Combustion Chambers types and details

1. INTERNAL COMBUSTION ENGINES-II CI Combustion Chambers
University of Petroleum & Energy Studies
Dehradun

2. I C ENGINES – II : CI Combustion Chambers
CI combustion chamber :
- provide proper mixing of fuel and air in short time
- An organized air movement ;
swirl, turbulence,squish
- produce high relative velocity between fuel droplets and air
- Shape of combustion chamber control air motion
- CI engines classified as ;
Direct- Injection (DI) & Indirect- Injection (IDI)

3. I C ENGINES – II : CI Combustion Chambers
Direct- Injection (DI)
- entire volume of combustion chamber located in
main cylinder where fuel is injected. Also called
open combustion chamber.
Indirect- Injection (IDI)
- Combustion space divided into two parts ;
• one part main cylinder
• other part in cylinder head

4. I C ENGINES – II : CI Combustion Chambers
 Indirect- Injection (IDI)
- Classified as :
1. Swirl chamber ;
compression swirl generated
2. Precombustion chamber ;
combustion swirl induced
3. Air cell chamber ;
compression & combustion swirl induced

5. I C ENGINES – II : CI Combustion Chambers
 Direct- Injection (DI) Chambers
- open comb. Chamber, single cavity w/o
restrictions
- no large press. difference within the chamber
- induction swirl obtained by intake; passage,
valves or ports
- chambers consists of space between a flat
cylinder head and a cavity in piston crown
- fuel injected with multihole injectors at high pres

6. I C ENGINES – II : CI Combustion Chambers
Direct- Injection (DI) Chambers
Some of the Open Combustion Chamber Designs

7. I C ENGINES – II : CI Combustion Chambers
 Direct- Injection (DI) Chambers
- Shallow Depth Chambers: depth of cavity in piston is
quite small, usually adopted to low speed - large
engine,cavity dia. being very large squish is negligible.
- Hemispherical Chamber: depth to diameter ratio can
be varied to give desired squish which is generally
small.
- Cylindrical Chamber: modification of cylindrical
chamber in the form of a truncated cone with base

8. I C ENGINES – II : CI Combustion Chambers
Direct- Injection (DI) Chambers
angle of 30º. The swirl produced by masking the
intake valve for nearly 180º of circumference. Squish
can be varied by varying the depth.
- Toroidal Chamber: This shape provides a powerful
squish along with the air movement. Mask needed on
inlet valve is small providing spray cone angle of 150º
to 160º with better air utilization.

9. I C ENGINES – II : CI Combustion Chambers
Direct- Injection (DI) Chambers
Advantages :
-Minimum heat loss during compression because of lower
surface area to volume ratio and hence better efficiency.
- No cold start problems.
- Fine atomization because of multihole nozzles
Drawbacks :
- Complex design of fuel injection pump due to high fuel injection
pressure requirements
- Necessity of accurate metering of fuel by injection system , particularly for small engines

10. I C ENGINES – II : CI Combustion Chambers
Indirect- Injection (IDI) Chambers
- A divided combustion chamber space in two or more distinct compartments connected by restricted passages.
- During combustion, considerable pressure differences are created between the compartments.

11. I C ENGINES – II : CI Combustion Chambers
Indirect- Injection (IDI) Chambers
- Swirl Chamber: It is a spherical-shaped chamber
separated from cylinder and located in the
cylinder head as shown

12. I C ENGINES – II : CI Combustion Chambers
- About 50 % air is transferred during compression
stroke into the swirl chamber
- A throat connects the chamber to the cylinder
tangentially so that air gets strong rotary movement
inside the swirl chamber. After combustion the
products rush back into cylinder through same throat
at much higher velocity.
- The heat loss to the wall of passage is high
- applications; poor fuel quality, reliability under
adverse conditions

13. I C ENGINES – II : CI Combustion Chambers
- Precombustion Chamber: A typical precombustion
chamber consists of an antichamber connected to
main chamber through a number of small holes is as
shown :

14. I C ENGINES – II : CI Combustion Chambers
- The precombustion chamber located in cylinderhead
accounts for 40 % volume of total combustion space
- During compression piston forces air into precomb.
chamber, fuel injected and combustion initiated in it
-The flaming droplets together with air & combustion
products rush into main chamber at high velocity
through the holes
-Thus it creates turbulence and distribution of flaming
droplets all over the main chamber where bulk of
combustion take place amounting to about 80%
release of energy

15. I C ENGINES – II : CI Combustion Chambers
- The rate of press. rise and max. press. are lower
than the open type chambers
- Initial shock of combustion limited to prechamber
and because of high temp. it has multi-fuel capability
w/o modification in injection system.
-Air-Cell Chamber : The clearence volume is divided
into the main and the other called the energy cell
which is further divided into two parts; major & minor
connected to each other & main chamber by orifices

16. I C ENGINES – II : CI Combustion Chambers
Air-Cell Chamber :

17. I C ENGINES – II : CI Combustion Chambers
- A pintle type of nozzle injects fuel across main chamber towards the energy (air ) cell.
- During compression, press. in main is higher than
energy cell due to restricted passage. At TDC, air will
be forced into the cell and fuel injection also begins
-Combustion initially begins in main where temp. is
high but rate of burning low due to absence of air
motion. In energy cell fuel is well mixed with air and
high pressure forces hot burning gases blow out in
main .
-The high velocity jet produces swirling motion in main thereby
thoroughly mixes fuel with air resulting in complete combustion

18. I C ENGINES – II : CI Combustion Chambers
- Design is not suitable for variable speeds due to
combustion induced swirl .
- Energy cell is designed to run hot to reduce ignition lag.
Advantages :
- Low injection pressure requirements
- Injection spray direction is not important
Drawbacks :
- Poor cold starting performance require heater plugs
- High specific fuel consumption because of pressure loss due to air
motion through the ducts and heat loss due to large heat transfer
area.

19. I C ENGINES – II : CI Combustion Chambers
Methods of Mixture Formation in DI Engines
Volumetric Method
- Fuel injected directly into combustion chamber space
- Fuel composition is non-uniform distribution in spray
- Macro and Micro mixing attained using;
- Energy of fuel jet (atomization)
- Energy of moving air charge (swirl)

20. I C ENGINES – II : CI Combustion Chambers
- Drop in load or speed reduces fuel delivery per cycle
and also the atomizing energy
- Leads to poorer combustion & higher fuel consumption
- It may be noted that when mixture is formed in DI engines with combustion chamber in piston, some of the fuel gets onto the chamber walls
•

21. I C ENGINES – II : CI Combustion Chambers
Film Method of Mixture Formation
- Underlying idea is to allow the minimum amount of fuel to evaporate and mix with air during ignition delay
- With this aim the fuel is directed to the wall of Combustion chamber at an acute angle so that the droplets are not reflected but spread over the surface in the form of thin film

22. I C ENGINES – II : CI Combustion Chambers
Film Method of Mixture Formation
- Injection pressure should be sufficiently high for
# film to be formed rapidly, and
# fine droplets and fuel vapors formed move towards
hottest place – centre of chamber where mixture
ignites and burns
- Heat needed to evaporate fuel is supplied by piston
- Intensive motion of air promote rapid evaporation of fuel film and carries away the vaporized fuel

23. I C ENGINES – II : CI Combustion Chambers
Film Method of Mixture Formation
- Improved performance ;
•minimum SFC lower
•high bmep (air utilization),
•high power with lower Pmax and Rate of Press. Rise ( smooth engine operation),
• wider range of fuels including gasoline may be
used
- Such a combustion ( M- process ) employed in
MAN combustion chamber

24. I C ENGINES – II : CI Combustion Chambers
MAN Type Combustion Chamber
- Combustion Chamber developed for small high
speed engine
- Direct injection with single-hole nozzle, in spherical
bowl-in-piston chamber with high swirl
- It differs DI open comb. chambers in respect to ;
fuel spray impinges tangentially and spreads over
the surface of spherical space in piston

25. I C ENGINES – II : CI Combustion Chambers
MAN Type Combustion Chamber
- Basic theory of MAN system is that ;
# enough spray will ignite before impingement so that
delay remains normal while most of spray evaporate
prior to combustion
# Thus second stage of combustion is slowed down
avoiding excessive rate of pressure rise
# Shrouded inlet valve used to give air swirl

26. I C ENGINES – II : CI Combustion Chambers
MAN Type Combustion Chamber
Advantages
- Low peak pressure
- Low rate of pressure rise
- Low smoke
Disadvantages
- Low volumetric efficiency
- Cold starting ( piston surface temp. )
- High HC emissions at starting

27. IC ENGINES-II
Course Outlines ADEG-222 LTP-3 1 1
I: BASIC THEORY
II: FUEL INJECTION SYSTEM
III: AIR MOTION, COBUSTION & COMBUSTION CHAMBERS
IV: SUPERCHARGING and TUBOCHARGING
V: DIESEL ENGINE TESTING & PERFORMAMCE