Nascent Titanium/Silicon-Containing Particle Formation in Corona Discharge Assisted Combustion

Abstract. Plasma-assisted combustion (PAC) is a technology that introduces high concentrations of charges, ions, and radicals, making the flame more stable and efficient. At the same time, PAC has also been shown to alter particle formation during combustion. Here, we investigate the effect of a high-frequency (~ 21 kHz) alternating current (AC) corona discharge on particle formation and growth in a premixed flame, especially at the initial stages (with particle sizes below 10 nm). We first examined the mobility size distribution of ions generated from non-plasma combustion and corona discharge-assisted combustion. The mobility size for positive ions does not change with the introduction of plasma. However, the negative ions change towards a larger size, likely due to different ion chemistry from plasma. We then introduced corona discharge with varying powers into the flame that contains titanium isopropoxide (TTIP) or tetraethyl orthosilicate (TEOS) and obtained the size distribution of the synthesized nanoparticles. We found that particle growth is suppressed by the corona discharge under relatively higher precursor feed rates (above ~ 29 mg h^-1 for TTIP and above ~ 60 mg h^-1 for TEOS). The mobility diameter is suppressed by up to 12 % for TTIP and by up to 20 % for TEOS. We further used different charging models to examine the impact of plasma on particle formation. In the case of higher precursor feed rates, the incipient particle concentration is high within the flame region. As higher number of charges accumulated on particles from negative charge carriers (including electrons and negative ions) than positive ions, the particles are preferentially charged negative. Such preferential charging results in particle-particle repulsion which suppresses coagulation particle growth. The findings of this study can guide nanoparticle synthesis and particulate matter control using PAC.