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ppt on engine


By: tara.chand01234 (90 month(s) ago)

ya give current informatuokmm

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Engine .The basic way all internal combustion engines work is to take a mixture of fuel and air, compress it, ignite it either with a spark plug or by self- igntion (in the case of a diesel engine), allow the explosion of combusting gasses to force the piston back down and then expel the exhaust gas. The vertical movement of the piston is converted into rotary motion in the crank via connecting rods. The crank then goes out to the gearbox via a flywheel and clutch, and the gearbox sends the rotary motion to the wheels, driving the vehicle forwards.

Engine layouts :

Engine layouts Below are some illustrations of the most common types of cylinder layout you'll find in engines today . Singles are typically used in motorbikes V-twins are also found in motorbikes. The triple is almost unique to Triumph motorbikes where they call it the Speed Triple Inline-fours are the mainstay of car engines Inline fives used to be used a lot in Audis but have found a new home in current Volvos The V5 is something you'll find in some VWs The V6 has the benefits of being smoother than an inline-four but without the fuel economy issues of a V8 . Boxer engines are found in BMW motorbikes (twins) and Porsches and Subarus (fours and sixes)

Engine layouts :

Engine layouts

Interference vs. non-interference engines :

Interference vs. non-interference engines It's worth mentioning the two sub-types of 4 stroke engine at this point. Because the valves always open inwards, into the combustion chamber, they take up some space at the top of the chamber. In an interference engine, the position of the piston at the top of its stroke will occupy the same physical space that the open valves do whilst the piston is at the bottom of its stroke. It's important to know if your engine is an interference engine because if the timing belt breaks, at least one set of valves will stop in the open position and the momentum of the engine will ram the piston in that cylinder up into the valves requiring a very expensive engine repair or replacement.

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In a non-interference engine, the valves do not occupy any space that the piston could move into, so if your timing belt snaps on one of these engines, in 99% of cases you won't suffer any valve damage because the piston cannot physically touch the open valves. That is the technical explanation of why its important to get your timing belt changed at the manufacturer-specified mileage.

Spark plugs :

Spark plugs And engine without a spark plug is useless, unless it's a diesel engine in which case it uses a glowplug instead. But we're talking about regular petrol engines here so the next topic to get to grips with is the spark plug. It does exactly what it says on the tin - it's a plug that generates a spark. Duh. So why spend time talking about it.They'll all do the job but the more you pay, the better the plug. All spark plugs share the same basic design and construction though.

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The high voltage from your vehicle's high-tension electrical system is fed into the terminal at the top of the spark plug. It travels down through the core of the plug (normally via some noise-suppression components to prevent electrical noise) and arrives at the centre electrode at the bottom where it jumps to the ground electrode creating a spark. The insulator basically keeps the high-tension charge away from the cylinder head so that the spark plug doesn't ground before it gets a chance to generate the spark.

How does the fuel-air mix happen:

How does the fuel-air mix happen The fuel and air are mixed in one of two main ways. The old-school method is to use a carburetor, whilst the new-tech approach is to use fuel injectors. The basic purpose is the same though, and that is to mix the fuel and air together in proportions that keep the engine running. Too little fuel and the engine runs 'lean' which makes it run hot. Too much fuel and it runs 'rich' which conversely makes the engine run cooler. Running rich can also result in fouled up spark plugs, flooded engines and stalling, not to mention wasting fuel. Finding the right balance normally involves about 10 milligrams of petrol for each combustion stroke.

Carburetors :

Carburetors Advantages : analogue and very predictable fuelling behaviour, simple and inexpensive to build and maintain. Disadvantages : carburetor icing in the venturi, imprecise fuel metering, float chambers don't work well if they're not the right way up.

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carburetor is basically a shaped tube. The shape of the tube is designed to swirl the incoming air and generate a vacuum in a section called the venturi pipe (or just the venturi ). In the side of the venturi is a fuel jet which is basically a tiny hole connected to the float chamber via a pipe. It's normally made of brass and has a miniscule hole in the end of it which determines the flow of fuel through it.The fuel is pulled through the jet by the vacuum created in the venturi . At the bottom of the tube is a throttle plate or throttle butterfly which is basically a flat circular plate that pivots along its centreline . It is connected mechanically to the accelerator pedal or twist-grip throttle via the throttle cable. The more you push on the accelerator or twist open the throttle, the more the throttle butterfly opens. This allows more air in which creates more vacuum, which draws more fuel through the fuel jet and gives a larger fuel-air charge to the cylinder, resulting in acceleration.

Carb icing. :

Carb icing. One of the problems with the spinning, compressing, vacuum-generating properties of the venturi is that it cools the air in the process. Whilst this is good for the engine (colder air is denser and burns better in a fuel-air mix), in humid environments, especially cool, humid environments, it can result in carburetor icing. When this happens, water vapour in the air freezes as it cools and sticks to the inside of the venturi . This can result in the opening becoming restricted or cut off completely.

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When carbs ice up, engines stop. In cars, there's normally a heat shield over the exhaust manifold connected via a pipe to a temperature-controlled valve at the air filter. When its cold, the valve is open and the air filter draws warm air from over the exhaust manifold and feeds it into the carburetor. As the temperature warms up, the valve closes and the carburetor gets cooler air because the risk of icing has reduced

Fuel injection :

Fuel injection Advantages : precise and variable fuel metering, better fuel efficiency and better emissions . Disadvantages : Fairly complex engineering that isn't very user-friendly. Binary on/off functionality at low throttles, which is especially noticable on motorbikes where the throttle becomes ' snatchy ' and it becomes hard to ride smoothly at low speed.

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Compared to carburettors , fuel injectors themselves are incredibly simple. They are basically electro-mechanically operated needle valves. The image on the right shows a cutaway of a representative fuel injector. When a current is passed through the injector electromagnetic coil, the valve opens and the fuel pressure forces petrol through the spray tip and out of the diffuser nozzle, atomising it as it does so. When current is removed, the combination of a spring and fuel back-pressure causes the needle valve to close.

Valves and valve mechanisms. :

Valves and valve mechanisms. Valves are what let the fuel-air mixture into the cylinder, and let the exhaust out. Seems simple enough, but there are some interesting differences in the various types of valve mechanism.

Popet Valves:

Popet Valves Their operation is simplicity itself and there are only really three variations of the same style. The basic premise here is that the spinning camshaft operates the valves by pushing them open, and valve return springs force them closed. The cam lobes either operate directly on the top of the valve itself, or in some cases, on a rocker arm which pivots and pushes on the top of the valve. The three variations of this type of valve-train are based on the combination of rocker arms (or not) and the position of the camshaft.

Tappet Valves:

Tappet Valves Tappet valves aren't really a unique type of valve but a derivative of Popet Valves. For the most part, the direct spring return valve described above wouldn't act directly on the top of the valve itself, but rather on an oil-filled tappet. The tappet is basically an upside-down bucket that covers the top of the valve stem and contains the spring. It's normally filled with oil through a small hole when the engine is pressurised . The purpose of tappets is two-fold. The oil in them helps quiet down the valvetrain noise, and the top of the tappet gives a more uniform surface for the cam lobe to work on.

Desmodromic Valves :

Desmodromic Valves Well in both the above systems, the closure mechanism on the valve relies on mechanical springs or hydraulics. There's nothing to actually force the valve to close. With the Ducati Desmodromic system, the camshaft has two lobes per valve, and the only spring is there to take up the slack in the closing system. That's right; Ducati valves are forced closed by the camshaft. In fact, the stroke length, rods, and pistons all play their part in valve timing and maximum engine speed - it's not just the springs and valve float. This is why F1 cars use such a small stroke and pneumatic valves springs. In truth, both systems, spring or Desmodromic only work well up to a limit

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