Search Results

The 4th Workshop of the Engine Combustion Network (ECN) was held September 5-6, 2015 in Kyoto, Japan. This manuscript presents a summary of the progress in experiments and modeling among ECN contributors leading to a better understanding of soot formation under the ECN “Spray A” configuration and some parametric variants. Relevant published and unpublished work from prior ECN workshops is reviewed. Experiments measuring soot particle size and morphology, soot volume fraction (fv), and transient soot mass have been conducted at various international institutions providing target data for improvements to computational models. Multiple modeling contributions using both the Reynolds Averaged Navier-Stokes (RANS) Equations approach and the Large-Eddy Simulation (LES) approach have been submitted. Among these, various chemical mechanisms, soot models, and turbulence-chemistry interaction (TCI) methodologies have been considered.

Multi-hole diesel fuel injectors have shown significant transients in spreading angle during injections, different than past fundamental research using single-hole injectors. We investigated the effect of a this transient spreading angle on combustion parameters such as ignition delay and lift-off length by comparing a three-hole nozzle (Spray B) and single-hole nozzle (Spray A) with holes of the same size and shape as targets for the Engine Combustion Network (ECN). With the temperature distribution for a target plume of Spray B characterized extensively in a constant-volume combustion chamber, the ignition delay and lift-off length were measured and compared. Results show that the lift-off length of Spray B increases and grows by approximately 1.5 mm after the initial stages of ignition, in an opposite trend compared to Spray A where the lift-off length decreases with time.

A full understanding and characterization of the near-field of diesel sprays is daunting because the dense spray region inhibits most diagnostics. While x-ray diagnostics permit quantification of fuel mass along a line of sight, most laboratories necessarily use simple lighting to characterize the spray spreading angle, using it as an input for CFD modeling, for example. Questions arise as to what is meant by the “boundary” of the spray since liquid fuel concentration is not easily quantified in optical imaging. In this study we seek to establish a relationship between spray boundary obtained via optical diffused backlighting and the fuel concentration derived from tomographic reconstruction of x-ray radiography. Measurements are repeated in different facilities at the same specified operating conditions on the “Spray A” fuel injector of the Engine Combustion Network, which has a nozzle diameter of 90 μm.

This work investigates the injection processes of an eight-hole direct-injection gasoline injector from the Engine Combustion Network (ECN) effort on gasoline sprays (Spray G). Experiments are performed at identical operating conditions by multiple institutions using standardized procedures to provide high-quality target datasets for CFD spray modeling improvement. The initial conditions set by the ECN gasoline spray community (Spray G: Ambient temperature: 573 K, ambient density: 3.5 kg/m3 (∼6 bar), fuel: iso-octane, and injection pressure: 200 bar) are examined along with additional conditions to extend the dataset covering a broader operating range. Two institutes evaluated the liquid and vapor penetration characteristics of a particular 8-hole, 80° full-angle, Spray G injector (injector #28) using Mie scattering (liquid) and schlieren (vapor).

The effects of charge dilution on low-temperature diesel combustion and emissions were investigated in a small-bore single-cylinder diesel engine over a wide range of injection timing. The fresh air was diluted with additional N2 and CO2, simulating 0 to 65% exhaust gas recirculation in an engine. Diluting the intake charge lowers the flame temperature T due to the reactant being replaced by inert gases with increased heat capacity. In addition, charge dilution is anticipated to influence the local charge equivalence ratio ϕ prior to ignition due to the lower O2 concentration and longer ignition delay periods. By influencing both ϕ and T, charge dilution impacts the path representing the progress of the combustion process in the ϕ-T plane, and offers the potential of avoiding both soot and NOx formation.

An accurate prediction of internal nozzle flow in fuel injector offers the potential to improve predictions of spray computational fluid dynamics (CFD) in an engine, providing a coupled internal-external calculation or by defining better rate of injection (ROI) profile and spray angle information for Lagrangian parcel computations. Previous research has addressed experiments and computations in transparent nozzles, but less is known about realistic multi-hole diesel injectors compared to single axial-hole fuel injectors. In this study, the transient injector opening and closing is characterized using a transparent multi-hole diesel injector, and compared to that of a single axial hole nozzle (ECN Spray D shape). A real-size five-hole acrylic transparent nozzle was mounted in a high-pressure, constant-flow chamber. Internal nozzle phenomena such as cavitation and gas exchange were visualized by high-speed long-distance microscopy.