3 REGENERATIVE-CYCLE GAS TURBINE

3.1 INTRODUCTION

The regenerative-cycle gas turbine is similar to the simple-cycle gas turbine except that in the former, the low-pressure hot exhaust gases are used to heat the high-pressure compressor discharge air in a heat exchanger (regenerator). This heated high-pressure air then enters the combustion chamber where it is mixed with fuel and burns. Recovery and transfer of heat from the hot exhaust gas to the compressor discharge air may be accomplished through the use of either a fixed-boundary heat exchanger or a moving-element heat exchanger.

• In the fixed-boundary heat exchanger (regenerator) the hot exhaust gas passes on one side of a thermally conductive barrier while the cooler compressor discharge air travels on the other side. The heat is transferred from the hot stream to the cooler stream through the barrier. The basic principle of the fixed-boundary heat exchanger is shown schematically in Fig. 3.1. This type of heat exchanger (regenerator) normally is used with large gas turbines (regenerative-cycle) for industrial applications and power-generating systems

 • In the moving element heat exchanger, heat transfer is accomplished by a moving element that passes through the hot exhaust gas, absorbs heat, and then releases the heat energy to cooler compressor discharged air. The schematic representation of a moving-element heat exchanger is shown in Fig. 3.2. This type of heat exchanger is smaller and is used with smaller gas turbines for vehicular applications. -

3.2 LARGE REGENERATIVE-CYCLE GAS TURBINES

3.2.1 Description
An understanding of regenerator design will aid in the understanding of performance characteristics, operation, and economics of regenerative-cycle gas turbines used for Integrated Community Energy Systems (ICES) applications. The next few sections provide basic design details of presently available commercial regenerators.

The basic flow pattern in a fixed-boundary regenerator normally is cross-flow, counter-flow, or cross-counter-flow. Modern high-performance regenerators have counter-flow or cross-counter-flow patterns.

The regenerators used in a regenerative gas turbine cycle can be classified according to their physical configuration as U-tube type and plate-fin type. The former is manufactured by Foster Wheeler Energy Corporation, and the latter by Harrison Radiator Division and Garrett/Air Research Manufacturing Company. The plate-fin design can be further classified into external strong back and internal pressure support according to its respective structural design.

• U-tube designs. The U-tube regenerator is a self-supporting box type structure, supported on structural steel columns, and containing a heat-transfer surface in the form of U-tubes as shown in Fig. 3.3. The U-tubes are supported at each end by tubesheets which, in turn, are incorporated into

headers. They are also laterally supported at appropriate intervals with special stainless-steel support grids. Each regenerator unit is fully shop-assembled and is shipped as a single, finished component. Field work consists of construction of the base at the site and connection of gas ducts and/or pipes to the unit.

• Plate-fin design (strongback design). The basic regenerator is of bar and plate construction as shown in Fig. 3.4. The exhaust gas tube consists of two plates, separated by a corrugated heat-transfer surface. The corrugated surface is copper-brazed to the plates. Each tube (gas passage) generally is 150 in. long, 28 in. wide, and approximately 1 in. high.

A tube bank is fabricated from several of these tubes, separated by spacers, and welded together to form an integral unit. The gap, formed by the spacers between the exhaust gas tubes, is the passage for compressed air. The number of tubes used depends on the particular flow conditions.

A regenerator assembly is constructed by welding together two tube banks separated by inlet and exhaust manifolds. The regenerator assembly is completed by adding strongbank structures, tie straps, and mounting legs. Figure 3.5 shows a vertically-mounted regenerator.

• Plate-Fin design (tension braze design). Figure 3.6 shows the basic core structure of tension braze concept. The corrugated fin surfaces are assembled in alternating exhaust gas and compressor discharge air passages, with passages separated by plates. The air passage corrugated fins are brazed with high-temperature, nickel braze alloy.

This type of brazing is both strong and oxidation-resistant at operating temperatures.

Figure 3.7 shows a single, completed block of a regenerator core. Because the internal forces, produced by high-pressure compressor discharge air in each air passage, are balanced by tensile forces in the fins inside the passage, the need for strong-back has been eliminated. Several (3 to 6, depending on the application) of these individual core assemblies are connected to make up a regenerator submodule.

Figure 3.8 shows two regenerator submodules arranged in parallel in a casing. The casing, which acts as support for the core submodules, also

contains the low-pressure exhaust gas. The regenerator, shipped in two halves is bolted together at the installation site.

3.2.2 Available Size Range
The regenerative cycle gas turbines are available from approximately 12,000 to 50,000 SHP.

The gas turbine and regenerators are transported separately to the site. Large regenerators are manufactured in submodules and are assembled at the site. The assembled regenerator then is connected to the gas turbine.

3.2.3 Dimensions and Shipping Weights
Dimensions and weights of regenerators vary considerably according to design configuration. Because plate-fin regenerators offer more heat-transfer area per unit volume than do tubular regenerators, they are smaller and weigh less.

The size and weight of the regenerator increase in applications that demand higher effectiveness.

Usually it is difficult to generalize dimensions of regenerators with respect to any particular parameter, unless specific information is known about several parameters, such as air flowrate, compressor pressure, and type of application. Table 3.1 shows the approximate dimensions for a typical plate-fin (tension braze design), a plate-fin (strong-back) and a tubular regenerator.

Many regenerators are of modular design, and the increase in turbine capacity is handled by the addition of one or more modules to the gas turbine. Table 3.2 shows the number of modules used for various General Electric gas turbines.²⁴

3.2.4 Material Balance
A regenerative-cycle gas turbine has two primary inputs: air and fuel. Air functions as the working fluid and is admitted to the system at the compressor. Fuel is admitted to the system at the burner and generally is either oil or natural gas. Most regenerative-cycle gas turbines are purchased for pipeline applications and burn natural gas. However, with increased fuel cost, more regenerators are being used for other industrial applications with fuels other than natural gas.

3.2.5 Energy Balance and Performance
Fuel is the primary energy input in a regenerative cycle gas turbine. The rate of fuel consumption is related to the system's efficiency. Regenerator effectiveness and regenerator total pressure drop are among the parameters that influence thermal efficiency of the regenerative cycle. Fig. 3.9 defines these two parameters.

 Regenerator effectiveness is defined by the ratio of the temperature rise of compressor discharge air through the regenerator to the difference between the turbine exhaust temperature and the compressor discharge air, and is given by the following equation:

 The regenerator total pressure drop is the sum of the air-side pressure drop divided by the air inlet pressure plus the gas-side pressure drop divided by the gas inlet pressure and is given by:

*The prime (') variable indicates actual temperature on T-S diagram (see Fig. A.2).

Figures 3.10 and 3.11 show the effect on the overall thermal efficiency of the system of regenerator effectiveness and total pressure drop, respectively.²⁵ It can be seen from Fig. 3.10 that, with increased regenerator effectiveness, the overall thermal efficiency increases. Figure 3.11 shows that an increase in total pressure drop results in a decrease of overall thermal efficiency. Figure 3.10 shows that peak efficiency increases at lower pressure ratios. This indicates that a gas turbine with lower pressure is more suitable for conversion to a regenerative cycle, because at high pressure ratios the compressor discharge air is at much higher temperatures, and the heat gain through the regenerator is smaller; thus, regenerator effectiveness is lowered.

One way to increase the effectiveness of a regenerator is to allocate more surface area for heat transfer. The increased surface area, in turn, increases the total pressure drop and thereby imposes a limit as to what extent effectiveness could be increased. Moreover, increased surface area rapidly increases regenerator costs. The actual design values of regenerator effectiveness and total pressure drop normally are fixed by the economics of fuel cost vs overall regenerator costs. Today's regenerators have a regenerator effectiveness of about 80% and total pressure drops of approximately 3 to 4%.

The full-load thermal efficiency of a regenerative-cycle gas turbine is defined as the ratio of net work output to fuel input and is expressed by the following equation: 

Equation 3.3 can be expanded into the following form:

A detailed derivation of Eq. 3.4 is given in Appendix A. The usefulness of the above equation is that it contains parameters related to the regenerator, such as regenerator effectiveness and pressure drop which facilitate an investigation of the system's overall thermal efficiency.

3.2.6 Full-Load Performance
The thermal efficiency of presently manufactured regenerative cycle gas turbines that have baseload ratings of 10,000 to 32,000 horsepower at full-load capacity is about 34%. Table 3.3 shows full-load thermal efficiency of a set of regenerative cycle gas turbines. Although the data in Table 3.3 belong to a single manufacturer, they can be considered as typical full-load efficiencies of today's regenerative-cycle gas turbines.

3.2.7 Part-Load Performance
Part-load performance data generally are derived empirically from test data for each gas turbine. Figure 3.12 shows the part-load thermal efficiency of a 13,300 HP simple-and regenerative-cycle gas turbine using nearly identical components.^l0 The thermal efficiency of regenerative units can be expressed by the following relation:

As shown by the lower curve on Fig. 3.12, fuel savings resulting from the addition of a regenerator, amount to 1/4 at full load and to about 1/3 at half load.

3.3 ENVTRONMRNTAL EFFECTS 

3.3.1 Thermal Discharge
The only significant thermal discharge from regenerative-cycle gas turbines is hot exhaust gas at a typical exhaust temperature of about 650°F.

3.3.2 Noise Attenuation
Basically there is no noise level difference between a simple-cycle unit or regenerative-cycle unit provided no sound-absorbing material is used on either unit. Lower sound level can be achieved by the use of sound-absorbing material around the regenerator casing, air inlets, and gee discharges.

 3.3.3 Effluent Discharge
Among the exhaust emissions only, NO_X emissions (Fig. 3.13) are of major concern in any combustion process. The solid lines in Fig. 3.13 indicate that regenerative cycle becomes a low emitter of NO_X at higher thermal efficiencies. This is in contrast with the simple cycle at a high pressure ratio, which benefits from high thermal efficiencies but suffers from high emissions of NO_X.

Figure 3.13 shows the NO_X emissions for simple and regenerative cycles.¹⁰ Tentative EPA rules require that the NO_X concentration be corrected to what it would have been had the exhaust contained only 15% oxygen. In Fig. 3.13, the broken lines indicate the larger concentrations of NO_X that would occur if fuel were increased to obtain 15% oxygen exhaust concentration.

3.4 OPERATING REQUIREMENTS

A regenerative-cycle unit retains most of the advantage of a simple-cycle unit such as automated, remote operation. If the regenerators are cold, the turbine operated at synchronous speed for about 30 min and full load is achieved in about 90 min.²⁶ This loading procedure normally is performed in regenerative-cycle gas turbines used in mid-range utility applications to minimize thermal loadings. In cyclic applications, electric strip heaters are mounted on the regenerator structure, and the stack closure damper is closed to reduce heat loss from the regenerator during the short shutdowns.²⁶ Modern regenerators can be used as fast as the gas turbine can be started. With modern regenerators, the operating procedure is virtually the same as for simple-cycle units.

3.5 MAINTENANCE AND RELIABILITY

3.5.1 Inspection and Cleaning
The extent of usage, operational environment, and field experience will determine the required inspection interval. Generally, the regenerator is inspected at engine inspection periods. At each inspection, the air and gas sides should be examined for evidence of mechanical damage or unusual deformation. 

Most regenerators are equipped with air side passage ways for access to the air manifold for inspection. The air side generally does not require cleaning. However, if cleaning becomes necessary, the method and procedure should be discussed with the manufacturer. The gas side cleaning becomes necessary when the operator's log indicates a drop in thermal efficiency or increased AP in the gas side because of deposits on the fins. Methods of cleaning usually are suggested by the manufacturer. Among the methods used are injection of walnut shells or flushing with water and detergent.

3.5.2 Leak Detection and Repair
If, during a routine inspection, evidence of leakage is found, or if operational monitoring of the system indicates leakage, a pressure decay check of the regenerator may be required.²⁷ This check is made by removing the air inlet and outlet ducts and then closing them, so that the regenerator air side can be pressurized. If the rate of decay exceeds leakage limits, the leakage must be located and repaired.

Leakage locations often are isolated by audible examination or soap bubble testing of the gas side when air side is pressurized.²⁷

Some leaks in the core manifold and gas inlet and outlet can be repaired by welding. The type of welding generally is specified by the manufacturer and is usually tungsten inert gas welding. The leaks that are in interior regions of the core are not accessible. The common procedure is to seal off an air passage as shown in Fig. 3.14.²⁷

The man-hour estimates for leak detection and repair are directly dependent on the type of installation, extent of damage, and type of regenerator.

3.5.3 Corrosion Protection
Regenerators are made of carbon steel or stainless steel. Moisture condensation on the regenerator core can cause corrosion. This problem is intensified by the presence in a marine or salt environment. Condensation is prevented during normal operation because both the regenerator core and the casing are hot. The regenerator will remain hot enough to prevent condensation for a shutdown of up to 24 hours. For a shutdown period of about 10 days, however, all the openings (inlets and exhausts) must be closed to prevent circulation of moist atmospheric air through the regenerator. For extended shutdowns, all the openings to the system should be closed, and an inhibitor material should be blown into air and gas sides of the regenerator. The type of inhibitor usually is specified by the manufacturer of the regenerator.

3.5.4 Expected Equipment Life
The expected life of a regenerator depends on the type of material used in the core structure (carbon steel or stainless steel) of the regenerator and the type of application. One manufacturer estimates that its regenerator (stainless core) is designed for 1,200,000 hours and 5,000 cycles without scheduled repair, with a life expectancy of 15 to 20 years.

3.5.5 Availability and Reliability
The availability and reliability are very high for regenerative-cycle gas turbines. Table 3.4 shows reliability and availability of several simple-cycle (SC) and regenerative-cycle (RC) gas turbines.¹⁰ All the

gas turbines studied were made by a single manufacturer and used natural gas. The gas turbines were mostly operated in domestic pipelines or petrochemical installations. As Table 3.4 indicates, reliability and availability were evaluated, based on total station data and then on basic turbine data, excluding controls, accessories, station controls, and load equipment.

3.6 COST CONSIDERATIONS

3.6.1 Regenerative-Cycle Gas Turbine Capital Cost
The cost of a regenerative-cycle gas turbine can vary widely with the type of gas turbine and regenerator. Generally, the following factors greatly influence the costs:

(1) type of turbine,
(2) type of regenerator (U-Tube, plate-fin),
(3) regenerator material (carbon steel, stainless steel),
(4) supporting structure requirement (horizontal, vertical),
(5) exhaust flowrate,
(6) pressure drop required, and
(7) number of modules involved -- with larger gas turbines the number of regenerator modules will increase, which accordingly lowers the unit price.

Figure 3.15 shows the approximate cost of factory-assembled regenerative-cycle gas turbines.

Figure 3.16 shows the approximate cost of simple and regenerative cycle turbine generator sets of a single manufacturer.²⁸ The data shown in

Figs. 3.15 and 3.16 are represented by the following expressions of cost vs turbine capacity (Q):

3.6.2 Regenerator Costs
The present approach to design of the regenerators has been based on the modular concept. Existing industrial gas turbines in the 5,000 to 7,000 hp range have a flowrate of 45 to 60 lb/sec. Based on this flowrate, at least one manufacturer has designed modular regenerators with each basic core handling 45--60 lb/see of the gas. For each engine manufactured in the power levels to 7,000 HP, from 15,000 HP to 30,000 HP; or from 60,000 HP to 120,000 HP, modules are combined to obtain the necessary performance characteristics. For example, a 30,000-HP engine will use a four-core module, and a 100,000-HP engine would use a twelve-core module. Although costs are greatly influenced by several factors, a rough order of magnitude price for plate-fin regenerators (tension braze design) is given in Table 3.5.

Another commercially available modular regenerator is the U-tube design. The approximate price for discussion purposes only is given in Table 3.6.

3.6.3 Cost of Conversion from Simple to Regenerative Cycle
Many simple-cycle gas turbines presently in operation were designed to facilitate conversion to the regenerative cycle. What distinguished these turbines from typical simple-cycle gas turbines is the addition of combustion wrappers to the combustion system during the manufacturing process. The conversion of simple-cycle gas turbines, not designed for changeover to the regenerative cycle, is generally more involved. This type of conversion requires rebuilding the combustion system to accommodate combustion air pipings to and from the regenerator. Moreover, regenerators, piping, new headers, outer and inner elbows, caps and liners, fuel nozzle gas tips, and flame detector bodies would be required in this conversion. The conversion cost is totally dependent on each individual case and is affected by various factors, such as type of regenerator and support structure.

Table 3.7 shows the estimated cost of conversion for several existing simple-cycle gas turbines manufactured by General Electric Company. These prices also include the combustion wrapper and the generator. 31 From Table 3.7 the estimated cost to add a regenerator to an existing simple-cycle FS-3002 would be $1,039,970. However, the cost of converting a simple cycle FS-3002 unit which already has factory provisions (combustion wrapper) for future conversion to a regenerative-cycle unit would be only $989,970.

3.6.4 Economic Analysis of Conversion to Regenerative Cycle
The increasing cost of fuel may justify conversion from simple-cycle to regenerative-cycle turbines. The manufacturer of the turbines should be contacted to determine whether the existing simple-cycle units can be converted to regenerative units.

Equation 2.7 in conjunction with Eq. 3.4 can be utilized to estimate the yearly fuel cost of an existing simple-cycle unit and increased in fuel efficiency of the same unit upon conversion to a regenerative unit. The following example illustrates the use of Eq. 2.2 and 3.4. All the symbols and equations in the proceeding section are defined in Appendix B. Typical values³² for the parameters involved in Eqs. 2.2 and 3.4 are:

The compressor and turbine efficiencies usually are provided by the manufacturer, but representative values for efficiencies, as well as specific heat ratios, are:

The only variable in Eq. 2.4 is the inlet temperature. The exhaust temperature and pressure ratio can be measured directly at the turbine site.

Ambient temperature = T₁ = 80°F (540°R)
Exhaust temperature = 1445°R
Atmospheric pressure = 14.0 psia
Compressor pressure ratio = 5.8

Temperature at point 3(T3) is calculated from Eq. A.6.

At this point all the parameters required to evaluate the thermal efficiency of this simple-cycle unit are known. Substituting these values into Eq. 2.2, thermal efficiency is calculated as follows:

Now, consider conversion of this unit to a regenerative unit with a regenerator having the following characteristics:

Knowing the efficiency of the simple-cycle unit and its converted regenerative version, it is possible to make an estimate of annual fuel savings. However, before proceeding further, a few other parameters should be known. The turbine manual provided by the manufacturer should give the percent of design thermal efficiency at the average power output. The yearly turbine use factor and average power output of the unit should be available from the operator's log. For demonstration purposes, the following numbers are assumed:

The annual fuel cost (AFC) can be evaluated from Eq. 3.8 as follows:³²

Assuming that average output remains the same after conversion, the AFC for converted units is:

AFC = $1,639,300 (regenerative-cycle unit).

The annual fuel savings is approximately $1,086,900, which can be compared to the retrofit cost of $1,039,970 for 10,000 HP unit (see Table 3.7).

The most important factor in considering conversion is the yearly use factor. Because gas turbines used by utilities for peak-load operation have very low yearly use factors, conversion to the regenerative cycle is uneconomical.

The older regenerators have a regenerator effectiveness of about 70 to 75%. Moreover, leakage rates normally are high because of corrosion and cracks. Both leakage and low effectiveness result in low unit thermal efficiency. Another consideration is the low availability of older units because of high downtime for maintenance. A thermal efficiency analysis of such a system may indicate the need for replacement of older units with newer, more efficient ones.

In an ICES application, in which thermal energy may be recovered from the turbine exhaust to meet thermal demand of the community, the comparative analysis would have to be based on the total fuel consumption to meet both electric and thermal loads instead of on thermal efficiency only of the turbine plant.

3.7 REGENERATIVE GAS TURBINES FOR VEHICULAR APPLICATIONS

3.7.1 Description
The major components of the gas turbines used for vehicular applications are the compressor, regenerator, combustor, turbine, fuel startup controls, and the transmission.

Compressor: The compressor generally is a single stage, centrifugal type, with a pressure ratio of about 4:1. The compressor efficiency is about 76 to 80% and is manufactured from aluminum alloys.

Regenerator: The rotary regenerators (moving element heat exchanger) are highly porous discs of either stainless steel or ceramic construction. The regenerator effectiveness is about 90% or more, with a total pressure loss (air side and gas side) of less than 10%, and a total leakage (carryover and seal) of less than 5%. 33

Combustor: The combustor is manufactured of steel or superalloy and is of fixed geometry configuration. There is a need for further development of a high performance low NO_X emittor combustor.

Turbine: The majority of the present gas turbines use a system of two turbines. The first turbine is a gasifier turbine where the expansion of gases produces power to drive the compressor and the engine accessories. The second turbine is the power turbine, located behind the gasifier turbine. The power turbine is mounted on an independent shaft which drives auxiliary accessories and is connected to the load through reduction gearing. This kind of gas turbine is also called a free turbine engine control system.

Control System: For gas turbines used in automobile power systems two basic subfunctions are involved: the mixture of air and fuel control, and power control. The primary sensed data are gasifier turbine speed, turbine inlet and outlet temperatures, atmospheric temperature, and power-level command which is sensed by throttle position.³³

The control systems are either hydromechanical or electromechanical. The hydromechanical systems are simpler and cost less; however, although the electromechanical systems are more expensive, they offer much greater flexibility.

3.7.2 Dimensions and Shipping Weight
Among the advantages of gas turbines over reciprocating engines are lighter weight and smaller size. A gas turbine does not need to produce as much horsepower to have the same torque characteristics as a reciprocating engine.³⁴ A gas turbine will have torque performance equivalent to a heavier reciprocating engine with more horsepower.

Weights of gas turbines vary from 3/4 lb/HP for an 800 HP gas turbine of simple design to 3 lb/HP for a regenerative unit. ³⁴ Table 3.8 shows dimensions and weights of various gas turbines.

3.7.3 Material Balance
The primary inputs into vehicular gas turbines are air and fuel. One of the advantages of this type of gas turbine is its ability to operate on a wide variety of fuels of different qualities, including unleaded gasoline, diesel fuel, distillate, gas, and kerosene. High-octane fuels are not necessary for the gas turbines. Fuels with lead additives can be harmful to the regenerator, because lead deposits can accumulate in the regenerator passages.³⁴ Figure 3.17 shows the brake specific fuel consumption (BSFC) of a gas turbine at various compressor inlet temperatures, ³⁴ where BSFC is defined as fuel flow divided by brake horsepower (also called shaft horsepower)

Figure 3.18 shows the fuel consumption characteristics of a free-turbine engine with variable power turbine nozzles and variable compressor inlet guide vanes. ³³

3.7.4 Energy Balance and Performance
Fuel is the primary energy input in the system. However, the turbine is started by energizing an electric motor to turn the compressor up to a required speed. Power for this process is supplied by a battery. The overall system efficiency is influenced by parameters such as, compressor and turbine efficiencies, regenerator effectiveness, and leakage rate.

Table 3.9 shows the overall thermal efficiency of various engine configurations for defined parameters.³³ The term "mature engine" in Table 3.9 refers to projected production versions. The mature version will operate at essentially the pressure ratios and turbine inlet temperatures of present engines. However, it will have lower fuel consumption, superior part-load performance, higher compressor and turbine efficiencies, and reduced weight.

Figures 3.19, 3.20, and 3.21 show the effect on the cycle efficiency³³ of regenerator effectiveness, compressor pressure ratio, and turbine inlet temperature, respectively.³³

These plots were obtained by holding all independent engine parameters constant at values given in Table 3.9, while the parameter of interest was changed. The results obtained through such a simplified analysis agreed well with actual performance data. Figures 3.22 and 3.23 show the performance of two manufactured engines at various engine speeds.^34,35

3.8 ENVIRONMENTAL EFFECTS

3.8.1 Thermal Discharge
The exhaust gases discharged from regenerative cycle engines are in a range of 525 to 600°F, which is lower than exhaust temperatures of reciprocating engines.

3.8.2 Noise Attenuation
Noise generated by a gas turbine is primarily a high-frequency whine that is attenuated in short distances. The noise level in a regenerative unit is low because the regenerators behave as muffling devices.

3.8.3 Effluent Discharge to Environment
Another major advantage of a gas turbine over a reciprocating engine is its low emission. This might be one factor that could greatly influence economics of building vehicular gas turbines. Figure 3.24 shows emission data from a General Motors' gas turbine manufactured for trucks and industrial application compared with 1977 California's emission requirements.³⁶ The same manufacturer had developed a new combustor to meet proposed 1983 California levels.

3.9 MAINTENANCE AND RELIABILITY

Maintenance requirements for automotive gas turbines are expected to be considerably lower than for a comparable auto engine because of the reduced number of parts (approximately 80% lower) in manufacturing gas turbines. It is anticipated that no regular oil filter or oil change is required. Periodic maintenance schedule is expected to follow the following routine.³³

(1) Replace air cleaner.
(2) Inspect regenerator core and seal.
(3) Change fuel filter.
(4) Check/adjust air fuel control system.
(5) Check/adjust power control system.
(6) Replace ignitor.
(7) Clean automizer nozzle.

Long-period maintenance items include the following.³³

(1) Replace regenerator seals.
(2) Replace fuel pump.
(3) Repair/replace power control components.
(4) Replace temperature sensor(s).
(5) Replace belts (if any).

 

3.9.1 Expected Equipment Life
Because gas turbines for vehicular applications have not been commercially available, actual prediction of their life expectancy is not possible. In terms of endurance testing, the component life of some Chrysler engines have over 2800 hours or 75,000 miles, with many parts accumulating over 3800 hours.³⁴

3.10 COST CONSIDERATIONS

No manufacturer currently offers gas turbines on a commercial scale for automobiles or trucks. The projected costs for future mass production are slightly higher than for present auto engines. The higher cost is due primarily to use of super alloys and stainless steel in high-temperature areas of the engine.

Figures 3.25 and 3.26 show projected costs of engines as a function of rated power.³³ The projected costs include material costs and labor rates in a mass-production environment.