A Numerical Investigation of Transient Flow and Cavitation Within Minisac and Valve-Covered Orifice Diesel Injector Nozzles

Abstract

Cavitating flow within diesel injector passages has been investigated numerically using the homogeneous equilibrium model (HEM), which uses the barotropic assumption and the variable speed of sound of the mixture. To apply the HEM, the KIVA-3V code was modified to implement a generalized equation of state, and injector needle movement is simulated by the arbitrary Lagrangian-Eulerian (ALE) approach and the snapper algorithm. It is demonstrated that the model can predict the effect of nozzle passage geometry on the flow structure and cavitation. The model is able to reproduce the transient fuel injection rate as a function of the needle lift profile. Special interest is focused on the transient behavior during the nozzle closing period, which shows that the fast decrease in flow rate can increase the cavitation in the nozzle passage. The effects of the pressure difference and environment pressure on cavitation augmentation at the end-of-injection were also investigated. Flow characteristics due to different shapes of the nozzle flow passage in axisymmetric single hole nozzles and multihole nozzle configurations (minisac and valve-covered orifice eight-hole nozzles) were compared with emphasis on the end-of-injection period.

Numerical investigation on effects of nozzle’s geometric parameters on the flow and the cavitation characteristics within injector’s nozzle for a high-pressure common-rail DI diesel engine

“…Payri et al [14] conducted experiments about the effects of geometric parameters on cavitation phenomena within a visual closed vessel by laser technologies, the results showed that the jet angle has noticeable effects on the cavitation behaviours; then the experimental results had been taken by Salvador et al [15] to validate the calculation code in OpenFOAM, the results proved that taking simulation method on the cavitation characteristics are very reasonable for the similar investigation; lately, Payri et al [16] studied the effects of fuels' types on the cavitation phenomenon within nozzle in a closed vessel, the results showed that, for all the four tested fuels, the cavitation behaviour is determined by both the upstream and downstream pressure conditions within nozzle. Lee and Reitz [17] conducted a numerical simulation via KIVA-3V on the cavitation characteristics within nozzle for both the injectors with and without small pressure chamber, and the results showed that quickly reducing injection rate would worsen the cavitation phenomenon within nozzle. Som et al [18] conducted a simulation via Fluent on the cavitation characteristics within nozzle under different pressure differences and needle lifts, the results showed that the cavitation characteristics within nozzle have been noticeably influenced by the dynamic characteristics of needle valve; and then they [19] conducted another simulation via Converge on the effects of orifice's geometric patterns on the cavitation within nozzle, the results indicated that, compared with the pattern of inverted cone, the cone-shaped orifice has better effects on the suppression on the generation of cavitation.…”

Validation of a Three-Dimensional Internal Nozzle Flow Model Including Automatic Mesh Generation and Cavitation Effects

“…Typically, the void fraction can be solved with a conservation equation dot dot di+Uid^rs ( 6) In the present work, the void fraction is not directly transported, as in Eq. (6).…”

“…By using the STAR-CD solver for the simulations, the work of Margot et al [4] and Payri et al [5] used a method with pure mesh motion without changing the number of cells in the do main. Lee and Reitz [6] used KIVA, which uses a snapper algo rithm for the needle motion. In KIVA, a structured hexahedral mesh is required in the entire flow domain, which significantly increases the difficulty of mesh generation when considering arbi trarily shaped injectors.…”

Diesel nozzle geometries on spray characteristics with a spray model coupled with nozzle cavitating flow

“…(Vijayakumar et al, 2011) also investigated the effect of the properties of the fluid on the cavitating flow through numerical simulations of nozzle flow characteristics for diethyl and dimethyl ether and diesel fuel in Fluent software. (Lee and Reitz, 2010) analyzed flow characteristics for different shapes of the nozzle flow passage in axisymmetric single hole nozzles and multi-hole nozzle configurations (mini-sac and valve-covered orifice eight-hole nozzles) with the HEM of the modified KIVA-3V and the emphasis was put on the end of injection period. On the basis of study on nozzle cavitating flow, in recent years, researchers also began trying to couple the flow parameters of cavitating and turbulent flow at the exit of the nozzle hole to the subsequent spray and perform the study on setting up the new spray models coupled with nozzle cavitating flow, such as (Huh and Gosman, 1991;Bianchi et al, 1999;2001;Arcoumanis et al, 1997).…”