**8.3.1 Portable power generation**

Regarding this use it can be distinguished military uses and civil applications, even if, these last one, have very limited use possibility.

### **8.3.1.1 Military applications**

The power demand of a soldier during a mission is remarkably increased during the last few years due to the adoption of new technologies. At the same time we have the necessity to limit the most possible equipment weight for the unit. In this case, use an UMGT could help in the reduction of the transported load and, at the same time, satisfy the power demand. Some of these applications are shown in figure 29.

Fig. 29. The "future" soldier

We can distinguish three various regimes for the military applications:

20W, with peaks of 50W, medium power 100W, with peaks of 200W 1000W, with peaks of 5000W 

The first group of device generates the required power for computer, radius and sensors. The second one finds application in the laser beam and the conditioning of the soldiers (uniform ventilation in external extreme climatic conditions); with this powers range the

own average temperature: this produces high infrared radiation emissions, that, especially in military applications, cannot be tolerated. A similar problem is found in the fuel cells in which, a lower value of the operational average temperature is reached. That infrared emissions is not the only problem for the UMGT. The high outlet temperatures of the exhaust gas, can produce problems during the operational life of the machine. To obviate to such disadvantage a regenerator, even built-in would have to be installed inside the device,

Multiple applications can be easy found for UMGT systems. In general terms, these ones can be divided in two groups: applications as portable power generation systems or as range

Regarding this use it can be distinguished military uses and civil applications, even if, these

The power demand of a soldier during a mission is remarkably increased during the last few years due to the adoption of new technologies. At the same time we have the necessity to limit the most possible equipment weight for the unit. In this case, use an UMGT could help in the reduction of the transported load and, at the same time, satisfy the power

20W, with peaks of 50W,

1000W, with peaks of 5000W

medium power 100W, with peaks of 200W

The first group of device generates the required power for computer, radius and sensors. The second one finds application in the laser beam and the conditioning of the soldiers (uniform ventilation in external extreme climatic conditions); with this powers range the

 

extender/prime mover in different vehicles (wheel vehicles, aircraft, ecc).

to cooling the UMGT components using Peltier effect.

**8.3 UMGT potential application** 

**8.3.1 Portable power generation** 

**8.3.1.1 Military applications** 

Fig. 29. The "future" soldier

last one, have very limited use possibility.

demand. Some of these applications are shown in figure 29.

We can distinguish three various regimes for the military applications:

loading of batteries is possible too. At last, 1-5 kW could be used for feeding of exoskeleton : these are robotic devices that allow to reduce the payload that weighs on the soldier.

### **8.3.1.2 Civil applications**

The UMGT civil applications, as portable power generators, undoubtedly are limited, due to the high system temperature. In fact, in this case the exhaust gas temperature is very high, and the customer safety is a primary objective in the design of the device and its utilization. However, some civil applications can be considered, as battery recharger for mobiles or for wireless tools. Also as micro cogeneration unit at small scale.

### **8.3.2 MAV**

The main application in this field resides in the so-called the MAV (micro aerial vehicles). Their main use is, once again, of military character. The power demanded by the group is lower because the considered vehicle mass is lower than 50 g with cruise speed between the 10 and 20 m/s: in the cruise regime the shaft demanded power is about 2.5 kW, while this doubles during the phase of takeoff and manoeuvres. Due to the high heat exchange during the flight and the low required power, there are not problems regarding the infrared emissions. Such systems have already been used in the Balkans, Afghanistan and Iraq during missions of strategic character.

### **8.3.3 Drones and UAV**

An unmanned aerial vehicle (UAV) is a machine which functions either by the remote control of a navigator or pilot or autonomously, that is, as a self-directing entity. Their largest use is within military applications. To distinguish UAVs from missiles, a UAV is defined as a powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or non lethal payload". UAVs typically divided in six functional categories (although multi-role airframe platforms are becoming more prevalent):


They can also be categorized in terms of range/altitude and the following has been advanced as relevant at such industry events as Unmanned Systems forum:


Ultra Micro Gas Turbines 47

It is a "standard" Brayton cycle, usually adopted in large scale turbogas. With the exception of the industrial cycles, for constructive reasons, the compression ratio is extremely low in this UMGT (p2/p1 ≈ 2), and therefore the total efficiency of the machine is corresponding low (7-8%). Increase of the compression ratio, recovery of the heat of the gas are possible modifications under investigation, to increase such efficiency: but such upgrading appear

The fuel used, suggested, chosen for all prototype is a liquid hydrocarbon (pentane-butane or similar). The kerosene use or other jet-fuel appears perfectly compatible. For the operational prototype, the possibility is being studied to use methane or hydrogen, but this

The analysis of existing prototypes indicates as the main design problems that can be

1. combustion chamber: low residence times (flammability threshold); mixing device;

6. thermo-fluid dynamic analysis: reliability of the design procedures, based on experiences achieved exclusively on large scale devices. The first simulations have

They are generally correlated to the availability of opportune high resistance materials (high thermo mechanical stresses) as well as the combustion chamber, turbine, regenerator, ecc. And to the productive technologies. While such problems will not have great influence on the realization of the prototypes, an engineering study to pass "to the productive" part (post-prototypal phase) will be necessary. Finally, the economic impact of these devices will be dependent on the performance levels and the manufacturing costs, both of which have yet to be proven. It is certainly possible, however, that UMGTs may, one day, be competitive with conventional machines in a cost per installed kilowatt. Even at much higher costs, they will be very useful as compact power sources for portable electronics, equipment, and small

[1] A.H. Epstein, S.A. Jacobson, J.M. Protz, L.G. Frechette, *"Shirtbutton-sized gas turbines: the* 

*engineering challenges of micro high speed rotative machinery"*; Proc. 8th Int. Symposium. on Transport Phenomena and Dynamics of Rotating Machinery

3. rotors: radial and bending/torsion instability, resistance to the high temperatures;

evidenced the necessity to adopt scale factors in the turbomachines design.

4. electric generators: practical feasibility and reliability, efficiency problems;

last one generates problems of tank design (high pressure, low power density).

2. bearings: reliability, duration (to the highest rotational speed);

**a. The thermodynamic cycle** 

**b. The fuel choice** 

**c. Design problems** 

vehicles.

**11. References** 

difficult to implement on an UMGT device.

previewed to this point are the following ones:

resistance to the high temperatures;

5. controls devices: stability, reliability;

**d. Technological and manufacturing problems** 

(ISROMAC-8), Honolulu HI, March 2000.


### **8.3.4 Range extender in hybrid vehicle**

In the last decade, governmental incentives and the ever stricter emissions regulations have prompted some of the largest world automakers to dedicate resources to the study, design, development and production of hybrid vehicles, which offer undisputed advantages in terms of emissions and fuel consumption with respect to traditional, reciprocating internal combustion engines. In fact, hybrid engines are substantially smaller than conventional ICE, because they are designed to cover the vehicle's "average" power demand, which ensures proper traction for about 99% of the actual driving time, and is exceeded only for prolonged mountain drives and instantaneous accelerations. When excess power is needed above this average, the hybrid vehicle relies on the energy stored in its battery pack. Hybrid cars are often equipped with braking energy recovery systems that collect the kinetic energy lost in braking, which would be dissipated into heat otherwise, and use it to recharge the battery. Smaller sizes and an (almost) constant operational curve lead to lower emissions. Moreover, a hybrid vehicle can shut down completely its gasoline engine and run off its electric motor and battery only, at least for a limited operational range: this "mixed operation" increases the net mileage and releases a substantially lower amount of pollutants over the vehicle lifetime. The most popular hybrid vehicles (HV) are mostly passenger hybrid cars equipped with a traditional ICE and an electric motor coupled in parallel. The thermal engine is sized, with some exceptions, for the average power, and the surplus power needed during rapid acceleration phases is supplied by the electric motor.
