Optimal design of a two-stroke Diesel engine for aeronautical applications concerning both thermofluidynamic and acoustic issues

Some aspects concerning the development of a prototype of a diesel engine suitable for aeronautical applications are discussed. The engine aimed at achieving a weight to power ratio equal to one kg/kW (220 kg for 220 kW) is conceived in a two stroke Uniflow configuration and constituted by six cylinders distributed on two parallel banks. Basing on a first choice of some geometrical and operational data, a preliminary fluid-dynamic and acoustic analysis is carried out at the sea level. This includes the engine-turbocharger matching, the estimation of the scavenging process efficiency, and the simulation of the spray and combustion process, arising from a Common Rail injection system. Both 1D and 3D CFD models are employed. In-cylinder pressure cycles are utilized to numerically predict the combustion noise. The acoustic study is based on the integration of FEM/BEM codes. In order to improve the engine performance and vibro-acoustic behaviour, the 1D model, tuned with information derived from the 3D code, is linked to an external optimiziation code (ModeFRONTIERTM). A constrained multi-objective optimization is performed to contemporary minimize the fuel consumption and the maximum in-cylinder temperature and pressure gradient. In this way a better selection of a number of engine parameters is carried out (exhaust valve opening, closing and lift, intake ports heights, start of injection, etc). The best found solution is finally compared to the initial one and some substantial design improvements are discussed.