GDI spray impact characterization by optical techniques for the assessment of 3D numerical models

Design and optimization of injection systems for internal combustion engines must be realized possibly by relying on detailed analyses, as those achievable through multidimensional engine modeling or by experimental investigations performed on optically accessible engines or under engine like conditions in confined vessels. As regards spark ignition engines, in particular, direct injection technology is being considered as an effective mean to achieve the optimal air-to-fuel ratio distribution at each engine operating condition, either through charge stratification around the spark plug, or by creating a stoichiometric mixture under the highest power demands. The impact of a spray on the piston or cylinder walls causes the formation of a liquid film (wallfilm) and the so-called secondary atomization of droplets. The wallfilm may have no negligible size, especially in cases where the mixture formation is realized under a wall guided mode. The present study is focused on the characterization of both a multi-hole spray and a single hole spray in their impact over a cold or hot plate. A 3D CFD model, whose assessment relies on the collected experimental data, is also developed with the future scope of its application within numerical simulations of entire engine working cycles. A free spray sub-model of high portability allows correctly predicting the spray dynamics at different injection conditions, while the spray-wall impingement sub-model makes evident the gasoline splashing and deposition phenomena.