Role of spray chamber experiments in understanding flame-flame interaction events in heavy-duty diesel engine combustion.

Artikel i vetenskaplig tidskrift, 2018

Combustion in spray-controlled heavy-duty (HD) engines is characterized by gas-phase interactions between the ignited fuel jets (flames) and piston walls rather than liquid fuel impingement on the walls. In the research on HD engine emissions and fuel consumption, enhancement of mixing late in the combustion cycle is important. Mixing late in the cycle depends on development of the flow field in the cylinder, which in turn is affected by phenomena such as turbulent flow near a stagnation point during jet-wall impingement, wall-jet development along the piston walls and flame-flame interactions. Optical diagnostics in single-cylinder engines and combustion computational fluid dynamics (CFD) simulations are well-known methods for studying in-cylinder flow events. Detailed optical experiments conducted in high temperature/high pressure spray chambers (SCs) with single-hole fuel nozzles are now widely used for generating validation data for modeling a freely developing single spray. However, to date, very few SC setups have included flame-flame interactions. In this paper, a new SC setup is presented comprising a HD double-hole nozzle and different wall geometries. The setup enabled detailed optical analysis of the aforementioned interaction events. Imaging of soot luminosity, OH chemiluminescence and laser soot shadow imaging were used to compare late-cycle mixing in a conventional bowl geometry with a new piston type able to lower soot emissions considerably (referred to as a wave piston). Together with combustion CFD simulations, the new experimental setup yielded useful results for understanding flame-flame interaction effects on late-cycle mixing in HD engine combustion.