fundamentals and designs of various types of combustion ... 5_6_diesel... · fundamentals and...
TRANSCRIPT
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IIT Kanpur Kanpur, India (208016)
Fundamentals and Designs of Various Types of Combustion Chambers for Diesel Engines
Dr. Avinash Kumar Agarwal Engine Research Laboratory,
Department of Mechanical Engineering, Indian Institute of Technology, Kanpur
INDIA [email protected]
Engine Research Laboratory, IIT Kanpur
The shape of the combustion chamber is one of the decisive factors: Determines
the quantity of combustion: Performance & exhaust characteristics.
Diesel Engine combustion is greatly influenced by air turbulence: Created by the
shape of combustion chamber area.
Each Combustion chamber shape creates its own unique turbulence pattern that is
right for some application while wrong for others.
Combustion Chambers in Diesel Engines
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Engine Research Laboratory, IIT Kanpur
To optimize the filling and emptying of the cylinder with fresh (unburnt) charge
respectively over the engines operating range (All loads and speeds).
To create the conditions in the cylinder for the air and fuel to mix thoroughly: Get
Excited into a highly turbulent state: Burning of the charge to be completed in the
shortest possible time.
The Objective of Good Combustion Chamber Design
Engine Research Laboratory, IIT Kanpur
Heat loss to combustion chamber walls Injection pressure. Nozzle design: Number, size, & arrangement of holes in the nozzle Maintenance Ease of starting Fuel requirement: Ability to use less expensive fuels Utilization of air: Ability to use maximum amount of air in cylinder Weight relation of engine to power output Capacity for variable speed operation Smoothness with which forces created by expanding gases are transmitted to the
piston.
Important Factors Considered in Combustion Chamber Design
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Engine Research Laboratory, IIT Kanpur
Characterization of Common Diesel Combustion systems
DirectInjection IndirectInjection
System Quiescent MediumSwirl HighSwirlM HighswirlMediumSpray
Swirlchamber Prechamber
Size Largest Medium Mediumsmaller Mediumsmall Smallest smallest
Cycle 2/4stroke 4stroke 4stroke 4stroke 4stroke 4stroke
TC/SC/NA TC/SC TC/NA TC/NA NA/TC NA/TC NA/TC
Mediumspeed(rpm)
1202100 18003500 25005000 35004300 36004800 4500
Bore,mm 900150 150100 13080 10080 9570 9570
Stroke/bore 3.51.2 1.31.0 1.20.9 1.10.9 1.10.9 1.10.9
Compressionratio
1215 1516 1618 1622 2024 2224
chamber Openorshallowdish
Bowlinpiston Deepbowlinpiston
Deepbowlinpiston
Swirlprechamber
Single/multiorificeprechamber
Airflowpattern Quiescent MediumSwirl HighSwirl Highestswirl Veryhighswirlinprechamber
VeryturbulentinPrechamber
No.ofNozzleholes
Multi Multi Single Multi Single single
Inj.Press. Veryhigh High Medium High Lowest Lowest
Engine Research Laboratory, IIT Kanpur
Direct Injection Combustion Chamber
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Engine Research Laboratory, IIT Kanpur
The proportion of DI is increasing due to their more economical fuel consumption (up to 20% savings).
For DI engine, piston crown recess is most widely used. In this design, the fuel is injected directly into the cylinder chamber.
Lower combustion surface wall area compared to combustion volume in comparison with IDI.
More combustion taking place in and on the piston and less contact with coolant.
DI chamber has highest fuel efficiency rating compared to other chamber design.
Direct Injection Combustion Chamber
Engine Research Laboratory, IIT Kanpur
Direct Injection CI Engine Combustion Systems
Quiescent chamber with multi hole nozzle
typical of larger engines
Bowl-in-piston chamber with swirl
and multi hole nozzle
Bowl-in-piston chamber with swirl
and single hole nozzle
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Engine Research Laboratory, IIT Kanpur
Direct injection engines have two design philosophies: High-swirl design, which have a deep bowl in the
piston, a low number of holes in the injector and moderate injection pressures.
Low-swirl or quiescent engines are characterized by having a shallow bowl in the piston, a large number of holes in the injector and higher injection pressures.
Smaller engines tend to be of the high-swirl type, while bigger engines tend to be of the quiescent type.
Direct Injection Engines
Air Swirl in DI Engine
Engine Research Laboratory, IIT Kanpur
DI engines are designed so that the adequate mixing of air and fuel is enhanced by a swirling action within the combustion chamber.
Engines are designed with a specific swirl ratio typically 2.5 (swirling rotation within cylinder versus engine speed).
Swirl ratio is defined as the ratio of the air rotation speed about cylinder axis to crankshaft rotational speed.
Swirl in Diesel Engine
Air intake being directed and swirled as in enters in combustion chamber
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Engine Research Laboratory, IIT Kanpur
Types of Swirl
Induction swirl
Compression swirl
Combustion swirl
Engine Research Laboratory, IIT Kanpur
During suction stroke forcing air for rotational movement (a)
By masking one side of inlet valve (b)
By lip over one side of inlet valve (c)
Induction Swirl
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Engine Research Laboratory, IIT Kanpur
Air from periphery is forced to the centre cavity of the piston during compression
stroke.
The squishing of air is created and forced to enter tangentially in the piston cavity
when the piston reach to TDC.
Compression Swirl
Engine Research Laboratory, IIT Kanpur
Created due to partial combustion so called as a COMBUSTION INDUCED
SWIRL.
Only for pre-combustion chamber.
Combustion during delay period in pre-combustion chamber so A/F mixture
becomes rich and forces the gases with high velocity into the main combustion
chamber.
Creates high temp and provides better combustion.
Combustion Swirl (For IDI Engines only)
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Engine Research Laboratory, IIT Kanpur
Suitable for large, slow and
medium speed engines running up
to 1500 rev/min
There is sufficient time for the fuel
to be injected into the cylinder and
for it to be distributed and
thoroughly mixed with the air
charge so that combustion takes
place over the most effective crank
angle movement just before and
after TDC, without having to resort
to induction swirl and large
amounts of compression squish.
Direct Injection Open Quiescent Quadruple Valve CC
Engine Research Laboratory, IIT Kanpur
Without air swirl in the combustion-chamber there is no high hot gas velocity,
which would increase the thermal impingement on the surfaces surrounding the
chamber space. Accordingly, there will be more heat available to do useful work
so that higher brake mean effective pressures can be obtained where mixing of
the fuel and air is achieved purely by the intensity of the spray and its ability to
distribute and atomize with the surrounding air.
This is made possible by locating the injector in the center of a four valve cylinder
head and using an injector nozzle with something like 8 to 12 holes all equally
spaced and pointing radially outwards so that they are directed towards the
shallow wall of the combustion chamber
The air movement is almost quiescent (the air is inactive) and mixing depends
entirely on the discharged spray distribution and atomizing fuel particles are
therefore known as quiescent open chambers.
Direct Injection Open Quiescent Quadruple Valve CC
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Engine Research Laboratory, IIT Kanpur
The piston crown has a flat narrow annular zone inside of which is the chamber
recess,, the base of the chamber from the center to the wall has a downward dish
shape which curves up and merges with the vertical wall of the chamber. The
contour of the chamber is such that it conforms to the expanding spray formation
so that it conforms to the expanding spray formation so that fuel particles do not
normally touch the chamber surfaces.
The heat loss with this open chamber is the least compared with all other semi-
open or divide combustion chambers, which is due to its very low ratio of surface
area to volume, and thus its relative efficiency is the highest.
Generally, open quiescent combustion chambers provide good cold starting and the
lowest specific fuel consumption values relative to semi open and divided
combustion chambers.
Direct Injection Open Quiescent Quadruple Valve CC
Engine Research Laboratory, IIT Kanpur
It consists of semi-swirl induction port with an inclined centrally located injector.
It has a slightly offset bowl in the piston combustion chamber surrounded by a large annular squish zone formed between the piston crown and flat cylinder head
The incoming air enters in a tangentially and downward direction due to the valve port and seat being positioned to one side of the cylinder axis.
Air is thus forced to spiral its way down and around the cylinder as it fills the space previously occupied by the outward moving piston.
Direct Injection Semi-Open Volumetric CC Phases
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Engine Research Laboratory, IIT Kanpur
At the end of the combustion stroke the piston
reverses its direction and then commences its
compression stroke. Towards the end of the
compression stroke the bump-clearance between the
flat annular piston crown and the cylinder head
quickly decreases causing it to squeeze the swirling
air charge inwards towards the inner chamber bowl.
The air stream from all sides of the annual squish
zone flows radially inwards meeting at the center
where it is then deflected downward into the bowl. At
the bottom, the air disperses radially outward and
then upwards to the lip of the chamber wall.
Direct Injection Volumetric Combustion Chamber Phases (Compression and Injection)
Engine Research Laboratory, IIT Kanpur
The upward moving air will be met by more inwardly moving compression squish
which again pushes the air towards the center and down.
The pressure behind the discharged fuel projects it radially outwards until it strikes
the chamber wall. Some of this fuel bounces off the wall while the remainder clings
and spreads over the wall.
The completion of the fuel injection period simply increases the amount of fuel
deposited or rebounded from the chamber wall until the metered quantity of fuel
per injection has been ejected.
Direct Injection Volumetric Combustion Chamber Phases (Compression and Injection)
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Engine Research Laboratory, IIT Kanpur
As the center core of the spray moves
radially outwards from the injector nozzle,
its outer layers first become finely atomized
and then transform into clouds of vapour.
The Compressed air occupying the spaces
between the spray will have reached the
fuels ignition threshold temperature, and so
the oxygen contained in the air in the
vicinity of the fuel spray therefore reacts
with the vapour, causing ignition to occur.
Direct Injection Volumetric Combustion Chamber Phases (Ignition)
Engine Research Laboratory, IIT Kanpur
The nuclei of flames, established randomly
around the vapor clouds, then propagate
rapidly towards the bulk of the mixture
concentration near the chamber walls, the
flames are then distributed and spread
throughout the bowl due to the general air
movement within the chamber.
During expansion on the power stroke the
outward movement of the piston enables
mixing of air and fuel to continue by the
combined effect of air swirl and reversed
squish.
DI Volumetric CC (Burning and Expansion)
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Engine Research Laboratory, IIT Kanpur
Direct Injection Volumetric Combustion Chamber Illustrating Phases of Combustion
Engine Research Laboratory, IIT Kanpur
The extra air movement is achieved by
utilizing a helical or partial vortex form of
induction port passage.
The incoming air flow is given a helical twist
or semi vortex motion about the valve stem
before it passes out between the opened
valve head and its seat in a tangential
direction to the cylinder axis.
As a result, a high degree of air swirl is
generated within the curved port passage
before it is expelled into the cylinder.
Small Direct Injection Semi-Open Combustion Chamber with Helical Induction Part
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Engine Research Laboratory, IIT Kanpur
It uses a two valve cylinder head with a high swirl or vortex type induction port
with an inclined injector, which is located to one side of the cylinder axis.
The combustion chamber is a spherical cavity in the piston crown with a small
secondary recess on one side which aligns with the injector in the cylinder head to
provide access for the fuel spray discharge.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Induction)
Engine Research Laboratory, IIT Kanpur
Air from the high swirl generating induction port enters the cylinder where it is
forced to rotate about the cylinder axis in a progressive spiral fashion as the piston
moves away from the cylinder head on its induction stroke.
After the cylinder has been filled with air having a high intensity of swirl, the inlet
valve closes and the air is compressed between the cylinder head and the inwardly
moving piston crown.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Induction)
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Engine Research Laboratory, IIT Kanpur
As the piston rapidly approaches TDC, air from
the annular squish area surrounding the
chamber recess is squeezed towards the center
of the chamber, it is then forced downwards
and, at the bottom, outwards, where it then
follows the contour of the spherical chamber
wall until it again emerges at the mouth of the
chamber, where further compression squish as
the bump clearance reduces, causes the
transverse rolling movement to repeat itself.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Compression and Injection)
Engine Research Laboratory, IIT Kanpur
The transference of air from the annular squish area to the inner chamber causes
the rotational movement of the air around the cylinder to be considerably
increased as it moves into the much smaller spherical chamber.
Just before the end of the compression stroke, fuel is injected into the cylinder
from two nozzle hole set at acute angles to the chamber walls so that after the
spray penetrates the swirling air and reaches the cylinder wall, it is not reflected
but spreads over the surface in the form of a thin film.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Compression and Injection)
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Engine Research Laboratory, IIT Kanpur
The discharge of liquid spray through the hot air charge causes the surrounding air to resist partially the jet penetration so that initial outer layers of fuel partially the jet penetration so that initial outer layers of fuel particles slow down very quickly to transform into vapour.
Immediately, this vapour commences to oxidize and to ignite
5 to 10% of the total quantity of fuel discharged per cycle burns in the spray stream near the injection nozzle with the minimum of delay.
The vaporized fuel is carried away by the air stream and burns in the flame front spreading from the initial ignition zone slightly beyond the injector nozzle and very nearly in the center of the chamber.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Ignition)
Engine Research Laboratory, IIT Kanpur
The energy released by the propagating combustion in the chamber bowl causes a rapid pressure rise and simultaneously an expansion of the burning charge.
Direct Injection Semi Open Film (M-type) Combustion Chamber (Burning and Expansion)
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Engine Research Laboratory, IIT Kanpur
Direct Injection Film (M type) Combustion Chamber Illustrated Phases of Combustion
Engine Research Laboratory, IIT Kanpur
Indirect Injection Combustion Chamber
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Engine Research Laboratory, IIT Kanpur
IDI combustion chamber types Pre-combustion chamber type Swirl chamber type
Good
Excellent mixing, turbulence characteristics Can burn lower quality fuel Lower injection pressure Less pronounced knock Low noise & exhaust emissions
Bad Very high temperature/pressure in injection chamber Higher emissions, especially NOx Harder to start - glow plugs Less efficient
Indirect Injection Engines
Engine Research Laboratory, IIT Kanpur
Small Indirect-Injection Diesel Engine Combustion System
Swirl Prechamber Turbulent Prechamber
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Engine Research Laboratory, IIT Kanpur
With swirl chambers, combustion is also initiated in a separate chamber that has approx. 60% 0f the compression volume.
As soon as combustion starts, the air/fuel mixture is forced under pressure through the connecting channel into the cylinder chamber where it is turbulently mixed with the remaining air.
Swirl Chamber System
Engine Research Laboratory, IIT Kanpur
The combustion process actually takes place in a two stage divided chamber
system. Initially, combustion takes place in a spherical swirl chamber housed in
the cylinder head whereas the second half of the process is completed in the twin
disc shaped recesses in the piston crown.
The swirl chamber in the form of sphere is located to one side and above the
cylinder wall in the cylinder head.
The upper half of the sphere is cast directly in the cylinder head whereas the lower
half is a separate heat resisting nimonic alloy member flanged and cylindrical in
shape with an upward facing semi-hemispherical chamber, it fits in a machined
recess so that its underside is flush with the flat face of the cylinder head.
It is located and secured by a ball and flange while the outer cylindrical vertical
wall stands away from the machined cylinder head recess to create an isolating air
gap.
Indirect Injection Divided Chamber Swirl-Combustion Chamber
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Engine Research Laboratory, IIT Kanpur
This chamber separator is commonly known as a heat regenerative member since
it absorbs heat from combustion and dissipates it during the compression stroke.
An inclined passage through the base of the lower regenerative member forms a
throat or neck between the spherical swirl chamber and twin adjacent circular
cavities cast in the piston crown.
A pintle soft conical spray injector is positioned over the chamber at an acute
angle to the swirl chamber whereas a cold start heater plug projects horizontally
into the side of the chamber wall.
The lower regenerative member forms the lower half of the combustion chamber.
Indirect Injection Divided Chamber Swirl-Combustion Chamber
Engine Research Laboratory, IIT Kanpur
The delivery and expulsion of air and exhaust gases are provided by the inlet and exhaust valve ports.
With the indirect-injected swirl chamber method of combustion control, a high level of induction swirl is not so critical so that the intake port can be designed to cater more for improved breathing rather than the generation of high intensity induction swirl.
Air is drawn tangentially into the cylinder via the twin induction port where it then moves in a circular downward path around the cylinder wall as the piston moves away from the cylinder head.
Indirect Injection Divided Chamber Swirl Combustion Chamber (Induction)
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Engine Research Laboratory, IIT Kanpur
On the return stroke, the air change is compressed causing something like 40% of the air mass per induction stroke to be transferred through the throat of the regenerative member into the spherical swirl chamber.
The angle of the inter-linking throat passage guides the air stream tangentially into the swirl chamber so that it is forced to follow the contour of the chamber wall in a vertical circular swirl many times during the compression stroke.
As air flows through the throat passage, it absorbs heat from the hot alloy mass and from the chamber walls as it circulates around the chamber so that once combustion has been established, any fresh air entering the swirl chamber quickly attains a temperature well above the threshold ignition temperature of the liquid fuel.
Indirect Injection Divided Chamber Swirl Combustion Chamber (Compression and Injection)
Engine Research Laboratory, IIT Kanpur
When the crankshaft is of the order of 20 to 25 before TDC, fuel is injected at an acute angle in a downstream direction to the air swirl to one side of the chamber, the spray penetrates the dense air change and impinges onto the spherical surface of the regenerative member. Instantly the liquid fuel spreads out to form a thin film, which then vaporizes and is immediately swept around with the air stream.
The fuel vapour, oxygen and heat then combine to cause the oxidation reaction which is essential for ignition at random nuclei sites surrounding the vapour clouds within the swirl chamber.
Rapid flame spread follows as unburnt vapour seeks out the oxygen in the dense but rapidly rotating air charge.
Indirect Injection Divided Chamber Swirl Combustion Chamber (Ignition)
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Engine Research Laboratory, IIT Kanpur
The high burning rate produces a corresponding rapid pressure rise in the swirl chamber. As a result, the burning charge will be blown down the throat of the regenerative member, after which it divides into two separate flame fronts as they enter the twin, shallow, disc shaped recess formed in the piston crown.
The tangential entry compels the flame fronts to swirl clockwise and anticlockwise around their respective cavity walls, which gives the burning and unburnt vapour the maximum opportunity to search out the oxygen and, simultaneously, to displace the burnt products of combustion.
Indirect Injection Divided Chamber Swirl Combustion Chamber (Burning and Expansion)
Engine Research Laboratory, IIT Kanpur
Indirect Injection Swirl Combustion Chamber Illustrating Phases of Combustion
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Engine Research Laboratory, IIT Kanpur
In Pre-combustion chamber, the fuel is injected through a pintle nozzle at a low pressure (upto 450 bar)
A specially shaped baffle in the
centre of the chamber diffuses the
jet of fuel that strikes it & mixes it
thoroughly with the
Pre-combustion Chamber
Engine Research Laboratory, IIT Kanpur
This divided-chamber two-stage combustion system incorporates a heat resisting
alloy pre-combustion chamber mounted in the cylinder head slightly to one side of
the single inlet and exhaust valve seats.
The pre-combustion chamber is a two-piece cylindrical unit consisting of a large
diameter flanged section which, houses the combustion chamber and a small
diameter extended nozzle section. At the end of the enclosed nozzle are five radial
holes, which communicate with the main chamber, while the upper flanged end is
opened up to accommodate the pintle injector.
Within the cylindrical casing is a spherical chamber with a narrow parallel passage
or throat leading to the radial nozzle holes. A transverse bar with a spherical bulge
in the middle is positioned in the lower half of the spherical chamber, whereas a
cold start heater plug intersects from the side of the upper half of the chamber
wall.
Indirect Injection Divided-Chamber Pre-Combustion Chamber
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Engine Research Laboratory, IIT Kanpur
When the inlet valve opens and the piston moves away from the cylinder head, air enters the cylinder tangentially so that it rotates in a downward direction about the cylinder axis.
Once the piston has reached BDC it reverses its direction and commences to move inwards towards the cylinder head until the inlet valve closes, this then completes the induction period.
Indirect Injection Divided-Chamber Pre-Combustion Chamber (Induction)
Engine Research Laboratory, IIT Kanpur
As the piston approaches TDC, the air charge
is compressed between the cylinder head and
the piston crown so that something like 35%
to 45% of the air is forced through the five
nozzle holes which protrude below the flat
cylinder head.
Air will the n be transferred from the cylinder
in to the pre-combustion chamber via the
nozzle holes and parallel throat passage
where it is exited into a vigorous and highly
turbulent mass.
Indirect Injection Divided-Chamber Pre-Combustion Chamber (Compression and Injection)
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Engine Research Laboratory, IIT Kanpur
Towards the end of the compression stroke, fuel is discharged from the injector
towards the center of the chamber where it strikes the transverse located semi-
spherical bar.
The spray is very slightly angled so that a proportion of the spray misses the
spherical bar and reaches the base of the chamber to one side of the nozzle throat.
The liquid fuel now spreads out over the spherical bar and the mouth or throat of
the nozzle passage. Immediately, the liquid film vaporizes and is torn away from
the bar and chamber wall by the turbulent air movement.
Indirect Injection Divided-Chamber Pre-Combustion Chamber (Compression and Injection)
Engine Research Laboratory, IIT Kanpur
Oxidation then commences causing random
nuclei flame sites to form, these quickly
propagate and spread throughout the hot
dense air mass.
The resulting pressure rise created by the
burning charge reverses the direction of air
flow. The burnt and unburnt rich vapour
charge is now blown down the throat of the
nozzle where it then expands radially
outwards through the five nozzle holes into
corresponding shallow guide channels
formed in the piston crown.
Indirect Injection Divided-Chamber Pre-Combustion Chamber (Ignition)
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Engine Research Laboratory, IIT Kanpur
The thrust of combustion projects these
directional jet-like flame-fronts towards the
cylinder walls and, in doing so, sweeps the
burnt gases and soot to one side while
exposing the remaining fuel vapour to fresh
oxygen.
Indirect Injection Divided-Chamber Pre-Combustion Chamber (Burning and Expansion)
Engine Research Laboratory, IIT Kanpur
Characterization of Common Diesel Combustion systems
DirectInjection IndirectInjection
System Quiescent MediumSwirl HighSwirlM HighswirlMediumSpray
Swirlchamber Prechamber
Size Largest Medium Mediumsmaller Mediumsmall Smallest smallest
Cycle 2/4stroke 4stroke 4stroke 4stroke 4stroke 4stroke
TC/SC/NA TC/SC TC/NA TC/NA NA/TC NA/TC NA/TC
Mediumspeed(rpm)
1202100 18003500 25005000 35004300 36004800 4500
Bore,mm 900150 150100 13080 10080 9570 9570
Stroke/bore 3.51.2 1.31.0 1.20.9 1.10.9 1.10.9 1.10.9
Compressionratio
1215 1516 1618 1622 2024 2224
chamber Openorshallowdish
Bowlinpiston Deepbowlinpiston
Deepbowlinpiston
Swirlprechamber
Single/multiorificeprechamber
Airflowpattern Quiescent MediumSwirl HighSwirl Highestswirl Veryhighswirlinprechamber
VeryturbulentinPrechamber
No.ofNozzleholes
Multi Multi Single Multi Single single
Inj.Press. Veryhigh High Medium High Lowest Lowest
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Engine Research Laboratory, IIT Kanpur
Quiescent DI chamber
Multuihole nozzle DI chamber with swirl
Combustion of four sprays in DI engine with counter-clockwise swirl
Combustion of a single spray burning under large DI engine conditions
Photographs of CI Combustion Process in Different CCs
Engine Research Laboratory, IIT Kanpur
Photographs of CI Combustion Process in Different CCs
M.A.N. M DI chamber
Ricardo Comet IDI swirl chamber
Combustion of single spray in M.A.N M DI diesel
Combustion in pre-chamber(on left) and main chamber(on right) in Ricardo Comet IDI swirl chamber
diesel
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Engine Research Laboratory, IIT Kanpur
Cylinder pressure, injector needle lift and injection system fuel line pressure as functions of crank angle
Engine Research Laboratory, IIT Kanpur
Typical DI Engine Heat-release-rate Diagram Identifying Different Diesel Combustion Phases
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Engine Research Laboratory, IIT Kanpur
Cylinder pressure , rate of fuel injection and net heat release rate as functions of crank angle
During combustion process, the burning proceeds in three stages.
In the first stage, the rate of burning is very high and lasts for only a few crank angle degrees. It corresponds to the period of rapid cylinder pressure rise.
The second stage correspond to a period of gradually decreasing heat-release rate. This is the main heat-release period and lasts about 40.
The third stage corresponds to the tail of the heat release diagram in which a small but distinguishable rate of heat release persists throughout much of the expansion stroke.
Engine Research Laboratory, IIT Kanpur
A. Fuel injection across the chamber with substantial momentum. Mixing
Proceeds immediately as fuel enters the chamber and is little affected by
combustion
B. Fuel deposition on the combustion chamber walls. Negligible mixing during the
delay period due to limited evaporation. After ignition, evaporation becomes rapid
and its rate is controlled by access of the hot gases to the surface, radial mixing
being induced by radial differential centrifugal forces. Burning is therefore,
delayed by the ignition lag.
C. Fuel distributed near the wall: Mixing Proceeds during the delay, but a rate
smaller than in mechanism A. After ignition, the mixing is accelerated by the same
mechanism as in B.
Three Basic Injection, Burning, Mixing Pattern in Diesel Engines
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Engine Research Laboratory, IIT Kanpur
Schematic injection-rate and burning-rate diagrams in different types of naturally aspirated diesel combustion system
DI engine with central multihole nozzle
DI M-type engine with fuel injected on wall
IDI swirl chamber engine
Engine Research Laboratory, IIT Kanpur
Summary DI vs IDI:
IDI Higher RPM Rapid
Combustion Only works 400-800cc/cyl
(1.4 4 cyl to 6.4 ltr V8) Reduced ignition delay More swirl 5-15% fuel efficiency
penalty More complicated
combustion chamber design
May require ceramic liner in pre chambers to limit heat transfer
DI Lower RPM limited by
piston speed (flame front must keep up with piston)
Longer ignition Delay More efficient Unlimited size Injectors exposed directly
to cylinder pressures More exotic injectors
required
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Engine Research Laboratory, IIT Kanpur