Diffusion flame combustor test results are presented for methane firing in steam/air mixtures containing up to 20% steam. The tests were conducted at atmospheric pressure with combustor inlet temperatures up to 700K. Steam and air were fully premixed before combustion. Combustion efficiency and NOX levels were measured. The well-known Θ loading parameter was modified by replacing the combustor inlet temperature with the flame temperature. The flame temperature was defined as the stoichiometric temperature of the steam/air mixture. The combustion efficiency obtained with and without steam correlated nicely with this modified loading parameter. Calculated NOX levels agreed well with the measurements, where NOX was predicted using the flamelet technique. This approach makes it possible to predict combustor efficiencies with steam by using combustor performance data taken without steam. Preliminary design analyses of gas turbine cycles with significant steam addition can now easily include the impact of the steam on combustor performance.

Modern concepts for reducing thermal NO emissions require the use of very lean fuel/air mixtures. Therefore a problem of lean quench should be solved during design process of gas turbine combustor and it’s operational development. Since maintenance of flame stability for wide range of gas turbine engine operational modes is essential, therefore there is a great demand for models which are able to predict lean blow out limits of turbulent, premixed and partially premixed, aerodynamically stabilized flames. In this paper a model describing flame destabilization process is presented. This model takes into account various physical processes, which lead to flame destabilization. The model is based on equation for reaction progress variable. An expression of source term of this equation contains turbulent flame speed, which is calculated with the use of Zimont’s formula modification, proposed by authors. The results of simulation were compared with test results for our lean premixed combustor. Fuel mass flow rate of pilot zone was decreased during test until heat release of pilot flame front became insufficient and couldn’t support a combustion process in a lean premixed zone. Our simulation with modified model allows to get prediction of lean blowout limit.

Calculations of NOx emissions were made for the original high pressure combustor and for the original and a modified design of the low pressure combustor used in a Compressed Air Energy Storage (CAES) plant. All were typical diffusion flame combustors. Since a CAES plant has an independent air supply, the relationship between combustor inlet temperature and pressure is not typical for gas turbines, and the pressure level for the HP combustor is unusually high (up to 4.5 MPa). Vitiated air from HP combustor exhaust is used as combustion air in the LP combustor. The NOx emissions prediction method, which was used, for calculations is based on a flamelet model which takes detailed kinetic schemes for fuel oxidation, NOx generation and turbulence/chemistry interaction into account. Site measurements over the entire load curve confirmed the numerical predictions for both the original combustors and the newly developed LP combustor design.

Laminar flamelet models have demonstrated good quality predictions of NOx emission from diffusion flame type combustors. In this paper, the NOx formation process is analyzed by using a flamelet model and 3D flow calculations to take a virtual look inside a combustor. The main phenomena affecting NOx emission are turbulent mixing and the turbulence-chemistry interaction. Local scalar dissipation is the main parameter responsible for the turbulence-chemistry interaction within the flamelet model. At the same time, scalar dissipation is also related to the mixing process. On one hand, higher values of scalar dissipation correspond to higher fuel consumption rates, which decrease the volume of the high temperature zones. On the other hand, higher values of scalar dissipation lead to higher NOx formation rates. Unfortunately, scalar dissipation is not commonly used by combustion engineers because of the difficulty of the clear physical interpretation of this variable and its relationship with the usual parameters. In this paper, the influence of several design features, such as primary zone equivalence ratio and air flow distribution along the liner, is studied relative to scalar dissipation distributions in the combustion zones and to NOx formation. A real industrial diffusion flame combustor is used as an example, and the results can provide a better understanding of real combustor processes. The NOx prediction results are in reasonable agreement with test data.

The investigation of local and spatial flow field features in the lean premixed propane/air flame with flashback happening continuously has been made. LDV measurements were supplemented with pressure and flame position measurements, flow and flame front structure visualizations. Two flow duct configurations with different inletioutlet conditions have been investigated.(configuration "B").