Mathematical description of the external characteristics of compression-ignition engine

In this paper is presented a calculation procedure based on Lagrange's interpolation formuła which has been used for describing the external characteristics of compression-ignition engine of the 359 type. The characteristic curves of specific fuel consumption and exhaust gas smokiness were chosen as an example, which had been obtained during examinations on engine test bed for a drive unitfuelled with four types of fuel. Measurements were carried out on a standard engine test bed which is part of laboratory facilities of the Department of Automotive Vehicles Operation, Western Pomeranian University of Technology in Szczecin. The study object was an unsupercharged four-stroke engine of domestic production of the 359 type. It is a six-cylinder compression-ignition drive unit with direct fuel injection system. Interpolating polynomials determined analytically for respective characteristics have been presented in the graphical form, while experimental examination results necessary for obtaining them have been additionally tabulated. The presented methodology allows simplification of particular experiment stages by giving possibility to estimate analytically the missing data and with preservation of a minimum number of measuring points. With small corrections, it may be used in similar examinations on other engine test beds. Its application should support the planning of particular experiment stages but does not, in any case, replace it since determination of engine characteristic curves is possible through research only.