Drone technology with growing aspects
By improving drone’s manufacturing process,
- We can use Brayton Cycles instead of a battery-based drone.
- We can decrease the drone weight and increase the fuel capacity instead.
- We can increase the hovering time by approximately four times more than even a Diesel based drone.
In the first article of the drone article series, we discussed a new criterion called ϑ. The second article was dedicated to the new technologies and technics for increasing the drone’s hovering time.
In this article, I am going to give you an inclusive but simple and clear description of the Brayton Cycle.
As discussed before, our goal is to find new ways of increasing the drones’ power and their flight time. So far, we understood that this goal is directly dependent on increasing the engine efficiency and decreasing its weight.
Therefore, if we would be able to find an engine lighter than electrical motors plus their battery, in addition to having a higher efficiency, then we will find our goal achieved.
So, let’s broaden the horizons of our thoughts by thinking beyond this limited border that implies: “It is the electrical motors that are the sole option for the drones”.
Let’s follow the new ways. In this article, I am willing to suggest the option of “Brayton Cycle”
This system is very small and compact. The Bryton cycle can provide 20 MW electrical energy in a room as small as 4 m3. Being so small makes the “Brayton Cycle” ideal for specific uses.
The efficiency of this cycle is completely dependent on inlet and outlet gas temperatures:
As illustrated in the diagram, if we increase the density ratio to 25, we would achieve an efficiency of 60%. However, in the lower density ratios, even in the density ratio of 7.5%, we would face an efficiency of 50%, which is a very good rate of efficiency.
Meanwhile, this cycle is not involved with a Crankshaft, Piston or the Connecting Rod and thus it is so light. Furthermore, there is no need to change the reciprocating movement to a rotary motion.
Another interesting characteristic is that the turbine can easily be connected to the propeller. By installation of a heat exchanger, the efficiency of the system will increase remarkably.
The Brayton Cycle is one of the most effective cycles of thermodynamics and among the simplest ones.
This cycle works based on the combustion of a gas type (presumably, natural gas) and is designed in accordance with the passage of the produced gases through the spokes/blades of a turbine. In this cycle, we are only dealing with two parts: Turbine and Compressor.
You can have a better picture of the Brayton Cycle illustrated in the figure below.
The compressor has a simple mechanism, i.e. a number of blades (sometimes 8 layers), which are turning co-axially with the central shaft. Each layer compresses the air slightly and passes it to the next blade. Eventually, this compressed air will mix with the natural gas in the combustion chamber and ignites. This combustion causes the amount of gas to burst out and to turn the turbine in its way, and this is the work done.
This simple mechanism, regarding the few number of elements, saves lots of space for the Brayton Cycle and provides a very small and light set for it. Therefore, it is ideal to be used for drones.
The increase of efficiency in this cycle is due to an elimination of piston for converting the reciprocating movement to the rotary motion (such as Diesel Cycle or Otto Cycle for gas engines). In some cases, the efficiency is 45% and 50% for this natural cycle and this is completely due to the method of designing the compressor. As mentioned before, installation of a heat exchanger can increase the efficiency even more.
Previously, I have compared the Diesel Cycle with the battery and electrical engines with regard to the hovering time. However, now if we compare using the Brayton Cycle with the Diesel Cycle, we will understand that this cycle is at least four times more effective. The reason is that in addition to the decrease of the weight of the engine (approximately half) the efficiency increases as well (approximately twice). Therefore, we can achieve more power and a longer hovering time.