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The optimization procedure adopted in the present investigation is based on Genetic Algorithms (GA) and allows different fitness functions to be simultaneously maximized. The parameters to be optimized are related to the geometric features of the combustion chamber, which ranges of variation are very wide. For all the investigated configurations, bowl volume and squish-to-bowl volume ratio were kept constant so that the compression ratio was the same for all investigated chambers. This condition assures that changes in the emissions were caused by geometric variations only. The spray injection angle was also considered as a variable parameter. The optimization was simultaneously performed for different engine operating conditions, i.e. load and speed, and the corresponding fitness values were weighted according to their occurrence in the European Driving Test.

In the present study, the influence of pressure waves propagating in the ducts of common rail injection systems on engine out emission has been investigated. The pressure waves originated by the closure of the injectors are characterized by an amplitude that can easily be greater than 10 MPa. When a multi injection strategy is adopted such fluctuations can strongly affect fuel delivery rate of subsequent injections and therefore emission levels and fuel consumption. The paper reports the results of an experimental investigation that has been carried out on a single cylinder engine equipped with a common rail electronically controlled high pressure injection system and an optical access, via endoscopes, for the visualization of soot and combustion process. The used injection strategy consisted of pilot and main injection. To allow the start of the main injection on a local pressure peak or valley without changing injection timing, injection system ducts of different length were used.

In the present investigation, a parametric study of the geometric characteristics of a two-cylinder four-stroke gasoline engine was carried out. Engine power, torque, specific consumption, engine efficiency, in-cylinder pressure for both the cylinders and pressure along the intake and exhaust manifolds at different positions were experimentally measured for engine speeds ranging from 5000 to 9500 rpm. All measurements were made under steady state conditions and full load. Engine characteristics were calculated by means of a 1-D model, which was used to calculate wave propagation in the intake and exhaust manifolds. A zero dimensional model was used to account for the in-cylinder phenomena. In the 1-D model the effects of pipe curvature, restriction geometry, gas friction, and heat transfer to the manifolds walls were considered. Numerical results showed good agreement with the measurements over the investigated range of operating conditions.