The document discusses the combustion process in diesel engines. It describes the four stages of combustion: 1) ignition delay, 2) rapid uncontrolled combustion, 3) lower rate combustion, and 4) tail of combustion. It also discusses knocking in diesel engines, the rating of diesel fuels using metrics like cetane number and diesel index, and the relationship between cetane number and octane number. The critical compression ratio is defined as the minimum ratio needed for ignition under specified conditions.

1. Combustion In
Diesel Engine

2. I- Description of Combustion Process in Diesel Engine
II- The Stages of the Diesel Engine Combustion Process.
III-Knocking In Diesel Engine.
IV- Rating of Diesel Engine fuels.
V- Relation Between Cetane Number and Octane Number.
VI- Critical Composition Ratio ( C C R ).
Presentation Outline

3. Description Of Combustion
Process
A- Air alone is compressed and fuel is injection towards the
end of compression stroke.
B- Spontaneous ignition.
C- Heterogeneous combustion.
D- Combustion process study through photography and
analysis of pressure crank angle ( P – theta ) diagrams.

4. Description Of Combustion
Process

5. Combustion in C.I . Engine

6. Mechanical Engineering
Dept. Combustion and Combustion Systems

7. Combustion in C.I . Engine

8. The combustion process may be divided into the
following four stages:
1 - Ignition delay.
2 - Rapid (uncontrolled ) combustion.
-3 Lower rate combustion.
4 - Tail of combustion.
II- The stages of the combustion process

9. A- No noticeable deviation of pressure diagram.
B- Starts by fuel injection and ends by fuel ignition.
C- May be estimated by the following empirical formula :
t = 0.44 e4650/ T
P1.19
t : time in ms. P : press. in atm T : temp. in K
1 – Ignition delay ( Delay period )

10. 1- Starts by ignition.
2- Prepared fuel during delay period is rapidly
combusted.
3- Depends on the duration of the delay period.
4- Combustion is pre- mixed in this stage, and it
gives little radiation and produces little carbon.
B- Rapid uncontrolled combustion

11. Lower rate combustion-C
1- The rate of combustion falls to a value that can be
maintained by preparation of fresh fuel.
2- Combustion depends on the need for fuel to find
oxygen.
3- Combustion is party regulated by the injection
process as well as by the mixing and diffusion
process.
4- Ends by the end of fuel injection.

12. Very low rate of combustion-D
1- combustion continues at a diminishing rate.
2- As the previous stage , it is characterized by diffusion
combustion with production and combustion of carbon
particles and a high rate of heat transfer by radiation.
3- Extends along expansion stroke.

13. Typical rate of heat release diagram.

14. Knocking In Diesel Engine-III
A It has opposite causes to that occurs in petrol engine.
B It is primarily due to too long delay period.
C It is worse at high speed, low C.R., low ambient temp.,
with fuel that have resistance to ignition
( compact structure )….
D Anti-knock characteristics ( ignition quality ) is
measured by Cetane Number.

15. Rating of Diesel Engine Fuels.-IV
A Ignition quality of fuel may be measured by the diesel
index.
Diesel index = (Aniline point ) x (A.P.I. gravity )
Aniline point is the lowest temp. at which equal volumes
of diesel fuel and freshly distilled water-free aniline are
completely miscible.
B A high diesel index fuel indicates a fuel of high ignition
quality.
C Centane number is the most important indicator of diesel
fuel ignition quality, and its anti-knock characteristics.

16. )ContinuedRating of Diesel Engine fuels (-IV
D Cetane number is considered
100 for cetane (Hexadecane C16 H34 ),
and zero for (alpha-methyl-naphthalene C11H10 )
E Hexadecane is very fast ignition fuel, and alpha-methyl-
naphthalene is a very slow ignition fuel.
F The Cetane number is measured by testing the unknown
fuel in a variable compression ratio co-operative fuel
research engine (C.F.R. engine)

17. IV- Rating of Diesel Engine Fuels (continued)
G The conditions of C.F.R. engine during the Cetane number test:
Engine speed 900 rpm
Jacket water temp. 100o C
Inlet air temp. 65.5o C
Injection timing 13o BTDC
Ignition delay period 13o

18. )continuedRating of Diesel Engine Fuels (-VI
H For the unknown fuel of Cetane number C, the engine
run and the C.R. is varied until ignition delay is 13o, the
C.R. is recorded R.
I The experiment is repeated for two reference fuels of
known cetane number C1 & C2 and the C.R. R1 & R2 are
noted for a delay period of 13o .
J
The Cetane number of the unknown fuel may be
determined as follows :
C =C1 + { C2 – C1 } (R - R1 )
R2 - R1
R1 < R2 & C1 > C2

19. Relation between Cetane Number-V
and Octane Number
- Octane number = 120 - 2 x Cetane Number.
- Cetane number = 60 - 0.5 x Octane Number.
- This linear relation is accurate within + 5 %

20. )Critical Compression Ratio (C.C.R-VI
A- It is defined as the minimum compression ratio
at which the ignition of the fuel in C.F.R. engine
under specified condition is obtained.
B- Critical composition ratio is sometimes used as
a measure of the ignition quality of the fuel.

21. Thank you
Prof. Dr . Mahmoud A. El Kady