The Effects of Ignition Environment and Discharge Waveform Characteristics on Spark Channel Formation and Relationship between the Discharge Parameters and the EGR Combustion Limit

This study set out to experimentally investigate spark ignition and the subsequent early flame development of lean airfuel mixtures of A/F = 20-30 under high-velocity flow conditions using a uniquely designed swirl chamber. The swirl chamber realizes a high-velocity flow of 65 m/s at the spark plug gap, as well as internal temperature and pressure histories that are equivalent to those of spark-ignition engines, being equipped with an optically accessible engine. The designed swirl chamber clearly captures the characteristic behavior of the spark channels and flames in the vicinity of the spark plug. The results show that the spark channels stretch downstream following the flow and are subject to short circuits or restrikes. In the case of a high ignition energy of 200 mJ, short circuits of the spark channels occur in the early part of the discharge, while restrikes occur in the later parts. With a decrease in the ignition energy, restrikes occur in the earlier parts of the discharge. With a low ignition energy of 65 mJ, restrikes can occur immediately after the electrical breakdown without any significant spark stretch. At a sufficiently low dilution degree of A/F = 20, flames can hold behind the ground electrode of the spark plug, which significantly suppresses the cycle dispersion while also enhancing the combustion in the early stage. With further air dilution, that is, A/F. 20, flames develop, flowing downstream without flame holding. However, temporal flame attachment to the ground electrode is observed during the discharge duration even at A/F = 30, while the attached flames eventually blow off downstream at the end of the spark discharge.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spark ignition and early flame development of lean mixtures under high-velocity flow conditions: An experimental study

Sayama

Kinoshita

Mandokoro

et al. 2018

“…The spark current can also be adjusted directly via the modulation of the voltage applied on the secondary coil after the spark breakdown. Development and examinations of such ignition systems were carried out on research engines and optical combustion vessels, such as the work reported by Shiraishi et al, 64 Hayashi et al, 30 Brandt et al, 31 and Yang et al 65 Depending on the electrical circuits' specific design, the characteristics of the discharge current vary among those ignition systems. The advantage lies in the ability to decouple the control of the discharge current and the spark duration, unlike in the conventional ignition systems where the current and duration are coupled with the amount of the total ignition energy.…”

Section: Discharge Current Controlled Ignitionmentioning

confidence: 99%

“…Shiraishi et al investigated the effect of ignition environment and discharge waveform characteristics on spark channel formation and the relationship between the discharge parameters and the EGR combustion limit. 64 The ignition coil was coupled with a DC-DC converter to supply current directly in the secondary coil. It was found that the increase in the spark current can delay the first restrike, thereby increasing the spark channel length and extending the EGR combustion limit, especially at high engine speed.…”

Section: High-energy Spark Ignitionmentioning

confidence: 99%

Future gasoline engine ignition: A review on advanced concepts

Zheng

2020

To meet the future requirements of fuel economy and exhaust emissions, high-efficiency gasoline engines tend to employ diluted combustion concepts along with intensified charge motion and stratified mixtures. Securing the ignition of such mixtures over the full engine operation range is challenging, because of the lowered mixture reactivity and increased discrepancy of stoichiometry. In recent years, increasing research efforts have been spending on innovations of ignition technologies to tackle the challenges. In this paper, the directions of ignition improvement are highlighted based on the fundamental understanding of the ignition mechanisms. The working principles of the primary types of advanced ignition systems are introduced; and relevant engine and combustion vessel test results are reviewed. The ignition systems are categorized as: (1) high-energy spark ignition, (2) pulsed nanosecond discharge ignition, (3) radio-frequency plasma ignition, (4) laser-induced plasma ignition, and (5) pre-chamber ignition. The advanced ignition systems are commented, regarding the ignition effectiveness and the implementation challenges, according to the literatures and the extensive empirical work at the authors’ laboratory.

“…SI engines demand ignition systems that can reliably ignite an air-fuel mixture with minimal energy consumption, despite being required to ignite a rapidly moving flow of a highly diluted mixture. [1][2][3][4][5][6][7] To realize this, an ignition system must be highly efficient.…”

Section: Introductionmentioning

confidence: 99%

Measurement of vibrational and rotational temperature in spark-discharge plasma by optical emission spectroscopy: Change in thermal equilibrium characteristics of plasma under air flow

Kinoshita

Fuyuto

Akatsuka

2018

The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy, and the influence of the air flow velocity and ambient pressure on these temperatures was investigated. The optical emissions from the plasma were led to an imaging spectroscope through an optical fiber. The temperature was estimated by fitting a theoretically calculated spectrum to that which had been acquired experimentally, formed by nitrogen molecule emission from 372 to 382 nm. The spark-discharge plasma was examined with a flow of ambient air at a discharge energy of 80 mJ. The air flow caused the spark-discharge channel to elongate downstream. At the center of the spark plug gap, the vibrational temperature in the plasma was 4000 K, whereas the rotational temperature was 2000 K. This plasma can be regarded as being in non-thermal equilibrium because the vibrational temperature was higher than the rotational temperature. At a position approximately 3 mm downstream from the spark plug gap, the vibrational and rotational temperatures increased to 4500 and 4000 K, respectively, while approaching each other. Both temperatures reached a maximum value. These results show that the plasma transitions from non-thermal equilibrium to thermal equilibrium as it is elongated by the air flow. Ignition efficiency improvements can be expected if the time required to transition from non-thermal to thermal equilibrium can be shortened.