Abstract
The representation of tank-to-wheel efficiency is for many modelling purposes simplified to a constant value. However, the relationship between tank-to-wheel efficiency and operational properties is not necessarily constant. As a result, situations with both favorable and unfavorable driving conditions will not be adequately represented in instruments for decision making. In this paper, we address this issue by estimating tank-to-wheel efficiency functions customized for use in transport and traffic modelling applications. The functions are estimated by sum of squares on aggregated data, with two different seed functions from a theoretical basis. The level of detail in the estimated functions provide more complexity for evaluations of transport systems in terms of energy and fuel usage, while avoiding too complex modelling of internal engine processes or vehicle specific type parameters. Data sets from vehicle type approval tests are used for the estimation process, and validation tests suggest that a tank-to-wheel efficiency function outperforms a constant value.
Highlights
The operational properties of specific car engines are not readily available
Engine processes are complex, where for instance the fuel consumption depends on variables such as load, speed, size and temperature of the engine, as well as ambient temperatures
As mentioned in the previous section, the measured aggregated CO2-emissions or electrical power-usage throughout the type approval test is provided for each vehicle in the datasets, along with certain vehicle specific characteristics, such as weight and engine size
Summary
The operational properties of specific car engines are not readily available. Engine processes are complex, where for instance the fuel consumption depends on variables such as load, speed, size and temperature of the engine, as well as ambient temperatures. A higher number of different vehicle types will increase the input requirements. In this case, a simpler approach may be appropriate, e.g. a constant value representing an average tank-towheel (TTW) efficiency. The TTW efficiency is determined by the total amount of losses, which in a combustion engine comprise thermal losses, pump losses and mechanical losses [3]. The thermal losses occur as not all of the fuel energy is transformed to mechanical energy, and most of these losses are dissipated through the exhaust. The combustion process is unable to utilize all the thermal energy, and the exhaust ends up at a higher temperature and pressure than the ambient air. The losses are mainly mechanical, and these friction forces
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