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Evaluation of Cottonseed Oil-Diesel Fuel Blends as Fuel for Automotive Diesel Engines
Published October 22, 2006 by Society of Automotive Engineers of Japan in Japan
The requirements for the reduction of greenhouse gas emissions and the raising oil prices have accelerated efforts to increase the share of non-fossil fuels in the total road-transport energy consumption. The current regulatory requirements in the European Union call for a minimum 2% of the total oil-derived gasoline and diesel consumed in 2005 to be replaced by biofuels and renewable fuels and the target becomes 5.75% in 2010. For diesel engines, fatty acid methyl esters (FAME), derived mainly by the transesterification of vegetable oils, have for many years been considered as potential fuels. In this paper however, we examine the possibility to blend cottonseed oil directly with fossil diesel as a fuel for diesel engines. This option has a lower cost and larger well-to-wheel greenhouse gas benefits than FAME fuels. The paper first examines the fuel properties, mainly density, viscosity and cetane number as a function of the volumetric mixing ratio of oil into diesel, in order to establish the permissible mixing ratios for the fuel to comply with relevant regulations. Second, a Euro 2 diesel car is tested using oil-diesel blends in different mixing ratios in order to examine the fuel effects on emissions of regulated pollutants and CO2. In parallel, particle emission characteristics are studied, including the total and solid particle number in several real-world cycles and the particle size distribution over steady states. The results indicate that fuel blends with up to 20% oil present good combustion characteristics and limited effects on regulated emissions. These results would justify using vegetable oils on a pilot fleet for a larger mileage, to examine their compatibility with different engines together with their effect on engine durability.