Mechanisms of spray formation and combustion from a multi-hole injector with E85 and gasoline

The spray formation and combustion characteristics of gasoline and E85 (85% ethanol, 15% gasoline) have been investigated using a multi-hole injector with asymmetric nozzle-hole arrangement. Experiments were carried out in a quiescent optical chamber using high-speed shadowgraphy (9 kHz) to characterise the spray sensitivity to both injector temperature and ambient pressure in the range of 20-120 °C and 0.5, 1.0 bar. Spray-tip penetrations and umbrella spray cone angles were calculated for all conditions. Phase Doppler Anemometry was also used to measure droplet sizes in the core of one of the spray plumes, 25 mm below the injector tip. To study the effect of fuel properties on vaporisation and mixture preparation under realistic operating conditions, a separate set of experiments was carried out in a direct-injection spark-ignition optical engine. The engine was run at 1500 RPM under cold and fully warmed-up conditions (20 °C and 90 °C) at part load and full load (0.5 and 1.0 bar intake pressure). Floodlit laser Mie-scattering images of the sprays on two orthogonal planes corresponding to the swirl and tumble planes of in-cylinder flow motion were acquired to study the full injection event and post-injection mixing stage. These were used to make comparisons with the static chamber sprays and to quantify the liquid-to-vapour phase evaporation process for both fuels by calculating the projected footprint of the sprays at different conditions. Analysis of the macroscopic structure and turbulent primary break-up properties of the sprays was undertaken in light of jet exit conditions described in terms of non-dimensional numbers. The effects on stoichiometric combustion were investigated by imaging the natural flame chemiluminescence through the engines piston crown (swirl plane) and by post-processing to derive flame growth rates and trajectories of flame motion. © 2009 The Combustion Institute

Cavitation, primary break-up and flash boiling of gasoline, iso-octane and n-pentane with a real-size optical direct-injection nozzle

Improvements to the direct-injection spark-ignition combustion system are necessary if the potential reductions in fuel consumption and emissions are to be fully realized in the near future. One critical link in the optimization process is the design and performance of the injectors used for fuel atomization. Multi-hole injectors have become the state-of-the-art choice for gasoline direct-injection engines due to their flexibility in fuel targeting by selection of the number and angle of the nozzle holes, as well as due to their demonstrated stability of performance under a wide range of operating conditions. Recently there has been increased attention devoted to the study of the flow through the internal passages of injectors because of the presence of particular fluid phenomena, such as large-scale vortical motion and cavitation patterns, which have been shown to influence the characteristics of primary break-up. Understanding how cavitation can be used to improve spray atomisation is essential for optimizing mixture preparation quality under early injection and stratified engine operating conditions but currently no data exist for injector-body temperatures representative of real engine operation, particularly at low-load conditions that can also lead to phase change due to fuel flash boiling. This paper outlines results from an experimental imaging investigation into the effects of fuel properties, temperature and pressure conditions on the extent of cavitation, flash boiling and, subsequently, primary break-up. This was achieved by the use of a real-size transparent nozzle of a gasoline injector from a modern direct-injection combustion system. Gasoline, iso-octane and n-pentane fuels were used at 20 and 90 °C injector-body temperatures for ambient pressures of 0.5 and 1.0 bar in order to simulate early homogeneous injection strategies for part-load and wide-open-throttle engine operation. © 2010 Elsevier Ltd. All rights reserved