This thesis presents results from an experimental investigation of the macroscopic and microscopic atomization and combustion behavior of B99 biodiesel, ethanol, B99-ethanol blends, methanol, and an F-76-Algae biodiesel blend. In addition, conventional F-76 and Diesel #2 sprays were characterized as a base case to compare with. The physical properties and chemical composition of each fuel were measured in order to characterize and predict atomization performance. A variety of B99-ethanol fuel blends were used which demonstrate a tradeoff between lower density, surface tension, and viscosity with a decrease in the air to liquid ratio. A plain jet air-blast atomizer was used for both non-reacting and reacting tests. The flow rates for the alternative fuels were set by matching the power input provided by the baseline fossil fuels in order to simulate use as a drop in replacement. For this study, phase Doppler interferometry is employed to gain information on drop size, SMD, velocity, and volume flux distribution across the spray plume. A high speed camera is used to gather high speed cinematography of the sprays for observing breakup characteristics and providing additional insight. Reacting flow tests captured NOx, CO, and UHC emissions along with high speed footage used to predict soot levels based on flame luminosity. The results illustrate how the fuel type impacts the atomization and spray characteristics. The air-blast atomizer resulted in similar atomization performance among the DF2, F-76, and the F-76/Algae blend. While methanol and ethanol are not suitable candidates for this air-blast configuration and B99 produces significantly larger droplets, the addition of ethanol decreased drop sizes for all B99-ethanol blends by approximately 5 microns. In regards to reacting conditions, increased ethanol blending to B99 consistently lowered NOx emissions while decreasing combustion efficiency. Overall, lower NOx and CO emissions were achieved with the fuel blends than for conventional diesels, while the neat biofuels emitted overall less NOx per CO than the baseline fuels. This research clearly demonstrated that blends of two renewable fuels (B99 and ethanol improved (1) atomization and (2) emissions performance for the burner studied when compared to the baseline fossil fuels DF2 and F-76.

Hydrogen derived from non-fossil sources is an attractive candidate to replace carbon based fuels in gas turbines, as it is inherently carbon free. Yet the unusual combustion properties of hydrogen requires some care to successfully use it in gas turbines. To attain the lowest NOx emissions, uniformly low reaction temperatures must be assured thus the reactants must be well mixed. This is accomplished in low emission gas turbines by mixing the reactants within a pre-mixer section prior to entry into the combustor. With the addition of hydrogen into the fuel, certain issues arise such as higher flame speeds compared to carbon based fuels. Flashback is a phenomena that occurs when the flame no longer propagates downstream of the injector but instead retracts and propagates upstream towards the pre-mixer and injector. Flashback occurs when the flame speed exceeds the local flow velocity. In the present work, studies are conducted under different levels of turbulence intensity. Higher turbulence intensity is known to increase turbulent burning velocity, hence the question of how flashback propensity is affected is raised. Studies are conducted at pressures from 3 to 8 atm. with preheated reactants up to 750 K utilizing hydrogen as the fuel. The results show that even with significantly different turbulence intensities (ratio of flow centerline turbulence to centerline axial velocity) boundary layer flashback is not strongly affected. This is attributed to the role of the quenching distance in connection with the boundary layer. Core flow flashback or other flashback mechanisms may be affected differently.

This study provides an experimental and numerical examination of pollutant emissions and stability of gaseous fueled reactions stabilized with two premixed-fuel-flexible and ultra-low NOx burner technologies. Both burners feature lean combustion technology to control the formation of nitrogen oxides (NOx). The first fuel–flexible burner is the low-swirl burner (LSB), which features aerodynamic stabilization of the reactions with a divergent flow-field; the second burner is the surface stabilized combustion burner (SSCB), which features the stabilization of the reactions on surface patterns.

For combustion applications the most commonly studied species are: NOx, carbon monoxide (CO), and unburned hydrocarbons (UHC). However these are not the only pollutants emitted when burning fossil fuels; other species such as nitrous oxide (N2O), ammonia (NH3) and formaldehyde (CH2O) can be directly emitted from the oxidation reactions. Yet the conditions that favor the emission of these pollutants are not completely understood and require further insight.

The results of this dissertation close the gap existing regarding the relations between emission of pollutants species and stability when burning variable gaseous fuels. The results of this study are applicable to current issues such as:

1. Current combustion systems operating at low temperatures to control formation of NOx.

2. Increased use of alternative fuels such as hydrogen, synthetic gas and biogas.

3. Increasing recognition of the need/desire to operate combustion systems in a transient manner to follow load and to offset the intermittency of renewable power.

4. The recent advances in measurement methods allow us to quantify other pollutants, such as N2O, NH3 and CH2O.

Hence in this study, these pollutant species are assessed when burning natural gas (NG) and its binary mixtures with other gaseous fuels such as hydrogen (H2), carbon dioxide (CO2), ethane (C2H6) and propane (C3H8) at variable operation modes including: ignition; lean blowoff; and variable air to fuel ratio. Some remarkable results of this dissertation include:

• At a fixed fire rate (117kW) the addition of hydrogen to NG raises the emission of NOx for the reactions stabilized with the LSB. Under the same conditions, the addition of H2 to NG will reduce the emission levels of the reactions stabilized with the SSCB.

• It was found experimentally that nitrous oxide (N2O) is emitted during ignition and blowoff events.

• Ammonia (NH3) is also emitted during ignition and blowoff events.

• It was found experimentally that at high concentrations of hydrogen in NG (H2>70%), reactions aerodynamically stabilized with the LSB will emit significant amounts of N2O.