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mcl721-32 (1).ppt
1. Gasoline Direct Injection Engines
P M V Subbarao
Professor
Mechanical Engineering Department
Next Generation Eco-friendly SI Engines….
2. Operating modes of the GDI engine
Superior output mode
• Injection in late intake stroke
• Wider spray with high penetration for charge homogenization
A/F – Stoichiometric
Homogeneous A-F Mixture
Complete Vaporization of Fuel
Ultra Lean combustion mode
• Very lean stratified mixture : A/F ~ 30
• Injection during compression
• Compact spray, deflected from the piston top to the spark plug
• Distinct Stratification
• At spark , ignitable mixture conditions
It is two engines in one place
3. Challenges in developing GDI Engine
• The fuel injection to the cylinder should meet two
requirements.
• First one, it should enable the homogeneous charge burning.
• Secondly, It should also enable obtaining a lean mixtures close
to cylinder walls.
• The injection system must allow for any quantitative and
qualitative formation of the charge and affect the way it is later
burnt.
• The macroscopic characteristic of fuel injection spray for SI
DI engines like penetration and spray angle are crucial for the
correct operation of the injection system.
4. Geometry of Cylinder &In-cylinder Flow
• Carburetor Era : Flat piston & Flat Cylinder --- Wedge shaped
cylinder with flat piston.
• SPI & MPI Era : Wedge shaped cylinder head --- special
manifold for generation more turbulence – Optimized location
of spark plug.
• GDI Era : To design entire cylinder, piston and manifold
geometry using computational and experimental fluid
mechanics.
• More the use of Fluid Mechanics, the better will be the
engine.
• Three dimensional turbulent flow simulation will be
culmination of IC Engine Development.
5. Challenging Fluid Mechanics of Fuel Admission
Driving
Pressure
Technology of Fuel Admission
Carburetor : 20 – 50 Pa
Single Point Injection 2 – 3 bar
Multi Poin Injection : ~ 5 bar
GDI : 50 – 100 bar
6. Fluid Mechanics of Fuel Admission
Droplet
size
Technology of Fuel Admission
Carburetor : 1 ~ 3 mm
Single Point Injection 100 – 300mm
Multi Poin Injection : ~ 200mm
GDI : 20 – 50 mm
8. Expected Good Side Effects in GDI Engine
• High Compression ratio
• Precise control over Air/Fuel distribution inside the
combustion chamber
• Improved volumetric efficiency
9. New Knowledge to Develop GDI Engines
• Understand the behaviour of GDI engines under different
operating and design conditions.
• Generation of Optimal GDI configurations.
• Study of homogeneous & stratified charge formation for
each geometry.
• Effect of Geometrical and Spray Parameters
(a) Injector location,
(b) Spray orientation,
(c) Injection timing,
(d) Droplet diameter,
(e) Spray cone angle,
(f) Type of spray,
(g) Fuel temperature
10. Experimental Development
• A special purpose test rig was developed in IC engine
laboratory of Mechanical Engineering Department, IIT
Delhi, to investigate the characteristics of GDI engines.
• A four stroke engine of Kawasaki Bajaj two wheeler is
modified to work as GDI engine.
• A mechanical driven petrol injector is placed in the
cylinder head.
• Pistons with various geometries of cavities (Cylindrical,
Conical & Spherical) are tested using a compression ratio
of 9.3 at various speeds.
• Following preliminary results are obtained.
11.
12. Performance of SI Engine with Inector
0.6
0.7
0.8
0.9
1
1.1
2750 2800 2850 2900 2950 3000 3050 3100
Speed, RPM
BSFC,
kg/kWhr
Carburetor
Injector 1
Injector 2
23. Fuel Injection System in GDI Engines
• Currently the most widely used
injector for GDI applications, is the
single-fluid, swirl-type unit.
• This uses an inwardly opening pintle,
a single exit orifice and a fuel
pressure, in the range of 70-100 bar.
• The liquid emerges from the single
discharge orifice as an annular sheet
that spreads radially outward to form
an initially hollow-cone spray.
• Pressure energy is transformed into
rotational momentum that enhances
atomization.
24. Fuel Injection System in GDI Engines
• The initial spray angle ranges between
25°-150° and the
• Sauter Mean Diameter (SMD) varies
from 14-23 μm.
• Surface roughness may, however,
produce streams of fuel in the fuel sheet,
resulting in formation of pockets of
locally rich mixture.
• The spray has a leading edge that
penetrates away from the nozzle tip for
about 50mm in less then 20ms.
A Toroidal vortex is also attached to the periphery.
The leading edge of the spray contains a separate sac
spray.
25. Injection and Atomization models
• Nagaoka’s approach treats the liquid jet exiting the injector
as a liquid sheet till it reaches its breakup length.
• The sheet is analyzed discretizing its volume in small
quantities and applying to them the momentum
conservation equation:
ug is the velocity vector related to the gas
uf is the velocity vector related to the liquid sheet.
Subscript n refers to the sheet normal directions.
26. Breakup Length of Fuel Sheet
• A sheet of liquid floating in a turbulent gas medium is
highly unstable and picks and gets infected by several
fluctuating flow variables.
• An infected sheet will show symptoms of pressure waves.
• The ratio (F) between the amplitude of these pressure
waves that arise in viscous flow over those in a unviscous
flow is measure of damping generated by the viscosity.
• The breakup is inversely proportional to the thickness of
the liquid sheet (hf).
27. Design Variables to Control Breakup Length
• K0 represents the sheet thickness variation,
• L the distance from the injector
• θ is the angle respect to the injector axis.
• h0 represents the sheet thickness at the exit of the injector.
• w0 represents the characteristic length so it was put equal
to the nozzle diameter, d0.
• We : Weber Number
28. Viscous Damping factor : F
• F is the ratio between the amplitude of the pressure waves
that arise in viscous flow over those in a inviscid flow.
• F is evaluated as follows:
29. Two Level Breakup Model : Primary Breakup
• The interaction between the two phases leads to primary
breakup of liquid sheet into ligaments of characteristic
size dL on the surface of the conical sheet:
30. Two Level Breakup Model : Secondary Breakup
• These ligaments detach as droplets of diameter dD
• There exist a relation between these droplets and the
ligament size:
OhL is the Ohnesorge number of the ligament
dD is proportional to the characteristic size to be used in
the Rosin-Rammler distribution function to get size
distribution of droplets.
Usually for internal combustion engines applications 1.5
<q< 4. C1 is an empirical factor, generally equal to 1.
34. Model of the turbulent flame speed, ST
Turbulence Intensity
L
dx
u
L
u O
2
1
u
ST
4
1
2
1
Pr
Re
1
Da
A
S
S T
L
T
35. Empirical Correlations to Select Combustion Parameters
p
T
p
T
S
T
p
S ref
ref
p
L
flamelet
p
L
flamelet
298
,
, ,
,
T in K & p in atm.
f f f
SL0
36.
37. Heywood Model : Effect of equivalence ratio
2
, , m
m
p
L
flamelet B
B
T
p
S f
f
f
1
8
.
0
18
.
2
f
1
22
.
0
16
.
0
f
