Performance of vegetable derived fuels in diesel engine vehicles
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Publication date: 2005-05-01
Combustion Engines 2005,121(2)
Alternative renewable fuels are more and more important due to increasing of oil prices, environmental concern (greenhouse and other pollutant gases) and, in some regions, their potential to help to conserve agricultural activity (previously aimed to food destination). For the case of vegetable oils several possibilities can be considered, such as mixtures of diesel fuel with both raw oil and oil-derived methyl-esters, where mixture proportions range between zero(pure diesel fuel) and 100% (pure alternative fuel). A third possibility is the use of mixtures of bio-ethanol (obtained om sugar or starch crops) and diesel fuel (e-diesel). Detailed results are presented relative to sunflower methyl-ester performance in engines (test bench), car vehicles (European test cycle) and endurance road tests for car vehicles and urban buses. These results show a favourable trend in the use of sunflower oil derived fuels in terms of emissions, with minor deterioration of power and fuel consumption. The trend is even more favourable if other aspects are considered such as positive energy balance of methyl-esters, relative simplicity of the transformation process, compatibility with the present diesel engine and car technology, possibility to deliver the alternative fuel through established automotive fuels distribution networks, etc. The main results of the presented tests can be summarised as follows: The mixtures of sunflower oil methyl diesel and diesel fuel, and especially those with less than 20% of ester, present perfectly valid properties and characteristics for their use in diesel engines without the need of modification. The current specification for Diesel fuel, EN 590, allows the presence of up to 5% of methyl ester, while, according to the authors results, this amount could be increased without consequences up to 20%. The results in engine test rigs confirm the general trends or other results. There is a reduction of full load power and torque, due to a lower heating value methyl esters, in accordance with an increase in fuel consumption (up to 16% for pure methyl ester). CO and HC are reduced for pure methyl ester and high contents of this, in spite of the fact that a moderate increase was observed for small contents of methyl ester at low engine rpm. NOx emissions show a very weak trend to increase as methyl ester content increases. The results obtained in two passenger cars running a European Driving Cycle presented the same trends. The endurance test covered 80,000 km in a passenger car with a fuel containing 10% of sunflower methyl ester. No problem was detected in lubricant, injection valve choking, fuel consumption and fuel filters. All the results were in accordance with it is expected for the same car running with pure diesel fuel.