Effect of various working fluid compositions on combustion noise in diesel engines

Increasingroad traffic has brought about legislation aimed at reducing noise from vehcle engines. Noise is transmitted throughout the engine block and other rigidly attached components as vibration. These vibrations can exists across the entire spectrum of frequencies. When they are in the range at which a healthy human ear can hear they radiatefrom the engine structure as audible. This noise and vibration can create severe problems for the engine structure, its operators, and the surroundings. Engine noise can be grouped into one of three categories; air flow, mechanical and combustion noise. Most of previous research undertakenhas investigated means of reducing air flow and mechanical noise primarily through the use of dampers, better balancing techniques and acoustic enclosures. Such solutions require extensive and usually expensive physical modifications to the engine structure. However, reduction of the prima~y noise source, combustion noise, requires detailed insight into and modification of the combustion process itself. Combustion noise can be the predominant source of noise in diesel engines and in high compression lightweight gasoline engines. High compression ratio engines have a tendency to exhibit faster rates of combustion chamber pressure rise and are, therefore, more prone to elevatedlevels of combustion noise. Although not the only factor to effect combustion noise, rate of pressure rise is most definitely a primary parameter. In thls paper an investigation is reported on the effect whlch variation in intake mixture composition have on combustion noise in an indirect injection (IDI) hesel engine across a wide range of audible and inaudible frequencies. Pressure rise and rate of pressure rise are also monitored to provide a better understandmg of the relationshp between the combus tion process and noise production. Relationships were establishedrelating combustion noise levels, rate of pressure rise, intake mixture composition andload. These are given in here. Introduction The use of intake mixture modification through such techniques as exhaust Gas Recirculation (EGR) with sparkignition engines has become a common technique used for reducing the emissions of automobile pollutants. However, until recently especially outside of Europe, diesel engines were seldom equipped wi th similar environmentally beneficial EGR equipment. However, a form of EGR diesel unit, commonly called the closed cycle diesel, has been used and investigated sporadically for over 80 years for utilisation as an airindependent submarine power system [I]. Recent investigations into EGR systems have shown that the technique used to make the diesel operate independentof air may have many land based environmental benefits by being developedas a method of emission control for diesel engines