Application of interval interpolation for the description of compression-ignition engine performance characteristics

Abstract

In this paper is presented a calculation method based on Lagrange's interpolation formula which has been used for mathematical description of the performance characteristics of a compression-ignition engine of the 359 type of the Polish production. Its application allows simplification of experimental tests through preservation of a minimum number of measuring points and estimation of other data analytically. In order to minimise the interpolation error occurring with polynomials of high degrees and constant node distances, the characteristics were approximated by spline functions with both solutions being shown comparatively in the graphical form. As calculation examples, the curves of specific fuel consumption and infrared radiation absorption coefficient were chosen, which had been obtained during examinations on engine test bench for a drive unit fuelled with four types of fuel. In addition, results of the experiment required for their determination were tabulated. The presented method may be used in further tests of a given engine as well as on other experimental benches, aiding long-lasting and expensive optimisation of operating parameters when using fuels of plant origin. Description of any performance characteristics by means of interval interpolation is convenient from the practical side and does not cause greater calculation problems since polynomials of low degrees are being used in the procedure.