High-Speed Flow and Fuel Imaging Study of Available Spark Energy in a Spray-Guided Direct-Injection Engine and Implications on Misfires

Abstract

The spark energy transferred under the highly stratified conditions during late injection in a spray-guided spark-ignition direct-injection (SG-SIDI) engine is not well characterized. The impact of high pressures, temperatures, velocities, and variations in local fuel concentration along with temporal and/or spatial variations on spark performance must be better characterized. Previous spark ignition studies have not addressed the full range of conditions that are present in SG-SIDI engines. Therefore, high-speed particle image velocimetry (PIV) experiments are conducted to characterize the spark energy dependence for a wide range of well-defined homogeneous fuel-air equivalence ratios (W 5 0-2.9) and average air velocities (0-8 m/s) in an optical SG-SIDI engine. A moderate dependence of spark energy on equivalence ratio is shown to exist with average values of spark energy increasing by 21 per cent for the equivalence ratio range of W 5 0-2.3. Air injection into the motored engine is used to prepare well-defined flow conditions without the complications of fuel concentration gradients that are present during fuel injection. This allows the study of the effects of velocity, shear strain rate, and vorticity on spark energy. The spark energy increases with velocity at the spark plug. This observation is consistent with findings reported in the literature for low-pressure conditions. A linear increase is shown between shear strain rate and spark energy, while vorticity and spark energy are only weakly correlated. Simultaneous high-speed PIV, planar laser-induced fluorescence, and spark-discharge electrical measurements are also performed in the optical SG-SIDI engine to measure flow properties and fuel concentrations under late injection. Operating parameters are chosen to be near peak indicated mean effective pressure performance, but they occasionally provide a random misfired or partial burned cycle. Misfired cycles occur under stoichiometric-to-lean mixtures and low velocities near the spark plug. The lower spark energies observed under these conditions are in agreement with the observations made under well-controlled mixture and flow conditions reported in this study. All mixture conditions found in misfiring and partially burning cycles are within the ignitability range and fall within the general population of all, predominantly well-burning, cycles. There is no predominant impact of shear strain rate and vorticity under late injection operation on misfires and partial burns.

An experimental database on the effects of single- and split injection strategies on spray formation and spark discharge in an optical direct-injection spark-ignition engine fuelled with gasoline, iso-octane and alcohols

“…This was in agreement with conclusions cited therein by [46][47], that a large ignition window led to fast early flame kernel development, because it masked the effects of in-cylinder variation in local AFR. These findings were also in agreement with other researchers [48][49][50] and have also been discussed more recently in [32,51].…”

“…Previous work has offered some useful insights into the spark's behaviour in DISI engines [32][33][34][35] and the present paper also aimed at reporting on the spark's behaviour in conjunction with the same set of injection strategies employed for spray development analysis.…”

Evaluation of the flame propagation within an SI engine using flame imaging and LES

“…3). This is corroborated by the fact that seeded oil-droplet densities are not enough to sustain a flame kernel [50]. Figure 4 shows a schematic of the experimental setup used for flame imaging.…”

On the turbulent flow in piston engines: Coupling of statistical theory quantities and instantaneous turbulence

“…The large-scale tumbling flow, which has an axis of rotation perpendicular to the cylinder axis, is intrinsically instable near the end of compression and leads to the tumble breakdown where the kinetic energy from the tumble motion is transferred to small-scale turbulence 4,7 . The resulting mean flow and turbulence uniquely describes thermal transport 5,8,9 , fuel-air preparation [10][11][12][13][14][15] , ignition behavior 16,17 , and flame-and species-transport [18][19][20] , which accurately describes the instantaneous burning rate. The creation of an organized large-scale tumble rotation is challenged by varying initial conditions, periodically varying boundary conditions during the cycle, and stochastic flow events that result in large-scale cycle-to-cycle flow variations 21 .…”