4 combustion in-diesel_engine

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