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The occurrence of knock is the most limiting hindrance for modern Spark-Ignition (SI) engines. In order to understand its origin and move the operating condition as close as possible to onset of this potentially harmful phenomenon, a joint experimental and numerical investigation is the most recommended approach. A preliminary experimental activity was carried out at IM-CNR on a 0.4 liter GDI unit, equipped with a flat transparent piston. The analysis of flame front morphology allowed to correlate high levels of flame front wrinkling and negative curvature to knock prone operating conditions, such as increased spark timings or high levels of exhaust back-pressure. In this study a detailed CFD analysis is carried out for the same engine and operating point as the experiments. The aim of this activity is to deeper investigate the reasons behind the main outcomes of the experimental campaign.

The use of alcohols as alternative to gasoline for fuelling spark-ignition (SI) engines is widespread. Growing interest is paid for n-butanol because of its characteristics that are similar to gasoline. If compared with other alcohols, n-butanol has higher energy content and miscibility with gasoline, lower hygroscope and corrosive properties making it an attractive solution for gasoline replacement. Even if several studies have been conduced to characterize the n-butanol combustion within Spark Ignition engines, few data are available on atomization and spray behavior. This paper reports the results of an experimental investigation to characterize the velocity vector field of two fuel-sprays injected by a 6-hole nozzle for Direct Injection Spark Ignition (DISI) engine. 2D Mie-scattering and Particle Image Velocimetry (PIV) measurements were carried out in an optically accessible vessel at ambient temperature and pressure.

Alcohols are largely used in spark-ignition (SI) engines as alternative fuels to gasoline. Particularly, the use of butanol meets growing interest due to its properties that are similar to gasoline, if compared with other alcohols. This paper aims to make a comparative analysis on the atomization process of gasoline and n-butanol fuel injected by a multi-hole injector nozzle for spark ignition engines. Phase Doppler Anemometry technique was applied to investigate the behavior of a spray emerging from a six-hole nozzle for direct injection spark ignition engine applications. Commercial gasoline and pure n-butanol were investigated. The fuels were injected at two pressures: namely at 5 and 10 MPa, in a test vessel at quiescent air conditions, ambient temperature and backpressure. Droplets diameter and velocity were estimated along the axis and on the edge direction of a jet through Phase Doppler Anemometry in order to provide useful information on the atomization process.