Bibliography - X. L. Zheng
- Zheng, X. L., T. F. Lu, Chung K Law, C. K. Westbrook, and H. J. Curran, 2005: Experimental and Computational Study of Nonpremixed Ignition of Dimethyl Ether in Counterflow. Proceedings of the Combustion Institute, 30(1), doi:10.1016/j.proci.2004.08.241 1101-1109
[ Abstract ]The ignition temperature of nitrogen-diluted dimethyl ether (DME) by heated air in counterflow was
experimentally determined for DME concentration from 5.9% to 30%, system pressure from 1.5 to
3.0 atm, and pressure-weighted strain rate from 110 to 170 s-1. These experimental data were compared
with two mechanisms that were, respectively, available in 1998 and 2003, with the latter being a substantially
updated version of the former. The comparison showed that while the 1998-mechanism uniformly
over-predicted the ignition temperature, the 2003-mechanism yielded a surprisingly close agreement for
all experimental data. Sensitivity analysis for the near-ignition state based on both mechanisms identified
the deficiencies of the 1998-mechanism, in particular, the specifics of the low-temperature cool flame chemistry
in effecting ignition at higher temperatures, as the fuel stream is being progressively heated from its
cold boundary to the high-temperature ignition region around the hot-stream boundary. The 2003-mechanism,
consisting of 79 species and 398 elementary reactions, was then systematically simplified by using
the directed relation graph method to a skeletal mechanism of 49 species and 251 elementary reactions,
which in turn was simplified further by using computational singular perturbation method and quasisteady-
state species assumption to a reduced mechanism consisting of 33 species and 28 lumped reactions.
It was demonstrated that both the skeletal and reduced mechanisms mimicked the performance of the
detailed mechanism with high accuracy.
- Zheng, X. L., and Chung K Law, 2004: Ignition of Premixed Hydrogen/Air by Heated Counterflow under Reduced and Elevated Pressures. Combustion and Flame, 136(1-2), doi:10.1016/j.combustflame.2003.09.016 168-179
[ Abstract ]The temperature of an inert jet required to ignite a counterflowing lean premixed hydrogen/air jet was experimentally
determined over the pressure range of 0.6 to 7 atm and computationally simulated using detailed
chemistry and transport. Results show that, compared to the homogeneous explosion limits, ignition takes place
at higher temperatures and exhibits five limits over the pressure range investigated. The first and second ignition
limits resemble the corresponding first and second homogeneous explosion limits, except they have steeper
slopes in the pressure–temperature response, with the first limit being affected by the significant transport loss
of the H radical and the second limit modified by the activation of the otherwise metastable HO2 radicals
by the diffusively enriched H2. The third and fifth ignition limits are respectively manifestations of the lowand
high-pressure responses of the third homogeneous explosion limit behavior, which is nevertheless punctuated
by the fourth ignition limit characterized by the HO2–H reactions. Furthermore, the fourth ignition limit
runs fairly parallel to the crossover temperature, but is shifted to lower temperatures. An explicit expression,
2k1 = {2k10/(k10 +k11)}k9[M], was derived and found to describe well this limit as well as the extended second
limit observed in previous flow reactor studies. It is further shown that, since transport effects are inherently important
for the present premixed system because of the diffusive loss of H to the hot, inert side of the counterflow, the
ignition temperature increases substantially with increasing strain rate at all pressures and that such a sensitivity
can be moderated by doping the inert flow with a small amount of oxygen.
- Zheng, X. L., J. D. Blouch, D. L. Zhu, Thomas Kreutz, and Chung K Law, 2002: Ignition of Premixed Hydrogen/Air in Heated Counterflow. Proceedings of the Combustion Institute, 29(2), doi:10.1016/S1540-7489(02)80201-2 1637-1644
[ Abstract ]The inert temperature required to ignite a lean premixed hydrogen/air mixture in a counterflow was
determined experimentally and numerically using detailed chemistry and transport. It was found that above
Φ = 0.2, the ignition temperatures increased with increasing equivalence ratio. This effect is due to the
fact that the ignition kernel is located on the hot, inert side of the flow and preferential diffusion of hydrogen
makes the flow self-stratifying, resulting in a rich mixture in the ignition kernel even for a very lean freestream
mixture. The dearth of O2 in the kernel reduces the reaction rates to the point where diffusive loss
becomes significant relative to the rates of kinetic production and consumption. In the presence of this
significant transport loss mechanism, premixed ignition temperatures are much higher than non-premixed
ignition temperatures and the influence of the strain rate is likewise increased. Adding a few percent of
O2 to the hot inert side of the flow lowers the kernel equivalence ratio and increases the reaction rates to
the point where diffusive effects are no longer of the same order as kinetic effects. In these cases, the
ignition temperatures drop significantly to values close to those of non-premixed ignition even though the
free-stream flow is still predominantly premixed.
Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=4267
