Think consumption varies between petrol grades? Think again...
Researchers in Finland have discovered that no difference exists between the commercial petrol grades 95E10 and 98E5 with respect to consumption of fuel during normal driving conditions. The study was funded in part by the TRANSECO ('TransEco-tutkimusohjelman [Research programme on road transport energy efficiency]') initiative, which has clinched EUR 3 million under the ERA-NET Transport II Scheme of the EU's Seventh Framework Programme (FP7).
Scientists at the VTT Technical Research Centre of Finland conducted driving tests at the Otaniemi Neste Oil service station in Espoo using six used cars of various makes under laboratory conditions. The model years of the cars were between 1999 and 2010 and, based on their manufacturers' recommendations, compatible with E10-fuel. The Finnish Customs Laboratory set the ethanol contents of the fuel batches to make sure that ethanol contents complied with the specifications outlined in the study. The findings showed 4.7 % for the E5-grade and 9.4 % for the E10-grade.
The VTT team says the majority of people think that fuel consumption is much higher with 95E10 petrol compared to its forerunner 95E or the 98E5 petrol that is currently available to consumers.
'The point of this study was to highlight how fuel consumption should actually be measured to give comparable results,' says VTT principle scientist Juhani Laurikko. 'Measuring fuel consumption very accurately is not as simple as it seems, because other factors affect consumption besides the fuel itself. In laboratory conditions, we can eliminate these other factors.'
Based on their calculations, the VTT has found that the cars tested used an average of 10.30 litres of 95E10 per 100 kilometres (km), against 10.23 litres of 98E5 per 100 km. The team says the 0.07 difference favours the 98E5 on average. So using 95E10 petrol actually boosts consumption by 0.7 % because it has a higher ethanol content.
After normalising measurement results of each single test run with observed slight scatter in actual work done over the driving cycle, the researchers found a 1.0 % higher overall difference.
They also found that the calorific values based on approximate fuel composition were 1.1 % in favour of E5, being consistent with the 1.0 % difference in consumption. The researchers contend that the calorific value of the fuel — the energy content per unit of volume or mass — plays a key role for fuel consumption.
The TRANSECO research programme targets increasing road traffic energy use, developing technologies that reduce emissions, and bringing the results of the development work to market.
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