טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShashank Judah
SubjectFundamental Combustion Study using Counterflow Combustor
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Emeritus Yeshayahou Levy


Abstract

An emerging goal within the aviation industry is to replace conventional jet fuel with alternative fuel sources. However, the combustion properties of these potential fuels must be thoroughly characterized before they can be considered as replacements in turbomachinery applications.  Furthermore, alternative fuels are developed in order to meet existing fuel standards and, therefore, will not require modification to existing vehicle fleets.

The adoption of alternative or drop-in fuels is limited due to their limited understood fundamental combustion properties. Specifically, combustion temperatures, radical concentration, and emissions characteristics still have to receive further study. This lies in contrast with the requirement that alternative fuels behave similarly to conventional fuels, and furthermore these properties must be well understood for engine design modifications.

Opposed Jet Combustor (OJC) is well-suited to evaluate the characteristics of alternative fuels and their similarity to their comparative fossil based fuels. The OJC geometry is compact, has well-controlled boundaries and is axisymmetric. It allows efficient testing of the fluid dynamics and turbulence, fuel evaporation and combustion models. With regards to validation of computer model of combustion process, the OJC simple configuration enables to perform accurate simulation with sufficient resolution while using limited computational power.

Current research work dealt with designing of a versatile turbulent OJC to serve as a test bench and performing tests to evaluate the combustion properties of gaseous and liquid fuels. Within the scope of the present research work, OJC setup was built, calibrated and operated to reveal the combustion characteristics of several fuels as well as their comparison to simulated data from chemical kinetics models.

Two main flow configurations were investigated, cold flow and reactive flow under opposed jet configuration. The cold flow configuration was investigated to calibrate the flow field and to establish proper flow conditioning of both nozzles. Planar measurements of the droplet size and axial velocity component were measured by Phase Doppler Particle Analyzers (PDPA).

Reactive flow experiments were conducted using different liquid and gaseous fuels to characterize temperature, gaseous concentrations and radicals’ concentrations profiles for their comparison with chemical kinetics model.

 The combustion characteristics of four different fuels were studied under OJC; LPG, propane, heptane and methanol. In order to compare all characteristics, fuels were burnt at stoichiometry. The flames were obtained by introducing fuel and air at the bottom nozzle and air at the top. In this flow configuration, a premixed and diffusion flame were established simultaneously near stagnation plane. Temperature of the flame was measured by using a fine-wire thermocouple of type R, whereas, concentrations of emission gases (CO2 and O2) were measured by a gas analyzer. Experimental temperature and emission data were compared against simulations carried out using the OPPDIF module in CHEMKIN-PRO software, which resulted in a very similar trend. In the presence of measurement probes (thermocouple and gas sampler), flame broadening was observed due to the holding of flame on the probe surface. However, while measuring optically the radical concentrations (OH* and CH*), a much better correlation between radical concentration to flame thickness was found.