Effects of Ethanol Addition in RON 95 Gasoline on GDI Stratified Combustion 2011-24-0055
The aim of this work is to study the effect of ethanol/gasoline blends on stratified operation in a single-cylinder GDI engine and to build up a large database that will be used to improve engine simulation codes. The effects of three different fuel blends are compared: a reference RON 95 fuel without oxygenates, E20 with 20% in volume of ethanol added to the RON 95 fuel, and E85 corresponding to 85% of ethanol added to the RON 95 fuel. The engine was equipped with a centrally-mounted piezoelectric injector. A wide range of engine speed and load operating conditions were studied: from 1000 to 4000 rpm and from 1.5 to 9 bar IMEP. Injection strategies were optimized using up to three injections per working cycle. It was shown that multi-injection is necessary to improve stratified combustion stability and to limit particulate emissions. Main effects of ethanol addition in gasoline are increasing laminar flame speed, lowering adiabatic flame temperature and elevating the latent heat value of the fuel. It was shown that ethanol addition leads to limited particulate emissions. It also has a positive effect on exhaust NOx emission reduction. For higher loads, exhaust CO emissions are reduced with ethanol addition. Ethanol addition in gasoline significantly improves combustion robustness to spark advance, start of injection timing and spark plug penetration in the combustion chamber. However, when decreasing load and engine speed, ethanol has a negative effect on the indicated efficiency. This is probably due to enhanced wall heat transfers with ethanol blends since a longer spray penetration may lead to combustion closer to the walls of the combustion chamber. The penalty on the lower heating value-corrected fuel specific consumption reached 19% with E85 vs. E0 at 1000 rpm / 2 bar IMEP. In the upper speed and load zone, at 3500 rpm / 8 bar IMEP, a 5% gain was observed.