GS2-09
Paper No.

Proceedings
ofthe
theProceeding of
1stInternational
International Forum
Forum onon HeatHeatTransfer
Transfer
1stNovember
Kyoto, Japan
Japan
November24-26,
24-26, 2004,2004, Kyoto,

PERFORMANCE EVALUATION OF MICRO GAS TURIBINEOPERATED USING LOW HEATING VALUE FUEL
Daisuke Yamashita*, Kazuya Tatsumi* and Kazuyoshi Nakabe** Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
E-mail : tatsumi@energy.osakafu-u.ac.jp
Keywords : Micro gas turbine, Low heating value fuel, Turbine inlet temperature, System efficiency, Exhaust gas analysis
ABSTRACTA practical micro gas turbine (MGT) has been operated under
low heating value fuel conditions. The low heating value fuel wassimulated by diluting the LPG by N2 in the present study.
Efficiencies at each component were calculated using the measured
temperature and pressure. Exhaust gas analysis was also conducted.
Under the condition of a fixed mass flow rate of the supplied fuel,the turbine inlet temperature (TIT) of the MGT decreases as theN2-LPG mixing ratio increases, resulting in a deterioration of theoverall system efficiency. This N2-dilution also significantly affected
the characteristic of the gas emission. These are believed to berelated to the incomplete combustion occurring at the combustor.
Nevertheless, the MGT was eventually successful in operating at thecondition of heating value less than 1/2 of the LPG maintaining astable combustion, demonstrating its applicability to such low
heating value fuels.

by installing thermocouples and pressure gauges in each location
shown in Fig. 1. CO and NOx in the exhaust gas from the PGT aremeasured by using an electrochemical sensor.

1. INTRODUCTION
MGT is well known as one of the key technologies which frame
the distributed power supply system. It is compact, provides lessNOx and COx emissions and is easy for maintenance compared to
the reciprocated engines. On the other hand, considerable problems
still exist. One of these is the applicability for various fuel sources.
To address the global energy problems and the variety of the local
area energy supplies, it is important to examine to what extent thecurrent MGT system is applicable to various types of fuels.
Especially, applicability for low heating value fuels is a matter ofconcern. For example, the heating values of the exhaust gas from thefuel cells or the gasified biomass are less than 1/4~1/10 of that ofthe pure propane. In the present study, the aforementioned
applicability of the MGT for such fuels is investigated by operatinga practical MGT system using low heating value fuels.

Fig. 1 System flowchart.
2.2 ConditionsFirstly, experiment was carried out under the condition ofapplying 100% LPG fuel to the system. The valve opening was set
at three different levels, i.e. 100, 66 and 50%, and for each case, theTIT (=T3) was varied from 650 to 800ºC by controlling the fuelsupply rate.
For the diluted fuel case, the valve opening was fixed at 100%.
In this case, the MGT was first started up by using 100% LPG fueland was operated until T3 reached a certain value (referred to as‘starting temperature’), i.e. 700, 750 and 800ºC. Then N2 wasinjected and mixed with LPG, having the mixing ratio changed byseveral steps.

2. EXPERIMENTAL METHODS
2.1 Apparatus
Figure 1 shows the system flowchart of the MGT system. Thegas turbine system corresponds to a two-axial Brayton cycle
consisted of two commercial turbo-chargers where the first one
operates as a gas-generating turbine (GGT) and the other as apower-generating turbine (PGT) (Mori, 2000). The low heating
value fuel is simulated by diluting LPG with N2 using the gas mixer
and is then supplied to the combustor. In the present study, insteadof a dynamo, the compressor of the second turbocharger plays a roleof actual load. The load is controlled by changing the valve openingof the throttle valve mounted at the downstream side of thecompressor. Temperature and pressure measurements are established

3. RESULTS AND DISCUSSION
The characteristics of the MGT operated under 100% LPG fuelcondition are first discussed here. Figure 2 shows the relation
between the system thermal efficiency Ș and T3 for eachvalve-opening rate. Ș is defined by the ratio of the work output ofthe PGT to the heat supplied from the fuel. The values shown here
are the averaged values of several measurements. Higher efficiency
is obtained as the TIT increases and the load effect appears to besmall. The thermal efficiency of the present system is 7~10% and isrelatively small since no recuperator is installed for heat recovery.
In Fig. 3, the relation between Ș and T3 is shown for the diluted
fuel case. As mentioned in Section 2.2, experiment is conducted firststarting with 100% LPG condition and then increasing the mixing__LPG N287 __Proceeding of the1st International Forum on Heat Transfer
November 24-26, 2004, Kyoto, Japan

Paper No.

REFERENCES
H. Mori, Y. Tsujimoto and K. Yokota, Development ofTurbo-Burner System and its use in Education, Proc. ISROMAC-8,
vol. 1, pp. 364-370, 2000.
1200

CO [ppm ] (O2 0%)

1000

System efficiency K

0.10
0.09

2000.00.2

0.4

0.60.81.0Mixing ratio mN /mLPG

160

Loading compressor
outlet valve opening
100%
66%
50%

1.2

1.4Starting temp.
o700 Co
750 Co800 C

140120
10080
00.0

0.2

0.4

0.60.81.0Mixing ratio mN /mLPG

1.2

1.4

2Fig. 5 NOx concentrations.

0.06
600

650

700

750 o

GGT inlet temperature T3 [ C]D. Yamashita received the B.E. (2002) inOsaka Prefecture Univ. and is now in the2nd-year of Master course of Dept. ofEnergy Systems Eng., Osaka Prefecture
Univ.
His current interests include micro gas
turbine and hydrogen fuel reformer.

800Fig. 2 System thermal efficiency (LPG 100% case).
0.12: larger mixing ratio mN /mLPG

0.11

System efficiency K

Starting temp.
o700 Co750 C
o800 CFig. 4 CO concentrations.

0.07

20.10

K. Tatsumi received M.E. (1999) and PhD(2003) in Kyoto Univ. Dept. Mech. Eng. Heis now a Research Assistant of Dept. ofEnergy Systems Eng., Osaka Prefecture
Univ. His current interests include compact
heat exchangers, hydrogen fuel reformer andmicro energy supply systems.

0.09
0.08

Starting temp.
o700 Co
750 Co800 C

0.07
0.060.05

400

1800.08

0.05

60020.12
0.11

8000NOx [ppm ] (O2 0%)

ratio of N2. The filled symbols in Fig. 3 indicate the point fromwhich each measurement is started (starting temperature) and thearrows show the history when N2 mixing ratio is increased. Figures
4 and 5 illustrate the concentration profiles of the CO and NOx inthe exhaust gas emitted from the PGT in relation to the N2-LPG
mixing ratio, respectively. In Fig. 3 we can see that increase of N2
incurs a decrease of TIT which eventually accompanies
deterioration of the system efficiency. It should be marked here that
combustion pressure P3 and GGT revolution number decreased also
when N2-LPG mixing ratio increased.
As is shown in Fig. 4, when the N2-LPG mixing ratio exceeds 0.4,
CO concentration increases rapidly, which indicates that a poor
combustion is occurring. On the other hand, in Fig. 5, NOxconcentration decreases as N2-LPG mixing ratio increases. Thereason for this is considered as follows. As the mixing quantity ofN2 enlarges, larger sensible heat for temperature rise of N2 isrequired, hence, the total combustion temperature decreases. For
example, under the condition of N2-LPG mixing ratio larger than 0.4
and the gas temperature of 1000K, the required heat for rising N2temperature from 300K to 1000K is more than 10% of the supplied
LPG heating value. Consequently, this produces the combustion
pressure decrease and disturbs the local reaction, whichaccompanies the increase of CO, and reduces the generation of thethermal NOx.

600650700750 o

GGT inlet temperature T3 [ C]800

K. Nakabe received M.E. (1983) in Kyoto
Univ. Dept. Mech. Eng and PhD (1991) inOsaka University. He is now Prof. of Dept.
of Energy Systems Eng., Osaka Prefecture
Univ. His current interests are in the fieldsof turbulent mixing, micro mixer, heattransfer and combustion.

Fig. 3 System thermal efficiency (N2 mixed case, valve opening100%).
ACKNOWLEDGEMENTThe authors gratefully acknowledge Prof. Y. Tsujimoto of Osaka
University and Prof. K. Teshima of Okayama University of Science
for their support and experienced advices.

__88 __