Chemical kinetics of hydrocarbon ignition in practical combustion systems

Abstract

Chemical kinetic factors of hydrocarbon oxidation are examined in a variety of ignition problems. Ignition is related to the presence of a dominant chain branching reaction mechanism that can drive a chemical system to completion in a very short period of time. Ignitio n in laboratory environments is studied for problems including shock tubes and rapid compression machines. Modeling of the laboratory systems are used to develop kinetic models that can be Used to analyze ignition in practical systems. Two major chain branching regimes are identified, one consisting of high temperature ignition with a chain branching reaction mechanism based on the reaction between atomic hydrogen with molecular oxygen, and the second based on an intermediate temperature thermal decomposition of hydrogen peroxide. Kinetic models are then used to describe ignition in practical cOmbustion environments, including detonations and pulse combustors for high temperature ignition, and engine knock and diesel ignition for intermediate temperature ignition. The final example of ignition in a practical environment is homogeneous charge, compression ignition (HCCI) which is shown to be a problem dominated by the kinetics intermediate temperature hydrocarbon ignition. Model results show why high hydrocarbon and CO emissions are inevitable in HCCI combustion. The conclusion of this study is that the kinetics of hydrocarbon ignition are actually quite simple, since only one or two elementary reactions are dominant.

Ignition of isomers of pentane: An experimental and kinetic modeling study

“…Low-temperature reactions produce an increasing amount of H 2 O 2 that is stable until its decomposition temperature is reached; since this reaction is part of the H 2 /O 2 reaction submechanism, it is independent of the specific hydrocarbon fuel being studied. Past kinetic modeling studies have demonstrated that this same decomposition reaction is responsible for the onset of knock in spark-ignition engines [21,25,26], ignition in diesel engines [26,27], and ignition under homogeneous charge compression ignition (HCCI) conditions [26,28].…”

Experimental and kinetic modeling study of the shock tube ignition of a large oxygenated fuel: Tri-propylene glycol mono-methyl ether

“…The reactivity of these isomers can be qualitatively compared by examining the reactivity of the various sites in the isomer and their relative position to each other. For example, it is known that 6-membered RȮ 2 radical isomerizations (in reaction class 15) lead to low temperature chain branching by addition of ̇O OH to O 2 (reaction class 26) and subsequent isomerization (reaction class 27) [25]. Thus the presence of two CH 2 groups (secondary C-H sites) that are β to each other allows a fast 6-membered ring RȮ 2 radical isomerization that leads to low-temperature chain branching and indicates that such isomers would be particularly reactive.…”

Modeling and experimental investigation of methylcyclohexane ignition in a rapid compression machine

“…Many chemical kinetic studies in recent years have examined oxidation of nalkane and branched alkane hydrocarbons [1][2][3][4] over the low and intermediate temperature ranges that influence ignition phenomena in many practical combustion systems [5] including spark-ignition, diesel, and homogeneous charge, compression ignition (HCCI) engines. The importance of low temperature oxidation and heat release, and the role of a region of negative temperature coefficient (NTC) are now firmly established.…”