spark igniton engine report file by ramkaran yadav

1. Spark-ignition engine
1.INTRODUCTION:
The term spark-ignition engine refers to internal combustion engines, generally petrol
engines, where the combustion process of the air-fuel mixture is ignited by a spark from a
spark plug. This is in contrast to compression-ignition engines, typically diesel engines,
where the heat generated from compression together with the injection of fuel is enough to
initiate the combustion process, without needing any external spark.
Spark-ignition engines are commonly referred to as "gasoline engines" in America, and
"petrol engines" in Britain and the rest of the world. However, these terms are not preferred,
since spark-ignition engines can (and increasingly are) run on fuels other than petrol/gasoline,
such as autogas (LPG), methanol, ethanol, bioethanol, compressed natural gas (CNG),
hydrogen, and (in drag racing) nitromethanethe working cycle of both spark-ignition and
compression-ignition engines may be either two-stroke or four-stroke.
A four-stroke spark-ignition engine is an Otto cycle engine. It consists of following four
strokes: suction or intake stroke, compression stroke, expansion or power stroke, exhaust
stroke. Each stroke consists of 180 degree rotation of crankshaft rotation and hence a four-
stroke cycle is completed through 720 degree of crank rotation. Thus for one complete cycle
there is only one power stroke while the crankshaft turns by two revolutions See also
Compression-ignition engine Multifuel engine.

2. CHAPTER -2
ENGINE & WORKING PRINCIPLE
A heat engine is a machine, which converts heat energy into mechanical energy. Thecombusti
on of fuel such as coal, petrol, diesel generates heat. This heat is supplie toaworking substanc
e at high temperature. By the expansion of this substance in suitabemachines, heat energy is c
onverted into useful work. Heat engines can be further divided into
two types:
(i) External combustion and
(ii) Internal combustion.
Ina steam engine the combustion of fuel takes place outside the engine and the steamthus for
med is used to run the engine. Thus, it is known as external combustion engine.
In thecase of internalcombustion engine, the combustion of fuel takes place inside the engine
cylinder itself.
The IC engine can be further classified as: (i) stationary or mobile, (ii) horizontal or verti-
cal and (iii) low, medium or high speed. The two distinct types of IC engines used for either
mobile or stationary operations are: (i) diesel and (ii) carburettor.
1.1Spark Ignition (Carburettor Type) IC Engine
In this engine liquid fuel is atomised, vaporized and mixed with air in correct proportion
before being taken to the engine cylinder through the intake manifolds. The ignition of the
mixture is caused by an electric spark and is known as spark ignition.
1.2Compression Ignition (Diesel Type) IC Engine
In this only the liquid fuel is injected in the cylinder under high pressure.
1.3.CONSTRUCTIONAL FEATURES OF IC ENGINE:
1. Cylinder
2. Spark plug
3. Cylinder head

3. 4. inlet valve
5. Piston
6. exhaust valve
7. Connecting rod
8. cooling fins
9. crank and crankshaft
10.carburretor
11.Crank pin and bearings
12.flywheel
13.Piston rings
14.main bearings
15.Gudgeon pin
16.valve mechanism
1. CYLINDER:
The cylinder of an IC engine constitutes the basic and supporting portion of the engine power
unit. Its major function is to provide space in which the piston can operate to draw in the fuel
mixture or air (depending upon spark ignition or compression ignition), compress it, allow it
to expand and thus generate power. The cylinder is usually made of high-grade cast iron. In
some cases, to give greater strength and wear resistance with less weight, chromium, nickel.
2. SPARK PLUG:
A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a 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. The central electrode,
which may contain a resistor, is connected by a heavily insulated wire to the output terminal
of an ignition coil or magneto. The spark plug's metal shell is screwed into the engine's
cylinder head and thus electrically grounded.
Spark plugs may also be used for other purposes; in Saab Direct Ignition when they are not
firing, spark plugs are used to measure ionization in the cylinders – this ionic current
measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire
measurement function.Spark plugs may also be used in other applications such as furnaces
wherein a combustible fuel/air mixture must be ignited. In this case, they are sometimes
referred to as flame igniters.

4. 2.1.SPARK PLUG CONSTRUCTION:
A spark plug is composed of a shell, insulator and the central conductor. It passes through the
wall of the combustion chamber and therefore must also seal the combustion chamber against
high pressures and temperatures without deteriorating over long periods of time and extended
use.Spark plugs are specified by size, either thread or nut (often referred to asEuro), sealing
type (taper or crush washer), and spark gap.
2.2.PARTS OF THE SPARK PLUG:
Terminal
The top of the spark plug contains a terminal to connect to the ignition system. The exact
terminal construction varies depending on the use of the spark plug. Most passenger car spark
plug wires snap onto the terminal of the plug, but some wires have eyelet connectors which
are fastened onto the plug under a nut.
Insulator
The main part of te insulator is typically made from sintered alumina, a very hard ceramic
material with high dielectric strength, printed with the manufacturer's name and identifying
marks, then glazed to improve resistance to surface spark tracking.

5. Ribs
By lengthening the surface between the high voltage terminal and the grounded metal case of
the spark plug, the physical shape of the ribs functions to improve the electrical insulation
and prevent electrical energy from leaking along the insulator surface from the terminal to the
metal case.
Insulator tip
On modern (post 1930s) spark plugs, the tip of the insulator protruding into the combustion
chamber is the same sintered aluminium oxide (alumina) ceramic as the upper portion,
merely unglazed. It is designed to withstand 650 °C (1,200 °F) and 60 kV.
The dimensions of the insulator and the metal conductor core determine the heat range of the
plug. Short insulators are usually "cooler" plugs, while "hotter" plugs are made with a
lengthened path to the metal body, though this also depends on the thermally conductive
metal core.
Seals
Because the spark plug also seals the combustion chamber or the engine when installed, seals
are required to ensure there is no leakage from the combustion chamber. The internal seals of
modern plugs are made of compressed glass/metal powder, but old style seals were typically
made by the use of a multi-layer braze.
Metal case/shell
The metal case/shell (or the jacket, as many people call it) of the spark plug withstands the
torque of tightening the plug, serves to remove heat from the insulator and pass it on to the
cylinder head, and acts as the ground for the sparks passing through the central electrode to
the side electrode. Spark plug threads are cold rolled to prevent thermal cycle fatigue.
Central electrode
Central and lateral electrodes

6. The central electrode is connected to the terminal through an internal wire and commonly a
ceramic series resistance to reduce emission of RF noise from the sparking. Non-resistor
spark plugs, commonly sold without an "R" in the plug type part number, lack this element to
reduce electro-magnetic interference with radios and other sensitive equipment. The tip can
be made of a combination of copper, nickel-iron, chromium, or noble metals.
Side (ground, earth) electrode
The side electrode (also known as the "ground strap") is made from high nickel steel and is
welded or hot forged to the side of the metal shell. The side electrode also runs very hot,
especially on projected nose plugs. Some designs have provided a copper core to this
electrode, so as to increase heat conduction. Multiple side electrodes may also be used, so
that they don't overlap the central electrode.
Spark plug gap
Gap gauge: A disk with sloping edge; the edge is thicker going counter-clockwise, and a
spark plug will be hooked along the edge to check the gap.
Spark plugs are typically designed to have a spark gap which can be adjusted by the
technician installing the spark plug, by bending the ground electrode slightly. The same plug
may be specified for several different engines, requiring a different gap for each. Spark plugs
in automobiles generally have a gap between 0.6–1.8 mm (0.024"–0.070"). The gap may
require adjustment from the out-of-the-box gap.
Variations on the basic design
Over the years variations on the basic spark plug design have attempted to provide either
better ignition, longer life, or both. Such variations include the use of two, three, or four
equally spaced ground electrodes surrounding the central electrode.
Surface-discharge spark plug
A piston engine has a part of the combustion chamber that is always out of reach of the
piston; and this zone is where the conventional spark plug is located. A Wankel engine has a
permanently varying combustion area; and the spark plug is inevitably swept by the tip seals.
Clearly, if a spark plug were to protrude into the Wankel's combustion chamber it would foul

7. the rotating tip; and if the plug were recessed to avoid this, the sunken spark might lead to
poor combustion.
Tip protrusion
Different spark plug sizes. The left and right plug are identical in threading, electrodes, tip
protrusion, and heat range. The centre plug is a compact variant, with smaller hex and
porcelain portions outside the head, to be used where space is limited. The rightmost plug has
a longer threaded portion, to be used in a thicker cylinder head.

8. CHAPTER -2
FOUR STROKE SI ENGINE
this gasoline is mixed with air, broken up into a mist and partially vaporized in a carburettor
(Fig. 5). The mixture is then sucked into the cylinder. There it is compressed by the upward
movement of the piston and is ignited by an electric spark. When the mixture is burned, the
resulting heat causes the gases to expand. The expanding gases exert a pressure on the piston
(power stroke). The exhaust gases escape in the next upward movement of the piston. The
strokes are similar to those discussed under four-stroke diesel engines.
The various temperatures and pressures are shown in Fig. 6. The compression ratio varies
from4:1 to 8:1 and the air-fuel mixture from 10:1 to 20:1. The first petrol combustion engine
(one cylinder, 121.6 cm3 displacement) was prototyped in 1882 in Italy by Enrico Bernardi.
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.
Fig.1. Principle of operation of four-stroke petrol engine

9. 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. A stroke refers to the full
travel of the piston along the cylinder, in either direction. The four separate strokes are termed.
Each of its stroke consists of 180 degree rotation of crankshaft rotation and hence a four-
stroke cycle is completed through 720 degree of crank rotation. Thus for one complete cycle
there is only one power stroke while the crankshaft turns by two revolutions.
 Suction stroke
 Compression stroke
 Expansion stroke
 Exhaust stroke
1.Suction stroke: This stroke of the piston begins at top dead center (T.D.C.) and ends at
bottom dead center (B.D.C.). In this stroke the intake valve must be in the open position
while the piston pulls an air-fuel mixture into the cylinder by producing vacuum pressure into
the cylinder through its downward motion.
2.Compression stroke: This stroke begins at B.D.C, or just at the end of the suction
stroke, and ends at T.D.C. In this stroke the piston compresses the air-fuel mixture in
preparation for ignition during the power stroke (below). Both the intake and exhaust valves
are closed during this stage.
3.expansion stroke(power): This is the start of the second revolution of the four stroke
cycle. At this point the crankshaft has completed a full 360 degree revolution. While the
piston is at T.D.C. (the end of the compression stroke) the compressed air-fuel mixture is
ignited by a spark plug (in a gasoline engine) or by heat generated by high compression
(diesel engines), forcefully returning the piston to B.D.C. This stroke produces mechanical
work from the engine to the crankshaft.
4.Exhauststroke:During the exhaust stroke, the piston once again returns from B.D.C.
toT.D.C. while the exhaust valve is open. This action expels the spent air-fuel mixture
through the exhaust valve.

10. fig2.1 Four Stroke SI Engine
2.1. Otto cycle:
An Ottocycle is an idealized thermodynamiccycle thatdescribesthe functioningof atypical spark
ignition piston engine.Itisthe thermodynamic cycle most commonlyfoundin automobile
engines.
Pressure-Volume diagram

11. Temperature-Entropy diagram
The idealized diagrams of a four-stroke Otto cycle Both diagrams:the intake (A) stroke is
performed by an isobaric expansion, followed by an adiabatic compression(B) stroke.
Through the combustion of fuel, heat is added in an a constant volume (isochoric process)
process, followed by an adiabatic expansion process power (C) stroke. The cycle is closed by
the exhaust (D) stroke, characterized by isochoric cooling and isentropic compression
processes.
The Otto cycle is a description of what happens to a mass of gas as it is subjected to changes
of pressure, temperature, volume, addition of heat, and removal of heat. The mass of gas that
is subjected to those changes is called the system. The system, in this case, is defined to be
the fluid (gas) within the cylinder. By describing the changes that take place within the
system, it will also describe in inverse, the system's effect on the environment. In the case of
the Otto cycle, the effect will be to produce enough net work from the system so as to propel
an automobile and its occupants in the environment.
The Otto cycle is constructed from:Top and bottom of the loop: a pair of quasi-parallel and
isentropic processes (frictionless, adiabatic reversible).Left and right sides of the loop: a pair
of parallel isochoric processes (constant volume).
The isentropic process of compression or expansion implies that there will be no inefficiency
(loss of mechanical energy), and there be no transfer of heat into or out of the system during
that process. Hence the cylinder, and piston are assumed impermeable to heat during that
time. Work is performed on the system during the lower isentropic compression process.
Heat flows into the Otto cycle through the left pressurizing process and some of it flows back
out through the right depressurizing process. The summation of the work added to the system
plus the heat added minus the heat removed yields the net mechanical work generated by the
system.

12. The processes are described by:
 Process 0–1: it is a mass of air is drawn into piston/cylinder arrangement at constant
pressure.
 Process 1–2: it is an adiabatic (isentropic) compression of the air as the piston moves
from bottom dead centre (BDC) to top dead centre (TDC).
 Process 2–3: it is a constant-volume heat transfer to the working gas from an external
source while the piston is at top dead centre. This process is intended to represent the
ignition of the fuel-air mixture and the subsequent rapid burning.
 Process 3–4:it is an adiabatic (isentropic) expansion (power stroke).
 Process 4–1:it is completes the cycle by a constant-volume process in which heat is
rejected from the air while the piston is at bottom dead centre.
 Process 1–0:it is the mass of air is released to the atmosphere in a constant pressure
process.
The Otto cycle consists of isentropic compression, heat addition at constant volume,
isentropic expansion, and rejection of heat at constant volume. In the case of a four-stroke
Otto cycle, technically there are two additional processes: one for the exhaust of waste heat
and combustion products at constant pressure (isobaric), and one for the intake of cool
oxygen-rich air also at constant pressure; however, these are often omitted in a simplified
analysis. Even though those two processes are critical to the functioning of a real engine,
wherein the details of heat transfer and combustion chemistry are relevant, for the simplified
analysis of the thermodynamic cycle, it is more convenient to assume that all of the waste-
heat is removed during a single volume change.
2.1.1.OTTO CYCLE ANALYSIS:
In processes 1–2 the piston does work on the gas and in process 3–4 the gas does work on the
piston during those isentropic compression and expansion processes, respectively. Processes
2–3 and 4–1 are isochoric processes; heat transfer occurs but no work is done on the system
or extracted from the system. No work is done during an isochoric (constant volume) process
because addition or removal of work from a system as that requires movement of the
boundaries of the system; hence, as the cylinder volume does not change, no shaft work is
added or removed from the system.
Four different equations are used to describe those four processes. A simplification is made
by assuming changes of the kinetic and potential energy that take place in the system (mass

13. of gas) can be neglected and then applying the first law of thermodynamics (energy
conservation) to the mass of gas as it changes state as characterized by the gas's temperature,
pressure, and volume.[2][7]
During a complete cycle, the gas returns to its original state of temperature, pressure and
volume, hence the net internal energy change of the system (gas) is zero. As a result, the
energy (heat or work) added to the system must be offset by energy (heat or work) that leaves
the system. In the analysis of thermodynamic systems, the convention is to account energy
that enters the system as positive and energy that leaves the system is accounted as negative.
Equation 1a.
During a complete cycle, the change of energy of the system is zero:
The above states that the system (the mass of gas) returns to the original thermodynamic state
it was in at the start of the cycle.
Where is energy added to the system from 1–2–3 and is energy is removed from 3–
4–1. In terms of work and heat added to the system
Equation 1b:
Each term of the equation can be expressed in terms of the internal energy of the gas at each
point in the process:
The energy balance Equation 1b becomes
If the internal energies are assigned values for points 1,2,3, and 4 of 1,5,9, and 4 respectively
(these values are arbitrarily but rationally selected for the sake of illustration), the work and
heat terms can be calculated.
The energy added to the system as work during the compression from 1 to 2 is
The energy added to the system as heat from point 2 to 3 is

14. The energy removed from the system as work during the expansion from 3 to 4 is
The energy removed from the system as heat from point 4 to 1 is
The energy balance is
Note that energy added to the system is counted as positive and energy leaving the system is
counted as negative and the summation is zero as expected for a complete cycle that returns
the system to its original state.
From the energy balance the work out of the system is:
The net energy out of the system as work is -1, meaning the system has produced one net unit
of energy that leaves the system in the form of work.
The net heat out of the system is:
As energy added to the system as heat is positive. From the above it appears as if the system
gained one unit of heat. This matches the energy produced by the system as work out of the
system.
Thermal efficiency is the quotient of the net work from the system, to the heat added to
system. Equation 2:
Alternatively, thermal efficiency can be derived by strictly heat added and heat rejected.
Supplying the fictitious values

15. In the Otto cycle, there is no heat transfer during the process 1–2 and 3–4 as they are
isentropic processes. Heat is supplied only during the constant volume processes 2–3 and heat
is rejected only during the constant volume processes 4–1.
The above values are absolute values that might, for instance, have units of joules (assuming
the MKS system of units are to be used) and would be of use for a particular engine with
particular dimensions. In the study of thermodynamic systems the extensive quantities such
as energy, volume, or entropy (versus intensive quantities of temperature and pressure) are
placed on a unit mass basis, and so too are the calculations, making those more general and
therefore of more general use. Hence, each term involving an extensive quantity could be
divided by the mass, giving the terms units of joules/kg (specific energy), meters3/kg
(specific volume), or joules/(kelvin·kg) (specific entropy, heat capacity) etc. and would be
represented using lower case letters, u, v, s, etc.
Equation 1 can now be related to the specific heat equation for constant volume. The specific
heats are particularly useful for thermodynamic calculations involving the ideal gas model.
Rearranging yields:
Inserting the specific heat equation into the thermal efficiency equation (Equation 2) yields.
Upon rearrangement:
Next, noting from the diagrams (see isentropic relations for an ideal gas),
thus both of these can be omitted. The equation then reduces to:
Equation 2:

16. Since the Otto cycle uses isentropic processes during the compression (process 1 to 2) and
expansion (process 3 to 4) the isentropic equations of ideal gases and the constant
pressure/volume relations can be used to yield Equations 3 & 4.[8]
Equation 3:
Equation 4:
where
is the specific heat ratio
The derivation of the previous equations are found by solving these four equations
respectively (where is the specific gas constant):
Further simplifying Equation 4, where is the compression ratio :
Equation 5:
From inverting Equation 4 and inserting it into Equation 2 the final thermal efficiency can be
expressed as.

17. Equation 6:
From analyzing equation 6 it is evident that the Otto cycle efficiency depends directly upon
the compression ratio . Since the for air is 1.4, an increase in will produce an increase in
. However, the for combustion products of the fuel/air mixture is often taken at
approximately 1.3. The foregoing discussion implies that it is more efficient to have a high
compression ratio. The standard ratio is approximately 10:1 for typical automobiles. Usually
this does not increase much because of the possibility of autoignition, or "knock", which
places an upper limit on the compression ratio.[2] During the compression process 1–2 the
temperature rises, therefore an increase in the compression ratio causes an increase in
temperature. Autoignition occurs when the temperature of the fuel/air mixture becomes too
high before it is ignited by the flame front. The compression stroke is intended to compress
the products before the flame ignites the mixture. If the compression ratio is increased, the
mixture may auto-ignite before the compression stroke is complete, leading to "engine
knocking". This can damage engine components and will decrease the brake horsepower of
the engine.
2.1.2 POWER:
The power produced by the Otto cycle is the energy developed per unit of time. The Otto
engines are called four-stroke engines. The intake stroke and compression stroke require one
rotation of the engine crankshaft.The power stroke and exhaust stroke require another
rotation. For two rotations there is one work generating stroke.
From the above cycle analysis the net work produced by the system was:
(again,using the sign convention, the minus sign implies energy is leaving the system as
work)
If the units used were MKS the cycle would have produced one joule of energy in the form of
work. For an engine of a particular displacement, such as one liter, the mass of gas of the
system can be calculated assuming the engine is operating at standard temperature (20 °C)
and pressure (1 atm).Using the Universal Gas Law the mass of one liter of gas is at room
temperature and sea level pressure:
V=0.001 m3
, R=0.286 kJ/(kg·K), T=293 K, P=101.3 kN/m2
M=0.00121 kg

18. At an engine speed of 2000 RPM there is 1000 work-strokes/minute or 16.7 work-
strokes/second.
Power is 16.7 times that since there are 16.7 work-strokes/second
If the engine is multi-cylinder, the result would be multiplied by that factor. If each cylinder
is of a different liter displacement, the results would also be multiplied by that factor. These
results are the product of the values of the internal energy that were assumed for the four
states of the system at the end each of the four strokes (two rotations). They were selected
only for the sake of illustration, and are obviously of low value. Substitution of actual values
from an actual engine would produce results closer to that of the engine. Whose results would
be higher than the actual engine as there are many simplifying assumptions made in the
analysis that overlook inefficiencies. Such results would overestimate the power output.
2.1.3INCREASING POWER AND EFFICIENCY:
The difference between the exhaust and intake pressures and temperatures suggest that some
increase in efficiency can be gained by removing from the exhaust flow some part of the
remaining energy and transferring that to the intake flow to increase the intake pressure. A
gas turbine can extract useful work energy from the exhaust stream and that can then be used
to pressurize the intake air. The pressure and temperature of the exhausting gases would be
reduced as they expand through the gas turbine and that work is then applied to the intake gas
stream, increasing its pressure and temperature. The transfer of energy amounts to an
efficiency improvement and the resulting power density of the engine is also improved. The
intake air is typically cooled so as to reduce its volume as the work produced per stroke is a
direct function of the amount of mass taken into the cylinder; denser air will produce more
work per cycle. Practically speaking the intake air mass temperature must also be reduced to
prevent premature ignition in a petrol fueled engine; hence, an inter-cooler is used to remove
some energy as heat and so reduce the intake temperature. Such a scheme both increases the
engine's efficiency and power density.
The application of a supercharger driven by the crankshaft does increase the power output
(power density) but does not increase efficiency as it uses some of the net work produced by
the engine to pressurize the intake air and fails to extract otherwise wasted energy associated
with the flow of exhaust at high temperature and a pressure to the ambient
2.2 COMPRESSION RATIO:
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 set statically or at idle at a minimum of 10 degrees
or so of crankshaft rotation before the piston reaches TDC, but at much higher values at

19. higher engine speeds 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.
2.3.SPEED AND EFFICIENCY:
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 more quickly than diesel. Because pistons in petrol engines
tend to have much shorter strokes than pistons in diesel engines, typically it takes less time
for a piston in a petrol engine to complete its stroke than a piston in a diesel engine. However
the lower compression ratios of petrol engines give petrol engines lower efficiency than
diesel engines.
2.4.APPLICATIONS:
Petrol engines have many applications:
 Automobiles
 Motorcycles
 Aircraft
 Motorboats
 Small engines, such as lawn mowers, chainsaws and portable engine-generators
2.5.DESIGN:
2.5.1WORKING CYCLES
4-Stroke Petrol engine.
Petrol enginesmayrunonthe four-stroke cycle orthe two-stroke cycle.Fordetailsof workingcycles
see:
 Four-stroke cycle
 Two-stroke cycle
 Wankel engine
2.5.2:CYLINDER ARRANGEMENT
Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in
V-formation. Flat engines – like a V design flattened out – are common in small airplanes
and motorcycles and were a hallmark of Volkswagen automobiles into the 1990s. Flat 6s are
still used in many modern Porsches, as well as Subarus. Many flat engines are air-cooled.
Less common, but notable in vehicles designed for high speeds is the W formation, similar to
having 2 V engines side by side. Alternatives include rotary and radial engines the latter
typically have 7 or 9 cylinders in a single ring, or 10 or 14 cylinders in two rings.

20. 2.5.3COOLING
Petrol engines may be air-cooled, with fins (to increase the surface area on the cylinders and
cylinder head); or liquid-cooled, by a water jacket and radiator. The coolant was formerly
water, but is now usually a mixture of water and either ethylene glycol or propylene glycol.
These mixtures have lower freezing points and higher boiling points than pure water and also
prevent corrosion, with modern antifreezes also containing lubricants and other additives to
protect water pump seals and bearings. The cooling system is usually slightly pressurized to
further raise the boiling point of the coolant.
2.5.4.IGNITION
Petrol engines use spark ignition and high voltage current for the spark may be provided by a
magneto or an ignition coil. In modern car engines the ignition timing is managed by an
electronic Engine Control Unit.
2.5.5.POWER MEASUREMENT
The most common way of engine rating is what is known as the brake power, measured at the
flywheel, and given in kilowatts (metric) or horsepower (Imperial/USA). This is the actual
mechanical power output of the engine in a usable and complete form. The term "brake"
comes from the use of a brake in a dynamometer test to load the engine. For accuracy, it is
important to understand what is meant by usable and complete. For example, for a car engine,
apart from friction and thermodynamic losses inside the engine, power is absorbed by the
water pump, alternator, and radiator fan, thus reducing the power available at the flywheel to
move the car along. Power is also absorbed by the power steering pump and air conditioner
(if fitted), but these are not installed for a power output test or calculation. Power output
varies slightly according to the energy value of the fuel, the ambient air temperature and
humidity, and the altitude. Therefore, there are agreed standards in the USA and Europe on
the fuel to use when testing, and engines are rated at 25 ⁰C (Europe), and 64 ⁰F
(USA)[citation needed] at sea level, 50% humidity. Marine engines, as supplied, usually have
no radiator fan, and often no alternator. In such cases the quoted power rating does not allow
for losses in the radiator fan and alternator. The SAE in USA, and the ISO in Europe publish
standards on exact procedures, and how to apply corrections for deviating conditions like
high altitude.
Car testers are most familiar with the chassis dynamometer or "rolling road" installed in
many workshops. This measures drive wheel brake horsepower, which is generally 15-20%
less than the brake horsepower measured at the crankshaft or flywheel on an engine
dynamometer. A YouTube video shows workshop measurement of a car's power. The
measured power curve in kW is shown at 3:39.