Analyzing and Optimizing Injection Nozzles

Injection Nozzle Development

AVL FIRE offers unique capabilities for analyzing and optimizing injection nozzles in respect of transient discharge rates, the occurrence of cavitation and potentially occurring material erosion.




AVL Approach

AVL FIRE offers indispensable capabilities when it comes to the development and optimization of injection nozzles. While a one-dimensional AVL BOOST HYDSIM model typically represents the complete injection system from fuel tank to the injector, AVL FIRE focuses on the three-dimensional calculation of the fluid flow in the injection nozzle.

Benefits at a Glance

Unrivalled simulation capabilities enable virtual design verification to:

  • Achieve higher engine out performance and lower engine out emissions
  • Reduce cavitation and avoid erosion
  • Prevent nozzle coking.

Performance Counts

In an early engine design stage, fuel injection details, such as needle lift and inlet pressure level are not known. In a virtual prototyping environment, coupled 1D/3D fuel injection simulations are extremely valuable. While AVL BOOST HYDSIM provides the information about longitudinal and radial needle displacements as well as pressure levels, AVL FIRE allows the accurate prediction of the fuel conditions in the injection nozzle and its impact on break-up, ignition and combustion in the IC Engines chamber. To get the maximum benefit out of both tools, BOOST and FIRE can be executed as a co-simulation with FIRE providing pressure forces on the injector needle and BOOST computing longitudinal and radial needle motion based on this information.

The Problem

Modern injection systems make use of high pump pressures to enhance droplet break-up and mixture formation in the combustion chamber targeting high performance, high efficiency and low engine out emissions. The resulting huge pressure difference between the fuel supply line and the combustion chamber leads to a phase change from liquid fuel to fuel vapor. While the vapor reduces the effective orifice outlet area and therefore the amount of liquid fuel transported into the combustion chamber during a single injection event, it also affects the conditions that determine the release of the fuel droplets downstream the nozzle orifices.

The Solution

To accurately account for the effect of cavitation on fuel penetration and propagation in the combustion chamber, AVL FIRE offers advanced cavitation modeling. Thus it becomes possible to calculate when, where and how much of the fuel in the injection nozzle undergoes phase changes. As a consequence, an accurate prediction of transient discharge rates and a detailed insight into the instationary flow conditions in the individual nozzle orifice exit areas can be obtained.

Tying up

The flow conditions predicted in any nozzle orifice exit area are recorded during the AVL FIRE injector flow simulation and serve as the input for subsequent in-cylinder mixture formation and combustion simulations. That way a perfect correlation accounting for flow non-uniformity out of the injector can be established between the flow conditions inside the nozzle and the conditions under which fuel is entering the combustion chamber.

Erosion Modelling

Cavitation in injection nozzles is often accompanied by material erosion and is strongly related to the durability of injection components. The prediction of an erosion probability helps to define design parameters that ensure constant nozzle (and engine) performance during the whole life cycle of the equipment. The cavitation/erosion model offered in AVL FIRE is a unique and extremely valuable capability that has already been proven to work reliably in many development projects.