Detailed Morphological Properties of Nanoparticles from Gasoline Direct Injection Engine Combustion of Ethanol Blends

Detailed properties of particulate matter (PM) emissions from a gasoline direct injection (GDI) engine were analyzed in terms of size, morphology, and nanostructures, as gasoline and its ethanol blend E20 were used as a fuel. PM emissions were sampled from a 0.55L single-cylinder GDI engine by means of a scanning mobility particle sizer (SMPS) for size measurements and a self-designed thermophoretic sampling device for the subsequent analyses of size, morphology and nanostructures using a transmission electron microscope (TEM). The particle sizes were evaluated with variations of air-fuel equivalence ratio and fuel injection timing. The most important result from the SMPS measurements was that the number of nucleation-mode nanoparticles (particularly those smaller than 10 - 15 nm) increased significantly as the fuel injection timing was advanced to the end-of-injection angle of 310° bTDC. In variation of fuel injection timing, no consistent fuel dependence was found for the total number of particles. The TEM morphology examination revealed the presence of those small nanoparticles, clearly discerned from large aggregate particles. Both nano-sized and large aggregate particles appeared to be agglomeration of a number of nearly-spherical primary particles, where the size of aggregate particles was dependent on the size of primary particles. In the TEM nanostructure examination, particles from gasoline combustion exhibited graphitic structures, regardless of fuel injection timing. However, the nanostructures of E20-derived particles were changed to amorphous as the injection timing was advanced to 310° bTDC. It was finally concluded that those results from SMPS and nanostructure analyses for the 310° bTDC injection timing are caused potentially by the increased amount of unburned hydrocarbons or volatile organics due to fuel impingement at that early fuel injection timing.