This document summarizes a study on simulating fuel deterioration in gas turbines. It used a bio-fouling model called Bio-fAEG to simulate the biodegradation of 5 deteriorated fuels over time. The degraded fuels were then modeled in a GE LM2500 gas turbine engine using performance simulation software. The results showed fuel degradation progressively affected key performance indicators like efficiency and fuel consumption as deterioration increased from 0-10%. Exhaust gas temperatures also rose with higher levels of degradation, indicating potential damage to turbine blades over time. The study demonstrates a method for predictive maintenance of gas turbines by simulating how fuel quality degradation impacts engine performance.

1. Towards Predictive Maintenance in Gas Turbines—
Simulation & Analysis of Fuel Deterioration
Tosin Onabanjo*, Di Lorenzo, Eric Goodger, Peri Pilidis
Introduction
Gas turbines are widely advanced with
commercial application in power generation, military
aviation, civil aviation and the marine industries [1].
One of the key advantages is the sizeable amount
of useful work generated with a relatively small size
and weight engine. In comparison with other prime
movers such as diesel engines, gas turbines emit
relatively lower levels of combustion pollutant [2].
In principle, it uses compressed working fluid
(air), subsequently expanded hot gas to generate
useful power or thrust. This is brought about by a
progressive series of compression, combustion with
fuel where chemical energy is extracted and
expansion of gas in the turbine [3].
Despite its clear benefits, the operation of gas
turbines is limited by component inefficiencies. Poor
fuel quality is one of the causes of such
inefficiencies and this is often initiated by microbes,
largely by bacteria.
Some of the observed degradatory effects
include clogging of fuel filters, excessive metal
corrosion in the fuel tanks, injectors and turbine
blades, seizure of rotating components, extending
sometimes to sudden failure and other cost
implications.
The aim of this work is to demonstrate the
application of a bio-mathematical model for
performance simulation and analysis of fuel
deterioration in gas turbines.
Method
Five (5) deteriorated gas turbine type fuels were
simulated using Bio-fAEG, a bio-fouling model (Fig.
1). Engine simulations were carried in a GE LM2500
type engine that was modelled using Turbomatch—
engine performance simulation software (Fig. 2).
Travel Grant―
Presidents Fund
t.o.onabanjo@cranfield.ac.uk*,
g.dilorenzo@cranfield.ac.uk,
e.m.goodger@cranfield.ac.uk,
p.pilidis@cranfield.ac.uk
References
1) Langston, S. & Opydyke, G. 1997. Gas Turbine News, 37(2), 1-9.
2) Soares, C. 2008. Gas turbines: Butterworth-Heinemann. London: Elsevier Inc.
3) Walsh, P. P. and Fletcher, P. 2008. 2nd eds, Blackwell Science Ltd: Oxford, UK.
4) Mariano, A. P., Tomasella, R. C., de Oliveira, L. M., Contiero, J. and de Angelis, D. F. (2008).
Biodegradability of diesel and biodiesel blends. African Jour. of Biotech., 7(9):1323-1328.
Figure 1: Representation of a typical gas turbine engine
(Source: Performance Marketing, 2011)
As observed in fuel filters in many real systems and
depending on fuel type, it is anticipated that visible effects of
microbial growth and impact of fuel deterioration will observed
in the engine fuel systems during the early phase of significant
fuel degradation, about 0-10%.
Performance simulation using 0-10% degraded fuels on
LM2500, a simple cycle, two-shaft gas turbine engine indicate
that performance indicators are readily affected as fuel
deterioration progresses (Fig. 5). The largest amount of
deviations were observed in engine thermal efficiency, fuel flow
and specific fuel consumption (SFC). The exhaust gas
temperature, which is an indication of the amount of heat
rejected in the exhaust system into the surroundings increased
by 0.4K, 2K and 4K in LE, ME and RI respectively. An increase
by a degree in turbine inlet temperature can reduce blade life
by 50%. And, since it is impractical to measure turbine inlet
temperatures, an increase in the exhaust gas temperature is an
indication of deteriorating health condition and reduction in
performance of an engine, overall at adverse cost to operators.
Results & Discussion
Fuel degradation analysis using Bio-fAEG model
predicts initial substrate utilization rates of the bio-
available fractions are 0.37mg/day, 0.31mg/day,
2.77mg/day, 1.06mg/day and 1.48mg/day for fuels A-E
respectively. With increasing residence time and
doubling capacity of the organisms, a near complete
degradation between 20 and 60 days was achieved. At
day 60, the total hydrocarbon loss of the bioavailable
fraction for fuels A-E were 93.1%, 92.8%, 93.8%,
100% and 100% respectively, equating to 0.001% at
the most of the entire oil (Fig. 3).
Figure 3: Aerobic biodegradation of diesel type fuels A, B, C, D and Biofuel
type fuel E a) hydrocarbon loss over 0-60 day(s) b) biomass concentration
over 0-60 day(s) [Xo=0.1mg/L: So=0.313mg/L]
Figure 4: Aerobic biodegradation of diesel type fuel A –E over 6 months
GT (Pure diesel–type fuel)
LE (1% degraded)
ME (5% degraded)
RI (10% degraded)
Figure 5: Performance Simulation in terms of thermal efficiency, SFC, fuel flow and
exhaust gas temperature
These values are within the range stated by Mariano et al.
(2008) of 26-68 days and 3-22 days for pure diesels and
biodiesels respectively. Assuming the degradation of fuels A-E
were not impeded and conditions for biodegradation remained
constant, Bio-fAEG model predicts that 81-100% of the entire
fuel will be affected in three (3) months, depending on fuel
type (Fig. 4).
Conclusion
1.Cumulative biodegradation of fuels is a function of the
residence time, initial microbial population, microorganism
capability and fuel type. Hence, Bio-fAEG model is useful for
simulating degraded fuels for performance simulation and
analysis.
2.Fuel degradation could be worrisome, if routine fuel microbial
checks are ignored.
3.The current threshold limit of 0.1% of water in diesel fuel is
sufficient to accommodate proliferation of microorganisms in fuel
systems.
4.Fuel deterioration affects gas turbine performance by reducing
engine health and increasing fuel consumption.
5.This simulation study is a step towards achieving predictive
maintenance and condition monitoring in use of liquid fuels in
gas turbines.
Figure 1: Flow chart of Bio-fAEG―a bio-fouling model
Figure 2: Flow chart of Turbomatch―a gas turbine performance simulation &
analysis software
GT LE ME RI