The Relationship between In-Cylinder Flow-Field near Spark Plug Areas, the Spark Behavior, and the Combustion Performance inside an Optical S.I. Engine

Abstract

The stringent regulations that were placed on gasoline vehicles demand significant improvement of the powertrain unit, not only to become cleaner but also more efficient. Therefore, there is a strong need to understand the complex in-cylinder processes that will have a direct effect on the combustion quality. This study applied multiple high-speed optical imaging to investigate the interaction between the in-cylinder flow, the spark, the flame, and combustion performance. These individual elements have been studied closely in the literature but the combined effect is not well understood. Simultaneous imaging of in-cylinder flow and flame tomography using high-speed Particle Image Velocimetry (PIV), as well as simultaneous high-speed spark imaging, were applied to port-injected optical gasoline imaging. The captured images were processed using in-house MATLAB algorithms and the deduced data shows a trend that higher in-cylinder flow velocity near the spark will increase the stretch distance of the spark and decrease the ignition delay. However, these do not have much effect on the combustion duration, and it is the flow-field in the entire area surrounding the flame development that will influence how fast the combustion and flame growth will occur.

Impact of Exhaust Gas Recirculation on Gaseous Emissions of Turbocharged Spark-Ignition Engines

“…As the EGR rate increases, laminar flame speed is deteriorated, which can be confirmed by the increase in the induction time reflected in the same graph. This induction time is defined as the lapse between the spark activation and 10% of the cumulative heat released, related to the initial kernel growth which is known to be greatly influenced by laminar flame speed as well as flow characteristics around the spark plug [34]. Regarding the oxygen content in the exhaust gases (upper right figure), it has to be highlighted that, since the engine is always running at stoichiometric conditions, this oxygen is significantly influenced by the aforementioned quenching phenomena.…”

Investigation of multi-event spark discharge strategy for lean methane-air combustion

“…[7][8][9][10] The flow field in the vicinity of the spark plug not only speeds up flame propagation, but also stretches the plasma channel out of the spark gap during discharge, leading to a longer plasma length and a bigger ignition volume, as shown in Figure 1. 3,[11][12][13] This is essential for flame kernel initiation. However, the spark plasma cannot be stretched to infinitely long.…”

“…If there is still certain amount of electrical energy left in the ignition coil after the plasma breaks off, a new plasma channel with shortened length is established near the spark gap, which is termed as restriking. 3,[11][12][13][14] Restrike happens more frequently when the discharge current is insufficient to hold the plasma under flow conditions. Frequent restriking is detrimental to flame kernel formation, because it reduces the effective plasma channel holding period and plasma length.…”

An Optical Method to Characterize Streamer Variability and Streamer-to-Flame Transition for Radio-Frequency Corona Discharges

“…Focusing on spark ignition (SI) engines, actual trends to obtain a cleaner and more efficient combustion are turbocharging, water injection, high exhaust gas recirculation (EGR) dilution, and lean combustion [1][2][3][4][5]. Because of all these features, it is critical to ensure an effective ignition able to start a robust combustion; conventional spark plugs show their limits [6,7] and an excessive cycle-to-cycle variability (CCV) is linked to the use of conventional igniters in these conditions. Actually, CCV depends on different factors and processes: manifold phenomena, fuel injection, in-cylinder motion, ignition, and gas exchange.…”