Introduction
Gas turbines are highly popular and widely applied in numerous fields owing to their improved design and operational attributes. They are application widespread in civil, marine and aeronautical fields. Gas turbines can be implemented in tow different categories of applications based on the function of the thrust produced. The torque generated by the engine can be utilized in generating shaft power, or it can be applied to produce thrust from an exhaust nozzle (Boyce, 2011). Gas turbine engines exhibit a relatively high power to weight ratio. Consequently, the engine is highly appropriate for generating motive power for transport vehicles. Also, the amount of emission from this type of engines is free from pollution.
Gas turbine engine presents itself as an efficient and effective means of producing a flexible kind of shaft power given that it is self-contained. It has undergone a series of changes to a completely functioning gas turbine engine. It outstanding performance attributes have led to its widespread applications in numerous fields; airborne and on ground applications as well (Kobayashi et al., 2015). The use of gas turbine engine in different areas presents numerous benefits owing to the design and performance characteristics demonstrated by the engine. The widespread application of gas turbine engine has been propagated by various attributes such as; it’s little specific weight as well as bulk, the engine has high reliability with few components, few vibrations, relatively low oil consumption rate, it accepts different types of fuels, exhibit an easy cold starting and it produces relatively low exhaust smoke.
Similar to any other technology and mechanisms, gas turbine engine exhibit certain shortcomings. Some of the most adverse disadvantages demonstrated by the gas turbine engine include; relatively higher specific fuel consumption, it is highly sensitive to alterations in air pressure, and a small part load performance (Timko, 2010). Nevertheless, it is worth noting that the specific fuel consumption comparatively small in improved gas turbine engines that demonstrate high compression (Schilling, 2010). Consequently, the benefits and the pitfalls illustrated by the gas turbine engine makes it suitable for application as the main driving force in light airplanes, in helicopters and as a constituent of a compound unit.
Objectives
The objectives of the experiment are as follows; to understand the design and operation characteristics of a gas turbine engine, to establish the component efficiencies of the gas turbine engine, and to develop the overall thermal efficiency of the gas turbine engine.
Theory
The operation and function of a gas turbine engine employ the use of Joule cycle. The limitation in efficiency exhibited by the gas turbine engines is a result of stress and temperature limitation of the material used to construct the engine. Temperature and the stress of the materials used in building the engine directly affect the efficiency of the machine.
Figure 1: Temperature and entropy curve showing the relationship between temperature and entropy (Joule cycle)
Temperature and entropy of the gas turbine engine assume the Brayton cycle as demonstrated in the diagram. The function and operation of the engine gas turbine employ the use of Joule cycle. It is significant to have knowledge of both temperature and pressure values at each point in the curve so as to be able to effectively analyze the cycle. The isentropic compression is represented by point 2 (Mollenhauer & Tschöke, 2010). This type of compression occurs between points 1 and three as indicated in the curve. On the other hand, isentropic expansion is demonstrated by the engine at point 6 as shown in the diagram. The region between the 5th and the 7th points indicate the region when the gas turbine engine exhibit isentropic expansion. The mass air flow is attained from the measurements of the intake air like air meter depression, atmospheric pressure, and inlet temperature T1.
The gas turbine engine isentropic efficiency is given the following equation;
лT= (T3-T4)/ (T3-T4’)
Alternatively, the compressor isentropic efficiency is obtained by;
лT= (T2’-T1)/ (T2-T1)
And the combustion efficiency is attained by;
лcomb= (T3-T2)/ (Tideal-T2)
The thermal efficiency is achieved by;
лthermal= W shaft/ (mfuelXLVC)
Equipment and Procedure
A sample set of results were utilized for this experiment since the laboratory gas turbine engine could no longer be activated live. The results made available on the Log Sheet were utilized in analyzing the attributes of the gas turbine engine. A Heenan Fraoude water dynamometer type DPX/2 was employed for the Rover IS/60 gas turbine test rig. It was applied so as to establish the torque and the speed gave that it is approximately the same as the one applied to the engine diesel rig in the laboratory. The operating parameters were evaluated using a fully instrumented test console.
Results
Where;
T1 Inlet air temperature
T2 Compressor exit air temperature
T4 Exhaust gas temperature
Δt Time to consume 2 liters of fuel (paraffin)
p2 Compressor exit pressure
ΔpF Airmeter depression
Δp41 Exhaust exit pressure - atmospheric pressure
F Brake load
Δp23 Combustor pressure drop (p2 -p3)
N Shaft speed
ptip Compressor impeller tip pressure
Density of paraffin: 0.85
Density of mercury: 13.6
LCV of paraffin: 42,000kJ/kg
Presentation
Calculations and student center activities
Thermal efficiency = W shaft/ (mfuelX LVC)
W shaft= FXN/ 26850 KW
Gas turbine isentropic efficiency
N= {actual work done/isentropic work done}
T2= T1{P2/P1} ^[(y-1)eff/y]
185=13.5{160/80}^[(1.4-1)eff/1.4]
185=27^[(1.4-1)eff/1.4]
185=27^[(0.4)eff/1.4]
Eff=0.87
Isentropic expansion efficiency
N= (ideal work done/actual work done)
T1= T2{P1/ P2} ^[(y-1)eff/y]
13.5=185{80/160}^[(1.4-1)eff/1.4]
13.5=185{0.2}^[(0.4)eff/1.4]
Eff=0.34
Isentropic pump efficiency
Discussion
The results obtained from the experiment indicate that it is increasingly a daunting task to obtain air compression without losses. There are several reasons as to why obtaining a lossless air compression is difficult. A substantial amount of energy is lost during the gas turbine engine operation. The application of the small single stage centrifugal compressor leads to energy losses in different ways. The air expansion inside the engine demonstrates a natural process (Timko, 2010). As a result, attaining a turbine expansion is not as daunting as witnessed in compression. The natural processes assumed by the expansion cycle ensures that the engine exhibit high expansion efficiencies as well as minimized losses. However, higher temperature operating gas exhibits improved energy quality thus generates additional mechanical work in a more effective way. It is worth noting that the thermal efficiency is directly affected by the turbine entry temperature.
References
Boyce, M. P., 2011. Gas turbine engineering handbook. Elsevier.
Kobayashi, S. and Harada, T., Toyota Jidosha Kabushiki Kaisha, 2015. Internal Combustion Engine. U.S. Patent 20,150,252,749.
Mollenhauer, K., & Tschöke, 2010. Handbook of diesel engines. Springer Science & Business Media.
Schilling, J. C., 2010. U.S. Patent No. 7,694,505. Washington, DC: U.S. Patent and Trademark Office.
Timko, M. T., Herndon, S. C., Wood, E. C., Onasch, T. B., Northway, M. J., Jayne, J. T., & Knighton, W. B., 2010. Gas turbine engine emissions—part I: volatile organic compounds and nitrogen oxides. Journal of Engineering for Gas Turbines and Power, 132(6), 061504.
