Correlation between the acoustic intensity measurements with and without an electronically fuel injection system for a small single cylinder Diesel engine.

Gaseous and particulate emissions requirements have lead to the use of higher engine fuel injection pressures. This approach has resulted to introduce, as a direct consequence, higher noise levels. In direct contrast, vehicle noise emission legislation and customer preferences are demanding lower engine radiated noise levels. It has encouraged the development of combustion systems that have relatively short ignition delay periods, and hence has reduced the 'maximum rate of pressure rise' which controls in-cylinder noise levels. The object of the work reported was to identify noise sources of a small single cylinder DI diesel engine used for agricultural and industrial applications as well as off road small vehicles. An ad hoc innovative high-pressure injection system (common rail), electronically controlled for multiple injections, was developed and adopted on the engine in order to verify the capability of this system to reduce the noise and gaseous emissions, and to find the better configuration between them. The experimental tests were conducted in accordance of standard ISO 9614/1 through a sound intensity probe for different operative conditions. With the use of this electronically controlled fuel injection system is possible to optimize the fuel delivery characteristics for every engine operating condition; as a consequence it can be reduce noise levels and gaseous emissions without due attention to in-cylinder noise. To control the noise emissions, different fuel injection strategies were explored. It was demonstrated that this new approach is very effective to control the engine noise for different operative conditions even if some of these strategies to minimize the noise are in contrast with the engine performance and pollutant emission optimisation. For these operative conditions is strongly recommended an optimization process in order to relate the better configuration of noise and emission levels.