THEORETICAL STUDIES ON COMBUSTION CHEMISTRY AND WAVES

Abstract

This thesis aims at extending combustion theory with detailed kinetics in three directions,

namely: Part I theoretically analyzes the explosion limits of homogenous mixtures; Part II

investigates the effects of low-temperature chemistry (LTC) in autoignition, flames and

detonations; and Part III explores several problems regarding accurate measurements and

modelling of laminar flame speeds.

In Part I, the canonical explosion limits of hydrogen-oxygen mixtures are first theoretically

analyzed. The present theory extends previous linear analysis with the participation of radicalradical reactions. Subsequently, the role of hydrogen addition to the explosion limits of carbon

monoxide-oxygen and methane-oxygen mixtures has been evaluated. Eigenvalue analysis shows

that carbon monoxide-oxygen mixtures are more sensitive to hydrogen addition. However, the

methane-oxygen mixtures show mild monotonic-to-nonmonotonic transition with respect to

hydrogen addition.

Part II investigates the role of LTC in autoignition and combustion waves. It first discusses

the LTC affected two-stage autoignition with emphasis on the LTC-controlled first-stage ignition.

Then, the role of LTC in the two canonical combustion waves, namely subsonic deflagration and

supersonic detonation, are examined respectively. For the LTC-affected deflagration, the cool

flame propagation is achieved through the planar flame near flammability limit with heat loss.

The extended flammability limits with cool flames are theoretical predicted by the related LTC

kinetic pathways. For the LTC-affected detonation, the ZND structure at highly diluted

conditions exhibits two distinct stages of energy release caused by low- and high-temperature

chemistries, respectively. Based on the ZND structure, the dynamic parameters of the cell size,

direct initiation energy and critical tube diameter of detonation within the LTC affected regime

are discussed.

Part III examines several problems on laminar flame propagation. First, the role of finite

flame thickness in the extrapolation of laminar flame speed from expanding spherical flame is

investigated. A new extrapolation expression allowing for finite flame thickness is proposed.

Next, the supercritical effect on laminar flame speed at high pressures is studied. By

progressively incorporating the real fluid models into the simulations, contributions of each

component are assessed and elucidated. Finally, the role of Soret diffusion on the flame

propagation and initiation is numerically probed.