Search Results

Ambient gas temperature and density, injection pressure, and orifice diameter effects on the flame lift-off length on a direct-injection (DI) diesel spray under quiescent conditions were experimentally investigated. The impacts of the observed lift-off length variations on air entrainment upstream of the lift-off location, soot formation, and the relationship between fuel vaporization and combustion were also examined. The research was conducted in a constant-volume combustion vessel using a common-rail fuel injector and a Phillips research grade #2 diesel fuel. The lift-off length measurements show that lift-off length decreases with increasing ambient gas temperature or density, and increases with increasing injection pressure or orifice diameter. The sensitivity of lift-off length to a change in either temperature or density was non-linear, with the sensitivity to either parameter decreasing as it increased.

The effects of reductions in the ambient gas oxygen concentration on the flame lift-off length on direct-injection (DI) diesel fuel jets under quiescent conditions were experimentally investigated. Reductions in the ambient (i.e., in-cylinder) gas oxygen concentration occur in an engine when exhaust gas recirculation is used to reduce the emission of nitrogen oxides. Also examined were the effects of the changes in lift-off length observed for various conditions on the total amount of oxygen entrained upstream of the lift-off location, soot formation, and the relationship between fuel vaporization and combustion processes. The research was conducted in a constant-volume combustion vessel using a common-rail fuel injector and a Phillips research grade #2 diesel fuel. The lift-off length measurements show that lift-off length is inversely proportional to the ambient gas oxygen concentration.

The reaction zone of a diesel fuel jet stabilizes at a location downstream of the fuel injector once the initial autoignition phase is over. This distance is referred to as flame lift-off length. Recent investigations have examined the effects of a wide range of parameters (injection pressure, orifice diameter, and ambient gas temperature, density and oxygen concentration) on lift-off length under quiescent diesel conditions. Many of the experimental trends in lift-off length were in agreement with scaling laws developed for turbulent, premixed flame propagation in gas-jet lifted flames at atmospheric conditions. However, several effects did not correlate with the gas-jet scaling laws, suggesting that other mechanisms could be important to lift-off stabilization at diesel conditions. This paper shows experimental evidence that ignition processes affect diesel lift-off stabilization.