Carburetor

The Carburetor, also known as carb or carbie for short, is a device that mixes air and fuel for an internal combustion (IC) engine. Carburetor are still found in small engines and some older or specialized automobiles such as those designed for stock car racing. However, fuel injection (FI), first introduced in late 1950s and first successfully commercialized in the early 1970s, is now the preferred method of automotive fuel delivery. The majority of motorcycles still are carbureted due to lower weight and cost, but as of 2005 many new models are now being introduced with fuel injection.

Most carbureted engines have single carburetor, though some engines use multiple carburetors. Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top. This had the advantage of never “Flooding” the engine, as any liquid fuel droplets would fall out of the carburetor instead of into the intake manifold; it also lent itself to use of an oil bath air cleaner, where a pool of oil below the mesh element below the carburetor is sucked up into the mesh and the air is drawn through the oil covered mesh; this was an effective system in a time when paper air filters did not exist. Small propeller driven flat aircraft engines still use the updraft carburetor design.

Functions of a Carburetor:

The major function which a carburetor is required to perform are:

·        To keep a small reserve of a fuel at a constant head,

·        To vaporize the fuel to prepare a homogeneous air fuel mixture,

·        To supply correct amount of the air fuel mixture the correct strength under all conditions of load and speed of the engine.

Principle of Carburetor:

The carburetor works on the Bernoulli’s principle: the fact that moving air has lower pressure than still air, and that the faster the movement of the air, the lower the pressure. The throttle or accelerator does not control the flow of liquid fuel. Instead, it controls the amount of air that flows through the carburetor. Faster flows of air and more air entering the carburetor draws more fuel into the carburetor due to the partial vacuum that s created.

Adjustments in Carburetor:

The procedure to make various adjustments differs in case of individual carburetor models. However, the common adjustments and their procedures may be outlined as given below:

1.      Idle adjustment

There is an idle adjustment screw provided in the carburetor. Screwing in the same decreases the idle port area and hence decreases the engine speed. The screw is adjusted till the engine runs smoothly at required speed. Generally, this is done by screwing in completely and then opening back by one or two turns. Another method for idle adjustment, which is precise, involves attaching a vacuum gage to the intake manifold and adjusting the idle screw till maximum vacuum is obtained on the gage.

2.      Throttle adjustment

On releasing the accelerator pedal throttle valve should be completely closed, while on pressing the pedal fully, it should be in full open position. This may be checked and if not found correct, the linkage may be adjusted, as provided for in the manufacturer’s manual.

3.      Other adjustments

Apart from the idle and throttle adjustments, the other adjustments which are provided in some carburetors are for accelerating pump, metering rod, floats, etc. They may be performed as laid down in the manual.

Turbocharged Engine

Mechanical Engineers, always make something better, cheaper, more efficient, in other words more environment friendly. 

It is always possible to build an engine that can go faster and travel further using less fuel. One way to improve an engine performance is to use a Turbocharger, a pair of fans that harness waste exhaust power from the back of engine to cram more air into the front, delivering more “oomph” than you’d otherwise get. When people talk about racing cars or high performance sports car, the topic of turbochargers usually comes up. A turbo can significantly boost an engine’s horsepower without significantly increasing its weight, which turns into a huge benefit that makes turbos so popular.

Turbocharger, also known as turbo, is a turbine driven force induction device that increases an internal combustion (IC) engine’s efficiency and net power output by forcing extra compressed air into the combustion chamber. Turbochargers are most often used with Otto cycle and Diesel cycle internal combustion engines. Originally known as Turbosuperchargers, when all forced induction devices were classified as superchargers. The major 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 engine’s exhaust gas. An engine with both a supercharger and a turbocharger is known as Twincharged engine. 

Working of Turbocharger:

A turbocharger consists of two little air fans (also called as impellers or gas pumps) placed on same metal shaft so that both spin around together. One of these fans, called as the turbine, is placed in the exhaust stream from the cylinders. As the cylinders blow hot gases past the fan blades, they rotate and the shaft they are connected to (technically called the center hub rotating assembly or CHRA) rotates as well. The second fan is called the compressor, is mounted inside the car’s air intake so, as it spins, it draws air into the car and forces into the cylinders.  These are covered by a snail shaped housing featuring an inlet port, which the wasted exhaust gases enter at a high pressure and outlet port through which gases is passed out.

The basic idea is that the exhaust gases drive the turbine which is directly connected to the compressor, which rams air into the engine.

·        Fresh air enters the engine’s air intake and moves towards the compressor,

·        The compressor fan suck air in and squeezes and heats up the incoming air and blows it out again,

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

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

·        As per requirement, cylinder burns more fuel producing energy more quickly and transfers more power to the wheels via the piston, shafts and transmission,

·        The hot exhaust gases blowing past the turbine fan make it rotate at high speed,

·        The spinning turbine is mounted on the same shaft as the compressor. So, as the turbine rotates the compressor rotates too,

·        The exhaust gas leaves the car, wasting less energy than it would otherwise.

In order to achieve such boost, the turbocharger uses the exhaust gas flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 250,000 rotations per minute (rpm), which is about 30 times faster than most car engines can go. Since, turbocharger is connected up to the exhaust, the temperature in the turbine is extremely high. So, they typically have an oil cooling system to make sure that they don’t run too hot.

Turbocharged engines produce more power in the same sized engine. This is because every stroke of the piston generates more power than in naturally aspirated engines. A good example of such engine is Ford’s decision to replace its standard 1.6L petrol engine with a 1L turbocharged unit, which it calls as EcoBoost. Today, all modern diesel cars are fitted with a turbocharger, improving fuel economy and reducing emissions.

Even on the smallest engines, turbocharger produce more torque, particularly lower down the rev range. It means car can get benefit from strong, nippy performance, which is great around worn and helps the engine to feel more refined at higher speeds on motorways.

As the air in a turbocharged engine is filtered through more pipes and components, the intake and exhaust noise is reduced and refined, making for a quieter and smoother engine noise. This was one of the most unexpected benefits of a turbocharged engine.

Pros:

·        A turbocharged engine is typically more fuel efficient than a regular engine at a given horsepower: pleasant punch for passing and merging.

Cons:

·        It can be thirstier than a regular engine if you have a heavy foot,

·        Turbochargers themselves can fail and be costly to replace,

·        Turbo lag is a brief delay in response after pressing the throttle, which can occur when the engine isn’t producing enough exhaust gas to spin the turbo’s intake turbine quick enough.

Curiosity, a Rover

Curiosity, is the name of the rover made and operated by NASA. It was launched on Nov 26, 2011 from Cape Canaveral LC-41. Atlas V541 (AV-028), was used to launch the rover into earth orbit. It headed towards the Red Planet, a 1-ton robotic beast that took planetary exploration to the next level. Curiosity is a car sized rover designed to explore the carter Gale on the Red planet (Mars) as part of NASA’s Mars Science. The dry mass of rover only is about 899 kg (1,982 lb). Primary mission duration of Curiosity was only about 668 sols (687 days) and currently it has been working for 2352 sols (2416 days) since landing.

The overall mission is referred to as the Mars Science Laboratory or MSL. Previously, of the 39 mission to the Mars, including orbiters and landers, only 15 have been successful.  The rover’s goals include an investigation of the Martian climate and geology, environmental conditions favorable for microbial life, including the role of water and planetary habitability studies in preparation for human exploration. Curiosity’s primary mission is to make sure that if Mars is, or was, suitable life. In early 2013, the rover beamed back information showing that Mars had habitable conditions in the past. When Curiosity performed first drill operation, the drill samples obtained included the elements of Sulfur, Nitrogen, Hydrogen, Oxygen, Phosphorus and Carbon, which are all considered as “Building blocks” or fundamental elements that could support life.  

Curiosity consists of Rover Environmental Monitoring Station (REMS) that comprises instruments to measure the Mars environment including humidity, pressure, temperatures, wind speeds and ultraviolet radiations.  All these sensors are placed around three elements namely: two booms attached to the rover’s mast, the ultraviolet sensor (UVS), provided by the Spanish Ministry of Education and Science, assembly located on the rover top deck, and the Instrument Control Unit (ICU) inside the rover body.

Working method of Rover:

Rover consists of highly advance instruments for Martian exploration.

·        On observation, if a particular surface is of interest, then Curiosity can vaporize a small portion of it with an infrared laser and examine the resulting spectra signature to study the rock’s elemental composition,

·        If that signature is fascinating, the rover uses its long arm to swing over a microscope and an X-ray spectrometer to have a closer observation,

·        Once the specimen warrants further analysis, Curiosity can drill into the surface and deliver a powdered sample to the either the SAM or the CheMin analytical laboratories inside the rover for further examination.

Facts about the Rover:

·        The curiosity rover weighs over 900 kilograms,

·        Depending on the condition of terrain on Mars, Curiosity can move at 30 meters per hour,

·        Curiosity has got 17 cameras for 360⁰ observation and 10 other scientific instruments,

·        Instruments like a mobile organic chemistry lab and a infrared laser that can vaporize rocks is included in it,

·        Curiosity is powered by a radioisotope thermoelectric generator and lithium-ion batteries,

·        Curiosity is 9 feet 10 inches long by 9 feet 1 inch wide and about 7 feet high. Curiosity’s wheels have a 20 inch diameter,

·        The two identical on-board rover computers, called Rover Computer Element (RCE) contain radiation hardened memory to tolerate extreme radiation from the space and to safeguard against power-off cycles,

·        Curiosity us equipped with significant telecommunication redundancy by several means: an X band transmitter and receiver that can communicate directly with Earth, and a UHF Electra-lite software defined radio for communicating with Mars orbiters.

Curiosity telecommunication included a small deep space transponder on the descent stage and a solid state power amplifier on the rover for X band. Signals between Earth and Mars take an average of 14 minutes, 6 seconds. According to the NASA statement released on Feb, 28, the Curiosity rover is back to gathering data on a clay rich region of Mars. The rover has two pairs of black and white navigation cameras mounted on the mast to support ground navigation. These cameras have a 45⁰ angle of view and use visible light to capture stereoscopic 3-D imagery. In total, the Curiosity carries 17 different cameras: HazCams *8, NavCams *4, MastCams *2, MAHLI *1, and ChemCam *1.

Achievements of Curiosity:

·        Just seven weeks after Curiosity touched down the Martian surface, mission scientists announced that the rover had found an ancient streambed where water once flowed roughly knee-deep for thousands of years at a time,

·        By drilling into Martian rocks, the rover discovered what are believed to be the key ingredients for life. The Rover found that ancient Mars likely had the right chemistry to support living microbes,

·        Curiosity detects dangerous level of radiation that exceed NASA’s career limit for astronauts, that helps the space agency’s engineers to build spacecraft and spacesuits that are able to protect humans on deep space missions,

·        Curiosity found different varieties of soil and rock in the Gale Crater.

Fighter Aircraft (F-22 Raptor)

A fighter aircraft is a military aircraft designed primarily for air to air combat against other aircrafts. It is also used for bombarding purposes on pre-specified targets. Fighter aircrafts changed the history of war. Any country with most advanced fighter not only rules the sky but also dominates the war going on land by carrying out air strikes. The hallmarks of a fighter are its speed, maneuverability and small size relative to other aircrafts. Many fighter aircrafts have secondary ground attack capabilities, and some are designed as dual purpose fighter bombers.

Since world war-I, the fighter aircrafts have maintained its air superiority over a battleground.

                                           

F-22 Raptor:

F-22 Raptor was one of the most advanced and deadliest aircrafts when it came in service in early 2000s.  The F-22 Raptor is considered as the first 5^th generation fighter in the US air inventory, using low observable techniques, modern avionics, and efficient engine to offer an air superiority fighter unmatched by any other military aircrafts. It is basically single seat, twin engine and all weather stealth tactical fighter aircraft designed for United States Air Force.

It has a glass cockpit with all digital flight instruments. The monochrome head-up display offers a wide range of view and serves as a primary flight instrument. The raptor has three weapons bays; a large main weapon bay under the fuselage, and other two on the sides of fuselage.

The F-22 Raptor, a critical component of the Global Strike Task Force, is designed to project air dominance and it cannot be matched by any known or projected fighter aircrafts. The F-22 has a significant capability to attack the ground targets.  It possesses a sophisticated sensor suite allowing the pilot to track, identify, shoot and kill the air to air threats before being detected. Advances in low observable technologies provides significantly improved survivability and lethality against air to air and surface to air threats.

The thrust produced by F-22 engines are comparatively more than any current fighter aircraft engine. The combination of sleek aerodynamic design and increased thrust allows the F-22 to cruise at supersonic airspeeds (greater than mach 1.5) without using afterburner. This characteristics is known as Supercruise, which greatly expands the F-22’s operating envelope in both speed and range over current fighters, which must fuel-consuming afterburner to operate at supersonic speeds.

The Raptor has received relatively few upgrades compared to legacy 4^th generation F-15 and F-16 fighter aircraft and now is significantly outdated in many ways. The F-22 raptor lacks many capabilities relative to 4^th generation.

Below, there are some specifications and performance analysis of F-22 raptor;

Specifications:

·        Crew: 1

·        Length: 62ft 1in (18.92 m)

·        Wingspan: 44 ft 6 in (13.56 m)

·        Height: 16 ft 8 in (5.08 m)

·        Wing area: 840 ft² (78.04 m²)

·        Empty weight: 43,340 lb (19,700 Kg)

·        Loaded weight: 64,840 lb (29,410 Kg)

·        Max takeoff weight: 83,500 lb (38,000 Kg)

·        Fuel Capacity: 18,000 lb (8,200 Kg)

·        Dry thrust: 26,000 lb (116 KN each)

·        Thrust with afterburner: >35,000 lb (> 156 KN each)

Performance:

·        Maximum speed: At altitude: mach 2.25 (1,500mph, 2,410 Km/h) and at Supercruise: mach 1.82 (1,220 mph, 1,960 Km/h)

·        Range: >1,600 nmi (2,960 Km)

·        Combat radius: 460 nmi

·        Ferry range: 1,740 nmi

·        Service ceiling: >65,000 ft (20,000m)

·        Wing loading: 77.2 lb/ft² (377 kg/m²)

·        Thrust/Weight: 1.08

·        Maximum design g- load: +9.0/- 3.0 g

Armament

·        Guns: 1*20 mm M61A2 Vulcan 6-barrel rotary cannon in right wing root, 480 rounds

·        Air to Air mission loadout

Ø  6* AIM-120 AMRAAM

Ø  2* AIM-9 Sidewinder

·        Air to ground mission loadout

Ø  2* 1,000 lb JDAM or 8* 250 lb GBU-39 small diameter bombs

Ø  2* AIM-120 AMRAAM

Ø  2* AIM-9 sidewinder

·        Hardpoints: 4* under-wing pylon stations can be fitted to carry 600 US gallon (2,270 L) drop tanks or weapons, each with a capacity 5,000 lb (2,270 kg). However, if mounted, external hardpoints will compromise the stealth of the fighter.

IC Engine Fuels

The subject of fuels for automobiles has been remained of interest for last many years as development basically depend upon the availability of good fuel. Lots of research have been done on this subject for last 100 years and still carried out.

The fundamental knowledge of types of fuels and their characteristics is essential for understanding combustion phenomenon. The properties and character of fuels will have profound effect on the design, power output, efficiency, fuel consumption and also the reliability and durability of engine.

The chemical reactions which are responsible for heat release are considerably fast but time taken in preparing the mixture of air and fuel depends upon the nature of fuel and method adopted to supply the same to the combustion chamber. Therefore, the fuels used in IC engines have to fulfill some basic requirements for better performance of the engine.   

Desirable Properties of good IC Engine fuels

The basic requirement of IC engine fuel is, the combustion should be fast with maximum amount of heat release without forming any deposits and should not have destructive effects on the engine parts and atmospheric air by exhaust gases.

A good IC engine fuel must possess the following properties:

·        It must have high energy density (kJ/Kg),

·        It should be easy to handle and store and free from hazard,

·        It must possess good combustion quality,

·        It must have thermal stability,

·        It must have low deposit forming tendency,

·        It should not have chemical reaction with engine components through which it flows,

·        It should easily mix with air and should evaporate as soon as possible (high h_fg),

·        Products after combustion should not create any corrosion to the engine parts,

·        It should have low toxicity,

·        Its effects on air pollution should be minimum,

·        It should be economically available in very large quantities.

Types of Fuels

The IC engines are mostly operated on liquid fuels or gaseous fuels. But 99% of the world IC engine uses liquid fuels and a few engines uses gaseous fuels where it is readily and economically available.

Different types of gaseous and liquid fuels are discussed below:

Gaseous Fuels:

The gaseous fuels are normally used in SI engines. The different gaseous fuels are listed below:

1.      Natural gas:

It is found in many parts of world but mainly in USA. It is also carried from the place of availability to the place of use through pipelines. Its composition varies with the source but mainly it contains CH₄ (75-95%) and remaining C₂H₆ and N₂.

The natural gas from some areas contains H₂S which is highly harmful to the engines.

2.      Manufactured gases:

Various methods are used to manufacture the gases. Coal gas is manufacture by heating soft coal in closed vessel. The contents of coal gas depend upon the type of coal and method of operation used in manufacturing. A clean coal contains 33% H₂ and 66% CH_4. Its energy content is about 50% of natural gas.

3.      By product gases:

The gases produced during the manufacture of other substances are known as by product gases. Blast furnace gas is by product gas of steel plants. It contains mainly CO and N_2. It contains large amount of dust particles. Therefore, more effective methods should be used to clean it before using it in engines.

4.      Sewage Sludge gas:

Sewage sludge gas is made available from present well developed sewage disposal plants. It mainly contains CH₄ and CO₂ with small presence of H₂S.

5.      Biogas Plants:

The biogas is produced from the cow dung which is available in large quantities. It can be easily manufactured with any chemical reaction and therefore it is easy to manufacture and use locally.

 Advantages of Gaseous fuel

·        It can be easily carried through pipes,

·        It can be easily compressed and stored,

·        The starting of engine is easy which uses gas as fuel,

·        The freezing of oil does not occur with gaseous fuel.

Disadvantages of Gaseous fuel

·        Storage volume per unit energy is very large compared to oil,

·        Cost of gases is high on the basis of energy content,

·        The size and weight of engine is considerably large compared to engine using liquid fuel,

·        The purifying cost of gaseous fuel is considerably high,

·        The capital and running cost for the plants used to manufacture gases is considerably high.

Liquid Fuels:

Liquid fuels carry lot of importance as 99% of the world IC engine use liquid fuel. All the liquid fuels which are used in IC engine are derived from crude petroleum which is naturally available in large quantities.

The liquid fuels are mainly classified into two groups. Liquid fuels which are vaporized easily are petrol and alcohol and are commonly used in SI engines. The other type which is directly injected in the combustion chamber is known as diesel or fuel oil.

All the liquid fuels have two basic elements, Carbon and Hydrogen and they are popularly known as hydrocarbons. The general chemical formula for hydrocarbon is C_nH_m. According to the values of n and m, the physical and chemical properties of hydrocarbon will vary. The hydrocarbon according to the structure of C and H are classified in four categories;

·        Paraffins (C_nH_2n+2)

·        Olefins (C_nH_2n)

·        Naphthenes (C_nH_2n)

·        Aromatics (C_nH_2n-6)

Within each group also, the physical properties of individual compound differ according to the number of carbon and hydrogen atoms in the molecule. The physical differences between compounds, even in any group, influence the way fuel evaporates and hence the formation of combustible mixture. The differences in chemical properties of hydrocarbon from different groups affect the combustion process and hence the properties of fuel and air requirements.