The Use of a Flash Vaporization System with Liquid Hydrocarbon Fuels in a Pulse Detonation Engine

Abstract

In recent research, 1,2 liquid fuel droplets were found to hinder the detonation process in a pulse detonation engine (PDE). In the current work, multi-phase effects are eliminated with a flash vaporization system that vaporizes the liquid fuels prior to mixing with air. Hydrocarbon and air mixtures have been transitioned from deflagration to detonations previously, 1 but exhibited long ignition and deflagration to detonation transition (DDT) times. Here, two liquid hydrocarbon fuels, with different octane numbers (ON), are detonated with air in a PDE to determine the effect of octane number on the ignition time and the DDT time. The premixed, combustible mixture fills the PDE tubes via an automotive valve and cam system described in detail elsewhere.3 N-heptane (ON-0) and isooctane (ON-100) are evaluated individually to determine the effects of automotive octane number on pulse detonation engine combustion performance. The ON has been considered previously 4 as an acceptable criterion in determining the detonability for PDEs, and it is derived based on the tendency to "knock" or detonate relative to isooctane in an automotive engine application. _____________________________ * Correspondence can be addressed to: kelly.tucker@wpafb.af.mil. The views expressed in this paper are those of the authors and do not reflect the official policy or position of the United States Air Force, the Department of Defense or the US Government. †This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.The goal of this research is to show that a flash vaporized liquid hydrocarbon fuel system can provide the fuel and air homogeneity required to achieve detonations. The octane number is studied to determine its influence on the ignition and DDT time for hydrocarbon fuels.The flash vaporization system provided an outstanding method for achieving the desired mixing and vaporization, and the systems operating points matched well with the liquid vapor equilibrium model results. The ignition times showed little dependence on fuel injection temperatures or octane number and no droplet effects were noted. The DDT trends were octane number dependent and the isooctane was difficult to detonate with wave speeds below the stable Chapman-Jouget (CJ) wave speeds. The heptane readily detonated and produced wave speeds at or above CJ.

Evaluation of Catalytic and Thermal Cracking in a JP-8 Fueled Pulsed Detonation Engine

“…This research marks the first evaluation of a PDE fueled with thermally and catalytically cracked JP-8 fuel. Previous research 8,9 demonstrated the benefits of preheating JP-8 to flash vaporization and supercritical temperatures. Tucker et al 8 demonstrated that flash vaporization of JP-8 reduces both ignition time and DDT time, as well as increases the ignition and detonation limits.…”

Liquid Hydrocarbon Detonation Branching in a Pulse Detonation Engine

“…The choice of fuel was based on previous single-tube PDE research using a vaporization system where nheptane had short DDT times and detonation speeds consistently at or above the Chapman-Jouguet (C-J) detonation velocity 3 . To avoid the coking that occurs when fuel is heated above 450 K 4 , the oxygen content in the n-heptane was decreased to less than 1 ppm using nitrogen sparging.…”

“…The use of detonation branching as an ignition source with hydrogen fuel has been demonstrated 2 , as has the use of liquid hydrocarbon fuels in a PDE with spark ignition 3 . This paper reports the first attempt at combining the two concepts, i.e., using a branch detonation as an ignition source in a PDE running on liquid hydrocarbon fuel.…”

Chamber Volume Effects on Hypergolic Pulse Detonation Rocket Engine

“…1 The need to initiate a new detonation for each cycle of a PDE has led to the development of clever ways to initiate detonations in an alternative to deflagration to detonation transition (DDT) methods. 2 Challenges still remain with improving operating frequency, the time between successive pulse detonations, to levels such that performance surpasses traditional steady state rocket engines. Key experiments in attempting to achieve continuous prolonged PDE operation have shown that repeatable detonation initiation and hardware longevity prove challenging.…”