Potential of low viscosity oils to reduce CO2 emissions and fuel consumption of urban buses fleets

Abstract

a b s t r a c tThis paper shows the results of a comparative fleet test the main objective of which was to measure the influence of Low Viscosity Oils (LVO) over the fuel consumption and CO 2 emissions of urban buses. To perform this test, 39 urban buses, classified into candidate and reference groups depending on the engine oil viscosity, covered a 60,000 km mileage corresponding to two rounds of standard Oil Drain Interval (ODI). In the same way, for 9 buses of the 39 buses, the effect of differential LVO over fuel consumption and their interaction with engine LVO was assessed during the second ODI.Test results confirm that the use of LVO could reduce fuel consumption, hence CO 2 emissions. However, special attention should be taken prior to its implementation in a fleet, particularly if the vehicles are powered by engines with high mechanical and thermal stresses during vehicle operation because this could lead to friction loss increase, loss of the potential fuel consumption reduction of LVO and, in the worst scenario, higher rates of engine wear.Ó 2015 Elsevier Ltd. All rights reserved. IntroductionNowadays research and development departments of road transportation OEMs are focused on CO 2 emission reduction, following the global trend of industry to tackle the Global Warming. This concern has been traduced in CO 2 emission standards in a vast number of industrialized countries. Although these regulations have been set for light duty passenger cars initially, the oncoming trend is to embrace Heavy Duty Vehicles (HDV) as well. It has to be mentioned that research in the HDV segment during the last years has been dedicated to reduce pollutant emissions, especially CO, NO x and particulate matter; this trend is evident when the progression limits of the Euro emission standards are analyzed (European Commission, 2014). For the above stated reasons, to reduce CO 2 emissions has become an important matter for the road transportation segment and, even when the number of HDV is small compared to the number of passenger vehicles, their share in the total amount of CO 2 emissions is remarkable. Getting deeper on this topic, Holmberg et al. (2014) have plotted that from the total energy used in transportation, nearly 73% corresponds to the road segment and of it 36% corresponds to HDV, making this segment a key target where an improvement in efficiency could lead to appreciable energy savings. Among many others, one interesting and specific type of HDV is the urban bus, in which energy shares are about 4% of the transportation sector. Some interesting characteristics of this type of vehicles are pointed out by Holmberg as well; they rely on diesel fuel due to the extended use of ICE, they have a repetitive duty cycle which leads to homogeneous energy http://dx.

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