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Non-intrusive, crank-angle resolved measurements of piston temperature have been performed in a single-cylinder direct-injection (DI) Diesel engine operating under highly-dilute low-temperature combustion (LTC) conditions. The laser-induced phosphorescence (LIP) technique exploits the temperature-dependent characteristics of rare-earth or transition metal doped ceramic phosphors. This paper describes the calibration procedure and subsequent application of the technique to measure piston surface temperature in a single-cylinder, optically-accessible Diesel engine for various parametric variations including fueling rate and injector nozzle characteristics. In addition, measurements of the nozzle tip temperature of a Diesel injector are also reported. Furthermore, a fiber-optic solution has been developed which enables piston surface temperature measurements to be performed in standard metal (i.e. non-optical) single-cylinder and multi-cylinder engines.

The influence of piston geometry on the in-cylinder mixture distribution and combustion process in an optically-accessible, direct injection HCCI Diesel engine has been investigated. A new, purpose-designed piston which allows optical access directly into the combustion chamber bowl permitted the application of a number of optical diagnostic techniques. Firstly, laser-induced exciplex fluorescence (LIEF) has been applied in order to characterize the fuel spray and vapor development within the piston bowl. Subsequently a detailed study of the auto-ignition and two-stage Diesel HCCI combustion process has been conducted by a combination of direct chemiluminescence imaging, laser-induced fluorescence (LIF) of the intermediate species formaldehyde (CH2O) which is present during the cool flame and LIF of the OH radical later present in the reaction and burned gas zones at higher temperature.