Study on the Parameters Influencing Efficiency of Micro ...

Study on the Parameters Influencing Efficiency of Micro-gas Turbines - A Review

Samarth Jain Delhi Technological University New Delhi, India

Soumya Roy Abhishek Aggarwal Delhi Technological University Delhi Technological University

Delh New Delhi, India New Delhi, India

Dhruv Gupta Delhi Technological University

New Delhi, India

Vasu Kumar Delhi Technological University

New Delhi, India

Naveen Kumar Delhi Technological University

New Delhi, India

ABSTRACT

The art and science of gas turbine has traditionally seen a

gradual and continuous change over the past few decades. Gas

turbines are classified into impulse and reaction types and

further into turbojet, turbofan, turboprop, after burning turbojet

and micro gas turbine. These turbines find applications in

airplanes, large scale industries etc. but these are less suitable

for the small scale power generation units due to several

factors. Micro gas turbines are set to play a significant role

particularly in small-scale power generation using combined

heat and power generation among all these types of turbines as

the future of power generation lies in decentralised and

distributed power generation systems. In the light of making

use of the high temperature exhaust of a gas turbine, combined

heat and power generation systems are being used to increase

the power output and overall efficiency. Micro gas turbines are

essentially single-stage, single-shaft and low pressure gas

turbines whose capacity ranges from 30-150 KW. In

comparison to the conventional turbines, micro gas turbines are

compact and have low lubricating oil consumption leading to a

simpler lube and sump oil system and because they have fewer

rotating parts, this leads to lesser balancing problems. The

analysis of micro gas turbines has shown that they are capable

of meeting current emission standards of NOx and other

pollutants. Even though the installation costs of micro gas

turbines are high due to the complexity in adjusting to electrical

grid frequency, still these distributed energy systems may prove

to be more attractive in a competitive market to those seeking

increased reliability as they empower these entities with the

capacity of self-generation. The following text reviews the

developments in the micro gas turbines with a special focus on

the efficiency of its components such as the recuperator, the

combustion chamber design and also explores the future

prospects of the technology in terms of viability of its

application in the automobile sector.

NOMENCLATURE

CO2 Carbon Dioxide

AES Advanced Energy System

MGT Micro Gas Turbine

SiC Silicon Carbide

CHP Combined Heat and Power

IAC Inlet Air Cooling

INTRODUCTION

Micro gas turbines (Fig 1) have experienced a growing interest

during the last decade. They are prime movers whose capacity

ranges from 15 to 300kW. Micro gas turbines consist of a

supersonic radial flow compressor and turbine connected by

hollow shaft capable of rotating at very high speeds. They have

the same basic operating cycle as that of macro turbines, which

is the Brayton cycle (Fig 2). But since only a limited

compression ratio can be achieved in a single stage turbine, the

micro turbine has to be used in conjunction with a regenerative

cycle.

Micro turbines used in combined heat and power have

the potential to reduce CO2 emissions to a large extent. A

recuperator is installed between the compressor and the

combustion chamber so that satisfactory power output and

efficiency is achieved [1]. They are also of interest for

distributed power generation in applications where heat and

power generation can be combined.

Proceedings of the ASME 2015 Power Conference POWER2015

June 28-July 2, 2015, San Diego, California

POWER2015-49417

1 Copyright © 2015 by ASME

PE Power Electronics

EG Electrical Generator

GC Gas Compressor

GT Gas Turbine

R Regenerator

HRB Heat Recovery Boiler

CC Combustion Chamber

BPV By Pass Valve

Fig 1: Layout of Micro Gas Turbine

Fig 2: Micro Gas Turbine Regenerative Brayton Cycle.

Ambient air compressed by the centrifugal compressor

enters the regenerator, where it gets preheated by the exhausts

coming from the turbine and subsequently goes into the

combustion chamber. Combustion process takes place and the

hot gases then expand through the turbine and enter the

regenerator. The high temperature exhaust can then be sent to a

heat recovery boiler which can be used to heat water. This

combined heat and power configured production increases the

fuel energy conversion efficiency. The core power unit fitted

with the micro turbine includes fuel lubrication, cooling, and

control systems. The fuel feeding system compresses the fuel to

the required injection pressure and regulates its flow to the

combustion chamber according to the current operating

condition. The lubrication system delivers oil to the rolling

components besides reducing friction. The cooling system

keeps the working temperatures of the different components

within optimum range. The function of the electronic control

system is to monitor MGT operation through continuous, real

time checking of its main operational parameters [2, 3].

Micro gas turbines have the advantages of having high

energy density potential, increased redundancy and reliability,

high operational flexibility, higher rotational speeds, fast start-

up and stop and low maintenance costs due to the presence of

fewer rotating parts. Micro gas turbines are capable of being

operated on a wide range of liquid and gaseous fuels, including

green alternatives like CNG and biofuels for their operation.

Micro gas turbines are compact, light and clean-burning jet

engines that have great potential to provide green and efficient

energy.

LITERATURE REVIEW CONFIGURATION OF A MICRO GAS TURBINE Thermodynamics The thermodynamic considerations for micro gas turbines are

the same as that of macro turbines. The basic cycle on which

the micro gas turbine operates is the Brayton cycle. The

Brayton cycle is preferred because it offers a greater power

density, simplified fabrication of the designed system, easier

initial demonstration, thermal anisotropy and better efficiency.

Thus, high power density (developed in micro turbines) for a

simple Brayton cycle requires high combustor exit

temperatures (1400-1800K) and pressure ratios above 2 and

preferably above 4. The principal advantages of the Brayton

cycle are its simplicity with only one moving part i.e. the rotor,

highest power density because of the high through flow Mach

number resulting in high mass flow per unit area and the

availability of compressed air for cooling and other uses [4]. The primary disadvantage is that a minimum

component efficiency (of the order of 40-50%) must be met for

the cycle to be self-sustaining; only then can net power be

produced.

Scaling A macro scale gas turbine (Fig 3) with 1 meter diameter air

intake area generates power of the order of 100 MW. Hence, if

such a device were to be scaled to millimeter size then tens of

watts of power would be generated if the power per unit of

airflow is maintained. Such power density requires combustor

exit temperatures of 1300-1700 K with the rotor tip speeds

reaching 300-600 m/s. Thus, the rotating structures get

centrifugally stressed to hundred MPa as the power density of

both fluid and electrical machines scale with the square of the

speed, as does the rotor material centrifugal stress [5].

Heat transfer is another aspect in which micro turbines

operate in a different design space than large scale machines.

As the viscous forces are larger hence the heat transfer

coefficients are also higher, by a factor of about 3 thereby


resulting in increased heat transfer rates across the structure as

well as within it [6].

The development of micro fluid machinery which will

be efficient at small scale and compatible with the constraints

of current fabrication technology, offers new challenges.

Firstly, the high pressure ratios per stage needed for an efficient

gas turbine requires the peripheral Mach numbers to be in the

transonic regime. But because the Reynolds number of the cold

regions remains in the range of tens of thousands, the flow

remains laminar and diffusion becomes difficult. The inability

of micro machining technology to fabricate “extruded”-like

geometries also poses a challenge.

Finally, turning the flow in the out fabrication plane

direction without incurring undo pressure loss and blockage

also poses a challenge to designing the fluid machinery [7].

Fig 3:Cross-section of a Micro Gas Turbine

Structure and Materials Used Materials with high specific strength are required to generate

the desired performance and sustain the high operating

temperatures. Ceramic materials generally have lower

densities, higher stiffness, lower thermal expansion

coefficients, and higher allowable operating temperatures than

the metals used in conventional, macro scale gas turbine

engines. These characteristics are attractive for turbo

machinery design at all scales, but success in introducing

ceramics into conventional gas turbines has been limited by the

low toughness of the materials [8].

The low toughness implies that the strength of

ceramics is extremely sensitive to flaws, introduced during

processing or subsequent service. However, the strength of

brittle materials is scale-dependent. Experimental studies [9]

have shown that small specimens, on average, exhibit higher

strengths than larger ones, simply because the probability of

there being a flaw larger than a critical size decreases with the

specimen size.

In the micro engine, the most critical component is the

turbine rotor, which experiences high centrifugal stress and

elevated temperatures, with the additional possibility of high

impact loads. Work is currently underway to design and

fabricate SiC and Si/SiC hybrid structures by chemical vapor

deposition of relatively thick silicon carbide layers (10-200

m) over silicon molds. The preliminary analysis and testing

suggests that this is a promising approach [10].

Combustion The functional requirements of a combustor for micro heat

engine are similar to those for a conventional gas turbine

combustor. The primary functional requirement is to convert

chemical energy to thermal and kinetic energy with low total

pressure loss. Other requirements include introduction and

mixing of fuel and air, ignition and stable operation for all

engine operating conditions.

Maintaining low-stressed, cooled structures, and a size

and shape that are compatible with the overall engine geometry

are the principal constraints associated with designing a

combustion chamber. In addition, designing a combustor for a

micro engine application introduces two new challenges. The

first is the limited flow residence time within the combustor

that comes with the small size of the device. This presents

difficulties, because while many of the fluid mechanical

processes such as injection and mixing may scale with the size

of the device, the chemical reaction time is independent of size.

The other challenge is associated with the increased surface

area-to-volume ratio which is such that heat loss to the walls of

the combustor can be significant relative to the heat released in

the combustion process [11-14].

CHP Mode Operation Combined heat and power (CHP) is the use of a heat engine or

power station to simultaneously generate electricity and useful

heat. Combined heat and power (CHP) integrates the

production of usable heat and power (electricity), in one single,

highly efficient process.CHP generates electricity whilst also

capturing usable heat that is produced in this process.

Cogeneration is a thermodynamically efficient use of fuel. This

contrasts with conventional ways of generating electricity

where vast amount of heat is simply wasted. In separate

production of electricity, some energy must be discarded as

waste heat, but in cogeneration this thermal energy is put to

use. All thermal power plants emit heat during electricity

generation, which can be released into the natural environment

through cooling towers, flue gas, or by other means. In

contrast, CHP captures some or all of the by-product for

heating, either very close to the plant, or as hot water for

district heating with temperatures ranging from approximately

80 to 130°C. This is also called combined heat and power

district heating (CHPDH). Small CHP plants are an example of

decentralized energy [15-17].

A straight forward modification of the simple gas

turbine cycle for CHP mode operation is the addition of a

recuperator. A recuperator is a heat exchanger located in the gas

turbine exhaust which enables the waste heat to be transferred

from the exhaust to the combustor inlet air, hence partially

replacing fuel. It reduces specific fuel consumption compared

to a conventional simple cycle gas turbine, while ensuring

exhaust temperature is still suitable for CHP. The biggest


challenge in designing heat exchangers for micro-turbines is

that efficiencies over 30% have to be achieved [18-22]

Actual CHP plants have utilization factors ranging

from 85-90% (large systems provide 40% electrical and 50%

thermal energy while small systems give 30% electrical and

60% thermal). Although a small part only of the heat will

disappear as losses before the heat reaches the consumers, the

total efficiency is still about 80% because of the heat losses.

Since this technology makes it possible to produce electricity

and heat using less fuel than a conventional specialized plant in

combination with a separate heat generation, the level of

emissions is correspondingly very low. The economics are

viable because electricity which is not used locally can be sold

to the grid, although see below as well [23-25].

The main non-technical barriers to the implementation

of CHP systems are that the investment payback period could

be high (up to 6 years) and this is primarily due to the high

investment cost. Also the price of excess electricity sold to the

grid is often low and the cost of grid connection might be high.

Besides the CHP technology and its benefits are not widely

known amongst most consumers [26-29].

COMPONENT DESIGN AND EFFICIENCIES Recuperator A recuperator is important to achieve efficiencies of over 30%

in micro turbines. In the thermal design of the recuperator, two

parameters are essential: the effectiveness and the pressure loss

across the recuperator. By increasing the heat transfer surface

in recuperator, the effectiveness would be apparently increased

but the pressure loss and size of the recuperator would also

greatly increase [30-32].

One of the designs which can be employed for a

recuperator is a counter-flow micro channel heat exchanger. It

consists of 6 recuperator blocks positioned around the gas

turbine. When optimization of the recuperator’s inner geometry was carried out by computing the dimensions of the hot and

cold channels; the number of channels for a set of cold and hot

side pressure drops, it was observed that the heat exchanger

effectiveness and pressure drop were conflicting requirements

in recuperator design as cycle efficiency increases. This means

that the cold and hot side pressure drops are uniquely correlated

and the pressure drop should be preferably located at the cold

side of the recuperator. For this reason, the hot channels should

be larger than the cold ones [33].

Besides this another innovative recuperator design

which can be incorporated in micro turbines is the Swiss-roll

type recuperator. This proposed recuperator is basically a

primary-surface type and is composed of two flat plates that are

wrapped around each other, creating two concentric channels of

rectangular cross section.

The idea for Swiss-roll type recuperators stems from

the fact these devices act like excess enthalpy burners. The

flammability limits can be effectively extended through the

recirculation of the thermal energy from the combustion

products to preheat the reactants. The reactants then have

higher total enthalpy because of the increased thermal enthalpy

from the preheating. Because of their geometry, they have

substantially less inclination to fouling at compact size. The

structure and the mechanical designs are simple and the

manufacturing processes could be reduced. By wrapping up the

heat exchanger in the Swiss-roll configuration, the combustor

heat dissipation to the surroundings can be effectively reduced

and the heat transfer taking place between the windings of the

roll with the combustion in the core becomes integral part of

the thermal system [34, 35].

Combustion Chamber The fundamental challenge which lies in designing a micro

turbine combustion chamber is to tailor the fluid flow so that

the flame is stabilized and there is effective mixing of the cold

reactants with the hot products. Effective completion of the

combustion process within a small volume is mainly limited by

the chemical reaction time of the fuel and this constraint is

aggravated by the enhanced heat transfer effects that result

from the large surface area-to-volume ratio of these devices.

Silicon micro fabrication can be very helpful in

achieving the economy and high tolerances which are

necessary to make a micro engine viable. Work has been going

on to develop a high power density silicon combustion system

consisting of a six-wafer micro-combustor. In this premixed

fuel-air enters the device axially followed by a 90° turn prior to

entering the compressor. Swirl vanes are included to replicate

the compressor exit flow angle of 80°. The flow then passes

through a duct which wraps around the combustion chamber.

This passage is referred to as the cooling jacket and it thermally

isolates the combustion chamber and cools the inner walls. In

addition it also acts like a simple recuperator for preheating the

reactants. This is also where fuel is injected in the non-

premixed mode of operation. The fuel-air mixture is then

burned in the combustion chamber. Two types of chamber

inlets are designed to create different flame holding

recirculation zones. The first is an annular inlet 1.2 mm wide.

The second is an array of 60 slots 2.2mm long intended to

create multiple small recirculation zones for more rapid and

uniform ignition of the incoming flow. The combustion

products then get passed through the turbine nozzle guide vanes

and exit axially from the device [36].

The dual-zone combustor is an improvement over the

six-wafer combustion design with significant changes in the

operating mode. A series of holes through the inner wall

connect the upper cooling jacket to the combustion chamber.

These holes allow inlet air to bleed into the combustion

chamber. This dilution air serves two purposes; first, it splits

the combustion chamber into two zones, and second, it dilutes

the hot combustion products reducing their temperature to the

desired turbine inlet temperature of 1600 K. This is similar to

conventional large-scale combustors [37, 38].

The low pressure ratio of the gas turbine cycle and the

low temperatures of the combustion air present a big challenge

for the evaporation of the liquid fuel film. This had led to the

development of another combustion chamber design which


means to utilize the lean premixed pre-vaporized combustion.

Because of the low pressure and low temperature, the liquid

fuel gets evaporated on a hot surface since compressor air

temperature is too low for an intense evaporation of a fuel

droplet spray. A reverse flow of hot combustion gases takes

place along the outer surface of an evaporator tube. The liquid

fuel film on the inner surface of the tube then gets evaporated

by heat transferred from the hot combustion gases through the

tube wall. The combustor wall is a multi-layered assembly

consisting of a ceramic inner liner, a compliant layer, and the

outer metal casing. This design helps in reaching near about

adiabatic conditions [39, 40].

Fuels and Emissions Air emissions in micro-turbines comply with the existing

standards and they are very competitive in comparison with

other technologies in these aspects. The use of micro gas

turbines in distributed energy systems adds other advantages

such as low emissions and fuel flexibility [41]. With the ability

of being powered by a wide variety of fuels, micro-turbines

have seen use both of liquid and gaseous fuels like diesel,

natural gas and biomass. When natural gas is used in a

Capstone turbine, 27% efficiency can be obtained at full load

while upto 24.5% can be obtained using diesel at full load [42].

Micro turbines emissions are very low at full load and do not

increase appreciably until the load is reduced below 60 – 70 %

of the full load. The primary pollutants from micro-turbines are

oxides of nitrogen (NOx), carbon monoxide (CO) and unburned

hydrocarbons. When there is insufficient residence time at high

temperature, it results in CO emissions. Emissions of CO also

heavily depend on operating load. The CO formation decreases

as the power output increases because of a rise in the flame

temperature. But simultaneously the emission of NOx also

increases. Micro turbines which use a lean premixed combustor

technology considerably reduce NOx formation [43].

Enhancing Efficiency of Micro Turbine Based CHP Systems Micro turbines have lower efficiencies when compared to their

adversaries such as reciprocating engines. Thus, efforts have

been made to improvise the micro turbine based CHP systems

in terms of electrical power output and efficiency. Some of

these include inlet air cooling (IAC), trigeneration and

bottoming organic Rankine cycles.

Inlet air cooling seeks to offset the power loss which

takes place due to rise in ambient temperatures. The air intake

system of a micro turbine consists of a single duct through air

enters into the cabinet of the turbine with the working air going

to the compressor and the remaining air going to the cooling

system. Since only the working air influences the performance

of the turbine hence if two separate flows are used with a

refrigerating engine being mounted on the working air intake

duct to cool the working air, it leads to improved efficiency.

The refrigerating engine and the condenser fans can be

electrically driven by means of inverters so as not to lower the

efficiency [44].

A trigeneration system is composed of three

subsystems which simultaneously produce electric, thermal and

cooling power. These three subsystems interact among each

other and compose a physical plant that can be categorized into

a cogeneration side and a cooling side [45, 46]. The CHP side

can be made up of a cogenerating micro turbine and a

combustion heat generator, for thermal back-up and peak

shaving. The cooling side can be composed of different

equipment for production of cooling power such as absorption

chillers. Use of trigeneration systems can help in increased

overall energy saving of 10% or even more.

Bottoming cycle systems seek to utilize the waste heat

and partially combusted waste gases from an industrial process

to generate electricity. If a micro turbine combined cycle is

used in conjunction with a bottoming organic Rankine cycle

then with reference to a micro gas turbine of size of about 100

kW, the combined configuration could increase the net electric

power by about 1/3, yielding an increase of the electrical

efficiency of up to 40%. This configuration would also mean

minimal changes to the standard CHP system since it merely

requires replacing the original heat recovery boiler with a heat

recovery vapor generator. The gas turbine exhaust would enter

the heat recovery vapor generator and discharged to the

environment after heating the bottoming working fluid. The

vapor generated would then expand through a turbine that

would drive an electrical generator. In the bottoming cycle the

working fluid should be a technically suitable organic fluid

which should be thermally stable, compatible with the plant’s process materials and low ozone depleting [47].

MICRO GAS TURBINE SYSTEMS—CURRENT SCENARIO

Micro-turbine systems being used today range in size from 25

to 80 kW. Future development of these systems aims to have an

increased power generation of upto 1000 kW.

The Environmental Technology Verification (ETV)

Program of the Environmental Protection Agency (EPA) made

an assessment of the micro-turbine systems which have been

employed for power generation in the US. The application of

micro-turbine based CHP systems which have been ETV

verified can help in the conservation of natural resources and

lead to cost savings for the consumer. ETV verification has also

led to wider technological acceptance of micro turbine based

CHP systems. One verified vendor has sold 13 MW of ETV-

verified micro-turbines for CHP applications in the United

States. Estimations by ETV suggests that sale in next five years

can lead to additional power generation of 55 MW. In the US micro-turbine market, Capstone has

launched a 30 kW product, Elliott has 45 and 80 kW products,

and Northern Research and Engineering Company has several

products in the 30 to 250 kW size range [48]. Elliott Energy

Systems (a subsidiary of Elliott Turbomachinery Company)

established a manufacturing and assembly unit in Stuart,

Florida with a production capacity of 4,000 units per year. It

launched two commercial prototypes: a 45 kW microturbine


(TA-45model) and another 80 kW (TA-80), and later, a 200

kW microturbine (TA-200). The TA-45 model is rated at 45

kW at ISO conditions and its main difference from other

manufacturers is that it has oil lubricated bearings and a system

starting at 24 volts, which is unique to micro-turbines. The TA-

80 and TA-200 micro-turbines models are similar to the TA-45

model. All three can generate electricity in 120/208/240V and

can work with different fuels: natural gas, diesel, kerosene,

alcohol, gasoline, propane, methanol and ethanol [49].

Honeywell Power Systems made use of four micro

turbines of 70 kW each, which were tested in the Jamacha

Landfill in New Hampshire - United States. The gas produced

in the landfills consisted of methane, carbon dioxide and air.

The gas was cooled to about 14 °C to remove moisture and

impurities and then compressed to about 550 kPa for the micro

turbine power. The turbines operated for 2000 hours without

showing any degradation in performance before being

uninstalled after 3 years [50].

In Europe, ABB Distributed Generation established a

50/50 joint venture with Volvo Aero Corporation in order to

develop a new generation of micro-turbines. This partnership

joined the experience of Volvo gas turbine for hybrid electric

vehicles with the experience of ABB in the generation and

energy conversion at high frequency resulting in the

development of a microturbine for cogeneration. Operating on

natural gas, the MT100 microturbine generates 100 kW of

electricity and 152 kW of thermal energy (hot water). As other

manufacturers of micro-turbines, the MT100 has a frequency

converter that allows the generator to operate at variable speed.

Turbec, which is among the leading micro-turbine

manufacturers, has developed a micro-turbine with an output of

100 kW. The company’s base product is the T100, a 100 kW

cogeneration unit which uses a single shaft recuperated

microturbine that rotates at 70,000 rpm. It is fuelled by natural

gas and uses a lean, pre-mix, low emission combustor

producing less than 15 ppm of NOx. Turbec aims to demonstrate the integration of three

technologies: micro-turbine, hot water fired absorption chiller

and ice storage thermal system [51]. It showcases the main

benefits resulting from the micro-trigeneration systems and a

flexible financing mechanism. The benefits embrace customers

(cost-effectiveness, reliability, power quality, and integrated

energy service), investors (low capital exposure and risk,

market opening, possibility to avoid major investments in new

centralized power plants) and the community as a whole. This

project contributes towards newer perspectives for micro-

turbine applications namely in South Europe with exports to

Brazil.

The present age utilization of the micro turbine is

limited due to the higher initial cost as compared to a

conventional power generation system. For example, based on

the use of a single Capstone micro gas turbine, the annual

energy cost of a non-cogeneration plant of the same capacity

was found to be 90,323 USD/year on a total investment of

23,077 USD. The payback period was found to be 3.1 years

and the minimal cost of electricity generation was 75

USD/MWh. In contrast, a cogeneration plant has a total

investment of 1, 36,797 USD and the annual energy cost was

found to be 65,416 USD/year. Therefore it is evident that

although the investment is higher, annual energy costs are

lower in the cogeneration case than in the conventional system.

Cogeneration systems can lead to savings of upto 24,907 USD

per year and the payback period is between 2.8 and 3.8 years

with the minimal cost of the electricity generated being 84

USD/MWh [52]. Therefore efforts have to be made so as to

reduce both the investment and the payback period in order to

make these systems economically feasible.

FUTURE PROSPECTS

The application area for micro gas turbines can be broadly

divided into two categories. One would be for portable power

generation and the other for production of thrust or power to

propel a vehicle.

Micro gas turbines have the primary advantage of high

specific energy and power density, making them ideal for

portable power generation. However since there are many

safety issues with the use of micro gas turbines such as the high

temperature exhaust limit, they should be used in a safely

controlled and protected environment. One such area where

micro gas turbines are attractive is in military where they can

replace primary batteries used in soldier-portable systems as

the main energy source. DARPA has come out with three

specific regimes in which portable micro gas turbines will find

place in future army applications. These are 20 W average with

a 50 W peak, 100 W average with a 200 W peak and 1 to 5 kW

power generator for high power drawing applications [53, 54].

Furthermore, micro gas turbines are also very well suited for

vehicle propulsion. The research and experimentation is being

done under two classes of applications in this field: the

propulsion of micro aerial vehicles (MAV) and distributed

propulsion, the concept of propelling a large unmanned vehicle

or a small manned aircraft using several small engines.

Gas turbines facilitate the realization of a small sized

unmanned aerial vehicle of dimensions less than 15 cm and

weighing less than 50 grams, known as MAV, which allow for

undercover surveillance operations by the military in outdoor

locations as well in interiors [55]. However, this application has

several obstacles in the form of development of a light weight

high power density turbine along with other components.

Conclusively, even though there are several obstacles

to the realization of practical application of micro gas turbines,

it holds a strong potential of overhauling the entire portable

power generation and vehicle propulsion scenario.

Automotive Industry Application Micro Gas Turbines hold the potential of bringing a

breakthrough in the automotive industry by enhancing their

range and overall performance. They reach their optimum

operating speed and temperature in seconds and so can be used

in short bursts to top up the batteries without compromising

fuel consumption or life-cycle. Depending on the energy


requirements, micro gas turbines operate either in sequence or

in combination to charge the batteries or to provide power

directly to the electric motors, as dictated by the propulsion

system supervisory system. Research is being extensively

carried out in the application of micro gas turbines in the

automotive industry with Jaguar Land Rover leading the front.

Jaguar Land Rover is working with SR Drives and

Bladon Jets and had received a grant from British Technology

Strategy Board in January 2010 to develop a micro gas turbine

for use in a powerful but low emissions car [56]. Jaguar

has unveiled the C-X75 concept, an extended range electric

vehicle that uses twin gas micro-turbines from Bladon Jets to

power two switched reluctance generators from SR Drives.

This plug-in, electric drive supercar has an all-electric range of

110 km (68 miles) with a potential top speed of 330 km/h (205

mph), acceleration from 0-100 km/h (62 mph) in 3.4 second

and 80-145 km/h (50-90 mph) in 2.3 seconds. The mid-

mounted 70 kW (94 bhp) micro gas-turbines can generate a

combined 140 kW (188 bhp) to charge the batteries and extend

the range of the car to 900 km (560 miles) and when in Track

mode, these micro gas turbines provide supplementary power

directly to the electric motors.

Wrightspeed Powertrains has developed a proprietary

truck technology “Route” and its powertrain is called a Range-

extended Electric Vehicle (REV). The Route system’s generator, instead of a gas or diesel internal combustion engine,

is a Capstone micro gas turbine which can run on CNG, diesel,

landfill gas and other fuels. It idles at 25,000 rpm and normally

operates at its peak-efficient speed of 96,000 rpm. The

microturbine charges the battery and once the batteries are

charged, it shuts off, as its job is only to supply electricity to

the vehicle.

Capstone Turbine Corporation has developed the

CMT-380, the world’s first microturbine-powered supercar.

This hybrid-electric sports car draws its power from lithium

polymer batteries and a Capstone C30 microturbine. The

electric generator and turbine components are mounted on a

single shaft, which is supported by air bearings so that no oil

changes are required ever. It uses a patented combustion system

to achieve extremely low exhaust emissions, and its patented

recuperator recycles the exhaust energy to get high fuel

efficiency.

It can be inferred that micro gas turbines when used in

plug-in hybrid vehicles can achieve extremely high fuel

economy, reduced greenhouse gas emissions and ultra-clean

vehicle emissions and still deliver the driving experience of a

high-performance vehicle. Thus, the future of the automotive

industry lies in the development and further application of

micro gas turbines in vehicle propulsion systems.

Aerial Vehicle Propulsion Systems Micro gas turbines possess the capability to be utilized as

distributed energy propulsion systems for Unmanned Aerial

Vehicles and small aircrafts. These micro gas turbines are

decentralized so that they can be embedded as small-scale

powerplants in the aircraft surface for flow/circulation-control

and thrust production. System studies have shown that by

employing hybrid systems utilizing micro gas turbines, as

much as 3 – 5% of total aircraft fuel burn reduction might be

realized from boundary layer ingestion [57].

French aerospace agency ONERA developed a micro-

UAV gas turbine engine which was tested at ONERA's Laerte

laboratory, near Paris. The micro gas turbine is 20mm in

diameter and height. Air and fuel, either hydrogen or propane,

are injected separately into the micro-turbine, which produces

mechanical energy that is then converted into electricity. With

the capacity to generate power in the range of 50-100W, it can

drive a micro-UAV with up to 20 cm wingspan for a duration of

30 minutes. Micro gas turbines ranging from 4kW to 11kW

have also been developed and manufactured by Locust Power

LLC to provide thrust for UAVs. These turbines rotate at

speeds up to 227,500rpm and can run on heavy fuels or natural

gas. They have the ability to operate with variable pitch fans

and propellers.

The flexibility thus offered by micro gas turbines to be

used as distributed energy systems for thrust production opens

up promising avenues in future propulsion technologies for

Unmanned Aerial Vehicles and small-sized aircrafts.

CONCLUSIONS

This paper, based on the literature survey, reviews the

development which has so far taken place in CHP generation

using micro gas turbines. It is evident that there is relatively a

big potential market for micro gas turbines due to the high

power density and low emissions being inherent in the system.

The constructional details of a micro turbine, the different

design details of the recuperator and combustor which can be

adopted in a micro turbine and the lucrativeness which lies in

using it in a hybrid CHP system present micro gas turbines as a

bright alternative to conventional power generation methods.

However, some safety issues, mainly related to the high

temperature levels obtained in these micro devices, still need to

be overcome. High sensitivity of electrical power production to

ambient temperature is another big problem faced in micro

turbine systems. The development of micro fluid machinery,

efficient at this very small length scale and compatible with the

constraints of current micro fabrication technology offers a big

challenge to developing the next generation of micro turbines.

Also, the cost effectiveness of micro turbine based CHP

systems in terms of the initial investment and the maintenance

cost remains a question. These systems usually result in greater

capital expenditures than non-cogeneration plants. This

incremental capital investment for cogeneration must be

justified by reduced annual energy costs and reduced payback

periods. The system efficiency attained for a mature technology

level is a key factor in determining which power source is the

best suited one for a particular application. When micro gas

turbines obtain efficiencies higher than or similar to those of

competing technologies such as by utilizing inlet air cooling,

trigeneration or bottoming organic Rankine cycles, several

fields of applications can be envisaged. A micro gas turbine


could namely be used both for the generation of the power

required for several portable systems (military and/or civil) as

well as for the propulsion of aerial vehicles. Furthermore, the

application of micro gas turbines in hybrid-electric vehicles has

shown promising results combining high fuel economy and

reduced emissions with high performance, proving its scope for

research and further application in the automotive industry at a

commercial scale.

REFERENCES

[1] Caresana, F.; Pelagalli, L., Comodi, G. &Vagni, S. (2008);

Micro combined plant with gas turbine and organic cycle,

Proceedings of the ASME Turbo Expo 2008, Volume 1,pp.

787-795, ISBN: 978-0-7918-4311-6, Berlin, May 2008

[2] GTW (2009) - Gas Turbine World Handbook 2009 –

Volume 27.

[3] ISO (1989). ISO 2314: 1989, “Gas turbines - Acceptance

tests”

[4] Jacobson, S. A., 1998, “Aero thermal Challenges in the

Design of a Micro fabricated Gas Turbine Engine”, AIAA 98-

2545,presented at 29th AIAA Fluid Dynamics Conference,

Albuquerque,NM.

[5] Bryzek, J., Petersen, K., McCulley, W., “Micro machines

on the March,” IEEE Spectrum, May 1994,pp. 20-31

[6] Epstein, A. H., Senturia, S. D., 1997, “Macro Power from

Micro Machinery”, Science, Vol. 276, p. 1211.

[7] Epstein, A.H. et al., 1997, “Micro-Heat Engines, Gas

Turbines, and Rocket Engines”, AIAA 97-1773, presented at

28th

AIAA Fluid Dynamics Conference, 4th AIAA Shear Flow

Control Conference, June 29-July 2, Snowmass Village CO.

[8] Nemeth, N.N., Manderscheid, J.M., Gyekenyesi, J.P.,

“Ceramic Analysis and Reliability Evaluation of Structures

(CARES),” NASA TP-2916, 1990.

[9] Spearing, S.M. and Chen, K.S., “Micro-Gas Turbine Engine

Materials and Structures,” presented at the21st Annual Cocoa Beach Conference and Exposition on Composites, Advanced

Ceramics, Materials and Structures, January 1997.

[10] Dawes, W.N., "The Practical Application of Solution-

Adaption to the Numerical Simulation of Complex

Turbomachinery Problems," Prog. Aerospace Science, Vol. 29,

1992, pp. 221-269.

[11] Youngren, H., "Analysis and Design of Transonic

Cascades with Splitter Vanes," Masters Thesis, Department of

Aeronautics and Astronautics, MIT, 1991

[12] Dhuler, V.R., Mehregany, M., Phillips, S.M., Lang, J.H.,

"A Comparative Study of Bearing Designs and Operational

Environments for Harmonic Side-Drive Micro motors," Proc.

IEEE Workshop on Micro Electro Mechanical Systems,

Travemunde, Germany, Feb. 1992, pp. 171-176.

[13] Piekos, E.S. and Breuer, K.S., "Design and Analysis of

Micro-fabricated High Speed Gas Journal Bearings," AIAA

Paper AIAA-97-1966, June 1997.

[14] Random Samples, Science, Vol. 275, 1997, p. 1571.

[15] M. Venturini, E. S. Barbieri, P. R. Spina, “Analysis of Innovative Micro-CHP Systems to Meet Household Energy

Demands, ICAE 2011.

[16] POLES 2.2: Prospective outlook on long-term energy

systems, Office for Official Publications of the European

Communities, Report EUR 17358 EN, 1996.

[17] Integration of renewable energy sources and distributed

generation in energy systems, Conference organised by the EC,

25–26 September 2001.

[18] P.A. Pilavachi, Power generation with gas turbine systems

and combined heat and power, Appl. Therm. Eng. 20(2000)

1421–1429.

[19] E. Macchi, S. Campanari, Future potential developments

of MTG: hybrid cycles and tri-generation, in: Conference on

Microturbine Generators, Institution of Mechanical Engineers,

1 December 2000.

[20] S. Minett, Thematic network on combined heat and

power––CHAPNET, EC ENERGY contract no. ENK5-

CT2001-00155, 2001.

[21] S. Minett, COGEN Europe, private communication, 2002.

[22] H. Cohen, G.F.C. Rogers, H.I.H. Saravanamuttoo, Gas

Turbine Theory, Prentice Hall, 1996.

[23] C.F. McDonald, Low-cost compact primary surface

recuperator concept for micro turbines, Appl. Therm. Eng.

20(2000) 471–497.

[24] Advanced Microturbine Systems, Program Plan for Fiscal

Years 2000 through 2006, US Department Of Energy, March

2000.

[25] H.J. Rasmusen, Optimised microturbine energy systems,

EC ENERGY Contract NNE5/20128/1999, 2001.

[26] A. Romier, R&D of high efficiency components for an

intercooled recuperated CHP gas turbine for combined heatand

efficient power, EC ENERGY Contract ENK5-CT2000-00070,

2000.

[27] G. Prata Dias, Trigeneration and integrated energy

services in south of Europe and Brazil, EC ENERGY

ContractNNE5/275/2001, 2002.

[28] S. Minett, Mini and micro CHP––market assessment and

development plan––MICROMAP, EC SAVE IIContract

4.1031/Z/00-023-2000, 2000.

[29] Work Programme: Energy, Environment and Sustainable

Development. Programme for Research, Technological

Development and Demonstration under the Fifth Framework

Programme, European Commission, 1999.

[30] C.F. McDonald, Heat recovery exchanger technology for

very small gas turbines, International Journal of Turbo and Jet

Engines 13 (4) (1996) 239–261.

[31] G. Lagerstrom, M. Xie, High performance and cost

effective recuperator for micro-gas turbines, in: Proceedings of

ASME Turbo Expo 2002, GT-2002-30402.

[32] C.F. McDonald, Recuperator considerations for future

higher efficiency microturbines, Applied Thermal Engineering

23 (12) (2003) 1463–1487.

[33]T. Nagasaki, R. Tokue, S. Kashima and Y.Ito, Conceptual

design of recuperator for ultramicro gas turbine, Proc. of Int.

Gas Turbine Congress, Tokyo, Japan, November 2003.


[34] C.F. McDonald, C. Rodgers, The ubiquitous personal

turbine-a power vision for the 21st century, Journal of

Engineering for Gas Turbines and Power 124 (4)(2002) 835–844.

[35] D.G. Wilson, Regenerative heat exchanger for micro

turbines, and improved type, in: Proceedings of ASME Turbo

Expo 2003, GT-2003-38871.

[36] C. M. Spadaccini, J. Lee,S. Lukachko, I. A.Waitz, “High

Power Density Silicon Combustion Systems for Micro Gas

Turbine Engines.” Proceedings of ASME TURBO EXPO 2002Amsterdam, The Netherlands, June 2002GT-2002-30082.

[37] Groshenry, C., “Preliminary Study of a Micro-Gas Turbine

Engine”, S.M. Thesis, Massachusetts Institute of Technology,1995

[38] Doddset al., “Combustion System Design”, Design of

Modern Gas Turbine Combustors, Mellor, A. M. (Editor),

Academic Press Limited, 1990.

[39] C. Rodgers, 25-5 kWe micro turbine design aspects,

ASME Paper00-GT-626, 2000.

[40] A.H. Lefebvre, Gas turbine combustion, Thermal Science

and Propulsion Center School of Mechanical Engineering,

Purdue University, 1983.

[41] B. Peters, K. Dielmann, "Capstone Microturbines:

Experiences with Different Gaseous and Liquid Fuels".

Workshop on Energy Efficiency & Emissions Reduction with

Micro Gas Turbines – Technology and Operating Experience,

October, 22nd, Tarragona,2002.

[42] P. Craig, The Capstone turbo generator as an alternative

power source, Society of Automotive Engineers, no. 970292,

1997.

[43] Weston, F., Seidman, N., L., James, C. Model Regulations

for the Output of Specified Air Emissions from Smaller-Scale

Electric Generation Resources, The Regulatory Assistance

Project, 2001.

[44] Zogg, R.; Bowman, J., Roth, K. &Brodrick, J. (2007).

Using MGTs for distributed generation. ASHRAE Journal, 49

(4), pp. 48-51 (2007), ISSN 0001-2491.

[45] P. Mancarella, From cogeneration to trigeneration: Energy

planning and evaluation in a competitive market framework,

Doctoral thesis, Politecnico di Torino, Torino, Italy, April 2006.

[46] P. Mancarella, Small-scale trigeneration systems:

components, models and applications, Proc. VI World Energy

System Conference, Torino, Italy, July 10-12, 2006, 234-241.

[47] Pepermans G.; Driesen J., Haeseldonckx, D., Belmans R.

&D’haeseleer, W. (2005). Distributed generation: definition,

benefits and issues, Energy Policy, 33 (2005), pp. 787–798,

ISSN 0301-4215.

[48] Advanced Microturbine Systems, Program Plan for Fiscal

Years 2000 through 2006, US Department Of Energy,

March 2000.

[49] Biasi, V. de Low cost and high efficiency make 30 to 80

kW microturbines attractive, Gas Turbine World, Jan.-Feb.,

Southport, 1998.

[50] Pierce, J. L. Microturbine Distributed Generation Using

Conventional and Waste

Fuel, Cogeneration and On-Site Power Production, James &

James Science Publishers, p. 45, v. 3, Issue 1, Jan-Feb, 2002.

[51] G. Prata Dias, Trigeneration and integrated energy

services in south of Europe and Brazil, EC ENERGY Contract

NNE5/275/2001, 2002.

[52] Marco Antônio Rosa do Nascimento, Micro Gas Turbine

Engine: A Review, Federal University of Itajubá – UNIFEI,

Brazil, DOI: 10.5772/54444

[53] Anon., “Meeting the energy needs of future warriors”, The national academies press, 2004.

[54] R.J. Nowak, “DARPA’s advanced energy technologies”, DARPA, 2000.

[55] R. Decuypere, D. Jerome, D. Hermans, “Paving the Way for Micro Aerial Vehicles”; International Symposium on

Innovative Aerial/Space Flyer Systems; University of Tokyo,

10-11 December 2004.

[56] Institution of MECHANICAL ENGINEERS, IMeche

News, December 2010.

[57] A.K. Sehra, W. Whitlow Jr., “Propulsion and power for 21st century aviation”, Progress in Aerospace Science, Vol. 40,

pp. 199-235, 2004.


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