Characterization of dual-fuel combustion processes

Abstract

Lean-burn concepts are an attractive solution for the compliance with future emission standards towards reduction of carbon dioxide (CO 2), combined with considerably lower particulate matter (soot) as well as nitrogen and sulfur oxide (NO X , SO X) emissions-all that with efficiency comparable to diesel combustion. In this regard, lean burn gas/dual-fuel engine market is spread over a wide range of application areas, particularly targeting maritime industry. However , dual-fuel ignition and combustion processes of pilot spray ignited lean-premixed gas/air charge still pose considerable challenges to ensure reliable operation between misfiring and knocking as well as in terms of cyclic stability. A novel "optical engine" test facility ("Flex-OeCoS") enables the investigation of pilot spray ignition and the ensuing transition to a turbulent premixed flame. The experimental test facility features ability to achieve engine relevant compression/combustion pressures and temperatures at variable speeds (flow/turbulence) for an adjustable range of gas/air charge composition. Process conditions are tunable with high operational flexibility (e.g. variable valve timing, number of cycles) to approach characteristic conditions of the parameters influencing ignition and combustion. The optically accessible combustion chamber enables the application of optical measurement methods to acquire inflammation time/location and flame propagation. The focus of the paper lies on the experimental test facility and its flexibility in terms of fundamental pilot spray ignited lean-burn methane/air charge dual-fuel investigations. Moreover, initial results of ignition process and flame propagation in the "Flex-OeCoS" test rig based on operation and boundary conditions will be presented. The influence of a variety of affecting parameters has been investigated: CH 4 /air charge composition, process gas temperatures and pressures, injection rate/duration, flow field (turbulence), and pilot fuels with different properties. Conclusions shall give extended insight into the thermo-chemical processes of dual-fuel combustion and the acquired reference data will be used to validate and further develop numerical CRFD methods.