Laser diagnostics of C2H4 and CH4 from n-butane pyrolysis

Combustion of fossil fuels remains the dominant source of energy which enables us sustain thrive in this planet. Meanwhile, the negative effects of burning fossil fuels, however, are devastating our climate and environment. Eliminating those negative effects while attaining energy supply from fossil fuels becomes urgent and prominent. It is, nevertheless, impossible without a thorough understanding of the combustion process.

Experimental approach remains one of the dominating approaches to study combustion despite the growing interest in numerical approach. The development of workstations and massive supercomputers is providing the computation ability that one has never imaged. Nevertheless, it still appears difficult to catch up with the ever-increasing computational power demand, especially in the area of combustion. Not only the intermediate species need to be studied experimentally, but also the reactions need to be verified using experimental approach.

Due to the nature of laser and Laser diagnostics, which conducts the diagnosis by measuring the responses of laser illumination, it is incredibly suitable for combustion research. Moreover, laser based diagnostics techniques provide the capabilities of remote, non-intrusive, in situ measurements with spatial and temporal accuracy that has never been achieved. In current study, two laser based diagnostics techniques are explored: Coherent microwave scattering from resonance enhanced multiphoton ionization (Radar REMPI) and Tunable diode laser absorption spectroscopy (TDLAS).

Combustion of heavy hydrocarbons is a complex process, which can be roughly divided into two sub-processes: pyrolysis and burning of lighter hydrocarbons. Ethylene and methane are two common products of heavy hydrocarbon pyrolysis, e.g. n-butane. Their detection under harsh environment, i.e. higher temperature and pressure, are explored using Radar REMPI and TDLAS.

Radar REMPI is used to detect ethylene under high temperature and pressure. The results obtained justified Radar REMPI as a promising detection technique for ethylene under combustion. On the other hand, TDLAS is used to detect methane in current study. A numerical absorption spectroscopic model is built which predicts methane’s concentration under different pressure and temperature. Methane from n-butane pyrolysis is detected and quantified using TDLAS.