This study conducted during the summers of 2000 and 2001 represents the first measurement and model intercomparison that tracks detailed gaseous and aerosol emissions through a gas turbine engine. Its primary objective was to determine the impacts of engine operational state on the evolution of carbonaceous aerosol and aerosol precursors. Emissions measurements were performed at the exit of a combustor and at the exit of a full engine for a gas turbine engine typical of the in-service, commercial aircraft fleet. Measurements were compared to model simulations of changes in gaseous chemistry. As predicted by the model simulations, results show no significant modifications to the aerosol distribution along the postcombustor flowpath. The oxidation of NO to HONO was measured. Trends with engine power setting and sulfur loading were at the level of estimated uncertainty limits. Simulations of the fluid and chemical processes through the turbine and exhaust nozzle correctly captured HONO trends and matched experimental data within measurement uncertainty. This suggests that the employed modeling approach is valid for HONO chemistry, and more generally, because HONO results from NO oxidation via the hydroxyl radical, indicates the importance of OH-driven oxidation through the engine. These results indicate that the chemical and physical processes occurring in the turbine are important in determining aircraft engine emissions. Nomenclature d g = geometric mean diameter EIM = mass based emission index EIN = number based emission index EISA = surface area based emission index M = mass N = size distribution in terms of number V = volume g = geometric standard deviation

The objective of the work described in this paper was to identify a method of making measurements of the smoke particle size distribution within the sector of a gas turbine combustor, using a scanning mobility particle sizing (SMPS) analyzer. As well as gaining a better understanding of the combustion process, the principal reasons for gathering these data was so that they could be used as validation for computational fluid dynamic and chemical kinetic models. Smoke mass and gaseous emission measurements were also made simultaneously. A “water cooled,” gas sampling probe was utilized to perform the measurements at realistic operating conditions within a generic gas turbine combustor sector. Such measurements had not been previously performed and consequently initial work was undertaken to gain confidence in the experimental configuration. During this investigation, a limited amount of data were acquired from three axial planes within the combustor. The total number of test points measured were 45. Plots of the data are presented in two-dimensional contour format at specific axial locations in addition to axial plots to show trends from the primary zone to the exit of the combustor. Contour plots of smoke particle size show that regions of high smoke number concentration once formed in zones close to the fuel injector persist in a similar spatial location further downstream. Axial trends indicate that the average smoke particle size and number concentration diminishes as a function of distance from the fuel injector. From a technical perspective, the analytical techniques used proved to be robust. As expected, making measurements close to the fuel injector proved to be difficult. This was because the quantity of smoke in the region was greater than 1000mg/m3. It was found necessary to dilute the sample prior to the determination of the particle number concentration using SMPS. The issues associated with SMPS dilution are discussed.

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A fuel injector has been designed with the capacity to change effective area and fuel placement by varying the swirl number. This gives more flexibility on fuel/air mixture control than current designs, allowing a potentially wide turndown to be achieved whilst maintaining low emissions at high power. The fuel injector utilises fluidic control, eliminating the need for mechanical moving parts in the hot region commonly found in current variable geometry fuel injector designs. The concept was evaluated and showed promising improvement in stability compared to the baseline fuel injector. The control flow system, using fluidics, was developed in isolation. The concept and control systems were then combined and evaluated. Although variable swirl using fluidic control was achieved, it was not sufficiently optimised to separate the downstream outer and inner airflow as with the concept design. As such the observed improvement in stability was not as good as expected. However, the ability to control effective area, and fuel placement without the need for moving parts was proven. It is therefore recommended that further work be performed to allow the optimisation of the device such that controllable improvements in stability performance can be achieved in line with the potential shown with concept testing.

This paper presents the progress made on the development of a dual spray, direct injection airblast fuel nozzle capable of variable fuel placement. It is anticipated that by varying the fuel placement within the confines of a combustion chamber it will be possible to control localised zonal ‘Fuel Air Ratio’ and thus extend both stability and emissions performance in respect of engine power range. The extension of combustion stability is particularly desirable to high pressure, temperature and turndown ratio aero engines where the ratio between maximum and flight idle fuel flow is extreme. Target performance data for the design has been derived from anticipated future engine cycles. A number of initial concepts were examined and recent development work has focused on the most successful design to date. Combustor testing has been performed at both atmospheric and high pressure. The combustor utilised was a single sector tubular combustor with combustor volume and airflow distributions representative of the cycle for which the fuel injector was designed. Two fuel injector configurations were examined, having different design flow structures. Combustion stability testing was performed with air inlet conditions of atmospheric pressure and 293K. Stability and ignition data were derived over a range of combustor pressure drops. Fuel injector AFRs of over 100:1 were achieved. An ignition loop was also derived although optimisation studies were not performed at this stage. High pressure emissions evaluation was also performed up to 13 Bar. Idle and scaled climb-out power conditions were tested, with a range of fuel scheduling between the pilot and main. Idle efficiency of over 99.5% was achieved. Low emissions performance was also achieved with less than 10 EINOx at climb out power settings. Future work will include testing at up to 40 Bar pressure to establish actual full power performance in addition to further development work on stability and ignition performance.