SPARK PLUG

     Spark plug is a device used to produce electric spark to ignite the compressed air fuel mixture inside the cylinder. The spark plug is screwed in the top of the cylinder so that it electrode project in the combustion chamber.

A spark plug consist of mainly three parts:

1. Center electrode or insulated electrode.
2. Ground electrode or outer electrode.
3. Insulation separating the two electrodes.

     The upper end of the center electrode is connected to the spark plug terminal, where cable from the ignition coil is connected. It is surrounded by insulator. The lower half portion of the insulator is fastened with a metal shell. The lower portion of the shell has a short electrode attached to one side and bent in towards the centre electrode, so that there is a gap between the two electrodes. The two electrodes are thus separated by the insulator. The sealing gaskets are provided between the insulator and the shell to prevent the escape of gas under various temperature and pressure conditions. The lower part of the shell has screw threads and the upper part is made in hexagonal shape like a nut, so that the spark plug may be screwed in or unscrewed from the cylinder head.


Cleaning the Spark Plug

     Due to the combustion of fuel in the cylinder, carbon particles deposit on and around the electrode which not only reduce the plug gap but also prevent the spark to occur. If the spark is still occurring, it is too weak that it cannot ignite the fuel. Hence the spark plug is to be cleaned. Carbon particles can deposit due to any reason like, nature of fuel, mixture strength, lubricating oil, etc. The spark plug can be cleaned by a sand paper.

TURBOCHARGER

          A turbocharger or turbo is a forced induction device used to allow more power to be produced for an engine of a given size. A turbocharged engine can be more powerful and efficient than a naturally aspirated engine because the turbine forces more intake air, proportionately more fuel, into the combustion chamber than if atmospheric pressure alone is used. Turbo are commonly used on truck, car, train, and construction equipment engines. Turbo are popularly used with Otto cycle and Diesel cycle internal combustion engines.

          There are two ways of increasing the power of an engine. One of them would be to make the fuel-air mixture richer by adding more fuel. This will increase the power but at the cost of fuel efficiency and increase in pollution levels… prohibitive! The other would be to somehow increase the volume of air entering into the cylinder and increasing the fuel intake proportionately, increasing power and fuel efficiency without hurting the environment or efficiency. This is exactly what Turbochargers do, increasing the volumetric efficiency of an engine.

          In a naturally aspirated engine, the downward stroke of the piston creates an area of low pressure in order to draw more air into the cylinder through the intake valves.  Now because of the pressure in the cylinder cannot go below 0 (zero) psi (vacuum) and relatively constant atmospheric pressure (about 15 psi) there will be a limit to the pressure difference across the intake valves and hence the amount of air entering the combustion chamber or the cylinder. The ability to fill the cylinder with air is its volumetric efficiency. Now if we can increase the pressure difference across the intake valves by some way we can make more air enter into the cylinder and hence increasing the volumetric efficiency of the engine. It increases the pressure at the point where air is entering the cylinder, thereby increasing the pressure difference across the intake valves and thus more air enters into the combustion chamber. The additional air makes it possible to add more fuel, increasing the power and torque output of the engine, particularly at higher engine speeds.

          Turbochargers were originally known as Turbo superchargers when all forced induction devices were classified as superchargers; nowadays the term "supercharger" is usually applied to only mechanically-driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that the latter is mechanically driven from the engine, often from a belt connected to the crankshaft, whereas a turbocharger is driven by the engine's exhaust gas turbine. Compared to a mechanically-driven supercharger, turbochargers tend to be more efficient but less responsive.

HISTORICAL PERSPECTIVE

The turbocharger was invented by Swiss engineer Alfred Büchi. His patent for a turbocharger was applied for use in 1905. Diesel ships and locomotives with turbochargers began appearing in the 1920s.

AVIATION:

During the First World War French engineer Auguste Rateau fitted turbochargers to Renault engines powering various French fighters with some success. In1918, General Electric engineer Sanford Moss attached a turbo to a V12 Liberty aircraft engine. The engine was tested at Pikes Peak in Colorado at 4,300 m to demonstrate that it could eliminate the power losses usually experienced in internal combustion engines as a result of reduced air pressure and density at high altitude.

Turbochargers were first used in production aircraft engines in the 1920s, although they were less common than engine-driven centrifugal superchargers. The primary purpose behind most aircraft-based applications was to increase the altitude at which the airplane could fly, by compensating for the lower atmospheric pressure present at high altitude.

PRODUCTION AUTOMOBILES:

The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938 .The first production turbocharged automobile engines came from General Motors in 1962. At the Paris auto show in1974, during the height of the oil crisis, Porsche introduced the 911 Turbo – the world’s first production sports car with an exhaust turbocharger and pressure regulator. This was made possible by the introduction of a waste gate to direct excess exhaust gasses away from the exhaust turbine. The world's first production turbo diesel automobiles were the Garrett-turbocharged Mercedes 300SD and the Peugeot 604, both introduced in 1978. Today, most automotive diesels are turbocharged.

1962 Oldsmobile Cutlass Jet fire
1962 Chevrolet Corvair Monza Spyder
1973 BMW 2002 Turbo
1974 Porsche 911 Turbo
1978 Saab 99
1978 Peugeot 604 turbo diesel
1978 Mercedes-Benz 300SD turbo diesel (United States/Canada)
1979 Alfa Romeo Alfetta GTV 2000 Turbo delta
1980 Mitsubishi Lancer GT Turbo
1980 Pontiac Firebird
1980 Renault 5 Turbo
1981 Volvo 240-series Turbo

OPERATING PRINCIPLE

A turbocharger is a small radial fan pump driven by the energy of the exhaust gases of an engine. A turbocharger consists of a turbine and a compressor on a shared shaft. The turbine converts exhaust heat to rotational force, which is in turn used to drive the compressor. The compressor draws in ambient air and pumps it in to the intake manifold at increased pressure resulting in a greater mass of air entering the cylinders on each intake stroke. The objective of a turbocharger is the same as a supercharger; to improve the engine's volumetric efficiency by solving one of its cardinal limitations. A naturally aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the intake valves. Because the pressure in the atmosphere is no more than 1 atm (approximately 14.7 psi), there ultimately will be a limit to the pressure difference across the intake valves and thus the amount of airflow entering the combustion chamber. Because the turbocharger increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen) will be forced in as the inlet manifold pressure increases. The additional air flow makes it possible to maintain the combustion chamber pressure and fuel/air load even at high engine revolution speeds, increasing the power and torque output of the engine. Because the pressure in the cylinder must not go too high to avoid detonation and physical damage, the intake pressure must be controlled by venting excess gas. The control function is performed by a waste gate, which routes some of the exhaust flow away from the turbine. This regulates air pressure in the intake manifold.

COMPONENTS OF A TURBOCHARGER

The turbocharger has four main components. The turbine (almost always a radial turbine) and impeller/compressor wheels are each contained within their own folded conical housing on opposite sides of the third component, the center housing/hub rotating assembly. The housings fitted around the compressor impeller and turbine collect and direct the gas flow through the wheels as they spin. The size and shape can dictate some performance characteristics of the overall turbocharger. The turbine and impeller wheel sizes dictate the amount of air or exhaust that can be flowed through the system, and the relative efficiency at which they operate. Generally, the larger the turbine wheel and compressor wheel, the larger the flow capacity. The center hub rotating assembly houses the shaft which connects the compressor impeller and turbine. It also must contain a bearing system to suspend the shaft, allowing it to rotate at very high speed with minimal friction. Waste gates for the exhaust flow.

TURBINE WHEEL:

           The Turbine Wheel is housed in the turbine casing and is connected to a shaft that in turn rotates the compressor wheel.

COMPRESSOR WHEEL (IMPELLER)

         Compressor impellers are produced using a variant of the aluminum investment casting process. A rubber former is made to replicate the impeller around which a casting mould is created. The rubber former can then be extracted from the mould into which the metal is poured. Accurate blade sections and profiles are important in achieving compressor performance. Back face profile machining optimizes impeller stress conditions. Boring to tight tolerance and burnishing assist balancing and fatigue resistance. The impeller is located on the shaft assembly using a threaded nut.

WASTE GATES:

          On the exhaust side, a Waste gate provides us a means to control the boost pressure of the engine. Some commercial diesel applications do not use a Waste gate at all. This type of system is called a free-floating turbocharger. However, the vast majority of gasoline performance applications require Waste gates. Waste gates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level.

ADVANTAGES

1. More specific power over naturally aspirated engine. This means a turbocharged engine can achieve more power from same engine volume.

2. Better thermal efficiency over both naturally aspirated and supercharged engine when under full load (i.e. on boost). This is because the excess exhaust heat and pressure, which would normally be wasted, contributes some of the work required to compress the air.

3. Weight/Packaging. Smaller and lighter than alternative forced induction systems and may be more easily fitted in an engine bay.

4. Fuel Economy. Although adding a turbocharger itself does not save fuel, it will allow a vehicle to use a smaller engine while achieving power levels of a much larger engine, while attaining near normal fuel economy while off boost/cruising. This is because without boost, less fuel is used to create a proper air/fuel ratio.

DISADVANTAGES

1. Lack of responsiveness if an incorrectly sized turbocharger is used. If a turbocharger that is too large is used it reduces throttle response as it builds up boost slowly otherwise known as "lag". However, doing this may result in more peak power.

2. Boost threshold- A turbocharger starts producing boost only above a certain rpm due to a lack of exhaust gas volume to overcome inertia of rest of the turbo propeller. This results in a rapid and nonlinear rise in torque, and will reduce the usable power band of the engine. The sudden surge of power could overwhelm the tires and result in loss of grip, which could lead to under steer/over steer, depending on the drive train and suspension setup of the vehicle. Lag can be disadvantageous in racing, if throttle is applied in a turn, power may unexpectedly increase when the turbo spools up, which can cause excessive wheel spin.

3. Cost- Turbocharger parts are costly to add to naturally aspirated engines. Heavily modifying OEM turbocharger systems also require extensive upgrades that in most cases requires most (if not all) of the original components to be replaced.

4. Complexity- Further to cost, turbochargers require numerous additional systems if they are not to damage an engine. Even an engine under only light boost requires a system for properly routing (and sometimes cooling) the lubricating oil, turbo-specific exhaust manifold, application specific downpipe, boosts regulation. In addition inter -cooled turbo engines require additional plumbing, while highly tuned turbocharged engines will require extensive upgrades to their lubrication, cooling, and breathing systems; while reinforcing internal engine and transmission parts.

TURBO LAG AND BOOST

           The time required to bring the turbo up to a speed where it can function effectively is called turbo lag. This is noticed as a hesitation in throttle response when coming off idle. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. The directly-driven compressor in a supercharger does not suffer from this problem. Conversely on light loads or at low RPM a turbocharger supplies less boost and the engine acts like a naturally aspirated engine. Turbochargers start producing boost only above a certain exhaust mass flow rate (depending on the size of the turbo). Without an appropriate exhaust gas flow, they logically cannot force air into the engine. The point at full throttle in which the mass flow in the exhaust is strong enough to force air into the engine is known as the boost threshold rpm. Engineers have, in some cases, been able to reduce the boost threshold rpm to idle speed to allow for instant response. Both Lag and Threshold characteristics can be acquired through the use of a compressor map and a mathematical equation.

APPLICATIONS

·        Gasoline-powered cars

Today, turbo charging is commonly used by many manufacturers of both diesel and gasoline-powered cars. Turbo charging can be used to increase power output for a given capacity or to increase fuel efficiency by allowing a smaller displacement engine to be used. Low pressure turbo charging is the optimum when driving in the city, whereas high pressure turbo charging is more for racing and driving on highways/motorways/freeways.

·        Diesel-powered cars

Today, many automotive diesels are turbocharged, since the use of turbocharging improved efficiency, driveability and performance of diesel engines, greatly increasing their popularity.

·        Motorcycles

The first example of a turbocharged bike is the 1978 Kawasaki Z1R TC. Several Japanese companies produced turbocharged high performance motorcycles in the early 1980s. Since then, few turbocharged motorcycles have been produced.

·        Trucks

The first turbocharged diesel truck was produced by Schweizer Maschinenfabrik Saurer (Swiss Machine Works Saurer) in 1938.

·        Aircraft

A natural use of the turbocharger is with aircraft engines. As an aircraft climbs to higher altitudes the pressure of the surrounding air quickly falls off. At 5,486 m (18,000 ft), the air is at half the pressure of sea level and the airframe experiences only half the aerodynamic drag. However, since the charge in the cylinders is being pushed in by this air pressure, it means that the engine will normally produce only half-power at full throttle at this altitude. Pilots would like to take advantage of the low drag at high altitudes in order to go faster, but a naturally aspirated engine will not produce enough power at the same altitude to do so.

          Here the main aim is to effectively utilize the non renewable energy such as petrol and diesel. Complete combustion of the fuels can be achieved. Power output can be increased. Wind energy can be used for air compression. We conclude that the power as well as the efficiency is increasing 10 to 15 % and pollution can also decrease. From the observation we can conclude that when the full throttle valve is open at that time the engine speed is 4000 rpm and by this the turbocharger generate 1.60 bar pressurized air. Generally the naturally aspirated engine takes atmospheric pressurized air to the carburetor for air fuel mixture but we can add the high density air for the combustion so as the result the power and the complete combustion take place so efficiency is increasing.

DTSI (Digital Twin Spark Ignition System)

It is very interesting to know about complete combustion in automobile engineering, because in actual practice, perfect combustion is not at all possible due to various losses in the combustion chamber as well as design of the internal combustion engine. Moreover the process of burning of the fuel is also not instantaneous. However an alternate solution to it is by making the combustion of fuel as fast as possible. This can be done by using two spark plugs which spark alternatively at a certain time interval so as increase the diameter of the flame & burn the fuel instantaneously. This system is called DTSI (Digital Twin Spark Ignition system). In this system, due to twin sparks, combustion will be complete.

This paper represents the working of digital twin spark ignition system, how twin sparks are produced at 20,000 Volts, their timings, efficiency, advantages & disadvantages, diameter of the flame, how complete combustion is possible & how to decrease smoke & exhausts from the exhaust pipe of the bike using Twin Spark System.

How Does It Works?

Digital Twin Spark ignition engine has two Spark plugs located at opposite ends of the combustion chamber and hence fast and efficient combustion is obtained. The benefits of this efficient combustion process can be felt in terms of better fuel efficiency and lower emissions. The ignition system on the Twin spark is a digital system with static spark advance and no moving parts subject to wear. It is mapped by the integrated digital electronic control box which also handles fuel injection and valve timing. It features two plugs per cylinder.

This innovative solution, also entailing a special configuration of the hemispherical combustion chambers and piston heads, ensures a fast, wide flame front when the air-fuel mixture is ignited, and therefore less ignition advance, enabling, moreover, relatively lean mixtures to be used. This technology provides a combination of the light weight and twice the power offered by two-stroke engines with a significant power boost, i.e. a considerable "power-to-weight ratio" compared to quite a few four-stroke engines.

Moreover, such a system can adjust idling speed & even cuts off fuel feed when the accelerator pedal is released, and meters the enrichment of the air-fuel mixture for cold starting and accelerating purposes; if necessary, it also prevents the upper rev limit from being exceeded. At low revs, the over boost is mostly used when overtaking, and this is why it cuts out automatically. At higher speeds the over boost will enhance full power delivery and will stay on as long as the driver exercises maximum pressure on the accelerator.

Main characteristics

• Digital electronic ignition with two plugs per cylinder and two ignition distributors.
• Twin overhead cams with camshaft timing variation.
• Injection fuel feed with integrated electronic twin spark ignition.
• A high specific power.
• Compact design and Superior balance.

Construction

Digital spark technology is currently used in Bajaj motor cycles in India, because they have the patent right. Digital twin spark ignition technology powered engine has two spark plugs. It is located at opposite sides of combustion chamber. This DTS-I technology will have greater combustion rate because of twin spark plug located around it. The engine combust fuel at double rate than normal. This enhances both engine life and fuel efficiency. It is mapped by the digital electronic control box which also handles fuel ignition and valve timing.

A microprocessor continuously senses speed and load of the engine and respond by altering the ignition timing there by optimizing power and fuel economy.

Advantages & Disadvantages

Advantages

• Less vibrations and noise

• Long life of the engine parts such as piston rings and valve stem.

• Decrease in the specific fuel consumption

• No over heating

• Increase the Thermal Efficiency of the Engine & even bear high loads on it.

• Better starting of engine even in winter season & cold climatic conditions or at very low temperatures because of increased Compression ratio.

• Because of twin Sparks the diameter of the flame increases rapidly that would result in instantaneous burning of fuels. Thus force exerted on the piston would increase leading to better work output.

Disadvantages

• There is high NOx emission

• If one spark plug get damaged then we have to replace both

• The cost is relatively more

Applications

It uses in automotive engines. In India Bajaj has patented for dts-i technology. At present platina, xcd125, 135, discover150, pulsar135, 150, 180, 200, 220 etc. are using the dts-i(digital twin spark ignition system). Which means the petrol enters into the cylinder burns more efficiently.


Hence the application of these technologies in the present day automobiles will give the present generation what they want i.e. power bikes with fuel efficiency. Since these technologies also minimize the fuel consumption and harmful emission levels, they can also be considered as one of the solutions for increasing fuel costs and increasing effect of global warming.

The perfect Combustion in Internal Combustion engine is not possible. So for the instantaneous burning of fuels in I.C. engine twin spark system can be used which producing twin sparks at regular interval can help to complete the combustion.

Electromagnetic Brake

          Electromagnetic brakes are the brakes working on the electric power & magnetic power. They works on the principle of electromagnetism. These are totally friction less. Due to this they are more durable & have longer life span. Less maintenance is there. These brakes are an excellent replacement on the convectional brakes  due to their many advantages. The reason for implementing this brake in automobiles is to reduce wear in brakes as it friction less. Therefore there will also be no heat loss. It can be used in heavy vehicles as well as in light vehicles. The electromagnetic brakes are much effective than conventional brakes & the time taken for application of brakes are also smaller. There is very few need of lubrication. Electromagnetic brakes gives such better performance with less cost which is today’s need. There are also many more advantages of Electromagnetic brakes. That’s why electromagnetic brakes are en excellent replacement on conventional brakes.

          Electromagnetic brakes are of today’s automobiles. A electromagnetic braking system for automobiles like cars, an effective braking system. And, by using this electromagnetic brakes, we can increase the life of the braking unit. The working principle of this system is that when the magnetic flux passes through and perpendicular to the rotating wheel the eddy current flows opposite to the rotating wheel/rotor direction. This eddy current trying to stop the rotating wheel or rotor. This results in the rotating wheel or rotor comes to rest/ neutral.

HISTORY

          It is found that electromagnetic brakes can develop a negative power which represents nearly twice the maximum power output of a typical engine, and at least three times the braking power of an exhaust brake. (Reverdin 1994). These performance of electromagnetic brakes make them much more competitive candidate for alternative retardation equipments compared with other retarders. By using by using the electromagnetic brakes are supplementary retardation equipment, the friction brakes can be used less frequently, and therefore practically never reach high temperatures. The brake linings would last considerably longer before requiring maintenance and the potentially “brake fade” problem could be avoided. In research conducted by a truck manufacturer, it was proved that the electromagnetic brake assumed 80% of the duty which would otherwise have been demanded of the regular service brake (Reverdin 1974). Further more the electromagnetic brakes prevents the danger that can arise from the prolonged use of brake beyond  their capability to dissipate heat. This is most likely to occur  while a vehicle  descending a long gradient at high speed. Ina study with a vehicle with 5 axles and weighting 40 tones powered by a powered by an engine of 310 b.h.p travelling down a gradient of 6% at a steady speed between 35 and 40 m.h.p, it can be calculated that the braking power necessary to maintain this speed ot the order of 450 hp. The brakes, therefore, would have to absorb 300 hp, meaning that each brake in the 5 axels must absorb 30 hp, that a friction brake can normally absorb with selfdestruction. The magnetic brake is wall suited to such conditions since it will independently absorb more than 300 hp (Reverdin 1974). It therefore can exceed the requirements of continuous uninterrupted braking, leaving the friction brakes cool and ready for emergency braking in total safety. The installation of an electromagnetic brake is not very difficulty if there is enough space between the gearbox and the rear axle. If did not need a subsidiary cooling system. It relay on the efficiency of engine components for its use, so do exhaust and hydrokinetic brakes. The exhaust brake is an on/off device and hydrokinetic brakes have very complex control system. The electromagnetic brake control system is an electric switching system which gives it superior controllability.

CONSTRUCTION

          The construction of the electromagnetic braking system is very simple. The parts needed for the construction are electromagnetic, rheostat, sensors and magnetic insulator. A cylindrical ring shaped electromagnet with winding is placed parallel to rotating wheel disc/ rotor. The electro magnet is fixed, like as stator and coils are wounded along the electromagnet. These coils are connected with electrical circuit containing one rheostat which is connected with brake pedal. And the rheostat is used to control the current flowing is used to control the magnetic flux. And also it is used to prevent the magnetization of other parts like axle and it act as asupport frame for the electromagnet. The sensor used to indicate the disconnection in the whole circuit. If there is any error it gives an alert, so we can avoid accident.

WORKING PRINCIPLE

          The working principle of the electric retarder is based on the electric retarder is based on the creation of eddy currents with in a metal discs rotating rotating between two electro magnets, which set up a force opposing the rotation of the discs. If the electromagnet is not energized, the rotation of the disc free and accelerates uniformly under the action of the weight to which its shaft is connected. When the electromagnet is energized, the rotation of the disc is retarded and the energy absorbed appears as heating of the discs. If the current exciting the electromagnet is varied by a rheostat, the raking force varies  indirect proportion of the value of the current. The development of this invention began when the French company Telma, associated with Raoul Sarazin, developed and marketed several generations of electric brake based on the functioning principle described above. A typical retarder consists of stator and rotor. The stator hold 16 induction coils, energized separately in group of four. The coils are made up of varnished aluminium wire mounted in epoxy resin. The stator assembly is supported resiliently through anti-vibration mountings on the chasis frame of the vehicle. The rotor is made up of two discs, which provide the braking force when subjected to the electromagnetic influence when the coil are excited. Care fully design of the fins, which are integral to the disc, permit independent cooling of the arrangement.

ADVANTAGES

1. Electromagnetic brakes can develop a negative power which represents nearly twice the maximum power output of a typical engine.

 2. Electromagnetic brakes work in a relatively cool condition and satisfy all

the energy requirements of braking at high speeds, completely without the use of friction. Due to its specific installation location (transmission line of rigid vehicles), electromagnetic brakes have better heat dissipation capability to avoid problems that friction brakes face times the braking power of an exhaust brake.

 3. Electromagnetic brakes have been used as supplementary retardation equipment in addition to the regular friction brakes on heavy vehicles.

 4. Electromagnetic brakes has great braking efficiency and has the potential to regain energy lost in braking.

 5. It’s component cost is less.

DISADVANTAGES

1. The installation of an electromagnetic brake is very difficult if there is

Not enough space between the gearbox and the rear axle.

2. Need a separate compressor. 

3. Maintenance of the equipment components such as hoses, valves has to done periodically. 

4. It cannot use grease or oil.

APPLICATIONS

1. Used in crane control system.

2. Used in winch controlling.

3. Used in lift controlling.

4. Used in automatic purpose.

          The lot’s of new technologies are arriving in world. They create a lot of effect. Most industries got their new faces due to this arrival of technologies. Automobile industry is also one of them. There is a boom in World’s automobile industry. So lot’s of research is also going here. As an important part of automobile, there are also innovations in brakes. Electromagnetic brake is one of them.

          A electromagnetic braking for automobiles like cars, an effective braking system. And, by using this electromagnetic brakes, we can increase the life of the braking unit. The working principle of this system is that when the electromagnetic flux passes through and perpendicular to the rotating wheel the eddy current is induced in the rotating wheel or rotor. This eddy current flows opposite to the rotating wheel. This eddy current tries to stop the rotating wheel or rotor. This results in the rotating wheel or rotor comes to rest.

CRDI (Common Rail Direct Injection)

     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.

History

     The common rail system prototype was developed in the late 1960s by Robert Huber of Switzerland and the technology further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (est.1995) in Oberägeri. The first successful usage in a production vehicle began in Japan by the mid-1990s. Modern common rail systems, whilst working on the same principle, are governed by an engine control unit (ECU) which opens each injector electronically rather than mechanically. This was extensively prototyped in the 1990s with collaboration between Magneti Marelli, Centro Ricerche Fiat and Elasis. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 2.4 JTD, and later on that same year Mercedes-Benz C 220 CDI.

     Common rail engines have been used in marine and locomotive applications for some time. The Cooper-Bessemer GN-8 (circa 1942) is an example of a hydraulically operated common rail diesel engine, also known as a modified common rail. Vickers used common rail systems in submarine engines circa 1916. Early engines had a pair of timing cams, one for ahead running and one for astern. Later engines had two injectors per cylinder, and the final series of constant-pressure turbocharged engines were fitted with four injectors per cylinder. This system was used for the injection of both diesel oil and heavy fuel oil (600cSt heated to a temperature of approximately 130 °C). The common rail system is suitable for all types of road cars with diesel engines, ranging from city cars such as the Fiat Nuova Panda to executive cars such as the Audi A6.

Operating Principle

     Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity, 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 optimizing 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.

     Common rail engines require very short (< 10 second) or no heating-up time at all , dependent on ambient temperature, and produce lower engine noise and emissions than older systems. Diesel engines have historically used various forms of fuel injection. Two common types include the unit injection system and the distributor/inline pump systems (See diesel engine and unit injector for more information). While these older systems provided accurate fuel quantity and injection timing control, they were limited by several factors:

• They were cam driven, and injection pressure was proportional to engine speed. This typically meant that the highest injection pressure could only be achieved at the highest engine speed and the maximum achievable injection pressure decreased as engine speed decreased. This relationship is true with all pumps, even those used on common rail systems; with the unit or distributor systems, however, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator, and thus the relationship is more prominent and troublesome.


• They were limited in the number and timing of injection events that could be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.


• For the typical distributor/inline system, the start of injection occurred at a pre-determined pressure (often referred to as: pop pressure) and ended at a pre-determined pressure. This characteristic resulted from "dummy" injectors in the cylinder head which opened and closed at pressures determined by the spring preload applied to the plunger in the injector. Once the pressure in the injector reached a pre-determined level, the plunger would lift and injection would start.

     In common rail systems, a high-pressure pump stores a reservoir of fuel at high pressure — up to and above 2,000 bars (psi). The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high-pressure fuel. This simplifies the purpose of the high-pressure pump in that it only has to maintain a commanded pressure at a target (either mechanically or electronically controlled). The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated, a hydraulic valve (consisting of a nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are electrically actuated, the injection pressure at the start and end of injection is very near the pressure in the accumulator (rail), thus producing a square injection rate. If the accumulator, pump and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events.

Advantages & Disadvantages

Advantages

     CRDi engines are advantageous in many ways. Cars fitted with this new engine technology are believed to deliver 25% more power and torque than the normal direct injection engine. It also offers superior pick up, lower levels of noise and vibration, higher mileage, lower emissions, lower fuel consumption, and improved performance.

     In India, diesel is cheaper than petrol and this fact adds to the credibility of the common rail direct injection system.

Disadvantages

     Like all good things have a negative side, this engine also have few disadvantages. The key disadvantage of the CRDi engine is that it is costly than the conventional engine. The list also includes high degree of engine maintenance and costly spare parts. Also this technology can’t be employed to ordinary engines.

Applications

     The most common applications of common rail engines are marine and locomotive applications. Also, in the present day they are widely used in a variety of car models ranging from city cars to premium executive cars.

     Some of the Indian car manufacturers who have widely accepted the use of common rail diesel engine in their respective car models are the Hyundai Motors, Maruti Suzuki, Fiat, General Motors, Honda Motors, and the Skoda. In the list of luxury car manufacturers, the Mercedes-Benz and BMW have also adopted this advanced engine technology. All the car manufacturers have given their own unique names to the common CRDi engine system.

     However, most of the car manufacturers have started using the new engine concept and are appreciating the long term benefits of the same. The technology that has revolutionized the diesel engine market is now gaining prominence in the global car industry.

     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, more power is developed, increased fuel efficiency, reduced noise, more stability, pollutants are reduced, particulates of exhaust are reduced, exhaust gas recirculation is enhanced, precise injection timing is obtained, pilot and post injection increase the combustion quality, more pulverization of fuel is obtained, very high injection pressure can be achieved, the powerful microcomputer make the whole system more perfect, it doubles the torque at lower engine speeds. The main disadvantage is that this technology increase the cost of the engine. Also this technology can’t be employed to ordinary engines.