Quantitative evaluation of the breakdown process of spark discharge for spark-ignition engines

For spark-ignition (SI) engines, downsizing, exhaust gas recirculation and lean burn are promising methods for meeting more stringent emission regulations and lower fuel consumption requirements. With these technologies, high density and high flow velocity around the spark plug at spark timing bring severe challenges for stable ignition. The ignition processes could be affected by breakdown phases and restrikes under high-density conditions. A quantitative evaluation for the breakdown phase is of great significance especially for high power density engines. In this study, the experiments with pressure up to 40 bar and temperature up to 450?K are established to evaluate the breakdown voltage and current, with different spark plug gaps. The breakdown voltage is related to the ambient density, spark plug gap distance and gas composition. The coil parameters have little effects on the breakdown voltage. The breakdown current shows positive correlation with the breakdown voltage, and is also affected by the coil characteristics. The breakdown voltage and current show the nonlinear correlations with the pressure and gap distance. With the increase of pressure or gap distance, the increase rates of the breakdown voltage and current decrease. The fuel concentration and species have little effects on the breakdown voltage when the fuel concentration is applicable for engine operations. Finally, a novel expression of the breakdown voltage is constructed as a function of ambient pressure, temperature and spark plug gap distance. The newly developed expression is valuable for simulating spark ignition processes for a wide range of ambient density for SI engines.