Controlling a Multistage Ignition Assisted by a High-Frequency Corona Discharge

Within the frame of the modern strategy of low-temperature combustion (LTC), it is proposed to use lean fuel-air mixtures that are sensitive to the equivalence ratio. Such mixtures display a multistage ignition behavior. Nanosecond discharge impact on a multistage ignition provides the key to controlling oxidation and combustion processes in systems for practical applications. Using propane-air mixture it is shown by modeling that a nanosecond discharge does not suppress, but stimulates the development of cool flame and increases its intensity; and also reduces the non-monotonic oxidation of mixture with increasing the initial temperature, up to suppression of the negative temperature coefficient of oxidation rate. Based on these results, the method is proposed for organizing the combustion of lean mixture in the HCCI engine by changing the reaction path of LTC stage by activating the mixture with a high-frequency corona discharge (5 MHz) and stimulating the auto-ignition due to compression. This method allows us to improve the exhaust composition for CO, UHC, NO_x.  The possibility of controlling the propagation mode of combustion wave with the transition to propagation of auto-ignition waves using a high-frequency corona discharge is shown. The discharge does not directly ignite the mixture due to a small specific energy input. These results can be applied to a hybrid engine, which in stable conditions operates as HCCI engine, and in unstable conditions, a high-frequency corona discharge could be an initiator of combustion.