## Abstract

An important question for future aeroengine combustors is how partial vaporization influences the $NOx$ emissions of spray flames. In order to address this question an experimental study of the combustion of partially vaporized kerosene/air mixtures was conducted. This assesses the influence of the degree of fuel vaporization on the $NOx$ emissions in a wide range of equivalence ratios covering the entire lean burning regime. The tests were performed at atmospheric pressure, inlet air temperatures of $313–376K$, a reference mean air velocity of $1.35m∕s$, and equivalence ratios of 0.6, 0.7, and 0.9 using Jet A1 fuel. An ultrasonic atomizer was used to generate a fuel spray with a Sauter Mean Diameter of approximately $50μm$. The spray and the heated air were mixed in a glass tube of $71mm$ diameter and a variable length of $0.5–1m$. The temperature of the mixing air and the length of the preheater tube were used for the control of the degree of vaporization. Downstream of the vaporizing section, the mixture was ignited and the flame was stabilized with a hot wire ring that was electrically heated. For local exhaust measurements a temperature controlled suction probe in combination with a conventional gas analysis system were used. The vaporized ratio of the injected fuel was determined by a Phase Doppler Anemometer (PDA). In order to optimize the accuracy of these measurements extensive validation tests with a patternator method were performed and a calibration curve was derived. The data collected in this study illustrates the effect of the vaporization rate $ψ$ upstream of the flame front on the $NOx$ emissions which changes with varying equivalence ratio and degree of vaporization. In the test case with low prevaporization the equivalence ratio only has a minor influence on the $NOx$ emissions. Experiments made with air preheat and higher degrees of vaporization show two effects: With increasing preheat air temperature, $NOx$ emissions increase due to higher effective flame temperatures. However, with an increasing degree of vaporization, emissions become lower due to the dropping number and size of burning droplets, which act as hot spots. A correction for the effect of the preheat temperature was developed. It reveals the effect of the degree of prevaporization and shows that the $NOx$ emissions are almost independent of $ψ$ for near-stoichiometric operation. At overall lean conditions the $NOx$ emissions drop nonlinearly with $ψ$. This leads to the conclusion that a high degree of vaporization is required in order to achieve substantial $NOx$ abatement.

1.
Jansohn
,
P.
,
Ruck
,
T.
,
Steinbach
,
C.
,
Knöpfel
,
H. -P.
,
Troger
,
C.
, and
Sattelmayer
,
T.
, 1997, “
Development of the Advanced EV (AEV) Burner for the ABB GTX100 Gas Turbine
,” ASME Paper No. 97-AA-139.
2.
Cooper
,
L.
, 1980, “
Effect of Degree of Fuel Vaporization Upon Emissions for a Premixed Partially Vaporized Combustion System
,” NASA Technical Paper No. 1582, Lewis Research Center, Cambridge, MA.
3.
Lee
,
L.
,
Malte
,
P.
, and
Benjamin
,
M.
, 2001, “
Low NOx Combustion for Liquid Fuels: Atmospheric Pressure Experiments Using a Staged Prevaporizer-Premixer
,” ASME Paper No. 2001-GT-0081.
4.
Rizk
,
N. K.
, et al.
, 2002, “
Prediction of NOx Formation Under Combined Droplet and Partially Premixed Reaction of Diffusive Flame Combustors
,”
J. Eng. Gas Turbines Power
0742-4795,
124
, pp.
31
38
.
5.
Gärtner
,
F.
, 1982, “
Vergleich der Bildung von Stickstoffoxid in Methanol-Luft-und Kohlenwasserstoff-Luft-Flammen
,” Ph.D. thesis, Technische Hochschule Darmstadt.
6.
Turns
,
S. R.
, 2000,
An Introduction to Combustion
, 2nd ed.,
McGraw-Hill
,
New York
.
7.
Particle Dynamics Analyzer: Supplement of the Users Manual
. DANTEC Measurement Technology, Skovlunde, Denmark, 1991.
8.
BSA Flow Software v.2.1.
, DANTEC Measurement Technology, Skovlunde, Denmark, 2003.
9.
Qiu
,
H. H.
, and
Sommerfeld
,
M.
, 1992, “
A Reliable Method for Determining the Measurement Volume Size and Particle Mass Fluxes Using Phase-Doppler Anemometry
,”
Exp. Fluids
0723-4864
13
, pp.
393
404
.
10.
Dullenkopf
,
K.
, et al.
, 1998, “
Comparative Mass Flux Measurements in Sprays Using a Patternator and the Phase-Doppler Technique
,”
Part. Part. Syst. Charact.
0934-0866,
15
, pp.
81
89
.
11.
Ochs
,
M.
, 2000, “
Verdunstung Monodisperser, Frei Beweglicher Brennstoff-Tropfen in Einer Turbulenten Heissluftströmung
,” Ph.D. thesis, ETH Zürich.
12.
Kaiser
,
E.
, 1996, “
,” Technical Report No. BMFT 2124/513-8891-LVF 9102, TU Dresden.
13.
Morikita
,
H.
, et al.
, 1998, “
Application of Shadow Doppler Velocimetry to Paint Spray: Potential and Limitations in Sizing Optically Inhomogeneous Droplets
,”
Meas. Sci. Technol.
0957-0233,
9
, pp.
221
231
.
14.
Saffman
,
M.
, 1987, “
Automatic Calibration of LDA Measurement Volume Size
,”
Appl. Opt.
0003-6935,
26
(
13
), pp.
2592
2597
.
15.
Sattelmayer
,
T.
, et al.
, 1998, “
NOx-Abatement Potential of Lean-Premixed GT Combustors
,”
ASME J. Eng. Gas Turbines Power
0742-4795,
120
, pp.
48
59
.
16.
Naha
,
S.
, and
Aggarwal
,
S. K.
, 2004, “
Fuel Effects on NOx Emissions in Partially Premixed Flames
,”
Combust. Flame
0010-2180,
139
, pp.
90
105
.
17.
Held
,
T. J.
,
Marchese
,
A. J.
, and
Dryer
,
F. L.
, 1997, “
A Semi-Empirical Reaction Mechanism for n-Heptane Oxidatation and Pyrolysis
,”
Combust. Sci. Technol.
0010-2202,
123
, pp.
107
146
.
18.
Li
,
S. C.
, and
Williams
,
F. A.
, 1999, “
NOx Formation in Two-Stage Methane-Air Flames
,”
Combust. Flame
0010-2180,
118
, pp.
399
414
.