Ali Moghaddas

Casey Bennett

Department of Mechanical and Industrial

Engineering,

Northeastern University,

Boston, MA 02115

Kian Eisazadeh-FarDepartment of Aerospace and Mechanical

Engineering,

University of Southern California,

Los Angeles, CA 90089

Hameed MetghalchiDepartment of Mechanical and Industrial

Engineering,

Northeastern University,

Boston, MA 02115

Measurement of Laminar BurningSpeeds and Determination ofOnset of Auto-Ignition of Jet-A/Airand Jet Propellant-8/Air Mixturesin a Constant Volume SphericalChamberThe laminar burning speeds of Jet-A/air and three different samples of jet propellant (JP-8)/air mixtures have been measured and the onset of auto-ignition in JP-8/air premixedmixtures has been determined. The experiments were made in a constant volume spheri-cal vessel, which can withstand high pressures up to 400 atm. Burning speed was calcu-lated from dynamic pressure rise due to the combustion process in the vessel. Athermodynamic model based on the pressure rise was used to determine the burningspeed. The burning speeds were measured in lean mixtures for pressures of 1–4.5 atmand temperatures of 493–700 K. The onset of auto-ignition of JP-8 fuels was evaluatedby observing intense fluctuations of pressure data during the explosion of the unburnedgas. It was revealed that Jet-A and JP-8 have very similar burning speeds; however,auto-ignition temperatures of various samples of JP-8 were slightly different from eachother. Auto-ignition of these fuels was much more sensitive to temperature rather thanpressure. [DOI: 10.1115/1.4006480]

Keywords: jet fuel, laminar burning speed, auto-ignition, spherical chamber

1 Introduction

JP-8 is regarded by the United States Army and Air Force asthe main fuel source for military land vehicles and aircraft. TheNorth Atlantic Treaty Organization has decided to use the samefuel across all battlefields under the “single fuel concept” [1–3].JP-8 is nearly identical in composition to the kerosene based com-mercial aviation fuel known as Jet-A, since JP-8 is simply Jet-Awith a military additives package added to it to improve thermalstability characteristics. This additives package typically containsan ice inhibitor to prevent water in the fuel from freezing, corro-sion inhibitors to protect fuel distribution components, and a staticdissipater to prevent ignition due to static discharge during fuel-ling [2,4,5].

As kerosene based fuels, Jet-A and JP-8 have complex chemicalcompositions that are comprised of thousands of hydrocarbonswhich can be divided into three general classes—aromatics(�20%), n-alkanes and isoalkanes (�60%), and cycloalkanes(�20%) [2,6,7]. In addition to the complex compositions, the rela-tive concentrations of these hydrocarbons can vary significantlyfrom one batch to another and from one manufacturer to another,depending on the crude oil and processes used [2,7]. These com-positional variations make the development of chemical kineticsmechanisms and surrogates of kerosene fuels very difficult. Thefuel samples in this study were obtained from the Wright Patter-son Air Force Base (WPAFB). The four samples are referred inthis paper as Jet-A (4658), JP-8 (4658), JP-8 (3773), and JP-8(4177). The four-digit number appended to each fuel is used byWPAFB for sample logging purposes and only serves to identify

the particular fuel. The sample designated Jet-A (4658) is a mix-ture of five Jet-A fuels from five different manufacturers and isthus an “average Jet-A.” The fuel designated JP-8 (4658) is theJet-A (4658) with JP-8 additives package added to it and hencecan be thought of as an “average JP-8.”

It is important to study the thermodynamic and thermophysicalproperties of various samples of Jet-A and JP-8 to see if there areany remarkable differences between these kerosene based fuels.Many researchers have attempted to identify surrogates for jetfuels with similar properties [6–8]. In order to verify proper surro-gates and chemical kinetics mechanisms, there is a need for reli-able experimental data. Laminar burning speed is a fundamentalproperty of a fuel which can be used to make these verifications[9,10]. JP-8 is intended to replace diesel fuel (DF-2) in internalcombustion engines; therefore, its explosion limits and auto-ignition properties should be studied. However, there is notenough experimental study on the explosion limits and auto-ignition of JP-8/air mixtures in the conditions which are identicalto internal combustion engines. Investigation of auto-ignitionfrom an experimental approach is a challenging issue. It occurs ina very short period of time, and precise devices are needed torecord the details of this phenomenon [11]. Poschl and Sattel-mayer [12] investigated the effect of temperature inhomogeneitieson auto-ignition occurrence. They concluded that inhomogeneoustemperature field has remarkable effects on the initiation processof auto-ignition. Kumar and Sung [13] experimentally studied theauto-ignition characteristics of conventional jet fuels using aheated rapid compression machine in the low-to-intermediate tem-perature range under elevated pressure conditions.

In this paper, we present the laminar burning speeds of Jet-A/air and three different samples of JP-8/air mixtures. The burningspeeds are measured in lean mixtures for pressures of 1–4.5 atmand temperatures of 493–700 K. The onset of auto-ignition of

Contributed by the Advanced Energy Systems Division of ASME for publicationin the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received November14, 2011; final manuscript received March 22, 2012; published online April 26,2012. Assoc. Editor: Gregory Jackson.

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these fuels is also explored. The experiments have been performedin a constant volume spherical vessel with specific initial tempera-ture and pressure. The auto-ignition can be characterized byintense fluctuations in pressure data and audible noise.

2 Experimental Facility

The spherical chamber consists of two hemispheric headsbolted together to make a sphere with an inner diameter of 15.24cm. The chamber was designed to withstand pressures up to 400atm and was fitted with ports for spark electrodes, ionizationprobes, and for filling and evacuation purposes. A thermocoupleinserted in one of the chamber ports is used to check the initialtemperature of the gas inside the chamber. A Kistler 603B1 piezo-electric pressure transducer with a Kistler 5010B charge amplifieris used to record the dynamic pressure rise during the experi-ments. Ionization probes mounted flush with the wall located atthe top and the bottom of the chamber are used to measure the ar-rival time of the flame at the wall and to check for spherical sym-metry and buoyant rise. Figure 1 shows the sketch of the vesselwith all the elements. The spherical vessel is housed in an ovenwhich can be heated up to 500 K. A data acquisition system isused to capture the pressure–time data as well as the signals fromionization probes. A computer driven system is used to make themixture with the required fuel and oxidizer and to initiate thecombustion process. Liquid fuel is stored in a reservoir which isattached to a liquid fuel manifold. The liquid fuel manifold is

equipped with two cartridge heaters to evaporate the liquid fuelbefore it enters the combustion chamber. The partial pressure ofthe fuel vapor is measured by a high temperature strain gauge(Kulite XTE-190). The method of partial pressures is used to setthe initial fuel air equivalence ratio. Figure 2 shows the schematicof the experimental setup.

3 Burning Speed Model

A thermodynamic model has been used to calculate the laminarburning speed based on the pressure rise during the flame propa-gation inside a constant volume vessel. This model was developedby Metghalchi and Keck [14,15] and was modified to account forthe energy losses due to electrodes and vessel wall and radiationfrom the burned gas to the wall as well as the temperature gradientin the preheat zone. It is assumed that gases in the combustionchamber can be divided into burned and unburned gas regionsseparated by a reaction layer of negligible thickness. Also, burnedand unburned gases are ideal, pressure throughout the chamber isuniform, and compression of both burned and unburned gases isisentropic. Figure 3 shows the schematic of the model. The burnedgas in the center of chamber is divided into a number of shellswhich the number of shells is proportional to the combustion dura-tion. STANJAN is used to find the equilibrium states of the burnedgases. Thermodynamic properties of some species were calculatedusing the model developed by Hui et al. [16,17]. The burned gasesare surrounded by a preheat zone (dph) having variable tempera-ture, which is itself surrounded by unburned gases. A thermalboundary layer (dbl) separates the unburned gas from the wall.A detailed description of the model is demonstrated in Refs.[18–24]. The equations of state, volume, and energy will besolved simultaneously

Pv ¼ RT (1)

where P is the pressure, v is the specific volume, R is the specificgas constant, and T is the temperature. The mass conservationequation for the burned and unburned gas regions is

m ¼ mb þ mu ¼ PiðVc � VeÞ=RTi (2)

Fig. 1 Sketch of the spherical vessel

Fig. 2 Schematic diagram of experimental facilitiesFig. 3 Schematic of different zones and their correspondingtemperatures in the thermodynamic model

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where m is the total mass of the chamber, mb is the mass of theburned gas zone, and mu is the mass of the unburned gas zone. Vc

is the volume of the chamber and Ve is the volume of the sparkelectrodes. In this equation, subscript i denotes the initial condi-tions, and subscripts u and b denote the unburned and burned gasconditions, respectively. The total volume of the gas in the com-bustion chamber is

Vi ¼ Vc � Ve ¼ Vb þ Vu (3)

And the energy conservation equation is

Ei � Qe � Qw � Qr ¼ Eb þ Eu (4)

where Ei is the initial energy of the gas, Qe is the conductiveenergy loss to the electrodes, Qw is the energy loss to the wall,and Qr is the radiation energy loss. Volume (mass balance) andenergy balance equations can be written as

ðxb

0

ðvbs � vusÞdx ¼ vi � vus þ ðVeb þ Vwb þ VphÞ=m (5)

ðxb

0

ðebs � eusÞdx ¼ ei � eus þ ðPVph=ðcu � 1Þ þ PVeb=ðcb � 1Þ

þ PVwb=ðcu � 1Þ � QrÞ=m (6)

where vi ¼ ðVc � VeÞ=m and ei ¼ Ei=m are the initial specific vol-ume and energy of the unburned gas in the chamber, vbs is the spe-cific volume of isentropically compressed burned gas, and vus isthe specific volume of isentropically compressed unburned gas.Vwb, Vph, and Veb are displacement volume of wall boundary layer,displacement volume of preheat zone ahead of the reaction layer,and displacement volume of electrode boundary layer, respec-tively. ebs, eus, and cu are the specific energy of isentropicallycompressed burned gas, specific energy of isentropically com-pressed unburned gas, and specific heat ratio of unburned gas,respectively. The above equations must be solved for twounknowns: burned gas mass fraction and the burned gas tempera-ture of the last shell. Given pressure as a function of time (meas-ured in the experiments), they can be solved numerically to findthe burned mass fraction xbðtÞ and radial temperature distributionTðr; tÞ.

Ultimately, laminar burning speed may be defined as

Su ¼ _mb=quAb ¼ m _xb=quAb (7)

where Ab is the area of the sphere having a volume equal to thatof the burned gas.

4 Results and Discussion

At least three runs at each initial condition were made to pro-vide a good statistical sample. It was found that three runs are suf-ficient to achieve a 95% confidence level [19]. Burning speedmeasurements have been performed on Jet-A/air and JP-8/air pre-mixed mixtures with initial pressure and temperature of 1 atm and493 K, respectively. The experiments were done at three equiva-lence ratios of 0.8, 0.9, and 1 and for pressures of 1–4.5 atm andtemperatures of 493–700 K. A previous study [24] on the structureof JP-8/air flames over the range of lean premixed mixtures withsimilar initial conditions revealed that the assumption of smooth

Fig. 5 Laminar burning speeds of JP-8 (3773) and (4177) ini-tially at 493 K and 1 atm

Fig. 6 Comparison of laminar burning speeds of different JP-8and Jet-A initially at 493 K and 1 atm

Fig. 4 Laminar burning speeds of Jet-A (4658) initially at 493 Kand 1 atm

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and spherical flame is valid throughout the entire flame propaga-tion. All reported burning speeds are in the regions wherer/R> 0.5 (r and R are the radii of the flame and the chamber,respectively). It was shown that in these conditions the effect ofstretch on the laminar burning speed is negligible [20,24,25]. Fig-ure 4 shows the measured burning speed of Jet-A (4658) for threedifferent equivalence ratios along the isentropes. As it is assumedthat the unburned gas is compressed isentropically, the pressurescorresponding to the temperatures in this figure could be foundfrom the isentropic compression relation (P ¼ PiðT=TiÞc=ðc�1Þ

). Itcan be seen that burning speed decreases as the mixture becomeslean. Figure 5 shows the burning speed of two samples of JP-8 atthree equivalence ratios. This figure shows that burning speeds ofthese two fuels are very close to each other and the same is truefor other two fuels as well. Figure 6 shows the comparison of theburning speeds of stoichiometric mixtures of Jet-A and three sam-ples of JP-8. It can be seen that the laminar burning speeds ofthese kerosene based fuels are very close to each other.

Auto-ignition experiments were carried out for JP-8 (3773) andJP-8 (4177) with an initial pressure of 8 atm in the spherical

chamber. Auto-ignition occurs at specific temperature and pres-sure during the compression of unburned gas due to flame propa-gation. The initial conditions are very important since the auto-ignition is strongly dependent on equivalence ratio and tempera-ture. The auto-ignition process in an unburned gas mixture is arapid process with intense pressure fluctuations. Abnormal pres-sure fluctuations can be considered as a trace of auto-ignition inthe unburned gas zone. In an ideally homogeneous mixture, it canbe assumed that auto-ignition occurs everywhere instantaneously.In these conditions, it is assumed that the mixture is perfectly uni-form and there is no temperature, pressure, or equivalence ratiogradient in the mixture. In practical combustors such as internalcombustion engines, it is hard to have homogeneous mixturessince these gradients do exist.

Figure 7 shows the pressure–time record of a stoichiometric mix-ture of JP-8 (3773) initially at pressure and temperature of 8 atmand 479 K, respectively. An abrupt rise in the pressure can be seenat the point denoted “A” along with audible noise. This is an

Fig. 9 Comparison of pressure–time record of auto-ignition ofJP-8 (3773) initially at 479 K and 8 atm at three different equiva-lence ratios

Fig. 10 Comparison of pressure–time record of auto-ignitionof JP-8 (4177) initially at 480 K and 8 atm at three differentequivalence ratios

Fig. 8 Rate of pressure rise (dP=dt) for auto-ignition of stoichi-ometric mixture of JP-8 (3773) initially at 479 K and 8 atm

Fig. 7 Pressure–time record of auto-ignition of stoichiometricmixture of JP-8 (3773) initially at 479 K and 8 atm

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indicator that the charge has auto-ignited. After repeating theexperiments and ensuring the reproducibility, the correspondingauto-ignition pressure and temperature of unburned gas were meas-ured at point “A.” The auto-ignition pressure was determined byfinding the point at which the value of dP/dt becomes discontinuousas seen in Fig. 8. The auto-ignition trace of Fig. 7 is similar to thosein internal combustion engines provided by Heywood [26].

Figures 9 and 10 show the pressure–time records of auto-ignition of JP-8 (3773) and JP-8 (4177) air mixtures at three dif-ferent equivalence ratios, respectively. These figures show thatincreasing the equivalence ratio in these experiments advances theunburned gas explosion. Figure 11 demonstrates the temperaturesand pressures at which auto-ignition took place for two samples ofJP-8. The explosion temperature in a flame propagating combustoris the temperature where the ignition delay time of the unburnedgas mixture is smaller than the time scale of flame propagation. Itcan be seen that there is a specific range of temperature for theexplosion of JP-8/air mixtures. The temperature varies from 680K to 695 K for JP-8 (3773) and JP-8 (4177), respectively. The dif-ference between auto-ignition temperatures of different samplesof JP-8 might be due to their respective crude oil source and refin-ery process. This figure shows that the onset of auto-ignition ismuch more sensitive to temperature rather than pressure.

5 Summary

The burning speeds and the onset of auto-ignition of Jet-A/airand different samples of JP-8/air were studied in a set of experi-ments in a constant volume spherical chamber. The burning speedmeasurements were done in lean premixed mixtures and over thepressures of 1–4.5 atm and temperatures of 493–700 K. Resultsshowed that these kerosene type fuels have very similar laminarburning speeds. The diagnosis of auto-ignition was done by ana-lyzing the pressure and ionization probes data. It was observedthat auto-ignition is characterized by intense pressure fluctuationsand abrupt change in the rate of pressure rise. The auto-ignitionwas very sensitive to temperature and it was shown that there is aspecific explosion temperature for each sample of JP-8 over awide range of equivalence ratios.

Acknowledgment

This work was supported by the Army Research Office (ARO)corresponding to the Grant No. W911NF0510051. The authors

would like to thank Dr. Tim Edwards from the Air Force ResearchLaboratory (AFRL) for providing the fuels.

NomenclatureA ¼ flame surface areae ¼ specific energy

m ¼ massP ¼ pressureQ ¼ energy lossr ¼ flame radiusS ¼ burning speedt ¼ time

T ¼ temperaturev ¼ specific volumex ¼ burned mass fractionc ¼ ratio of specific heatsd ¼ boundary thickness/ ¼ equivalence ratioq ¼ density

Subscriptsb ¼ burned gas

bl ¼ thermal boundary layerbs ¼ isentropically compressed burned gaseb ¼ electrode boundary layer

i ¼ initial conditionph ¼ preheat zoneu ¼ unburned gas

us ¼ isentropically compressed unburned gaswb ¼ wall boundary layer

References[1] Fernandes, G., Fuschetto, J., Filipi, Z., Assanis, D., and McKee, H., 2007,

“Impact of Military JP-8 Fuel on Heavy Duty Diesel Engine Performance andEmissions,” Proc. Inst. Mech. Eng., Part D (J. Automob. Eng.), 221(8), pp.957–970.

[2] Maurice, L. Q., Lander, H., Edwards, T., and Harrison, W. E., “Advanced Avia-tion Fuels: A Look Ahead via a Historical Perspective,” Fuel, 80, pp. 747–756.

[3] Kouremenos, D. A., Rakopoulos, C. D., and Hountalas, D. T., 1997,“Experimental Investigation of the Performance and Exhaust Emissions of aSwirl Chamber Diesel Engine Using JP8 Aviation Fuel,” Int. J. Energy Res.,21(12), pp. 1173–1185.

[4] Rawson, P., 2001, “AMRL Evaluation of the JP8þ100 Jet Fuel Thermal Stabil-ity Additive,” DSTO Aeronautical and Maritime Research Laboratory, Air-frames and Engines Division, Technical Report No. DSTO-TR-1135.

[5] Heneghan, S. P., Zabarnick, S., Ballal, D. R., and Harrison, W. E., III, 1996,“JP-8þ100: The Development of High-Thermal-Stability Jet Fuel,” ASME J.Energy Resour. Technol., 118, pp. 170–179.

[6] Dagaut, P., and Cathonnet, M., 2006, “The Ignition, Oxidation, and Combustionof Kerosene: A Review of Experimental and Kinetic Modeling,” Prog. EnergyCombust. Sci., 32(1), pp. 48–92.

[7] Agosta, A., Cernansky, N. P., Miller, D. L., Faravelli, T., and Ranzi, E., 2004,“Reference Components of Jet Fuels: Kinetic Modeling and ExperimentalResults,” Exp. Therm. Fluid Sci., 28(7), pp. 701–708.

[8] Humer, S., Frassoldati, A., Granata, S., Faravelli, T., Ranzi, E., Seiser, R., andSeshadri, K., 2007, “Experimental and Kinetic Modeling Study of Combustionof JP8, its Surrogates and Reference Components in Laminar NonpremixedFlows,” Proc. Combust. Inst., 31(1), pp. 393–400.

[9] Dam, B., Ardha, V., and Choudhuri, A., 2010, “Laminar Flame Velocity ofSyngas Fuels,” ASME J. Energy Resour. Technol., 132, p. 044501.

[10] Monteiro, E., and Rouboa, A., 2011, “Measurements of the Laminar BurningVelocities for Typical Syngas–Air Mixtures at Elevated Pressures,” ASME J.Energy Resour. Technol., 133, p. 031002.

[11] Yilmaz, N., and Burl Donadlson, A., 2007, “Modeling of Chemical Processesin a Diesel Engine With Alcohol Fuels,” ASME J. Energy Resour. Technol.,129, pp. 355–359.

[12] Poschl, M., and Sattelmayer, T., 2008, “Influence of Temperature Inhomogene-ities on Knocking Combustion,” Combust. Flame, 153(4), pp. 562–573.

[13] Kumar, K., and Sung, C. J., 2010, “An Experimental Study of the AutoignitionCharacteristics of Conventional Jet Fuel/Oxidizer Mixtures: Jet-A and JP-8,”Combust. Flame, 157, pp. 676–685.

[14] Metghalchi, M., and Keck, J. C., 1980, “Laminar Burning Velocity of Propane-AirMixtures at High Temperature and Pressure,” Combust. Flame, 38, pp. 143–154.

[15] Metghalchi, M., and Keck, J. C., 1982, “Burning Velocities of Mixtures of Airwith Methanol, Isooctane, and Indolene at High Pressure and Temperature,”Combust. Flame, 48, pp. 191–210.

[16] Hui, H., Metghalchi, M., and Keck, J. C., 1999, “Estimation of the Thermody-namic Properties of Unbranched Hydrocarbons,” ASME J. Energy Resour.Technol., 121, pp. 45–50.

Fig. 11 Auto-ignition temperatures versus pressures forJP-8=air mixtures

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[17] Hui, H., Metghalchi, M., and Keck, J. C., 2000, “Estimation of the Thermody-namic Properties of Branched Hydrocarbons,” ASME J. Energy Resour. Tech-nol., 122, pp. 147–152.

[18] Elia, M., Ulinski, M., and Metghalchi, M., 2001, “Laminar Burning Velocity ofMethane-Air-Diluent Mixtures,” ASME J. Eng. Gas Turbines Power, 123, pp.190–196.

[19] Parsinejad, F., Arcari, C., and Metghalchi, H., 2006, “Flame Structure andBurning Speed of JP-10 Air Mixtures,” Combust. Sci. Technol., 178, pp.975–1000.

[20] Eisazadeh-Far, K., Moghaddas, A., Al-Mulki, J., and Metghalchi, H., 2011,“Laminar Burning Speeds of Ethanol/Air/Diluent Mixtures,” Proc. Combust.Inst., 33, pp. 1021–1027.

[21] Rahim, F., Eisazadeh-Far, K., Parsinejad, F., Andrews, R. J., and Metghalchi,H., 2008, “A Thermodynamic Model to Calculate Burning Speed of Methane-Air-Diluent Mixtures,” Int. J. Thermodyn., 11, pp. 151–161.

[22] Eisazadeh-Far, K., Moghaddas, A., Metghalchi, H., and Keck, J. C., 2011, “TheEffect of Diluent on Flame Structure and Laminar Burning Speeds of JP-8/oxidizer/diluent Premixed Flames,” Fuel, 90, pp. 1476–1486.

[23] Eisazadeh-Far, K., Moghaddas, A., Rahim, F., and Metghalchi, H., 2010, “BurningSpeed and Entropy Production Calculation of a Transient Expanding SphericalLaminar Flame Using a Thermodynamic Model,” Entropy, 12, pp. 2485–2496.

[24] Eisazadeh-Far, K., Parsinejad, F., and Metghalchi, H., 2010, “Flame Structureand Laminar Burning Speeds of JP-8/Air Premixed Mixtures at High Tempera-tures and Pressures,” Fuel, 89, pp. 1041–1049.

[25] Moghaddas, A., Eisazadeh-Far, K., and Metghalchi, H., 2012, “Laminar Burn-ing Speed Measurement of Premixed n-Decane/Air Mixtures Using SphericallyExpanding Flames at High Temperatures and Pressures,” Combust. Flame, 159,pp. 1437–1443.

[26] Heywood, J., 1988, Internal Combustion Engine Fundamentals, McGraw-HillSeries in Mechanical Engineering, McGraw-Hill, Singapore, pp. 457–470.

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