Combined Effects of Multi-Pulse Transient Plasma Ignition and Intake Heating on Lean Limits of Well-Mixed E85 DISI Engine Operation

• Published in: SAE International Journal of Engines 2014-10, Vol.7 (4), p.1781-1801, Article 2014-01-2615
• Main Authors: Sjöberg, Magnus, Zeng, Wei, Singleton, Daniel, Sanders, Jason M, Gundersen, Martin A
• Format: Article
• Language: English
• Subjects: Combustion; Combustion temperature; Datasets; Engines; Flames; Fuel consumption; Fuel economy; Gas temperature; Heating; Ignition; Ignition systems; Imaging; Spark ignition; Spark plugs
• ISSN: 1946-3936; 1946-3944; 1946-3944
• DOI: 10.4271/2014-01-2615

Well-mixed lean SI engine operation can provide improvements of the fuel economy relative to that of traditional well-mixed stoichiometric SI operation. This work examines the use of two methods for improving the stability of lean operation, namely multi-pulse transient plasma ignition and intake air preheating. These two methods are compared to standard SI operation using a conventional high-energy inductive ignition system without intake air preheating. E85 is the fuel chosen for this study. The multi-pulse transient plasma ignition system utilizes custom electronics to generate 10 kHz bursts of 10 ultra-short (12ns), high-amplitude pulses (200 A). These pulses were applied to a custom spark plug with a semi-open ignition cavity. High-speed imaging reveals that ignition in this cavity generates a turbulent jet-like early flame spread that speeds up the transition from ignition to the main combustion event. Performance testing shows that lean operation with heated intake air enables a 17% improvement of fuel economy at ϕ = 0.59 for both ignition systems, relative to that of stoichiometric operation. Moreover, multi-pulse transient plasma ignition offers more stable ultra-lean operation, with IMEPn variability less than 5% down to ϕ = 0.49. The ability to operate stably at such lean conditions is attributed to a more stable flame initiation offered by both the increased charge temperature and the multi-pulse transient plasma ignition that allows a later spark timing due to the very fast transition to fully turbulent deflagration.