Particulate Characterization and Size Distribution in the Exhaust of a Gasoline Homogeneous Charge Compression Ignition Engine

Agglomeration, coagulation, surface condensation, adsorption and oxidation processes are a part of particulate evolution process and lead to significant changes in characteristics of particulate matter (PM), when they enter the atmosphere. PM formation can be significantly reduced by advanced combustion concepts such as homogeneous charge compression ignition (HCCI). In the present study, experiments were performed in a modified gasoline fuelled HCCI engine at varying intake air temperatures (T-i), exhaust gas recirculation (EGR) rates and relative air-fuel ratios (lambda). For particulate characterization, a partial flow dilution tunnel was used to collect particulate samples on a filter paper. These particulate samples were analysed for benzene soluble organic fraction (BSOF), trace metals, and particulate morphology using scanning electron microscopy (SEM). Physical characterisation of particulates was done using engine exhaust particle sizer (EEPS), which measured the particle size-number distribution. In the experiments, higher PM was found for richer fuel-air mixtures and it further increased with application of EGR. Trace metals were found to be significantly lower for HCCI generated PM, which increased with increasing EGR. BSOF was negligible as compared to total PM which showed relatively lower toxicity of gasoline HCCI particulates. Total number of particles reduced with increasing lambda, however particulate size-number distribution curve shifted away from accumulation mode, indicating that the particulate size decreased with increasing lambda. Higher particle size-number distribution and particle size-mass distribution were observed for increasing T-i. Particulate surface area and volume also increased with increasing T-i and mixture strength.