---
title: "Gas turbine combustion chamber: requirements and types"
subject: "Turbo Machines"
chapter: 3
key: "semester_7/turbo_machines:combustion-chamber-requirements-types"
source: https://www.bctengineer.com/q/semester_7/turbo_machines/combustion-chamber-requirements-types
site: BCT Engineering
---

# Gas turbine combustion chamber: requirements and types

Turbo Machines · Chapter 3: Gas Turbine

- Asked in: year not given, 5 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/turbo_machines/combustion-chamber-requirements-types
- Whole chapter: https://www.bctengineer.com/md/semester_7/turbo_machines/chapter-3

## Question

Explain the requirements of a gas turbine combustion chamber. Describe the primary, secondary and dilution zones, and the can, annular and can-annular types. Define combustion efficiency and pressure loss factor.

## Short answer

Requirements: complete combustion, low pressure loss (2-8%), stable flame, uniform outlet temperature. Primary zone burns near stoichiometric, secondary completes combustion, dilution zone mixes air for turbine inlet temperature. Types: can, annular, can-annular. Combustion efficiency η_b = actual/ideal heat release; pressure loss factor PLF = Δp0/(m_dot^2/(2ρ2 A_m^2)).

## Answer

#### Requirements
- Complete combustion with high **combustion efficiency** over the whole operating range.
- Low total pressure loss (typically 2 to 8% of the compressor delivery pressure).
- A stable flame over a wide air-fuel ratio range, with no blow-out at altitude or during rapid throttle changes.
- Uniform outlet temperature (low "pattern factor") to protect the turbine blades.
- Reliable ignition on the ground and at altitude, small size and weight, low smoke and emissions, and long life.

#### Zones of a combustor
```text
 air in -> | primary | secondary | dilution | -> to turbine
           |  zone   |   zone    |   zone   |
 fuel -->  (burn at  (complete   (mix cool air,
            near      burning,    set outlet
            stoich)   cooling)    temperature)
```
1. **Primary zone:** about 15 to 20% of the air; burns the fuel near the stoichiometric ratio at high temperature; a swirler produces recirculation that anchors the flame.
2. **Secondary (intermediate) zone:** more air, admitted through holes, completes combustion and reduces dissociation losses.
3. **Dilution zone:** the remaining air (about 50 to 60%) reduces the gas temperature to the turbine inlet limit and evens out the temperature profile. A portion also cools the liner wall.

#### Types
| Type | Description | Use |
|---|---|---|
| Can (tubular) | Several separate cylindrical liners, each in its own casing | Early engines, industrial |
| Annular | One ring-shaped liner between the inner and outer casings | Modern aircraft; light, low pressure loss |
| Can-annular (cannular) | Separate cans arranged inside a common annular casing | Medium engines; easy to test and maintain |

#### Definitions
- **Combustion efficiency:** $\eta_b = \dfrac{\text{actual heat release}}{\text{ideal heat release}} = \dfrac{(\dot m_a + \dot m_f) h_3 - \dot m_a h_2}{\dot m_f \cdot LHV}$; 98 to 99% at design.
- **Pressure loss factor (PLF):** the stagnation pressure loss across the chamber divided by a reference dynamic head based on the maximum cross-sectional area $A_m$ of the chamber:
$$
PLF = \frac{\Delta p_0}{\dot m^2 / (2\rho_2 A_m^2)} = K_1 + K_2\left(\frac{T_{03}}{T_{02}} - 1\right)
$$
  $K_1$ represents the "cold" (friction and mixing) loss in the liner and $K_2$ the "fundamental" loss due to the momentum rise caused by heating. The overall fractional loss $\Delta p_0/p_{02}$ (2 to 8%) follows from the PLF and the flow conditions at inlet.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is the role of the primary zone?
   A. Dilute gases to turbine temperature
   B. Burn fuel near stoichiometric ratio with swirl recirculation anchoring the flame
   C. Cool the compressor air
   D. Complete expansion
   Answer: B. The primary zone gets 15-20% of air, burns near stoichiometric and swirl-induced recirculation stabilises the flame. (Key point: Zones)

2. What does the dilution zone do?
   A. Burns fuel at highest temperature
   B. Prevents flame blow-out
   C. Adds fuel
   D. Admits the remaining air to cut the gas temperature and even out the outlet profile
   Answer: D. About 50-60% of air enters here to reduce temperature to the turbine limit and give a uniform profile. (Key point: Dilution zone)

3. Which type has one ring-shaped liner between inner and outer casings?
   A. Annular
   B. Can
   C. Can-annular
   D. Tubular
   Answer: A. Annular combustors are light with low pressure loss and used on modern aircraft. (Key point: Combustor types)

4. The pressure loss factor is:
   A. Heat release over ideal heat release
   B. Fall of total pressure across the chamber as a fraction of inlet total pressure
   C. Outlet temperature over inlet temperature
   D. Air flow over fuel flow
   Answer: B. It is delta p0 / p02, caused by liner friction and the momentum rise from heating. (Key point: Pressure loss factor)

## Related in Turbo Machines

- [Actual gas turbine cycle with component efficiencies](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Aactual-brayton-cycle-numerical) — Turbo Machines, chapter 3
- [Gas turbine power from isentropic efficiency](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Agas-turbine-power-isentropic-efficiency) — Turbo Machines, chapter 1
- [Fuel-air ratio in a gas turbine combustor](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Acombustion-chamber-fuel-air-ratio-numerical) — Turbo Machines, chapter 3
- [Axial gas turbine stage design calculation](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Aaxial-turbine-stage-gas-numerical) — Turbo Machines, chapter 2
- [Gas turbine nozzle: principle and types](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Anozzle-principle-types) — Turbo Machines, chapter 4
- [Modifications of the basic gas turbine cycle](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Avariations-basic-gas-turbine-cycle) — Turbo Machines, chapter 6

## Related in other subjects

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- [Ideal gas turbine 100 kW: pressure ratio, work, efficiency](https://www.bctengineer.com/question.md?key=semester_2%2Ffundamental_of_thermodynamics_and_heat_transfer%3Aideal-gas-turbine-100kw-pressure-ratio) — Fundamental of Thermodynamics & Heat Transfer, chapter 6
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