Experimental investigation on the use of argon to improve FMEP determination through motoring method

Abstract

In the ever increasing challenge of developing more efficient and less polluting engines, friction reduction is of significant importance and its investigation needs an accurate and reliable measurement technique. The Pressurized Motoring method is one of the techniques used for both friction and heat transfer measurements in internal combustion engines. This method is able to simulate mechanical loading on the engine components similar to the fired conditions. It also allows measurement of friction mean effective pressure (FMEP) with a much smaller uncertainty as opposed to that achieved from a typical firing setup. Despite its advantages, the FMEP measurements obtained by this method are usually criticized over the fact that the thermal conditions imposed in pressurized motoring are far detached from those seen in fired conditions. In light of these considerations, the authors have put forward a modification to the method, employing Argon in place of Air as pressurization medium. Due to the higher heat capacity ratio, very high in-cylinder gas temperatures, possibly near to the fired conditions, can be achieved using Argon. This allowed better emulation of the fired engine and hence a more representative FMEP measurement. In this publication, experimental results obtained from a testing campaign with different Argon to Air concentration are presented. Tests were carried out on the fully instrumented test bench consisting of a direct-injection compression ignition, four cylinder engine, at different engine speeds and a peak in-cylinder pressure of 84bar. At each set point of speed, the Argon to Air concentration in the manifolds was varied to achieve different in-cylinder temperatures. The measured FMEP values, their uncertainty and their dependence on the different engine operating parameters are reported. It was found that the FMEP in the motored condition was not a function of peak in-cylinder temperature. This insensitivity to in-cylinder temperature further shows the advantage of the pressurized motored method.