Influence of plasma-assisted ignition on flame propagation and performance in a spark-ignition engine

Lean-burn is an attractive concept for reasons of high thermal efficiency and low nitrogen oxide (NOx) emissions, however, successful implementation in spark-ignition (SI) engines turned out to be challenging because of misfire or partial burn caused by attenuated flame propagation. In order to overcome this issue, microwave-assisted plasma ignition system (MAPIS) has been applied in combustion systems. The MAPIS consists of a conventional ignition coil, a non-resistor spark plug, a mixing unit, a waveguide, and a magnetron (2.45GHz, 3kW). A series of experiments was carried out to understand discharge characteristics and to validate its performance in a constant volume vessel as well as in a single-cylinder spark-ignition engine. The fundamental investigation based on optical emission spectroscopy and flame imaging showed that the ejection of the microwave was beneficial to produce more reactive species such as OH and O radicals thanks to higher electron temperature than conventional spark ignition. The lean limit was able to be extended up to an equivalence ratio of 0.5 based on a larger initial flame kernel size with MAPIS in the vessel test. Meanwhile, in the engine test, combustion stability was noticeably improved showing smaller cycle-to-cycle fluctuations in in-cylinder pressure. Improvement in fuel efficiency up to 6% could be achieved by stable operation under fuel-lean conditions. In terms of emissions, MAPIS was advantageous to reduce carbon monoxide (CO) emissions by promoting more complete combustion

Spatio-temporally Resolved Emission Spectroscopy of Inductive Spark Ignition in Atmospheric Air Condition

Current transistorized coil ignition (TCI) system consists of ignition coil and spark plug, whose electrical properties, structure and gas composition determine entire discharge processes and therefore the early stage of combustion. In this work, a new measurement and diagnostic technique were developed and tested to investigate the early phases of spark ignition process. The spark discharge of commercial TCI system was analyzed by using spatio-temporally resolved optical emission spectroscopy to find out the Interrelation of the characteristic evolution of discharge with the formation of reactive species inside the activated volume. The emission spectra of inductive spark discharge in atmospheric air were measured at the range of wavelength from 300 to 800 nm, while the secondary voltage and current of spark ignition system were acquired simultaneously. An optical probe with linearly arranged glass fiber bundle was used to achieve spatial distribution of emission intensity vertically along the electrode gap of spark plug. At the same time, the time series of emission spectra were illustrated by using the precise gate shift operation of intensified CCD camera mounted on the spectrograph. The emission of electronically excited species such as molecular nitrogen, atomic oxygen and electrode material were effectively measured with the spectral resolution of 0.2 nm. During the abrupt increase of current in breakdown phase, only molecular nitrogen emission was exclusively detected. It was followed by the atomic oxygen and electrode material, which are closely related to the flame initiation and electrode wear respectively. The activated volume of spark discharge near cathode showed higher emission intensity for all the aforementioned species in comparison with the region near anode. The electronic, vibrational and rotational temperatures of the discharge were calculated by using additional spectra measurement at selective wavelength range with spectral resolution of 0.1 nm. Alongside the calorimetric measurement, the temperature profile over position and time allowed the quantitative evaluation of energy-transfer efficiency of spark discharge into the gas mixture

Influence of the Electrical Parameters of the Ignition System on the Phases of Spark Ignition

Untersucht wurde der Einfluss der Kapazität auf das Spektrum der Funkenzündung. Im Mittelpunkt der Untersuchung standen die Spektren von N2 bei 337nm, N2+ bei 391nm, N bei 500nm und O bei 777nm. Dabei wurde ein Zündfunken mit verschiedenen, unmittelbar vor der Zündkerze, montierten Kapazitäten zeitlich abgetastet. Dabei konnte vor allem eine starke Erhöhung der kapazitiv gespeisten Bogenentladung beobachtet werden. Diese resultiert in eine Erhöhung der Nickelemission im Gas. Die 2. pos. Gruppe von Stickstoff bei 337nm weist in dem kapazitiven Bogen eine höhere Intensität auf sobald die Kapazität wächst. Zusätzlich zeigt das Spektrum der 1. neg. Gruppe von Stickstoff bei 391nm erst zum Einsetzen der Glimmentladung eine hohe Leuchterscheinung welche sich auf die Kathode beschränkt. Des Weiteren konnte atomarer Stickstoff nur im Bereich des Durchbruchs und der kapazitiven Bogenentladung gefunden werden. Bei atomarem Sauerstoff konnte eine Reduktion der Emission beobachtet werden

Flow and flame interaction in spark-ignited premixed mixtures

Imperial Users onl

레이저 유도 플라즈마가 기상 유동에 미치는 영향

International audienceAs the initial stage of laser ignition, the effect of laser-induced plasma on nearby gaseous flow can have a considerable effect on further flame propagation. Laser-induced plasma is generated by concentrating a laser beam into a single point using a focusing lens. This paper presents a quantitative description of the perturbation of laser-induced plasma into a gaseous flow. Single-point laser-induced plasma generates fluctuations in the surrounding gaseous flow in a very short time (less than 200 ms), and the time-resolved velocity field can be obtained by the particle image velocimetry technique. Based on the angle and velocity of the velocity fields, it is possible to explain the movement of gaseous air flow quantitatively.1. 서 론 레이저(유도) 점화는 집적된 레이저 빔을 이용 하여 연료를 점화하는 방법으로, 최근 강화되는 환경 규제와 연소 성능 향상의 요구가 증가되는 가운데 각종 수송 분야에서 주목을 받고 있다. 레 이저 유도 점화는 기존 스파크를 이용한 전기 점 화 방식과는 다르게 연소실 내로 돌출된 부분이 없고 광학 장치를 통해 점화를 시킴으로써 불필요 한 열손실을 줄이고 소염 가능성도 줄일 수 있다. 또한 점화 위치의 조정이나 에너지 분배에도 자유 롭기 때문에 점화 시기·시점을 최적화할 수 있게 되고 이를 통해 빠른 화염 전파와 높은 연소 효율 을 구현할 수 있게 된다. 레이저 유도 플라즈마(LIP: Laser-Induced Plasma) 는 집적된 레이저 빔이 생성한 스파크를 일컫는 말로 레이저에 의한 에너지가 짧은 시간(10ns 이 하) 동안 특정 위치에 집중되면서 고온(10 5 K 이 상) 고압(10 3 Bar 이상)의 상태를 형성하는 것을 의 미한다. 이 플라즈마에 의한 점화 과정은 다음과 같다. 1. 일부 분자의 다광자 photo-dissociation과 이어 지는 inverse bremsstrahlung process를 통해 광자를 흡수하는 전자들이 생성 2. 광자들이 다른 분자들과 충돌하면서 이온화 를 촉진하고, 이것이 electron cascade로 이어지면서 gas breakdown(스파크, 레이저 유도 플라즈마) 형