Nitrogenated Hydrocarbon Cross-Product Formation during Combustion of Ammonia Co-Fired with Regular Hydrocarbons

Yale University, New Haven CT

Investigators

Abstract

Arguably the greatest challenge confronting our society today is to satisfy our energy needs while reducing emissions that warm the planet. In this regard, ammonia is gaining attention as a carbon-free fuel that can be burned with no direct carbon dioxide emissions. It can be produced domestically from air and water using clean electricity and is much more easily liquified than hydrogen. Since ammonia has poor burning characteristics, in many applications it will be co-fired with hydrocarbon fuels such as natural gas. This opens the door to a novel area of fundamental combustion chemistry: the formation of nitrogenated cross-products that combine carbon atoms from the hydrocarbon portion of the fuel with nitrogen atoms from the ammonia. We have preliminary data that verifies the formation of such cross-products and suggests that they chemically suppress formation of soot particles from the hydrocarbon portion of the fuel by sequestering carbon in a form that cannot grow to soot. The objective of the proposed project is to systematically explore the formation of cross-products when ammonia is burned with conventional fuels, determine their relationship to soot formation, and identify the chemical mechanisms that produce them. This project will use flame sampling and online photoionization mass spectrometry to generate the first database of trace hydrocarbon concentration profiles measured with a sensitive, broadband diagnostic in flames fueled with ammonia + methane, ethylene, and other hydrocarbons. It will measure soot volume fractions in the same flames and test the hypothesis that cross-product formation chemically suppresses soot formation from the co-fired hydrocarbons. It will characterize the morphology, nanostructure, and atomic composition of soot particles sampled thermophoretically from the flames to further determine the relationship between cross-products and soot. The measurements will use a novel experimental design to distinguish the chemical effects of ammonia from its physical effects by comparing the ammonia + hydrocarbon flames with a corresponding set of nitrogen + hydrocarbon flames. The flames will be thoroughly characterized with respect to temperature, major species, and boundary conditions so that they can be computationally simulated to test and improve detailed kinetic mechanisms for cross-products. The temperature measurements will further the development of a novel X-ray fluorescence diagnostic that is uniquely capable of measuring thermal boundary conditions and in-situ temperatures in all regions of sooting flames with negligible interferences from particles. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.