Modelling lubricant related fuel economy in heavy duty diesel engines

Abstract

Current and future legislation controlling the exhaust emissions from Heavy Duty Diesel (HDD) vehicles requires an overall improvement in engine efficiency as well as the use of specialised after treatment systems to remove harmful species from the exhaust gas, and prevent these from entering the environment. Engine efficiency can be improved in a number of ways, and a combination of all approaches is required to ensure that the desired levels can be achieved. One approach is to improve the fuel efficiency of crankcase lubricants to optimise fuel consumption and minimise the amount of harmful combustion gas generated. In addition to the environmental benefits, reductions in overall fuel consumption in heavy duty diesel vehicles will represent significant cost savings to transport fleet operators. It is well known that vehicle fuel economy can be improved significantly by using oils of lower viscosity grades. More recently it has been shown that improvements in HDD fuel economy can also be achieved by optimisation of the lubricant additive package, and that the appropriate selection of lubricant viscometrics and additive package can generate improvements in fuel economy without compromising wear performance. In this study, the impact of both lubricant viscometrics and additive type and treat on HDD fuel economy has been evaluated in a series of laboratory bench tests which measure friction under different lubrication regimes, and also in a full driveline rig. It will be shown that fuel economy improvements of up to 4% can be achieved in a fired engine by moving from a 15W40 crankcase lubricant to an optimised 0W20. In addition, it will be shown that within a single viscosity grade, significant improvements in fuel economy can be achieved by tailoring the viscometrics and also by optimising the additive package. Finally, it will be shown that by using laboratory bench test data to model quantitatively the response in the fired engine, the relative importance of different lubrication regimes in determining overall HDD vehicle fuel economy can be estimated.