Lean Burn Combustion of Iso-Octane in a Rapid Compression Machine Using Dual Mode Turbulent Jet Ignition System

Turbulent jet ignition (TJI) is a pre-chamber initiated combustion technology that has been demonstrated to provide low temperature, faster burn rate combustion of lean and intake charge diluted air-fuel mixtures. Dual mode turbulent jet ignition (DM-TJI) is a novel concept wherein a separate air supply is provided for the pre-chamber apart from the conventional auxiliary fuel as supplied for TJI systems. The current study aims to extend the lean flammability limit of a gasoline-fueled engine using DM-TJI. Ignition delay time and combustion behavior of ultra-lean iso-octane/air mixture (Lambda ≅ 3.0) was studied using a TJI-based optically accessible rapid compression machine. High-speed fuel spray recordings in the pre-chamber were obtained using borescope imaging setup. Images of the reacting turbulent jet and subsequent combustion in the main chamber were captured using a visible color camera. The focus of the current study was to investigate (i) the effect of auxiliary fuel injection timing in TJI mode and (ii) the influence of having pre-chamber air injection in DM-TJI mode, on jet propagation and combustion behavior in the main chamber. Combustion behavior was analyzed by visually inspecting the particulates present in the chamber. Including an auxiliary air injection pulse during the auxiliary fuel injection event enhanced the combustion burn rates and mitigated particulate formation. Also, fuel injection timing and air injection pressure showed some differences in flame propagation and more noticeable differences in the particulate content.