Study of Stoichiometric and Lean Combustion in a Spark Ignition, Direct Injection Optical Engine Using E10 and ETBE20 Fuels

Biofuels are a promising alternative to fossil fuels as their availability has been reduced during the last decades and they are the main sources of greenhouse gases emissions. Moreover, the targets of the international regulations include reduction of fossil fuels consumption, and improvement of the sustainability of the vehicle fleet. Blending gasoline with biofuels will result in changes in fuel blending procedures and combustion process especially for the gasoline direct injection (GDI) engines. In this article, flame visualization using chemiluminescence techniques in a Single Cylinder Optical Research Engine (SCORE) is presented, with an adjusted intake pressure of 850 mbar and early intake single injection (280 CAD BTDC), by using 100% hydrocarbon-based gasoline, E10 (90% gasoline - 10% ethanol) and ETBE20 (80% gasoline - 20% ethyl tert-butyl ether). ETBE20 is a potential alternative for E10, as it contains the same amount of renewable fuel and has low water solubility. Moreover, ETBE20 does not have the issues of increased volatility as E10. The injection pressure was adjusted to 100 bar and the measurements were conducted at two different air / fuel ratios, stoichiometric (λ=1) and lean (λ=1,2) at 2000 RPM. Flame boundaries were identified by chemiluminescence images using an in-house algorithm and it was found that Ε10 showed faster flame development and its MFB (Mass Fraction Burned) ratio increased faster than ETBE20 for both stoichiometric and lean combustion conditions. The maximum COV_IMEP (covariance of IMEP) was observed for E10 lean combustion at 2000 RPM, and it was equal to 2.1. In most cases the ETBE20 showed the lowest COV_IMEP.