N recent years significant attention has been drawn towards plasma-assisted combustion (PAC), whereby plasma effects can induce the formation of “active” particles (ie, free radicals, excited and charged molecules) and subsequently play an important role in the reactivity of a given mixture [1-3]. PAC as a combustion enhancement technique has proven the potential to improve the future design of several advanced combustion systems ranging from gas turbines [4-8], pulsed-detonation engines [9], internal combustion engines [10-15], hypersonic combustion engines [16-24] and even fuel conversion systems [25, 26]. The effectiveness of a plasma source is determined by its extent to exist in a non-equilibrium state. This can be defined as the ratio of energy deposited into higher internal degrees of freedom (eg, vibrational and electronic states) to the total energy deposited into the gas. The chemical reactivity of a gas mixture with a high value of this ratio is many orders of magnitude higher than its equilibrium state, subjected to the same total energy deposition [27]. It is for this reason significant progress has been made to develop generators that can sustain strongly nonequilibrium plasmas. A number of results have shown that the most efficient non-equilibrium plasmas are generated using nanosecond duration, high-voltage pulses [27-31]. The basic idea is to create large volume ionization in a gas flow by the application of 5-50 kV pulses (~ 10 nsec in duration) with 1-100 kHz pulse repetition rates. There are two main advantages to this type of plasma discharge. Firstly, the very short pulse duration is much shorter than the time scale of Joule heating and ionization instability [31]. This reduces the risk of generating glow-to-arc transitions while improving plasma stability. Stable repetitively pulsed plasmas can generate diffuse, volume filling discharges at higher pressures with lower plasma gas temperatures. Secondly, the high reduced electric field, E/N, during the high-voltage pulse can produce large amounts of chemically active species at relatively low power inputs [29]. It is extremely important to understand the mechanism by which non-equilibrium plasmas have an effect on the combustion of gaseous mixtures from both a fundamental and a technological standpoint. The study of PAC has become a global research initiative, where considerable efforts have been made to develop new techniques with varying diagnostic approaches to study the chemical interactions between plasma effects and the basic combustion phenomena. Despite earnest efforts, the underlining kinetic enhancement mechanism remains largely unknown and highly debated. This can be attributed to the vastly different characteristics of the chemistry at play. For instance the plasma chemistry contributing to these enhancements happens at very small time scales (~ nanoseconds) at relatively low temperatures, whereas the combustion chemistry normally occurs at higher temperatures and at larger time scales (~ micro-and milliseconds)[32]. The major consensus is that the primary process in PAC involves the reaction of the long-lived plasma species with fuel and oxidizer at low temperatures. This consequently links the fast plasma chemistry with the high-temperature combustion chemistry [32]. Up until now, this assertion has proven valid for chemical systems close to the" self-ignition" threshold (T> 800 K) and simple fuels (ie, H2 and hydrocarbons less than C3).

To embark on elucidating such as task, well-defined experiments capable of isolating interacting phenomena is necessary, where minimizing the uncertainty in the combustion experiments is critical to decouple the effects of …