Studying the relationship between the vibration signature and the combustion process in diesel engines

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. Moreover, typical combustion pressure transducers are expensive, unreliable in the hostile engine environment, and require special modifications of the engine head. Recently it has been proposed to evaluate the relative contribution of each cylinder by means of indirect measurements, by using vibration measurements of the engine block. The methodology introduced in the present work suggests a newly developed approach towards analyzing the vibration analysis of diesel engines. The method is based on fundamental relationship between the engines vibration pattern and the relative characteristics of the combustion process in each different cylinder. The present report describes the method, setup, and the experimental results of this methodology.