gp3 teamwork meeting minute3 28feb

Meeting Minute 3 Group 3

Minute prepared by Raphael Rubiano Vasco 1

28/February/2014

Universidad Europea de Madrid

Meeting Duration: 1h 45minutes

Work done, description:

Gathering of the research on new fuels for aircraft engines applications and particular applications of new fuel

Fuel cells applications for aircraft engine

Exergy analysis of a turbofan and turbojet

Task Answer questions. Set next meeting date: 7th February.

Work to do in next meeting:

Put in common all the information gathered by each member of the team.

Share and summarize information gathered by each member.

Assess information quality and relevance to the project objectives.

Set new meeting dates and meeting date prior to the project uploading deadline.

Attendants: Raphael Rubiano Vasco

Pedro Perez Peinado

Bosco Campomanes Varela

Carlos Sanso Ajo



Contents Diesel engines on aircraft. ................................................................................................................... 3

Advantages and disadvantages ....................................................................................................... 3

Algae Fuel ............................................................................................................................................ 3

How Is The Oil Produced From Algae? ............................................................................................ 4

Most Important Benefits of Using Algae ......................................................................................... 4

Disadvantages of Algae-Fuel ........................................................................................................... 4

Fuel Cells ............................................................................................................................................. 4

Applications ..................................................................................................................................... 5

Exergy Analysis .................................................................................................................................... 5

Exergy Analysis of a Turbofan Engine: Cf6-80 ................................................................................. 6

Brayton cycle ............................................................................................................................... 6

Assumptions made ...................................................................................................................... 7

Exergy Analysis ............................................................................................................................ 8

Results and Discussion ................................................................................................................ 8

Exergetic Analysis of an Aircraft Turbojet Engine with an Afterburner .......................................... 9

Cycle .......................................................................................................................................... 10

Results and discussion ............................................................................................................... 11

Conclusions for the exergetic analysis .............................................................................................. 11

Conclusions of the exergetic analysis for a turbojet ..................................................................... 11

Conclusions of the exergetic analysis for a turbofan .................................................................... 12



Diesel engines on aircraft.

These engines are starting to be used more often in small aircraft such as Cessna’s and other 2 to 4 passengers’ aircrafts. Most of these engines are bought directly from car manufacturers such as Mercedes’ 1.7liter diesel engine from the a-class. Therefor diesel engines are 2 or 4-stroke piston engines, which means that they can only be used in small aircraft due to size affaires. If the Airbus A-380 were to have a diesel engine, it would rather not fit anywhere.

On the other hand, any kind of turbine would provide a small Cessna with an unnecessary amount of power. For this reason, the target for diesel engines on aircraft is to take over the small aircraft market and making used of new or improved fuels.

Advantages and disadvantages

Advantages Disadvantages

Cheaper than aviation fuel

Lubricates

Ignition by compression

Higher ignition point

Safe storage

More robust engines

Longer mileage

Efficient liquid cooling

Can also use jet-A

Weight penalty

Failures at high alt. & low temp.

More emissions

Algae Fuel

Algae or more correctly microalgae, are very small aquatic organisms that converts sunlight into energy and that under the right conditions could be converted into biofuel. Algae could produce up to 60 times more oil per acre than oil-based plants.



Extract that oil and you have the energy to run trucks, cars and planes. In the future, everything that uses gasoline or diesel could be replaced by algae without excessive modifications on the current propulsion systems.

How Is The Oil Produced From Algae?

The oil is produced by breaking down the cell structure of the algae. This can be done using solvents and sound waves. After the oil is extracted then is further processed at an integrated biorefinery, or in the future in a normal refinery.

Most Important Benefits of Using Algae

Like plants, algae needs carbon dioxide, it takes the CO2 out of the atmosphere, making it a nearly carbon-neutral fuel source and environmental friendly.

There might be even opportunities to build algae farms, next to power plants that use fossil fuels, actually using CO2 exhaust to feed algae ponds. So, the creation of CO2 will ‘only’ remain in the fossil plants, because the fuels used from algae can absorb that big amount of CO2 produced by the power plants, then when algae will be burned it will create CO2 but in this case only the one created by the big power plants, because previously it would have been absorbed during the creation of algae.

Disadvantages of Algae-Fuel

There are over 100.00 different strains of algae. Some grow better in different climates, or in fresh water, salt water or even waste water. Scientist are testing algae in many different conditions to find the best strains and develop the most efficient farming practices.

Another disadvantage is that commercial production is still a ways off, because there is not sufficient advances yet in technology that permits to find the best strains. Anyway algae holds a great promise to become a reliable homegrown fuel source.

Fuel Cells

All transport industries are very interested in the fuel cells not only aerospace industry. Using Oxygen and Hydrogen from the air, a fuel cell produces water so non harmful emissions for the



environment and the most important fact is that it produces mainly electricity. The ideal goal will be to achieve a very light aircraft and able to fly entirely long-distance with fuel cells.

Applications

Nowadays, there isn’t the necessary technology to get flying an aircraft only with fuel cells, since firstly it would be needed large tanks to store the hydrogen, and secondly as a consequence the aircraft configuration will have to adapt to carry out this tanks and have enough space for passengers.

So taking in account these facts the use of fuel cell are currently focused on its using in other applications.

Example:

An airbus A-320 was tested with the fuel cells to see if it will works properly or if it won’t work well in aircraft. It was used to run the hydraulic systems of the aircraft. The test worked extremely well, fuel cells operated perfectly in normal and also in extreme conditions.

So after the success of the experiment, the aviation is looking forward for the next step, and think about which other applications could achieve the fuel cells.

One of the most important applications is that it could be substitute of the APU (Auxiliary Power Unit) which runs with kerosene generating noise and emission while operating on ground. By replacing this system with fuel cells, better performance would be achieve, such as reduction of noise and a supply of energy to the aircraft (lighting, air conditioning, etc.).It would also produce water, as product of the reaction, which could be used to fill the water tanks of the aircraft. Another relevant application is the used of the inactive gases that it produces as fire protection system.

So it would make the ground operations simpler, faster and cleaner, with no need of ground generators or other external ground units.

Exergy Analysis

Exergy analysis is a powerful method, which has been widely used as a tool in the design, operation and performance assessment of energy systems by many engineers and researchers.

The aviation industry is responsible for the 2.5-5% of the total world energy consumption itself, indicating a very useful study area for the exergetic assessments and considering the environmental aspects, using energy in the most efficiency ways will have positive effects over the ecological balance and the all kinds of pollutions.



For a certain amount of output, now there will be possible to need fuel with a less quantity. Therefore, this will mean less waste and longer energy source lives

In this document, both an exergy analysis for a turbofan engine and for a turbojet are going to be developed. According to the results, it is concluded that the most irreversible unit in the system is the combustion chamber as mentioned in practice 2.

So, Exergy analysis is a practical and useful tool for such activities, with many engineers and scientists suggesting that exergy analysis is a highly effective method for evaluating and enhancing thermodynamic performance, and superior to energy analysis.

Exergy Analysis of a Turbofan Engine: Cf6-80

Turbofans, which housed a fan unit at the front of the compressor, have made possible to compress the air flow before the compressor. Thus, it has been increased significantly the propulsion efficiency compare to a typical turbojet engine and also have allowed us to get serious gains in the field of noise, fuel consumption and size of the engines.

The airflow passing through the fan follows two paths:

One (primary flow) to the direction of the compressor, combustion chamber, turbine.

Second (secondary flow) passing through the fan and discharging from the cold nozzle without subject to any burning or turbo machinery processing.

The by-pass ratio, which is the ratio of the secondary flow to the primary flow is the determining factor of the thrust, SFC, and the engine size. The very first turbofan engines had small by-pass ratios, such as 0.3 of Conway engine, at the present it is targeted to a level of 10-11 (Rolls-Royce, 2006). However increasing the by-pass ratio is not unlimited because of the higher by-pass ratio leads to a larger inlet diameter and larger drag.

Brayton cycle

This thermodynamic cycle is the one used on the gas turbine engines, which are mainly used at aircrafts and a very wide range of power plants, which produce electrical energy and steam.

In an aircraft gas turbine engine, there are generally five parts. These include inlet, compressor, combustion chamber, turbine and exhaust, also there could be other parts such as the fan (explained previously) and the afterburner.



The afterburner unit is used to fire the burned gas one more time behind the turbine unit, producing additional thrust, which can be required for a short take off, exceeding the sonic speed barrier and gaining maneuverability superior.

Assumptions made

The following assumptions are made

1. The flows in the engine are ideal gas.

2. The air composition at the inlet of the engine is 77.48% nitrogen, 20.59% oxygen, 0.03%

carbon dioxide and 1.9% water vapor as used in the Ref. (Bejan et al, 1996).

3. For obtaining a healthy vaporization, the fuel must be sprayed at a high pressure. The fuel

temperature and pressure values are 288 K and 60.166 bar at sea level, respectively.

4. Fan, compressor and turbine are considered to be adiabatic.

5. Using the real data, the isentropic efficiencies of the fan, compressor and the HP-LP

turbines are calculated to be 0.88, 0.93, 0.81 and 0.81, respectively.

6. Pumps (fuel, oil and hydraulic) and heat exchangers (fuel/air or fuel/oil) are not included

in the analysis.



7. The change in the chemical exergy of the fuel versus altitude is assumed that the chemical

exergy of the fuel at the sea level decreases to a rate of 0.6% at the 15000 m altitude

(Etele et al., 2001).

8. The ambient air temperature and pressure are taken as 306.5 K and 1 bar, respectively.

9. The engine data are taken from Ref. (General Electric, 1983)

Exergy Analysis

In this analysis, both the physical and chemical exergies are used. The potential exergy are

negligible as well as the kinetic exergy, so both are neglected. Considering the aircraft speed at the

opposite direction, the net airflow speed will be small compare with the exergy values, which are

bigger at the inlet and outlet of the combustion chamber-

In addition to the exergetic efficiency of a unit, there are some other thermodynamic parameters,

which are useful for the evaluation of the system such as:

1. Exergy destruction rate

2. Relative exergy destruction

3. Fuel depletion ratio

4. Productivity lack

5. Exergetic factor

6. Rate of exergetic improvement potential

For a detailed study of these parameters, one can refer to Refs. (Van Gool, 1997; Xiang et al.,

2004). The exergy efficiencies of the major parts are calculated as the ratio of the product to the

fuel

Results and Discussion

Based on the results of exergy analysis, the most exergy destructive units are found, while the

exergetic efficiency, relative exergy destruction, fuel depletion ratio, productivity lack and

exergetic factor of every units are calculated.

According to the results, the most exergy destructive unit is found as combustion chamber with

35.76 MW. The exergy destructions of the other units are calculated to be 3.61 MW for fan, 3.07

MW for HP turbine and 2.84 for compressor.



It has been seen that the efficiencies of all units increase with increasing isentropic efficiencies,

however the variations of the exergy destructions are likely to the exergy efficiencies, but

decrease by increasing the isentropic efficiencies.

The exergy destruction of the fan is so high and the reason for this can be explained by the

necessity of high power for operation of this relatively heavy engine part. But despite to this high

destruction ratio, since 75-80% of thrust is obtained by the fan and with the other advantage, it is

an indispensable engine part.

The combustion chamber has the largest fuel depletion ratio with 9.72%, while the other units are

smaller than 1%

Considering the exergy destruction parameter, it is notable that 78% of the total exergy

destruction of the engine has occurred in the combustion chamber, followed by the fan with 8%,

compressor with 6%, HP turbine with 5% and LP turbine with 3%.

As a result of this analysis it is has been found that the combustion chamber could have the most

research chance to be studied in more detail. However, despite the positive progresses over the

combustion scope (e.g., more efficient combustion chambers, less emission production), it is not

seen possible to exceed some limitations with the present thermodynamic laws accepted.

Exergetic Analysis of an Aircraft Turbojet Engine with an Afterburner

Most of modern aircraft use gas turbine engines to produce the required thrust force, which compare with turbojet engines are relatively light and compact and have a high power to weight ratios.

A J85-GE-21 turbojet engine is going to be used to develop this exergetic analysis, where the main parts are: diffuser, compressor, combustion chamber, turbine, afterburner, and nozzle.



Cycle

The turbojet has an axial compressor with nine stages, each having a 1.2 compression ratio with a total average compression ratio of 9. The combustion chamber 12 fuel injectors which spray liquid fuel at high pressure.

The turbine has two stages and produces the mechanical power needed by the compressor, hydraulic pump, and generator. 20 fuel injectors spray liquid fuel into the afterburner, where it reacts with all the oxygen in the turbine exhaust to produce more power and thrust.

Exhaust gas from turbojet engine is expanded to medium pressure by the nozzle.



Results and discussion

The highest component exergy efficiency is exhibited by the compressor at 96.7%. The next highest exergy efficiencies are for the nozzle (93.7%) and turbine (92.3%). The lowest exergy efficiencies are for the afterburner (54.8%), followed by the combustion chamber (80.4%).

The low fuel efficiency of the afterburner compared to the combustion chamber results in it burning almost three times the fuel of the combustion chamber, in order to increase the thrust force by about one third.

The entropy production rates also help identify the components with the highest irreversibilities. The greatest entropy production rate in the engine is observed for the afterburner, followed by the combustion chamber. Hence, the combustion processes in the aircraft engine are highly irreversible. The nozzle, due to the rapid changes in cross-sectional area has in the third highest entropy production rates.

The exergy efficiencies of the overall engine for all the components decrease as the engine velocity decreases due to the reduction air mass flow rate.

The effect of inlet air temperature on exergy efficiency for the aircraft engine is the reduction of about 0.45% for each centigrade degree increase in inlet air temperature. The cause of this phenomenon is the decrease in air density due to the increase in temperature. This observation suggests that flying in early hours of the day or at night is economic due to the lower ambient temperature.

The exergy analysis of the selected aircraft engine with afterburner operating on kerosene fuel for various altitudes and air speeds reveals useful insights, as does the investigation of the effects of aircraft inlet air temperature on exergy efficiency. The relations are quantified between exergy efficiency and entropy generation for the components of the aircraft engine.

Conclusions for the exergetic analysis

Conclusions of the exergetic analysis for a turbojet

The highest component exergy efficiency is observed at sea level for the compressor (96.7%), followed by the nozzle (93.7%), and turbine (92.3%). Similarly, the highest exergy efficiency at an altitude of 11,000 m is exhibited by the compressor (95.7%), followed by the nozzle (94.8%), and the diffuser (90.5%).

The lowest component exergy efficiency at sea level is observed for the afterburner (54.8%), followed by the combustion chamber (80.4%). Correspondingly, the entropy production rates at sea



level indicate that the most irreversible process is the afterburner, followed by the combustion chamber and nozzle.

Reducing aircraft velocity at sea level reduces the exergy efficiency of the aircraft engine and its components. The aircraft engine exergy efficiency is reduced 0.45% per centigrade degree increase in inlet air temperature.

Conclusions of the exergetic analysis for a turbofan

The main conclusions we could get from this analysis are that compare with the other parts of the engine the exergy destructions in combustion chamber is quite higher. However increasing the isentropic efficiency of fan, compressor and turbine could decrease exergy destruction belongs to these units but increasing the cost.

The combustion chamber is found to be the main irreversible unit in this system with 35.76 MW

among the other units. So that, unless an unconventional combustion process is developed,

probably it will not possible to achieve considerable gains, since it has a high ratio of unavoidable

destruction.

The exergy efficiency values are calculated to be 90.79%, 95.19%, 95.15% and 95.54% for the fan,

compressor, HP turbine and LP turbine, respectively at a reference (dead state) temperature of

306.5 K.

Making and exergoeconomic analysis with the data achieve, it could be possible to decide whether

using more advanced and more expensive turbo machineries cost is offset by the decreasing

exergy destruction.

gp3 teamwork meeting minute3 28feb

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