Study of Condensed Phase Reactions Between Hypergolic Propellants using Microreactors
Open Access
- Author:
- Saksena, Pulkit
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 28, 2014
- Committee Members:
- Richard A Yetter, Dissertation Advisor/Co-Advisor
Srinivas A Tadigadapa, Dissertation Advisor/Co-Advisor
Stefan Thynell, Committee Member
Donghai Wang, Committee Member
Siyang Zheng, Committee Member - Keywords:
- Hypergolic
Propellants
Combustion
Microfluidic
Microreactor - Abstract:
- The testing of hypergolic propellants has been carried out for decades and the use of hypergolic propellants at a systems level is very well understood. Extensive testing has provided the design and construction of rocket engines which have been very reliable. Safety procedures have been developed for the handling and storage for hypergolic propellants, which all too often are highly toxic. But the condensed phase chemistry for these hypergolic propellants is not very well understood. The models in place for ignition and combustion do not handle the coming together of two liquid streams of these hypergols and the two-phase aspects that are expected once the reactions occur. Moreover, it is not clear what makes a fuel and oxidizer pair hypergolic in nature. The coupling of physical and chemical factors that control the ignition of hypergolic propellants makes the direct study of the transient ignition process difficult. The current study presents a novel method to study hypergolic propellants (very fast liquid reactions) using microreactors instead of conventional drop tests, modified versions thereof or impinging jet tests. Planar counterflow microreactors are used to isolate liquid-phase reactions from secondary gas phase reactions that occur later during the ignition process and thus provide valuable insight in to the pre-ignition mechanism. The microreactor fabrication, flow field characterization, reactivity results from experiments performed using a variety of fuels and nitric acid as the oxidizer and numerical simulation results of reactive flow in the microreactor are presented in this study. Particle image velocimetry measurements and numerical simulations were conducted to characterize the laminar velocity flow-field in the microreactor and strain rates at the stagnation point along the centerline of the microreactor. Temperature measurements at the stagnation zone, the exit and positions along the length of the microreactor were used as a measure for the extent of the reaction or the heat released from the reaction. For the hypergols, an increase in reactant flow (or equivalently strain rate at the stagnation point) was found to initially increase temperatures at both the stagnation zone as well as along the length of the reactor, but eventually resulted in a decrease in temperature, revealing a maxima in temperature and reactivity. The trends indicated a reaction that was initially diffusion or heat loss controlled, which transitioned towards kinetic control at higher strain (flow) rates. Numerical simulations of the reactive flow in the microreactor stagnation zone were also carried out in which the reaction zone in the microreactor was treated similar to the reaction zone occurring in a counter-flow diffusion flame. These simulations showed that the flow rates at which the peak in temperature occurred was dependent on the rate of the reaction occurring between the hypergol pairs. The numerical simulations also show that heat loss from the top and bottom surfaces can play a role on the temperature trends seen in the microreactor. This study details the first comprehensive measurements and analysis of the condensed phase interfacial reactions occurring between hypergols.