Experimental investigation of ethanol-gasoline dual-fuel on particle emissions of a small engine

The concerns on the air pollutants harmful effects on the human health and the environment and the depletion in the supply of fossil fuels have prompted to the necessity of engine efficiency improvements and exhaust emissions reduction. For these reasons great attention was paid to direct injection systems and oxygenated alternative fuels. Despite the higher complexity and cost, in fact, the direct injection system is even more applied also on spark ignition engines as the higher thermal efficiency and power output, as well as the lower fuel consumption and lower CO2 emissions. On the other hand, direct injection spark ignition (DISI) engines are characterized by large particle emissions since less time is available for fuel evaporation and mixing and because of the fuel impingement. For this reason particle mass and number regulation has been introduced from Euro 6 also for gasoline light duty car. The alternative fuels are gaining even more attention both in Europe and USA as they can reduce both the exhaust emissions and the fossil fuel consumption. Among the liquid alternative fuel ethanol is the most widely used as it can improve engine efficiency by using higher compression thanks to its increased knock - limit due to its higher octane number. Typically, the blending of the conventional and alternative fuels takes place outside of the cylinder. The dual fuel modes, instead, allow an alternative approach to using gasoline- biofuel blends. In this case, in fact, the blend is formed inside the cylinder as the fuels are separately injected through a port fuel injection (PF) and direct injection (DI) systems. This configuration allows the blending of the fuel at different ratios according to the engine operating conditions. Typically, the fossil fuel is injected using the PFI system, while the biofuel is injected using DI. This configuration allows to exploit the charge-cooling effect of ethanol to lower the in-cylinder temperature and then increase knock limit and reduce NOx emissions, and the beneficial effect of the oxygenated fuel on particle emissions reduction. The aim of the paper is the analysis of the effect of ethanol-gasoline dual fuel on particle emissions. The experimental activity was carried out on a small single-cylinder four stroke engine representative of the most wide spread motorcycles in Europe. The engine can operate both in gasoline direct injection (GDI) and port fuel injection (PFI) configuration. Ethanol was directly injected in the combustion chamber (DI fuel). The measurements were performed under steady state conditions at different engine operating conditions and dual-fuel ratios. The particle concentration was measured by means of a smoke meter. Moreover, the particle size distribution function was measured in the range from 5.6 nm to 560 nm by means of an Engine Exhaust Particle Sizer (EEPS). For dual fuelling was observed a strong decrease of particle emissions in terms of mass concentration. Nevertheless, the analysis of the particle size distribution highlighted for DF engine configuration a larger emission of ultrafine particles, which are the most dangerous for human health