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T. Lauer, M. Heiß, S. Fischer, M. Klein:
"Prediction Of The Wall Film Formation And Performance Of An Engine Operated With The Ethanol Blend E85";
Vortrag: EAEC European Automotive Congress, Valencia (eingeladen); 13.06.2011 - 16.06.2011; in: "13th EAEC European Automotive Congress", (2011).

Efforts will have to be made to reduce the CO2-emission of future vehicles. For example, a fleet emission limit of 120 g/km will be introduced in Europe by 2012. In addition a steadily growing number of vehicles faces limited oil resources. Therefore, low carbon fuels and fuels from biomass with an improved CO2-balance like ethanol are considered as an important alternative to conventional fuels for SI engines.
However, ethanol has a different stoichiometric air/fuel-ratio, a lower heating value and a higher heat of vaporization than conventional fuels. This has a high impact on the engine process. Therefore, detailed investigations on the engine process are necessary to predict the differences of the gas exchange, the engine efficiency and the full load performance when switching to ethanol.
A turbocharged SI engine with port fuel injection was investigated at the Institute for Powertrains and Automotive Technology of the Vienna University of Technology in order to show the potentials when being operated with the ethanol blend E85. Numerical studies with the code GT-Power and measurements at the engine test bench have been carried out to explain the mixture preparation with conventional fuel and E85.
It could be shown with the help of detailed CFD-simulations that an extensive wall film formation takes place in the inlet port during the fuel injection. Therefore, the heat of vaporization is rather taken from the material than from the aspirated air. This effect decreases the evaporative cooling of the mixture and, as a result, a higher boost pressure than predicted by simulation is required to reach a defined torque. There is a significantly higher impact observable for E85 compared to conventional fuel because of its higher heat of vaporization and lower stoichiometric air/fuel-ratio. Therefore, the mixture formation for E85 must be considered in more detail when analysing the engine process. In the following, a predictive model of the wall film formation in the inlet ports and thermal models of the port walls were used for the numerical studies.
With the improved model the gas exchange and necessary boost pressure were in good agreement with measurements from the engine test bench for both fuels. The investigations have shown that particularly for alternative fuels with fluid properties that differ from those of conventional fuel the standard simulation models do not remain valid and an analysis of the whole process, employing measurements and numerical methods, is necessary.

CO2-emission, SI engine, ethanol, wall film, numerical simulation