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The presented work concerns the development of a novel measurement system for determining the instantaneous rotational speed of an engine with high accuracy. The developed system is mainly based on a commercially available optical sensor and appropriate data acquisition / post-processing procedure. The accuracy of the system is high; speed recording with a resolution of one degree of crank angle has been succeeded when measuring the speed of a one cylinder four stroke S.I. motored engine. The deduced experimental results were compared with the corresponding theoretical ones obtained by appropriate simulations, validating the proper functionality of the developed system. Furthermore, the system was also integrated into a typical four cylinder low power industrial engine successfully. Key-features of the proposed measurement configuration are accuracy, simplicity and low-cost suggesting numerous potential applications.

The continuous increase of the green house emissions in conjunction with the limited and finite fuel resources make the improvement of efficiency of all engines, converting fuel chemical energy to mechanical energy, imperative. Even small increase in engine's mechanical efficiency, can be proved significant in economical and environmental terms. Towards this direction, the tribology studies of the Internal Combustion Engines, mainly used as propulsion, power generation and auxiliary drives, are considered important for the design of new engines and the improvement of existing ones. The objective of this paper is to present a simplified (analytical) model for the prediction of the instantaneous friction, developed on the main components of the piston-crank-slider mechanism of an internal combustion engine, including complete piston ring packs, piston skirts, connecting rod bearings and crankshaft main bearings.

A general purpose engine friction model, based on lubrication theory was developed and is presented in this paper. The model takes into account the friction components of the complete ring pack, piston skirt, main/connecting rod bearings and valve train mechanism. Using the developed model, it is possible to predict the complete engine friction (either in crank angle resolution or in engine cycle resolution (Friction Mean Effective Pressure, FMEP), the trajectory of moving components (e.g. piston secondary motion, journal movements in bearings, piston rings motion towards cylinder liner), the pressure field developed by the lubricant. The model was used with data from a four-stroke medium speed marine diesel engine installed in the National Technical University of Athens/Laboratory of Marine Engineering test-bed. The effect of engine speed and engine load on predicted frictional losses was examined and compared with results obtained from other semi-empirical FMEP models.