INTRODUCTION OF ENGINE
Theoretical background:
Power-producing engines have served human beings for over two and a half centuries. For the first 150 years, water, converted to steam, was interposed between the combustion gases produced by burning the fuel and the work-producing piston-in-cylinder expander. It was not until the 1860s that the internal combustion engine became a practical reality.1, 2 The early engines developed for commercial use burned coal-gas air mixtures at atmospheric pressure — there was no compression before combustion. J. J. E. Lenoir (1822–1900) developed the first marketable engine of this type. Gas and air were drawn into the cylinder during the first half of the piston stroke. The charge was then ignited with a spark, the pressure increased, and the burned gases then delivered power to the piston for the second half of the stroke. The cycle was completed with an exhaust stroke. Some 5000 of these engines were built between 1860 and 1865 in sizes up to six horsepower. Efficiency was at best about 5%. A more successful development — an atmospheric engine introduced in 1867 by Nicolaus A. Otto (1832–1891) and Eugen Langen (1833–1895) — used the pressure rise resulting from combustion of the fuel-air charge early in the outward stroke to accelerate a free piston and rack assembly so its momentum would generate a vacuum in the cylinder. Atmospheric pressure then pushed the piston inward, with the rack engaged through a roller clutch to the output shaft. Production engines, of which about 5000 were built, obtained thermal efficiencies of up to 11%. A slide valve controlled intake, ignition by a gas flame, and exhaust.
Beau de Rochas also outlined the conditions under which maximum performance and efficiency in an internal combustion engine could be achieved. These were:
- The largest possible cylinder volume with the minimum boundary surface
- 2. The greatest possible working speed
3. The greatest possible expansion ratio
4. The greatest possible pressure at the beginning of expansion
Engine types:
There are various types of engines depending on the energy giving mechanism and difference in working fluid, engines can also be differ in terms of number strokes. Some types of engines are given below:
Internal combustion engine
Straight-four engine
Diesel engine
V engine
Four-stroke engine
Inline engine
In Line Six Cylinder
Flat engine
W engine
Turbojet
Engine components:
Rocker Arm:
Lifting of the cam lobe causes the rocker arm to push down upon the valve stem. This movement opens the associated valve.
Tappet Clearance:
The space between the valve stem and rocker arms. The tappet clearance allows for thermal expansion of the engine parts when warming up, this ensures the valves open and close correctly. Tappet clearance is also known as valve lash.
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Valve Spring:
Springs used for returning the valves back to the closed position and maintaining the valves in their closed position when force from the rocker arms is absent.
Fuel Injector:
Fuel is pumped to the fuel injector and then through the injector nozzle into the engine cylinder.
The top of this injector connects to an electrical solenoid which is used for more accurate injection timing.
Fuel Inlet Pipe:
Fuel is supplied to the injector through this pipe.
Valve:
On this model there are two suction inlet valves and two exhaust discharge valves .The suction valves supply air whilst the discharge valves discharge the exhaust gas. This type of valve is often referred to as a poppet valve.
Fuel Injector Nozzle:
Fuel is sprayed into the engine cylinder through the fuel injector nozzle. It is important that the fuel injection ports do not become blocked. Any blockage of the nozzle will change the injection spray pattern and reduce engine efficiency.
Clearance Volume:
The clearance volume is the distance from the top dead centre of the stroke and the top of the cylinder liner.
Cylinder Bore:
The cylinder bore represents the internal diameter of the cylinder liner. It is possible to calculate the cylinder displacement by calculating the cylinder bore and piston stroke.
Top Dead Centre (TDC) :
TDC represents the maximum transit of the piston in the direction of the cylinder valves. Push Rod The push rod transfers radial movement from the cam lobe to the rocker arms.
Piston Crown:
Due to its location, the piston crown encounters significant pressures and temperatures. The design of the crown varies considerably, as many crowns have a unique topography to distribute the exhaust gasses created by the combustion process.
Piston Ring Grooves:
The piston rings are located in the piston ring grooves. Note that the piston rings for this model are not displayed.
Stroke:
The stroke represents a measurement of the total distance travelled by the piston (TDC to BDC). The reference point is measured from the top of the piston crown.
Piston:
The force generated by combustion is transferred to the piston. The piston is split into many parts, this includes a piston skirt, piston crown, piston rod and piston pin. See our 3D piston model for more information.
Piston Skirt:
The type of skirt shown here is a ‘full’ skirt.
Piston Pin / Gudgeon Pin:
The pin joins the piston skirt to the piston rod.
Cylinder Wall:
An arrow indicating the cylinder wall, also referred to as the ‘cylinder liner’. The cylinder liner forms the combustion chamber.
Camshaft:
The camshaft is used to control the timing of the engine. This includes when fuel is injected and when the air inlet and exhaust valves open and close.
Cam:
Cams are used to open and close the inlet and exhaust valves. On larger engines cams are also used to operate fuel pumps. A cam is also referred to as a ‘cam lobe’.
Cam Follower:
The cam follower is lowered and raised by the cam lobe. The follower transfers movement from the camshaft to the load (valve, pump etc.).
Bottom Dead Centre (BDC) :
BDC represents the piston’s point of maximum transit in the direction of the cylinder base. In other words, the piston will not travel further towards the cylinder base than the BDC reference point.
Connecting Rod:
Note that the term ‘connecting rod’ and ‘piston rod’ are sometimes used intermittently. Large two stroke engines have both, with the piston rod always being the rod between the crosshead and piston pin.
Reciprocating Motion:
Rotary motion is converted by the engine design into a reciprocating linear motion. This conversion allows the piston skirt to move up and down the cylinder rather than rotating.
Crank Web:
The crankshaft is connected to the piston rod via the crank webs and crank pins. Crank webs allow the reciprocating piston motion to be converted to a rotary motion.
Crankpin Journal Bearing:
The crankpin journal bearing is installed between the connecting rod and crankpin. Bearing materials vary although softer metals such as white metal (babbit metal) are often used.
Main Journal Bearing:
Main journal bearings are plain metal bearing that seat upon the crankshaft. Unlike crankpin journal bearings, main journal bearings align with the crankshaft centre axis of rotation.
Crankshaft:
The crankshaft is not a single straight shaft as it is separated at intervals by the crank webs. The alignment of the crankshaft though is constant throughout the engine.
Rotary Motion:
This engine is an internal combustion engine. The force created by the combustion process is transferred to the piston and then the crankshaft. The process causes the crankshaft to rotate and the piston to reciprocate linearly.
Flange:
The flange often connects to a flywheel although it can connect to any load requiring rotary motion.
