Wednesday, 23 May 2012

engine construction 3D

Tuesday, 22 May 2012

4 types of engine

4 cylinder i type

radial 5 cylinder

types of engine

parts of engine

inline 4 cylinder engine

opposed(flat)engine

opposed engine

radial engine

radial engine 7 cylinder

rotary engine

rotary engine 3D

v type engine

w type 12 cylinder engine

Internal combustion engines are one of the building blocks of modern civilization. In an internal combustion engine, the combustion takes place inside a confined chamber. All internal combustion engines burn a mixture of air & fuel. The fuel can be gasoline, diesel, methane, propane etc.

The piston is the heart of an internal combustion engine..The concept of the piston engine is that a supply of air-and-fuel mixture is fed to the inside of the cylinder where it is compressed and then burnt. This internal combustion releases heat energy which is then converted into useful mechanical work as the high gas pressures generated force the piston to move along its stroke in the cylinder. It can be said, therefore, that a heat-engine is merely an energy transformer.

To enable the piston movement to be harnessed, the driving thrust on the piston is transmitted by means of a connecting-rod to a crankshaft whose function is to convert the linear piston motion in the cylinder to a rotary crankshaft movement (Fig. 1.1-1). The piston can thus be made to repeat its movement to and fro, due to the constraints of the crankshaft crankpin’s circular path and the guiding cylinder.

The backward-and-forward displacement of the piston is generally referred to as the reciprocating motion of the piston, so these power units are also known as reciprocating engines.

another defination

Animation of two-stroke engine in operation, with a tuned pipe exhaust

An automobile engine partly opened and colored to show components.

The internal combustion engine is an engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine. This force is applied typically to pistons, turbine blades, or a nozzle. This force moves the component over a distance, transforming chemical energy into useful mechanical energy. The first functioning internal combustion engine was created by Étienne Lenoir.^[1]
The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the six-stroke piston engine and the Wankel rotary engine. A second class of internal combustion engines use continuous combustion: gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described.^[1]
The internal combustion engine (or ICE) is quite different from external combustion engines, such as steam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed with, or contaminated by combustion products. Working fluids can be air, hot water, pressurized water or even liquid sodium, heated in some kind of boiler.
A large number of different designs for ICEs have been developed and built, with a variety of different strengths and weaknesses. Powered by an energy-dense fuel (which is very frequently gasoline, a liquid derived from fossil fuels). While there have been and still are many stationary applications, the real strength of internal combustion engines is in mobile applications and they dominate as a power supply for cars, aircraft, and boats.

Comparison of SI and CI Engine

Comparison of S.I. and C.I. engines is made from various aspects is made below:

Fuel economy

The chief comparison to be made between the two types of engine is how effectively each engine can convert the liquid fuel into work energy. Different engines are compared by their thermal efficiencies. Thermal efficiency is the ratio of the useful work produced to the total energy supplied. Petrol engines can have thermal efficiencies ranging between 20% and 30%. The corresponding diesel engines generally have improved efficiencies, between 30% and 40%. Both sets of efficiency values are considerably influenced by the chosen compression-ratio and design.

Power and torque

The petrol engine is usually designed with a shorter stroke and operates over a much larger crankshaft-speed range than the diesel engine. This enables more power to be developed towards the upper speed range in the petrol engine, which is necessary for high road speeds; however, a long-stroke diesel engine has improved pulling torque over a relatively narrow speed range, this being essential for the haulage of heavy commercial vehicles.

At the time of writing, there was a trend to incorporate diesel engines into cars. This new generation of engines has different design parameters and therefore does not conform to the above observations.

Reliability

Due to their particular process of combustion, diesel engines are built sturdier, tend to run cooler, and have only half the speed range of most petrol engines. These factors make the diesel engine more reliable and considerably extend engine life relative to the petrol engine.

Pollution

Diesel engines tend to become noisy and to vibrate on their mountings as the operating load is reduced. The combustion process is quieter in the petrol engine and it runs smoother than the diesel engine. There is no noisy injection equipment used on the petrol engine, unlike that necessary on the diesel engine. The products of combustion coming out of the exhaust system are more noticeable with diesel engines, particularly if any of the injection equipment components are out of tune. It is questionable which are the more harmful: the relatively invisible exhaust gases from the petrol engine, which include nitrogen dioxide, or the visible smoky diesel exhaust gases.

Safety

Unlike petrol, diesel fuels are not flammable at normal operating temperature, so they are not a handling hazard and fire risks due to accidents are minimized.

Cost

Due to their heavy construction and injection equipment, diesel engines are more expensive than petrol engines.

Difference b/w 2 & 4 stroke petrol engine

Difference Between Two & Four Stroke Cycle Petrol Engines

The differences between two- and four-stroke-cycle petrol engines regarding the effectiveness of both engine cycles are given below:

a) The two-stroke engine completes one cycle of events for every revolution of the crankshaft, compared with the two revolutions required for the four-stroke engine cycle.

b) Theoretically, the two-stroke engine should develop twice the power compared to a four-stroke engine of the same cylinder capacity.

c) In practice, the two-stroke engine's expelling of the exhaust gases and filling of the cylinder with fresh mixture brought in through the crankcase is far less effective than having separate exhaust and induction strokes. Thus the mean effective cylinder pressures in two-stroke units are far lower than in equivalent four-stroke engines.

d) With a power stroke every revolution instead of every second revolution, the two-stroke engine will run smoother than the four-stroke power unit for the same size of flywheel.

e) Unlike the four-stroke engine, the two-stroke engine does not have the luxury of separate exhaust and induction strokes to cool both the cylinder and the piston between power strokes. There is therefore a tendency for the piston and small-end to overheat under heavy driving conditions.

f) Due to its inferior scavenging process, the two-stroke engine can suffer from the following:

i) inadequate transfer of fresh mixture into the cylinder,

ii) excessively large amounts of residual exhaust gas remaining in the cylinder,

iii) direct expulsion of fresh charge through the exhaust port. These undesirable conditions may occur under different speed and load situations, which greatly influences both power and fuel consumption.

g) Far less maintenance is expected with the two-stroke engine compared with the four-stroke engine, but there can be a problem with the products of combustion carburizing at the inlet, transfer, and exhaust ports.

h) Lubrication of the two-stroke engine is achieved by mixing small quantities of oil with petrol in proportions anywhere between 1:16 and 1:24 so that, when crankcase induction takes place, the various rotating and reciprocating components will be lubricated by a petrol-mixture mist. Clearly a continuous proportion of oil will be burnt in the cylinder and expelled into the atmosphere to add to unwanted exhaust emission.

i) There are fewer working parts in a two-stroke engine than in a four-stroke engine, so two-stroke engines are generally cheaper to manufacture.

valve timing diagram

Valve timing diagram of a four stroke engine gives a clear idea about the actual position of the piston during the opening & closing of inlet & exhaust valves. In practice, the events of the four-stroke cycle do not start and finish exactly at the two ends of the strokes - to improve the breathing and exhausting, the inlet valve is arranged to open before TDC and to close after BDC and the exhaust valve opens before BDC and closes after TDC. These early and late opening and closing events can be shown on a valve timing diagram such as Fig. 1.1-4.

Valve lead This is where a valve opens so many degrees of crankshaft rotation before either TDC or BDC.

Valve lag This is where a valve closes so many degrees of crankshaft rotation after TDC or BDC.

Valve overlap This is the condition when both the inlet and the exhaust valves are open at the same time during so many degrees of crankshaft rotation.

compression ratio

Compression-ratio is a very important parameter for measuring engine performance.The compression-ratio may be defined as the ratio of the maximum cylinder volume when the piston is at its outermost position (BDC) to the minimum cylinder volume (the clearance volume) with the piston at its innermost position (TDC) - that is, the sum of the swept and clearance volumes divided by the clearance volume,

Vs þVc i:e: CR ¼ Vc

where CR ¼ compression ratio

Vs ¼ swept volume (cm3) Vc ¼ clearance volume (cm3)

Petrol engines have compression-ratios of the order of 7:1 to 10:1; but, to produce self-ignition of the charge, diesel engines usually double these figures and may have values of between 14:1 and 24:1 for naturally aspirated (depression-induced filling) types, depending on the design.

In an engine cylinder, the gas molecules are moving about at considerable speed in the space occupied by the gas, colliding with other molecules and the boundary surfaces of the cylinder head, the cylinder walls, and the piston crown. The rapid succession of impacts of many millions of molecules on the boundary walls produces a steady continuous force per unit surface which is known as pressure (Fig. 1.1-12).

When the gas is compressed into a much smaller space, the molecules are brought closer to one another. This raises the temperature and greatly increases the speed of the molecules and hence their kinetic energy, so more violent impulses will impinge on the piston crown. This increased activity of the molecules is experienced as increased opposition to movement of the piston towards the cylinder head.

The process of compressing a constant mass of gas into a much smaller space enables many more molecules to impinge per unit area on to the piston. When burning of the gas occurs, the chemical energy of combustion is rapidly transformed into heat energy which considerably increases the kinetic energy of the closely packed gas molecules. Therefore the extremely large number of molecules squeezed together will thus bombard the piston crown at much higher speeds. This then means that a very large number of repeated blows of considerable magnitude will strike the piston and so push it towards ODC.

This description of compression, burning, and expansion of the gas charge shows the importance of utilising a high degree of compression before burning takes place, to improve the efficiency of combustion. The amount of compression employed in the cylinder is measured by the reduction in volume when the piston moves from BDC to TDC, the actual proportional change in volume being expressed as the compression-ratio.

MAJOR engine components

Identification of major engine components makes it easier to understand its working principle. Some major engine components are, cylinder block, piston, piston rings, connecting-rod, cylinder head, crankcase, crankshaft etc. The following briefly describes the major engine components and some terms associated with them.

Cylinder block

This is a cast structure with cylindrical holes bored to guide and support the pistons and to harness the working gases. It also provides a jacket to contain a liquid coolant.

Cylinder head

This casting encloses the combustion end of the cylinder block and houses both the inlet and exhaust poppet-valves and their ports to admit air- fuel mixture and to exhaust the combustion products.

Crankcase

This is a cast rigid structure which supports and houses the crankshaft and bearings. It is usually cast as a mono-construction with the cylinder block.

Sump

This is a pressed-steel or cast-aluminum-alloy container which encloses the bottom of the crank-case and provides a reservoir for the engine's lubricant.

Piston

This is a pressure-tight cylindrical plunger which is subjected to the expanding gas pressure. Its function is to convert the gas pressure from combustion into a concentrated driving thrust along the connecting-rod. It must therefore also act as a guide for the small-end of the connecting-rod.

Piston rings

These are circular rings which seal the gaps made between the piston and the cylinder, their object being to prevent gas escaping and to control the amount of lubricant which is allowed to reach the top of the cylinder.

Gudgeon-pin

This pin transfers the thrust from the piston to the connecting-rod small-end while permitting the rod to rock to and fro as the crankshaft rotates.

Connecting-rod

This acts as both a strut and a tie link-rod. It transmits the linear pressure impulses acting on the piston to the crankshaft big-end journal, where they are converted into turning-effort.

Crankshaft

A simple crankshaft consists of a circular-sectioned shaft which is bent or cranked to form two perpendicular crank-arms and an offset big-end journal. The unbent part of the shaft provides the main journals. The crankshaft is indirectly linked by the connecting-rod to the piston - this enables the straight-line motion of the piston to be transformed into a rotary motion at the crankshaft about the main-journal axis.

Crankshaft journals

These are highly finished cylindrical pins machined parallel on both the centre axes and the offset axes of the crankshaft. When assembled, these journals rotate in plain bush-type bearings mounted in the crankcase (the main journals) and in one end of the connecting-rod (the big-end journal).

Small-end

This refers to the hinged joint made by the gudgeon-pin between the piston and the connecting-rod so that the connecting-rod is free to oscillate relative to the cylinder axis as it moves to and fro in the cylinder.

Big-end

This refers to the joint between the connecting-rod and the crankshaft big-end journal which provides the relative angular movement between the two components as the engine rotates.

Main-ends

This refers to the rubbing pairs formed between the crankshaft main journals and their respective plain bearings mounted in the crankcase.

Line of stroke

The centre path the piston is forced to follow due to the constraints of the cylinder is known as the line of stroke.

Inner and outer dead centers

When the crank arm and the connecting-rod are aligned along the line of stroke, the piston will be in either one of its two extreme positions. If the piston is at its closest position to the cylinder head, the crank and piston are said to be at inner dead centre (IDC) or top dead centre (TDC). With the piston at its furthest position from the cylinder head, the crank and piston are said to be at outer dead centre (ODC) or bottom dead centre (BDC). These reference points are of considerable importance for valve-to-crankshaft timing and for either ignition or injection settings.

Clearance volume

The space between the cylinder head and the piston crown at TDC is known as the clearance volume or the combustion-chamber space.

Crank-throw

The distance from the centre of the crankshaft main journal to the centre of the big-end journal is known as the crank-throw. This radial length influences the leverage the gas pressure acting on the piston can apply in rotating the crankshaft.

Piston stroke

The piston movement from IDC to ODC is known as the piston stroke and corresponds to the crankshaft rotating half a revolution or 180°. It is also equal to twice the crank-throw.

i.e. L = 2R

where L = piston stroke and R = crank-throw

Thus a long or short stroke will enable a large or small turning-effort to be applied to the crankshaft respectively.

Cylinder bore

The cylinder block is initially cast with sand cores occupying the cylinder spaces. After the sand cores have been removed, the rough holes are machined with a single-point cutting tool attached radially at the end of a rotating bar. The removal of the unwanted metal in the hole is commonly known as boring the cylinder to size. Thus the finished cylindrical hole is known as the cylinder bore, and its internal diameter simply as the bore or bore size.

4 stroke cycle petrol engine

FOUR STROKE CYCLE S.I.(Spark ignition)/PETROL ENGINE.

Gasoline or petrol engines are also known as spark-ignition (S.I.) engines. Petrol engines take in a flammable mixture of air and petrol which is ignited by a timed spark when the charge is compressed. The first four stroke spark-ignition (S.I.) engine was built in 1876 by Nicolaus August Otto, a self-taught German engineer at the Gas-motoreufabrik Deutz factory near Cologne, for many years the largest manufacturer of internal-combustion engines in the world. It was one of Otto's associates - Gottlieb Daimler - who later developed an engine to run on petrol which was described in patent number 4315 of 1885. He also pioneered its application to the motor vehicle.

Four stroke Spark-ignition (S.I) engines require four piston strokes to complete one cycle: an air-and-fuel intake stroke moving outward from the cylinder head, an inward movement towards the cylinder head compressing the charge, an outward power stroke, and an inward exhaust stroke.

Induction stroke.

The inlet valve is opened and the exhaust valve is closed. The piston descends, moving away from the cylinder head . The speed of the piston moving along the cylinder creates a pressure reduction or depression which reaches a maximum of about 0.3 bar below atmospheric pressure at one-third from the beginning of the stroke. The depression actually generated will depend on the speed and load experienced by the engine, but a typical average value might be 0.12 bar below atmospheric pressure. This depression induces (sucks in) a fresh charge of air and atomized petrol in proportions ranging from 10 to 17 parts of air to one part of petrol by weight.

An engine which induces fresh charge by means of a depression in the cylinder is said to be 'normally aspirated' or 'naturally aspirated'.

Compression stroke.

Both the inlet and the exhaust valves are closed. The piston begins to ascend towards the cylinder head . The induced air-and-petrol charge is progressively compressed to something of the order of one-eighth to one-tenth of the cylinder's original volume at the piston's innermost position. This compression squeezes the air and atomized-petrol molecules closer together and not only increases the charge pressure in the cylinder but also raises the temperature. Typical maximum cylinder compression pressures will range between 8 and 14 bar with the throttle open and the engine running under load.

Power stroke.

Both the inlet and the exhaust valves are closed and, just before the piston approaches the top of its stroke during compression, a spark-plug ignites the dense combustible charge. By the time the piston reaches the innermost point of its stroke, the charge mixture begins to burn, generates heat, and rapidly raises the pressure in the cylinder until the gas forces exceed the resisting load. The burning gases then expand and so change the piston's direction of motion and push it to its outermost position. The cylinder pressure then drops from a peak value of about 60 bar under full load down to maybe 4 bar near the outermost movement of the piston.

Exhaust stroke.

At the end of the power stroke the inlet valve remains closed but the exhaust valve is opened. The piston changes its direction of motion and now moves from the outermost to the innermost position. Most of the burnt gases will be expelled by the existing pressure energy of the gas, but the returning piston will push the last of the spent gases out of the cylinder through the exhaust-valve port and to the atmosphere. During the exhaust stroke, the gas pressure in the cylinder will fall from the exhaust-valve opening pressure (which may vary from 2 to 5 bar, depending on the engine speed and the throttle-opening position) to atmospheric pressure or even less as the piston nears the innermost position towards the cylinder head.

4 stroke cycle diesel engine

FOUR STROKE CYCLE COMPRESSION IGNITION (DIESEL) ENGINE.

Compression-ignition (C.I) engines burn fuel oil which is injected into the combustion chamber when the air charge is fully compressed. Burning occurs when the compression temperature of the air is high enough to spontaneously ignite the finely atomized liquid fuel. In other words, burning is initiated by the self-generated heat of compression (Fig. 1.1-8). Compression-ignition (C.I) engines are also referred to as 'oil engines', due to the class of fuel burnt, or as 'diesel engines' after Rudolf Diesel, one of the many inventors and pioneers of the early C.I. engine. Note: in the United Kingdom fuel oil is known as 'DERV', which is the abbreviation of 'diesel-engine road vehicle'.

Just like the four-stroke-cycle petrol engine, the Compression-ignition (C.I.) engine completes one cycle of events in two crankshaft revolutions or four piston strokes. The four phases of these strokes are (i) induction of fresh air, (ii) compression and heating of this air, (iii) injection of fuel and its burning and expansion, and (iv) expulsion of the products of combustion.

Induction stroke.

With the inlet valve open and the exhaust valve closed, the piston moves away from the cylinder head.The outward movement of the piston will establish a depression in the cylinder, its magnitude depending on the ratio of the cross-sectional areas of the cylinder and the inlet port and on the speed at which the piston is moving. The pressure difference established between the inside and outside of the cylinder will induce air at atmospheric pressure to enter and fill up the cylinder. Unlike the petrol engine, which requires a charge of air-and-petrol mixture to be drawn past a throttle valve, in the diesel-engine inlet system no restriction is necessary and only pure air is induced into the cylinder. A maximum depression of maybe 0.15 bar below atmospheric pressure will occur at about one-third of the distance along the piston's outward stroke, while the overall average pressure in the cylinder might be 0.1 bar or even less.

Compression stroke.

With both the inlet and the exhaust valves closed, the piston moves towards the cylinder head.

The air enclosed in the cylinder will be compressed into a much smaller space of anything from 1/12 to 1/24 of its original volume. A typical ratio of maximum to minimum air-charge volume in the cylinder would be 16:1, but this largely depends on engine size and designed speed range.

During the compression stroke, the air charge initially at atmospheric pressure and temperature is reduced in volume until the cylinder pressure is raised to between 30 and 50 bar. This compression of the air generates heat which will increase the charge temperature to at least 600 °C under normal running conditions.

Power stroke.

With both the inlet and the exhaust valves closed and the piston almost at the end of the compression stroke (Fig. 1.1 -8(c)), diesel fuel oil is injected into the dense and heated air as a high-pressure spray of fine particles. Provided that they are properly atomized and distributed throughout the air charge, the heat of compression will then quickly vaporize and ignite the tiny droplets of liquid fuel. Within a very short time, the piston will have reached its innermost position and extensive burning then releases heat energy which is rapidly converted into pressure energy. Expansion then follows, pushing the piston away from the cylinder head, and the linear thrust acting on the piston end of the connecting-rod will then be changed to rotary movement of the crankshaft.

Exhaust stroke.

When the burning of the charge is near completion and the piston has reached the outermost position, the exhaust valve is opened. The piston then reverses its direction of motion and moves towards the cylinder head.

The sudden opening of the exhaust valve towards the end of the power stroke will release the still burning products of combustion to the atmosphere. The pressure energy of the gases at this point will accelerate their expulsion from the cylinder, and only towards the end of the piston's return stroke will the piston actually catch up with the tail-end of the outgoing gases.

2 stroke cycle diesel engine

. Two-Stroke Cycle Diesel Engine A two-stroke diesel engine shares the same operating principles as other internal combustion engines. It has all of the advantages that other diesel engines have over gasoline engines. A two-stroke diesel engine does not produce as much power as a four-stroke diesel engine; however, it runs smoother than the four-stroke diesel. This is because it generates a power stroke each time the piston moves downward; that is, once for each crankshaft revolution. The two-stroke diesel engine has a less complicated valve train because it does not use intake valves. Instead, it requires a supercharger to force air into the cylinder and force exhaust gases out, because the piston cannot do this naturally as in four-stroke engines.

The two-stroke diesel takes in air and discharges exhaust through a system called scavenging. Scavenging begins with the piston at bottom dead center. At this point, the intake ports are uncovered in the cylinder wall and the exhaust valve is open. The supercharger forces air into the cylinder, and, as the air is forced in, the burned gases from the previous operating cycle are forced out.

COMPRESSION STROKE.— As the piston moves towards top dead center, it covers the intake ports. The exhaust valves close at this point and seals the upper cylinder. As the piston continues upward, the air in the cylinder is tightly compressed . As in the four-stroke cycle diesel, a tremendous amount of heat is generated by the compression.

POWER STROKE.— As the piston reaches top dead center, the compression stroke ends. Fuel is injected at this point and the intense heat of the compression causes the fuel to ignite. The burning fuel pushes the piston down, giving power to the crankshaft. The power stroke ends when the piston gets down to the point where the intake ports are uncovered. At about this point, the exhaust valve opens and scavenging begins again

. Valve Train The operation of the valves in a timed sequence is critical. If the exhaust valve opened in the middle of the intake stroke, the piston would draw burnt gases into the combustion chamber with a fresh mixture of fuel and air. As the piston continued to the power stroke, there would be nothing in the combustion chamber that would

2 stroke cycle petrol engine

A Very Basic 2 Stroke Engine

Please note-the diagram below represents a very simple version of a 2 stroke engine, in reality, they are a little bit more complicated!!!

Engine Terminology

Stroke: Either the up or down movement of the piston from the top to the bottom or bottom to top of the cylinder (So the piston going from the bottom of the cylinder to the top would be 1 stroke, from the top back to the bottom would be another stroke)

Induction: As the piston travels down the cylinder head, it 'sucks' the fuel/air mixture into the cylinder. This is known as 'Induction'.

Compression: As the piston travels up to the top of the cylinder head, it 'compresses' the fuel/air mixture from the carburetor in the top of the cylinder head, making the fuel/air mix ready for igniting by the spark plug. This is known as 'Compression'.

Ignition: When the spark plug ignites the compressed fuel/air mixture, sometimes referred to as the power stroke.

Exhaust: As the piston returns back to the top of the cylinder head after the fuel/air mix has been ignited, the piston pushes the burnt 'exhaust' gases out of the cylinder & through the exhaust system.

Transfer Port: The port (or passageway) in a 2 stroke engine that transfers the fuel/air mixture from the bottom of the engine to the top of the cylinder

The 2 Stroke Cycle

We have simplified this explanation as much as possible so some of the 'correct' terms have been replaced. There are many more factors which enable an engine to run, such as fuel/air ratios, ignition timing & shaped piston heads (extensively used in 2 stroke engines) but the explanation below outlines the basic differences between 2 & 4 stroke engine operation.

Stroke	Piston Direction	Actions Occurring during This Stroke	Explanation
Stroke 1	Piston travels up the cylinder barrel	Induction & Compression	As the Piston travels up the barrel, fresh fuel/air mix is sucked into the crankcase (bottom of the engine) & the fuel/air mix in the cylinder (top of the engine) is compressed ready for ignition
Stroke 2	Piston travels down the cylinder barrel	Ignition & Exhaust	The spark plug ignites the fuel/air mix in the cylinder, the resulting explosion pushes the piston back down to the bottom of the cylinder, as the piston travels down, the transfer port openings are exposed & the fresh fuel/air mix is sucked from the crankcase into the cylinder. As the fresh fuel/air mix is drawn into the cylinder, it forces the spent exhaust gases out through the exhaust port.