Ethylene flame-holding in a shock tunnel

Abstract

The aim of the thesis is to investigate the flame-holding characteristics of ethylene in a shock tunnel. To begin with, flame-holding in supersonic flows is one of the most fundamental issues related to the development of supersonic combustion ramjet(scramjet) engine. Flame-holding techniques are necessary to sustain hydrocarbon combustion due to its slow chemical rates. From the literature, the experimental data on the hydrocarbon flame-holding in high-enthalpy flows are few and focuses mainly on the parts of the overall engine system. In light of the above, this study used a shock tunnel to examine the ethylene flame characteristics and the validity of sustaining combustion in different models.

Two types of model were investigated in this thesis. First, a contoured wedge model was used in a shock tunnel to replicate the scramjet combustor environment. The model consists of a contoured wedge, wall cavity and a cowl

a transverse fuel injection orifice is also located upstream of the cavity. Different cowl locations were considered to observe the effect of shock impingement on flame-holding. The experiments showed that, depending on the cowl shock location, the flame-holding can be categorized into three different types of interactions. Based on the result from the first part, it was found that the ethylene flame can be maintained at 1860K using a suitable shock impingement method.

The second part of the experiments was conducted using a double-compression inlet model. The model consists of a double-compression ramp with a wall cavity and a cowl. Three different injection modules were located from inlet to cavity to observe the interaction between the fuel injection and the flame-holding. With the experiments conducted by a flow of total temperatures that varied from 1280K to 1880K, shadowgraph and flame luminosity images were taken to capture flow-field and flame characteristics. The experiments show that the flame can be maintained at 1530K using the inlet model. Moreover, depending on the fuel injection location and pressure, a variety of flame-holding patterns can be observed in relation to the supersonic flow-field. Full details of the experimental setup and results are included in the full thesis.