Chapter 1 engine components and classification

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This my lecture slideshow-Mr Hilmi Politeknik Sultan Mizan Zainal Abidin(PSMZA)

Text of Chapter 1 engine components and classification

  • The topic covers basic theoretical knowledge and understanding of engine components, classifications and terminologies. Areas involving engine construction, operating principles and valve train
  • Understand engine construction Explain various types of internal combustion engines construction and operation: two-stroke petrol and diesel four-stroke petrol and diesel rotary/Wankel Understand basic engine terminologies Explain basic engine terminologies such as TDC, BDC, stroke, bore, displacement, compression ratio etc.
  • Understand cylinder head and valve train construction State the purpose of cylinder head Describe various type of valve train: OHV OHC Multivalve Explain typical valve timing diagram Explain basic operating principles of: VTEC MIVEC VVTI CPS DVVT
  • Engine provides the power to drive the vehicles wheel. Biggest part of the engine is the cylinder block. The cylinder block is a large casting of metal that is drilled with holes to allow for the passage of lubricants and coolant through the block and provide spaces for movement of mechanical parts. The block contains the cylinders, which are round passageways fitted with pistons. The block houses or holds the major mechanical parts of the engine.
  • The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinder. The combustion chamber is an area into which the air-fuel mixture is compressed and burned. The cylinder head contains all or most of the combustion chamber. The cylinder head also contains ports through which the air-fuel mixture enters and burned gases exit the cylinder and the bore for the sparkplug.
  • The valve train is a series of parts used to open and close the intake and exhaust ports. A valve is a movable part that opens and closes the ports. A camshaft controls the movement of the valves. Springs are used to help close the valves.
  • The up-and-down motion of the pistons must be converted to rotary motion before it can drive the wheels of a vehicle. This conversion is achieved by linking the piston to a crankshaft with a connecting rod. The upper end of the connecting rod moves with the piston. The lower end of the connecting rod is attached to the crankshaft and moves in a circle. The end of the crankshaft is connected to the flywheel.
  • Operational cycles. (4 stroke or 2 stroke) Number of cylinders. (3,4,5,6,8,10,12 cylinders) Cylinder arrangement. (Flat, inline, V-type) Valve train type. (OHC,OHV, DOHC) Ignition type (Spark, Compression) Fuel type (gasoline, natural gas, methanol, diesel, propane, fuel cell, electric, hybrid)
  • Types of internal combustion engines construction: 4 Stroke petrol and diesel 2 Stroke petrol and diesel Rotary/wankel
  • Intake Stroke Compression Stroke Power Stroke Exhaust Stroke
  • The first stroke of the cycle is the intake stroke. As the piston moves away from top dead center (TDC), the intake valve opens. The downward movement of the piston increases the volume of the cylinder above it, reducing the pressure in the cylinder. Low pressure (engine vacuum) causes the atmospheric pressure to push a mixture of air and fuel through the open intake valve. As the piston reaches the bottom of its stroke, the reduction in pressure stops, causing the intake of air-fuel mixture to slow down. It does not stop because of the weight and movement of the air-fuel mixture. It continues to enter the cylinder until the intake valve closes. The intake valve closes after the piston has reached bottom dead center (BDC). This delayed closing of the valve increases the volumetric efficiency of the cylinder by packing as much air and fuel into it as possible.
  • The compression stroke begins as the piston starts to move from BDC. The intake valve closes, trapping the air-fuel mixture in the cylinder. The upward movement of the piston compresses the air-fuel mixture, thus heating it up. At TDC, the piston and cylinder walls form a combustion chamber in which the fuel will be burned. The volume of the cylinder with the piston at BDC compared to the volume of the cylinder with the piston at TDC determines the compression ratio of the engine.
  • The power stroke begins as the compressed fuel mixture is ignited. With the valves still closed, an electrical spark across the electrodes of a spark plug ignites the air-fuel mixture. The burning fuel rapidly expands, creating a very high pressure against the top of the piston. This drives the piston down toward BDC. The downward movement of the piston is transmitted through the connecting rod to the crankshaft.
  • The exhaust valve opens just before the piston reaches BDC on the power stroke. Pressure within the cylinder causes the exhaust gas to rush past the open valve and into the exhaust system. Movement of the piston from BDC pushes most of the remaining exhaust gas from the cylinder. As the piston nears TDC, the exhaust valve begins to close as the intake valve starts to open. The exhaust stroke completes the four-stroke cycle. The opening of the intake valve begins the cycle again. This cycle occurs in each cylinder and is repeated over and over, as long as the engine is running.
  • It takes two full revolutions of the crankshaft to complete the four-stroke cycle. One full revolution of the crankshaft is equal to 360 degrees of rotation; therefore, it takes 720 degrees to complete the four- stroke cycle. During one piston stroke, the crankshaft rotates 180 degrees.
  • The operation of a diesel engine is comparable to a gasoline engine. They also have a number of components in common, (crankshaft, pistons, valves, camshaft, and water and oil pumps. However, diesel engines have compression ignition systems. Rather than relying on a spark for ignition, a diesel engine uses the heat produced by compressing air in the combustion chamber to ignite the fuel. The compression ratio of diesel engines is typically three times (as high as 25:1) that of a gasoline engine. As intake air is compressed, its temperature rises to 700C to 900C. Just before the air is fully compressed, a fuel injector sprays a small amount of diesel fuel into the cylinder. The high temperature of the compressed air instantly ignites the fuel. The combustion causes increased heat in the cylinder and the resulting high pressure moves the piston down on its power stroke.
  • This engine requires only two strokes of the piston to complete all four operations: intake, compression, power, and exhaust. This is accomplished as follows: Movement of the piston from BDC to TDC completes both intake and compression. When the piston nears TDC, the compressed air/fuel mixture is ignited, causing an expansion of the gases. During this time, the intake and exhaust ports are closed. Expanding gases in the cylinder force the piston down, rotating the crankshaft. With the piston at BDC, the intake and exhaust ports are both open, allowing exhaust gases to leave the cylinder and air-fuel mixture to enter.
  • Although the two-stroke-cycle engine is simple in design and lightweight because it lacks a valve train, it has not been widely used in automobiles. It tends to be less fuel efficient and releases more pollutants into the atmosphere than four-stroke engines.
  • The rotary engine, or Wankel engine, is similar to the standard piston engine in that it is a spark ignition, internal combustion engine. Its design, however, is quite different. For one thing, the rotary engine uses a rotating motion rather than a reciprocating motion. In addition, it uses ports rather than valves for controlling the intake of the air-fuel mixture and the exhaust of the combusted charge.
  • The rotating combustion chamber engine is small and light for the amount of power it produces, which makes it attractive for use in automobiles. However, the rotary engine at present cannot compete with a piston gasoline engine in terms of durability, exhaust emissions, and economy.
  • Bore cylinder diameter measured in inches(in) or milimeters (mm). Stroke length of the piston travel between TDC & BDC. TDC Top dead center BDC Bottom dead center If bore = stroke, the engine is called a square engine. If bore > stroke, the engine is called a oversquare engine. If bore < stroke, the engine is called a undersquare engine.
  • Cylinder Displacement volume of the cylinder when the piston is at BDC. Engine displacement sum/total of the displacement of each of the engine cylidners. Typically, an engine with a larger displacement produces more torque than a smaller displacement engine. Compression ratio comparison of a cylinders volume when the piston is at BDC to the cylinders volume when the piston is at TDC. The higher the compression ratio, the more power an engine theoretically can produce.
  • Volumetric efficiency describes the engines ability to have its cylinders filled with air- fuel mixture. If the engines cylinders are able to be filled with air-fuel mixture during its intake stroke, the engine has a volumetric efficiency of 100%. Typically, engines have a volumetric efficiency of 80% to 100%.
  • Purpose of cylinder head The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinder. The cylinder head also contains ports through which the air-fuel mixture enters and burned gases exit the cylinder and the bore for the sparkplug.
  • Overhead Valve (OHV) Overhead Cam (OHC) Multivalve
  • The intake and exhaust valves in an OHV engine are mounted in the cylinder head and are operated by a camshaft located in the cylinder block. This arrangement requires the use of valve lifters, pushrods, and rocker arms to transfer camshaft rotation to valve