Development of Alternative Fuel Emission Models

Military gas turbine engines are a large consumer of jet fuel and a major source of emissions. The Department of Defense (DoD) is devoting considerable effort to reducing fuel costs and emissions by developing advanced gas turbine engines as well as reducing the dependence on foreign oil by developing and testing alternative fuels. In anticipation of an increased use of alternative fuels across DoD, new tools are needed to predict the formation of air emissions from advanced engines burning alternative fuels. To address future air quality concerns, SERDP is funding two projects that are developing a more fundamental understanding of the formation of air emissions in gas turbine engines.

SERDP project WP-2151 is focusing on developing demonstrably predictive computational tools for nitrogen oxides (NOx) and soot emissions from alternative fuel combustion. The fundamental kinetic modeling of pollutants will provide insight into the formation mechanisms that can be used to design better alternative fuel blends. The comprehensively validated computational models can be used directly for simulating aircraft engines burning alternative fuels, and the experimental data can be used for future model development and validation.

To accomplish this, the WP-2151 project team is studying the complex process of soot formation in modern aircraft engines, where chemical reactions at the molecular scale are impacted by the highly chaotic fluid flow inside the combustor. To understand these nonlinear interactions, a simpler flow system is studied. The advantage of this so-called temporal jet is that many of the key physical processes can be studied using models with unprecedented detail while reproducing essential flow features found inside engines. By understanding the conditions under which soot is produced, it is possible to incorporate design elements to minimize emissions in future aircraft engines.

SERDP project WP-2145 is building the science base needed to develop accurate models and establishing a science-based methodology for selecting practical alternative fuels that minimize emissions. High fuel efficiency, high-performance engines operate at high pressures and temperatures that are conducive to increasing NOx, non-volatile particulate matter (PM), unburned hydrocarbon (UHC), and carbon monoxide (CO) emissions. This problem is further complicated if the engines operate on alternative fuels, which are only starting to be studied. Improved combustor models are needed to aid in optimizing combustor designs for low emissions and fuel tolerance.

An additional factor leading to uncertainty in alternative fuel emissions and performance is the diverse sources from which alternative fuels can be derived. Predictive computational tools, like the ones being developed by SERDP, can significantly reduce engine design time for a variety of fuels leading to substantial cost benefits to the DoD.

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