Optical Investigation of a Partial Fuel Stratification Strategy to Stabilize Overall Lean Operation of a DISI Engine Fueled with Gasoline and E30

Abstract

This paper offers new insights into a partial fuel stratification (PFS) combustion strategy that has proven to be effective at stabilizing overall lean combustion in direct injection spark ignition engines. To this aim, high spatial and temporal resolution optical diagnostics were applied in an optically accessible engine working in PFS mode for two fuels and two different durations of pilot injection at the time of spark: 210 µs and 330 µs for E30 (gasoline blended with ethanol by 30% volume fraction) and gasoline, respectively. In both conditions, early injections during the intake stroke were used to generate a well-mixed lean background. The results were compared to rich, stoichiometric and lean well-mixed combustion with different spark timings. In the PFS combustion process, it was possible to detect a non-spherical and highly wrinkled blue flame, coupled with yellow diffusive flames due to the combustion of rich zones near the spark plug. The initial flame spread for both PFS cases was faster compared to any of the well-mixed cases (lean, stoichiometric and rich), suggesting that the flame propagation for PFS is enhanced by both enrichment and enhanced local turbulence caused by the pilot injection. Different spray evolutions for the two pilot injection durations were found to strongly influence the flame kernel inception and propagation. PFS with pilot durations of 210 µs and 330 µs showed some differences in terms of shapes of the flame front and in terms of extension of diffusive flames. Yet, both cases were highly repeatable.

Octane Requirements of Lean Mixed-Mode Combustion in a Direct-Injection Spark-Ignition Engine

“…The injector was clocked such that two of the plumes straddle the spark plug gap, as shown in Figure b. The configuration of the injector and spark plug enables fully stratified charge operation as well as partial fuel stratification (PFS), where a very small quantity of fuel is injected to initiate more stable and faster deflagration under globally dilute and fuel-lean operation …”

“…The configuration of the injector and spark plug enables fully stratified charge operation as well as partial fuel stratification (PFS), where a very small quantity of fuel is injected to initiate more stable and faster deflagration under globally dilute and fuel-lean operation. 19 For each operating point, a sufficient amount of time was spent to stabilize all measured parameters before recording data. During the data acquisition, fuel-flow rate and temperatures from thermocouple readouts were averaged over 1 minute.…”

Numerical Analysis of GDI Flash Boiling Sprays Using Different Fuels

“…Gasoline direct injection (GDI) engines have penetrated the automotive market at a high rate in the past decade. Significant advantages, such as increased efficiency, lower knocking tendency, volumetric efficiency enhancement, and improved transient response have diverted the research focus from the well-known port fuel injection (PFI) towards GDI systems [1][2][3]. With these benefits, new challenges manifest themselves requiring further optimization strategies in order to reduce soot and particulate matter emissions that may result from phenomena such as tip wetting and wall-impingement [4,5].…”

A Eulerian Multi-Fluid Model for High-Speed Evaporating Sprays

“…The partially premixed combustion approach [6] is one of the various strategies that should allow high efficiencies and minimize emissions. Even the spark-ignited engines have several methods for reducing emissions and increasing efficiencies, e.g., the corona ignition condition [7], where the electron dissociation reaction replaces the classic hydrocarbon oxidation, and partial fuel stratification combustion strategies [8]. Optimal fuel-air mixing is a prerequisite for emissions reduction, and is directly coupled to the flow conditions occurring in the nozzle.…”