TURBULENT COMBUSTION
PROCESS IN DIESEL ENGINE
MVK 135: Turbulent CombustionLund Institute of technology
Xue-Song BAI
Henrik GummessonFanny DavidJihye HwangGuillaume Becquin
http://www.made-in-china.com/image/2f0j00OCcTrbPlgDoGM/R6105C-Marine-Diesel-Engine.jpg
Cliquez sur l'icône pour ajouter une imageM is working with a big diesel engine that has open combustion chambers, direct injection and operates at 310 rpm. The engine has 26-cm bores and a 73-cm stroke, and compression ratio 16.5. M wants to know more details about how the engine works.
SUBJECT
INTRODUCTION Configurations of diesel engines and the
flow field
Typical fuels for diesel engine combustion
Features of turbulent combustion process in diesel engines
Phenomenological analysis of the combustion process in diesel engines
I. CONFIGURATIONS OF DIESEL ENGINES AND FLOW FIELD
Mean piston speed: Stroke = 0.73 m Bore = 0.26 m n=310 rpm N=310/60 L = S = 0.73 m
Sp = 2*L*N
Sp= 7.543 m/s
I. CONFIGURATIONS OF DIESEL ENGINES AND FLOW FIELD Turbulent motions in cylinder:
SwirlTumbleSquish
Turbulence intensity and swirl
Intake valve configuration and swirl
a,c,d: centered intake valveb: non centered intake valve
I. CONFIGURATIONS OF DIESEL ENGINES AND FLOW FIELD
Intake valve design and swirl
I. CONFIGURATIONS OF DIESEL ENGINES AND FLOW FIELD
Cylinder head configuration and swirl
« May Fireball »
I. CONFIGURATIONS OF DIESEL ENGINES AND FLOW FIELD
II. TYPICAL FUEL FOR DIESEL ENGINE COMBUSTION Auto-ignition time:
Factors affecting the auto ignition time:
Temperature (τ ∞ 1/T) and pressure Compression ratio (τ ↓ when rc ↑) Injection timing Concentration of oxygen Fuel composition:
Cetane number : ↑ CN → ↓ Ignition delay time
II. TYPICAL FUEL FOR DIESEL ENGINE COMBUSTION Auto-ignition time:
From The Internal Combustion Engine Fundamentals, by John B.Heywood is the mean piston speed ( ) is the temperature in the combustion chamber :
is the pressure in the combustion chamber:
is defined as:
0,63
1 1 21,217,90 12,4
( ) 0,36 0,22AE RT p
id CA Sp e
Sp 17,543 Sp ms
T
1nTC i cT T r 1,25 1298.16,5 600,603TCT K
Pn
TC i cP Pr 1,251,01325.16,5 33,695 TCP Bars
618,84025AE CN
8,595AE
( ) 1,25324 id CA ( ) 0,67378id ms ms
AE
Fuels in diesel engine:
Common diesel fuel: C10H20 to C15H28
Most used: C12H23
Mean characteristics:
II. TYPICAL FUEL FOR DIESEL ENGINE COMBUSTION
Mean range Number we keep
Cetane number 37-56 47
Dynamic viscosity 3 – 10· (Kg/m.s) 7.10-5
Density kg/m3 850
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
Different stages:
Injection of fuel
Auto-ignition
Premixed flame propagation
Diffusion flame structure
Diffusion flame propagation after the end of fuel injection
Injection of fuel
High speed injection ≈ 150m/s
Fuel sprayed in small drops
Vaporization of the fuel due to temperature and pressure conditions
Mixing of the fuel and air before auto-ignition: Large eddies in air flow: depends on bore diameter Large eddies in fuel flow: depends on the nozzle diameter Mixing time ≈ large eddy time
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
Auto ignition
Piston raises up = Temperature Pressure
Auto ignition of the premixed air/fuel mixture(propagation of the premixed flame through the rich and lean mixture)
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
Diffusion flame structure
The premixed flame reach the fuel jet = non- premixed flame appears
Stabilization around stoichiometric mixture fraction
Stabilization at the lift off distance from the injection nozzle
Mixing time >>> reaction time Burke-Schumann structure
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
Diffusion flame propagation after the fuel injection:
The flame follows the instantaneous line where Z=Zst
Quenching of the diffusion flame:Fuel concentration
Lean fuel reaction
Temperature
Quenching
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
Effect of engine speed and turbulence:
Engine speed Turbulence level
Auto ignition time
Diffusion Flame lenght
Duration of combustion
III. FEATURES OF TURBULENT COMBUSTION PROCESS IN DIESEL ENGINES
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES Air-flow:
Integral scale:
Kolmogorov scale:
Flame scales:
Ka and Da:
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
Fuel flow: Same constants than in air flow
Integral scale:
Kolmogorov scale:
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
Flame scales:
Ka and Da:
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES The structure of the flame in diesel
engine
OH radical distribution Turbulent non-premixed flame Thin zone -> Thicker zone OH zone becomes wrinkled Flame broadening by
turbulence
Regime of the combustion process
A-B: Ignition delay B-C: Premixed or rapid combustion phase C-D: Mixing-controlled combustion phase D-E: Late combustion phase
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
Factors controlling the flame temperature and emissions: Emissions: Nox, CO, unburned hydrocarbon,soot High peak temperature rapid NO formation Injection timing Wall quenching Fuel bubble falling
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
For reducing emissions: Temperature reduction Low-Nox burner Oxy/Gas combustion Reburn
Fuel injection velocity:
Flame lenght:
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
Fuel injection timing changes ignition delay time
Retarded fuel injection reduces Nox emission
Controlling injection rate:Injector area pressurefuel/air mixing rate heat release rate
CO emission:Fuel/air equivalence ratio
IV. PHENOMENOLOGICAL ANALYSIS OF THE COMBUSTION PROCESS IN DIESEL ENGINES
CONCLUSION Applied project:
Using the theories seen in lecture Formulas application Working in team Dealing with short deadline Overcome difficulties (which hypothesis; how to
find fuels features….)
Dealing with real engineering problem
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