Extending Lean and Exhaust Gas Recirculation Dilute Operating Limits of a Modern Gasoline Direct Injection Engine Using a Low Energy Transient Plasma Ignition System

Abstract

The efficiency improvement and emissions reduction potential of lean and exhaust gas recirculation (EGR)dilute operation of sparkignition gasoline engines is well understood and documented. However, dilute operation is generally limited by deteriorating combustion stability with increasing inert gas levels. The combustion stability decreases due to reduced mixture flame speeds resulting in significantly increased combustion initiation periods and burn durations. A study was designed and executed to evaluate the potential to extend lean and EGRdilute limits using a lowenergy transient plasma ignition system. The lowenergy transient plasma was generated by nanosecond pulses and its performance compared to a conventional transistorized coil ignition (TCI) system operated on an automotive, gasoline directinjection (GDI) singlecylinder research engine. The experimental assessment was focused on steadystate experiments at the part load condition of 1500 rpm 5.6 bar indicated mean effective pressure (IMEP), where dilution tolerance is particularly critical to improving efficiency and emission performance. Experimental results suggest that the energy delivery process of the lowenergy transient plasma ignition system significantly improves part load dilution tolerance by reducing the early flame development period. Statistical analysis of relevant combustion metrics was performed in order to further investigate the effects of the advanced ignition system on combustion stability. Results confirm that at select operating conditions EGR tolerance and lean limit could be improved by as much as 20% (from 22.7 to 27.1% EGR) and nearly 10% (from خ»â€‰= 1.55 to 1.7) with the lowenergy transient plasma ignition system.