Date of Award
Master of Science (MS)
To effectively reduce particulate emissions and maximize the effectiveness of renewable fuels entering the industrial and transportation markets, an accurate understanding of the combustion characteristics of these fuels is a necessary undertaking. Typical engines used in the heavy-duty engine industry primarily rely on mixing-controlled combustion, which has the potential to produce soot under locally rich combustion conditions. A rapid compression machine (RCM) is an experimental reaction vessel used to investigate the ignition and pollutant behaviors of fuels at compressed conditions relevant to engine studies. In this study, an RCM has been prepared with line-of-sight optical accessibility such that a laser extinction diagnostic can be used to measure the concentration of soot produced in an RCM experiment using the Beer-Lambert law. By conducting tests across a range of fuel-air mixture conditions relevant to soot formation in mixing-controlled combustion, the sooting tendencies of potential fuels can be analyzed for useful comparisons and quantified for the use of validating chemical kinetic modeling. The fuels selected for testing are iso-octane and ethanol. Iso-octane is a surrogate fuel commonly used to represent gasoline, which is seeing increased interest to the heavy-duty engine market due to the introduction of EV technology lowering the light-duty engine fuel demand. Ethanol is commonly mixed with gasoline for the purpose of reducing greenhouse gas emissions and is therefore of interest to heavy-duty engine development with the potential to allow farmers to grow their own fuel. This study will measure the sooting tendencies of both fuels over a range of mixing conditions relevant to mixing-controlled combustion, such that the results can be used to validate chemical-kinetic modeling and grasp a better understand of the sooting tendencies between different fuel types. The oxygenated nature of ethanol combined with various published studies suggests that ethanol will have a higher resistivity to soot formation at matched mixing conditions compared to iso-octane. This study also investigates the soot production sensitivity of both fuels to pressure by conducting equivalence ratio sweeps at 10 bar and 20 bar for iso-octane, and 20 bar and 30 bar for ethanol. At matched compressed pressure conditions of 20 bar, iso-octane starts soot production at a critical equivalence ratio of 1.76 while ethanol has a critical equivalence ratio of 2.35, displaying ethanol’s higher resistivity to soot formation. A positive relation between compressed pressure and soot formation was found, with iso-octane’s critical ratio increasing to 1.82 when compressed to 10 bar and ethanol’s critical ratio decreasing to 2.19 when compressed to 30 bar. Additionally, this study investigates the parameters and methods relevant towards properly preparing a homogeneous charge of air and fuel for a chemical-kinetic study at mixing conditions relevant for soot analysis as well as considerations for maximizing the effectiveness of a laser extinction diagnostic setup.