Combustion processes can be greatly improved using reactive species created in non-equilibrium plasma for the initiation of fuel oxidation and pyrolysis. One such process is volumetric ignition, inherent to homogeneous charge compression ignition (HCCI) engines. The HCCI engine has high efficiency and low emissions of both nitrous oxide (NO) and carbon monoxide (CO), and does not produce soot particles. However, HCCI technology is currently limited by control difficulties and has a narrow operating range when compared to the traditional compression ignition or spark ignition engines.
The present study seeks to control ignition timing by reforming a fuel-air mixture in a plasma discharge. A small charge of n-heptane/air mixture is subjected to a plasma discharge and then mixed with a main charge in order to modify ignition characteristics. The effects of the reformed charge on ignition timing are investigated using zero-dimensional time dependent models. Plasma reaction calculations employ an open-source zero-dimensional discharge solver ZDPlaskin, incorporating BOLSIG+ to obtain electron transport coefficient and for pre-processing the plasma chemistry mechanism, including rates of electron collision reactions. Ignition delay of fuel-air mixture with species created in the discharge is calculated using Cantera.
Ignition delay was shortened significantly using a small amount of reformed fuel, especially at low temperatures of 600 to 800K. At higher temperatures, the change is less pronounced; however, there is a decrease in ignition delay with the increase in activated species molar mass. The results show potential as a method to control ignition timing in advanced engine technologies.
