Four stroke Petrol Engine with its parts

Engine:-

               A machine with moving parts that converts power into motion.

              "the roar of a car engine"

                

                                

Heat Engine:-

                       A device for producing motive power from heat.

For example:-

                    1)  Steam engine

                     2) Petrol engine

                     3) Diesel engine

                     

Types of Engine:-

                                                     1)  External combustion (E.C.) Engine.

                                        2) Internal Combustion (I.C.) Engine.

1) External Combustion Engine:-

                            An external combustion engine (EC engine) is a heat engine where a working fluid, contained internally, is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid then, by expanding and acting on the mechanism of the engine, produces motion and usable work.

For example:- Steam power plant

                       Steam engine

2) Internal combustion engine:-

                                 An engine whose fuel is burned inside the engine itself rather than in an outside furnace or burner. Gasoline and diesel engines are internal-combustion engines, as are gas turbine engines such as turbojets. Compare steam engine.

There are two types:-

1)    Petrol Engine

2)    Diesel Engine

Stroke:-

                       Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke. The term is also used to mean the length of the stroke.

Types of IC engines on the basis of stroke:-

1)       4-stroke petrol engine

2)       2-stroke petrol engine

3)       4-stroke diesel engine

4)       2-stroke diesel engine

                                   4-Stroke petrol Engine

                                

A four-stroke cycle engine is an internal combustion engine that utilizes four distinct piston strokes (intake, compression, power, and exhaust) to complete one operating cycle. The piston make two complete passes in the cylinder to complete one operating cycle.                        In 4-stroke petrol engine in power stroke a spark is needed for ignition.

                                            

                              

But in 4-stroke diesel engine we do not have required any spark plug for ignition in power stroke.

Parts of 4-stroke petrol engine:-

                            The parts of 4-stroke petrol engine are given below in details:-

Valves:-

                      All four-stroke internal combustion engines employ valves to control the admittance of fuel and air into the combustion chamber. Two-stroke engines use ports in the cylinder bore, covered and uncovered by the piston, though there have been variations such as exhaust valves.

                      

Piston engine valves:-

                                 In piston engines, the valves are grouped into 'inlet valves' which admit the entrance of fuel and air and 'outlet valves' which allow the exhaust gases to escape. Each valve opens once per cycle and the ones that are subject to extreme accelerations are held closed by springs that are typically opened by rods running on a camshaft rotating with the engines' crankshaft.

                                                               

Exhaust systems:-

                                      Internal combustion engines have to effectively manage the exhaust of the cooled combustion gas from the engine. The exhaust system frequently contains devices to control both chemical and noise pollution. In addition, for cyclic combustion engines the exhaust system is frequently tuned to improve emptying of the combustion chamber. The majority of exhausts also have systems to prevent heat from reaching places which would encounter damage from it such as heat-sensitive components, often referred to as Exhaust Heat Management.

                                           

Cooling systems:-

                                 Cooling systems usually employ air (air-cooled) or liquid (usually water) cooling, while some very hot engines using radiative cooling (especially some rocket engines). Some high-altitude rocket engines use ablative cooling, where the walls gradually erode in a controlled fashion. Rockets in particular can use regenerative cooling, which uses the fuel to cool the solid parts of the engine.

                                                 

                                   

Piston:-

                     A piston is a component of reciprocating engines. It is located in a cylinder and is made gas-tight by piston rings. Its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. In two-stroke engines the piston also acts as a valve by covering and uncovering ports in the cylinder wall.

                                     

Crankshaft:-

                      Most reciprocating internal combustion engines end up turning a shaft. This means that the linear motion of a piston must be converted into rotation. This is typically achieved by a crankshaft.

                                  

Flywheels:-

                        A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have an inertia called the moment of inertia and thus resist changes in rotational speed. ... For example, flywheels  are used in reciprocating engines because the energy source, torque from the engine, is intermittent.

                                                

                          

Connecting Rod:-

               In a reciprocating piston engine, the connecting rod or con rod connects the piston to the crank or crankshaft. Together with the crank, they form a simple mechanism that converts reciprocating motion into rotating motion. Connecting rods may also convert rotating motion into reciprocating motion.

                                                                            

Cylinder:-

                       A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels.^[1] Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work. Cylinders may be sleeved (lined with a harder metal) or sleeveless.A sleeveless engine may also be referred to as a "parent-bore engine"

                           

                                           

Crankcase:-

                              In an internal combustion engine of the reciprocating type, the crankcase is the housing for the crankshaft. The enclosure forms the largest cavity in the engine and is located below the cylinder(s), which in a multi cylinder engine is usually integrated into one or several cylinder blocks.

                                         

Carburetor:-

                           A carburetor is a device that blends air and fuel for an internal combustion engine.  To carburet  is to blend the air and fuel or to equip  with a carburetor for that purpose Carburetors have largely been supplanted in the automotive and, to a lesser extent, aviation industries by fuel injection. 

                                                    

Compression rings of piston:-

                                 A piston ring is a split ring that fits into a groove on the outer diameter of a piston in a reciprocating engine such as an internal combustion engine or steam engine.

The three main functions of piston rings in reciprocating engines are :

1.   Sealing the combustion chamber so that there is minimal loss of gases to the crank case.

2.   Improving heat transfer from the piston to the cylinder wall.

3.   Regulating engine oil consumption by scraping oil from the cylinder walls back to the sump.

                              

Oil rings of shaft of engine:-

                                        An oil ring includes two thin rails or running surfaces. Holes or slots cut into the radial center of the ring allow the flow of excess oil back to the oil reservoir. Oil rings are commonly one piece, incorporating all of these features. Some on-piece oil rings utilize a spring expander to apply additional radial pressure to the piston ring.

Spark plug:-

                                     A spark plug  is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a porcelain insulator.

                               

Cylinder Swept Volume (V_c):

where:

            V_c= cylinder swept volume [cm³ (cc) or L]

            A_c = cylinder area [cm² or cm²/100]

            d_c = cylinder diameter [cm or cm/10]

            L = stroke length (the distance between the TDC and BDC) [cm or cm/10]

BDC = Bottom Dead Center

            TDC = Top Dead Center

* Increase the diameter or the stroke length will increase the cylinder volume, the ratio between the cylinder diameter/cylinder stroke called “bore/stroke” ratio.

- “bore/stroke” >1 is called over square engine, and is used in automotive engines

- “bore/stroke” =1 is called square engine

- “bore/stoke” <1 is called= under square engine, and is used in tractor engine

 Engine Swept Volume (V_e):

 

where:

            V_e = engine swept volume [cm³ (cc) or L]

            n = number of cylinders

            V_c = cylinder swept volume [cm³ (cc) or L]

A_c = cylinder area [cm² or cm²/100]

d_c =  cylinder diameter [cm or cm/10]

* The units of cylinder swept volume is measured in (cm³, cubic centimeter (cc), or liter)

- V_e  for small engines, 4 cylinder engines is (750 cc:1300 cc)

- V_e for big engine, 8 cylinder engines is (1600 cc:2500 cc)

 Compression Ratio (r):

where:

            r = compression ratio

            V_s = cylinder swept volume (combustion chamber volume) [cc, L, or m³]

            V_c = cylinder volume     [cc, L, or m³]

* Increase the compression ratio increase engine power

- r (gasoline engine) = 7:12, the upper limit is engine pre ignition

- r (diesel engine) = 10:18, the upper limit is the stresses on engine parts

           4-Strokes of petrol engine:-

Four-stroke cycle used in gasoline/petrol engines. 1 = Intake, 2 = Compression, 3 = Power, 4 = Exhaust. ... A four-stroke engine (also known as four cycle) is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft.

                                              

Intake

During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).

                                            

                                                       

Compression                                                                                                         As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture.

                                                              

Power

At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.

                                                                  

Exhaust                                                               

At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.