STUDI KOMPUTASIONAL DEFLAGRATION-TO-DETONATION TRANSITION PADA PULSE DETONATION ENGINE

• Main Author: Kartawijaya, Dion
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67099
• Institution: Institut Teknologi Bandung

Pulse detonation engine (PDE) is a mean of propulsion utilizing detonation as the source of its thrust. Detonations are supersonic explosions, with explosions denoting the result of rapid gas expansion due to mechanical or physical changes, with deflagrations signifying subsonic explosions. Detonation in PDE originates from deflagration-to-detonation transition (DDT) occuring inside the PDE detonation tube. DDT itself is a phenomenon of flame acceleration from subsonic speeds to supersonic speeds, which occurs in line with an increase in pressure and decrease in volume downstream. The DDT phenomenon consists of 4 phases, starting by conductive combustion, convective combustion, compressive combustion, and ends with detonation. The occurence of DDT in PDE relies on obstacles used in the detonation tube, together with the control of fuel and air as an oxidizer input, where hydrogen can be used as fuel. The study was done on the effects of changes to obstacle geometry and hydrogen-air mixture composition towards DDT phenomenon inside a PDE, by the creation of a computational fluid dynamics (CFD) model by simulation using ANSYS CFX software. The simulation was done on 3 different geometric models with 5 mixture variations for each geometry. Each geometry variation was made based on the difference of obstacle to tube cross sectional area, or blockage ratio (BR), with the values of BR 0.43, 0.51, and 0.64. The 5 chemical mixtures used are stochiometric and lean mixtures, lean mixtures having air excess of 5%, 10%, 15%, and 20%. The resulting models are then compared, especially based on flame velocity parameter. The model was validated using experimental data with an error of 7.58% above experimental data maximum speed. Observation shows the occurrence of flame velocity channeling around the cross section center in line with holes on obstacles, increase of initial pressure, decrease in downstream volume, as well as increase in temperature, consistent with combustion reaction and detonation. Models with larger obstacles reaching higher maximum velocities, which increases with air excess until it reaches stagnation at a certain amount, the amount being lower for tubes with larger obstacles. Stagnation on detonation tubes with BR of 0.43 and 0.51 starts at 10% excess air, while it starts at 5% excess air for the tube with BR of 0.64.