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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.

The optimization of the combustion process in diesel engines is one of the challenges to improve performance, emissions, fuel consumption and NVH characteristics. This work constitutes one of the last steps of a comprehensive research program in which vibration sensors are used with the purpose of developing and setting up a methodology that is able to monitor and optimize the combustion process by means of non-intrusive measurements. Previously published results have demonstrated the direct relationship that exists between in-cylinder pressure and engine block vibration signals, as well as the sensitivity of the engine surface vibration to variation of injection parameters when the accelerometer is placed in a sensitive location of the engine block.

This paper presents the results of an experimental study on the application of an engine block vibration transducer. The aim of the study was to accomplish a real time management of the control unit using the vibration signal as a feedback to correct the injection parameters setting. The continuously strengthened exhaust emission regulations and the constrains related to the fuel consumption and noise, vibration and harshness (NVH) characteristics, have determined increasing interest towards investigation of the potentiality of new combustion technologies and fuel blends capable of reducing particulate matter and NOx emissions. Focus has also been paid to non-intrusive techniques for the combustion process characterization by means of sensors, such as microphones and accelerometers.

To ensure compliance with emerging Diesel emission standards and demands for reduced fuel consumption, the optimization of the engine operation is imperative under both stationary and real operation conditions. This issue imposes a strict control of the combustion process that requires a closed-loop algorithm able to provide an optimal response of the engine system not only to warm-up, accelerations, changes in the slope of the road, etc., but also to engine aging and variations of fuel properties. In this paper, with the final purpose of accomplishing an innovative control strategy based on non intrusive measurement, the engine block vibration signal is used to extract useful information able to characterize the in-cylinder pressure development during the combustion process. In the previous research activity, the same methodology was applied to stationary operation of the engine.

Besides pollutant emissions, fuel consumption and performance, vehicle NVH constitutes a further object during engine development and optimization. In recent years, research activity for diesel engine noise reduction has been devoted to investigate aerodynamic noise due to intake and exhaust systems and surface radiated noise. Most of the attention has been concerned with the identification and analysis of noise sources in order to evaluate the individual contribution (injection, combustion, piston slap, turbocharger, oil pump, valves) to the overall noise with the aim of selecting appropriate control strategies. Several studies have been devoted to analyze combustion process that has a direct influence on engine noise emission; the impact of injection strategies on the combustion noise has been evaluated and approaches able to separate engine combustion and mechanical noise components have been presented.

Many studies have demonstrated that an efficient control of the combustion process is crucial in order to comply with increasingly emerging Diesel emission standards and demanding for reduced fuel consumption. Methodologies based on real-time techniques are imperative and even if newly sensors will be available in the near future for on-board installation inside the cylinder, non intrusive measurements are still considered very attractive. This paper presents an experimental activity devoted to analyze the noise emission from a small displacement two-cylinder Diesel engine equipped by HPCR (high pressure common rail) fuel injection system. The signals acquired during stationary operation of the engine are analyzed and processed in order to highlight the different sources contributing to the overall emission. Particular attention is devoted to the specific samples of the signal that are mainly caused by the combustion process in order to extract the combustion contribution.