Pulse Jet Research at NCSU
January 2, 2007

Exploring new frontiers and putting knowledge to use has always been the aim and outcome of research. One such exploration did result in a new, unconventional method of propulsion, called the pulse jet. A pulse jet is a very simple internal combustion engine where combustion occurs in pulses. The advantage of this is that no rotating machinery is necessary. A typical pulse jet is comprised of an air intake, a combustion chamber* , and an acoustically resonant* exhaust pipe as well as a fuel supply. The fuel (gas or liquid) is supplied through reed valves in a valved pulse jet and though an open end in front of the pulse jet in a valveless pulse jet. The operational principle of the pulse jet is highly complex as opposed to its construction and is not completely understood. Pulsating combustion began development as early as 1600 but the use of pulsating combustion as a mode of propulsion did not occur until the beginning of the 20 th century; the most famous example being the German V-1 “buzz bomb.” Various organizations, both private and public, continued limited pulse jet research in the period 1940-1970, but with the improvements in power and efficiency of turbojets, pulse jets ceased to receive attention. Recently, however, with the interest in UAV's, various agencies and contractors have started looking for ways to propel these tiny vehicles with an efficient, affordable, and robust power source.

This is where research at NC State's applied energy research laboratory began under the guidance of Professor William Roberts (Experimentations) and Professor Andrey Kuznetsov (Computations), with invaluable help and advice from Professor Terry Scharton (Acoustics). The investigation in pulse combustion engines was initially funded by the Defense Advanced Research Projects Agency (DARPA) to investigate the scalability of such engines. The team of students who worked and are working on the project, in the order of graduation, are Mike Schoen, Adam Kiker, Rob Ordon, Christian McCalley, Tao Geng, Fei Zheng, Ranjith Kumar A.K, Wes Boyette and Todd Travis.

5cm and 4cm Pulsejets

8cm Pulsejet

The miniaturization of pulse jet engines was the first focus and the effects of engine performance with changes in engine geometry were investigated also. Later work focused on development of micro-scale pulse jets and the result was a record 8cm long, air breathing, hydrogen fueled pulse jet.

Following miniaturization of the pulse jet, the team worked on the hobby-scale (50cm) pulse jet, both valved and valveless, and proposed an analytical model which could predict the operating frequency of any pulse jet. The next step was the design of a pulse jet which would run on kerosene, an alternative to JP-8 (used by the military). Students also worked on special inlets or “Spike inlets” for the valveless configuration which would give better thrust output. The team's computational group works under the guidance of Professor Kuznetsov and contributes to the experimental team under Professor Roberts. The computational work is aimed at providing physical insight into the pulse jet operation and helping to design pulse jets with simulation predictions. In the previous work, computational models were validated by experimental measurements for various pulse jet lengths and configurations.

25 cm jet with Spike inlet Running on Kerosene

25 cm jet running on Gasoline

Currently the team is working on investigating the effects of a flared geometry, vortex generation at the exhaust, ram compression in the valveless pulse jet inlet and the effects of unsteady thrust ejectors on hobby scale and large scale pulse jets.

Valveless pulse jet in 50 m/s free stream

Vorticity and velocity vector plot of the 50cm valved pulsejet