High-Speed Infrared Imaging for Analysis of a Diesel Engine Supplied with a Premixed Methane-Air Charge

Efforts are continuously made for improving internal combustion engines (ICEs) efficiency. Lowering fuel consumption and reducing soot formation are among the challenges being addressed when seeking to improve engine designs. In this work, ICEs characterization was carried out on an elongated single-cylinder transparent diesel engine equipped with the multi-cylinder head of a commercial passenger's car and a common rail injection system. The engine uses a conventionally extended piston where part of the piston's crown is replaced by a sapphire window. In this configuration, a full view of the combustion bowl can be achieved while the engine is in operation by looking at a 45° fixed mirror located in the extended piston axis. Infrared imaging was carried out at 26 kHz, leading to a temporal resolution of about 0.35° crankshaft angle, at 1500 RPM, in the engine's reference frame. The different phases of a combustion cycle, i.e. intake, compression, fuel injection, working stroke and exhaust, were investigated using four different spectral filters (broadband, CO2 red-spike, through-flame and hydrocarbons). In the experiment, air was replaced by a premixed air-methane charge in order to improve combustion and lower the amount of soot deposits. The results illustrate the potential of high-speed IR imaging as a diagnostic tool for ICEs.