Effect of Spark Discharge Duration and Timing on the Combustion Initiation in a Lean Burn SI Engine

Meeting the increasingly stringent emission and fuel efficiency standards is the primary objective of the modern automotive research. Lean/diluted combustion is a promising avenue to realize high-efficiency combustion and reduce emissions in SI engines. Under diluted conditions, the flame propagation speed is reduced because of the reduced charge reactivity. Enhancing in-cylinder charge motion and turbulence, and thereby increasing the flame speed, is a possible way to harness the combustion process in SI engines. However, charge motion can have a significant effect on the spark ignition process because of the reduced discharge duration and frequent restrikes. A longer discharge duration can aid in the formation of a self-sustained flame kernel and subsequent stable ignition. Therefore, an empirical study is undertaken to investigate the effect of discharge duration and ignition timing on the ignition and early combustion in a port fueled SI engine, operated under lean conditions. Discharge duration is modulated from 1 ms to 8 ms through a continuous discharge strategy. Discharge current and voltage measurements are recorded during the engine operation to characterize the discharge process. In-cylinder charge is diluted using fresh air to achieve lean combustion. In-cylinder pressure measurement and heat release analysis are used to investigate the ignition and combustion characteristics of the engine. Preliminary results indicate that the impact of discharge duration is more pronounced in lean conditions and in the vicinity of the spark advance limit, when ignition process encounters significant challenge. While the discharge duration has a marginal effect on the ignition delay, cyclic variations and stability of the ignition process are notably impacted.