Investigation on the effects of butanol and ethanol fueling on combustion and PM emissions in an optically accessible DISI engine

Generalization of direct injection and use of alternative fuels in spark ignition engines, are two trends that require detailed analysis of specific phenomena. Within this context, the present investigation was aimed at improved understanding of the effects of fuel injection phasing and engine speed on the emission of nanoparticles. Measurements were performed on a wall guided power unit with optical accessibility, that was fueled with gasoline, ethanol and butanol. Thermodynamic results were combined with exhaust gas measurements, particle size distribution and cycle-resolved imaging. The characterization was executed with stoichiometric fueling, for three different start of injection settings during the intake stroke. Engine speed effects were evaluated during slightly lean operation, so that spark timing could be maintained fixed for all trials without the occurrence of abnormal combustion. Visualization of flame front propagation and localized diffusive oxidation induced by unevaporated fuel, allowed the observed variations in engine performance and emissions, to be correlated to liquid film distribution within the combustion chamber. Changes were found to be minor for gasoline when injection phasing was modified, while the alcohols featured noticeable sensitivity. A major effect was observed on the emission of particles, more so for butanol. Through the complete characterization of thermodynamic, exhaust and visualization data, the mechanism of fuel jets impinging on the combustion chamber walls was identified as the main influence. The alcohols' higher latent heat of evaporation and low saturation pressure were recognized as determining fuel properties that induced the observed changes.