The influence of in-cylinder flows and bulk gas density on early Spray G injection in an optical research engine

A well-characterized multi-hole gasoline injector, the Engine Combustion Network’s (ECN) Spray G injector, was investigated in an optically accessible research engine under four motored operating conditions with early injection. The experiments were conducted at intake pressures of [Formula: see text] and [Formula: see text], nearly matching the ECN’s standard early injection operating conditions, Spray G2 (flash boiling) and Spray G3 (early injection), respectively. This was combined with two engine speeds at [Formula: see text] and [Formula: see text]. Using particle image velocimetry and volumetric Mie scatter imaging, the in-cylinder flows were evaluated and the effects on the spray morphology were characterized. The in-cylinder flow was evaluated to understand the spray-flow interaction, including the turbulent kinetic energy. Little effect on turbulent energy was observed in the region examined near the exit of the fuel injector nozzle shortly after injection. Mie scatter imaging was used to characterize the spray morphology and wall wetting was clearly visible on the spark plug. Cyclic variability of the sprays was found to be insignificant; and major differences in spray morphology are attributed to the in-cylinder velocity and intake pressure at the time of injection. Decreasing the bulk gas density by decreasing the intake pressure had a number of effects on the evolution of the spray including faster evaporation, increased axial liquid penetration, and decreased spray angle. Increasing the in-cylinder flow magnitudes by increasing the engine speed had a similar effect on spray morphology by also increasing the evaporation rate, increasing the axial penetration, and decreasing the spray opening angle. Comparison of the motored spray cases with a no-flow case (when the fuel is sprayed into the engine without the piston present) further illustrated the extent to which the intake flow influenced the spray shape.

Rapidly rotating precessing cylinder flows: forced triadic resonances

Rapidly rotating cylinder flows subjected to low-amplitude precessional forcing are studied numerically over a range of cylinder and precessional rotation rates. For sufficiently small rotation rates, viscous effects lead to a forced overturning flow that is steady in the precession (table) frame of reference. Increasing the rotation rates, this forced flow loses stability in a Hopf bifurcation, which can be either supercritical or subcritical, and may preserve or break the symmetry of the system, depending on the parameter regime studied. Regardless of these details of the Hopf bifurcation, it is found that the Hopf instability is associated with a slightly detuned triadic resonance between the forced overturning flow and two free Kelvin modes (inviscid eigenmodes of the rotating cylinder). Further increases in rotation rates lead to a sequence of secondary instabilities which also follow a generic pattern irrespective of the parameter regime investigated. The relationship between this sequence of instabilities and the resultant nonlinear dynamics with the experimentally observed phenomenon of resonant collapse is discussed.

In-Cylinder Flow Evolution Using Tomographic Particle Imaging Velocimetry in an Internal Combustion Engine

In-cylinder flows in internal combustion (IC) engines have always been a focus of study in order to gain better understanding of fuel–air mixing process and combustion optimization. Different conventional experimental techniques such as hot wire anemometry (HWA), laser Doppler anemometry (LDA), and numerical simulations have been grossly inadequate for complete understanding of the complex 3D flows inside the engine cylinder. In this experimental study, tomographic particle imaging velocimetry (PIV) was applied in a four-valve, single-cylinder optical research engine, with an objective of investigating the in-cylinder flow evolution during intake and compression strokes in an engine cycle. In-cylinder flow seeded with ultra-fine graphite particles was illuminated by a high energy, high frequency Nd:YLF laser. The motion of these tracer particles was captured using two cameras from different viewing angles. These two-directional projections of flowfield were used to reconstruct the 3D flowfield of the measurement volume (36 × 25 × 8 mm3), using multiplicative algebraic reconstruction technique (MART) algorithm. Captured images of 50 consecutive engine cycles were ensemble averaged to analyze the in-cylinder flow evolution. Results indicated that the in-cylinder flows are dependent on the piston position and spatial location inside the engine cylinder. The randomness of air-flow fields during the intake stroke was very high, which became more homogeneous during the compression stroke. The flows were found to be highly dependent on Z plane location inside the engine. During the intake stroke, flows were highly turbulent throughout the engine cylinder, and velocities vectors were observed in all directions. However, during the compression stroke, flow velocities were higher near the injector, and they reduced closer to the valves. Absolute velocity during compression stroke was mainly contributed by the out of plane velocity (Vz) component.