Sammendrag
Using ammonia as fuel in retrofitted large marine vessels or heavy-duty vehicles has the potential to reduce CO2 emissions. However, ammonia is hard to burn in an internal combustion engine (ICE) due to its poor combustion properties, i.e. having high autoignition temperatures and low flame speeds. This results in the need for a highly reactive secondary fuel or an improved ignition system for achieving complete and stable combustion. This study investigates a radical technology for the ignition of a fuel-air mixture using carbon nanotubes. The technology consists of injecting a mixture of multi-walled carbon nanotubes and ferrocene (CNT-Fe) into a fuel-air mixture and subjecting the particles to a bright flash of light. Due to the photochemical properties of CNT-Fe particles, the absorbed light initiates ignition. The burning particles thereby ignite the gas mixture at multiple points in the chamber, resulting in a flame front propagating faster compared to when using conventional methods like spark plugs. This study investigates the concept in a constant volume chamber filled with mixtures of methane and air, where the CNT-Fe is dispersed inside the chamber and ignited by an externally located xenon flash tube through a quartz window. The aim of the study was to provide a proof of concept, showing that an external light source can initiate combustion in a chamber by CNT-Fe, potentially demonstrating that the technology can be transferred to an engine. Different mixtures of methane/air and chamber pressures were tested. The results show that photo ignition of methane/air is achieved for mixtures with equivalence ratios of 0.65-0.9, whilst for spark ignition the equivalence ratio range was 0.7-1.4. A qualitative assessment of the flame spread is made through optical measurements of the flame front, showing that dispersed CNT-Fe achieves faster burn rates.
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