Engines Volume 1.pdf Flashcards
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Engines Volume 1.pdf Flashcards
Engines Volume 1.pdf Flashcards
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Describe turbine engines and their characteristics.
Turbine engines, also known as gas turbines or combustion turbines, are classified as internal combustion engines where fuel combustion occurs when a special oxidizer mixes with the fuel in a combustion chamber. They are used to power helicopters, jets, tanks, small power plants, and are simpler in operation than piston engines with more powerful energy output.
Describe the two-stroke and four-stroke cycles in engines.
The two-stroke cycle in a diesel engine eliminates the need for valves and involves the piston moving downward due to combustion pressure. The four-stroke cycle consists of intake, compression, power, and exhaust strokes, requiring two full rotations or 720 crankshaft degrees for a complete cycle.
Explain reciprocating engines and their operation.
In reciprocating engines, the working fluid moves a piston in a linear motion, which is then converted to rotary motion by a crank-slider connecting rod/crankshaft. This type of engine is commonly used in cars, trucks, and off-highway vehicles. Reciprocating engines can be further categorized into two-stroke and four-stroke engines based on the number of strokes the piston makes in a cycle.
Describe the components of a piston assembly in an engine.
The piston assembly consists of the piston (usually made of aluminum or steel material), piston rings, wrist pin, conn rod, and travels up and down in the cylinder to transfer force from the ignition in the combustion chamber to the crankshaft and flywheel drive line.
Explain the function of the exhaust system in an engine.
The exhaust manifold collects cylinder end gases and delivers them to the turbocharger and exhaust piping or directly to the exhaust piping in naturally aspirated engines.
Differentiate between internal combustion engines and external combustion engines.
In internal combustion engines, the combustion products or reactants (air and fuel) serve as the working fluid. This type of engine powers cars, trucks, trains, and most marine vessels and can be fueled with petrol, diesel, or gas fuels. On the other hand, external combustion engines deliver energy through a heat exchanger to a working fluid separate from the combustion products or reactants.
What is a four stroke engine?
A four-stroke engine is an engine where the piston makes four strokes in a cycle. The cycle starts on the intake stroke where fuel and air enter the cylinder and ends on the exhaust stroke where spent fuel and waste gases exit the engine to the exhaust system. This means that all cylinders have fired with two rotations, totaling 720 degrees of the crankshaft rotation.
What is the compression ratio in an engine?
Compression ratio is a measure of the cylinder volume at BDC versus TDC. In diesel engines, compression ratios typically fall between 16:1 and 17:1, with modern high-speed turbocharged engines.
Explain the difference between spark ignited and compression ignited engines.
Both two-stroke and four-stroke reciprocating internal combustion engines can be either spark ignited (SI) or compression ignited (CI). Spark ignited systems use a pre-mixed charge of fuel and air ignited by an external ignition source like a spark plug. Compression ignited engines rely on internal cylinder heat generated by compressing air and fuel, with diesel-fueled engines using compression ignition.
What is the purpose of a harmonic balancer in an engine?
To absorb vibration in the drive line and balance against the thrust generated by the compression stroke, and to add momentum to the rotational movement of the crankshaft.
What is the purpose of the engine control module (ECM) in modern engines?
The ECM is the brain of modern engines, receiving input and sending output information to control engine speed, using data link communication from other machine ECMs to ensure proper engine operation.
What is the function of valves and camshafts in an engine?
Valves and camshafts work together where rockers are levers that transfer camshaft motion to the valves and mechanically actuated injectors. Camshafts have egg-shaped lobes that push the valves open, connecting to the rocker arms via pushrods or directly in some designs.
Describe the major engine components and systems in an engine.
The major engine components and systems include the intake and exhaust system, engine powertrain, engine valve train assembly, engine lubrication circuit, engine cooling circuit, and engine breathing system. These components are essential for the operation and performance of the engine.
Explain the role of cylinder heads in an engine.
Cylinder heads seal the engine cylinders, manage cylinder breathing, intake and exhaust valves, and in diesel applications, they are usually cast iron assemblies machined with breathing tracts, ports, cooling and lubrication circuit manifolds, fuel manifolds, and injector bores.
What is a two stroke engine?
A two-stroke engine is an engine where the intake and exhaust strokes are eliminated, and the complete power cycle is completed with a single piston stroke up and a single piston stroke down. This means that in 360 degrees of rotation, each cylinder has fired one rotation of the crankshaft. Two-stroke engines are common in mopeds, particularly Vespas.
Explain the concepts of bore and stroke in an engine.
Bore is the cylinder diameter, stroke is the length of travel of the piston, or the throw of the crankshaft on its stroke from BDC to TDC. Engine displacement is the swept volume of all engine cylinders expressed in cubic inches or centimeters/litres.
Describe rotary engines, specifically Wankel engines.
In rotary engines, also known as Wankel engines, the working fluid spins a rotor that is connected to the output shaft. They use an eccentric rotary design to convert pressure into rotating motion. Radial rotary engines have pistons arranged around an axis and were common in early airplanes.
Define torque, horsepower, and brake horsepower in engines.
Torque is the turning effort in an engine, horsepower is derived from James Watts theory, and brake horsepower is measured at the flywheel of an engine, always lower than indicated power due to internal friction and pumping losses.
What is the role of the camshaft in engine timing?
The camshaft is a component used to ensure precise intervals for all engine components' functions in relation to the piston. It has egg-shaped lobes that mechanically push the valves open using linkages like pushrods and rocker arms.
Explain the number and arrangement of cylinders in engines.
The number of cylinders refers to the total amount of pistons in the engine block, powering the engine in a sequence known as the firing order. Common diesel engines have cylinders arranged in either inline or V configuration. The engine layout can vary, such as V16 diesel engines, inline diesel engines, or two-stroke six-cylinder diesel engines.
Describe the intake system and components in an engine.
The intake manifold delivers air to the cylinders, usually bolted to the cylinder heads enclosing intake ports and valves. Turbos are part of this system and boost intake volumetric pressure.
What is Thermal Efficiency?
Thermal efficiency is a measure of combustion efficiency, comparing the heat energy potential of the fuel with the usable mechanical work produced at the flywheel. It is calculated by the percentage of potential energy converted into useful mechanical energy.
What is the function of flywheels in an engine?
Flywheels are used to support drive torque converters and clutches, have a ring gear on the outer circumference to provide a drive for the starter motor, and the housing houses the flywheel and mounts rear components like torque converters and clutches.