Performance metrics for fueled and unfueled turbulent jet igniters in a rapid compression machine

Abstract

Turbulent jet ignition (TJI) system is an advanced ignition device that uses turbulent jets of hot combusting gases to initiate combustion in the main chamber. TJI system can enable knock mitigation in stoichiometric and lean mixtures, and increase burn rates in ultra-lean mixtures thereby improving efficiency. TJI nozzle design directly affects combustion efficiency since it determines the nature of jet spread in the main chamber. In this study a TJI system using methane as the fuel is used for assessing the performance of single and dual orifice TJI systems in a rapid compression machine (RCM). The prechamber is tested in both active and passive configurations and the volume is fixed at 2% of the main chamber clearance volume. Combustion metrics are derived using the main chamber pressure measurements and high-speed direct imaging of the combustion process. Stoichiometry in the main chamber is varied from λ = 1.0 until the lean limit (λ ~ 3.0). Prechamber fueling begins for mixtures leaner than λ = 1.5 to improve burn rates and extend the lean limit in comparison to the unfueled configuration. Pressure data is used to calculate burn rates and to identify inflection points from the curves of the pressure derivatives. High speed images are used for visualization and to measure flame area and jet penetration. A systematic approach of analyzing TJI nozzle performance is currently lacking and this study aims to address the issue by evaluating the suitability of the metrics used in this work.