Search Results

The present work aims at developing and setting up a methodology in which non-intrusive measurements (engine block vibration) are used for monitoring combustion characteristics (combustion diagnosis, combustion development). The engine block vibration appears as a very complex signal in which different sources can be identified, since every moving component or physical process involved in the operation of the engine produces a vibration signal (exhaust valve open/close, inlet valve open/close, fuel injection, combustion, piston slap). Aimed at monitoring the engine running condition, the information carried by the vibration signal has to be broken down into its various contributions and then they have to be related to their respective excitation sources. Concerning combustion-induced vibration, experimental measures has been at first devoted to the selection of the best location where to place the piezoelectric accelerometer.

The performances of high pressure fuel-injection systems and their effects on diesel engine combustion are strongly influenced by the injector characteristics and the set up of the whole equipment control system. High-pressure system based on the common-rail architecture allows a multi-stage injection, which is of paramount importance in controlling combustion noise, fuel consumption, operation roughness and exhaust pollutant emissions. Common rail fuel injection equipment for automotive diesel engine, together with its control system have been analysed by using AMESim environment; both standard library elements and self-developed sub-models have been adopted. At first the different components have been considered one by one; in this way the behaviour of high pressure pump (radial-jet), pressure regulator, rail, injectors, system control (e. c. u.) has been investigated; the results have been compared with experimental measurements.

Relatively recent investigations, basing on experiments as well as on modeling, have highlighted that the needle displacement in common-rail diesel injectors is affected by radial components. The effects of such “off-axis” needle displacement on fuel flow features have been so far investigated within the nozzle, only. The objective of this work is to extend the attention towards the formation of fuel sprays, when needle off-axis condition is encountered. In such a viewpoint, the development of each fuel spray has been modeled taking into account the hole-to-hole variations induced by the needle misalignment. The investigation has been carried out basing on 3D-CFD campaigns, in AVL FIRE environment. The modeling of diesel nozzle flow has been interfaced to the spray simulation, initializing the break-up model on the basis of the transient flow conditions (fuel velocity, turbulence and vapor fraction) at each hole outlet section.