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When the relative contribution of an individual cylinder to the engine output is different from its counterparts, the engine is operating under non-balanced conditions. This may cause power deterioration, higher fuel consumption and excessive engine emissions in the short term, and a mechanical damage breakdown in the long term. To improve the engine quality, there is a strong need for information concerning the imbalance between the cylinders. This can be used as data for a closed-loop control system to manage the amount of fuel injected to each individual cylinder, or may provide useful diagnostic information concerning a possible developing problem that may lead to an engine failure. Direct measurements of the combustion pressure signal can provide the required indication for the imbalance. It however needs a special-purpose transducer and an intrusive approach to the cylinder, and therefore, can be hardly considered as a good candidate for this purpose.

Imbalance between cylinders is a major concern of a proper operation of reciprocating engines. An engine reliability and performance envelop, including life span, fuel consumption and emission, are strongly affected by an improper operation of the cylinders. To improve the engine quality, there is a strong need for a closed-loop control system to manage the amount of fuel injected to each individual cylinder. An advanced system to detect imbalance related faults in reciprocating engines which is based on the analysis of the engine's mechanical vibrations have been developed. The system is based on a firm theoretical background that provides a fundamental relation between the engine's vibration pattern and the relative characteristics of the combustion process in the different cylinders. With a single accelerometer mounted on the engine's block, online information related to the combustion process in each cylinder is provided by the system.

A high-pressure fuel injector has been designed to produce a spray having a lower SMD than that obtained typically with a common-rail fuel injection system for the same injection pressure. In the present design, a mixture of fuel and dissolved gas (CO2 or N2) is introduced continuously to an injector unit. The downstream part of the injector consists of an inlet orifice, an expansion chamber, a swirl duct, and a discharge orifice. When the mixture enters the expansion chamber, a part of the dissolved gas is transformed into tiny bubbles that grow inside the expansion chamber. When the mixture is discharged through the discharge orifice, these bubbles undergo a rapid flashing process while the liquid bulk disintegrates into small droplets. In the present work, we investigate experimentally the effect of the design parameters (geometrical proportions and injection pressure) on the SMD and cone angle of a continuous spray.

Vibrations analysis methods are common as fault detection and diagnosis tools for rotating machines. The successful implementation of this method in various maintenance programs motivates its application to the class of SI engines. In this work, our goals in applying the method are to provide alerts for abnormal operation, to enable detection of the source of the abnormality, and to provide the means to estimate the severity of malfunctions evolving in the engine. Experiments were performed with a four-stroke, four-cylinder in-line, carbureted SI engine. The vibrations were measured at two points around the rear crankshaft bearings in addition to two opposing points on the sides of the engine-block. At each point the vibrations were measured along the axial, the radial and the tangential directions relative to the crankshaft axis.

Advanced engine maintenance programs incorporate various methods for monitoring the engine parts so as to be able to foresee malfunctions and interruptions of normal operation. The present study is concerned with the development of a vibration signature analysis method for early fault detection and diagnosis in internal combustion engines. The successful implementation of this simple and straightforward method in many maintenance programs motivates the application of this method to the class of SI engines. An acceleration transducer is mounted on the engine and the vibration signals are recorded during the engine operation. The measurements are then transformed to the frequency domain where the frequencies and the amplitudes of the harmonic components of the vibrations waveform are analyzed and compared to the corresponding vibration signature under normal operation conditions.