Showing papers by "Land Rover published in 2019"

Unballanced Performance of Parallel Connected Large Format Lithium Ion Batteries for Electric Vehicle Application

Abstract: The integration of cells that exhibit differing electrical characteristics, such as variations in energy capacity and internal resistance can degrade the overall performance of the energy storage system (ESS) when those cells are aggregated into single battery pack. When cells are connected electrically in parallel, such variations can lead to significant individual differences in battery load current, state of charge (SOC) and heat generation. Further, if consideration is given to small variations in cell interconnection resistance, the detrimental effect on load imbalance is amplified. Given that cell resistance is known to be a function of both SOC and temperature, the impact of the imbalance is compounded as the performance of cells further diverge under load. During extended periods of excitation, variations in cell depth of discharge (DOD) and the occurrence of temperature gradients across the parallel connection will accelerate cell ageing and, if unmanaged, may present safety concerns such as the onset of thermal runaway. In this paper the impact of varied SOC and temperature on the overall performance of the ESS with parallel connected cells has been investigated. The results highlight that 8% variation in the initial SOC can result in a current difference of 62% among the cells, while a temperature variation of 8°C results in a current deviation of 14%. Moreover, it was found that the interconnection resistance can significantly increase the inhomogeneity.

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.