an investigation on the smoke pollution issued by the turbofan … · an investigation on the smoke...

ECOTERRA - Journal of Environmental Research and Protection

www.ecoterra-online.ro 2016, Volume 13, Issue 4

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An investigation on the smoke pollution issued by the turbofan engines Sebastian M. Zaharia Faculty of Technological Engineering and Industrial Management, Transilvania University

of Brasov, Brasov, Romania. Corresponding author: S. M. Zaharia, [email protected]

Abstract. Aggressiveness on the environment is no longer a problem to be left to nature. Manufacturing propulsion systems that are quieter and have lower levels of pollutant emissions is the main direction to which aviation engine manufacturers are heading. The need to solve chemical pollution of aircraft has become a serious problem in recent years, along with the increase of air pollution with pollutants, especially in large urban areas. In this paper it was carried out a statistical analysis of the data simulated by Monte Carlo method regarding the smoke emissions of an aircraft’s turbofan engine. In the case study were simulated values of smoke number for a turbofan engine at take-off and landing regime. Key Words: chemical pollution, turbofan engine, smoke number, pollutant emissions.

Introduction. Turbofan engine is built on the principle of a fan followed by a main engine (which includes a gas turbine), being surrounded by an area of air circulation, air introduced by the main fan. A part of the airflow sucked by the fan passes through the main engine where is burned to power the fan (Hunecke 1997). Most of the airflow passes around the main engine and produce the most part of thrust (80%). The fan and the fan’s turbine are composed of many blades and are connected via an additional shaft (Figure 1). At the double flow turbojet with separate stream flows, the total flow rate of air entering the intake is divided into the primary flow that passes through the compressor, combustion chamber and turbine, and the exhaust gas is discharged to the outside. Secondary air flow passes through the fan and then is routed out through its own reaction nozzle (Cumpsty 2015).

Figure 1. Turbofan engine components (olympus-ims).

The progress from the aerospace industry led among others, to the modernization of the aircrafts, which are sources of production of harmful substances that raises acute environmental problems and concern, but also obliges aviation authorities to find fast and effective solutions to limit the negative effects. With increase in the air traffic, elements that disturb the human and the environment are also signalled, namely chemical and sound pollution (Zaharia 2015). In order to reduce pollution, there are currently concerns and aeronautical regulations that are designed to make air travel much less harmful. In connection with the chemical pollution phenomenon, the Romanian scientist Henri



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Coandă said: "You have to make the human as conscious as possible of the responsibility it has towards the environment. To develop noxious industries without severe environmental measures and to irrationally cut forests that are naturally and constantly refreshing the breathable atmosphere, is equivalent to a suicide" (Ispas 1980).

Major advances have been made in order to reduce harmful products at idle, through systematic use of combustion chambers in which the reduction of visible smoke is made using improved injection techniques, providing a partial premix. Advanced methods of levelled injection and variable geometry reduced emissions, but their application requires costly processes. Chemical pollution produced by propulsion systems used in aviation is generated particularly by burning fuel in the combustion chamber. To fight pollution the following measures are pursued: the manufacturing process of the fuel used for the propulsion systems; developing innovative technologies for the manufacture of the combustion chambers; as efficient and as detailed knowledge of the combustion process as possible. The chemical phenomena that occur in the combustion process and the aerodynamic phenomena occurring on the aircraft add up and determine the evolution of the chemical combustion (Ispas 1980).

The pollutants of propulsion systems can be classified into four categories (Lieuwen & Yang 2013):

- SOx emissions at the engine exhaust primarily occur in the form of gaseous SO2, but a small portion of the fuel sulfur is typically emitted as a range of heavier sulfur species classified as volatile particulate matter;

- NOx emissions are primarily comprised of NO and NO2. At idle conditions, NOx emissions are about half NO and half NO2, while at high power, roughly 90 percent of NOx

is in the form of NO; - unburned hydrocarbons contain many hydrocarbons ranging from large fuel

molecules to very light hydrocarbons, and include several species classified as hazardous air pollutants (HAPs) because they are toxic or carcinogenic;

- particulate matter includes both nonvolatile soot (small carbonaceous particles that make up visible smoke) and volatile hydrocarbons and sulfur oxides that condense as the engine exhaust plume cools through mixing with the ambient air. The analysis of pollution caused by smoke emissions produced by aircraft propulsion systems. It is known that aircraft propulsion systems emit fumes that can be observed and affect the environment (Figure 2).

Figure 2. Pollution by smoke emitted by the airplane engine (Conserve Energy Future 2016).

During emission certification tests, an engine is tested at thrust levels of the four phases of flight specified by LTO cycle: Take-off Climb, Approach, Taxi (Figure 3). The flow of fuel and emissions of CO, HC, NOx and smoke are measured at each level of thrust, using



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sampling, gas analysis and measurement methods of smoke number specified by ICAO in Annex 16, Volume II. Smoke is measured by passing a standard volume of engine exhaust through white filter paper. The resulting smoke level, expressed as smoke number, is based on the change in reflectance of the filter paper (Lieuwen & Yang 2013).

Figure 3. LTO cycle of an aircraft (EASA 2016).

Smoke Number (SN) is determined in accordance with SAE/ARP 1179c, which is the standard test for evaluation of smoke based on the colouring of a filter paper - Whatman # 4 with a sample size of 0.0230 lbm/in2 of the exhaust gas in the filtering area. The smoke number is reported on a scale of 0 to 10, as shown in Figure 4. The measuring method has an accuracy of +/- 3. This diagnostic provide only empirical information on the soot particles. Therefore, the researchers conducted a series of studies to report data regarding the smoke number of quantitative soot emissions produced by a propulsion system (Lieuwen & Yang 2013).

Figure 4. Method of measurement for the smoke number (Lieuwen & Yang 2013).

Regulations on smoke emitted by propulsion systems. Dp/Foo or average value SN is the average characteristic level of a pollutant gas or smoke for a certain type of engine. At the stage of certification for an engine, the manufacturer will select a number of engines that are tested. For other engines in the same series, the results are extrapolated and the principle applied will be that the engines should not exceed the level of pollution required by aviation regulations. For the exhaust of an engine, the levels measured at each level of thrust are expressed in grams of CO, HC and NOx (as NO2) per kilogram of fuel. For each engine, the mass of emissions generated during each phase of flight is calculated as (Lefebvre & Ballal 2013):

Emission (g/KN) = Time in mode (hr) × Fuel flow (kg fuel/hr KN) × Emission index (g/kg fuel)



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European Aviation Safety Agency (EASA) hosts a Databank on behalf of ICAO on exhaust gases emissions of engines that have gone into production. The information was provided by engine manufacturers who are solely responsible for its accuracy. EASA also sets out the basic terms that are used by engine manufacturers to determine smoke emissions (Figure 5).

Figure 5. The specific terms of smoke emissions (EASA 2016).

For the type or model engines having production date was after 1 January 2014 gas emission levels are indicated by ICAO (Annex 16 "International standards and recommended practices, Environmental protection" with Amendment 3, 20 March 1997) and should not exceed the regulatory levels determined by the following relationships (Table 1):

Table 1

SN relations for engines produced after 2014 (EASA 2016)

Types of engine Relation For engines with a pressure ratio of 30 or less. For engines

with a maximum rated thrust of more than 89.0 kN Dp/Foo = 7.88 + 1.4080πoo

For engines with a maximum rated thrust of more than 26.7 kN but not more than 89.0 kN

Dp/Foo = 40.052 + 1.5681πoo - 0.3615Foo - 0.0018 πoo x Foo

For engines with a pressure ratio of more than 30 but less than 104.7. For engines with a maximum rated thrust of

more than 89.0 kN

Dp/Foo = -9.88 + 2.0πoo

For engines with a maximum rated thrust of more than 26.7 kN but not more than 89.0 kN

Dp/Foo = 41.9435 + 1.505πoo - 0.5823Foo + 0.005562πoo x Foo

For engines with a pressure ratio of 104.7 or more Dp/Foo = 32 + 1.6πoo The standard provided by ICAO for measuring smoke emissions is expressed in terms of smoke number (SN), which is closely linked to engine’s take-off power (Foo) with the expression (1):

SN = 83.6·(Foo)−0.274 (1) Case study. In this paper were simulated by Monte Carlo method, smoke emission values using the concept of Smoke Number for a turbofan engine on take-off and landing regime.



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The Monte Carlo method is a statistical method, which models the operation process of a system using a probabilistic model that is tested repeatedly. The method involves the generation of pseudo-random values, uniformly distributed over an interval, and their conversion into non-uniform distributed quantities, that have a particular significance in the operation of the turbofan engine. This method of generating smoke emissions values are highly topical and are often used in articles and technical reports of prestigious companies in the manufacture of propulsion systems (Zaharia & Martinescu 2012). For simulated tests it was used a Weibull ++7 and the Generate Monte Carlo data option (Figure 6a for take-off, Figure 6b for landing).

Figure 6. The simulation of the Monte Carlo method parameters: a) simulation of take-off

parameters; b) simulation of landing parameters.

For the SN values simulation through the Monte Carlo method, it was chosen the normal distribution and the ten points which will be determined (Figure 7a for take-off, Figure 7b for landing).



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Figue 7. Simulation Monte Carlo method of SN values: a) SN take-off simulation values;

b) SN landing simulation values

Simulated values of Smoke Number obtained by Monte Carlo method (take-off and landing) for a turbofan engine are described in Table 2.

Table 2 The simulated values of SN for take-off and landing of a turbofan engine

Smoke number take-off Smoke number landing 10.9 2.7 11.7 3 10.1 3.2 11.7 4.1 12.6 5.7 20.6 6.9 11 7

13.9 7.3 16.8 10.7 7.6 12.2



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For statistical data analysis on smoke emissions of a turbofan engine at take-off and landing SPSS Statistics 23 software was used. With SPSS Statistics 23 the following values were obtained as described by the distributions of occurrence frequencies of SN for take-off and landing (Figure 8).

Figure 8. Simulation of SN values using the Monte Carlo method.

In Figure 9 it can be seen that much of SN values are contained in the rectangle described by the 25th percentile and 75th percentile. As it can be seen in the graph there is an abnormal value namely SN at landing (SN = 12.2). In statistical is used a BOXPLOT to determine "mild" and "extreme" outliers. Mild outliers are any score more than 1.5*IQR (inter-quartile range) from the rest of the scores, and are indicated by open dots. Extreme outliers are any score more than 3*IQR from the rest of the scores (SPSS 2016).



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Figure 9. Simularea valorilor SN prin metoda Monte Carlo.

In Table 3 are described the main statistical indicators (mean, median, mode, variance, standard deviation, coefficient of variation, median and quartiles) for values of SN of turbofan engines tested at take-off and landing.

Table 3 The main statistical indicators of SN for take-off and landing

Smoke Number Take off Smoke Number Landing

Valid 10 10 N Missing 0 0

Mean 12.6900 6.2800 Median 11.7000 6.3000 Mode 11.70 2.70

Std. Deviation 3.67528 3.24339 Variance 13.508 10.520 Minimum 7.60 2.70 Maximum 20.60 12.20

25 10.7000 3.1500 50 11.7000 6.3000

Percentiles

75 14.6250 8.1500 Conclusions. The level of emission of pollutants is influenced primarily by the operating regime of the engine and especially of the combustion chamber. Significant influence on the emission of pollutants will have new types of fuel for aircraft engines. In this paper it was carried out a case study on the level of smoke emitted by the turbofans engines using the Monte Carlo method. There were simulated ten smoke number values for take-off and landing regimes corresponding to a turbofan engine. Through the Monte Carlo simulation method it can be estimated the mean and momentary values for the indicators of reliability and availability and can determine also their distribution functions. Through the Monte Carlo method is enabled the modelling for the operation of a propulsion system which is very close to the real operation, offering the possibility to take into account of any known characteristics.

Determining the concentrations of hydrocarbons (HC), CO (carbon monoxide), CO2

(carbon dioxide) and NOx samples from turbofans engines’ exhaust is done using the



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calibration tools and charts and is a major and costly activity in the process of the engines’ certification. References Conserve energy future, 2016 Available at: http://www.conserve-energy-

future.com/causes-effects-solutions-of-air-pollution.php. Accessed: September, 2016.

Cumpsty N., 2015 Jet propulsion. Cambridge University Press, pp. 58-70. European Aviation Safety Agency (EASA), 2016 Available at:

https://www.easa.europa.eu/eaer/figures-tables/reference-landing-and-take-lto-cycle. Accessed: September, 2016.

European Aviation Safety Agency (EASA), 2016 Available at: https://www.easa.europa.eu/document-library/icao-aircraft-engine-emissions-databank. Accessed: September, 2016.

Hunecke K., 1997 Jet engines: fundamentals of theory, design and operation. Crowood Press Ltd, pp. 4-6.

Ispas S., 1980 [Turbojet engine]. Editura Tehnică, Bucuresti, pp. 232-264. [in Romanian] Lefebvre A. H., Ballal D. R., 2010 Gas turbine combustion: alternative fuels and

emissions. CRC, Hoboken, pp. 362-365. Lieuwen T. C., Yang V., 2013 Gas turbine emissions. Cambridge University, pp. 80-90. Olympus - Visual Inspections of Commercial Jet Engines, Available at:

http://www.olympus-ims.com/en/applications/rvi-passenger-jet-engine/. Accessed: September, 2016.

SPSS, 2016 Available at: http://www.psychwiki.com/wiki/Detecting_Outliers_-_Univariate. Accessed: September, 2016.

Zaharia S. M., 2015 Evaluation and impact of noise pollution caused by turbojet engines on people and the environment. Ecoterra 12(4):19–25.

Zaharia S. M., Martinescu I., 2012 [Reliability tests]. University Transylvania Brasov, pp. 87-96. [in Romanian]

Received: 27 October 2016. Accepted: 20 November 2016. Published online: 30 December 2016. Author: Sebastian Marian Zaharia, Transilvania University, Brasov, Department of Manufacturing Engineering, 29 Eroilor Street, 500036 Brasov, Romania, e-mail: [email protected] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited. How to cite this article: Zaharia S. M., 2016 An investigation on the smoke pollution issued by the turbofan engines. Ecoterra 13(4):52-60.

an investigation on the smoke pollution issued by the turbofan … · an investigation on the smoke...

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