Mixing Process of Direct Injection Hydrogen Jet in a Constant Volume Vessel by Using Spark-Induced Breakdown Spectroscopy

Hydrogen spark-ignition (SI) engines based on direct-injection (DI) have been investigated because of their potential for high thermal efficiency and solving the problems related to knocking, backfiring, and pre-ignition. Wide range flammability limits in hydrogen engine enable smooth engine operation for a very lean mixture with low NO_X. However, a too lean mixture may increase ignition delay and causes severe cyclic variations. There is a possibility that the turbulence occurred during injection of fuel surround the spark plug in the combustion chamber is major contributor to this phenomenon. To overcome this problem, a better understanding of the spark discharge and spark ignition during transient hydrogen jet is necessary. Therefore, it is very important to study an effect of local equivalence ratio and behavior of spark discharge in SI engine.

This paper describes a mixing process of hydrogen jet using spark-induced breakdown spectroscopy (SIBS) in a constant volume vessel. Spark discharge fluctuation images was visualized by high speed camera with the concentration measurement simultaneously. The SIBS sensor was developed from a commercial spark plug with an optical fiber embedded in the spark plug. This technique was used to detect the component of samples using the light emitted by spark-induced plasma. Spectrally resolved emission of plasma generated by the SIBS sensor was detected simultaneously by spectrometer. In this study, the strongest intensity peak of H_α(656nm) and N(501) was chosen to measure the local concentration. Comparing the intensity peaks of atomic emissions from hydrogen and nitrogen gives local hydrogen concentration in the measured volume.