Rolf Gabrielsson

Computational and Experimental Investigation of Emissions in a Highly Humidified Premixed Flame

Emission formation and flame stability were investigated, both experimentally and computationally, for premixed combustion with varying amounts of water vapor in the mixture. Emission measurements were made in a gas turbine combustor at atmospheric conditions, using Danish Natural Gas (NG) as fuel. The emissions were mapped as a function of humidity, inlet air temperature, equivalence ratio and aerodynamic load. Operating conditions were chosen to match what can be expected from e.g. an EvGT cycle for power generation. The inlet air temperature was slightly lower than the inlet temperatures that would be found in a recuperated cycle. The degree of humidity was varied from 0w% to 33w% of the airflow in the experiment, while the air inlet temperature was varied from 500K to 800K. Computations were made using a single Perfectly Stirred Reactor (PSR) model and a reaction scheme with 821 reactions and 69 species. It was found that the NOX emissions were strongly reduced by the addition of water. Most of this decrease vanishes in practical combustion since richer combustion is required to keep CO emissions (combustion efficiency) at a tolerable level. The maximum humidity was found to be dependent on inlet air temperature and aerodynamic load. In this experiment, the maximum humidity achieved was 33%. (Less)

Chemical Analysis of Combustion Products From a High-Pressure Gas Turbine Combustor Rig Fueled by Jet A1 Fuel and a Fischer-Tropsch-Based Fuel

A comparative experimental investigation has been performed, comparing the emissions from a synthetic jet fuel and from Jet AI. In the investigation, the unburned hydrocarbons were analyzed chemically and the regulated emissions of NOX, CO and HC were measured. All combustion tests were performed under elevated pressures in a gas turbine combustor rig. A Swedish company, Oroboros AB, has developed a novel clean synthetic jet fuel, LeanJet [registered trademark] . The fuel is produced synthetically from synthesis gas by a Fischer-Tropsch process. Except for the density, the fuel conforms to the Standard Specification for Aviation Turbine Fuels. The low density is due to the lack of aromatics and polyaromatics. Organic emissions from the gas turbine combustor rig were collected by adsorption sampling and analyzed chemically. Both the fuels and the organic emissions were analyzed by gas chromatography/flame ionization (GC/FlD) complemented with gas chromatography/mass spectrometry (GC/MS). Under the operating conditions investigated, no significant differences were found for the regulated emissions, except for emission of CO from the synthetic fuel, which, at leaner conditions, was one-quarter of that measured for Jet Al. Detailed analysis of the organic compounds showed that the emissions from both fuels were dominated by fuel alkanes and a significant amount of naphthalene. It was also found that Jet Al produced a much higher amount of benzene than the synthetic fuel. Copyright (Less)

Progress on the AGATA Project: A European Ceramic Gas Turbine for Hybrid Vehicles

The European EUREKA project EU 209 or AGATA - Advanced Gas Turbine for Automobiles is a program dedicated to the development of three critical ceramic components; i. catalytic combustor, ii. radial turbine wheel, iii. static heat exchanger, designed for a 60 kW turbogenerator hybrid electric vehicle. The objective is to develop and test the three components as a full scale feasibility study with an industrial perspective. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in France and Sweden. The program has been running since early 1993 with good progress in all three sub-projects.The turbine wheel design is now completed. FEM calculations indicate that the maximum stress occur during cold start and is below 300 MPa. Extensive mechanical testing of the Si3N4 materials from AC Cerama and C&C has been performed.The catalytic combustor operates uncooled at 1350°C. This means a severe environment for both the active catalyst and the ceramic honeycomb substrates. Catalysts with high activity even after aging at 1350°C have been developed. Ceramic honeycomb substrates that survive this temperature have also been defined. The catalytic combustor final design is ready and the configurations which will be full scale tested have been selected.The heat exchanger will be a ceramic recuperator with 90 % efficiency. Both a tube concept and a plate concept have been studied. The plate concept has been chosen for further work. Sub-scale plate recuperators made of either cordierite or SiC have been manufactured by C&C and tested.Copyright

Comparison of Combustion Properties Between a Synthetic Jet Fuel and Conventional Jet A1

Aviation fuel is a petroleum product that fulfills the Standard Specification for Aviation Turbine Fuels. Crude oil has been the raw material for production of aviation fuels for many years. Since the availability of crude oil is predicted to be limited in the future, alternative raw materials for aviation fuels are highly desirable. A Swedish company, Oroboros AB, has developed a novel clean synthetic jet fuel, LeanJet. The fuel is produced synthetically from synthesis gas (Syngas) by the Fischer-Tropsch process. A comparative experimental investigation of combustion properties has been performed, comparing the synthetic jet fuel with Jet A1. The following parameters were investigated in an atmospheric combustor, which was originally designed for a Volvo Aero turbine (VT40): Emissions of NOx, CO and HC Ignition and extinction points Liner temperatures Soot levels in the combustor. The emission measurements showed good combustion efficiency with low HC and CO for both fuels. With very lean mixtures, however, both the CO and the HC levels increased for the synthetic fuel. The nitrous oxides for the synthetic jet fuel were reduced over the operation conditions investigated. Qualitative reduction of soot levels was also seen for the synthetic jet fuel. The fuels showed no difference in material temperature along the combustor wall. Small differences in ignition characteristics were found, but no differences in extinction were observed. Copyright (Less)

Catalytic Combustor Development Within the AGATA Program

The European AGATA programme (Advanced Gas Turbine for Automobiles), is a programme dedicated to the development of three critical ceramic components — a catalytic combustor, a radial turbine wheel and a static heat exchanger — for a 60 kW turbogenerator in a hybrid electric vehicle. These three components, which are of critical importance to the achievement of low emissions and high efficiency, have been designed, developed, manufactured and tested as part of a full-scale feasibility study. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in both France and Sweden. The AGATA project commenced in early 1993 and has occupied a 5-year period until April 1998. This paper summarises the results from the development of the catalytic combustor.The catalytic combustor operates at temperatures in the catalytic section from inlet 935°C to the exhaust 1350°C. Therefore all structural components in the hot section are made of ceramic materials.The testing and validation have been run through a component test campaign from which it was concluded that:• The catalytic section substrates showed good behaviour during the high temperature tests.• Palladium was chosen as the active catalytic material after extensive testing at pilot scale. Ageing at high temperature (1270°C) has a strong effect on catalyst deactivation.• Emissions levels of the preheater are in agreement with the state of the an for small aero-engines according to the ICAO legislation.The complete full scale combustor testing was run in the following steps:• Initial gas analysis tests at inlet temperature 200° lower than the nominal value• CARS and gas analysis• Comparison diesel and ethanol fuels• Final testing at maximum design temperatures and pressureThe catalytic combustor was run on diesel fuel during the complete test period. A test campaign comparing exhaust emissions when running on ethanol fuel was performed at Volvo Aero Turbines. These results showed that the catalyst reaction rate and CO/HC/NOx emissions were similar. This means that the chosen catalytic combustor can be used as a dual fuel combustor diesel/ethanol.The final test campaign at ONERA, France, was run up to temperatures slightly above the specified maximum design temperatures. Inlet temperature 962°C (design 935°C) and exhaust temperature 1362°C (design 1350°C). These tests showed that NOx emission levels below 4 ppm @15% O2 were obtained when low CO and HC emissions levels were measured at full load conditions. This promising performance level was reached with technologies that still have to be thoroughly evaluated in terms of durability and low cost potential for industrial applications.© 1999 ASME

CFD investigation of the effects of different diluents on the emissions in a swirl stabilized premixed combustion system

Recently, new cycles for power generation, such as wet cycles and cycles for CO2 capture, have gained increasing interest. These new cycles use some sort of dilution in the air/fuel mixture, e.g. steam or CO2. Gas turbine cycles using LCV gases can also be said to fit this description. Almost all modern gas turbines use a lean premixed combustion system, since it combines low NOX emissions with high combustion efficiency. The main objective of this paper is to study the influence of different diluents on the NOX and CO emissions at different inlet temperature, equivalence ratio, pressure and mass flow. The studied combustor was a premixed swirl stabilized combustor with optical access and emission sampling equipment. The combustor uses Danish natural gas as its main fuel. Computational fluid dynamics (CFD) has been employed to perform the investigations. It is common knowledge that turbulence models based on the Buissinesq assumption are not generally capable of handling a highly swirling flow in a correct way. Therefore, a differential Reynolds stress model (DRSM) has been employed for modeling of the turbulence. The turbulent combustion has been modeled with the level-set flamelet library approach (FLA). In this approach a laminar flamelet is linked to turbulent flow field via a non-reacting scalar G and its variance. The laminar flamelet is modeled with separate code. This code solves the combustion development with a detailed reaction mechanism for a laminar, non-stretched and premised one-dimensional flame. This is of great importance when emissions are to be predicted. All fluid dynamics computations were performed with the commercial CFD code Star-CD, version 3.20, where the FLA combustion model was implemented through Fortran based user subroutines. The computed flow field was validated against experimental data during non-reaction flow conditions. The computations showed good agreement with the experimental data. The computed CO and NOX emissions showed the same trends as the experimental data for the reacting case with an undiluted flame, when the equivalence ratio was altered. The computed emissions were used to build up an emission map for different dilutions during different operation conditions. Copyright (Less)

Design and evaluation of an LCV combustor for the volvo VT4400 industrial gas turbine

A combustion system was developed to burn a low value gas in the VT4400 IGT engine demonstrator. The combustor was designed in an engine configuration consisting of a single LCV combustor operating in combination with six LP combustors.

Status of the European Gas Turbine Program — AGATA

The European Gas Turbine Program “AGATA” which started in 1993 now has reached its verification phase. The objective of the program is to develop three critical ceramic components aimed at a 60 kW turbogenerator in a hybrid electric vehicle — a catalytic combustor, a radial turbine wheel and a static heat exchanger. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in both France and Sweden. Each of the three ceramic components is validated separately during steady state and transient conditions in separate test rigs at ONERA, France, where the high pressure/temperature conditions can be achieved. A separate test rig for laser measurements downstream of the catalytic combustor is set up at Volvo Aero Turbines, Sweden.The catalytic combustor design which includes preheater, premix duct and catalytic section operates at temperatures up to 1623 K. Due to this high temperature, the catalyst initially has undergone pilot tests including ageing, activity and strength tests. The premix duct flow field also has been evaluated by LDV measurements. The full scale combustion tests are ongoing.The turbine wheel design is completed and the first wheels have been manufactured. FEM calculations have indicated that stress levels are below 300 MPa. The material used is a silicon nitride manufactured by AC Cerama (Grade CSN 101). Cold spin tests with complete wheels have started. Hot spin tests at TTT 1623 K will be performed in a modified turbo charger rig and are expected to start in February 1998.The heat exchanger is of a high efficiency plate recuperator design using Cordierite material. Hot side inlet temperature is 1286 K. Therefore initial tests with test samples have been run to evaluate the thermomechanical properties at high temperatures. Tests are now proceeding with a 1/4 scale recuperator prototype to evaluate performance at steady state conditions. Manufacturing of the full scale heat exchanger is now in progress.Copyright

Progress on the European Gas Turbine Program: AGATA

The four-year European Gas Turbine Program “AGATA” was started in Jan 1993 with the objective to develop three critical components aimed at a 60 kW turbogenerator in an hybrid electric vehicle — a catalytic combustor, a radial turbine wheel and a static heat exchanger. The AGATA partners represent car manufacturers as well as companies and research institutes in the turbine, catalyst and ceramic material fields in both France and Sweden.This paper outlines the main results of the AGATA project for the first three year period. During the third year of the program, the experimental verification of the components has started. A high pressure/temperature test rig for the combustor and the heat exchanger tests has been built and is now being commissioned. A high temperature turbine spin rig will be ready late 1995.The turbine wheel design is completed and ceramic Si3N4 spin discs have been manufactured by injection moulding and Hot Isostatic Pressing (HIP). A straight blade design has been selected and FEM calculations have indicated that stress levels which occur during a cold start are below 300 MPa.The catalytic combustor final design for full scale testing has been defined. Due to the high operating temperature, 1350°C, catalyst pilot tests have included ageing, activity and strength tests. Based on these tests, substrate and active materials have been selected. Initial full scale tests including LDV measurements in the premix duct will start late 1995.The heat exchanger design has also been defined. This is based on a high efficiency plate recuperator design. One critical item is the ceramic thermoplastic extrusion manufacturing method for the extremely thin exchanger plates another is the bonding technique: ceramic to ceramic and ceramic to metal. Significant progress on these two items has been achieved. The manufacturing of quarter scale prototypes is now in process.Copyright