Control of Pressure-Rise Rates of Compression Ignition by Stratification of Reformed Premixture Using Pulsed DBD Irradiation

Dielectric barrier discharge (DBD) was applied to control the pressure-rise rate of homogeneous compression ignition, which is an important obstacle for homogeneous charge combustion engines. DBD can produce nonthermal plasmas and has been generated in air/fuel mixtures to reform some of the fuel molecules found in such mixtures. This generally shortens the ignition delay of compression ignition of the air/fuel premixture. Stratification of the reformed premixture in the combustion chamber was achieved by pulsed DBD irradiation during the induction process. The formation of inhomogeneous distribution of the reformed premixture is expected by the formation of discharge at the end of the intake processes. A demonstrative experiment was conducted by using a rapid compression and expansion machine. A simple plasma reactor was developed and installed at the intake tube. High-voltage, high-frequency pulses were applied to form plasmas. n-Heptane was used as fuel. Characteristic oscillation was observed at the maximum of pressure history in the compression ignition experiment without using plasma. This oscillation is supposed to be induced by the fast pressure rise initiated by simultaneous ignition in the combustion chamber. Suppression of this oscillation was observed to result from DBD irradiations. The ignition behaviors were observed by a fast-imaging camera. The possibility of using this method for combustion phasing was also examined.