*Cogeneration by Naresh Meena 10EMBME036 MECHNICAL 8th SEM.

*TO THE TRAINERThis PowerPoint presentation can be used to train people about the basics of cogeneration. The information on the slides is the minimum information that should be explained. The trainer notes for each slide provide more detailed information, but it is up to the trainer to decide if and how much of this information is presented also.

Additional materials that can be used for the training session are available on www.energyefficiencyasia.org under Energy Equipment and include:Textbook chapter on this energy equipment that forms the basis of this PowerPoint presentation but has more detailed informationQuiz ten multiple choice questions that trainees can answer after the training sessionWorkshop exercise a practical calculation related to this equipmentOption checklist a list of the most important options to improve energy efficiency of this equipmentCompany case studies participants of past courses have given the feedback that they would like to hear about options implemented at companies for each energy equipment. More than 200 examples are available from 44 companies in the cement, steel, chemicals, ceramics and pulp & paper sectors

* Cogeneration

IntroductionTypes of cogeneration systemsAssessment of cogeneration systemsEnergy efficiency opportunities

*

*IntroductionGeneration of multiple forms of energy in one system: heat and powerDefined by its prime moversReciprocating enginesCombustion or gas turbines, Steam turbinesMicroturbinesFuel cells

Whats a Cogeneration/CHP System?

*A Cogeneration system or a Combined Heat & Power System (CHP) is the sequential or simultaneous generation of multiple forms of useful energy. It is usually mechanical (power) and thermal (heat) in a single, integrated system.It is the type of equipment, or prime mover that drives the overall system, that typically identifies the CHP system. Prime movers for CHP systems include reciprocating engines, combustion or gas turbines, steam turbines, microturbines, and fuel cells. These prime movers are capable of burning a variety of fuels, including natural gas, coal, oil, and alternative fuels to produce shaft power or mechanical energy.

*IntroductionIncreased efficiency of energy conversion and useLower emissions, especially CO2Ability to use waste materialsLarge cost savingsOpportunity to decentralize the electricity generationPromoting liberalization in energy markets

Benefits of Cogeneration / CHP)

*Provided the cogeneration is optimized in terms of sized according to the heat demand, it brings the following benefitsIncreased efficiency of energy conversion and useLower emissions to the environment, in particular of CO2, the main greenhouse gasIn some cases, biomass fuels and some waste materials such as refinery gases, process or agricultural waste (either anaerobically digested or gasified), are used. These substances which serve as fuels for cogeneration schemes, increases the cost-effectiveness and reduces the need for waste disposalLarge cost savings, providing additional competitiveness for industrial and commercial users while offering affordable heat for domestic users alsoAn opportunity to move towards more decentralized forms of electricity generation, where plants are designed to meet the needs of local consumers, providing high efficiency, avoiding transmission losses and increasing flexibility in system use. This will particularly be the case if natural gas is the energy carrierAn opportunity to increase the diversity of generation plant, and provide competition in generation. Cogeneration provides one of the most important vehicles for promoting liberalization in energy markets.

Type of Cogeneration SystemsSteam turbineGas turbineReciprocating engineOther classifications:

- Topping cycle- Bottoming cycle

*

Type of Cogeneration SystemsWidely used in CHP applicationsOldest prime mover technologyCapacities: 50 kW to hundreds of MWsThermodynamic cycle is the Rankin cycle that uses a boilerMost common types Back pressure steam turbine Extraction condensing steam turbine

Steam Turbine Cogeneration System

*Steam turbines are one of the most versatile and oldest prime mover technologies that are still in general production. Steam turbines are widely used for combined heat and power (CHP) applications.The capacity of steam turbines can range from 50 kW to several hundred MWs for large utility power plants. The thermodynamic cycle for the steam turbine is the Rankine cycle. This cycle is the basis for conventional power generating stations and consists of a heat source that converts water to high-pressure steam. The developed condensate from the process returns to the feedwater pump for continuation of the cycle. The two types of steam turbines most widely used are the back pressure and the extraction-condensing types. The choice between backpressure turbine and extraction-condensing turbine depends mainly on the quantities of power and heat, quality of heat, and economic factors.

*Steam exits the turbine at a higher pressure that the atmospheric

Back Pressure Steam Turbine

Fuel

Figure: Back pressure steam turbineAdvantages:Simple configurationLow capital costLow need of cooling water High total efficiency

Disadvantages:Larger steam turbineElectrical load and output can not be matched

Type of Cogeneration Systems

*Back pressure steam turbine is the most simple configuration. Steam exits the turbine at a pressure higher or at least equal to the atmospheric pressure. This is why the term back- pressure is used. After the steam exits the turbine, it is fed to the load where it releases heat and is condensed. The condensate then returns to the system.(click once) The back pressure system has the following advantages: Simple configuration with few components; low capital costs; reduced or no need of cooling water; high total efficiency as there is no heat rejection to the environment through a condenser. (click once) The back pressure system has the following disadvantages: The steam turbine is larger for the same power output because it operates under lower enthalpy difference of steam. The generated electricity is controlled by the thermal load. This results in little or no flexibility to match electrical output to electrical load.

*Steam obtained by extraction from an intermediate stageRemaining steam is exhaustedRelatively high capital cost, lower total efficiencyControl of electrical power independent of thermal load

Extraction Condensing Steam Turbine

Figure: Extraction condensing steam turbineType of Cogeneration Systems

*In an extraction condensing steam turbine system, the steam for the thermal load is obtained through extraction from one or more intermediate stages at appropriate pressure and temperature. The remaining steam is exhausted to the pressure of the condenser. In comparison to the back - pressure system, the condensing type turbine has a higher capital cost and generally a lower total efficiency. To its advantage is that the extraction condensing steam turbine can control the electrical power independent of the thermal load by proper regulation of the steam flow rate through the turbine to a certain extent.

*Operate on thermodynamic Brayton cycleatmospheric air compressed, heated, expandedexcess power used to produce powerNatural gas is most common fuel1MW to 100 MW rangeRapid developments in recent yearsTwo types: open and closed cycle

Gas Turbine Cogeneration System

Type of Cogeneration Systems

*Gas turbine systems operate on the thermodynamic cycle that is known as the Brayton cycle. In a Brayton cycle, atmospheric air is compressed, heated, and then expanded. It is the excess of power produced by the turbine or expander, over that consumed by the compressor, that is used for power generation.Gas turbine cogeneration systems can produce all or a part of the energy requirement of the site. Though natural gas is most commonly used, other fuels such as light fuel oil or diesel can also be employed. The typical range of gas turbines varies from a fraction of a MW to around 100 MW. Gas turbine cogeneration has probably experienced the most rapid development in the recent years due to the greater availability of natural gas, rapid progress in the technology, significant reduction in installation costs, and better environmental performance. There are two types of gas turbine cogeneration systems: open cycle and close cycle. These are explained on the next slides

*Open Brayton cycle: atmospheric air at increased pressure to combustor

Open Cycle Gas Turbine

Old/small units: 15:1 New/large units: 30:1Exhaust gas at 450-600 oC High pressure steam produced: can drive steam turbine

Figure: Open cycle gas turbine cogenerationType of Cogeneration Systems

*Most of the currently available gas turbine systems operate on the open Brayton cycle where a compressor takes in air from the atmosphere and derives it at increased pressure to the combustor. This is also called Joule cycle when irreversibilities are ignored. The air temperature is also increased due to compression. Older and smaller units operate at a pressure ratio in the range of 15:1, while the newer and larger units operate at pressure ratios approaching 30:1. Looking at this figure, the air is delivered through a diffuser to a constant-pressure combustion chamber, where fuel is injected and burned. Combustion takes place with high excess air and the exhaust gases exit the combustor at high temperature and with oxygen concentrations of up to 15-16%. The highest temperature of the cycle appears at this point; with current technology this is about 1300C. The high pressure and high temperature exhaust gases enter the gas turbine and produce mechanical work to drive the compressor and the load. The exhaust gases leave the turbine at a considerable temperature (450-600C), which makes high-temperature heat recovery ideal. The produced steam can have high pressure and temperature. This makes it appropriate not only for thermal processes but also for driving a steam turbine thus producing additional power.

*Working fluid circulates in a closed circuit and does not cause corrosion or erosionAny fuel, nuclear or solar energy can be used

Closed Cycle Gas TurbineFigure: Closed Cycle Gas Turbine Cogeneration SystemType of Cogeneration Systems

*In the closed-cycle system, the working fluid is usually helium or air and it circulates in a closed circuit. It is heated in a heat exchanger before entering the turbine, and it is cooled down after the exit of the turbine releasing useful heat. This way the working fluid remains clean and it does not cause corrosion or erosion. Source of heat can be the external combustion of any fuel. Nuclear energy or solar energy can also be used.

*Used as direct mechanical drives

Reciprocating Engine Cogeneration Systems

Many advantages: operation, efficiency, fuel costsUsed as direct mechanical drivesFour sources of usable waste heat

Type of Cogeneration Systems

*Reciprocating engines are well suited to a variety of distributed generation applications, as well as industrial, commercial, and institutional facilities for power generation and CHP.Reciprocating engines have many advantages:Operation: reciprocating engines start quickly, follow load well, have good part-load efficiencies, and generally have high reliabilities. In many cases, multiple reciprocating engine units further increase overall plant capacity and availability. Efficiency & costs: Reciprocating engines have higher electrical efficiencies than gas turbines of comparable size, and therefore lower fuel-related operating costs. Reciprocating engines are also used extensively as direct mechanical drives in applications such as water pumping, air and gas compression and chilling/refrigeration.While the use of reciprocating engines is expected to grow in various distributed generation applications, the most prevalent on-site generation application for natural gas SI engines has traditionally been CHP, and this trend is likely to continue. There are four sources of usable waste heat from a reciprocating engine: exhaust gas, engine jacket cooling water, lube oil cooling water, and turbocharger cooling.

*Supplied fuel first produces power followed by thermal energyThermal energy is a by product used for process heat or otherMost popular method of cogeneration

Topping Cycle

Type of Cogeneration Systems

*Cogeneration systems are normally classified according to the sequence of energy use and the adopted operating schemes. A cogeneration system can be classified as either a topping or a bottoming cycle on the basis of the sequence of energy use.(click once) In a topping cycle, the supplied fuel is used to first produce power and then thermal energy, which is the by-product of the cycle. This is used to satisfy process heat or other thermal requirements. Topping cycle cogeneration is widely used and is the most popular method of cogeneration.Examples include a combined-cycle topping system; steam turbine topping system; and gas turbine topping system

*Bottoming Cycle

Primary fuel produces high temperature thermal energyRejected heat is used to generate powerSuitable for manufacturing processes

Type of Cogeneration Systems

*In a bottoming cycle, the primary fuel produces high temperature thermal energy and the rejected heat from the process is used to generate power through a recovery boiler and a turbine generator. Bottoming cycles are suitable for manufacturing processes that require heat at high temperature in furnaces and kilns, and that reject heat at significantly high temperatures. Typical areas of application include cement, steel, ceramic, gas and petrochemical industries.

Assessment of Cogeneration SystemsOverall Plant Heat Rate (kCal/kWh):

Ms= Mass Flow Rate of Steam (kg/hr)hs= Enthalpy of Steam (kCal/kg)hw= Enthalpy of Feed Water (kCal/kg)

Overall Plant Fuel Rate (kg/kWh)

Performance Terms & Definitions

*Overall Plant Heat Rate is Ms x (hs hw) / Power output (kW), where Ms = Mass Flow Rate of Steam; hs = Enthalpy of Steam; hw = Enthalpy of Feed Water.(Click once) Overall Plant Fuel Rate is Fuel consumption *(kg/hr) / Power output (kW)

*Steam turbine efficiency (%):

Steam Turbine PerformanceGas Turbine PerformanceOverall gas turbine efficiency (%) (turbine compressor):

Assessment of Cogeneration Systems

*For steam turbine performance the steam turbine efficiency is calculated according to the formula (let audience reflect over the formula before continuing).(click once) For gas turbine performance, the overall turbine efficiency is calculated according to the formula.An example calculation of the performance of a steam turbine cogeneration system is included in the cogeneration chapter.

*Heat recovery steam generator efficiency (%):

Ms= Steam Generated (kg/hr)hs= Enthalpy of Steam (kCal/kg)hw= Enthalpy of Feed Water (kCal/kg)Mf= Mass flow of Flue Gas (kg/hr)t-in= Inlet Temperature of Flue Gas (0C)t-out= Outlet Temperature of Flue Gas (0C)Maux= Auxiliary Fuel Consumption (kg/hr)Heat Recovery Steam Generator (HRSG) Performance

Assessment of Cogeneration Systems

*In addition to the turbine, the cogeneration system also has a heat recovery steam generator, which also impacts the performance of the cogeneration system. The formula used to calculate its efficiency is shown on this slide. The chapter Waste Recovery has more details.

*Energy Efficiency OpportunitiesSteam turbine:Keep condenser vacuum at optimum valueKeep steam temperature and pressure at optimum valueAvoid part load operation and starting & stopping

Steam Turbine Cogeneration System

*First we will look at the energy efficiency opportunities in steam turbine cogeneration systems. Condenser vacuum or back-pressure is the most important factor as a small deviation from optimum can produce a significant change in efficiency. There are a number of reasons why condenser vacuum may vary from the optimum value such as when the cooling water inlet temperature is different from the design value. This is the most common reason for variations in condenser vacuum because the temperature of the cooling water is significantly influenced by weather conditions such as temperature and humidity. Condenser vacuum may also change because of cooling water flow rate, or that the condenser tubes are fouled, and due to air leaks into the condenser. If the steam temperature and pressure conditions at the inlet to the steam turbine vary from the design optimum conditions, the turbine may not be able to operate at maximum efficiency. Variations in steam conditions can be due to errors in plant design, incorrect plant operation or fouling within the boiler.Market decisions to operate the generating unit at certain loads for certain periods can have the major influence on its average thermal efficiency. Similarly, market decision on when the plant is to come on and off line also has a bearing on average thermal efficiency because of energy losses while starting or stopping the system.

*Energy Efficiency OpportunitiesGas Turbine Cogeneration System

Gas turbine manage the following parameters:

Gas temperature and pressurePart load operation and starting & stoppingTemperature of hot gas and exhaust gasMass flow through gas turbineAir pressure

*Finally, we will look at the energy efficiency opportunities in gas turbine cogeneration systems. If the gas temperature and pressure conditions at the gas turbine inlet vary from the design optimum conditions, the turbine may not be able to operate at maximum efficiency. Variations in gas conditions can be due to errors in plant design or incorrect plant operation.Generating unit efficiencies at part loads can be maintained close to the design values by giving attention to all the above items. However, once again market decisions to operate the generating unit at certain loads for certain periods will have the major influence on its average thermal efficiency. The temperature of the exhaust gas is also a factor. Increased temperature generally results in increased power output. Reduced temperature generally results in increased power output. Also, higher mass flows result in higher power output.

*

THANK YOU

*Hello.

*TO THE TRAINERThis PowerPoint presentation can be used to train people about the basics of cogeneration. The information on the slides is the minimum information that should be explained. The trainer notes for each slide provide more detailed information, but it is up to the trainer to decide if and how much of this information is presented also.

Additional materials that can be used for the training session are available on www.energyefficiencyasia.org under Energy Equipment and include:Textbook chapter on this energy equipment that forms the basis of this PowerPoint presentation but has more detailed informationQuiz ten multiple choice questions that trainees can answer after the training sessionWorkshop exercise a practical calculation related to this equipmentOption checklist a list of the most important options to improve energy efficiency of this equipmentCompany case studies participants of past courses have given the feedback that they would like to hear about options implemented at companies for each energy equipment. More than 200 examples are available from 44 companies in the cement, steel, chemicals, ceramics and pulp & paper sectors

*

*A Cogeneration system or a Combined Heat & Power System (CHP) is the sequential or simultaneous generation of multiple forms of useful energy. It is usually mechanical (power) and thermal (heat) in a single, integrated system.It is the type of equipment, or prime mover that drives the overall system, that typically identifies the CHP system. Prime movers for CHP systems include reciprocating engines, combustion or gas turbines, steam turbines, microturbines, and fuel cells. These prime movers are capable of burning a variety of fuels, including natural gas, coal, oil, and alternative fuels to produce shaft power or mechanical energy.

*Provided the cogeneration is optimized in terms of sized according to the heat demand, it brings the following benefitsIncreased efficiency of energy conversion and useLower emissions to the environment, in particular of CO2, the main greenhouse gasIn some cases, biomass fuels and some waste materials such as refinery gases, process or agricultural waste (either anaerobically digested or gasified), are used. These substances which serve as fuels for cogeneration schemes, increases the cost-effectiveness and reduces the need for waste disposalLarge cost savings, providing additional competitiveness for industrial and commercial users while offering affordable heat for domestic users alsoAn opportunity to move towards more decentralized forms of electricity generation, where plants are designed to meet the needs of local consumers, providing high efficiency, avoiding transmission losses and increasing flexibility in system use. This will particularly be the case if natural gas is the energy carrierAn opportunity to increase the diversity of generation plant, and provide competition in generation. Cogeneration provides one of the most important vehicles for promoting liberalization in energy markets.

*

*Steam turbines are one of the most versatile and oldest prime mover technologies that are still in general production. Steam turbines are widely used for combined heat and power (CHP) applications.The capacity of steam turbines can range from 50 kW to several hundred MWs for large utility power plants. The thermodynamic cycle for the steam turbine is the Rankine cycle. This cycle is the basis for conventional power generating stations and consists of a heat source that converts water to high-pressure steam. The developed condensate from the process returns to the feedwater pump for continuation of the cycle. The two types of steam turbines most widely used are the back pressure and the extraction-condensing types. The choice between backpressure turbine and extraction-condensing turbine depends mainly on the quantities of power and heat, quality of heat, and economic factors.

*Back pressure steam turbine is the most simple configuration. Steam exits the turbine at a pressure higher or at least equal to the atmospheric pressure. This is why the term back- pressure is used. After the steam exits the turbine, it is fed to the load where it releases heat and is condensed. The condensate then returns to the system.(click once) The back pressure system has the following advantages: Simple configuration with few components; low capital costs; reduced or no need of cooling water; high total efficiency as there is no heat rejection to the environment through a condenser. (click once) The back pressure system has the following disadvantages: The steam turbine is larger for the same power output because it operates under lower enthalpy difference of steam. The generated electricity is controlled by the thermal load. This results in little or no flexibility to match electrical output to electrical load.

*In an extraction condensing steam turbine system, the steam for the thermal load is obtained through extraction from one or more intermediate stages at appropriate pressure and temperature. The remaining steam is exhausted to the pressure of the condenser. In comparison to the back - pressure system, the condensing type turbine has a higher capital cost and generally a lower total efficiency. To its advantage is that the extraction condensing steam turbine can control the electrical power independent of the thermal load by proper regulation of the steam flow rate through the turbine to a certain extent.

*Gas turbine systems operate on the thermodynamic cycle that is known as the Brayton cycle. In a Brayton cycle, atmospheric air is compressed, heated, and then expanded. It is the excess of power produced by the turbine or expander, over that consumed by the compressor, that is used for power generation.Gas turbine cogeneration systems can produce all or a part of the energy requirement of the site. Though natural gas is most commonly used, other fuels such as light fuel oil or diesel can also be employed. The typical range of gas turbines varies from a fraction of a MW to around 100 MW. Gas turbine cogeneration has probably experienced the most rapid development in the recent years due to the greater availability of natural gas, rapid progress in the technology, significant reduction in installation costs, and better environmental performance. There are two types of gas turbine cogeneration systems: open cycle and close cycle. These are explained on the next slides

*Most of the currently available gas turbine systems operate on the open Brayton cycle where a compressor takes in air from the atmosphere and derives it at increased pressure to the combustor. This is also called Joule cycle when irreversibilities are ignored. The air temperature is also increased due to compression. Older and smaller units operate at a pressure ratio in the range of 15:1, while the newer and larger units operate at pressure ratios approaching 30:1. Looking at this figure, the air is delivered through a diffuser to a constant-pressure combustion chamber, where fuel is injected and burned. Combustion takes place with high excess air and the exhaust gases exit the combustor at high temperature and with oxygen concentrations of up to 15-16%. The highest temperature of the cycle appears at this point; with current technology this is about 1300C. The high pressure and high temperature exhaust gases enter the gas turbine and produce mechanical work to drive the compressor and the load. The exhaust gases leave the turbine at a considerable temperature (450-600C), which makes high-temperature heat recovery ideal. The produced steam can have high pressure and temperature. This makes it appropriate not only for thermal processes but also for driving a steam turbine thus producing additional power.

*In the closed-cycle system, the working fluid is usually helium or air and it circulates in a closed circuit. It is heated in a heat exchanger before entering the turbine, and it is cooled down after the exit of the turbine releasing useful heat. This way the working fluid remains clean and it does not cause corrosion or erosion. Source of heat can be the external combustion of any fuel. Nuclear energy or solar energy can also be used.

*Reciprocating engines are well suited to a variety of distributed generation applications, as well as industrial, commercial, and institutional facilities for power generation and CHP.Reciprocating engines have many advantages:Operation: reciprocating engines start quickly, follow load well, have good part-load efficiencies, and generally have high reliabilities. In many cases, multiple reciprocating engine units further increase overall plant capacity and availability. Efficiency & costs: Reciprocating engines have higher electrical efficiencies than gas turbines of comparable size, and therefore lower fuel-related operating costs. Reciprocating engines are also used extensively as direct mechanical drives in applications such as water pumping, air and gas compression and chilling/refrigeration.While the use of reciprocating engines is expected to grow in various distributed generation applications, the most prevalent on-site generation application for natural gas SI engines has traditionally been CHP, and this trend is likely to continue. There are four sources of usable waste heat from a reciprocating engine: exhaust gas, engine jacket cooling water, lube oil cooling water, and turbocharger cooling.

*Cogeneration systems are normally classified according to the sequence of energy use and the adopted operating schemes. A cogeneration system can be classified as either a topping or a bottoming cycle on the basis of the sequence of energy use.(click once) In a topping cycle, the supplied fuel is used to first produce power and then thermal energy, which is the by-product of the cycle. This is used to satisfy process heat or other thermal requirements. Topping cycle cogeneration is widely used and is the most popular method of cogeneration.Examples include a combined-cycle topping system; steam turbine topping system; and gas turbine topping system

*In a bottoming cycle, the primary fuel produces high temperature thermal energy and the rejected heat from the process is used to generate power through a recovery boiler and a turbine generator. Bottoming cycles are suitable for manufacturing processes that require heat at high temperature in furnaces and kilns, and that reject heat at significantly high temperatures. Typical areas of application include cement, steel, ceramic, gas and petrochemical industries.

*Overall Plant Heat Rate is Ms x (hs hw) / Power output (kW), where Ms = Mass Flow Rate of Steam; hs = Enthalpy of Steam; hw = Enthalpy of Feed Water.(Click once) Overall Plant Fuel Rate is Fuel consumption *(kg/hr) / Power output (kW)

*For steam turbine performance the steam turbine efficiency is calculated according to the formula (let audience reflect over the formula before continuing).(click once) For gas turbine performance, the overall turbine efficiency is calculated according to the formula.An example calculation of the performance of a steam turbine cogeneration system is included in the cogeneration chapter.

*In addition to the turbine, the cogeneration system also has a heat recovery steam generator, which also impacts the performance of the cogeneration system. The formula used to calculate its efficiency is shown on this slide. The chapter Waste Recovery has more details.*First we will look at the energy efficiency opportunities in steam turbine cogeneration systems. Condenser vacuum or back-pressure is the most important factor as a small deviation from optimum can produce a significant change in efficiency. There are a number of reasons why condenser vacuum may vary from the optimum value such as when the cooling water inlet temperature is different from the design value. This is the most common reason for variations in condenser vacuum because the temperature of the cooling water is significantly influenced by weather conditions such as temperature and humidity. Condenser vacuum may also change because of cooling water flow rate, or that the condenser tubes are fouled, and due to air leaks into the condenser. If the steam temperature and pressure conditions at the inlet to the steam turbine vary from the design optimum conditions, the turbine may not be able to operate at maximum efficiency. Variations in steam conditions can be due to errors in plant design, incorrect plant operation or fouling within the boiler.Market decisions to operate the generating unit at certain loads for certain periods can have the major influence on its average thermal efficiency. Similarly, market decision on when the plant is to come on and off line also has a bearing on average thermal efficiency because of energy losses while starting or stopping the system.

*Finally, we will look at the energy efficiency opportunities in gas turbine cogeneration systems. If the gas temperature and pressure conditions at the gas turbine inlet vary from the design optimum conditions, the turbine may not be able to operate at maximum efficiency. Variations in gas conditions can be due to errors in plant design or incorrect plant operation.Generating unit efficiencies at part loads can be maintained close to the design values by giving attention to all the above items. However, once again market decisions to operate the generating unit at certain loads for certain periods will have the major influence on its average thermal efficiency. The temperature of the exhaust gas is also a factor. Increased temperature generally results in increased power output. Reduced temperature generally results in increased power output. Also, higher mass flows result in higher power output.

*Hello.