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<div class="section abstract"><div class="htmlview paragraph">Mechanical friction is a significant power dissipater in the internal combustion engine. In the effort of designing more efficient and less pollutant engines, friction reduction is certainly on the agenda to be investigated. Such investigation cannot be possible without an accurate measurement of the same quantity. This publication regards a continued study on the mechanical friction determination in an internal combustion engine using the Pressurised Motoring Method. In this work, the friction mean effective pressure of a four-cylinder compression ignition engine was investigated with varying engine speed and manifold pressurisation, using a dedicated high precision sensor for the correct determination of the cylinder Top Dead Centre position. Two different measurement sessions were carried out; in the first, air was employed as pressurisation medium, testing 32 different setpoints; in the second, instead, with the aim to test the effect of the variation of thermochemical properties of fluids on the thermodynamic loss angle, Argon was used in place of air in 18 different setpoints. In the motored condition it is widely accepted that the brake torque is a measure of the losses of the engine and therefore has to be supplied by the driver, in our case the AC motor. The 2000 rpm region was explored with the aim to investigate the high motoring brake torque observed in a previous work from the same authors [<span class="xref">1</span>]. An investigation of the volumetric efficiency effect on motoring brake torque is also presented in the paper. Values of IMEP, BMEP, FMEP, peak in-cylinder pressure, loss angle and other parameters are given. The loss angle measured at each setpoint using the TDC sensor is compared with the loss angle evaluated by the use of two thermodynamic methods developed by Stas’ [<span class="xref">2</span>] and Pipitone [<span class="xref">3</span>].</div></div>

<div class="section abstract"><div class="htmlview paragraph">Mechanical friction and heat transfer in internal combustion engines have long been studied through both experimental and numerical simulation. This publication presents a continuation study on a Pressurized Motoring setup, which was presented in SAE paper 2018-01-0121 and found to offer robust measurements at relatively low investment and running cost. Apart from the limitation that the peak in-cylinder pressure occurs around 1 DegCA BTDC, the pressurized motoring method is often criticized on the fact that the gas temperatures in motoring are much lower than that in fired engines, hence might reflect in a different FMEP measurement. In the work presented in SAE paper 2019-01-0930, Argon was used as the pressurization gas due to its high ratio of specific heats. This allowed to achieve higher peak in-cylinder temperatures which close further the gap between fired and motored mechanical friction tests. In 2019-24-0141, Argon was mixed in different proportions with Air to synthesize gases with different ratios of specific heats in the aim of observing any abrupt transitions in the FMEP with different peak in-cylinder temperatures. In this publication, a higher loading test matrix to that published in 2019-24-0141 is presented, with an engine speed ranging from 1400 rpm to 3000 rpm and ratios of specific heats varying from that of Air (<b><i>γ</i></b> = 1.4) to that of Argon (<b><i>γ</i></b> = 1.67). The peak in-cylinder pressure was kept at a constant 103 bar. Results obtained in this work strengthen further the observations made in 2019-24-0141; where the measured FMEP is found to be insensitive to the different peak in-cylinder temperatures. In this study, a fast-response thermocouple of the eroding type was also fitted in the combustion chamber and gas-wall interface temperature histories were recorded. The transient heat flux was also computed through a spectral analysis and reported in this publication.</div></div>

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