Fuel direct injection represents one of the key turning points in the development
of the Diesel engines. The appeal of this solution has been growing thanks
to the parallel advancement in the technology of the injection hardware and in
the knowledge of the physics involved in the spray formation and combustion.
In the present thesis, the effect of partial needle lift and injection rate shaping
has been investigated experimentally using a multi-orifice Diesel injector.
Injection rate shaping is one of the most attractive alternatives to multiple
injection strategies but its implementation has been for long time impeded by
technological limitations. A novel direct-acting injector prototype made it possible
to carry out the present research: this injector features a mechanical coupling
between the nozzle needle and the piezo-stack actuator, allowing a fully flexible
control on the nozzle needle movement and enabling partial needle lift as well
as the implementation of alternative injection rate shapes typologies. Different
optical diagnostics were applied to study the spray development and combustion
in a novel continuous flow test chamber that allows an accurate control on a
wide range of thermodynamic conditions (up to 1000K and 15MPa). In addition,
hydraulic characterization tests were carried out to analyze the fuel flow through
the injector nozzle.
Partial needle lift has been found to affect the injection event, reducing the
mass flow rate (as expected) but also causing a reduction in the effective orifice
area and an increase on the spreading angle. Moreover, at this condition, higher
hole-to-hole dispersion and flow instabilities were detected. Needle vibrations
caused by the needle interactions with fuel flow and by the onset of cavitation in
the needle seat are likely the causes of this behavior.
Injection rate shaping has a substantial impact on the premixed phase of the
combustion and on the location where the ignition takes place. Furthermore, the
results proved that the modifications in the internal flow caused by the partial
needle lift are reflected on the ignition timing. On the other hand, the analysis of
the experimental data through a 1D spray model revealed that an increasing mass
flow rate (e.g. ramp or boot injection rate profiles) causes an increase in the fuelair
equivalence ratio at the lift-off length and a consequent higher soot formation
during the diffusive phase of the combustion. Finally, the wide range of boundary
conditions tested in all the experiments served to draw general conclusions about
the physics involved in the injection/combustion event and, in some cases, to
obtain statistical correlations. / Bardi, M. (2014). PARTIAL NEEDLE LIFT AND INJECTION RATE SHAPE EFFECT ON THE FORMATION AND COMBUSTION OF THE DIESEL SPRAY [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37374
| Identifer | oai:union.ndltd.org:upv.es/oai:riunet.upv.es:10251/37374 |
| Date | 12 May 2014 |
| Creators | Bardi, Michele |
| Contributors | Payri Marín, Raúl, Universitat Politècnica de València. Departamento de Máquinas y Motores Térmicos - Departament de Màquines i Motors Tèrmics |
| Publisher | Universitat Politècnica de València |
| Source Sets | Universitat Politècnica de València |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/acceptedVersion |
| Source | Riunet |
| Rights | http://rightsstatements.org/vocab/InC/1.0/, info:eu-repo/semantics/openAccess |
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