Rocket Engine Propulsion Research Articles

Numerical analysis of LOx-BioLPG combustion in high-pressure liquid rocket engine propulsion system

The present work numerically investigates the steady state LOx-BioLPG combustion in a high-pressure liquid rocket engine propulsion system, based on the RANS approach using Eulerian single-phase thermo-chemical modeling with Peng-Robinson equation of state. The study primarily focuses on the less carbon emission and the economical range of operation for various equivalence ratios. The critical equivalence ratio (Φ) is predicted to be 0.62, below which the combustion does not initiate. The maximum CO emission in combustion is found at Φ = 2.32, and the maximum specific impulse (Isp) is obtained 327.92 at Φ = 1.50. However, for clean burning of the fuel and less carbon footprint, lean mixture combustion is desirable. The CO emission for Φ = 1.50 is 41%, which is considerably a higher carbon emission percentage for this combustion process. On the other hand, the lean mixture at Φ = 0.80 has a CO emission of 14.7% at the nozzle outlet which is relatively small. The developed power is 57.73 MW with an Isp of 310.96 at Φ = 0.80 which is close to the Isp obtained for Φ = 1.50. Thus, for eco-friendly clean burring, combustion of LOx-BioLPG fuel for Φ = 0.80 is found to be the best in this analysis.

Collision-induced jet-like mixing for droplets of unequal-sizes

The internal mixing of droplets upon coalescence is of fundamental importance to a number of applications in microfluidics, micro-scale heat and mass transfer, and rocket engine propulsion. Compared to the well-known surface-tension-induced jet-like mixing in the coalescence of inertialess droplets, collision-induced jet-like mixing was observed recently and remains inadequately understood. In the present study, the collision dynamics and internal mixing of droplets of unequal sizes was numerical simulated by using the lattice Boltzmann phase-field method, with emphasis on unraveling the mechanism of the internal jet formation and therefore on exploring strategies to facilitate such a mixing pattern. The results show that the formation of the internal jet requires two synergetic flow motions favoring low Oh number and high We number: the capillary-pressure-driven radial converging flow induced by the crater restoration to detach the spreading smaller droplet from the surface, and the impact-inertia-driven axial motion along the crater surface to drive the penetration of the detached fluid. The jet-like structure was found to correlate with the evolution of a main vortex ring, which is formed by the vorticity generation on the interface during initial impact, and transported into the droplet during subsequent oscillations. However, due to the absence of the bulge retraction that generates a significant amount of vorticity and to the extended duration for the jet formation, the main vortex is much less intensive compared to that formed by the inertialess droplet coalescence and is therefore less capable of inducing obvious vortex-ring structure in the mixing pattern. Further simulations by manipulating the disparity of the droplet sizes and the disparity of the liquid viscosities show that, the collision of a larger droplet with lower viscosity with a smaller droplet with higher viscosity is effective in facilitating jet-like mixing.

Liquid Oxygen Rotating Friction Ignition Testing of Aluminum and Titanium with Monel® and Inconel® for Rocket Engine Propulsion System Contamination Investigation

Abstract Metallic contaminant was found in the liquid oxygen (LOX) pre-valve screen of the shuttle main engine propulsion system on two orbiter vehicles. To investigate the potential for an ignition, NASA Johnson Space Center White Sands Test Facility performed (modified) rotating friction ignition testing in LOX. This testing simulated a contaminant particle in the low-pressure oxygen turbo pump (LPOTP) and the high-pressure oxygen turbo pump (HPOTP) of the shuttle main propulsion system. Monel® K-500 and Inconel® 718 samples represented the LPOTP and HPOTP materials. Aluminum foil tape and titanium foil represented the contaminant particles. In both the Monel® and Inconel® material configurations, the aluminum foil tape samples did not ignite after 30 s of rubbing. In contrast, all of the titanium foil samples ignited regardless of the rubbing duration or material configuration. However, the titanium foil ignitions did not propagate to the Monel and Inconel materials. Based on these results, NASA determined that the risk of a fire occurring in the turbo pumps was acceptably low.