Extraction of oil and gas from ocean

OFF-SHORE DRILLING

                Offshore drilling is a mechanical process where a wellbore is drilled below the seabed, just like in case of onshore drilling, at first seismic survey is needed for exploration of the resource. It is typically carried out in order to explore for and subsequently extract petroleum which lies in rock formations beneath the seabed. Most commonly, the term is used to describe drilling activities on the continental shelf, though the term can also be applied to drilling in lakes, inshore waters and inland seas.

                There are many different types of facilities from which offshore drilling operations take place. These include bottom founded drilling rigs, combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) including semi-submersibles and drill ships. These are capable of operating in water depths up to 3,000 metres (9,800 ft). In shallower waters the mobile units are anchored to the seabed, however in deeper water (more than 1,500 metres (4,900 ft) the semisubmersibles or drill ships are maintained at the required drilling location using dynamic positioning.

HOW DO SEISMIC SURVEYS WORK?                                                        

                Sound waves help scientists or geologist map the ocean floor and geology beneath it, these sounds waves are produced by bubble explosion or blasting under seabed. These released sound waves into the water gets reflected off subsurface rock layers and are “heard” by sensors(hydrophone). Scientists or geologist analyze the collected data and use it to create maps of geologic structures that could contain energy resources beneath the ocean floor. The sound produced during seismic surveys is comparable in magnitude to many naturally occurring and other man-made ocean sound sources, including wind and wave action, rain, lightning strikes, marine life, and shipping.

SOME TYPES OF OFFSHORE DRILLING RIGS

There are different types of rigs which are designed to work according to the specific needs of oil and gas companies. These rigs are designed to perform in hard conditions like shallow water, the deep depths of the ocean or areas with unstable and difficult weather conditions.

SUBMERSIBLE RIGS

            A submersible oil rig can be used in shallow water where the depth of water is about 80 ft or less. These rigs are towed to the location of the oil reserves and submerged in the water until the rigs lie on the ocean floor. Anchors are sometimes used to secure the position of the submersible rigs. The submersible drilling platform is supported on large pontoon-like structures. These pontoons provide buoyancy allowing the unit to be towed from location to location. Once on the location, the pontoon structure is slowly flooded until it rests securely on its anchors, of which there are usually two per corner.

                The operating deck is elevated 100 feet above the pontoons on large steel columns to provide clearance above the waves. After the well is drilled, the water is pumped out of the buoyancy tanks and the vessel is re-floated and towed to the next location.

SEMI-SUBMERSIBLE RIGS

            The semi-submersible design was first developed for offshore drilling activities. These rigs are built to withstand harsh weather conditions. Depending on their design, the semi-submersible oil rigs may be either self-propelled or towed to the location. Once the rig is in position, ballast is used to drown the rig into the depths of the ocean. The movement of a semi-submersible rig can be controlled with the help of computers in case of modern rig or anchors in the case of older rigs.

PRODUCTION PLATFORMS

            Production platforms are constructed on the surface of the spot where oil or gas reserves are found. It is only constructed when exploratory drilling at the spot reveals oil or gas reserves which is worthy of a massive expense. These production platforms are permanent structures that are design to last decades and cannot be moved once they are built. They are often constructed far from land and in some of the most worst waters on Earth.

JACK-UP RIGS

            When oil drilling moved into offshore waters, fixed platform rigs and submersible rigs were built, but were limited to shallow waters. When demands for drilling equipment was needed in water depths greater than 100 feet, then the jackup rigs were built.

                Jack-up rigs are kept in position over the surface at the spot where the oil reserves are located. The jack-up rigs are maneuvered into position with the help of legs that are jacked down from the surface. These rigs can be used at depths of about 600 feet below the surface. The rig should rest about fifty feet above the surface of the water before the drilling work begins.

DRILLSHIP

            Drill-ships are useful in undertaking drilling work of new oil and gas reserve wells even at significant depths. A drillship is a vessel that has been fitted with a drilling device and can propel itself to where the oil deposits are present. The drillship can also be constructed from an existing ship. Older drillships use anchors to maintain the ship’s position in the ocean. Newer drillships utilize computer-controlled thrusters to better control the position of the ship. The drillships that are controlled by computers can be used to navigate even in very deep water. They have extensive mooring or positioning equipment, as well as a helipad to receive supplies and transport staff. Typically employed in deep and ultra-deep waters, drillships work in water depths ranging from 2,000 to more than 10,000 feet (610 m to 3,048 m).

 IMPACTS ON THE ENVIRONMENT DUE TO DRILLING

                Offshore oil production involves environmental risks, most notably oil spills from oil tankers or pipelines transporting oil from the platform to onshore facilities, and from leaks and accidents on the platform. Produced water is also generated, which is water brought to the surface along with the oil and gas; it is usually highly saline and may include dissolved or un-separated hydrocarbons.

How onshore drilling is done?

ONSHORE DRILLING

                Drilling into the Earth for exploring valuable natural fossil resources is called onshore drilling. At first seismic survey is needed for exploration of the resource. It is typically carried out in order to explore for and subsequently extract petroleum which lies in rock formations beneath or within the earth surface. Most commonly, the term is used to describe drilling activities on the land, though the term can also be applied to drilling in low altitude hilly areas.

TYPES OF ONSHORE DRILLING

There are two main types of onshore drilling percussion or ‘cable tool’ drilling and rotary drilling:-

I. CABLE TOOL DRILLING

Cable tool, consists of raising and dropping a heavy metal bit into the ground, effectively punching a hole down through the earth. Cable tool drilling is usually used for shallow, low pressure formation. It is recognized by many as the first drilling method employed to dig wells into the earth for the purpose of reaching petroleum deposits and water.

The basic concept for cable tool drilling consists of repeatedly dropping a heavy metal bit into the ground, eventually breaking through rock and punching a hole through to the desired depth. The bit, usually a blunt, chisel shaped instrument, can vary with the type of rock that is being drilled. Water is used in the well hole to combine with all of the drill cuttings, and is periodically bailed out of the well when this ‘mud’ interferes with the effectiveness of the drill bit.

Innovations, such as the use of steam power in cable tool drilling, greatly increased the efficiency and range of percussion drilling. Conventional man-powered cable tool rigs were generally used to drill wells 200 feet or less, while steam powered cable tool rigs, consisting of the familiar derrick design, had an average drilling depth of 400 to 500 feet. The deepest known well dug with cable tool drilling was completed in 1953, when the New York Natural Gas Corporation drilled a well to a depth of 11,145 feet.

II. ROTARY DRILLING

Rotary drilling, consists of a sharp, rotating metal bit used to drill through the Earth’s crust. This type of drilling is used primarily for deeper wells, which may be under high pressure.

Despite the historical significance of cable tool drilling, modern drilling activity has shifted mainly toward rotary drilling methods. However, the foundation of knowledge laid by years of cable tool drilling is, in many cases, directly transferable to the practice of rotary drilling.

III. HORIZONTAL DRILLING

Most modern type of drilling, horizontal drilling is flexible in that it allows for the extraction of natural gas that had previously not been feasible.  Although on the surface it resembles a vertical well, beneath the surface, the well inclines so that it runs parallel to the natural gas formation. These legs can go in different directions at different depths and can be more than one mile long horizontally, in addition to the vertical well that can be thousands of feet below the surface.  Horizontal drilling allows one surface well to branch out underground and tap many different natural gas resources.  It also allows the well to make contact with larger areas within productive formations.

Horizontal drilling also permits the development of natural resources with minimal above ground disturbance, reducing the environmental footprint of natural gas operations and the cost and potential disturbance of existing roads or other infrastructure.  Directional drilling and horizontal drilling terms are often used interchangeably.  Directional drilling refers to drilling at a slant or angle to increase contact with the resource.  Horizontal drilling is a type of directional drilling.  Horizontal drilling uses a technique known as hydraulic fracturing in order to extract natural gas from geologic formations.

WHAT IS SEISMIC SURVEY?        

Seismic survey also can be called as Land Seismic Exploration Technique. This is a type of exploration technique used to explore under the earth surface. Most common method is blasting technique.

In this method explosives are used or blasting under the earth surface(at a suitable specified depth) for generating a sound waves or shock waves travelling downward through the subsurface and being partially reflected at each rock interface. The reflected energy is recorded at the surface by the Seismic Recording System via a 2 to 10 km long Seismic Cable to which ground motion sensors called Geophones are attached.

The Geophones are moved by the upward travelling sound waves, generating a small electrical current within the geophone. The small electrical signals are added to improve Signal to Noise Ratio and are digitized to 24 bit accuracy with the digital signal then being transmitted to the Recording Truck connected to the Seismic Cable.

This is a geophysical technique used to map in 2D or 3D, an image of the earth’s subsurface. Reflection Seismic is used by Oil & Gas, Coal Seam Gas, Minerals and Coal Exploration and Production companies to develop a clear understanding of subsurface rock structure and other geologic properties.

COMPARING TURBOCHARGER AND SUPERCHARGER

DIFFERENCE BETWEEN TURBOCHARGER AND SUPERCHARGER

                Turbochargers were originally known as turbosuperchargers when all forced induction devices were classified as superchargers. Nowadays the term "supercharger" is usually applied only to mechanically driven forced induction devices. The key difference between a turbocharger and a conventional supercharger is that a supercharger is mechanically driven by the engine, often through a belt connected to the crankshaft, whereas a turbocharger is powered by a turbine driven by the engine's exhaust gas. Compared to a mechanically driven supercharger, turbochargers tend to be more efficient, but less responsive. Twin-charger refers to an engine with both a supercharger and a turbocharger.

                In contrast to turbochargers, superchargers are mechanically driven by the engine. Belts, chains, shafts, and gears are common methods of powering a supercharger, placing a mechanical load on the engine. For example, the supercharger uses about few horsepower. Yet the benefits outweigh the costs, for that few horsepower  to drive the supercharger the engine generates an additional horsepower(3 times more). This is where the principal disadvantage of a supercharger becomes apparent; the engine must withstand the net power output of the engine plus the power to drive the supercharger.

WORKING OF TURBOCHARGER

The basic idea is that the exhaust drives the turbine, which is directly connected to  the compressor, which increases the flow of air into the engine(cylinder). This can be explained in the following steps:-

i. Atmospheric cool air enters the engine's air intake and heads toward the compressor.

ii. The compressor fan helps to suck air in.

iii. The compressor squeezes and heats up the incoming air and blows it out again.

iv. Hot, compressed air from the compressor passes through the heat exchanger, which cools it down.

v. Cooled, compressed air enters the cylinder's air intake. The extra oxygen helps to burn fuel in the cylinder at a faster rate.

vi. Since the cylinder burns more fuel, it produces energy more quickly and can send more power to the wheels via the piston, shafts, and gears.

vii. Waste or exhaust gas from the cylinder exits through the exhaust outlet.

viii. The hot exhaust gases blowing past the turbine fan make it rotate at high speed.

ix. The spinning turbine is mounted on the same shaft as the compressor. So, as the turbine spins, it makes the compressor to spin as well.

x. The exhaust gas leaves the car, so wasting less energy.

WORKING OF SUPERCHARGER

A supercharger is a belt driven device that forces air into an internal combustion engine. It consists of a drive belt, drive, the driven gears inside, and a centrifugal compressor wheel. The belt drives the gear and compressor wheel. The compressor wheel pumps air into the engine. The intake air comes in from the back, and goes out of the bottom, the belt drives the wheel in the front.

Supercharger are installed on top of the intake manifold on V-type engines and on the side of inline engines. Since they’re belt driven, supercharger speed is dependent on engine speed and is most efficient at higher engine speeds. There are two main types of supercharger positive displacement and dynamic compression

        Positive-displacement pumps deliver a nearly fixed volume of air per revolution at all speeds (minus leakage, which is almost constant at all speeds for a given pressure, thus its importance decreases at higher speeds). Major types of positive-displacement pumps include:-

i. Roots type.

ii. Lysholm twin-screw.

iii. Sliding vane.

iv. Scroll-type supercharger, also known as the G-Lader.

        Dynamic compressors rely on accelerating the air to high speed and then exchanging that velocity for pressure by diffusing or slowing it down. Major types of dynamic compressor are:-

i. Centrifugal type.

ii. Multi-stage axial-flow.

iii. Pressure wave supercharger.

ADVANTAGES OF TURBOCHARGER OVER SUPERCHARGER

i. Some superchargers(especially Roots type) has lower adiabatic efficiency as compared to turbochargers.

ii. Roots superchargers impart significantly more heat to the air than turbochargers.

iii. For a given volume and pressure of air, the turbocharged air is cooler, and as a result denser, containing more oxygen molecules, and therefore more potential power than the supercharged air.

iv. In practical application the disparity between the two, turbochargers often produces 15% to 30% more power based solely on the differences in adiabatic efficiency.

SOME TYPES OF JET ENGINES

 JET ENGINES

                Jet engines date back to the invention of the aeolipile before the first century AD. This device directed steam power through two nozzles to cause a sphere to spin rapidly on its axis. So far as is known, it did not supply mechanical power and the potential practical applications of this invention did not receive recognition. Instead, it was seen as a curiosity.

                Jet propulsion only took off, literally and figuratively, with the invention of the gunpowder-powered rocket by the Chinese in the 13th century as a type of fireworks, and gradually progressed to propel formidable weaponry. However, although very powerful, at reasonable flight speeds rockets are very inefficient and so jet propulsion technology stalled for hundreds of years.

                A jet engine is a reaction engine discharging a fast moving jet that generates thrust by jet propulsion in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, and pulse jets. In general, jet engines are combustion engines but non-combusting forms also exist. The term jet engine loosely refers to an internal combustion air breathing jet engine. These typically consist of an engine with a rotary (rotating) air compressor powered by a turbine ("Brayton cycle"), with the leftover power providing thrust via a propelling nozzle. Jet aircraft use these types of engines for long-distance travel. Early jet aircraft used turbojet engines which were relatively inefficient for subsonic flight. Modern subsonic jet aircraft usually use high-bypass turbofan engines. These engines offer high speed and greater fuel efficiency than piston and propeller aero engines over long distances.

APPLICATIONS

i. Jet engines power aircraft, cruise missiles and unmanned aerial vehicles.

ii. In the form of rocket engines they power  model rocketry, spaceflight, and military missiles.

iii. Jet engines have propelled high speed cars, particularly drag racers, with the all-time record held by a rocket car.

iv. Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines or marine power plants.

v. These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower.

vi. Jet engines are also sometimes developed into, or share certain components such as engine cores, with turbo shaft and turboprop engines, which are forms of gas turbine engines that are typically used to power helicopters and some propeller-driven aircraft.

VARIOUS TYPES OF JET ENGINES

Water jet

For propelling boats; squirts water out the back through a nozzle.

Motor jet

Most primitive air breathing jet engine. Essentially a supercharged piston engine with a jet exhaust. Higher exhaust velocity than a propeller, offering better thrust at high speed.

Turbojet

A tube with a compressor and turbine sharing a common shaft with a burner in between and a propelling nozzle for the exhaust. Uses a high exhaust gas velocity to produce thrust. Has a much higher core flow than bypass type engines. Simplicity of design, efficient at supersonic speeds.

Turbofan

A turbofan is a type of jet engine, similar to a turbojet. It essentially consists of a large ducted fan with a smaller diameter turbojet engine mounted behind it that provides propulsion and also powers the fan. Part of the airstream from the ducted fan passes through the turbojet, providing oxygen to burn fuel to power the turbojet. But part, usually most, of the flow bypasses the turbojet, and is accelerated by turbine blades acting like a propeller. The combination of these two processes produces thrust more efficiently than other jet designs. Turbofans have a net exhaust speed that is much lower than a turbojet. This makes them much more efficient at subsonic speeds than turbojets, and somewhat more efficient at supersonic speeds up to roughly Mach 1.6.

All of the jet engines used in currently manufactured commercial jet aircraft are turbofans. They are used commercially mainly because they are highly efficient and relatively quiet in operation. Turbofans are also used in many military jet aircraft.

Low-bypass Turbofan

One- or two-stage fan added in front bypasses a proportion of the air through a bypass chamber surrounding the core. Compared with its turbojet ancestor, this allows for more efficient operation with somewhat less noise. This is the engine of high-speed military aircraft, some smaller private jets, and older civilian airliners such as the Boeing 707, the McDonnell Douglas DC-8, and their derivatives.

High-bypass Turbofan

First stage compressor drastically enlarged to provide bypass airflow around engine core, and it provides significant amounts of thrust. Compared to the low-bypass turbofan and no-bypass turbojet, the high-bypass turbofan works on the principle of moving a great deal of air somewhat faster, rather than a small amount extremely fast. Most common form of jet engine in civilian use today- used in airliners like the Boeing 747, most 737s, and all Airbus aircraft.

Scramjet

Similar to a ramjet without a diffuser; airflow through the entire engine remains supersonic. Few mechanical parts, can operate at very high Mach numbers (Mach 8 to 15) with good efficiencies.

Ramjet

Intake air is compressed entirely by speed of oncoming air and divergent shape, and then it goes through a burner section where it is heated and then passes through a propelling nozzle. Very few moving parts, Mach 0.8 to Mach 5+, efficient at high speed (> Mach 2.0 or so), lightest of all air-breathing jets (thrust / weight ratio up to 30 at optimum speed), cooling much easier than turbojets as no turbine blades to cool.

Pulsejet

Air is compressed and combusted intermittently instead of continuously. Some designs use valves. Very simple design, commonly used on model aircraft.

Pulse detonation engine

Similar to a pulsejet, but combustion occurs as a detonation instead of a deflagration, may or may not need valves.

Rocket

Carries all propellants and oxidants on-board, emits jet for propulsion. Very few moving parts, Mach 0 to Mach 25+, efficient at very high speed (> Mach 10.0 or so), thrust / weight ratio over 100, no complex air inlet, high compression ratio, very high speed (hypersonic) exhaust, good cost / thrust ratio, fairly easy to test, works in a vacuum-indeed works best exo-atmospheric which is kinder on vehicle structure at high speed, fairly small surface area to keep cool, and no turbine in hot exhaust stream

Air-augmented rocket

Essentially a ramjet where intake air is compressed and burnt with the exhaust from a rocket.

Turbo-rocket

A turbojet where an additional oxidizer such as oxygen is added to the airstream to increase maximum altitude. Very close to existing designs, operates in very high altitude, wide range of altitude and airspeed.

Pre-cooled jets

Intake air is chilled to very low temperatures at inlet in a heat exchanger before passing through a ramjet and / or turbojet and / or rocket engine. Easily tested on ground. Very high thrust / weight ratios are possible (~14) together with good fuel efficiency over a wide range of airspeeds, mach 0-5.5+; this combination of efficiencies may permit launching to orbit, single stage, or very rapid, very long distance intercontinental travel.

Brief idea on diesel engine

DIESEL ENGINE

                The diesel engine (also known as a compression-ignition or 'CI' engine) is an internal combustion engine in which ignition of the fuel that has been injected into the combustion chamber is initiated by the high temperature which a gas achieves when greatly compressed (adiabatic compression). This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to gasoline), which use a spark plug to ignite an air-fuel mixture.

                The diesel engine has the highest thermal efficiency (engine efficiency) of any practical internal or external combustion engine due to its very high compression ratio and inherent lean burn which enables heat dissipation by the excess air. A small efficiency loss is also avoided compared to two-stroke non-direct-injection gasoline engines since unburnt fuel is not present at valve overlap and therefore no fuel goes directly from the intake/injection to the exhaust. Low-speed diesel engines (as used in ships and other applications where overall engine weight is relatively unimportant) can have a thermal efficiency that exceeds 50%.

WORKING

Diesel engines work by internal combustion. First, air is allowed into the cylinder and the piston compresses it—but much more than in a petrol engine. In a petrol engine, the fuel-air mixture is compressed to about a tenth of its original volume. But in a diesel engine, the air is compressed by anything from 14 to 25 times. If you've ever pumped up a bicycle tire, you'll have felt the pump getting hotter in your hands the longer you used it. That's because compressing a gas generates heat. Imagine, then, how much heat is generated by forcing air into 14-25 times less space than it normally takes up. So much heat, as it happens, that the air gets really hot—usually at least 500°C (1000°F) and sometimes very much hotter. Once the air is compressed, a mist of fuel is sprayed into the cylinder typically (in a modern engine) by an electronic fuel-injection system, which works a bit like a sophisticated aerosol can. The air is so hot that the fuel instantly ignites and explodes without any need for a spark plug. This controlled explosion makes the piston push back out of the cylinder, producing the power that drives the vehicle or machine in which the engine is mounted. When the piston goes back into the cylinder, the exhaust gases are pushed out through an exhaust valve and, the process repeats itself.

REASONS FOR MANUFACTURING

Diesel engines are manufactured in two-stroke and four-stroke versions. They were originally used as a more efficient replacement for stationary steam engines. Since the 1910s they have been used in submarines and ships. Use in locomotives, trucks, heavy equipment and electricity generation plants followed later. In the 1930s, they slowly began to be used in a few automobiles. Since the 1970s, the use of diesel engines in larger on-road and off-road vehicles in the USA increased. According to the British Society of Motor Manufacturing and Traders, the EU average for diesel cars account for 50% of the total sold, including 70% in France and 38% in the UK.

The world's largest diesel engine is currently a Wärtsilä-Sulzer RTA96-C Common Rail marine diesel, which produces a peak power output of 84.42 MW (113,210 hp) at 102 rpm.

 APPLICATION

i. Diesel engines are commonly used as mechanical engines, power generators and in mobile drives.

ii. They find wide spread use in locomotives, construction equipment, automobiles, and countless industrial applications.

iii. Industrial diesel engines and diesel powered generators have construction, marine, mining, hospital, forestry, telecommunications, underground, and agricultural applications, just to name a few.

iv. Power generation for prime or standby backup power is the major application of today's diesel generators.

ADVANTAGES

i. Diesel engines have several advantages over other internal combustion engines:

ii. They burn less fuel than a petrol engine performing the same work, due to the engine's higher temperature of combustion and greater expansion ratio.

iii. The longevity of a diesel engine is generally about twice that of a petrol engine due to the increased strength of parts used.

iv. Diesel fuel has better lubrication properties than petrol as well.

v. Diesel fuel is considered safer than petrol in many applications.

vi. The low vapour pressure of diesel is especially advantageous in marine applications, where the accumulation of explosive fuel-air mixtures is a particular hazard.

vii. For any given partial load the fuel efficiency (mass burned per energy produced) of a diesel engine remains nearly constant.

viii. They generate less waste heat in cooling and exhaust.

ix. Diesel engines can accept super- or turbo-charging pressure without any natural limit, constrained only by the strength of engine components.

x. Biodiesel is an easily synthesized, non-petroleum-based fuel.

DISADVANTAGES

i. Diesel engines are expensive than petrol engines.

ii. Higher maintenance cost.

iii. Higher engines noise.

iv. Higher engine vibration.

v. Diesel engine emits more harmful gases to the environment.

vi. Sluggish acceleration.

Brief idea on petrol engine.

PETROL ENGINES

                A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. It was invented in 1876 in Germany by German inventor Nikolaus August Otto. The first petrol combustion engine (one cylinder, 121.6 cm³ displacement) was prototype in 1882 in Italy by Enrico Bernardi. In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites.

WORKING

i. Suction of air (is also known as breathing or aspiration).

ii. Mixing of the fuel with air after breaking the liquid fuel into highly atomised / mist form.

iii. Igniting the air-fuel mixture with an electric spark using spark plug.

iv. Burning of highly atomised fuel particles; which results in releasing / ejection of heat energy.

TYPES OF FUEL INJECTION SYSTEM IN PETROL ENGINES

Continuous type:-

In this type petrol is injected in to the inlet manifold continuously when the engine is running.

Intermittent type:-

In this type petrol is injected during the suction stroke only it is also known as timed or jerk type.

Direct type:-

In this type petrol is feed directly in to the glider.

Indirect type:-

In this type petrol is injected in to the inlet port or in to the inlet manifold.

Single point:-

In this type the petrol is injected through single injector.

Multi point :-

In this type petrol is injected by number of injector it is more advance and recent development it is computer control system it is having high fuel efficiency.

Electronic petrol injection system(commonly known as fuel injection):-

- In this system electronically controlled metering valve is used.

- The metering valve meters the desired quantity of petrol and supplied to injector.

- The opening injector is also controlled by electronically controlled so that electronic unit known as ECU which consider computer and sensor.

- The sensors sense the various engine conditions [tempter load speed air pressure] and sends the singles to the computer [E.C.U/E.C.M] the computer reads the singles to the sensor to operate the pump and nozzle.

Some disadvantage of using carburetor:

i.  With single carburetor it is difficult to supply to mixture uniformly to all cylinder.

ii. Ventura throat of carburetor restricts the smooth flow of mixture.

iii. Chock restricts the flow of mixture.

To solve the above said problem, electronic injection is necessary.

WORKING CYCLES

Petrol engines may run on the four-stroke cycle or the two-stroke cycle. For details of working cycles see:

·         Four-stroke cycle

·         Two-stroke cycle

·         Wankel engine

CYLINDER CONFIGURATION

Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in V-formation. Flat engines – like a V design flattened out – are common in small airplanes and motorcycles and were a hallmark of Volkswagen automobiles into the 1990s. Flat 6sare still used in many modern Porsches, as well as Subarus. Many flat engines are air-cooled. Less common, but notable in vehicles designed for high speeds is the W formation, similar to having 2 V engines side by side. Alternatives include rotary and radial engines the latter typically have 7 or 9 cylinders in a single ring, or 10 or 14 cylinders in two rings.

COOLING

Petrol engines may be air-cooled, with fins (to increase the surface area on the cylinders and cylinder head); or liquid-cooled, by a water jacket and radiator. The coolant was formerly water, but is now usually a mixture of water and either ethylene glycol or propylene glycol. These mixtures have lower freezing points and higher boiling points than pure water and also prevent corrosion, with modern antifreezes also containing lubricants and other additives to protect water pump seals and bearings. The cooling system is usually slightly pressurized to further raise the boiling point of the coolant.

IGNITION

Petrol engines use spark ignition and high voltage current for the spark may be provided by a magneto or an ignition coil. In modern car engines the ignition timing is managed by an electronic Engine Control Unit.

ADVANTAGES

i. Cheaper than a diesel engine.

ii. Less maintenance cost.

iii. Easy to construct and repair.

iv. Can be used in light weight vehicles.

v. Smooth, less vibration and better acceleration than a diesel engine.

DISADVANTAGES

i. Less mileage.

ii. Supply of is decreasing and one will petrol supplies will be exhausted.

iii. Price of petrol is increasing everyday.

iv. Burning of petrol affects the environment as it produces carbon.

v. Transport of petrol is dangerous.      

vi. The volatile components of petrol cause smog.
vii. Less durable than diesel engine.

CONCLUSION

                Petrol engines run at higher speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft (a design efficiency made possible by lower compression ratios) and due to petrol burning more quickly than diesel. Because pistons in petrol engines tend to have much shorter strokes than pistons in diesel engines, typically it takes less time for a piston in a petrol engine to complete its stroke than a piston in a diesel engine. However the lower compression ratios of petrol engines give petrol engines lower efficiency than diesel engines.