Characterisation of Spray Development from Spark-Eroded and Laser-Drilled Multi-Hole Injectors in an Optical DISI Engine and in a Quiescent Injection Chamber

Abstract

This paper addresses the need for fundamental understanding of the mechanisms of fuel spray formation and mixture preparation in direct injection spark ignition (DISI) engines. Fuel injection systems for DISI engines undergo rapid developments in their design and performance, therefore, their spray breakup mechanisms in the physical conditions encountered in DISI engines over a range of operating conditions and injection strategies require continuous attention. In this context, there are sparse data in the literature on spray formation differences between conventionally drilled injectors by spark erosion and latest Laser-drilled injector nozzles. A comparison was first carried out between the holes of sparkeroded and Laser-drilled injectors of same nominal type by analysing their in-nozzle geometry and surface roughness under an electron microscope. Then the differences in their spray characteristics under quiescent conditions, as well as in a motoring optical engine, are discussed on the basis of highspeed imaging experiments and image processing methods. Specifically, the spray development mechanism was quantified by spray tip penetration and cone angle data under a range of representative low-load and high-low engine operating conditions (0.5 bar and 1.0 bar absolute, respectively), as well as at low and high injector body temperatures (20 °C and 90 °C) to represent cold and warm engine-head conditions. Droplet sizing was also performed with the two injectors using Phase Doppler Anemometry in a quiescent chamber.

An Approach to Modeling Flash-Boiling Fuel Sprays for Direct-Injection Spark-Ignition Engines

“…The spark-ignition engine injector and conditions under study here relate to 0.2 mm nozzle dimeter and 150 bar injection pressure, leading to typical nozzle Reynolds numbers of about 30,000 and 50,000 at 293 K, 1 bar (Aleiferis and van Romunde, 2013), depending on fuel type. The r/D ratio was estimated at ~0.05-0.1 from the electron microscope images of Butcher et al (2013Butcher et al ( , 2015. This value is situated within the range suggested of 0.01-0.08 being equivalent to sharp and rounded injector radii, respectively.…”

“…Flash boiling of gasoline fuel sprays in direct-injection engine applications can have a positive effect on air-fuel mixing, due to the increased evaporation rate and smaller droplet sizes (van Romunde and Behringer et al, 2014). However, depending on exact plume orientation and injector nozzle type, flashing and spray collapse may lead to decreased liner wall wetting but increased piston wall wetting due to increased axial momentum of the spray (Butcher et al, 2015).…”

Spray development of iso-octane, ethanol, hydrous ethanol and water from a multi-hole injector under ultra cold fuel temperature conditions

“…The length to diameter ratio for each part of the hole (inner, outer) was of the order unity. The nozzle holes have been characterised by silicon castings and microscopy in great detail and the interested reader is guided to references [29,30] for further information. The injector used was the production version of a prototype injector of very similar geometry and nozzle hole orientation that has been tested with many different fuels over a wide range of fuel temperatures from 20 °C to 180 °C and air pressures from 0.3 bar to 5 bar in constant volume injection chambers [31][32][33] and in an optical engine [34][35][36][37][38].…”

“…The injector used was the production version of a prototype injector of very similar geometry and nozzle hole orientation that has been tested with many different fuels over a wide range of fuel temperatures from 20 °C to 180 °C and air pressures from 0.3 bar to 5 bar in constant volume injection chambers [31][32][33] and in an optical engine [34][35][36][37][38]. Fuel pressure was maintained at 150 bar and the injector flow rate at this pressure can be found in [29,30], with modelled sprays at the respective flow rate found in [39][40][41]. Studies of the injector/driver delays have been presented in [32], whilst a range of further details on injector delays and injector flow rate variations for the same generation of hardware can be found in [42].…”

“…It is noted that PDA data quality can be significantly affected by various system settings and so detailed tests were carried out initially using considerable in-house expertise in order to identify the most appropriate set of parameters for this measurement campaign. The effect of temperature dependence of the refractive index of the fuels was considered on the basis of previously published work in this area [30,33,[44][45][46]. The injection chamber was purged for 2 s after each injection event and time was allowed for any residual airflow settling before the next injection.…”