This is another review of papers from the 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit (JPC) which took place from 25th to 28th of July 2010, in Nashville, TN. The third review can be found here. And the first review can be found here.
There are significant advancements being made by researchers in China on detonation based engines. Unfortunately, none of the Chinese delegation were able to come and present at the JPC 2010 Conference, probably due to them being denied visas. There were 3 papers on detonation engines that would have been of great value to read, but since AIAA follows the “No Paper-No Podium, No Podium-No Paper” rule, these papers were withdrawn. I am pretty sure that they will be presented at another conference soon.
Two papers were from researchers at Nanjing University of Aeronautics and Astronautics, Nanjing, China, on an experimental PDE (1.2 m long, 29 mm internal diameter) running on kerosene-air mixtures. The kerosene was pre-mixed with pre-heated air and they tested various Shchelkin spirals and orifice plate configurations for achieving DDT. The engine also featured a high energy spark/arc ignition system, which also provided the timing of the engine operation. Air was supplied through a one-way “aero-valve”. They successfully ran the engine, with consistent detonation waves developing, at various frequencies between 25 Hz and 50 Hz, and a maximum speed of 62.5 Hz.
Another paper from China was from a researcher at National University of Defense Technology, Hunan, China on a computational solver for reacting flows for simulating a rotating detonation wave engine.
I am looking forward to reading about these developments either from journal papers or future conference papers, because it does seem like they have successfully broken several barriers in PDE development.
There were also 2 papers from Japan related to detonation engines. The first one entitled “Study on Valve Systems for Pulse Detonation Engines” (AIAA 2010-6672) was by researchers at the University of Tsukuba, Tsukuba, Ibaraki, Japan and the PD Aerospace company, in Nagoya, Aichi, Japan. They developed and tested a compact, low-weight rotary valve system, featuring a rotary disk turned by an electric motor, capable of delivering 3 gases, namely fuel (ethylene), oxidizer (oxygen) and purge gas (helium), in metered doses at the required rate and frequency. The detonation chamber had an internal diameter of 43 mm and a length of just over 1230 mm. They successfully ran the engine for 2 second durations at frequencies between 5 Hz and 33.3 Hz. The highest time-averaged thrust of 31.7 N (7.1 lbf)was measured at a frequency of 33.3 Hz with propellant supply pressure of 1 MPa (145 psig, 9.8 atm). The highest specific impulse was measured as 249.5 s at the operating frequency of 33.3 Hz and propellant supply pressure of 0.7 MPa (101.5 psig, 6.9 atm). The thrust does seem low and the thrust vs. time chart in the paper shows a peak thrust close to 45 N during the initial few milliseconds of the run following by a quick tapering off which leveled at about 35 N for the remainder of the engine run time. This suggests to me that they had misfiring or detonation failure following the initial favorable phase. Perhaps the valves became de-synchronized and the fuel-oxygen supply became less than optimum. Or the ignition was not fired at the right time due to de-synchronized magnetic pickup of the valve position. Ignition could have also failed because of the destruction of the igniters in the oxygen rich environment. In oxygen supplied detonators, there is rapid deterioration of the igniters and the formation of hot spots causing pre-ignition to occur. This is one more reason why we should use air as an oxidizer and why purging is important to cool off the internal engine parts. The main reason being that oxygen storage on board is costly.
The second Japanese paper was entitled “Development of a Hydrogen-fueled Pulse Detonation Combustor for 1 kW-class Micro Gas Turbine” (AIAA 2010-6881) and was prepared and presented by researchers from the Tokyo Metropolitan University in Hino, Tokyo, Japan. This is an interesting paper to read. They developed a PDE with a detonation chamber having a rectangular cross-section with the internal dimensions of 20 mm X 30 mm X 200 mm. That is a very compact engine made possible by the choice of fuel, namely hydrogen. Hydrogen-air mixture has cell sizes of about 10 mm at an equivalence ratio of 1. They also allowed for the length to exceed 10X the cell size for DDT. The rectangular design was also due to the fact that the sidewalls were made of quartz glass to allow for optical access for schlieren photography. They used a constant temperature hot platinum wire fuel concentration sensor to measure hydrogen concentrations in the air. They had a unique dual-pre-detonator design, where two small (7.5 cc)pre-detonators, each with its own hydrogen and air solenoid injectors and igniters, fed into the main combustion chamber at about 60 degrees to the horizontal (pointing towards the back end wall). Hydrogen is also injected along the side walls. Air is injected at the back end of the combustor. It is not clear at what frequency or for how long the tests were conducted. Detonation was obtained within 180 mm without Shchelkin spirals. Detonation wave velocities of 2000 m/s, greater than the Chapman-Jouguet velocity of 1960 m/s, were measured at locations within the combustor. No thrust measurements were made available either. The fuel fill-time for such a small engine was found to be about 7 ms. The impinging flow injection from the dual pre-detonators also allowed for faster filling and thorough mixing of the flows. They did not actually test the PDE with a micro-gas turbine. The team intends to use a small automotive turbocharger for their future work.
The Chinese and Japanese authors often have slight problems expressing themselves in English, often producing amusing commentaries and grammatical mishaps, probably the results of inaccurately using their electronic translators. Take the Japanese authors of the first article above, for instance, who claimed that “we anointed sliding surfaces with silicon oil.” However, the language issues notwithstanding, Chinese and Japanese researchers are top-class and it does seem like they have the means and the will to overtake the detonation engine researchers in the US.