oxygen excess control of industrial combustion through the use of automotive lambda sensor

*Corresponding author (L.C. de Lima). Tel/Fax: +55-85-31019902. E-mail addresses: [email protected]. 2011. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Volume 2 No.3. ISSN 2228-9860. eISSN 1906-9642. Online Available at http://TuEngr.com/V02/365-373.pdf

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International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies

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Oxygen Excess Control of Industrial Combustion Through the Use of Automotive Lambda Sensor Lutero C. de Limaa*, Humberto A. Carmonaa, Cesar V. M. da Silvaa, and Francisco S. Cavalcante Juniora a Graduate Program on Applied Physics, State University of Ceará, BRAZIL A R T I C L E I N F O

A B S T RA C T

Article history: Received 30 April 2011 Received in revised form 20 July 2011 Accepted 25 July 2011 Available online 26 July 2011 Keywords: Flue gases; Industrial combustion; Lambda sensor; Oxygen concentration; Thermal control

The objective of this study is to present a simple and low cost method of determining the flue gases oxygen concentration. The method makes use of the Lambda sensor, a part of the fuel injection system of the modern automobile’s engine. A combustion chamber was mounted with a heated Lambda sensor installed in its chimney. Residual oxygen concentrations in the flue gases were estimated by the use of the Nernst equation and compared to a reference combustion analyser. The observed average deviation in the measurements was of about 5 % which is in the range of interest to the industrial combustion.

2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies. Some Rights Reserved.

1. Introduction Laws and environmental regulations for the control of air pollution are turning more

stringent mainly where the combustion of fossil fuels or biomass is present. After

Wulfinghoff (2000), the efficiency control of combustion generally is made through the

measurement of oxygen, carbon monoxide or carbon dioxide concentration in the flue gases.

The measurement of oxygen concentration is better suited for the efficiency test of a

combustion process because oxygen and excess air is almost independent of the fuel type.

When the optimum excess air setting is approached, the relative change in oxygen

concentration is much more accentuated than the relative change in carbon monoxide or

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies 2011 International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies.

366 Lutero C. de Lima, Humberto A. Carmona, Cesar V. M. da Silva, and F. S. Cavalcante Junior

carbon dioxide for a given change in excess air. The Orsat analyser is the pioneer of

combustion efficiency testers. This chemical testing apparatus in which flue gases are mixed

with a liquid reagent that changes volume as a result of the reaction is simple and accurate.

However, the apparatus is built of delicate glass tubing and requires a fine touch.

Still after Wulfinghoff (2000), most of the modern combustion testers is based on electro-

chemical sensors. For the detection of oxygen the most common sensor used is a zirconium

oxide element that develops a voltage difference across two platinum electrodes separated by

a porous ceramic layer if there is a difference in oxygen concentration. The combustion

process in the modern automobiles generally is controlled by an oxygen sensor known as

Lambda sensor (Figure 1).

Figure 1: Commercial Lambda sensors.

McDonald, et al. (1998) used unheated and heated Lambda sensors for the monitoring

residential oil burners. They observed that even being a little more expensive the heated

Lambda sensor presented better accuracy and low response time when compared to the

unheated one. The unheated Lambda sensor takes about 5 minutes of warm-up in order to be

operational. Unéus, et al. (1999) applied Lambda sensor for the measurement of oxygen

percentage in the range of 12 to 15 % in industrial boilers. Wiesendorf, et al. (1999) used

this sensor for the monitoring of fluidized bed combustors. Gibson, et al. (1999) developed a

new technique of working with Lambda sensor which consist of applying a potential in one

and in the opposite directions of the sensor terminal and the electrical currents measured. The

ratio between forward and reverse currents presents linear correspondence to the oxygen

percentage in the combustion environment. Pickenacker, et al. (2000) determined


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experimentally air excess in boilers and furnaces using the concept of Wobbe which was

determined through the use of Lambda sensor. Auckenthaler, et al. (2002) were the first

researchers to study the transient behavior of Lambda sensor. Niklasson, et al. (2003) studied

air-fuel ratio in a fluidized bed furnace through fluctuating signals from zirconia cell probes.

Eskilsson, et al. (2004) used Lambda sensor to monitor oxygen concentration, combustion

efficiency and emissions in pellet burners. Johansson, et al. (2007) used a Lambda probe to

indicate whether the combustion environment was in oxidizing or reducing conditions.

Varamban, et al. (2005) extended the perturbation method developed by Gibson, et al. and

proposed a scheme to measure the emf and short circuit current of a potentiometric (zirconia)

sensor simultaneously.

In the present article an automotive Lambda sensor was installed in the chimney of a

combustion chamber where its voltage difference and the flue gases temperature were

monitored and the oxygen concentration determined through the use of the Nernst equation.

Results indicate that it is relatively simple the construction of low cost equipment to monitor

industrial combustion.

2. Materials and methods The Lambda sensor being an electrochemical cell when inserted in a situation where

there is a difference of oxygen concentration as, for example, between the inside of a

combustion chamber and the atmospheric air, and at a temperature above 300 °C, starts to

conduct oxygen ions from the region of high to the region of low electrochemical potential.

The migration of oxygen ions inside the electrochemical cell generate a voltage which

decrease exponentially with the oxygen concentration inside the combustion chamber, taking

as reference the air outside with oxygen concentration of 20.96 %.

The equation which relates the oxygen concentration with a voltage developed inside the

Lambda sensor is the Nernst equation in its inverse under the following form:

₂ % 20.96 / (1),

where z is the number of electrons migrating from one electrode to another electrode inside


the Lambda sensor, F is the Faraday constant, E is the voltage developed in the sensor, R is

the universal gas constant and T is the absolute temperature inside the Lambda sensor.

A commercial Lambda sensor was installed in the chimney of the combustion chamber

shown in Figure 2. The combustion chamber has a Weishaupt LPG burner of 50 kW. Close

to the Lambda sensor was installed a type K thermocouple. It was developed an electronic

circuit which feed the heating element of the Lambda sensor in order to maintain constant the

inside temperature of sensor no matter how is the temperature of the flue gases.

Figure 2: Experimental setup.

The voltage signal of the Lambda sensor was monitored by a FLUKE 189 multimeter

with resolution of 0.01 mV and accuracy of 0.4 %. The thermocouple signal was recorded by

a temperature controller showing resolution of 1 °C and accuracy of 0.5 %. The oxygen

concentration was measured by the TESTO 300 XL combustion gas analyser with resolution

of 0.1 % and accuracy of 0.2 %.

3. Results and Discussion Figure 3 presents signal of a Lambda sensor in mV calculated by the Nernst equation

(1) for different levels of temperature and as a function of oxygen concentration. As can be

seen by that figure when the oxygen concentration comes to the extreme points, as for

example, 0 % and 20.96 % the voltage signal of the Lambda sensor go to infinite and zero

respectively. This behavior of the Lambda sensor limits its application to the measurement


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of oxygen concentration outside of such range.

Figure 3: Output signal of a Lambda sensor as calculated by the Nernst equation.

The relationship between the temperatures of the heating element of the Lambda sensor

against its electrical resistance is shown in Figure 4. It was permitted to the combustion

chamber to warm until 300 ºC. The burner was turn off and the electrical resistance of the

heating element inside the Lambda sensor was recorded during the cooling period. It is very

important to know the electrical resistance of the heating element of the Lambda sensor as a

function of temperature because the electronic circuit responsible for the maintenance of

constant temperature inside the sensor works controlling its resistance feeding more or less

power.


Figure 4: Curve of electrical resistance of the heating element against temperature.

Figure 5: Flue gases oxygen percentage against measurements of the reference monitor.

Figure 5 presents the percentage of oxygen in flue gases calculated by equation (1) with

the input of the voltage furnished by the Lambda sensor and temperature given by the

thermocouple for different situations of combustion of LPG against measurements taken from


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the reference combustion monitor. The average deviation of the set of measurements was

about 5 %. The correlation factor was of 0.97 demonstrating good agreement between the

measurements of the proposed method of determining oxygen concentration of combustion

flue gases and the measurements made by the reference monitor. In the range higher than 15

% of oxygen concentration the deviation was more accentuate (about 10%) and this is due the

logarithmic nature of the sensor’s output, as can be seen in the Figure 3.

Figure 6: Output of the Lambda sensor at the constant temperature of 500 °C as a function of

the oxygen concentration.

Figure 6 presents the evolution of the output of the proposed method as a function of the

oxygen concentration while the temperature inside the Lambda sensor was maintained

constant at about 500 °C and independent of the flue gases temperature. As it is shown in that

figure the measurements follow very closely the Nernst law equation.

4. Conclusion In this work it was presented a simple method of determining oxygen concentration in the

exhaust gases of combustion particularly the industrial combustion. Results demonstrated the


feasibility of the proposed method when the Lambda sensor is operated inside a usual

combustion chamber. The heating time of about 5 minutes and the logarithmic response of

the Lambda sensor are its main drawbacks if it is wanted to develop the herewith presented

method of measuring oxygen concentration in flue gases of industrial combustion.

5. Acknowledgements The authors thank the Brazilian National Council for Scientific and Technological

Development (CNPq) for financial support. A very special thank you is due to Dr.João

Batista Furlan Duarte for insightful comments, helping clarify and improve the manuscript.

6. References Auckenthaler, T.S., C. Onder, and H.P. Geering. (2002). Control- oriented investigation of

Switch-type air/fuel ratio sensor, in: Proceedings of the IFAC World Congress, Barcelona, Spain, CD-ROM.

Eskilsson, D., M. Ronnback, J. Samuelson and C. Tullin. (2004). Optimisation of efficiency and emissions in pellet burners. Biomass and Bioenergy, 27, 541-546.

Gibson, R.W., R.V. Kumar and D.J. Fray. (1999). Novel sensors for monitoring high oxygen concentrations. Solid State Ionics, 121, 43-50.

Johansson, A., F. Johnsson, F. Niklasson and L.E. Armand. (2007). Dynamics of furnace processes in a CFB boiler. Chemical Engineering Science, 62, 550-560.

McDonald, R.J., T.A. Butcher and R.F. Krajewski. (1998). Development of self tuning residential oil burner – oxygen sensor assessment and early prototype system operating experience. Brookhaven National Laboratory, Informal Report BNL-66045, 26 pages, Upton, NY, USA.

Niklasson, F., F. Johnsson and B. Leckner. (2003). Local air ratio measured by zirconia cell in a circulating fluidised bed furnace. Chem. Eng. J. , 96, 145-155.

Pickenacker, K., D. Trimis and K. Wawrzinek. (2001). Development of a Wobbe number sensor for controlled combustion of gaseous fuels with varying quality, in: Proceedings of International Conference on Technologies and Combustion for a Clean Environment (Clean Air VI), Porto, Portugal, V.1, 1-11.

Unéus, L., P. Ljung, M. Mattson, P. Martensson, R. Wigren, P. Tobias, I. Lundstrom, L.G. Ekedahl and A. Lloyd Spetz. (1999). Measurements with MISIC and MOS sensors in flue gases, in: Proccedings of Eurosensors XIII, Hague, Netherland, 521-524.

Varamban, S.V., R. Ganesan and G. Periaswami. (2005). Simultaneous measurement of emf and short circuit current for a potentiometric sensor using perturbation technique, Sensors and Actuactors B, 104, 94-102.


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Wiesendorf, V., E.U. Hartage, J. Wether, F. Johansson, J. Sternéus, B. Leckner, D. Montat, and P. Briand. (1999). The CFB boiler in Gardanne – an experimental investigation of its bottom zone, in: Proceedings of the 15th Int. Conf. On Fluidized Bed Combustion, Savannah, Georgia, USA, May 16-19, ASME, Paper FBC99-0151.

Wulfinghoff, D. R. (2000). Energy Efficiency Manual. Published by Energy Institute Press, USA.

Dr.Lutero Carmo de Lima graduated in Physics by the University of Santo Amaro, M.Sc. and Dr. Eng. in Mechanical Engineering by the Federal University of Santa Catarina and University of São Paulo, respectively. He is presently Adjunct Professor at the State University of Ceará and basically works in fundamental problems of the thermal science, clean energy and instrumentation. He was awarded a Fulbright Fellow and inducted as Vice President of PHI BETA DELTA, Chapter Beta Theta, Honour Society for International Scholars, USA.

Dr.Humberto de Andrade Carmona is an Adjunct Professor in the Program for Applied Physical Science at the Ceara State University working mainly with alternative energies, particularly with material science applied to problems involving thermal science and solar energy. He holds a PhD in Physics from the University of Nottingham, England, as well as MS and graduation from the Federal University of São Carlos, Brazil. He has vast experience with electronic transport in semiconductor devices, and computer modeling of materials.

César Vinicius Mota da Silva graduated in Physics by the State University of Ceará. He is presently colaborating at the State University of Ceará working in fundamental problems of the thermal science, clean energy and instrumentation. He is currently also working as a monitor of the project Science Traveling with experiments in various areas of Physics.

Francisco dos Santos Cavalcante Junior holds a degree in physics from the State University of Ceará. He is currently a student at the Master Program in Applied Physics of that university. In that program he conducts research related to renewable energy with emphasis on biomass combustion.

Peer Review: This article has been internationally peer-reviewed and accepted for publication

according to the guidelines given at the journal’s website.

oxygen excess control of industrial combustion through the use of automotive lambda sensor

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