- Author
-
Miziolek, A. W.
|
Sausa, R. C.
- Title
- Photochemical Ignition Studies. Part 1. Laser Ignition of Flowing Premixed Gases.
- Coporate
- Army Ballistic Research Lab., Aberdeen Proving Ground, MD
- Report
-
BRL-TR-2644,
February 1985,
29 p.
- Keywords
-
lasers
|
gas mixtures
|
photochemical reactions
|
combustion gases
|
minimum ignition energy
|
radicals
- Abstract
- Gas mixtures of CH4/air, CH4/N2O, C3H8/air, C3H8/N2Ogkl, and C2H2/air were ignited above a slot burner by focusing three different laser beams whose wavelengths are 193 nm, 248 nm, and 532 nm. Minimum ignition energies were determined over a wide range of equivalence ratios and over the energy range of 0.1-40 mjoule/pulse for each gas/laser combination. A substantial wavelength dependence of the minimum ignition energy was observed for the ArF (193 nm) and KrF (248 nm) lasers acting on the different gas mixtures and was attributed to molecule-specific multiphoton-indiced photochemistry of the various fuel and oxidizer molecules. Here, the necessary radicals and/or ions which are needed to cause ignition to occur are apparently produced in a controlled way. The Nd:YAG second harmonic (532 nm) laser exhibited a much smaller minimum ignition energy range for the various gas mixtures due to a different ignition mechanims involving gas breadkown, i.e., a laser-produced spark. This process appears to be much harder to control with respect to energy deposition than the photochemical one. The most efficient laser-driven ignition system was the one where the ArF (193 nm) laser acted on C2H2/air and laser energies as low as 0.2 mjoule caused ignition. Our results further indicate that there should be a number of ways to improve the efficiency of the photochemical ignition process. Thus, this new type of ignition source appears to possess considerable potential for utility in both practical applications as well as in allowing direct, time-resolved studies of the chemistry of ignition itself, which is an area of considerable current interest.