UNIVERSITY OF WEST BOHEMIAFACULTY OF MECHANICAL ENGINEERING

DEPARTMENT OF POWER SYSTEM ENGINEERING

JET ENGINESJET ENGINES

COMBUSTION CHAMBERSCOMBUSTION CHAMBERS

INTRODUCTION

PURPOSE● In combustion chamber provides conversion of fuel chemical

energy to heat energy

● The combustion chamber has the difficult task of burning large quantities of fuel, supplied through the fuel spray nozzles, with extensive volumes of air, supplied by the compressor, and releasing the heat in such a manner that the air is expanded and accelerated to give a smooth stream of uniformly heated gas at all conditions required by the turbine. This task must be accomplished with the minimum loss in pressure and with the maximum heat release for the limited space available

INTRODUCTION

REQUIREMENTS● Easy and safety mixture ignition in every

working conditions● Stable mixture burning in every engine mode● Uniform pressure and velocity field in outlet● Low hydraulic losses● Short length of flame

INTRODUCTION

MAIN PROBLEMS● Very hight heat load of combustion area● High heat dilatation● Very high combustion temperature ( up to

2000K )● Problematic ignition● Stability of burning

MAIN CONSTRUCTION

COMBUSTION PROCESS

● Air from compressor enters the combustion chamber at a velocity approximately 100-150 m.s-1

● At first air is apportioned in CC snout to:● Primary flow (20-40% of air)

● Secondary flow (60-80% of air)

● In primary flow provides a fuel burning and dilution

● This velocity of inlet air from compressor is far too high for combustion and it is necessary to decelerate it

● Deceleration is provided by swirl vanes and flare

● Air is decelerated to speed of burning which is around 15-20 m.s-1

● In primary zone is air mixed with fuel from spray nozzle and it is ignited by electric spark. Temperature in core of burning achieve 1800-2000 °C.

● Air from secondary flow enter through holes and cool the flame tube

● In dilution zone air from secondary stabilize and make uniform the outlet flow

COMBUSTION PROCESS

Fig. Combustion process in p-V and T-s diagram

PARAMETERS

Fig. Evolution of parameters through CC

APPORTIONING OF AIR

Primaryflow

Secondaryflow

Fig. Apportioning of air in CC

FLAME STABILIZING

Fig. Flame stabilizing in CC

HEAT INLET TO CC

● Burning – chemical proces ( severe oxidation )● Exothermically reaction – release of heat● Condition of burning – it's necessary two

components● Fuel ( JET A-1, PL – 7)

– Oil-based hydrocarbon compound ( 86% C + 14% H2)

● Oxygen ( O2 is 23,3% of air)

HEAT INLET TO CC

● Types of burning● Ideal burning

● C+O2 = CO

2 + heat

● H2+1/2*O

2 = H

2O + heat

● Non-ideal burning● 2C+O

2 → 2CO

2 + heat

● 2H2+O

2 → 2H

2O + heat

HEAT INLET TO CC

● Qualitatively ( from molecular weight):

12kg C + 32kg.O2 →44kg.O

2 + heat

1kg C + 8/3kg.O2 →11/3kg.CO

2 + 33.106 [J]

2kg H2+16kg.O

2 → 18kg.H

2O + heat

1kg.H2+8kg.O

2 → 9kg.H

2O + 121.106 [J]

NECESSARY OXYGEN/AIR

● Necessary oxygen for burning of 1kg fuel:

mO2=8mH+8/3mC

mO2=8*0,14+8/3*0,86

mO2=3,14 kg O

2

● Assumption: O2 is 23,2% of air

mAIR

=mO2/0,232=14,68 kg AIR = l

0

l0 - theoretical quantity of air for burning of 1kg

hydrocarbon fuel

NECESSARY OXYGEN/AIR

● Of course l0 is not enough, because temperature of gases is too high and its

necessary to mix with cooler air. Its mean that is necessary provide α*l0 air

for burning of 1kg of fuel

Qv – air flow through CC [kg.s-1]

Qf – fuel flow through CC [kg.s-1]

α – coefficient of air overflow [1] (3,5 – 4,5)

l0 – theoretical quantity of air for burning of 1kg hydrocarbon fuel

Q v=Q f l0

BASIC PARAMETERS

α – coefficient of air overflow

=real quantity of air for burning of 1 kg of fuel l

theoretical quantity of air for burning of 1 kg of fuel l0

BASIC PARAMETERS

● Heat (calorific) value of fuel Hu

● Define heat properties of fuel● Define a quantity of heat at ideal fuel burn● For PL-6 – 43123 [kJ.kg-1]

● Heat (calorific) value of mixture Hum

H um=H u

1 l 0

BASIC PARAMETERS

● Absolute pressure losses

● Burning efficiency

CC=p3T

p2T

[1]

b=real heat release during burning

theoretical heat release during burning

BASIC PARAMETERS

● Quantum of released head

● Equation of energy conservation

q=bH u

q=i 3gc3

2

2 1 l0−i 2ac2

2

2 l 0

CONSTRUTION TYPES

● Multiple● Annular● Turbo-annular (combined) ● Pooled

Multiple Annular Combined

MULTIPLE CONSTRUCTION

MULTIPLE CONSTRUCTION

Multiple combustion chamber - VK-1

ANNULAR CONSTRUCTION

ANNULAR CONSTRUCTION

Annular combustion chamber - R-29B-300

TURBO-ANNULAR CONSTRUCTION

TURBO-ANNULAR CONSTRUCTION

Turbo-annular combustion chamber - R11F-300

POOLED CONSTRUCTION

REFERENCES

● Otis, Vosbury: Aircraft gas turbine powerplants – Jeppesen: 2002

● Rolls royce – The jet engine, 1996● Hanus D., Maršálek J, : Studijní modul 15,

Turbínový motor, CERM, s.r.o. Brno 2004● Kadrnožka J.: Tepelné turbíny a

turbokompresory, CERM, s.r.o. Brno 2004

DISCUSSION...

...QUESTIONS