ME6016 ADVANCED I.C.ENGINES

primed by
K.SENGOTTAIYAN
senengg2@gmail.com

Types of Injection systems:
1. According to location of Injector
Throttle Body Injection (TBI), Port Injection and Direct
Injection
2. According to duration and timing of fuel injection
Continuous type, Intermittent type and sequential type
3. According to number of injectors
single point interjection and Multi point injection
4. According to control method
Mechanical and Electronic
Gasoline Injection Systems

Fig: Mechanical Petrol Injection system

Theoretical Combustion in SI engines

I - Stage: Ignition Lag or
preparation stage.
II - Stage: Main combustion
stage
III – Stage: After burning

 Temperature, Pressure and Density Factors
 Time Factors
 Composition Factors
 Effect of Design
15

 The basic requirements of a good combustion
chamber are to provide:
1. High power output
2. High thermal efficiency and low specific fuel
consumption
3. Smooth engine operation
4. Reduced exhaust pollutants.

Fuel injection system for diesel engine
19

Air Injection System
 Here, the fuel is injected by means of high pressure air at about 70 bar into the combustion
chamber.
 It needs compressor to supply compressed air & the fuel pump to draw the desired fuel from
fuel tank both to be supplied to the injector.
Advantages
I. Provides good atomization of fuel.
II. Heavy viscous fuel can be used .
Disadvantages
I. Air compressor needs extra maintenance.
II. System is bulky and expensive.
20

Solid or Airless Injection System
 Here, fuel is directly injected into the cylinder without the aid of compressed air.
 The fuel does not vaporize at ordinary temperatures & also the fuel supplied needs to be
atomized & mix with air, it requires high injection pressure over 70 bar.
Types of solid Fuel Injection System
I. Mechanical Injection
II. Electronic Injection
Mechanical Injection is further classified as:
a) Common rail direct injection (CRDI) system
b) Individual pump system
c) Distributor system
21

Common-Rail Direct Injection (CRDI) System
22

Advantages
I. This system is simple & easy to maintenance.
II. It Can control fuel supply as per load & speed of engine.
III. It has only one pump needed for a multi-cylinder engine.
Disadvantages
I. System needs accurate design .
II. There is a chance of developing leakage at the valve seat.
III. Injection pressure used are in range of 200 – 300 bar pressure.
23

Fuel Injection Pumps
Objectives
I. To deliver accurately metered quantity of fuel.
II. High pressures in the range of 100 bar to 300 bar needed depending upon the
compression ratio of engine to achieve required atomization of fuel.
III. Fuel must be injected and terminated at the correct timing.
Types of Injection Pumps
I. Jerk type injection pump ( Bosch fuel injection pump )
II. Distributor type injection pump
26

Nozzles
 Nozzle is the part of an injector through which the fuel is injected into the
combustion chamber.
 Design of nozzle should be such that the liquid fuel leaving the nozzle is atomized
which helps in proper mixing of fuel & air.
 Type of nozzle used in an injector depends on the type of combustion chamber used
in an engine.
Various types of Nozzles:
I. The pintle nozzle
II. The single hole nozzle
III. The multi-hole nozzle
IV. The pintaux nozzle
30

Pintle Nozzle
I. Have thin ends in the form of pin.
II. Shape of the pin can be varied.
III. Hollow cylindrical jet or a wide angle spray
can be obtained.
Specifications:
Advantages
I. It avoids dribbling of fuel in the
combustion chamber
31

Single hole nozzle
Specifications
I. A single hole is bored at bottom tip of nozzle.
II. Hole diameter is of 0.2 mm.
III. Spray cone angle obtained ranges from 5-20
degrees.
Advantages
I. Suitable for open combustion
chamber
Disadvantages
I. Gives small spray cone angle.
II. Have a tendency to dribble.
32

Multiple hole Nozzle
Specifications
I. Have multiple holes bored at the tip of the
nozzle.
II. Number of holes vary from 4 to 8.
III. Diameter vary from 0.2 mm to 0.35 mm.
Advantages
I. It ensures proper mixing of fuel
in the chamber.
Disadvantages
I. It requires high injection pressures in
the range of 180 to 200 bar.
33

Pintaux Nozzle
Specifications
I. Pintle type of nozzle with an auxiliary hole drilled in it.
II. Auxiliary hole injects fuel in a direction upstream the direction of air before the main
injection starts.
Advantages
I. It reduces the delay period due to better heat transfer
between fuel & air.
II. It results into better cold starting performance.
34

 The classical diesel
compression and
combustion pressure
diagram shown in Figure
has been proved to be an
acceptable model and can
be roughly divided into
four broad stages:
1. Ignition delay period
2. Rapid or uncontrolled
combustion
3. Mixing-controlled
combustion phase
4. Late combustion phase
or afterburning.
35

 Ignition delay period
 The processes that take place during
the ignition delay can be divided into
the following physical and chemical
processes.
 The physical processes are:
 Spray disintegration and droplet
formation
 Heating of the liquid fuel and
evaporation
 Diffusion of the vaporized fuel
into the air to form an ignitable
mixture.
 The chemical processes are:
 Decomposition of the heavy
hydrocarbons into lighter
components
 Pre-ignition chemical reactions
between the decomposed
components and oxygen.
36

 Rapid or uncontrolled
combustion
 In this phase, combustion of the fuel, which has
mixed with air to within flammability limits during
the ignition delay period, occurs rapidly in a few
crank angle degrees.
 Ignition in one place is followed by ignition
elsewhere, so rapid combustion of the prepared foel
follows the first ignition.
 The rate and quantity of combustion in the second
phase is thus dependent on the duration of the
delay period and the rate of preparation of fuel
during this period.
 The speed of this reaction deter mines the rate of
pressure rise (dp/dϴ) in the cylinder.
 The magnitude of the pressure rise during the
second period may determine the value of the peak
pressure of the cycle. For structural reasons, to
reduce mechanical stresses it is important to
 limit the peak pressure as well as the rate of
pressure rise. As the peak pressure increases, the
peak temperature also increases, which increases (a)
the NOx emission, (b) the thermal loads on the
cooling system, and (c) the temperature and thermal
stressing of the combustion chamber walls.
 Therefore, to limit the pressure and temperature
rise during the second period, it is important to
keep the delay period as short as possible.
37

 Mixing-controlled
combustion phase
 Once the fuel and air which
premixed during the ignition
delay have been consumed at
the end of the period of rapid
combustion, the temperatures
within the cylinder are so high
that any fuel injected after this
time will bum as soon as it finds
oxygen, and any further rise in
pressure is controlled by the
injection rate as well as by the
mixing and diffusion processes.
 Engines running at low rpm
should be designed to secure
rapid mixing of fuel and air
during the third stage in order
to complete the combustion
process as early as possible in
the expansion stroke.
38

Late combustion phase or afterburning.
 A very low rate of combustion,
sometimes referred to as the tail of
combustion, occurs well down the
expansion stroke of the engine.
 There are several reasons for this. A
small fraction of fuel may not yet
have burned. The cylinder charge is
non uniform and mixing during this
period promotes more complete
combustion and less dissociated
product gases.
 The kinetics of the final burnout
processes become slower as the
temperature of the cylinder gases fall
during expansion.
 The late combustion phase is
undesirable because it reduces the
power output and produces smoky
exhaust.
 This can be eliminated by supplying
more excess air and creating more
turbulence.
39

 The period a-b represents the
ignition delay. No heat is released
during this period.
 The period b-c represents the rapid
combustion phase. The high heat
release rate is the characteristic of
this phase.
 The period c-d represents the
controlled combustion phase. During
this period the heat release rate may
or may not reach a second (usually
lower) peak. It decreases as this
phase progresses.
 The period d-e represents the late
combustion phase, the heat release
rate decreases further and continues
at a lower rate well into the
expansion stroke.
41
A typical heat release rate diagram of a
direct injection compression ignition
engine, identifying the different diesel
combustion phases is shown in Figure

 Combustion knock in CI engines is associated with an extremely
high rate of pressure rise during the second phase of
combustion (rapid or uncontrolled combustion) and also with
heavy vibration accompanied by a knocking sound, thus causing
overheating of the piston and the cylinder head drop in power,
damage to bearings and possible piston seizure.
 The injection process of a fuel takes place over a definite period
of time in terms of degree crank angle. As a result, the first few
drops which are injected into the chamber pass through the
ignition delay while the additional droplets are being injected
into the chamber.
 Normally, the fuel Injected period is more than the delay period.
If the delay period of the injected fuel is short, the first few
droplets will commence the burning phase in a relatively short
time after injection, and a relatively small amount of fuel will be
accumulated in the chamber when actual burning commences.
42

 As a result, the rate of burned mass of fuel will be
such as to produce a rate of pressure rise that will
exert a smooth force on the piston, as shown in
Figure (a).
 If, on the other hand the delay period is longer, the
burning of the first few droplets is delayed and
therefore a greater quantity of fuel droplets will
accumulate in the chamber. When the actual burning
commences, the additional fuel may cause rapid rate
of pressure rise as in Figure (b), resulting in rough
engine operation.
 If the delay period is too long, much fuel will be
accumulated resulting in instantaneous rise in
pressure as in Figure (c).
 Such a situation produces pressure waves striking
on cylinder walls, piston crown and cylinder head,
producing audible knock and vibrations.
 In fact, the combustion mechanism of diesel engine
is based on the auto-ignition of the charge and
hence, mild knock may always be present. When it
exceeds a certain limit, the engine is said to be
knocking.
 Though the long ignition delay improves the mixing
process of fuel and air and makes the mixture more
homogeneous, it helps the process of auto-ignition
and makes the engine more prone to knock.
43

 While knocking in the SI engine and in CI engine have
essentially the same basic cause, i.e. auto-ignition followed by a
rapid pressure rise, it is important to note the following
differences:
 (a) In the SI engine, knocking occurs due to auto-ignition of the
last part of the charge (end gas), i.e. at the end of combustion,
while in the CI engine knocking occurs in the first part, i.e. at
the start of combustion.
 (b) In the SI engine, it is the homogeneous charge that
auto-ignites and causes knocking, resulting in a very high
rate of pressure rise and high peak pressure. In the CI engine
the fuel and air are not homogeneously mixed and hence the
rate of pressure rise is normally lower than that in the knocking
part of the charge in the SI engine. However, the peak pressure
is higher due to a high compression ratio.
 (c) In the Cl engine only the air is compressed during the
compression stroke and the ignition can take place only after
the fuel is injected just before TDC. Therefore, there is no
question of pre-ignition occurring in the CI engine, whereas
pre-ignition may occur in the SI engine due to the presence of
both fuel and air during compression.
 (d) In the SI engine, knocking can easily be detected by human
ear but in the CI engine there is no clear distinction between
knocking and normal combustion, since normal combustion in
the CI engine is itself by auto-ignition and a mild knock may
always be present.
44

45
• Those factors which tend to prevent knock in SI engines, the same very factors
promote knock in CI engines. To prevent knock in SI engines, the auto-ignition of
the last part of the charge should not take place; this requires a long delay period
and a high self-ignition temperature.
• To prevent knock in CI engines, the auto-ignition of the first part of the charge
should be achieved as early as possible and therefore it requires a short delay
period and a low self-ignition temperature. It may also be noted that a good SI
engine fuel is a bad CI engine fuel and vice-versa.
• Table presents a comparative statement of the various factors to be varied in order
to reduce knock in SI and CI engines.

Combustion Chamber
with a Pre-chamber for
Lean Burn Engine.

Ricardo
Turbulent
Head Side
Valve
Combustion
Chamber

54
lean flame region: Ignition nuclei will be formed at several locations where the mixture is most suitable for
autoignition. Ignition combustion in the lean flame region, the flame propagates towards the core of the spray.
Between these two regions the fuel droplets are larger. They give heat by radiation from the already
established flames and evaporate at a higher rate. The increase in temperature also increases the rate of
vapour diffusion. These droplets may get completely or partially evaporated. If they are completely evaporated,
the flame will burn all the mixture with the rich ignition limit. The droplets which do not get ', esstarts
near the leading edge of the spray. Once the ignition starts, small independent nonluminous flame fronts
propagate from the ignition nuclei and ignite the combustible mixture around them. This mixture is leaner
than the stoichiometric mixture and the region is called the 'lean flame region'.
Lean flame-out region: Near the far leading edge of the spray, the mixture is too lean to ignite or support
combustion. This region is called the 'lean flame-out region'. Within this region some fuel decomposition and
partial oxidation take place. The decomposition products consist of lightercompletely evaporated will be
surrounded by a diffusion type of flame. The combustion in the core of the jet depends mainly upon the local
fuel/ air ratio.
Spray tail: The last part of the fuel to be injected usually forms large droplets because of the relatively less
pressure difference acting on the fuel near the end of the injection process. This is caused by a decreased fuel
injection pressure and increased cylinder gas pressure. The penetration of this part of the fuel is usually poor.
This portion is known as the spray tail.
After-injection: When the injector valve remains open for a short time after the end of the main injection, a
small amount of fuel is further injected, called 'after-injection hydrocarbon molecules and this region is
believed to be the main contributor to the unburned hydrocarbons in the exhaust. The partial oxidation
products may contain aldehydes and other oxygenates.
Spray core: Following ignition and pecially under medium and high load conditions.
Fuel deposited on the walls: Some fuel sprays impinge on the walls. Because of the shorter spray path and the
limited number of sprays, this is a especially the case in small, high speed direct injected CI engines. If the
surrounding gas has a high relative velocity and contains enough oxygen, the flame will propagate from wall to
a small distance within the chamber.

Catalytic converter
 The catalyst used in the converter is mostly a
precious metal such as platinum, palladium and
rhodium. Platinum is used as a reduction catalyst
and as an oxidation catalyst. Although platinum is
a very active catalyst and widely used, it is very
expensive and not suitable for all applications.

Conventional fuels
 Fossil fuels (petroleum), coal, and nuclear
materials such as uranium.
Alternative fuels
 also known as non-conventional fuels,
 any materials or substances that can be used as
fuels, other than conventional fuels.
 which is consumed to provide energy to power an
engine.

 Mainly produced by the sugar fermentation process.
 Can also be manufactured by the chemical process
of reacting ethylene with steam.
 A clear colorless liquid, it is biodegradable, low in
toxicity and causes little environmental pollution if
spilt.
 Ethanol is a high octane fuel and has replaced lead
as an octane enhancer in petrol.
 Widely sold in the United States.

Advantages
 Much cleaner, it burns
more cleanly (more
complete combustion)
 Can reduce the net
emissions of greenhouse
gases
 The fuel spills are more
easily biodegraded or
diluted to non toxic
concentrations.
 Can use any plant for
production.
Disadvantages
 Destroyed habitats
including rainforests.
 Will increase food prices
around the world.
 Pure ethanol is also
difficult to vaporise
 Not as efficient as
petroleum

 Liquefied Petroleum Gas (LPG).
 Clean-burning fossil fuel that can be used to
power internal combustion engines.
 Lower amounts of some harmful emissions and
the greenhouse gas carbon dioxide (CO2)
 Most LPG used in U.S
 Transportation fuel since 1912

 Propane is stored as a liquid in a relatively low-
pressure tank
 The supply of propane to the engine is controlled by
a regulator or vaporizer, which converts the liquid
propane to a vapor
 The vapor is fed to a mixer located near the intake
manifold, where it is metered and mixed with filtered
air before being drawn into the combustion chamber
where it is burned to produce power

 90% of propane used in U.S. comes from domestic
sources
 Less expensive than gasoline
 Potentially lower toxic, carbon dioxide (CO2), carbon
monoxide (CO), and non methane hydrocarbon
(NMHC)
 Propane is clean, cost effective, safe and a reliable
alternative fuel

 Limited availability
 A few large trucks and vans can be special
ordered from manufacturers; other vehicles can
be converted by certified installers
 Less readily available than gasoline & diesel
 Fewer miles on a tank of fuel

 Biodiesel contains no petroleum, but it can be
blended at any level with petroleum diesel
 To create a biodiesel blend in different concentrations
of B100, B20, B5, B2.
 It can be used in compression-ignition (diesel)
engines with little or no modifications.
 Biodiesel is a form of diesel fuel manufactured from
 vegetable oils,
 animal fats,
 recycled restaurant greases.

Advantages Disadvantages
• Can be used in most diesel
engines, especially newer
ones
• Less air pollutants (other
than nitrogen oxides)
• Less greenhouse gas
emissions (e.g., B20
reduces CO2 by 15%)
• Non-toxic
• Use of blends above B5
not yet approved by many
auto makers
• B100 generally not
suitable for use in low
temperatures
• Concerns about B100's
impact on engine
durability

 A potentially emissions-free alternative fuel
produced from domestic resources.
 Not widely used today as a transportation fuel
 Not occur free in nature in useful quantities, but it
is manufactured in a number of ways.

Advantages
 Emits only water vapour, assuming there is no
leakage of hydrogen gas
 It can store up to 3x as much energy as
conventional natural gas.
 Produced domestically.
 Environmentally friendly.
Disadvantages
 It still costs a considerable amount of money to
run a hydrogen vehicle
 Dangerous

 a fossil fuel substitute for gasoline (petrol), Diesel fuel
and propane/LPG
 a more environmentally "clean" alternative to
conventional fuels.
 It is much safer than other fuels in the event of a spill,
because natural gas is lighter than air and disperses
quickly when released
 made by compressing natural gas (which is mainly
composed of methane, CH4), to less than 1 percent of the
volume it occupies at standard atmospheric pressure

Advantages
 it can be efficiently and
safely stored.
 more environmentally
friendly due to its low
emissions after burning.
 most of the natural
reserves of natural gas
field are underutilized.
 Improve lubrication
because the cylinders are
not washed by petrol
excess
Disadvantages
 still does create
greenhouse gas emissions.
 highly volatile and can be
dangerous is handled or
transported carelessly.
 they aren't as roomy as
gasoline cars.
 higher overall costs of a
natural-gas vehicle
compared to a gasoline-
powered car.

 IC engine in which air-fuel ratio isn't equal throughout the cylinder.
 Rich mixture is provided close to the spark plug and combustion
promotes ignition of a lean mixture in the remainder of the cylinder.
 Stratified charge is a process for petrol engine. It is similar in some ways
to the Diesel cycle, but running on normal gasoline.
 Input of air is such that it generates a swirl in the cylinder.
 In a stratified charge engine, the fuel is injected into the cylinder just
before ignition. This allows for higher compression ratios without
"knock," and leaner air/fuel mixtures than in conventional internal
combustion engines.
 As the fuel is ignited and burned, the surrounding air provides almost
complete combustion before the exhaust port opens which further
burns the lean mixture.
Stratified charge engines

10
0
The phases of injected fuel stream during work on the
stratified charge

10
1
Spray
controlled
Wall
controlled
Flow
controlled
Spark plug near
injector
Spark plug away from
injector
Spark plug away
from injector
Spark plug fouling
at higher loads
No spark plug fouling at
higher loads
No spark plug
fouling at higher
loads
Formation of
mixture takes
longer hence
initial heat release
rates are small
and larger
combustion
duration.
Although the fuel initially
evaporates quite rapidly
due to hot walls, but it
takes longer to evaporate
all the injected fuel. Thus,
the end of combustion is
significantly delayed.
Shortest
combustion
duration due to
better mixture
preparation and
turbulence.

1. The overall air-fuel ratio can be very lean
reaching 40:1 to 50:1giving high fuel
efficiency.
2. The mixture being rich near spark plug
good ignition characteristics without misfire
are obtained.
3. The end gases being very fuel lean, pre-
combustion reactions would be very slow
leading to reduced knocking tendency.
Hence, a higher compression ratio can be
used further improving the fuel efficiency.
4. Presence of rich mixture near spark plug
keeps the formation of NOx at low levels.
The mixture that burns early is deficient in
oxygen although it attains high combustion
temperatures.
10
2

 Injectors add significant cost to
the system but fuel efficiency
advantages are overcoming this.
 With increasing load, the
efficiency matches with that of
conventional engines due to
stoichiometric mixture.
 High cyclic variability can
disrupt the formation (and
location) of the stratified areas,
reducing the effect of the spark
- if the rich area is not near the
spark then combustion either
may not occur properly.
10
3

 HCCI is a combustion process. HCCI is not an
engine concept. HCCI must be incorporated in
an engine concept.
 HCCI is a low temperature chemically controlled
(flameless) combustion process.
 HCCI can be considered as a hybrid form
between the diesel and Otto combustion
process.
 However combustion process is different. So
there is neither Diffusion flame (as in a diesel
engine) nor a flame front traveling through a
premixed charge ( as in SI engine).

 Homogenous charge(mixture of air & fuel) should be mixed
before combustion and compress to high enough temperature
to achieve spontaneous ignition of the charge.
 Thus HCCI is similar to SI in the sense that both processes use
premixed charge and that of CI as both rely on autoignition for
combustion initiation.

 Fuel injected through fuel injectors.
 Air induction through intake plenum.
 Air & Fuel mixed in combustion chamber.
 As piston moves back up(compression stroke) sufficient heat
has accumulated.
 This heat (no spark) spontaneously combust A/F mixture which
forces piston down for power stroke.
 This process is lean , low temp. ,flame-less energy released.
 Entire mix. burned simultaneously produces equivalent power
using much less fuel & low emissions.
 At exhaust stroke , exhaust valves closes early ,trapping some
latent combustion heat & preserved.
 Now small amount of fuel injected in chamber for pre-charging
before next stroke.

 15% increase in fuel efficiency over SI engines.
 Can be operated at high compression ratios(>15).
 Can be operate on gasoline , diesel fuel and most alternative
fuel.
 Omission of throttle losses improves efficiency.
 No shock wave propagation ,so no knocking.
 Cleaner combustion and lower emission.

 High in-cylinder peak pressure.
 Engine wear due to high heat release and pressure rise.
 Auto-ignition is difficult to control.
 Small power range, constrained at low loads,high loads.
 Carbon Monoxide(CO) & Hydrocarbons(HC) emissions are
higher.

ME6016 ADVANCED I.C.ENGINES

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