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