The current research investigates next-generation alternative biofuels for internal combustion engines. This research is part of the Co-Optimization of Fuels and Engines initiative (Co-Optima) from the US Department of Energy. This initiative is focused on accelerating the introduction of scalable, affordable, and sustainable biofuels for highly efficient burning and low emissions internal combustion engines. The experiment consists of a Gasoline Direct Injector (GDI) designed for a Control Volume Combustion Chamber (CVCC) equipped with a viewing window to capture high-speed broadband chemiluminescent imaging. Time-resolved spray images were analyzed to extract the dispersion flow dynamic behavior for medium to heavy-duty engine biofuels known as Butylcyclohexane, Dodecane, Formaldehyde Dibutyl Acetyl, and Nonanol. These biofuels were compared to the conventional Diesel neat and a volumetric fraction basis of 10 and 30 percent with Diesel. Macroscopic analysis of the injector revealed that the temporal evolution of spray cone angle is a function of the Aerodynamic Weber Number for the neat fuels. The breakup length extracted from the tip penetration was inversely related to the Aerodynamic Weber Number. Blend characterization revealed a dampening effect on the spray cone angle compared to the neat fuel, and the breakup lengths were coupled to Diesel. The primary breakup mechanism of each fuel injected by a GDI injector was studied using a novel modal analysis technique called Robust Multi-Resolution Dynamic Mode Decomposition (RMrDMD), which deconstructs the nonlinear dynamical systems into multiresolution time-scaled components that capture the intermittent coherent structures. It was found that using the RMrDMD, the dominant route of breakup for these biofuels injected with a Continental GDI injector occurred at a unique Strouhal number of 0.18 related to a specific spatial breakup mechanism that portrayed globule breakup. The critical secondary atomization parameter Sauter Mean Diameter (SMD) was examined with a Particle Doppler Interferometer (PDI). The SMD extracted was utilized with an evaporation model for each neat fuel. Results show that Dodecane has the fastest evaporation rate in comparison to all the other fuels. Within the CVCC, direct fuel injection combustion characteristics, specifically emissions, heat release rate, ignition delay, and Direct Cetane number, were investigated and compared. In addition, a local fuel-air distribution map was constructed for each of the fuel and their blends using the relationship between the chemiluminescence intensity ratio of C2* and Ch* and the premixed equivalence ratio


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Graduation Date





Ahmed, Kareem


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Mechanical and Aerospace Engineering

Degree Program

Aerospace Engineering









Release Date

August 2026

Length of Campus-only Access

5 years

Access Status

Doctoral Dissertation (Campus-only Access)

Restricted to the UCF community until August 2026; it will then be open access.