A scramjet test was conducted in Australia by University of Queensland. It seems the test was successful even though they are still analyzing the data collected from the test flight. So before we go in details of the launch news lets get to know what a scramjet is? I am sure everybody is wondering or asking himself/herself this question “What the hell is this Scramjet, I only know a Jet?”. In simple terms Scramjet is a jet engine in which the air and fuel mixture is burnt in supersonic speed, and this type of combustion is very difficult to attain in the engine. And India is one of the very few countries in the world which has successfully demonstrated that this type of combustion is possible. It was demonstrated by none other than our ISRO.
What is a Scramjet???
A scramjet (supersonic combustion ramjet) is a variation of a ramjet where the flow of the air and combustion of the fuel air mixture through the engine is done at supersonic speeds. This allows the scramjet to achieve greater speeds than a conventional ramjet which slows the incoming air to subsonic speeds before entering the combustion chamber. Projections for the top speed of a scramjet engine (without additional oxidiser input) vary between Mach 12 and Mach 24 (orbital velocity). By way of contrast, the fastest conventional air-breathing, manned vehicles, such as the U.S. Air Force SR-71, achieve slightly more than Mach 3.2.
Like a ramjet, a scramjet essentially consists of a constricted tube through which inlet air is compressed by the high speed of the vehicle, fuel is combusted, and then the exhaust jet leaves at higher speed than the inlet air. Also like a ramjet, there are few or no moving parts. In particular there is no high speed turbine as in a turbofan or turbojet engine that can be a major point of failure.
A scramjet requires supersonic airflow through the engine, thus, similar to a ramjet, scramjets have a minimum functional speed. This speed is uncertain due to the low number of working scramjets, relative youth of the field, and the largely classified nature of research using complete scramjet engines. However it is likely to be at least Mach 5 for a pure scramjet, with higher Mach numbers 7-9 more likely. Thus scramjets require acceleration to hypersonic speed via other means. A hybrid ramjet/scramjet would have a lower minimum functional Mach number, and some sources indicate the NASA X-43A research vehicle is a hybrid design. Recent tests of prototypes have used a booster rocket to obtain the necessary velocity. Air breathing engines should have significantly better specific impulse while within the atmosphere than rocket engines. However scramjets have weight and complexity issues that must be considered.
Principle of the Scramjet
Click on the image to enlarge it.
Working of a Scramjet
A scramjet is a type of engine which is designed to operate at the high speeds normally associated with rocket propulsion. It differs from a classic rocket by using air collected from the atmosphere to burn its fuel, as opposed to an oxidizer carried with the vehicle. Normal jet engines and ramjet engines also use air collected from the atmosphere in this way. The problem is that collecting air from the atmosphere causes drag, which increases quickly as the speed increases. Also, at high speed, the air collected becomes so hot that the fuel doesn’t burn properly any more.
The scramjet is a proposed solution to both of these problems, by modifications of the ramjet design. The main change is that the blockage inside the engine is reduced, so that the air isn’t slowed down as much. This means that the air is cooler, so that the fuel can burn properly. Unfortunately the higher speed of the air means that the fuel has to mix and burn in a very short time, which is difficult to achieve.
To keep the combustion of the fuel going at the same rate, the pressure and temperature in the engine need to be kept constant. Unfortunately, the blockages which were removed from the ramjet were useful to control the air in the engine, and so the scramjet is forced to fly at a particular speed for each altitude. This is called a “constant dynamic pressure path” because the wind that the scramjet feels in its face is constant, making the scramjet fly faster at higher altitude and slower at lower altitude.
The inside of a very simple scramjet would look like two kitchen funnels attached by their small ends. The first funnel is the intake, and the air is pushed through, becoming compressed and hot. In the small section, where the two funnels join, fuel is added, and the combustion makes the gas become even hotter and more compressed. Finally, the second funnel is a nozzle, like the nozzle of a rocket, and thrust is produced.
Note that most modern scramjet designs are “waveriders”, which means that the intake and nozzle of the engine are asymmetric, and formed by the lower side of the aircraft.
I hope all of this explains the working of the scramjet.
Now read the news clip about the scramjet launch which was conducted at University of Queensland.
A$2 million scramjet experiment was launched at Woomera, 500km north of Adelaide, South Australia at approximately 1.45pm local time.
he University of Queensland-led HyShot™ III experiment uses a scramjet engine developed by UK company, QinetiQ.
The scramjet was attached to a Terrier-Orion rocket combination and aimed to fly at an estimated Mach 8 (or about 8000km/hr).
The rocket and the precious payload were taken to an altitude of 314km during a 10-minute flight.
They were then re-oriented to point backwards to the Earth. The experiment was set to take place in a tiny six-second window of opportunity shortly before impact.
An international team of researchers, led by The University of Queensland, is analysing data from the experiment.
HyShot™ program leader Professor Allan Paull said the liftoff was perfect and the rocket motors worked fine but it was too soon to tell if the launch had been a success.
“It looks good. We got data all the way,” he said.
Professor Paull said scramjet powered passenger jets were still a long way off but it might be possible to have a scramjet powered vehicle within the next 10 years or so for applications such as carrying vital organs for urgently needed medical transplant operations.
HyShot™ team member Associate Professor Michael Smart said the flight followed the nominal trajectory and has now landed 400km down range.
“We know the area where it is,” he said.
Dr Smart said it appeared from radar tracking of the experiment that everything was going to plan.
He had not appreciated he would feel so emotional at the takeoff.
“I almost had tears running down my cheeks.”
QinetiQ researcher Rachel Owen said it was “very exciting” and she was very proud to see the scramjet fly.
Professor Paull said the team may be in a better position to make a statement about the experiment later today.
Source: University of Queensland
The photographs of the launch can be viewed here.
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