# Study of Discharge Characteristics on Ignition Performance via High-Speed Imaging in a CVCC
## 3 Results and Discussion  
### Combustion Results  
Figure 7 shows the ignition probability of all the coils under different conditions. Ignition probability is the ratio of the successful ignition cases and the total number of experimental cases (10 times). The blue column stands for coil A (standard coil), the orange column denotes coil B (high current coil), and the gray column represents coil C (high energy coil). According to Figure 7, it can be observed that three types of coils have the same ignition probability ratio at the basic condition. There is no misfire case under the basic condition for all the coils. However, the differences among the three coils occur when increasing the mixture dilution ratio or enhancing the flow velocity, high current coil B gets the lowest ignition probability when under the high diluted condition compared to other coils, while standard coil A and high energy coil C still have no misfires cases under such conditions. When under the high flow condition, standard coil A gets the lowest ignition probability, while high energy coil C gets the highest ignition probability. High current coil B is better than the standard coil A. It reveals that the high energy coil C resulted in high level ignition probability under all the conditions. This means that enhancing the ignition energy can improve the ignition probability remarkably. However, high energy will increase the wear and tear of the spark plug due to the increased discharge current and prolonged discharge duration, hence, coil A and coil B with the same lower ignition energy need to be considered in particular. Standard coil A with a longer discharge duration has a better ignition probability under the high diluted condition. In contrast, high current coil B with a higher discharge current has a better ignition probability under the high flow \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{} & **Coil A** & **Coil B** & **Coil C** \\ \hline Discharge current [mA] & 65 & 170 & 180 \\ Discharge duration [ms] & 2.2 & 1.3 & 1.9 \\ Ignition energy [m] & 95.0 & 95.0 & 165.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detail specifications of the ignition coil. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Conditions**} & \multicolumn{1}{c}{**Basic**} & \multicolumn{1}{c}{**High Diluted Condition**} & \multicolumn{1}{c}{**High Flow**} \\  & **Condition** & & & **Condition** \\ \hline Nitrogen (N\({}_{2}\)) dilution & 24\% & 28\% & 24\% \\ Mixture composition & C\({}_{3}\)H\({}_{8}\): 3.06\%, O\({}_{2}\): 15.29\%, N\({}_{2}\): & C\({}_{3}\)H\({}_{8}\): 2.90\%, O\({}_{2}\): 14.49\%, N\({}_{2}\): & C\({}_{3}\)H\({}_{8}\): 3.06\%, O\({}_{2}\): 15.29\%, N\({}_{2}\): \\ Flow velocity & 81.65\% & 82.61\% & 81.65\% \\ Equivalence ratio & 8 m/s & 8 m/s & 18 m/s \\ Initial temperature & & 1 & 358 K \\ Initial pressure & & 4 Bar & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of experimental conditions. Figure 6: Discharge characteristics of the ignition coils. (**a**) Discharge energy; (**b**) Discharge current. condition. Ignition probability can reflect the ignition performance by and large, when comparing results of the basic condition and the high diluted condition, due to the lowest ignition probability ratio of coil B under the high diluted condition, and, one thing that can be found is that the discharge duration is more important than the discharge current with regard to affecting the ignition probability when only increasing the mixture dilution ratio; when focusing on the results of the basic condition and high flow condition, it is notable that the discharge current becomes the dominant factor compared to the discharge duration when enhancing the gas flow velocity, since coil A gets the lowest ignition probability.