# Study of Discharge Characteristics on Ignition Performance via High-Speed Imaging in a CVCC
## 1 Introduction
Moreover, the in-cylinder ambient environment parameters, such as gas flow velocity, gas composition, and ambient pressure et al., are challenging to separate and analyze independently due to the complexity of such parameters interactions. On the other hand, the mixture concentration in the vicinity of the spark plug is not always the same at every firing cycle, and under the actual engine bench test, the ignition swing will also alter the indicating parameters of engine performance. While the experiments in a constant volume combustion chamber (CVCC) help fill in the gap in this aspect. Therefore, to understand the effects of individual factors on the ignition process, it is necessary to carry out the experiments in a constant volume combustion chamber (CVCC) to provide a deep insight into the discharge characteristics at various ambient conditions. [PERSON] et al. used the schlieren photography method to investigate the initial flame formation. The results indicated that an attached flame kernel could be formed by either increasing the discharge current or prolonging the discharge duration under the flow velocity of 25 m/s [17]. [PERSON] et al. demonstrated that multi-strike discharge was able to generate kernels that merge and lead to initial flame propagation [18]. [PERSON] et al. discovered that a high current was necessary to maintain the discharge channel extension under the strong flow condition [19]. However, the lower flow conditions were still not clear. [PERSON] et al. had demonstrated that increasing the discharge duration resulted in the increase in the maximum length of the discharge channel by a specially designed arc test rig [20]. However, the actual discharge current duration was about 0.3 ms to 0.9 ms, shorter than the conventional ignition system. Furthermore, the technologies of cooling infrared cameras have been improved in recent years and are accessible in many fields. [PERSON] et al. applied a high-speed infrared camera to the bottom view of an optical visualization diesel engine to observe the spray combustion of biofuels in the CO2 and HCs bands. Due to this, it is possible to detect the reaction immediately after SOC of the pilot injection and after the end of visible combustion in the infrared range. Furthermore, it is possible to evaluate the spray evaporation and mixing process, and the combustion evolution after the main injection [21]. Besides, [PERSON] et al. measured the temperature of spark plugs as an example of applyingthe near-infrared region to a spark-ignition engine. The results indicated that the factors of pre-ignition depend on the engine operating conditions [22]. In general, the discharge characteristics, such as discharge current and duration, have been widely studied in the literature, however, the ignition energy was changed when only focusing on the discharge current or the discharge duration in the previous studies. Under the same ignition energy, the roles of discharge current and duration of the ignition performance at various ambient conditions is still unclear. Therefore, this study uses three types of ignition coils to conduct the test, two of which have the same ignition energy. Moreover, combustion products such as CO and CO\({}_{2}\) have a specific absorption band in the infrared region. There is no report of detecting the initial flame within the CO infrared region during the ignition to the author's knowledge. Hence, this study used the simultaneous visualization method of high-speed infrared and natural imaging in the constant volume combustion chamber to provide the initial flame formation and discharge channel behaviors during the ignition process.