Air Quality Implications of Using Ammonia as a Renewable Fuel: How Low Can NOx Emissions Go?

In addition to their lifecycle carbon emissions, another important issue with decarbonized energy pathways is their air quality, water, or land use implications. This paper considers the air quality issue for ammonia combustion. When directly combusting ammonia, reactions of its N atom with atmospheric oxygen lead to NOx emissions that are O(103) ppm, 2 orders of magnitude higher than EPA limits or the amount emitted by current natural-gas-fired technologies. In order to provide guidance to policymakers and technologists on what is fundamentally possible, this Perspective analyzes the fundamental minimum NOx emissions that can be produced from ammonia combustion. The analysis shows that it is possible to achieve quite low NOx emission levels of O(10) ppm, but these designs differ markedly from those used in today's lean, premixed combustion systems.

Simultaneous multiple laser beam intensity profile correction and its application to a vitiated bluff body combustor field.

Simultaneous high-speed stereo-particle image velocimetry, OH planar-laser-induced fluorescence (PLIF), and CH2O PLIF measurements in a vitiated bluff body combustor are considered. An ex situ, simultaneous, time-resolved laser sheet intensity profile correction procedure is introduced. This procedure is easily implemented experimentally and is capable of correcting multiple sheets at the same time. As a proof of concept, the procedure is applied to perform correction of the CH2O PLIF images in vitiated and unvitiated conditions. The challenges associated with CH2O PLIF under these combustor operating conditions are also discussed.

Fiber-coupled LWIR hyperspectral sensor suite for non-contact component surface temperature measurements.

We report on the development of a robust fiber-coupled long-wavelength infrared (LWIR) hyperspectral sensor suite for accurate and reliable non-contact surface temperature measurements in propulsion systems with limited optical access. We first experimentally investigate various state-of-the-art LWIR optical fibers and identify the ideal fiber for efficient coupling and transmission of LWIR signals. The effects of the fiber material, structure, bending, and thermal heating on LWIR fiber transmission are characterized. Subsequently, we discuss the development of a fiber-coupled LWIR hyperspectral sensor using a multi-mode polycrystalline fiber. The temperature measurement accuracy and precision of the sensor are determined using a well-calibrated blackbody radiation source and heated thermal barrier coating. The sensor is integrated into a homemade water-cooled probe housing and environmental protection box and subsequently used for reliable combustor liner temperature measurements in a high-pressure, liquid-fueled combustor rig with no built-in optical access. We also discuss the measurement challenges associated with flame interference and potential solutions. The LWIR sensor shows significant promise in its application to surface temperature measurements, and our findings can aid propulsion system engineers and researchers in system design and operation optimization.