Determination of the pressures within an injector: Experimentation and model validation.
Date
2011-10-12
Authors
Sprich, Thomas Karl.
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Abstract
Amid concerns of global warming, it has become necessary to reduce the emissions
produced by engines. One method of achieving this is by controlling the air/fuel mixture
formed by the spray of the injector within the combustion chamber. In comparing
previous experimental results and the equations which describe the spray structure disagreement
was found, which is expected to be caused by having insufficient information
of the injection pressure; a required input of the equation. The aim of this research is
to predict this injection pressure by modelling a mechanical injector, and testing and
modelling a common rail injector. The mechanical injector simulations show that the
injection pressure is lower than the line and opening pressure and is dependent on the
number of discharge orifices, throttling condition and opening pressure of the injector.
Consequently, the line and opening pressures are not sufficient approximations of the
injection pressure and must not be used to predict spray properties. The simulations
showed the injected flow rate is higher for a three hole injector at high engine loads
and higher opening pressures, resulting in a more atomised and penetrating spray. The
common rail injector model agrees with the experimental results and both show the
injection pressure being about 90% of the rail pressure. The rail pressure is therefore
suitable for use in the penetration equations. A sensitivity analysis of the common rail
model showed that it could be used to diagnose injector problems because each varied
parameter changed the injected flow rate differently, allowing the source of the problem
to be easily identified.