Discharge Characteristics of Current Boosted Spark Events Under Flow Conditions

Abstract

With the advancement of spark ignition engines, lean or diluted in-cylinder charge is often used to improve the engine performance. Enhanced in-cylinder charge motion is widely applied under such conditions to promote the flame propagation, which raise challenges for the spark ignition system. In this work, the spark discharging process is investigated under different flow conditions via both optical diagnosis and electrical measurement. Results show that the spark plasma channel is stretched under flow conditions. A higher discharge current can maintain the stretched spark plasma for a longer duration. Re-strikes are observed when the spark plasma is stretched to a certain extent. The frequency of re-strikes increases with increased flow velocity and decreased discharge current level. The discharge duration reduces with the increased flow velocity. The effects of gas flow on the ignition and flame kernel development are studied in a constant volume optical combustion chamber with premixed lean and stoichiometric methane air mixture. Two spark strategies with low and high discharge current are used for the ignition. The flame propagation speed of both lean and stoichiometric mixtures increases with the increased gas flow velocity. A higher discharge current level retains a more stable spark channel and improves the flame kernel development for both lean and stoichiometric conditions, especially under the higher gas flow velocity of 20 m/s.

Flow directed spark stretch and flame propagation in a high-tumble production engine

“…23 The spark plasma sustainability is related to the magnitude of the flow through the spark gap because higher flow velocity would require a higher spark current due to the increased resistance. 24 In high tumble engines, higher flow magnitude is expected to impact the spark plasma stretch and resulting flame propagation more significantly. However, the direct comparison between the measured flow fields and spark/flame development is lacking in a realistic multi-cylinder engine condition.…”

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.…”

“…Frequent restriking is detrimental to flame kernel formation, because it reduces the effective plasma channel holding period and plasma length. [12][13][14] Therefore, enhancing the ignition source to have a longer plasma channel under intensified flow field is of great importance.…”

“…[18][19][20] In terms of glow phase discharge enhancement, the discharge current during glow phase can be boosted by adding an external power supply to the secondary circuit of the TCI system. 12,13 The boosted discharge current can hold the plasma channel to a longer length under flow conditions, enabling better combustion phasing control. 12 Apart from the single discharge strategy, another glow phase discharge advancement is the coil-based multi-event spark strategy, which refers to energizing the ignition coils multiple times within one combustion cycle.…”