Gas turbine engines are a major source of PM2.5 emissions produced by the Department of Defense (DoD). Most of the PM2.5 emissions consist of soot particles. Although technology advancements have resulted in significant reductions in soot emissions from gas turbine engines, additional reductions will be needed to meet future PM2.5 National Ambient Air Quality Standards (NAAQS). Computational fluid dynamic (CFD) models will play a key role in designing future engines for low soot emissions from JP-8 or alternate fuels. Unfortunately, current models for soot formation and oxidation are insufficient to allow accurate predictions of emissions in CFD simulations. SERDP funded five programs that worked in concert to establish a fundamental database for developing and validating soot models for use in designing low emissions gas turbine combustors. The collective effort is referred to as the SERDP Soot Science Program.

The primary objective of this research program was to aid the DoD in meeting current and future NAAQS PM2.5 regulations by establishing the fundamental science base needed to develop and validate accurate soot models for realistic fuels. This program focused on understanding the fundamental effects of fuel chemistry and pressure on soot production and burnout, and on evaluating soot models as well as combustion chemistry mechanisms needed for accurate soot predictions.

The approach involved strongly coupled, mutually supportive experimental and simulation efforts conducted in concert with other members of the SERDP Soot Science Team. The approach included a series of well-controlled laboratory experiments that methodically progress in complexity in a way that supports a systematic analysis and interpretation of results. State-of-the-art soot models and detailed chemical mechanisms for hydrocarbon fuels have been integrated into a unique simulation code called UNICORN.

The results and accomplishments include establishing a database for soot emissions in shock tube, co-flow diffusion flames, opposed jet flames, centerbody flames, and swirl stabilized flames. Fuels investigated included: ethylene, m-xylene, dodecane, and a surrogate JP-8, developed in collaboration with the SERDP Soot Science Team. Detailed chemical kinetics models for ethylene and the JP-8 surrogate fuels with PAH chemistry up to pyrene are also developed in conjunction with the SERDP Soot Science Team. UNICORN simulations are used to interpret experimental results and evaluate the detailed soot and combustion chemistry models in the different experiments. A Sooting NETwork of Perfectly Stirred Reactors (SNETPSR) model for estimating the emissions of actual combustors is further developed in this program. The model incorporates the detailed chemical model for the JP-8 surrogate, which can also simulate paraffinic alternative fuels. This model can be used as a design tool for developing low-sooting gas turbine combustors.

This program advanced the ability to develop and evaluate models for predicting soot emissions from gas turbine combustors through the creation of a validation database for a surrogate JP-8 and alternative fuels, and through the creation and validation of chemical kinetic models for the surrogate fuels.