Internal Combustion Engine

Introduction

The internal combustion engine converts chemical energy into useful mechanical energy by burning fuel. Chemical energy is released when the fuel-air mixture is ignited by the spark in the combustion chamber. The gas produced in this reaction rapidly expands forcing the piston down the cylinder on the power stroke. The basic components for a combustion cycle in a four stroke engine are the combustion chamber (cylinder), piston, intake port and outlet or exhaust port. The piston reciprocates inside the cylinder, exhaust and intake ports open and close during various stages of the cycle. The movement of the piston up or down the cylinder makes up one stroke of the four stroke cycle (Otto cycle). The linear motion is then converted to rotary motion by the crankshaft. The crankshaft is shaped to balance the pistons which are fired in a particular order to reduce engine vibration (typically for a 4-cylinder engine, 1-2-4-3 or 1-3-4-2). The flywheel then helps smooth out the linear movement of the pistons.

Within the field of engine research many experimental techniques have been developed to take measurements within the combustion chambers of internal combustion engines. There are many different aspects to the combustion process, by studying these various aspects to develop a more detailed understanding of the combustion cycle, low emission more efficient engines may be developed.

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.

The 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.

History of I.C engines

The AbbéHautefeuille described in 1678, an engine for raising water, in which the motive power was obtained by burning gunpowder in a cylinder and cooling the remaining gases with water. The idea was similar to that expressed in the early forms of the steam engine, but Hautefeuille does not appear to have preformed any actual experiments. The same idea was suggested by Huygens in 1680, but experiments made by him and later by Denis Papinwere not attended by success and were abandoned, though they are interesting as representing the first actual attempts at the building of internal-combustion engines.

      A long period of inaction followed. The discovery of the distillation of gas from coal and the demonstration, by Murdock in 1792, of the application of coal gas for lighting purposes roused new interest in the subject. The introduction of the steam engine for commercial purposes about this time was also a powerful incentive, though for many decades the steam engine was too firmly entrenched and fitted the existing conditions too well to afford much opportunity for competition. About 1791 John Barber explained in a patent how a wheel with vanes could be driven by the released pressure of an orifice close to the vanes. In the century and a quarter that have elapsed since that day, no economical gas turbine has been constructed. 

The first internal-combustion engine, according to our modern ideas, was that of Robert Street, patented in England in 1794. In this the bottom of a cylinder was heated by fire and a small quantity of tar or turpentine was projected into the hot part of the cylinder, forming a vapor. The rising of the piston sucked in a quantity of air to form the explosion mixture and also flame for ignition. The cycle was that which was used later by Lenoir in the first commercially successful engine. About 1800 Phillippe Lebon patented in France an engine using compressed air, compressed gas and electricity for ignition. Some authorities believe that his early death retarded the development of the internal-combustion engine half a century, as all of the features mentioned are necessary to the highly efficient engines of today, though they did not come into use for three-quarters of a century after his death.

The next engine to attain any considerable prominence was that of Samuel Brown, who secured several patents in England about 1825. His engine did not represent an advance, since the old ideas of Huygens were employed instead of the advanced ideas of Street. The success of the atmospheric steam engines was probably responsible for this. Brown's engine consisted of a number of large chambers, in which the hot gases produced by flame were cooled by the injection of water, thus

forming a partial vacuum. The working pistons, in cylinders adjacent to the large chambers, were operated by atmospheric pressure, all pistons being connected to the same crankshaft, as shown in Fig. 1. Since the burning did not occur in the working cylinder, the engine can scarcely be called an internal-combustion engine in the accepted sense of the term. The inventor appears to have been a man of considerable force, and a number of his engines were built for pumping and for driving carriages and boats. In 1833, W. L. Wright patented in England, the engine illustrated in Fig. 2. The gas and air were supplied by separate pumps to a working cylinder. The charge was contained in the spherical bulbs near the ends of the cylinder, ignition occurring while the piston was at the end of the stroke. The engine was double acting, water jacketed, with poppet exhaust valves and a fly-ball governor. It represented a great advance in design and was probably built, though no records of its performance are known to exist.

  In 1838 William Barnett patented in England an engine which was an advance upon preceding types in that country. It compressed the gas and air separately, igniting the mixture when the piston

was at the end of its stroke. The third engine described by this inventor is shown in Fig. 3, and is interesting because it embodies several features of the modern two-cycle engine. In the figure the piston is supposed to be moving upward, compressing a mixture of gas and air. Ignition occurs when the piston has reached its highest position, and the piston driven down, expansion occurring until the piston passes the exhaust port at the middle of the cylinder. During the latter half of the stroke the pumps are forcing gas and air into space below the piston, The compression being completed by the working piston and an explosion occurring when the piston reaches its lowest position. One of the interesting features of this engine was the use of spongy platinum for ignition, though Barnett also devised an exceedingly ingenious igniting cock of burning gas jets.

 To the American the most interesting part of the development of internal-combustion engines is that played by Brayton about 1872 to 1874. This engine is shown in Fig. 5. The Brayton engine was to some extent the precursor of the present Diesel engine. The mixture of gas and air burned at

constant pressure and gave a card resembling somewhat that of the steam engine. This engine was manufactured for a while, but was not able to compete with the Otto-Langen free-piston engine in economy. It was adapted for both gas and petroleum.

The well-known Otto engine was invented by Dr. Nicholas Otto, of Germany, and was patented in this country in 1877. It follows the cycle that has been described by Beau de Rochas , now known as the four-cycle, or sometimes as the Otto cycle. The engine was first known as the Otto-Silent, to distinguish it from the free-piston engine, which was rather noisy. It immediately established the internal-combustion engine on a firm footing, and the engines of the four-cycle type sold today show merely minor improvements. The sliding valve on 1876 has been replaced by poppet valves, and the flame ignition has been replaced by the electric spark. Otherwise, the Otto cycle of 1876 has persisted and at this time thousands of them are being manufactured.

      The development of the Diesel engine for oil began about 1894. As has been stated, this engine is similar to the Brayton. Air is compressed to about 500 pounds pressure and oil is sprayed into this highly compressed air. It burns spontaneously at nearly constant pressure, which is followed by a long expansion. The extremely high temperature of the air previous to the injection of the fuel, and the high temperature maintained during this injection, together with the long expansion, give the engine the highest efficiency of any thermal motor. The development of the Diesel engine has been so recent that it is not necessary to elaborate upon it. At this time, it is being manufactured in all of the European countries and in America, and there is a tendency on the part of many of the American manufacturers who are bringing out new engines to adopt the features of the Diesel. The gas turbine is as yet in the experimental stage. A number have been built and are of course, extremely interesting. The success of the steam turbine has encouraged many to believe that the

gas turbine will achieve similar success. Nothing of recent development can be said to encourage this view. The difficulties in the way of successful gas turbines are very great, and while some turbines have been designed and run, none of them has shown an efficiency at all comparable to that of ordinary four-cycle engines. 

Applications

Internal combustion engines are most commonly used for mobile propulsion in vehicles and portable machinery. In mobile equipment, internal combustion is advantageous since it can provide high power-to-weight ratios together with excellent fuel energy density. Generally using fossil fuel(mainly petroleum), these engines have appeared in transport in almost all vehicles (automobiles, trucks, motorcycles, boats, and in a wide variety of aircraft and locomotives).

Where very high power-to-weight ratios are required, internal combustion engines appear in the form of gas turbines. These applications include jet aircraft, helicopters, large ships and electric generators.

Combustion chamber

Internal combustion engines can contain any number of combustion chambers (cylinders), with numbers between one and twelve being common, though as many as 36 (Lycoming R-7755) have been used. Having more cylinders in an engine yields two potential benefits: first, the engine can have a larger displacement with smaller individual reciprocating masses, that is, the mass of each piston can be less thus making a smoother-running engine since the engine tends to vibrate as a result of the pistons moving up and down. Doubling the number of the same size cylinders will double the torque and power. The downside to having more pistons is that the engine will tend to weigh more and generate more internal friction as the greater number of pistons rub against the inside of their cylinders. This tends to decrease fuel efficiency and robs the engine of some of its power. For high-performance gasoline engines using current materials and technology, such as the engines found in modern automobiles, there seems to be a point around 10 or 12 cylinders after which the addition of cylinders becomes an overall detriment to performance and efficiency. Although, exceptions such as the W16 engine from Volkswagen exist.

Radial aircraft engines had from three to 28 cylinders; examples include the small Kinner B-5 and the large Pratt & Whitney R-4360. Larger examples were built as multiple rows. As each row contains an odd number of cylinders, to give an even firing sequence for a four-stroke engine, an even number indicates a two- or four-row engine. The largest of these was the Lycoming R-7755 with 36 cylinders (four rows of nine cylinders), but it did not enter production.

Motorcycles commonly have from one to four cylinders, with a few high-performance models having six; although, some 'novelties' exist with 8, 10, or 12.

Snowmobiles usually have one to four cylinders and can be both 2-stroke or 4-stroke, normally in the in-line configuration; however, there are again some novelties that exist with V-4 engines

Small portable appliances such as chainsaws, generators, and domestic lawn mowers most commonly have one cylinder, but two-cylinder chainsaws exist.

Large reversible two-cycle marine diesels have a minimum of three to over ten cylinders. Freight diesel locomotives usually have around 12 to 20 cylinders due to space limitations, as larger cylinders take more space (volume) per kwh, due to the limit on average piston speed of less than 30 ft/sec on engines lasting more than 40,000 hours under full power.

Ignition system

The ignition system of an internal combustion engines depends on the type of engine and the fuel used. Petrol engines are typically ignited by a precisely timed spark, and diesel engines by compression heating. Historically, outside flame and hot-tube systems were used, see hot bulb engine.

Spark

The mixture is ignited by an electric spark from a spark plug — the timing of which is very precisely controlled. Almost all gasoline engines are of this type. Diesel engines timing is precisely controlled by the pressure pump and injector.

MAGNETO IGNITION SYSTEM

The simplest form of spark ignition is that using a magnet. The engine spins a magnet inside a coil, or, in the earlier designs, a coil inside a fixed magnet, and also operates a contact breaker, interrupting the current and causing the voltage to be increased sufficiently to jump a small gap. The spark plugs are connected directly from the magneto output. Early magnetos had one coil, with the contact breaker (sparking plug) inside the combustion chamber.

MAGNETO IGNITION

In about 1902, Bosch introduced a double-coil magneto, with a fixed sparking plug, and the contact breaker outside the cylinder. Magnetos are not used in modern cars, but because they generate their own electricity they are often found on piston-engined aircraft engines and small engines such as those found in mopeds, lawnmowers, snowblowers, chainsaws, etc. where a battery-based electrical system is not present for any combination of necessity, weight, cost, and reliability reasons.

Compression

Ignition occurs as the temperature of the fuel/air mixture is taken over its autoignition temperature, due to heat generated by the compression of the air during the compression stroke. The vast majority of compression ignition engines are diesels in which the fuel is mixed with the air after the air has reached ignition temperature. In this case, the timing comes from the fuel injection system. Very small model engines for which simplicity and light weight is more important than fuel costs use easily ignited fuels (a mixture of kerosene, ether, and lubricant) and adjustable compression to control ignition timing for starting and running.

Ignition timing

For reciprocating engines, the point in the cycle at which the fuel-oxidizer mixture is ignited has a direct effect on the efficiency and output of the ICE. The thermodynamics of the idealized Carnot heat engine tells us that an ICE is most efficient if most of the burning takes place at a high temperature, resulting from compression — near top dead center. The speed of the flame front is directly affected by the compression ratio, fuel mixture temperature, and octane rating or cetane number of the fuel. Leaner mixtures and lower mixture pressures burn more slowly requiring more advanced ignition timing. It is important to have combustion spread by a thermal flame front (deflagration), not by a shock wave. Combustion propagation by a shock wave is called detonation and, in engines, is also known as pinging or Engine knocking.

So at least in gasoline-burning engines, ignition timing is largely a compromise between a later "retarded" spark — which gives greater efficiency with high octane fuel — and an earlier "advanced" spark that avoids detonation with the fuel used. For this reason, high-performance diesel automobile proponents, such as Gale Banks, believe that

There’s only so far you can go with an air-throttled engine on 91-octane gasoline. In other words, it is the fuel, gasoline, that has become the limiting factor. ... While turbocharging has been applied to both gasoline and diesel engines, only limited boost can be added to a gasoline engine before the

fuel octane level again becomes a problem. With a diesel, boost pressure is essentially unlimited. It is literally possible to run as much boost as the engine will physically stand before breaking apart. Consequently, engine designers have come to realize that diesels are capable of substantially more power and torque than any comparably sized gasoline engine.

Fuel systems

Animated cut through diagram of a typical fuel injector, a device used to deliver fuel to the internal combustion engine.

Fuels burn faster and more efficiently when they present a large surface area to the oxygen in air. Liquid fuels must be atomized to create a fuel-air mixture, traditionally this was done with a carburetor in petrol engines and with fuel injection in diesel engines. Most modern petrol engines now use fuel injection too — though the technology is quite different. While diesel must be injected at an exact point in that engine cycle, no such precision is needed in a petrol engine. However, the lack of lubricity in petrol means that the injectors themselves must be more sophisticated.

Carburetor

Simpler reciprocating engines continue to use a carburetor to supply fuel into the cylinder. Although carburetor technology in automobiles reached a very high degree of sophistication and precision, from the mid-1980s it lost out on cost and flexibility to fuel injection. Simple forms of

carburetor remain in widespread use in small engines such as lawn mowers and more sophisticated forms are still used in small motorcycles.

Fuel injection

Larger gasoline engines used in automobiles have mostly moved to fuel injection systems (see Gasoline Direct Injection). Diesel engines have always used fuel injection system because the timing of the injection initiates and controls the combustion.

Autogas engines use either fuel injection systems or open- or closed-loop carburetors.

Fuel pump

Most internal combustion engines now require a fuel pump. Diesel engines use an all-mechanical precision pump system that delivers a timed injection direct into the combustion chamber, hence requiring a high delivery pressure to overcome the pressure of the combustion chamber. Petrol fuel injection delivers into the inlet tract at atmospheric pressure (or below) and timing is not involved, these pumps are normally driven electrically. Gas turbine and rocket engines use electrical systems.

Oxidiser-Air inlet system

Some engines such as solid rockets have oxidisers already within the combustion chamber but in most cases for combustion to occur, a continuous supply of oxidiser must be supplied to the combustion chamber.

Naturally aspirated engines

When air is used with piston engines it can simply suck it in as the piston increases the volume of the chamber. However, this gives a maximum of 1 atmosphere of pressure difference across the inlet valves, and at high engine speeds the resulting airflow can limit potential output.

Superchargers and turbochargers

A supercharger is a "forced induction" system which uses a compressor powered by the shaft of the engine which forces air through the valves of the engine to achieve higher flow. When these systems are employed the maximum absolute pressure at the inlet valve is typically around 2 times atmospheric pressure or more.

Turbochargers are another type of forced induction system which has its compressor powered by a gas turbine running off the exhaust gases from the engine.

Turbochargers and superchargers are particularly useful at high altitudes and they are frequently used in aircraft engines.

Duct jet engines use the same basic system, but eschew the piston engine, and replace it with a burner instead.

Liquids

In liquid rocket engines, the oxidiser comes in the form of a liquid and needs to be delivered at high pressure (typically 10-230 bar or 1–23 MPa) to the combustion chamber. This is normally achieved by the use of a centrifugal pump powered by a gas turbine — a configuration known as a turbopump, but it can also be pressure fed

Parts

An illustration of several key components in a typical four-stroke engine.

For a four-stroke engine, key parts of the engine include the crankshaft (purple), connecting rod (orange), one or more camshafts (red and blue), and valves. For a two-stroke engine, there may simply be an exhaust outlet and fuel inlet instead of a valve system. In both types of engines there are one or more cylinders (grey and green), and for each cylinder there is a spark plug (darker-grey, gasoline engines only), a piston (yellow), and a crankpin (purple). A single sweep of the cylinder by the piston in an upward or downward motion is known as a stroke. The downward stroke that occurs directly after the air-fuel mix passes from the carburetor or fuel injector to the cylinder (where it is ignited) is also known as a power stroke.

A Wankel engine has a triangular rotor that orbits in an epitrochoidal (figure 8 shape) chamber around an eccentric shaft. The four phases of operation (intake, compression, power, and exhaust) take place in what is effectively a moving, variable-volume chamber.

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 valve

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.

Control valves

Continuous combustion engines—as well as piston engines—usually have valves that open and close to admit the fuel and/or air at the startup and shutdown. Some valves feather to adjust the flow to control power or engine speed as well.

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 pollution, 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.

For jet propulsion internal combustion engines, the 'exhaust system' takes the form of a high velocity nozzle, which generates thrust for the engine and forms a colimated jet of gas that gives the engine its name.

Cooling systems

Combustion generates a great deal of heat, and some of this transfers to the walls of the engine. Failure will occur if the body of the engine is allowed to reach too high a temperature; either the engine will physically fail, or any lubricants used will degrade to the point that they no longer

protect the engine. The lubricants must be clean as dirty lubricants may lead to over formation of sludge in the engines.

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.

Propelling nozzle

For jet engine forms of internal combustion engines, a propelling nozzle is present. This takes the high temperature, high pressure exhaust and expands and cools it. The exhaust leaves the nozzle going at much higher speed and provides thrust, as well as constricting the flow from the engine and raising the pressure in the rest of the engine, giving greater thrust for the exhaust mass that exits.

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.

It typically connects to a flywheel and to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsional vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

A crankshaft for a 4-cylinder engine

Flywheels

The flywheel is a disk or wheel attached to the crank, forming an inertial mass that stores rotational energy. In engines with only a single cylinder the flywheel is essential to carry energy over from the power stroke into a subsequent compression stroke. Flywheels are present in most reciprocating

engines to smooth out the power delivery over each rotation of the crank and in most automotive engines also mount a gear ring for a starter. The rotational inertia of the flywheel also allows a much slower minimum unloaded speed and also improves the smoothness at idle. The flywheel may also perform a part of the balancing of the system and so by itself be out of balance, although most engines will use a neutral balance for the flywheel, enabling it to be balanced in a separate operation. The flywheel is also used as a mounting for the clutch or a torque converter in most automotive applications.

Starter systems

All internal combustion engines require some form of system to get them into operation. Most piston engines use a starter motor powered by the same battery as runs the rest of the electric systems. Large jet engines and gas turbines are started with a compressed air motor that is geared to one of the engine's driveshafts. Compressed air can be supplied from another engine, a unit on the ground or by the aircraft's APU. Small internal combustion engines are often started by pull cords. Motorcycles of all sizes were traditionally kick-started, though all but the smallest are now electric-start. Large stationary and marine engines may be started by the timed injection of compressed air into the cylinders — or occasionally with cartridges. Jump starting refers to assistance from another battery (typically when the fitted battery is discharged), while bump starting refers to an alternative method of starting by the application of some external force, e.g. rolling down a hill.

Heat shielding systems

Flexible ceramic heat shield commonly used on high-performance automobiles

These systems often work in combination with engine cooling and exhaust systems. Heat shielding is necessary to prevent engine heat from damaging heat-sensitive components. The majority of older cars use simple steel heat shielding to reduce thermal radiation and convection. It is now most common for modern cars are to use aluminium heat shielding which has a lower density, can be easily formed and does not corrode in the same way as steel. Higher performance vehicles are beginning to use ceramic heat shielding as this can withstand far higher temperatures as well as further reductions in heat transfer.

Lubrication systems

Internal combustions engines require lubrication in operation that moving parts slide smoothly over each other. Insufficient lubrication subjects the parts of the engine to metal-to-metal contact, friction, heat build-up, rapid wear often culminating in parts becoming friction welded together e.g. pistons in their cylinders. Big end bearings seizing up will sometimes lead to a connecting rod breaking and poking out through the crankcase.

Several different types of lubrication systems are used. Simple two-stroke engines are lubricated by oil mixed into the fuel or injected into the induction stream as a spray. Early slow-speed stationary and marine engines were lubricated by gravity from small chambers similar to those used on steam engines at the time — with an engine tender refilling these as needed. As engines were adapted for automotive and aircraft use, the need for a high power-to-weight ratio led to increased speeds, higher temperatures, and greater pressure on bearings which in turn required pressure-lubrication for crank bearings and connecting-rod journals. This was provided either by a direct lubrication from a pump, or indirectly by a jet of oil directed at pickup cups on the connecting rod ends which had the advantage of providing higher pressures as the engine speed increased.

FOUR STROKE AND TWO STROKE ENGINES

TWO STROKE ENGINE-

A two-stroke, two-cycle, or 2-cycle engine is a type of internal combustion engine which completes a power cycle in only one crankshaft revolution and with two strokes, or up and down movements, of the piston in comparison to a "four-stroke engine", which uses four strokes to do so. This is accomplished by the end of the combustion stroke and the beginning of the compression stroke happening simultaneously and performing the intake and exhaust (or scavenging) functions at the same time.

Two-stroke engines often provide high power-to-weight ratio, usually in a narrow range of rotational speeds called the "power band", and, compared to 4-stroke engines, have a greatly reduced number of moving parts.

The first commercial two-stroke engine involving in-cylinder compression is attributed to Scottish engineer Dugald Clerk, who in 1881 patented his design, his engine having a separate charging

cylinder. The crankcase-scavenged engine, employing the area below the piston as a charging pump, is generally credited to Englishman Joseph Day.

Gasoline (spark ignition) versions are particularly useful in lightweight (portable) applications such as chainsaws and small, lightweight and racing motorcycles, and the concept is also used in diesel compression ignition engines in large and weight insensitive applications, such as ships, locomotives and electricity generation. The heat transfer from the engine to the cooling system is less in a two-stroke engine than in a traditional four-stroke, a fact that adds to the overall engine efficiency, however, traditional 2-strokes have a poor exhaust emissions feature.

FOUR STROKE ENGINES-

A four-stroke engine (also known as four-cycle) is an internal combustion engine in which the piston completes four separate strokes—intake, compression, power, and exhaust—during two separate revolutions of the engine's crankshaft, and one single thermodynamic cycle.

There are two common types of four-stroke engines. They are closely related to each other, but have major differences in design and behavior. The earliest of these to be developed is the Otto cycle engine developed in 1876 by Nikolaus August Otto in Cologne, Germany,[1] after the operation principle described by Alphonse Beau de Rochas in 1861. This engine is most often referred to as a petrol engine or gasoline engine, after the fuel that powers it.[2] The second type of four-stroke engine is the Diesel engine developed in 1893 by Rudolph Diesel, also of Germany. Diesel created his engine to maximize efficiency, which the Otto engine lacked. There are several major differences between the Otto cycle engine and the four-stroke diesel engine. The diesel engine is made in both a two-stroke and a four-stroke version. Otto's company, Deutz AG, now primarily produces diesel engines.

The Otto cycle is named after the 1876 engine of Nikolaus A. Otto, who built a successful four-stroke engine based on the work of Jean Joseph Etienne Lenoir.[1] It was the third engine type that Otto developed. It used a sliding flame gateway for ignition of its fuel — a mixture of illuminating gas and air. After 1884, Otto also developed the magneto to create an electrical spark for ignition, which had been unreliable on the Lenoir engine.

Today, the internal combustion engine (ICE) is used in motorcycles, automobiles, boats, trucks, aircraft, ships, heavy duty machinery, and in its original intended use as stationary power both for kinetic and electrical power generation. Diesel engines are found in virtually all heavy duty applications such as trucks, ships, locomotives, power generation, and stationary power. Many of these diesel engines are two-stroke with power ratings up to 105,000 hp (78,000 kW).

The four strokes refer to intake, compression, combustion (power) and exhaust strokes that occur during two crankshaft rotations per power cycle.

INTAKE stroke: on the intake or induction stroke of the piston, the piston descends from the top of the cylinder to the bottom of the cylinder, increasing the volume of the cylinder. A mixture of fuel and air, or just air in a diesel engine, is forced by atmospheric (or greater) pressure into the cylinder through the intake port. The intake valve(s) then closes. The volume of air/fuel mixture that is drawn into the cylinder, relative to the maximum volume of the cylinder, is called the volumetric efficiency of the engine.

COMPRESSION stroke: with both intake and exhaust valves closed, the piston returns to the top of the cylinder compressing the air or fuel-air mixture into the combustion chamber of the cylinder head. During the compression stroke the temperature of the air or fuel-air mixture rises by several hundred degrees.

POWER stroke: this is the start of the second revolution of the cycle. While the piston is close to Top Dead Centre, the compressed air–fuel mixture in a gasoline engine is ignited, usually by a spark plug, or fuel is injected into a diesel engine, which ignites due to the heat generated in the air during the compression stroke. The resulting pressure from the combustion of the compressed fuel-air mixture forces the piston back down toward bottom dead centre.

EXHAUST stroke: during the exhaust stroke, the piston once again returns to top dead centre while the exhaust valve is open. This action expels the spent fuel-air mixture through the exhaust valve(s).

A Common List of Advantages and Disadvantages

Advantages of 2 Stroke Engines:- Two-stroke engines do not have valves, simplifying their construction. - Two-stroke engines fire once every revolution (four-stroke engines fire once every other revolution). This gives two-stroke engines a significant power boost. - Two-stroke engines are lighter, and cost less to manufacture. - Two-stroke engines have the potential for about twice the power in the same size because there are twice as many power strokes per revolution.

Disadvantages of 2 Stroke Engines:- Two-stroke engines don't live as long as four-stroke engines. The lack of a dedicated lubrication system means that the parts of a two-stroke engine wear-out faster. Two-stroke engines require a mix of oil in with the gas to lubricate the crankshaft, connecting rod and cylinder walls.- Two-stroke oil can be expensive. Mixing ratio is about 4 ounces per gallon of gas: burning about a gallon of oil every 1,000 miles.- Two-stroke engines do not use fuel efficiently, yielding fewer miles per gallon. - Two-stroke engines produce more pollution. From: -- The combustion of the oil in the gas. The oil makes all two-stroke engines smoky to some extent, and a badly worn two-stroke engine can emit more oily smoke.-- Each time a new mix of air/fuel is loaded into the combustion chamber, part of it leaks out through the exhaust port.

OTTO CYCLE-

A petrol engine (known as a gasoline engine in North America) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. It was invented in 1876 in Europe.

ACTUAL INDICATOR DIAGRAM

In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites.

OTTO CYCLE

With both air and fuel in a closed cylinder, compressing the mixture too much poses the danger of auto-ignition — or behaving like a diesel engine. Because of the difference in burn rates between the two different fuels, petrol engines are mechanically designed with different timing than diesels, so to auto-ignite a petrol engine causes the expansion of gas inside the cylinder to reach its greatest point before the cylinder has reached the "top dead center" (TDC) position. Spark plugs are typically fired 10 degrees or so of crankshaft rotation before the piston reaches TDC, to allow time for the fuel-air charge to substantially complete combustion before too much expansion has occurred - gas expansion occurring with the piston moving down in the power stroke. Higher octane petrol burns slower, therefore it has a lower propensity to auto-ignite and its rate of expansion is lower. Thus, engines designed to run high-octane fuel exclusively can achieve higher compression ratios.

Petrol engines run at higher speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft (a design efficiency made possible by lower compression ratios) and due to petrol burning faster than diesel. However the lower compression ratios of a petrol engine give a lower efficiency than a diesel engine. To give an example, a petrol engine is like operating a bicycle in its lowest gear where each push from your feet adds little energy to the system, but you still expend energy to move your legs back to the TDC position.

DIESEL CYCLE-

The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine, invented by Rudolph Diesel in 1897. It is assumed to have constant pressure during the first part of the "combustion" phase ( to in the diagram, below). This is an idealized mathematical model: real physical Diesels do have an increase in pressure during this period, but it is less pronounced than in the Otto cycle. The idealized Otto cycle of a gasoline engine approximates constant volume during that phase, generating more of a spike in a p-V diagram.

DIESEL CYCLE

The image on the left shows a p-V diagram for the ideal Diesel cycle; where is pressure and is specific volume. The ideal Diesel cycle follows the following four distinct processes (The color

references refer to the color of the line on the diagram.): Process 1 to 2 is isentropic compression of the fluid (blue color)

Process 2 to 3 is reversible constant pressure heating (red)

Process 3 to 4 is isentropic expansion (yellow)

Process 4 to 1 is reversible constant volume cooling (green)

The Diesel is a heat engine: it converts heat into work. The isentropic processes are impermeable to heat: heat flows into the loop through the left expanding isobaric process and some of it flows back out through the right depressurizing process, and the heat that remains does the work.

Work in is done by the piston compressing the working fluid. Heat in is done by the combustion of the fuel. Work out is done by the working fluid expanding on to the piston (this produces usable torque).Heat out is done by venting the air

VALVE TIMING DIAGRAM-

In a piston engine, the valve timing is the precise timing of the opening and closing of the valves.

In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine operation by the relatively new technology of variable valve timing. It is also affected by the adjustment of the valve mechanism, and particularly by the tappet clearance. However, this variation is normally unwanted.

Many two-stroke cycle and all wankel engines do not have a camshaft or valves, and the port timing can only be varied by machining the ports, and/or modifying the piston skirt (two stroke applications).

SCAVENGING-

In automotive usage, scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air ready for the next cycle.

This process is essential in having a smooth-running internal combustion engine. Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.

UNIFLOW SCAVENGING

To increase scavenging potential, the entire path from intake to exhaust (i.e. all powertrain parts) to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of this exhaust gas is what will hinder the scavenging potential.

For example, fast flowing heads and a tunnel ram intake combined with a poorly planned camshaft and exhaust system will cause the air to "slow down" and "speed up" throughout its journey, thus reducing its scavenging potential. So, to increase scavenging potential, the air must maintain a positive linear acceleration curve.

FUEL RATINGS

OCTANE RATING-

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance. In contrast, fuels with low octane numbers (but high cetane numbers) are ideal for diesel engines. Use of gasolines with low octane numbers may lead to the problem of engine knocking.

FUEL WITH DIFFERENT OCTANE RATINGS

Octanes are a family of hydrocarbon that are typical components of gasoline. They are colourless liquids that boil around 125 °C (260 °F). One member of the octane family, isooctane, is used as a reference standard to benchmark the tendency of gasoline, petrol, or benzin fuels to resist self-igniting. Self-ignition leads to inefficiencies (or even engine damage) if it occurs during compression prior to the desired position of the piston in the cylinder as appropriate for valve and ignition timing. The problem of premature ignition is referred to as pre-ignition and also as engine knock, which is a sound that is made when the fuel ignites too early in the compression stroke.

CETANE NUMBER-

Cetane number or CN is a measurement of the combustion quality of diesel fuel during compression ignition. It is a significant expression of the quality of a diesel fuel. A number of other measurements determine overall diesel fuel quality - these other measures of diesel fuel quality include density, lubricity, cold-flow properties, and sulfur content.

Testing and performance of IC engines

POWER

An IC engine is used to produce mechanical power by combustion of fuel. Power is referred to as the rate at which work is done. Power is expressed as the product of force and linear velocity or product of torque and angular velocity. In order to measure power one needs to measure torque or force and speed. The force or torque is measured by Dynamometer and speed by Tachometer. The power developed by an engine and measured at the output shaft is called the brake power (bp) and is given by,

AIR FUEL RATIO

It is the ratio of mass of fuel to mass of air in mixture.

It affects the phenomenon of combustion and used for determining flame propagation velocity, the heat released in combustion chamber. For practice always relative fuel air ratio is defined. It is the ratio of actual fuel-air ratio to that of the stoichiometric fuel air ratio required for burning of fuel which is supplied.

VOLUMETRIC EFFICIENCY

It is the ratio of the actual volume of the charge drawn in during the suction stroke to the swept volume of the piston.The amount of air taken inside the cylinder is dependent on the volumetric efficiency of an engine and hence puts a limit on the amount of fuel which can be efficiently burned and the power output. Value of volumetric efficiency of a normal engine lies between 70 to 80 percent, but for supercharged engine it may be more than 100 percent.

Morse Test

The i.p. and the mechanical efficiency of a multi-cylinder auto engine is found out in a very

short time by this test. During the test the engine is run at a constant speed and at same throttle opening. First the b.p. of the engine with all cylinders operative is measured by means of dynamometer. Next, the b.p. of the engine is measured with each cylinder rendered inoperative one by one by shorting the spark plug in case of petrol engine or by cutting off the fuel supply in case of diesel engine. When any cylinder is rendered inoperative, the speed abruptly goes down. Before taking any reading, the initial speed must be restored by adjusting the load. It is assumed that the f.p. of the inoperative cylinder remains the same as it were when the cylinder was operative.

Heat balance sheet

A heat balance sheet is an account of heat supplied and heat utilised in various ways in the system . Necessary information concerning the performance of the engine is obtained from the heat balance sheet . The heat balance sheet is generally done on second basis or minute basis or hour basis.

The engine should equipped with suitable loading arrangement to measure the brake power of the engine. Provisions are also made to measure the amount of air intake .amount of fuel consumed , temperature of cooling water at inlet and outlet of the engine amount of cooling water circulated and temperature of exhaust gases .

The heat supplied to the engine is only in the form of fuel – heat and is equal to .

Qs = mf x C.V

Where,

mf = mass of fuel used in kg/min

C.V = Calorific value of fuel in KJ /kg

The various way in which the heat is utilised are

1. Heat equivalent to brake power of the engine.2. Heat carried away by the cooling water3. Heat carried away by the exhaust gases4. Unaccounted heat losses.

Heat equivalent to B.P:The brake power in KW is converted into KJ/minQB.P = B.P x 60 = _________ KJ/min

Heat carried away by the cooling water : (Qw)

Qw = Mw x CPw (Two – Twi ) in KJ/min

Where,Mw = mass of cooling water circulated in kg/minCPw = Specific heat of cooling water = 4.186 KJ/kgKTwi = Temperature of cooling water at inlet in °CTwo = Temperature of cooling water at outlet of the engine in °C

Heat carried away by the exhaust gases : (Qg)Qg = mg CPg (Tg – TR )mg = mass of the exhaust gases in kg/minma = mass of air consumed in kg/min

mf = mass of fuel consumed in kg/minCpg = Specific heat of exhaust gases = 1.005 KJ/kgKTg = Temperature of exhaust gases in °CTR = Room temperature in °C

Unaccounted heat losses :Qun = Qs - (Q.B.P + Qw + Qg ) in KJ / min

MPFI-

The term MPFI is used to specify a technology used in Gasoline/petrol Engines. For Diesel Engines, there is a similar technology called CRDI. We will discuss CRDI in a separate article to avoid confusion.

MPFI System is a system which uses a small computer (yes, a small computer without keyboard or mouse, its more like a microchip) to control the Car’s Engine. A Petrol car’s engine usually has three or more cylinders or fuel burning zones. So in case of an MPFI engine, there is one fuel –injector installed near each cylinder, that is why they call it Multi-point (more than one points) Fuel Injection.

In plain words, to burn petrol in an Engine to produce power, Petrol has to be mixed with some air, ignited in a cylinder (also called combustion chamber), which produces energy and runs the engine. I will not talk of further internal details because it will make this article for Engineers and not common people.

Common rail direct fuel injection

Common rail direct fuel injection is a modern variant of direct fuel injection system for petrol and diesel engines.

On diesel engines, it features a high-pressure (over 1,000 bar or 15,000 psi) fuel rail feeding individual solenoid valves, as opposed to low-pressure fuel pump feeding unit injectors (Pumpe/Düse or pump nozzles). Third-generation common rail diesels now feature piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar or 26,000 psi.

In gasoline engines, it is used in gasoline direct injection engine technology.

Gasoline direct injection

In internal combustion engines, Gasoline Direct Injection(GDI), also known as Petrol Direct Injection or Direct Petrol Injection or Spark Ignited Direct Injection(SIDI) or Fuel Stratified Injection(FSI), is a variant of fuel injection employed in modern two-stroke and four-stroke gasoline engines. The gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.

In some applications, gasoline direct injection enables a stratified fuel charge (ultra lean burn) combustion for improved fuel efficiency, and reduced emission levels at low load.