Air-fuel Mixture Preparation for Internal Combustion Engines:Optical Techniques for Diagnosis of the Spray Developments

Nobody escapes the importance of the air/fuel mixture preparation in internal combustion engines, whatever is the thermodynamic cycle they work on and the adopted fuel. The short time between the fueling and the start of the combustion is crucial for the best mixture formation and its burning for energy optimization and the pollutant production. The always stringent vehicle emissions rules led engine research toward the use of high-pressures and direct-injection systems for allowing a best atomization/vaporization of the fuel while, as drawback, the downsizing of the combustion system results in increasing of fuel impact on the combustion chamber and cylinder line with HC and particulate matter increase at the exhaust. A complete description of the injected fuel, its spread in the chamber with primary and secondary breakups, the vaporization, the mixture with the air and the combustion are of basic importance to govern the process and help new design architectures. Optical characterization has shown it’s powerful in describing these processes without interfering with their evolution both in stationary and reciprocating devices. Imaging and spectroscopic techniques allow us to follow the physic-chemical transformations of the initial bulk of fuel in the mixture, production of primary and secondary species and individuate the potential sites of pollutant production. Furthermore, the results constitute a data set for initializing and calibrating numerical codes for provisional, results and behavior of diverse injecting systems and at different ambient conditions, and last but not the least inside the engine. In this paper, a tracking shot of optical techniques adopted to depict the fuel spread in a quiescent optical accessible vessel at engine-like conditions is reported for practices of fuel direct injection in engines.