Inverted Brayton Cycle With Exhaust Gas Recirculation—A Numerical Investigation

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Martin Henke ◽  
Thomas Monz ◽  
Manfred Aigner
Keyword(s):  
Atmospheric Pressure ◽  
Electrical Power ◽  
Exhaust Gas Recirculation ◽  
Coolant Temperature ◽  
Total Efficiency ◽  
Brayton Cycle ◽  
Exhaust Gas ◽  
Electrical Efficiency ◽  
Gas Recirculation ◽  
Cycle Efficiency

Microgas turbine (MGT) based combined heat and power (CHP) units provide a highly efficient, low-pollutant technology to supply heat and electrical power from fossil and renewable energy sources; however, pressurized MGT systems in an electrical power range from 1 to 5 kWel utilize very small turbocharger components. These components suffer from higher losses, like seal and tip leakages, resulting in a reduced electrical efficiency. This drawback is avoided by an inverted Brayton cycle (IBC) based system. In an IBC hot gas is produced in a combustion chamber at atmospheric pressure. Subsequently, the exhaust gas is expanded in a turbine from an atmospheric to a subatmospheric pressure level. In order to increase electrical efficiency, heat from the turbine exhaust gas is recuperated to the combustion air. After recuperation, the gas is compressed to atmospheric pressure and is discharged from the cycle. To decrease the power demand of the compressor, and thereby increasing the electrical cycle efficiency, it is crucial to further extract residual thermal power from the gas before compression. Coolant flows provided by heating applications can use this heat supply combined with heat from the discharged exhaust gas. The low pressure levels of the IBC result in high volumetric gas flows, enabling the use of large, highly efficient turbocharger components. Because of this efficiency benefit and the described cooling demand, micro-CHP applications provide an ideal field for utilization of the IBC. To further increase the total efficiency, discharged exhaust gas can be partially recirculated to the air inlet of the cycle. In the present paper a steady state analysis of an IBC with exhaust gas recirculation (EGR) is shown, and compared to the performance of a conventional Brayton cycle with equivalent component properties. Using EGR, it could be found that the sensitivity of the electrical cycle efficiency to the coolant temperature further increases. The sequent discussion focuses on the trade-off between total efficiency and electrical efficiency, depending on coolant temperature and EGR rate. The results show that EGR can increase the total efficiency by 10% to 15% points, while electrical efficiency decreases by 0.5% to 1% point. If the coolant temperature is below 35 °C, condensation of water vapor in the exhaust gas leads to a further increase of heat recovery efficiency. A validated in-house simulation tool based on turbocharger maps has been used for the calculations.

Inverted Brayton Cycle With Exhaust Gas Recirculation: A Numerical Investigation

2013 ◽  
Author(s):  
Martin Henke ◽  
Thomas Monz ◽  
Manfred Aigner
Keyword(s):  
Atmospheric Pressure ◽  
Electrical Power ◽  
Exhaust Gas Recirculation ◽  
Coolant Temperature ◽  
Total Efficiency ◽  
Brayton Cycle ◽  
Exhaust Gas ◽  
Electrical Efficiency ◽  
Gas Recirculation ◽  
Cycle Efficiency

Micro gas turbine (MGT) based CHP units provide a highly efficient, low-pollutant technology to supply heat and electrical power from fossil and renewable energy sources; however, pressurized MGT systems in an electrical power range from 1 to 5 kWel utilize very small turbocharger components. These components suffer from higher losses, like seal and tip leakages, resulting in a reduced electrical efficiency. This drawback is avoided by an Inverted Brayton Cycle (IBC) based system. In an IBC hot gas is produced in a combustion chamber at atmospheric pressure. Subsequently, the exhaust gas is expanded in a turbine from atmospheric to sub-atmospheric pressure level. In order to increase electrical efficiency, heat from the turbine exhaust gas is recuperated to the combustion air. After recuperation, the gas is compressed to atmospheric pressure and is discharged from the cycle. To decrease the power demand of the compressor, and thereby increasing the electrical cycle efficiency, it is crucial to further extract residual thermal power from the gas before compression. Coolant flows provided by heating applications can use this heat supply combined with heat from the discharged exhaust gas. The low pressure levels of the IBC result in high volumetric gas flows, enabling the use of large, highly efficient turbocharger components. Because of this efficiency benefit and the described cooling demand, micro-CHP applications provide an ideal field for utilization of the IBC. To further increase the total efficiency, discharged exhaust gas can be partially recirculated to the air inlet of the cycle. In the present paper a steady state analysis of an IBC with exhaust gas recirculation (EGR) is shown, and compared to the performance of a conventional Brayton Cycle with equivalent component properties. Using EGR, it could be found that the sensitivity of the electrical cycle efficiency to the coolant temperature further increases. The sequent discussion focuses on the trade-off between total efficiency and electrical efficiency, depending on coolant temperature and EGR rate. The results show that EGR can increase the total efficiency by 10 to 15 %-points, while electrical efficiency decreases by 0.5 to 1 %-point. If the coolant temperature is below 35 °C, condensation of water vapor in the exhaust gas leads to a further increase of heat recovery efficiency. A validated in-house simulation tool based on turbocharger maps has been used for the calculations.

Development of an experimental test bench and a psychrometric model for assessing condensation on a low-pressure exhaust gas recirculation cooler

2020 ◽  
pp. 146808742090973 ◽  
Author(s):  
Jose Galindo ◽  
Roberto Navarro ◽  
Daniel Tarí ◽  
Francisco Moya
Keyword(s):  
Internal Combustion Engines ◽  
Test Bench ◽  
Exhaust Gas Recirculation ◽  
Low Pressure ◽  
Coolant Temperature ◽  
Exhaust Gas ◽  
Warm Up ◽  
Mass Flow Rates ◽  
Cold Starts ◽  
Gas Recirculation

A test bench has been designed to assess condensation formation produced on the interior of a low-pressure exhaust gas recirculation cooler working with hot stream of humid air representing an engine warm-up stage, when its coolant starts from very cold conditions. An experimental campaign has been conducted with three different exhaust gas recirculation mass flow rates, four exhaust gas recirculation inlet temperatures and three different coolant initial temperatures, covering common conditions found in the low-pressure exhaust gas recirculation system of internal combustion engines under cold starts. The transient experimental results are analyzed and compared with a simple psychrometric condensation model, obtaining a good correlation and reproducing the trends of the condensation, even though an overprediction of the condensates of around 20%–40% exists due to the strong hypotheses assumed. The warm-up tests are most sensitive to the initial coolant temperature. For example, an engine starting at –10 °C ambient temperature could require 10 min to stop producing water in the low-pressure exhaust gas recirculation cooler, with an accumulated quantity during the warm-up of about 100 mL of condensates.

Investigation of a FLOX®-Based Combustor for a Micro Gas Turbine With Exhaust Gas Recirculation

2017 ◽  
Author(s):  
S. Hasemann ◽  
A. Huber ◽  
C. Naumann ◽  
M. Aigner
Keyword(s):  
Gas Turbines ◽  
Combustion Process ◽  
Exhaust Gas Recirculation ◽  
Chemical Kinetic ◽  
Working Fluid ◽  
Total Efficiency ◽  
Exhaust Gas ◽  
Low Oxygen ◽  
Micro Gas Turbine ◽  
Gas Recirculation

Micro gas turbines (MGT) offer interesting advantages for the use in combined heat and power (CHP) systems. A possibility to raise the total efficiency of a MGT is the introduction of an external exhaust gas recirculation (EGR). The composition of the working fluid due to EGR affects the combustion process and the formation of pollutants. Changes in flame position, flame volume and flame intensity as well as rising CO emissions in state of the art industrial burners have been described by several authors before. This paper describes the experimental investigation of a single stage FLOX®-based combustor for a MGT in the power range of 1–3 kWel applied with EGR. The tests were performed on an atmospheric test rig with optical access. The combustion air was preheated up to 718 °C and diltued with N2, CO2 and steam. A probe of the exhaust gas was analyzed for emissions and OH* chemiluminescence measurements were performed. In addition to the experiments, chemical kinetic simulations were performed. Results show, that the examined combustor is able to work stable even at very low oxygen levels (down to 12.6 %) at combustor inlet, although the possible range of operation under EGR conditions is reduced. The measured increase of CO emissions matches to the performed simulations.

Effect of Engine Operating Conditions and Coolant Temperature on the Physical and Chemical Properties of Deposits From an Automotive Exhaust Gas Recirculation Cooler

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Bhaskar Prabhakar ◽  
André L. Boehman
Keyword(s):  
Heat Exchanger ◽  
Load Condition ◽  
Exhaust Gas Recirculation ◽  
Control Flow ◽  
Operating Conditions ◽  
Coolant Temperature ◽  
Exhaust Gas ◽  
Low Load ◽  
Egr Cooler ◽  
Gas Recirculation

The effect of engine operating conditions on exhaust gas recirculation (EGR) cooler fouling was studied using a 6.4 L V-8 common rail turbodiesel engine. An experimental setup, which included a custom-made shell and tube heat exchanger (EGR cooler) with six surrogate tubes, was designed to control flow variables independently. The engine was operated at 2150 rpm, 203 Nm and 1400 rpm, 81 Nm, representing medium and low load conditions, respectively, and the coolant to the heat exchanger was circulated at 85 °C and 40 °C. Heat exchanger effectiveness and pressure drop was monitored throughout the tests. Deposits from the EGR cooler were collected every 1.5 h for a total of 9 h, and their microstructure was analyzed using a scanning electron microscope while their chemical composition was analyzed using a pyrolysis GC-MS apparatus, and the elemental weight percentages were obtained using a CHN analyzer. The results of these analyses showed that the effectiveness of the EGR cooler drops rapidly initially and asymptotes in a few hours. The medium load condition had a higher effectiveness loss due to a greater accumulation of deposits inside the EGR cooler, mostly due to increased thermophoresis, and produced smaller and coarse particles. The low load condition had lower effectiveness loss but produced bigger particles mostly due to excess hydrocarbons. Coolant temperature played a significant role in altering the deposit microstructure and in increasing the amount of condensed hydrocarbons. More deposits were produced for the cold coolant condition, indicating that lower coolant temperature promotes greater hydrocarbon condensation and thermophoresis. These results indicate the complex nature of fouling in automotive heat exchangers.

Low NOX Combustion of DME by Exhaust Gas Recirculation Under the High Pressure

2011 ◽  
Author(s):  
Hiroaki Takeuchi ◽  
Tatsuro Tanikawa ◽  
Ryosuke Matsumoto ◽  
Mamoru Ozawa
Keyword(s):  
High Pressure ◽  
Combustion Chamber ◽  
Oxygen Concentration ◽  
Atmospheric Pressure ◽  
Exhaust Gas Recirculation ◽  
Nox Emission ◽  
Exhaust Gas ◽  
Mixing Ratio ◽  
Low Nox Combustion ◽  
Gas Recirculation

This study focuses on the fundamental characteristics of DME (Dimethyl ether) combustion with exhaust gas recirculation EGR, aiming at development of the low NOx combustion technology of DME under the high pressure. EGR reduces the NOx emission by recirculating the exhaust gas into the combustion chamber to control the oxygen concentration and the combustion gas temperature. EGR at the high mixing ratio, however, may lead to unstable combustion of conventional fuels, methane or city gas. On the other hand, DME has high potential of applicability of EGR even at the high mixing ratio because of its high burning velocity and low ignition temperature. In this experiment, the oxygen concentration and the combustion air temperature were systematically regulated, so that the exhaust gas recirculation was simulated. The combustion test was conducted with laboratory-scale 8kW combustor. Initial air ratio λ was 1.5. At the atmospheric pressure, the exhaust gas recirculation can be applied to 54% of the EGR ratio. The NOx concentration reduces to 10ppm at 0%-O2, which corresponds to about 22% of NOx emission without EGR. However, the flame became unstable at 54% of the EGR ratio. By increasing the pressure in the combustion chamber, the NOx concentration increased the 84ppm at 0.3MPa-without EGR. The maximum EGR ratio can be applied to 59% under the pressure of 0.3MPa, wihch is almost the same with that at atmospheric pressure. The NOx emission in the exhaust gas decreases to 17ppm. The exhaust gas recirculation is effective to the low NOx combustion of DME at the high pressure.

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