Engine downspeeding is a promising concept for fuel economy improvement in long haul truck applications. AVL performed system simulations to quantify the remaining fuel saving potential and to analyze the corresponding challenges. Specifically the required base engine design modifications and the consequent changes in engine friction have been considered. The following conclusions can be drawn: Pure downspeeding without adjustment of the full load characteristics improves the cycle fuel economy by 1.5%. However, the number of gear shifting events considerably increases (it approximately doubles). In a second step the torque characteristic was increased in a way that the power at 1000 rpm is equivalent to the power of the baseline at 1150 rpm. This increases the maximum BMEP level from 23 to 27.5 bar and the peak firing pressure from 200 bar to 250 bar. By applying this full load characteristic the number of gear shift events of the baseline version can be kept. The fuel consumption saving increases to 2.0%. To gain the full potential of downspeeding the thermodynamic boundary conditions have to be adjusted. This means that the turbocharger matching and the combustion settings have to be adapted accordingly. The increase of the PFP to 250 bar requires significant design changes for the base engine. These are in particular larger crankshaft bearing diameters and higher oil- and coolant pump flows. Additionally, the increased fuel injection quantities increase the power consumption of the high pressure fuel pump. All these changes lead to higher FMEP levels however, they are still overcompensated by the benefits of downspeeding to 1000 rpm. Finally, the downspeeding was pushed even further - to a road load speed of 800 rpm. The necessary 300 bar PFP base engine design would result in a further FMEP increase. Nevertheless, such a concept would still achieve a benefit in the overall friction if compared to the baseline (1200 rpm/ 200 bar PFP). However, also disadvantages must be considered such as engine size, weight and cost as well as necessary driveline modifications (e.g. vibration damper, transmission with higher torque capability) and extremely high boost pressure levels. From today's standpoint these disadvantages of such an aggressive downspeeding concept can't be sufficiently compensated by the corresponding additional fuel saving benefits. The fuel saving potential of downspeeding decreases due to the necessary adaptations of the base engine design caused by the higher PFP demand. This can be seen in Figure 13.


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    Title :

    Potentials, Challenges and Limits of Downspeeding for Commercial Engines in Long Haul Trucks


    Contributors:


    Publication date :

    2015


    Size :

    17 Seiten, Bilder, Tabellen, Quellen




    Type of media :

    Conference paper


    Type of material :

    Print


    Language :

    English




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