Comparing infrared emission from hydrocarbon C-H stretch during direct injection with and without reaction in an optical heavy duty engine

We present new imaging data comparing IR emission near 3.4 micron of non-reacting and reacting fuel jets from a 9:1 skip-fired optical engine. Images are shown for 3, 5, 7, and 10 crank-angle degrees after the start of injection at three top-dead-center ambient gas temperatures, 800 K 900 K and 1000 K. In addition to presenting qualitative instantaneous 2D images, we quantify differences using ensemble averaged longitudinal profiles of the non-reacting and reacting jets. We see that reaction increases emission by a factor of 2 to 3 during the jet development, prior to bowl-wall interaction. Following bowl-wall interaction, emission increases by a factor of more than 7. The influence of soot emission on the infrared signal is investigated with references to the 'Spray A' free jet from the Engine Combustion Network (ECN). The engine experimental in-cylinder condition is the ECN 900 K, 15.2 kg/m3, 1500 bar rail-pressure injection with n-dodecane fuel. From prior ECN data, hot soot formed under similar conditions should emit 2 to 5 times more than unreacted vapor fuel. Improved diagnostics, e.g. simultaneous measurement of soot volume fraction with IR emission, are needed to provide insight about the fate and transport of unburned fuel in the presence of soot.