Dynamics of the in sac cavitating flow for diesel spray with split injection strategy

The development of the injector nozzle is a dynamic area in regard of several technical aspects. At first, the internal flow influences the near-field spray characteristics via various phenomena such as cavitation and turbulence. However, these phenomena are not fully understood due to their extremely fast, complex and multiscale nature. Furthermore, it governs the spray targeting inside the combustion chamber. High-speed X-ray imaging of GDI injector nozzles is performed in this study. The experimental results presented are related to the internal flow and primary breakup of discharged liquid jets. The injectors used are equipped with nozzles made of aluminum which have been specially developed for these investigations to enhance optical accessibility. The visualization of the needle motion, in-nozzle flow and the primary breakup region provides several exciting observations. First, the needle lift tracking exhibits short overshooting right before the steady-state of the injection phase. This event leads to a short-term, however, significant change in the associated performance of the breakup. This phenomenon is found to be a consequence of the transient behavior of the in-nozzle flow. It is shown that under some circumstances hydraulic flip may occur during this overshooting period. The primary jet breakup region is visualized and evaluated by means of image processing. Thus, the transient behavior of liquid jet expansion is quantified in the vicinity of the nozzle. It is observed that the liquid jet direction deviates from the hole axis already at the nozzle outlet, which is caused by internal flow characteristics.

Section: Nozzle Flow and Spray Theorymentioning

confidence: 99%

The effect of transient needle lift on the internal flow and near-nozzle spray characteristics for modern GDI systems investigated by high-speed X-ray imaging

Mamaikin

Knorsch

Rogler

et al. 2021

“…Numerical simulations have shed light to the effect on multi-phase flow development in various nozzle configurations, see for example, 11–17 while more recent investigation have quantified the needle valve motion using high energy X-rays 18–22 and real size optical nozzles. 23–26 Still, the flow phenomena taking place during the very short time scales (∼ 100 μ s ) of the opening and closing of the needle valve controlling the injection process are challenging to be quantified. In particular, fuel dribbling, which is the formation of poorly atomised unintended fuel jet after the closure of the needle valve is poorly understood.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of fuel dribbling and nozzle wall wetting

Gavaises

Murali-Girija

Rodríguez

et al. 2021

The present work describes a numerical methodology and its experimental validation of the flow development inside and outside of the orifices during a pilot injection, dwelt time and the subsequent start of injection cycle. The compressible Navier-Stokes equations are numerically solved in a six-hole injector imposing realistic conditions of the needle valve movement and considering in addition a time-dependent eccentric motion. The valve motion is simulated using the immersed boundary method; this allows for simulations to be performed at zero lift during the dwelt time between successive injections, where the needle remains closed. Moreover, the numerical model utilises a fully compressible two-phase (liquid, vapour) two-component (fuel, air) barotropic model. The air’s motion is simulated with an additional transport equation coupled with the VOF interface capturing method able to resolve the near-nozzle atomisation and the resulting impact of the injected liquid on the oleophilic nozzle wall surfaces. The eccentric needle motion is found to be responsible for the formation of strong swirling flows inside the orifices, which not only contributes to the breakup of the injected liquid jet into ligaments but also to their backwards motion towards the external wall surface of the injector. Model predictions suggest that such nozzle wall wetting phenomena are more pronounced during the closing period of the valve and the re-opening of the nozzle, due to the residual gases trapped inside the nozzle, and which contribute to the poor atomisation of the injected fluid upon re-opening of the needle valve in subsequent injection events.

“…The high injection pressures also accelerate the opening of the diesel injector which is beneficial for droplet atomisation. 25 Increasing the injection pressure has resulted in higher tumble charge motion, reduction in the temporal variations of the fuel economy, reduction in tipdiffusion flame combustion and coking deposits, and a reduction in the net specific THC levels. 6,26 In spite of these benefits, increased costs and higher power consumption by the pumping system associated with the higher injection pressures, which affects the mechanical efficiency, should also be considered.…”

Section: Introductionmentioning

confidence: 99%

“…The high injection pressures also accelerate the opening of the diesel injector which is beneficial for droplet atomisation. 25…”

Section: Introductionmentioning

confidence: 99%

Investigations of split injection properties on the spray characteristics using a solenoid high-pressure injector

Dhanji

Zhao

2021

An on-going challenge with Gasoline direct injection (GDI) engines is achieving rapid activation of the exhaust catalyst during cold starts, in order to reduce the Nitrogen Oxide (NOx) emissions. Injecting late in the compression stroke, in the efforts to form a stratified mixture, provides the fuel insufficient time to be entrained with the surrounding charge. This results in locally fuel rich diffusion combustion and the formation of high levels of particulate matter. Employing a split injection strategy can help tackle these issues. The current study examines the effects of a split injection strategy on the spray characteristics. Varying pulse width (PW) combinations, split ratios and dwell times are investigated using a Solenoid actuated high pressure injector. The injected quantity and the droplet characteristics of a target plume are investigated. The experiments were performed in a constant volume spray chamber. The droplet velocities and sizes were measured using Phase Doppler Particle Anemometry (PDA). Short and large PWs, in the range of 0.3–0.8 ms, were investigated. The results revealed that the highest injected quantity of fuel was measured with the shortest dwell time of 2 ms, owing to increased interactions between the injection events, which led to larger Sauter mean diameters (SMDs) measured. The SMDs for the shorter PW of 0.4 ms were generally larger than 0.8 ms PW. The droplets in this case were affected by the closely spaced opening and closing events of the Solenoid valve.