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A quantitative and time-resolved technique has been developed to probe the fuel distribution very near the nozzle of a high-pressure diesel injector. This technique uses the absorption of synchrotron x-rays to measure the fuel mass with good time and position resolution. The penetrating power of x-rays allows measurements that are difficult with other techniques, such as quantitative measurements of the mass and penetration measurements of the trailing edge of the spray. Line-of-sight measurements were used to determine the fuel density as a function of time. The high time resolution and quantitative nature of the measurement also permit an accurate measure of the instantaneous mass flow rate through the nozzle.

Propagation-based and phase-enhanced x-ray imaging was developed as a unique metrology technique to visualize the internal structure of high-pressure fuel injection nozzles. We have visualized the microstructures inside 200-μm fuel injection nozzles in a 3-mm-thick steel housing using this novel technique. Furthermore, this new x-ray-based metrology technique has been used to directly study the highly transient needle motion in the nozzles in situ and in real-time, which is virtually impossible by any other means. The needle motion has been shown to have the most direct effect on the fuel jet structure and spray formation immediately outside of the nozzle. In addition, the spray cone-angle has been perfectly correlated with the numerically simulated fuel flow inside the nozzle due to the transient nature of the needle during the injection.

An experimental study was carried out to characterize the exhaust flow structure inside the closed-coupled catalytic converter, which is installed on a firing four-cylinder 12-valve passenger car gasoline engine. Simultaneous velocity and pressure measurements were taken using cycle-resolved Laser Doppler anemometer (LDA) technique and pressure transducer. A small fraction of titanium (IV) iso-propoxide was dissolved in gasoline to generate titanium dioxide during combustion as seeding particles for the LDA measurements. It was found that the velocity is highly fluctuating due to the pulsating nature of the engine exhaust flow, which strongly depends on the engine operating conditions and the measuring locations. The pressure oscillation is correlated with the transient exhaust flow characteristics. The main exhaust flow event from each cylinder can only be observed at the certain region in front of the monolith brick.

Cavitating flows inside a two-dimensional valve covered orifice (VCO) nozzle were simulated by using the Space-Time Conservation Element and Solution Element (CE/SE) method in conjunction with a homogeneous equilibrium cavitation model. As a validation for present model, cavitation over a NACA0015 hydrofoil was predicted and compared with previous simulation results as well as experimental observations. The model was then used to investigate the effects on internal cavitating flows of different nozzle design parameters, such as the hole size, hole aspect-ratio, hydro-erosion radius, and orifice inclination. Under different conditions, cavitating flows through fuel injectors generated hydraulic flip, supercavitation, full cavitation, and cyclical cavitation phenomena, which are commonly observed in experiments.

An experimental study of sprayod structures from a regular dual-stream (RDS) injector and an air-shrouding dual-stream (ASDS) injector was carried out extensively to understand the spray characteristics of dual-stream (DS) port fuel injector for applications to 4-valve gasoline engines. The injectors were tested under steady and transient conditions at different injection pressures. The global spray structures were visualized using planar laser Mie scattering (PLMS) technique and spray atomization processes were quantified using phase Doppler anemometry (PDA) technique. The experimental results showed that at the beginning of fuel injection, the spray tip penetration for the RDS injector decreases with an increase in injection pressure; however, at the later stage of fuel injection, it increases when the injection pressure is increased. It is also found that the ligaments are dominant near the injector tip for the RDS injector with threads connecting the two streams.

An experimental study was carried out to characterize the spray atomization process of automotive port fuel injectors retrofitted to a novel pressure modulation piezoelectric driver, which generates a pressure perturbation inside the fuel line. Unlike many other piezoelectric atomizers, this unit does not drive the nozzle directly. It has a small size and can be installed easily between regular port injector and fuel lines. There is no extra control difficulty with this system since the fuel injection rate and injection timing are controlled by the original fuel-metering valve. The global spray structures were characterized using the planar laser Mie scattering (PLMS) technique and the spray atomization processes were quantified using phase Doppler anemometry (PDA) technique.

An experimental study was made to investigate the spray characteristics of high pressure fuel injectors for direct-injection gasoline engines. The global spray development process was visualized using two-dimensional laser Mie scattering technique. The spray atomization process was characterized by Phase Doppler particle analyzer. The transient spray development process was investigated under different fuel injection conditions as a function of the time after the fuel injection start. The effects of injector design, fuel injection pressure, injection duration, ambient pressure, and fuel property on the spray breakup and atomization characteristics were studied in details. Two clear counter-rotating recirculation zones are observed at the later stage or after the end of fuel injection inside the fuel sprays with a small momentum. The circumferential distribution of the spray from the large-angle injector is quite irregular and looks like a star with several wings projected out.

A computer model is developed for predicting pressure fluctuations inside an automotive electronic fuel rail system, which consists of six injectors connected in series through pipelines and a pressure regulator. The pressure fluctuations are mainly caused by opening and closing of injectors fired in a particular order. The needles that control the opening and closing of the injectors are modeled by mass- spring-dashpot systems, whose equations of motion are governed by a second order ordinary differential equations. A similar second order ordinary differential equation is used to describe the motion of the membrane with nonlinear stiffness inside the pressure regulator. The responses of injectors and pressure regulator are coupled by unsteady one-dimensional flow through the pipelines. The pressure fluctuations are also required to satisfy a one-dimensional damped wave equation. To validate this computer model, pressure fluctuations inside injectors and pipelines are calculated.

In diesel injector nozzles, the shape of the orifice entrance and the sac-volume play a significant role in determining the orifice internal flow characteristics and the subsequent spray formation process. The sac-volume of the injector nozzle determines injection characteristics like injection rate shape and discharge coefficients. The sac-volume is also important from emissions point of view, in that it controls the amount of Un-Burnt Hydrocarbons (UBHC). This paper demonstrates the use of commercial dynamic and computational fluid dynamics (CFD) programs in predicting the flow characteristics of various nozzle orifice and sac-volume configurations. Three single orifice nozzle tips with varying sac configurations and orifice entrance shapes are studied. Transient simulations are carried out in order to compare the injection rates, discharge coefficients and internal flow characteristics for the nozzle tips. The simulation results are compared with experimental results.

By taking advantage of high-intensity and high-brilliance x-ray beams available at the Advanced Photon Source (APS), ultrafast (150 ps) propagation-based phase-enhanced imaging was developed to visualize high-pressure high-speed diesel sprays in the optically dense near-nozzle region. The sub-ns temporal and μm spatial resolution allows us to capture the morphology of the high-speed fuel sprays traveling at 500 m/s with a negligible motion blur. Both quality and quantitative information about the spray feature can be readily obtained. In the experiment, two types of single-hole nozzles have been used, one with a hydroground orifice inlet and the other with a sharp one. Within 3 mm from the nozzle, the sprays from these nozzles behave differently, ranging from laminar flow with surface instability waves to turbulent flow. The sprays are correlated with the nozzle internal geometry, which provides practical information for both nozzle design and supporting numerical simulation models.

Experimental data is used in conjunction with multi-dimensional modeling in a modified version of the KIVA-3V code to characterize the emissions behavior of a high-speed, direct-injection diesel engine. Injection pressure and EGR are varied across a range of typical small-bore diesel operating conditions and the resulting soot-NOx tradeoff is analyzed. Good agreement is obtained between experimental and modeling trends; the HSDI engine shows increasing soot and decreasing NOx with higher EGR and lower injection pressure. The model also indicates that most of the NOx is formed in the region where the bulk of the initial heat release first takes place, both for zero and high EGR cases. The mechanism of NOx reduction with high EGR is shown to be primarily through a decrease in thermal NOx formation rate.

This paper presents a computer model for simulating dynamic responses inside an injector of an automotive fuel rail system. The injector contains a filter at the top, a coil spring in the middle, and a needle and orifices at the bottom. The equations of motion for unsteady one-dimensional flow are derived for the fluid flowing through the injector. The needle motion is described by a second order ordinary differential equation. The forces exerted on the needle include the magnetic force that controls the opening and closing of the injector and the coil spring force. To account for the loss of kinetic energy, we define two loss factors Ka and Kb. The former describes the loss of kinetic energy as fluid enters the injector through the filter at the top, and the latter depicts that as fluid is ejected into a large chamber through the passage between the needle and the needle seat and across four orifices at the bottom of the injector.

A long-distance microscope with pulse-laser as optical shutter up to 25kHz was used to magnify the diesel spray at the nozzle hole vicinity onto 35-mm photographic film through a still or a high-speed drum camera. The injectors examined are high-pressure valve-covered-orifice (VCO) nozzles, from unit injector and common rail injection systems. For comparison, a mini-sac injector from a hydraulic unit injector is also investigated. A phase-Doppler particle analyzer (PDPA) system with an external digital clock was also used to measure the droplet size, velocity and time of arrival relative to the start of the injection event. The visualization results provide very interesting and dynamic information on spray structure, showing spray angle variations, primary breakup processes, and spray asymmetry not observed using conventional macroscopic visualization techniques.

The improvement of spray atomization and penetration characteristics of GDI multi-hole injector sprays is a major component of the engine combustion developments, in order to achieve the fuel economy and emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to achieve optimum multi-objective spray characteristics. The Volume-of-Fluid Large-Eddy-Simulation (VOF-LES) of the injector internal flow and spray break-up processes offers a computational capability to aid development of a fundamental knowledge of the liquid jet breakup process. It is a unique simulation method capable of simultaneous analysis of the injector nozzle internal flow and the near-field jet breakup process. Hence it provides a powerful toll to investigate the influence of nozzle design parameters on the spray geometric and atomization features and, consequently, reduces reliance on hardware trial-and-tests for multi-objective spray optimizations.

The nozzle configuration for an injector is known to have an important effect on the fuel atomization. A comprehensive experimental and numerical investigation has been performed to determine the influence of various internal geometries on the primary spray breakup and development using the electronically controlled high-pressure diesel injection systems. Different types of multi-hole minisac and VCO nozzles with cylindrical and tapered geometries, and different types of single-hole nozzles with defined grades of Hydro Grinding (HG) were investigated. The global characteristics of the spray, including spray angle, spray tip penetration and spray pattern were measured from the spray images with a high-speed drum camera. A long-distance microscope with a pulsed-laser as the optical shutter was used to magnify the diesel spray at the nozzle hole vicinity. A CFD analysis of the internal flow through various nozzle geometries has been carried out with a commercial code.

A parametric study on the effects of critical injector design parameters of inwardly-opening pressure-swirl injectors was carried out using 3-D internal flow simulations. The pressure variation and the integrated momentum flux across the injector, as well as the flow distributions and turbulence structure at the nozzle exit were analyzed. The critical flow effects on the injector design identified are the swirler efficiency, discharge coefficient, and turbulence breakup effects on the spray structure. The study shows that as a unique class of injectors, pressure-swirl injectors is complicated in fluid mechanics and not sufficiently characterized or optimized. The swirler efficiency is characterized in terms of the trade-off relationship between the swirl-to-axial momentum-flux ratio and pressure drop across the swirler. The results show that swirl number is inversely proportional to discharge coefficient, and that hole diameter and swirler height is the most dominant parameters.

Improvement of spray atomization and penetration characteristics of the gasoline direct-injection (GDi ) multi-hole injector is a critical component of the GDi combustion developments, especially in the context of engine down-sizing and turbo-charging trend that is adopted in order to achieve the European target CO₂, US CAFE, and concomitant stringent emissions standards. Significant R&D efforts are directed towards optimization of the nozzle designs, in order to improve the GDi multi-hole spray characteristics. This publication reports VOF-LES analyses of GDi single-hole skew-angled nozzles, with β=30° skew (bend) angle and different nozzle geometries. The objective is to extend previous works to include the effect of nozzle-hole skew angle on the nozzle flow and spray primary breakup. VOF-LES simulations of a single nozzle-hole of a purpose-designed GDi multi-hole seat geometry, with three identical nozzle-holes per 120° seat segment, are performed.

Development of in-cylinder spray targeting, plume penetration and atomization of the gasoline direct-injection (GDi) multi-hole injector is a critical component of combustion developments, especially in the context of the engine downsizing and turbo-charging trend that has been adopted in order to achieve the European target CO2, US CAFE, and concomitant stringent emissions standards. Significant R&D efforts are directed towards the optimization of injector nozzle designs in order to improve spray characteristics. Development of accurate predictive models is desired to understand the impact of nozzle design parameters as well as the underlying physical fluid dynamic mechanisms resulting in the injector spray characteristics. This publication reports Large Eddy Simulation (LES) analyses of GDi single-hole skew-angled nozzles, with β=30° skew (bend) angle and different nozzle geometries.

Self recirculation casing treatment has been showed to be an effective technique to extend the flow range of the compressor. However, the mechanism of its surge extension on turbocharger compressor is less understood. Investigation and comparison of internal flow filed will help to understand its impact on the compressor performance. In present study, experimentally validated CFD analysis was employed to study the mechanism of surge extension on the turbocharger compressor. Firstly a turbocharger compressor with replaceable inserts near the shroud of the impeller inlet was designed so that the overall performance of the compressor with and without self recirculation casing treatment could be tested and compared. Two different self recirculation casing treatments had been tested: one is conventional self recirculation casing treatment and the other one has deswirl vanes inside the casing treatment passage.

In present GDI engines, multiple injection strategies are often employed for engine cold start mixture formation. In the future, these strategies may also be used to control the combustion process, and to prevent misfiring or high emission levels. While the processes occurring during individual injections of GDI injectors have been investigated by a number of researchers, this paper concentrates on the interactions of multiple injection events. Even though multiple injection strategies are already applied in most GDI engines, the impact of the first injection event on the second injection event has not been analyzed in detail yet. Different optical measurement techniques are used in order to investigate the interaction of the two closely timed injection events, as well as the effect of dwell time and the in-cylinder conditions. The injector investigated is a GDI piezo injector with an outwardly opening needle.