from cold, an electric exhaust gas heater can be employed.
10.4 SELECTIVE CATALYTIC REDUCTION
One of the most interesting approaches to diesel exhaust treatment is Selective Catalytic Reduction. In this approach, a reducing agent such as dilute urea solution is added to the exhaust in minutely measured quantities. A hydrolysing catalytic converter then converts the urea to ammonia, which reacts with NOx to form nitrogen and water. This system is so effective at reducing NOx emissions that leaner than normal air/fuel ratios can be used, resulting in improved fuel economy. The urea tank is filled at each service.
10.5 PARTICULATE FILTERS
Exhaust particulate filters are made from porous ceramic materials. When they become full, they can be regenerated by being heated to above 600 degrees C. This is a higher exhaust gas temperature than is normally experienced in diesels and to achieve this, retarded injection and intake flow restriction can be used to increase the temperature of the exhaust gas.
FIGURE10.2 PARTICULATE FILTERS
1. BMW’s D-engines
2. Fiat Groups ( Fiat, Alfa Romeo and Lancia)
3. Honda Groups
4. Hyundai Groups
6. Tata’s Dicor
7. Toyota’s D-4D
Common rail systems are capable of high pressures. Due to the high pressure in the system and the electromagnetically controlled injectors it is possible to inject correct amount of fuels at exactly right movement. This implies lower fuel consumption and less emissions.
1. INTERNAL COMBUSTION ENGINE – V.GANESAN (PAGE 342 TO 355)
2. AutoSpeed - Common Rail Diesel Engine Management, Part 1.mht
3. Common rail - Wikipedia, the free encyclopedia.mht
4. Application of CFD Methodology to Air Intake System of CRDI Engine.mht
5. Philippines Handyman DIY Portal - Diesel Quality and CRDI Engines.mht
6. INTERNAL COMBUSTION ENGINES – MATHUR & SHARMA
7. Feature Spotlight.mht
8. Diesel injection systems, diesel fuel injection, diesel injection, diesel fuel injection pumps, diesel injection pumps.mht
9. Common rail.pdf
10. Common rail system.pdf
11. Diesel engine – Wikipedia
12. injection system.pdf
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27-02-2011, 04:38 AM
report not showing the fig.....
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05-03-2011, 08:50 PM
any one can help me out with applicability of CRDi on combat vehicles?
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30-12-2011, 01:33 PM
Explained very well. This is one of the good quotes about the topic[/b]
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31-12-2011, 09:47 AM
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