Infrared Emission Detection as a Fuel-Vapor Penetration Diagnostic

Line-of-sight infrared (IR) imaging near 3.39 microns captures natural C-H stretch-band emission of hot fuel jets for quantification of jet penetration and dispersion angle. Simultaneous imaging of volume-illuminated laser-induced fluorescence (VLIF) of trace impurities in the n-dodecane fuel, excited at 266 nm and from a 30x30mm2 area, provides for comparison along the same optical path as the IR line-of-sight. In a first step [Eagle 2016], liquid length, vapor penetration, ignition delay and flame lift-off length were determined via Mie scattering, schlieren technique, and chemiluminescence imaging, respectively, for hole #1 of the Engine Combustion Network (ECN) Spray B injector in a 2.34L optical diesel engine. In the present work, IR emission images are added to measure penetration data among various isentropic-core top-dead-center conditions. The comparison of IR and LIF techniques provides benchmark data for the future use of the IR technique to independently determine penetration. The present activity contributes to the understanding of the IR emission tracking of fuel vapor without requiring an external light source to follow the interaction of evaporating/reacting fuel with the in-cylinder charge. Data analysis shows that the convolution of temperature and concentration must be carefully considered when interpreting images.