DEFINITION :- The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanical energy. The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines. TWO STROKE ENGINES :- Invention of the two-stroke cycle is attributed to Scottish engineer Dugald Clerk who in 1881 patented his design, his engine having a separate charging cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day (and Frederick Cock for the piston-controlled inlet port). A two-stroke engine is an internal combustion engine that completes the thermodynamic cycle in two movements of the piston compared to twice that number for a four-stroke engine. This increased efficiency is accomplished by using the beginning of the compression stroke and the end of the combustion stroke to perform simultaneously the intake and exhaust (or scavenging) functions. In this way two-stroke engines often provide strikingly high specific power. Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications such as chainsaws and the concept is also used in diesel compression ignition engines in large and non- weight sensitive applications such as ships and locomotives. FOUR STROKE ENGINES :- Today, internal combustion engines in cars, trucks, motorcycles, aircraft, construction machinery and many others, most commonly use a four-stroke cycle. The four strokes refer to intake, compression, combustion (power), and exhaust strokes that occur during two crankshaft rotations per working cycle of the gasoline engine and diesel engine. A less technical description of the four-stroke cycle is, "Suction, Compression, Ignition, Exhaust" The cycle begins at top dead center (TDC), when the piston is farthest away from the axis of the crankshaft. A stroke refers to the full travel of the piston from Top Dead Center (TDC) to Bottom Dead Center (BDC). Stroke 1 of 4 "Suction": On the intake or induction stroke of the piston, the piston descends from the top of the cylinder to the bottom of the cylinder, reducing the pressure inside the cylinder. A mixture of fuel and air is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then close. Stroke 2 of 4 "Compression": With both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the fuel-air mixture. This is known as the compression stroke. Stroke 3 of 4 "Ignition": While the piston is at or close to Top Dead Center, the compressed air– fuel mixture is ignited, usually by a spark plug (for a gasoline or Otto cycle engine) or by the heat and pressure of compression (for a diesel cycle or compression ignition engine). The resulting massive pressure from the combustion of the compressed fuel-air mixture drives the piston back down toward bottom dead center with tremendous force. This is known as the power stroke, which is the main source of the engine's torque and power. Stroke 4 of 4 "Exhaust": During the exhaust stroke, the piston once again returns to top dead center while the exhaust valve is open. This action evacuates the products of combustion from the cylinder by pushing the spent fuel-air mixture through the exhaust valve(s). DIESEL CYCLE :- The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897. It is assumed to have constant pressure during the first part of the "combustion" phase, v2 to v3 in the diagram. This is mostly a mathematical model: real physical diesels do have an increase in pressure during this period. The image shows a P-V diagram for the ideal diesel cycle; where P is pressure and V is specific volume. The ideal diesel cycle follows the following four distinct processes: * Process 1 to 2 is isentropic compression * Process 2 to 3 is reversible constant pressure heating * Process 3 to 4 is isentropic expansion * Process 4 to 1 is reversible constant volume cooling P-V Diagram for the Ideal Diesel cycle. The cycle follows the numbers 1-4 in clockwise direction. OTTO CYCLE :- The first person to build an engine based on this cycle was German engineer Nicolaus August Otto. That is why the four-stroke principle today is commonly known as the Otto cycle and four- stroke engines using spark plugs often are called Otto engines. The air-standard-Otto cycle is the idealized cycle for the spark-ignition internal combustion engines. This cycle is shown above on p-v and T-s diagrams. The Otto cycle 1-2-3-4 consists of following four process: Process 1-2: Reversible isentropic compression of air. Process 2-3: Heat addition at constant volume. Process 3-4: Reversible isentropic expansion of air. Process 4-1: Heat rejection at constant volume. CAMLESS ENGINES :- Most four-stroke piston engines today employ one or more camshafts to operate poppet valves. The lobes on the camshafts operate cam followers which in turn open the poppet valves. A camless (or, free valve engine) uses electromagnetic, hydraulic, or pneumatic actuators to open the poppet valves instead. Actuators can be used to both open and close the valves, or an actuator opens the valve while a spring closes it. As a camshaft normally has only one lobe per valve, the valve duration and lift is fixed. The camshaft runs at half the engine speed. Although many modern engines use camshaft phasing, adjusting the lift and valve duration in a working engine is more difficult. Some manufacturers use systems with more than one cam lobe, but this is still a compromise as only a few profiles can be in operation at once. This is not the case with the camless engine, where lift and valve timing can be adjusted freely from valve to valve and from cycle to cycle. It also allows multiple lift events per cycle and, indeed, no events per cycle—switching off the cylinder entirely. Camless engines are not without their problems though. Common problems include high power consumption, accuracy at high speed, temperature sensitivity, weight and packaging issues, high noise, high cost, and unsafe operation in case of electrical problems. LINEAR ACTUATORS :- A linear actuator is a device that applies force in a linear manner, as opposed to rotationally like an electric motor. There are various methods of achieving this linear motion. Some actually convert rotational motion into linear motion. TYPES OF LINEAR VALVE ACTUATORS USED FOR CAMLESS ENGINES :- PNEUMATIC VALVE SPRING :- Pneumatic valve springs are metal bellows filled with compressed air used as an alternative to the metal wire springs used to close valves in high-speed internal combustion engines. This system was introduced in the mid-1980s in Renault turbocharged 1.5 litre Formula One engines. Concept Racing engines often fail at high rotational speeds because mechanical springs are unable to retract the valves quickly enough to provide clearance for the piston. Renault's pneumatic valve technology replaced steel springs with light weight compressed air bellows. These could retract valves more quickly and reduce the possibility of piston-valve interference as long as pressure could be maintained. Additionally, the amount of seat tension required to keep a coil sprung valve under control results in greater peak lift loading, with added stress to the entire valve train as a result. Pneumatic systems, sharing a common reservoir of pressure retain a more static level of force, controlling the valve effectively, without any attendant peak lift load increase. ELECTRO MECHANICAL ACTUATORS :- Electro magnets are used to open and close the valve and hold it in position once moved. Electro-mechanical actuators are similar to mechanical actuators except that the control knob or handle is replaced with an electric motor. Rotary motion of the motor is converted to linear displacement of the actuator. There are many designs of modern linear actuators and every company that manufactures them tends to have their own proprietary method. The following is a generalized description of a very simple electro-mechanical linear actuator. This method of valve control is often found in camless engine designs. A proponent of this technology is Valeo, which indicates that its design will be utilized in volume production in 2009. Typically, a rotary driver (e.g. electric motor) is mechanically connected to a lead screw so that the rotation of the electric motor will make the lead screw rotate. A lead screw has a continuous helical thread machined on its circumference running along the length (similar to the thread on a bolt). Threaded onto the lead screw is a lead nut with corresponding helical threads. The nut is prevented from rotating with the lead screw (typically the nut interlocks with a non-rotating part of the actuator body). Therefore, when the lead screw is rotated, the nut will be driven along the threads. The direction of motion of the nut will depend on the direction of rotation of the lead screw. By connecting linkages to the nut, the motion can be converted to usable linear displacement. Most current actuators are built either for high speed, high force, or a compromise between the two. When considering an actuator for a particular application, the most important specifications are typically travel, speed, force, accuracy, and lifetime. There are many types of motors that can be used in a linear actuator system. These include dc brush, dc brushless, stepper, or in some cases, even induction motors. It all depends on the application requirements and the loads the actuator is designed to move. For example, a linear actuator using an integral horsepower AC induction motor driving a lead screw can be used to actuate a large valve in a refinery. In this case, accuracy and move resolution down to a thousandth isn't needed, but high force and speed is. Some of the problems which may be encountered with this methodology are: - Deceleration of the valve once set in motion is difficult to accomplish, and inadequate slowing down of the valve can cause significant deterioration of the valve seat and other parts. Utilizing springs to effect valve deceleration limits the engine to lower speeds and may still not effect a gentle landing of the valve on its seat at all engine speeds. - Springs utilized in this type of system may require very careful balancing with the valve movement in order to achieve gentle valve seating at differing engine speeds. As the springs deteriorate or the engine RPMs change, the valve mechanism may become unbalanced and ultimately lead to failure. - The electromagnets will draw a significant amount of electrical energy, which may require a higher capacity alternator, which will in turn reduce the potential fuel efficiency of the engine. - A powerful computer coupled with complex fast-acting control circuitry and devices will likely be necessary to control the valves in real time. HYDRAULIC ACTUATORS :- Hydraulic actuators or hydraulic cylinders typically involve a hollow cylinder having a piston inserted in it. The two sides of the piston are alternately pressurized/de-pressurized to achieve controlled precise linear displacement of the piston and in turn the entity connected to the piston. The valve open and close is affected by valve mechanisms controlling the flow of hydraulic fluids to and from the hydraulic cylinder. The physical linear displacement is only along the axis of the piston/cylinder. This design is based on the principles of hydraulics. A familiar example of a manually operated hydraulic actuator is a hydraulic car jack. Typically though, the term "hydraulic actuator" refers to a device controlled by a hydraulic pump. Various methods have been explored to utilize hydraulic mechanisms to move the engine valves. Some claim to be successful at low engine speeds, but few claim to achieve that goal meaningfully at the higher RPM requirements of passenger vehicles. Hydraulic systems suffer from 2 inherent problems: 1) The faster a liquid is moved, the more it tends to act like a solid. A fast-acting hydraulic system to activate automotive valves at the speeds required in passenger vehicles could require immense pressures, with all the incumbent problems, including the additional energy requirements of the hydraulic pump. Even if higher engine speeds were achieved, valve movement would likely be abbreviated and not fully follow the desired or optimum lift schedule. 2) Temperatures can vary seasonally over a wide range. The hydraulic medium could change viscosity as the temperatures change, which could cause variances in the system's performance which may be difficult to control. Utilizing valve springs to assist the hydraulic system may also prevent the engine attaining higher speeds. In order to achieve gentle valve seating, hydraulic systems must be carefully controlled. This control may require the use of powerful computers and very precise sensors. MECHANICAL ACTUATORS :- Mechanical actuators typically convert rotary motion of a control knob or handle into linear displacement via screws and/or gears to which the knob or handle is attached. A jackscrew or car jack is a familiar mechanical actuator. Another families of actuators are based on the segmented spindle. Rotation of the jack handle is converted mechanically into the linear motion of the jack head. Mechanical actuators are also frequently used in the field of lasers and optics to manipulate the position of linear stages, rotary stages, mirror mounts and other positioning instruments. For accurate and repeatable positioning, index marks may be used on control knobs. Some actuators even include an encoder and digital position readout. These are similar to the adjustment knobs used on micrometers except that their purpose is position adjustment rather than position measurement. COMMON RAIL DIRECT FUEL INJECTION (CRDi) ENGINES :- Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines. On diesel engines, it features a high-pressure (over 1,000 bar/15,000 psi) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors. Third- generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar/26,000 psi. 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 production vehicle began in Japan by the mid-1990s. Dr. Shohei Itoh and Masahiko Miyaki of the Denso Corporation, a Japanese automotive parts manufacturer, developed the common rail fuel system for heavy duty vehicles and turned it into practical use on their ECD-U2 common-rail system mounted on the Hino Rising Ranger truck and sold for general use in 1995. Denso claims the first commercial high pressure common rail system in 1995. 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. After research and development by the Fiat Group, the design was acquired by the German company Robert Bosch GmbH for completion of development and refinement for mass-production. In hindsight the sale appeared to be a tactical error for Fiat as the new technology proved to be highly profitable. The company had little choice but to sell, however, as it was in a poor financial state at the time and lacked the resources to complete development on its own. In 1997 they extended its use for passenger cars. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 1.9 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. Doxford Engines Ltd. (opposed piston heavy marine engines) used a common rail system (from 1921 to 1980) whereby a multi-cylinder reciprocating fuel pump generated a pressure of approximately 600bar with the fuel being stored in accumulator bottles. Pressure control was achieved by means of an adjustable pump discharge stroke and a "spill valve". Camshaft operated mechanical timing valves were used to supply the spring loaded Brice/CAV/Lucas injectors which injected through the side of the cylinder into the chamber formed between the pistons. 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 Nova Panda to executive cars such as the Volvo S80. 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 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. Common rail engines require no heating up time  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 on the number of 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 results 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 (29,000 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. HOMOGENOUS CHARGE COMPRESSION IGNITION (HCCI) ENGINES Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be transformed in an engine into work and heat. INTRODUCTION :- HCCI has characteristics of the two most popular forms of combustion used in IC engines: homogeneous charge spark ignition (gasoline engines) and stratified charge compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel and oxidizer are mixed together. However, rather than using an electric discharge to ignite a portion of the mixture, the density and temperature of the mixture are raised by compression until the entire mixture reacts spontaneously. Stratified charge compression ignition also relies on temperature and density increase resulting from compression, but combustion occurs at the boundary of fuel-air mixing, caused by an injection event, to initiate combustion. The defining characteristic of HCCI is that the ignition occurs at several places at a time which makes the fuel/air mixture burn nearly simultaneously. There is no direct initiator of combustion. This makes the process inherently challenging to control. However, with advances in microprocessors and a physical understanding of the ignition process, HCCI can be controlled to achieve gasoline engine-like emissions along with diesel engine-like efficiency. In fact, HCCI engines have been shown to achieve extremely low levels of Nitrogen oxide emissions (NOx) without an after treatment catalytic converter. The unburned hydrocarbon and carbon monoxide emissions are still high (due to lower peak temperatures), as in gasoline engines, and must still be treated to meet automotive emission regulations. HISTORY :- HCCI engines have a long history, even though HCCI has not been as widely implemented as spark ignition or diesel injection. It is essentially an Otto combustion cycle. In fact, HCCI was popular before electronic spark ignition was used. One example is the hot-bulb engine which used a hot vaporization chamber to help mix fuel with air. The extra heat combined with compression induced the conditions for combustion to occur. Another example is the "diesel" model aircraft engine. OPERATION :- Methods A mixture of fuel and air will ignite when the concentration and temperature of reactants is sufficiently high. The concentration and/or temperature can be increased by several different ways: * High compression ratio * Pre-heating of induction gases * Forced induction * Retained or re-inducted exhaust gases Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much chemical energy, combustion is too fast and high in-cylinder pressures can destroy an engine. For this reason, HCCI is typically operated at lean overall fuel mixtures. ADVANTAGES :- * HCCI provides up to a 30-percent fuel savings, while meeting current emissions standards. * Since HCCI engines are fuel-lean, they can operate at a Diesel-like compression ratios (>15), thus achieving higher efficiencies than conventional spark-ignited gasoline engines. * Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions. In fact, because peak temperatures are significantly lower than in typical spark ignited engines, NOx levels are almost negligible. Additionally, the premixed lean mixture does not produce soot. * HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. * In regards to gasoline engines, the omission of throttle losses improves HCCI efficiency. DISADVANTAGES :- * High in-cylinder peak pressures may cause damage to the engine. * High heat release and pressure rise rates contribute to engine wear. * The auto ignition event is difficult to control, unlike the ignition event in spark ignition (SI) and diesel engines which are controlled by spark plugs and in-cylinder fuel injectors, respectively. * HCCI engines have a small power range, constrained at low loads by lean flammability limits and high loads by in-cylinder pressure restrictions. * Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than a typical spark ignition engine, caused by incomplete oxidation (due to the rapid combustion event and low in-cylinder temperatures) and trapped crevice gases, respectively. VARIABLE VALVE TIMING WITH INTELLIGENCE (VVTi) ENGINES :- VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota, similar in performance to the BMW's VANOS. The Toyota VVT-i system replaces the Toyota VVT offered starting in 1991 on the 5-valve per cylinder 4A- GE engine. The VVT system is a 2-stage hydraulically controlled cam phasing system. VVT-i, introduced in 1996, varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt, scissor-gear or chain) and intake camshaft. Engine oil pressure is applied to an actuator to adjust the camshaft position. Adjustments in the overlap time between the exhaust valve closing and intake valve opening result in improved engine efficiency. Variants of the system, including VVTL-i, Dual VVT-i, VVT-iE, and Valvematic, have followed. VVTL-i :- VVTL-i (Variable Valve Timing and Lift intelligent system) is a version that can alter valve lift(and duration) as well as valve timing. In the case of the 16 valve 2ZZ-GE, the engine has 2 camshafts, one operating intake valves and one operating exhaust valves. Each camshaft has two lobes per cylinder, one low rpm lobe and one high rpm, high lift, long duration lobe. Each cylinder has two intake valves and two exhaust valves. Each set of two valves are controlled by one rocker arm, which is operated by the camshaft. Each rocker arm has a slipper follower mounted to the rocker arm with a spring, allowing the slipper follower to move up and down with the high lobe without affecting the rocker arm. When the engine is operating below 6000- 7000 rpm (dependent on year, car, and ECU installed), the low lobe is operating the rocker arm and thus the valves. When the engine is operating above the lift engagement point, the ECU activates an oil pressure switch which pushes a sliding pin under the slipper follower on each rocker arm. This in effect, switches to the high lobe causing high lift and longer duration. The system was first used in 1999 Toyota Celica SS-II with 2ZZ-GE. Toyota has now ceased production of its VVTL-i engines for most markets, because the engine does not meet Euro IV specifications for emissions. As a result, this engine has been discontinued on some Toyota models, including that of the Corolla T-Sport (Europe), Corolla Sportivo (Australia), Celica, Corolla XRS, Toyota Matrix XRS, and the Pontiac Vibe GT, all of which had the 2ZZ-GE engine fitted. The Lotus Elise continues to offer the 2ZZ-GE and the 1ZZ-FE engine, while the Exige offers the engine with a supercharger. DUAL VVT-i :- In 1998, Dual VVT-i which adjusts timing on both intake and exhaust camshafts was first introduced on the RS200 Altezza's 3S-GE engine. Dual VVT-i is also found in Toyota's new generation V6 engine, the 3.5-liter 2GR-FE first appearing on the 2005 Avalon. This engine can now be found on numerous Toyota and Lexus models. By adjusting the valve timing, engine start and stop occurs almost unnoticeably at minimum compression. In addition fast heating of the catalytic converter to its light-off temperature is possible thereby reducing hydrocarbon emissions considerably. Toyota's UR engine V8 also uses this technology. Dual VVT-i was later introduced to Toyota's latest small 4-cylinder ZR engines found in compact vehicles such as the new Toyota Corolla and Scion xD and in larger 4-cylinder AR engines found in the Camry and RAV4. VVT-iE :- VVT-iE (Variable Valve Timing - intelligent by Electric motor) is a version of Dual VVT-i that uses an electrically operated actuator to adjust and maintain intake camshaft timing. The exhaust camshaft timing is still controlled using a hydraulic actuator. This form of variable valve timing technology was developed initially for Lexus vehicles. This system was first introduced on the 2007MY Lexus LS 460 as 1UR engine The electric motor in the actuator spins together with the intake camshaft as the engine runs. To maintain camshaft timing, the actuator motor will operate at the same speed as the camshaft. To advance the camshaft timing, the actuator motor will rotate slightly faster than the camshaft speed. To retard camshaft timing, the actuator motor will rotate slightly slower than camshaft speed. The speed difference between the actuator motor and camshaft timing is used to operate a mechanism that varies the camshaft timing. The benefit of the electric actuation is enhanced response and accuracy at low engine speeds and at lower temperatures. Furthermore, it ensures precise positioning of the camshaft for and immediately after engine starting, as well as a greater total range of adjustment. The combination of these factors allows more precise control, resulting in an improvement of both fuel economy, engine output and emissions performance. VALVEMATIC :- It offers continuous adjustment to lift volume and timing. Valvematic made its first appearance in 2007 in the Noah and later in early-2009 in the ZR engine family used on the Avensis. This system is simpler in design compared to Valvetronic and VVEL, allowing the cylinder head to remain at the same height. CENTRAL PORT INJECTION (CPI) :- General Motors implemented a system called "central port injection" (CPI) or "central port fuel injection" (CPFI). It uses tubes with poppet valves from a central injector to spray fuel at each intake port rather than the central throttle-body . The 2 variants were CPFI from 1992 - 1995, and CSFI from 1996 and on . CPFI is a batch-fire system, in which fuel is injected to all ports simultaneously. The 1996 and later CSFI system sprays fuel sequentially. MULTI-POINT FUEL INJECTION :- Multi-point fuel injection injects fuel into the intake port just upstream of the cylinder's intake valve, rather than at a central point within an intake manifold. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke, batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke, or Simultaneous, in which fuel is injected at the same time to all the cylinders. Many modern EFI systems utilize sequential MPFI; however, it is beginning to be replaced by direct injection systems in newer gasoline engines. CONTINOUS INJECTION :- In a continuous injection system, fuel flows at all times from the fuel injectors, but at a variable rate. This is in contrast to most fuel injection systems, which provide fuel during short pulses of varying duration, with a constant rate of flow during each pulse. Continuous injection systems can be multi-point or single-point, but not direct. The most common automotive continuous injection system is Bosch's K-Jetronic (K for kontinuierlich, German for "continuous"- a.k.a. CIS- Continuous Injection System), introduced in 1974. Gasoline is pumped from the fuel tank to a large control valve called a fuel distributor, which separates the single fuel supply pipe from the tank into smaller pipes, one for each injector. The fuel distributor is mounted atop a control vane through which all intake air must pass, and the system works by varying fuel volume supplied to the injectors based on the angle of the air vane, which in turn is determined by the volume flow rate of air past the vane, and by the control pressure. The control pressure is regulated with a mechanical device called the control pressure regulator (CPR) or the warm-up regulator (WUR). Depending on the model, the CPR may be used to compensate for altitude, full load, and/or a cold engine. On cars equipped with an oxygen sensor, the fuel mixture is adjusted by a device called the frequency valve. The injectors are simple spring-loaded check valves with nozzles; once fuel system pressure becomes high enough to overcome the counter spring, the injectors begin spraying. K-Jetronic was used for many years between 1974 and the mid 1990s by BMW, Lamborghini, Ferrari, Mercedes- Benz, Volkswagen, Ford, Porsche, Audi, Saab, DeLorean, and Volvo. There was also a variant of the system called KE-Jetronic with electronic instead of mechanical control of the control pressure. Some Toyotas and other Japanese cars from the 1970s to the early 1990s used an application of Bosch's multipoint L-Jetronic system manufactured under license by DENSO. Chrysler used a similar continuous fuel injection system on the 1981-1983 Imperial. In piston aircraft engines, continuous-flow fuel injection is the most common type. In contrast to automotive fuel injection systems, aircraft continuous flow fuel injection is all mechanical, requiring no electricity to operate. Two common types exist: the Bendix RSA system, and the TCM system. The Bendix system is a direct descendant of the pressure carburetor. However, instead of having a discharge valve in the barrel, it uses a flow divider mounted on top of the engine, which controls the discharge rate and evenly distributes the fuel to stainless steel injection lines which go to the intake ports of each cylinder. The TCM system is even more simple. It has no venturi, no pressure chambers, no diaphragms, and no discharge valve. The control unit is fed by a constant-pressure fuel pump. The control unit simply uses a butterfly valve for the air which is linked by a mechanical linkage to a rotary valve for the fuel. Inside the control unit is another restriction which is used to control the fuel mixture. The pressure drop across the restrictions in the control unit controls the amount of fuel flowing, so that fuel flow is directly proportional to the pressure at the flow divider. In fact, most aircraft using the TCM fuel injection system feature a fuel flow gauge which is actually a pressure gauge that has been calibrated in gallons per hour or pounds per hour of fuel. DIGITAL TWIN SPARK IGNITION (DTSi) ENGINES :- DTSi stands for Digital Twin Spark Ignition, a Bajaj Auto trademark. Bajaj Auto holds an Indian patent for the DTSi technology. The Alfa Romeo Twin-Spark engines, the BMW F650 Funduro which was sold in India from 1995 to 1997 also had a twin-spark plug technology, and the Rotax motorcycle engines,more recently Honda's iDSI Vehicle engines use a similar arrangement of two spark-plugs. However very few small capacity engines did eventually implement such a scheme in their production prototypes. HYBRID ELECTRIC VEHICLE :- A hybrid electric vehicle (HEV) combines a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system. The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle, or better performance. A variety of types of HEV exist, and the degree to which they function as EVs varies as well. The most common form of HEV is the hybrid electric car, although hybrid electric trucks (pickups and tractors) also exist. Modern HEVs make use of efficiency-improving technologies such as regenerative braking, which converts the vehicle's kinetic energy into battery-replenishing electric energy, rather than wasting it as heat energy as conventional brakes do. Some varieties of HEVs use their internal combustion engine to generate electricity by spinning an electrical generator (this combination is known as a motor-generator), to either recharge their batteries or to directly power the electric drive motors. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system. A hybrid-electric produces less emissions from its ICE than a comparably-sized gasoline car, as an HEV's gasoline engine is usually smaller than a pure fossil-fuel vehicle, and if not used to directly drive the car, can be geared to run at maximum efficiency, further improving fuel economy. Ferdinand Porsche in 1900 developed the first hybrid (gasoline-electric) automobile in the world. The hybrid-electric vehicle did not become widely available until the release of the Toyota Prius in Japan in 1997, followed by the Honda Insight in 1999. TYPES OF POWERTRAIN :- Hybrid electric vehicles are classified three types according to the division of power between the two energy sources in the drivetrain: * Parallel hybrids have both the internal combustion engine (ICE) and the electric motor connected to the mechanical transmission and can simultaneously transmit power to drive the wheels. Honda's Insight, Civic, and Accord hybrids are examples of production parallel hybrids. Usually parallel hybrids can use a smaller battery pack as they rely more on regenerative braking and the internal combustion engine can also act a generator for supplemental recharging. Parallel hybrids are more efficient on highway driving as compared to urban stop-and-go conditions. * Series hybrids are driven only by the electric motor and the internal combustion engine (ICE) works as a generator to power the electric motor or to recharge the batteries that power the electric motor. The battery pack can recharged from regenerative braking or from the liquid fuel engine. Series hybrids usually have a smaller combustion engine but a larger battery pack as compared to parallel hybrids, which make them more expensive than parallels. Nevertheless, this configuration makes series hybrids more efficient in city driving. The Chevrolet Volt is a series plug-in hybrid, although GM prefers to describe the Volt as an electric vehicle equipped with a "range extending" gasoline powered ICE as a generator and therefore dubbed an "Extended Range Electric Vehicle" or E-REV. * Series-parallel hybrids have the flexibility to operate in either series or parallel mode. As a result of this dual mode operation, overall operation is more efficient, because they can operate as a series hybrid at lower speeds and as parallel at high speeds, but their cost is higher than a pure parallel. Hybrid powertrains currently used by Ford, Lexus, Nissan, and Toyota, which some refer to as ―series-parallel with power-split,‖ can operate in both series and parallel mode at the same time. TYPES OF HYBRID ENGINE :- GASOLINE :- Gasoline engines are used in most hybrid electric designs, and will likely remain dominant for the foreseeable future. While petroleum-derived gasoline is the primary fuel, it is possible to mix in varying levels of ethanol created from renewable energy sources. Like most modern ICE powered vehicles, HEVs can typically use up to about 15% bioethanol. Manufacturers may move to flexible fuel engines, which would increase allowable ratios, but no plans are in place at present. DIESEL :- Diesel-electric HEVs use a diesel engine for power generation. Diesels have advantages when delivering constant power for long periods of time, suffering less wear while operating at higher efficiency. The diesel engine's high torque, combined with hybrid technology, may offer substantially improved mileage. Most diesel vehicles can use 100% pure biofuels (biodiesel), so they can use but do not need petroleum at all for fuel (although mixes of biofuel and petroleum are more common, and petroleum may be needed for lubrication). If diesel-electric HEVs were in use, this benefit would likely also apply. Diesel-electric hybrid drivetrains have begun to appear in commercial vehicles (particularly buses); as of 2007, no light duty diesel-electric hybrid passenger cars are currently available, although prototypes exist. Peugeot is expected to produce a diesel-electric hybrid version of its 308 in late 2008 for the European market At the Frankfurt Motor Show in September 2009 both Mercedes and BMW displayed diesel- electric hybrids. Robert Bosch GmbH is supplying hybrid diesel-electric technology to diverse automakers and models, including the Peugeot 308. FedEx, along with Eaton Corp. in the USA and Iveco in Europe, has begun deploying a small fleet of Hybrid diesel electric delivery trucks. As of October 2007 Fedex now operates more than 100 diesel electric hybrids in North America, Asia and Europe. HYDROGEN :- Hydrogen can be used in cars in two ways: As a combustible heat source, or as a source of electrons for an electric motor. The burning of hydrogen is not being developed in practical terms; it is the hydeogen fuel-cell electric vehicle (HFEV)that is garnering all the attention. Hydrogen fuel cells create electricity that is fed into an electric motor to drives the wheels. Hydrogen is not burned, but it is consumed. This means that molecular hydrogen, H2, is combined with oxygen to form water. 2H2 (4e-) + O2 --> 2H2O (4e-). The molecular hydrogen and oxygen's mutual affinity drives the fuel cell to separate the electrons from the hydrogen, to use them to power the electric motor, and to return them to the ionized water molecules that were formed when the electron-depleted hydrogen combined with the oxygen in the fuel cell. Recaling that a hydeogen atom is nothing more than a proton and an electron; in essence, the motor is driven by the proton's atomic attraction to the oxygen nucleus, and the electron's attraction to the ionized water molecule. An HFEV is an all-electric car that has an open-source battery in the form of a hydrogen tank and the atmosphere. HFEV's may also contain closed-cell batteries for the purpose of power storage from regenerative breaking, but this does not change the source of the motivation. It means that the HFEV is an electric car with two types of batteries. So, since HFEV's are purely electric, and do not contain any type of heat engine, they are not hybrids.