E.A.Gritsenko, Yu.I.Tsybizov

JSC N.D.Kuznetsov STC, 2a S.Laso Street,

443026, Samara, Russia

Current trends in development of aircraft gas turbine engines and industrial gas turbines call forth the development of engine structure featuring high parameter thermodynamic cycle, long service life and operational reliability. The problem of such highly efficient engine development becomes more complicated due to aggravated requirements to environment protection from noxious substance (NS) emission of hydrocarbon fuel combustion products. More than 50-year experience of advanced aerospace technology samples successful development, as well as experience of converted industrial gas turbines application to drive gas pumping units and power generators accumulated at JSC N.D.Kuznetsov STC Design Bureau and generalized in NK-family engines allow to formulate methodology of developing highly efficient engine, its main components and low-emission combustion chamber (CC) in particular.

Priorities here are set as follows:

1. Environment. 2. Efficiency. 3. Operational effectiveness (Triad 3E).

Environmental protection from NS emission resulted from fuel combustion is considered to be the most important task challenging the developer of all neat engines without any exception.

Ecological aspects should dominate even over efficiency owing to great responsibility before animate/inanimate nature. In this connection it is necessary to improve combustion process in multistage CC layout. Highly efficient mixing of lean mixture (homogenization); main mixture combustion at 1800^oK or lower temperature, turbulent pulsation's lowering and combustion high efficiently provision determine the nature of this improved process.

Alternative fuels impact on combustion chamber performances and environment is also investigated. Besides, special attention is paid to operational effectiveness items and namely to elimination of defects revealed during operation including long operating time. These defects elimination as well as new technologies application (for example, cooling systems improvement, thick thermobarrier coatings (up to 600 m +) introduction, ceramics application, etc.) make the essence of the Combustion Chamber design and technological process development. Methodology main aspect consists in outstripping investigations of combustion chamber separate components development in special currently in use and newly developed test rigs of the enterprise. While doing this one shall make maximum use of well-proven and universally recognized scientific and technical solutions and structures. This concert was formulated under the influence of the following:

• absence at present of both a completed theory of combustion and analysis of combustor and its separate elements (similar to bladed machines analysis methods) which results in existence of individual concepts of CC development in most leading design bureaus;
• some lag of industry experimental base at the present stage;
• nonavailability of general conclusion on ecological characteristics;
• acute shortage of funding.

Thus, CC component and part development presents methodology base and is aimed at reducing development time and providing CC high level performance in operating conditions.

The experience shows that such an approach to CC design and development allows 40% reduction of time and money required for the final CC development as installed into the engine. JSC N.D. Kuznetsov STC uses the following conventional test rigs for component and part development:

1. Test rig for atomization and fuel-with-air mixing processes development.
2. Test rig for development of combustion efficiency in CC models.
3. Test rig for temperature field development.
4. Water channel and pneumatic channel for aerodynamic characteristics optimization.
5. Test rig for measurement of CC gas–air and flame tube passages flow characteristics.
6. Altitude test rigs simulating engine start at 10 km altitude and ignition at 12 km altitude.

Thrust measurement through weighing technique allowed defining with high accuracy not only combustion completeness but also optimum fuel distribution among contours. Control of air pressure drop on the walls of each CC using a special test rig provides the required cooling air flow across turbine blades, and the introduced technique of measuring corrected air flow through flame tube elements allows to control CC manufacture quality and to provide its characteristics stability.

Conversion of highly efficient NK–321 and NK–93 engines for ground application as a gas–pumping unit with low emission CC and as a power generator drive (NK–36ST, NK–38ST and NK–37–1 GT) caused the problem of preventing flash back and fuel air mixture (FAM) spontaneous ignition in burners fuel mixing zone at compressor pressure ratio p _c > 20.

To investigate this problem a special combustor module is developed which parameters of combustion process. Air-bleed is performed from NK-38ST HP compressor. This test section structure includes:

1. A blower- NK-38ST gas turbine where air-bleed is performed aft high-pressure compressor by air supplies and discharge elements.
2. The section itself - a cylindrical pipe.
3. A full-scale module of a separate flame tube with fuel supply and igniter plug.
4. Conical gas manifold and water-cooled nozzle.
5. An exhaust ejector with instrumentation elements and a sampler for a gas analyzer.
6. Fuel and air measurement, control and regulation system.

The problem of FAM flash back and spontaneous ignition in burners for zone burner development. Complicated hydraulic flow pattern is typical for 2-zone combustion chamber. In the process of these combustion chamber designing we came across the following fact: current techniques of flow hydraulic design are hardly useful in this case due to 3-dimensional effects unpredictability. In this connection much attention was paid to flow visualization (as in Rolls Royce). Complicated flow pattern special features are studied in flow channel and transparent models with proper quantitative estimation.

Before full-scale structure testing in the engine, fill-scale combustion chamber prototypes are developed in terms of combustion process parameters and reliability in special test rigs and reliability in special test rigs and facilities such as:

1. Strength development test rigs for:

• static and repeated static tests;
• vibration tests;
• thermocyclic tests;
• holographic investigations of combustion chamber element vibration mode and frequency.

2. High- pressure compressor test rig for combustion chamber development and measurement

of the following parameters:

• turbine inlet temperature field;
• combustion chamber outlet total pressure fields;
• combustion chamber element thermal state;
• lean mixture flameout limits.

3. Gas generator envisaging additional efforts on strain-gauging and environmental aspect at

take-off and cruise regimes.

Combustion chamber component development is performed practically at all engine-operating conditions. Endurance test, temperature, emission, vibration state, safety margin and other measurements are performed at the final stage of CC development as installed into the engine.

Our Design Bureau was the first to design multi–burner combustion chamber for subsonic (NK–8–2Y, NK–86, NK–86MA) and supersonic (NK–144, NK–321) aircraft engines burning kerosene and multi–burner combustion chamber for NK–88, NK–89 engines burning cryogenic fuel (hydrogen) and liquefied natural gas correspondingly. These NK family engine combustion chambers feature:

• high combustion efficiency;
• improved hydraulic characteristics;
• improved starting characteristics and combustion stability;
• low temperatures of combustion chamber walls;
• compliance with environmental regulations.

NK–86 engine multi-burner combustion chamber developed in this way was given "Certificate of compliance with pollutant emission requirements”. Implementation of the accumulated experience into multi-burner CC of NK–93 new generation by-pass turbofan engine afforded not only meeting advanced 2000 ICAO standards in this engine but also bringing this engine into the first row of currently existing and newly-developed engines. NK–93 NO_x emission is 28 g/ kN per takeoff-landing cycle, which is much lower that that of such foreign engines as CFM–56 and PW–2500.

Our experience of aircraft engines conversion into industrial gas turbines and for operation with cryogenic fuels shows the existing limits of adopting multi–burner principle of combustion organization with minimum additional work. This refers to gas turbines with p _c£ 13. NK-18ST multi-burner CC which is in service operation now has been manufactured according to this principle.

Two-zones annular combustion chamber allowing to meet NOx emission (£ 150 mg/Nm³⁾ GOST requirement has been optimized in NK-36ST (p _c=24) GT (converted NK-321 gas turbine engine) and introduced into serial production by present time.

Particular attention is given to requirements pertaining to operation service and technological efficiency .In this connection two-zones combustion chamber with separate flame tubes has been designed and pit in operation.

We set a task to lower NOx & CO emission levels down to £ 50mg/Nm^3. We plan to solve the task through further upgrading of operating process and development of combustor automatic control system and ceramic combustion chamber.

Thus combustion chamber development methodology which has been practically proven, makes it possible to provide the new quality of NK family engines low emission combustion chambers used in both aircraft engines and industrial gas turbines

E.A.Gritsenko, General Director – General Designer; Research-Technological Company of N.D.Kuznetsov’s name; Dr., Prof., Academician (Full Member of Academy of Aviation and Aeronautics Sciences); he scientific interests are the area of aviation and aerospace technics.

Yu.I.Tsybizov, Head of Department; Research-Technological Company of N.D.Kuznetsov’s name; Dr., Prof.; scientific interests are the area of aviation technics.