Development of Porous Injection Technology to Reduce Emissions for Dry Low NOx Combustors: Micromixer and Swirl Injectors

The Combustion and Fire Research Laboratory (CFRL) at the University of Cincinnati (UC) is working on the development of advanced next generation injectors for DLN combustors. Several inputs were received from the project partners during the development phase. In the present paper, developmental work on two novel injectors with Porous Injection Technology (PIT) is presented. The technology has the potential to reduce NOx emissions to single digit PPM level with a stable combustion across wide range of load conditions. One of the key factors that are essential for lowering NOx levels is the efficient mixing of fuel-air in both spatial and temporal domains. The porous injection technology has the potential to reduce the spatial and temporal gradients to a minimum. In the present paper, two measurement techniques were used to evaluate the fuel-air mixing under atmospheric conditions. The CO2 mixing technique was used to quantify the spatial variations in the fuel mass fraction. Planar Laser Induced Fluorescence (PLIF) was used to obtain both spatial and temporal fuel mass fractions. The CO2 mixing measurements were used to validate the PLIF data for quantification. The RMS fluctuations in spatial and temporal domains were quantified from PLIF data. The combustion experiments were carried out at atmospheric pressure with a preheated temperature of air of 500–650 K and equivalence ratio of 0.5–0.8. The pressure drop across the injector was 4%. Natural gas with 90% methane and 9% ethane was used as fuel. The results show a stable flame for both injectors without combustion instabilities. Both injectors show low NOx levels. For conventional swirl stabilized design with PIT, the NOx levels were of the order of 1.5 ppm at the firing temperature of 1866 K whereas for the novel micromixer design, the NOx levels were of the order of 4 ppm @ ∼1866 K.

Experimental Investigations of an Internal Flow Generated by Porous Injection

An anisothermal channel flow generated by a porous injection is investigated in details for different Reynolds numbers of the injection in order to highlight the impact of the microstructure of porous material on the flow development. Two types of porous materials, being characterized by different matrices and pore sizes are studied: a coarse bronze porous plate (30% porosity and 100 μm average pore diameter) and a stainless steel porous plate (30% porosity and 30 μm average pore diameter). Particle image velocimetry, hot-wire anemometry, and cold wire thermometer measurements lead to the comparison of mean profiles, rms profiles, and energy spectra for the velocity and temperature fields. Two-point spatial correlations for the fluctuating velocity are also calculated. In the case of the coarse bronze plate, the flow is slightly fluctuating with big space coherence. In the opposite, the results obtained with the fine pore plate show a flow close to a fully developed turbulent channel flow. The comparison of the aerodynamic field with computational simulations based on a Reynolds-averaged Navier-Stokes (RANS) model underlines the difficulties to reproduce exactly the evolution of the mean and fluctuating velocities in all the explored part of the channel.