In-Cylinder Sampling Analysis of Soot Precursors During Bio-Derived Lactone Combustion in a Single-Cylinder Diesel Engine

The development of new fuels for internal combustion engines requires further technical support by understanding the pollutant formation mechanism in various phases of combustion so that emissions can be minimized. This research will therefore utilize a bespoke in-cylinder sampling system to analyze the precursors of PAHs and particulates during bio-derived lactone combustion in a single-cylinder diesel engine. The sampling system was composed of a poppet-type in-cylinder sampling valve that displaced one of the engine intake valves and protruded into the combustion chamber beyond the flame quenching layer, and a Gas Chromatography Flame Ionization Detector (GC-FID) that examined the samples. The sampling valve was electromagnetically actuated, and its operation was referenced to the engine crank shaft encoder, allowing the valve to open at any Crank Angle Degree (CAD) within a timing resolution of 0.2 CAD. Lactones are oxygenated carbon ring molecules that can be generated from a diverse range of feedstocks. Initial experiments found that some lactones exhibited similar ignition and combustion characteristics compared to fossil diesel, suggesting that these fuels could displace a proportion of fossil fuel usage. During the lactone combustion, the sampling valve was first opened at Top Dead Center (TDC) to investigate intermediate species arising from lactone decomposition during ignition delay and the start of combustion, while the subsequent samples were taken at 10 CAD, 25 CAD, and 40 CAD after TDC. Intermediate species including C2-C6 molecules such as ethylene, acetylene, acetaldehyde, ethanol, 1,3 butadiene, and benzene were observed in the samples. The chemical types and the relative abundance of them during the progress of combustion provided insights into the lactone decomposition pathway and the soot formation mechanism in diesel engine combustion.