Investigation of the Lean Stable Limit of a Barrier Discharge Igniter and of a Streamer-Type Corona Igniter at Different Engine Loads in a Single-Cylinder Research Engine

Abstract

Currently, the Radio-Frequency Corona Ignition systems represent an important solution for reducing pollutant emissions and fuel consumption related to Internal Combustion Engines, while at the same time ensuring high performance. These igniters are able to extend the lean stable limit by increasing the early flame growth speed. Kinetic, thermal, and ionic effects, together with the peculiar configuration of the devices, allow the combustion process to start in a wider region than the one involved with the traditional spark. In this work two corona igniters, namely a Barrier Discharge Igniter and a Corona Streamer Igniter, were tested in a single-cylinder research engine fueled with gasoline at different engine loads in order to investigate the igniters’ performance through indicated analysis and pollutant emissions analysis. For each operating point, the devices’ control parameters were set to ensure maximum energy releasement into the medium with the aim of investigating, at the extreme operating conditions, the capability of the devices to extend the lean stable limit of the engine. The corona igniters were tested on a constant volume calorimeter as well, reproducing the engine pressure conditions at the corresponding ignition timing. The target was to give an estimation of the thermal energy released during the discharge and then to compare their capability to provide high-stability energy.

Streamers Variability Investigation of a Radio-Frequency Corona Discharge in an Optical Access Engine at Different Speeds and Loads

“…The differences in terms of streamer penetration P reported in Fig. 8 between the motored (red curve) and lean case (black curve) are due to different Vd and Pcyl conditions [12,15]. Nevertheless, it could be interesting to focus the attention on the streamer evolution.…”

“…Tests were carried out at four different speeds and two different loads, with the engine operating in motored conditions (Table2). At 1000 rpm, low load (from now on LL) condition was characterized by IMEP=4.5 bar @ λ=1 while the medium load (from now on ML) one by IMEP = 5.9 bar @ λ=1 [15].…”

“…In each test, maximum allowed corona duration ton=1500 μs [12,15] was used in order to deeply investigate the corona streamer evolution as pressure increases. For instance, at 1000rpm, ton=1500 μs corresponds to 9 CAD.…”

“…CSI discharge is based on the production of a strong electric field amplified through needles/ tips to generate filaments, named streamers [14]. These ionization waves propagate from the device-tips to the counter-electrode represented by the engine walls or by piston head, thus resulting in a larger amount of involved mixture [15]. Calorimetry tests also showed CSI capability to release into the medium higher thermal energy with respect to the one released by a conventional spark igniter [16].…”

Numerical Evaluation of the Effect of Fuel Blending with CO2 and H2 on the Very Early Corona-Discharge Behavior in Spark Ignited Engines

“…Furthermore, reduced standard deviation were reported for both the occurrence of the 50% Mass Fuel Burned (MFB50) and kernel formation at given EGR in the case of Corona ignition. Other relevant literature findings also report the potential of the Corona ignition device as lean limit extender to promote the stabilization of combustion events at very low equivalence ratio (φ, fuel-air ratio normalized against stoichiometric) [9][10][11][12]. Considering the high attention gained by the use of renewable hydrogen in fuel blends for the next on-road transportation, the exploration of technological solutions to support the ignition of such molecule is of primary interest.…”