Julien Manin

Understanding the Acoustic Oscillations Observed in the Injection Rate of a Common-Rail Direct Injection Diesel Injector

Measuring the rate of injection of a common-rail injector is one of the first steps for diesel engine development. The injected quantity as a function of time is of prime interest for engine research and modeling activities, as it drives spray development and mixing, which, in current diesel engines, control combustion. On the other hand, the widely used long-tube method provides results that are neither straightforward nor fully understood. This study, performed on a 0.09-mm axially drilled single-hole nozzle, is part of the Engine Combustion Network (ECN) and aims at analyzing the acoustic oscillations observed in the rate of injection signal and measuring their impact on the real injection process and on the results recorded by the experimental devices. Several tests have been carried out for this study, including rate of injection and momentum, X-ray phase-contrast of the injector, and needle motion or injector displacement. The acoustic analysis revealed that these fluctuations found their origin in the sac of the injector and that they were the results of an interaction between the fluid in the chamber (generally gases) or in the nozzle sac and the liquid fuel to be injected. It has been observed that the relatively high oscillations recorded by the long-tube method were mainly caused by a displacement of the injector itself while injecting. In addition, the results showed that these acoustic features are also present in the spray, which means that the oscillations make it out of the injector, and that this temporal variation must be reflected in the actual rate of injection.

A Progress Review on Soot Experiments and Modeling in the Engine Combustion Network (ECN)

The following individuals and funding agencies are acknowledged for their support. The authors from DTU acknowledge the Technical University of Denmark, Danish Strategic Research Council, and MAN Diesel & Turbo University of Wisconsin: Financial support provided by the Princeton Combustion Energy Frontier Research Center. ETH Zurich: Financial support from the Swiss Federal Office of Energy (grant no. SI/500818-01) and the Swiss Competence Center for Energy and Mobility (CCEM project “In-cylinder emission reduction”) is gratefully acknowledged. Argonne National Labs: Work was funded by U.S. DOE Office of Vehicle Technologies, Office of Energy Efficiency and Renewable Energy under Contract No. DE-AC02-06CH11357. We also gratefully acknowledge the computing resources provided on Fusion, a computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. Sandia National Labs, Combustion Research Facility: Work was supported by the U.S. Department of Energy, Office of Vehicle Technologies. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DEAC04-94AL85000. Chris Carlen and Dave Cicone are gratefully acknowledged for technical assistance. The authors from ANL and SNL also wish to thank Gurpreet Singh and Leo Breton, program managers at U.S. DOE, for their support.

Quantitative Mixing Measurements and Stochastic Variability of a Vaporizing Gasoline Direct-Injection Spray

Spark-ignition direct-injection engines operating in a stratified, lean-burn regime offer improved engine efficiency; however, seemingly random fluctuations in stratified combustion that result in partial-burn or misfire prevent widespread implementation. Eliminating these poor combustion events requires detailed understanding of engine flow, fuel delivery, and ignition, but knowing the dominant cause is difficult because they occur simultaneously in an engine. This study investigated the variability in fuel–air mixture linked to fuel injection hardware in a near-quiescent pressure vessel at high-temperature conditions representative of late, stratified-charge injection. An eight-hole spark-ignition direct-injection spray was interrogated using high-speed schlieren and Mie-scatter imaging from multiple, simultaneous views to acquire the vapor and liquid envelopes of the spray. The mixture fraction of vaporized sections of the spray was then quantified at a plane between plumes using Rayleigh scattering. Probability contours of the line-of-sight vapor envelope showed little variability between injections, whereas probability contours derived from planar, quantitative mixing measurements exhibit greater amounts of variability for lean-combustion-limit charge. The mixture field between plumes was characterized by multi-hole and end-of-injection dynamics that attract the plumes to each other and toward the injection axis, resulting in a liquid-fuel-droplet-dense merged central jet in the planar measurements. Supplemental long-working distance microscopy imaging showed the existence of fuel droplets far downstream in the region of the planar laser measurements.

Correction method for droplet sizing by laser-induced fluorescence in a controlled test situation

The linear sizing technique is used to evaluate the accuracy of a new correction strategy to limit scattering matters. The ratio of the elastic scattered light with fluorescence emission over monodispersed microspheres homogenously mixed in water is measured. Three cells filled with different concentrations of these fluorescent particles are illuminated with a thin laser beam that is moved inside the cell from the front to the back. A comparison of the linear sizing technique with and without correction is presented and shows that the correction enables the measurement of higher concentrations; the limits of the correction method are also shown. These results could be a potential step to apply this technique to sprays.

Onset and progression of soot in high-pressure n-dodecane sprays under diesel engine conditions

Soot onset in n-dodecane sprays is investigated both experimentally, by means of high-speed imaging data from the Sandia spray combustion vessel, and numerically, using the conditional moment closure combustion model and an integrated two-equation soot model in a Reynolds-averaged Navier–Stokes framework. Five operating conditions representative of modern diesel engines are studied at constant density (22.8 kg/m3) with variations in ambient oxygen concentration and temperature. The reference case at 15% O2 and 900 K is compared with measurements in terms of the evolving soot mass distribution and spatiotemporal distributions of formaldehyde and polycyclic aromatic hydrocarbons obtained by 355-nm laser-induced fluorescence (polycyclic aromatic hydrocarbons represented by C2H2 in simulation) and soot optical thickness (KL) signal obtained by diffused back-illumination extinction imaging. All operating points are validated in terms of ignition delay and lift-off length, soot onset time and location, soot mass evolution, and peak location. Measurements show that time lag between ignition and soot onset is considerably increased by a reduction in ambient oxygen or temperature. The trend of this time lag is captured very well by the simulations, as is the evolving axial distribution of soot, despite the simple soot model employed. Building on the good agreement between spatiotemporal distributions in experiment and simulation, further results from the latter are extracted to provide insight into relevant processes. The advancing soot tip lags behind the fuel–vapor spray tip due to soot oxidation. Tracking the Lagrangian time history of notional fluid particles from the soot onset location back to the injector orifice reveals that their trajectories evolve along rich conditions (φ > 1.5) throughout the entire path. Overall, novel insights obtained from experiments with respect to soot and soot precursor evolutions are complemented by simulations using the integrated conditional moment closure/soot modeling approach, showing encouraging results for prediction and understanding of transient soot processes in high-pressure diesel sprays.

Diffuse back-illumination setup for high temporally resolved extinction imaging

This work presents the development of an optical setup for quantitative, high-temporal resolution line-of-sight extinction imaging in harsh optical environments. The application specifically targets measurements of automotive fuel sprays at high ambient temperature and pressure conditions where time scales are short and perceived attenuation by refractive index gradients along the optical path (i.e., beam steering) can be significant. The illumination and collection optics are optimized to abate beam steering, and the design criteria are supported by well-established theoretical relationships. The general effects of refractive steering are explained conceptually using simple ray tracing. Three isolated scenarios are analyzed to establish the lighting characteristics required to render the observed radiant flux unaffected by the steering effect. These criteria are used to optimize light throughput in the optical system, enabling minimal exposure times and high-temporal resolution capabilities. The setup uses a customized engineered diffuser to transmit a constant radiance within a limited angular range such that radiant intensity is maximized while fulfilling the lighting criteria for optimal beam-steering suppression. Methods for complete characterization of the optical system are detailed. Measurements of the liquid-vapor boundary and the soot volume fraction in an automotive spray are presented to demonstrate the resulting improved contrast and reduced uncertainty. The current optical setup reduces attenuation caused by refractive index gradients by an order of magnitude compared to previous high-temporal resolution setups.

Understanding the Acoustic Oscillations Observed in the Injection Rate of a Common-Rail DI Diesel Injector

Measuring the rate of injection of a common-rail injector is one of the first steps for diesel engine development. At the same time, this information is of prime interest for engine research and modeling as it drives spray development and mixing. On the other hand, the widely used long-tube method provides results that are neither straightforward, nor fully understood. This study performed on a 0.09 mm axially drilled single-hole nozzle is part of the Engine Combustion Network (ECN) and aims at analyzing these features from an acoustic point of view to separate their impact on the real injection process and on the results recorded by the experimental devices. Several tests have been carried out for this study including rate of injection and momentum, X-ray phase-contrast of the injector and needle motion or injector displacement. The acoustic analysis revealed that these fluctuations found their origin in the sac of the injector and that they were the results of an interaction between the fluid in the chamber (generally gases) and the liquid fuel to be injected. It has been observed that the relatively high oscillations recorded by the long-tube method were mainly caused by a displacement of the injector itself while injecting. In addition, the results showed that these acoustic features also appear on the momentum flux of the spray which means that the real rate of injection should present such behavior.Copyright