1st Dessau Gas Engine Conference

Overview of presentations

Summary of the Discussion Contributions from 10./11. of June 1999

WTZ Roßlau has organized the 1th Dessau Gas Engine Conference on June, 10./11. 1999. The convention got in touch manufacturer companies with research scientists and user of gas engine technology and will be now a regular happened meeting for experience exchange at this professional area. The 1th conference have had following specialized contents:

Following a summary of the contributions. If you would have a deeper interest in this topic, you can order also the convention band.


New Gas Engines

Rod Thomas from Ricardo Consulting Engineers Ltd gave in his opening lecture of the conference a survey of the state of development and formulated as a demanding target for gas engines in future a coefficient of efficiency up 50% at simultaneously emission reduction which will be focused on nitrogen oxide and methane.

Volker Höppner from MWB Motoren & Anlagen GmbH & Co. described the previous rarely use of gas engines as a ship propulsion. The low spreading is caused in the point that Diesel fuel for inland water transport is not defeated to the mineral oil tax and because of this it is cheaper then natural gas, approximately between 10 and 15%. Therefore the field of application will be at a range where advantages for the environment are decisive, for example passenger ferries in tourist regions. Within this lecture, 2 projects where introduced with all usable engines, aspects of the logic concept (refueling, fuel storage) as well as safety questions.

David Meyers described the work of Southwest Research Institute for development of a gas-engined locomotive. At a Single-cylinder test engine 6 different combustion procedures were tested and the so-called LaCHIP (Late Cycle High Injection Pressure) was selected. It`s a combustion procedure for a Diesel-gas engine, where beside a small quantity of Diesel fuel also the originally fuel-gas is injected respectively blowed directly into the undivided combustion chamber. Essential parts of procedure optimization were made with assistance of CFD-calculations. The target, reduction of NOx-emissions at a range of 75% (during 10 % efficiency loss) in comparison with base Diesel engine was reached. If satisfied with a 50% reduction of nitrogen oxide the engine operates with the same efficiency like it would operates with Diesel fuel.

At the essay of Karl Schwarze the common works of SKL Motoren- und Systemtechnik GmbH and WTZ für Motoren- und Maschinenforschung Roßlau gGmbH for development of a gas engine going out from the MTU 4000 Diesel engine series were displayed. Target was to become lower then the limiting values of TA Luft at a range of 50 % during a efficiency of about 40 %. For realization a lean-combustion-engine concept with a precombustion chamber ignition was selected. Pre- and main combustion chamber were designed with assistance of CFD-calculations, but only with a mutual experimental optimization of the combustion chamber geometry as well as of their connection (number, cross section and blow angle of the injection holes) the above-mentioned targets could be reached.

The pressure of costs at the market for stationery gas engines guides to the point that engines with a nominal rpm of 1500 min-1 advances more and more in power ranges of above 1000 kW. Werner Steinmetz from Zeppelin Baumaschinen GmbH  described the strategy of Caterpillar for reaching this target, the so-called tandem motors. A 12- and a 16-cylinder engine of the series 3500 from Caterpilar are connected with a special developed clutch and drive together a generator. The advantages of this concept are lower investment costs in comparison with engines with a rotational speed of 1000 min-1, perfomance tuning isn`t achieved about higher use pressure or higher piston speed and high availability and lifetime of the engines can be reached.


Gas Engine Accessories

At the first lecture of this section Günter Herdin from Jenbacher Energiessysteme AG described two systems for monitoring and controlling of gas engines. Per higher and higher use pressure and more leaner modern gas engines works, the demand on ignition plugs rises and the probability of lifetime decreases. MONIC (monitoring ignition control) is a system, which measured the ignition voltage of an ignition plug on the high-voltage side and allows together with modern control systems a adaptation of ignition energy, to rise the lifetime of the ignition plug. For allocation of occured ignition miss in a multicylinder engine to the caused cylinder, Jenbacher has developed an optical method (OCA). For detection of a successful ignition, the radiant emittance of a characteristic radical is used. The missing of such a signal is a safe mark for a failured ignition. A system, which also can make statements about ignition miss of single cylinders and is based on a ignition pressure measurement following the wire resistance strain gauge principle, was introduced by Stefan Neumann from IMES GmbH. It isn`t necessary to cool the pressure sensor. Nevertheless through an integrated temperature sensor a pressure measurement accuracy of ±0,5% will be achieved.

Ioannis Vlaskos, ABB Turbo Systems, has reported about the development of ABB-turbocharger of the series TPS with VTG (variable turbine geometry). The new at the ABB-design consists in that point that dead space between turbine-vane grate and case, which drop the turbocharger efficiency, are prevented without affection of the guide vane mobility at thermal deformations or because of deposits. Within 2 years of field-tests at lean-burn engines a engine efficiency gain of about 1 - 2 % in comparison with turbocharger without VTG and the behaviour at continous operation could be verificated.

Markus Umierski from FEV Motorentechnik GmbH has introduced a new combustion procedure for gas engines. The combustion chamber was designed at this kind that the twist is transformed effective in turbulence and as a result of this the combustion speed becomes higher. At a single-cylinder-test engine it was showed that this engine has a low knocking tendency, a very lean engine operating is possible and because of the reduced crushing flow the hydrocarbon emissions are relative low. If will be the engine tuned with respect to the nitrogen oxide for maintenance of TA Luft -limit values, at a use pressure of 25 bar a efficiency between 42 and 43 % will be possible.

Kelly Benson explained in his essay the operating principle of the gas proportioning and mixing unit Tecjet and as well the associated control unit EGS-01, both of them were developed from Woodward Governor. It is a central (single point) gas mixer, which have separated the functions of proportioning and mixing. For this reason a application of various gas with strong different thermal power is possible.

The logarithmic opening characteristic of the proprotioning valve guarantees also an exactly proportioning for small gas quantities. The use of a moving coil as a control element leads at engine load-alteration to a very fast regulation. Involuntary load-alteration caused by changing of the gas structure will be compensated from the control unit through an automatic adaptation of the combustion air proportion so that the engine will have the same power and NOx-emissions after a short time.


Special Gas

Recycling economy law and the Technische Anleitung Siedlungsabfälle causes medium-term a reduction of the deposited waste and changing of the composition. Alexander Schmitt, G.A.S. Energietechnik, stressed in his lecture that landfill gas will be signed through decreased methane content in future and discussed the possibilities for landfill operators to use the gas for commercial and energy recovery.

Firedamp, which diffused out of coal-mines, can form together with air an explosive mixture. Many times safety solutions has the disadvantage to let the climatic relevant methane directly into the atmosphere. Stefan Langhabel, Stadtwerke Saarbrücken GmbH, has presented an unit, consisting of an evacuation installation and a 225 kWel-block-combined heat and power station-module, who allows the energy recovery of the firedamp. During 10 years of operating lifetime the emissions of climatic relevant gas could be reduced of about 60 %. At simultaneous using of the waste heat there will be electrical costs at a range of 7 and 15 cents/kWh.

The items of Hinrich Mohr, B+V Industrietechnik GmbH, were concentrated on the effects, caused by different gas qualities, of ignition pressure and course of combustion in Diesel-gas engines. In comparison with ignition plugs the ignition energy disposed through a pilot injection is about 4 or 5 ten-power higher. With that ideal assumption are given to burn away also gas with a high inert gas content with a good efficiency. For example the course of combustion and efficiency of a natural gas with a methane content of only 36% are nearly identical with them of a natural gas with a methane content of about 98%. Differences shows only gases with the main burn component carbon monoxide.


Computer Simulation and Laser Spectroscopy

Modern CFD-programms (Computational Fluid Dynamics) Stephan Laiminger from the TU Graz in his essay. Because of the complex reaction kinetics inside of a combustion engine simplified kinetic approaches, for example Magnussen model, must be used. Towards to them delivers the PDF-model mostly better results, because of the explicit consideration of turbulence and reaction kinetic. If the models will be adapted on experimental determined courses of pressure and combustion, CFD-calculations can be used for parameter studies in the gas engine development. At a single-cylinder-prechamber-gas engine could achieved an efficiency rise of 3% during reduced NOx-emissions through mathematical optimization of the prechamber volume as well as injection hole geometry.

Essential for verification of the above-mentioned calculation models are measurements of pollutant concentration and temperatures within the combustion chamber. Christof Schulz, Universität Heidelberg, showed, how to determine with assistance of laser spectroscopy absolut values of temperatures and NOx-conzentrations with high dimensional and temporal resolution within the combustion chamber of an engine. A special item of the described measurements are the determination of temperature with Rayleigh scattering and nitrogen oxid concentration with laser-driven fluorescence at the same time. Because of this, modifications of temperature profil can be correlated directly with NOx-concentrations.

The experimental determination of the flame spread caused by an ignition process of a stoichiometric mixture of methane and air requires a temporal resolution at an order of magnitude of 1ms. Through a cooperation between Universität Stuttgart and Lund Institute of Technology such measuremnets become possible for the first time worldwide. Laser-driven fluorescence of hydroxyl radicals with the help of a Nd:YAG-laser system with very high repeat frequency (some kHz) was measured. Among laminar conditions the ignition process could be modeled very good. Like Steffen Lindenmaier stressed, LIF measurements of an ignition at a turbulent flow were made, but the complete numeric process simulation succeded not up to now.


Application Experiences

Karl-Friedrich Henke, Norddeutsche Energieagentur, introduced in his lecture the commercial embedment of a BCHP in a district heating network in Stralsund. The 3 MWM-lean-burn engines, every with an electrical power of 1938 kW, cover up 25 % of the required thermal output within the district heating network and achieve because of this appoximately 6500 full load operating hours p.a.. Through consistent use of waste gas heat an overall energy use coefficient of 92,8% is achieved. During 2 years of operating time the engine standstill times caused by malfunctions was that kind of slightly that the overall availability of the unit lies with 99,8% clear above them of heavy power plants.

With each annual operating hour the BCHP become more economical. However, at emergency power supplier the safety requirements stands at the foreground. Ulrich Prochaska, ETA GmbH, showed in his essay that both targets can be combined. For use of a BCHP as a safety power source in continuous operating, special requests on the load power up ability of the engines must be set. While working as network reserve the switching in must follow a priority list and the control unit must ignore malfunctions of subordinated priorities if necessary. In case of power failure the gas delivery must be guaranteed or a network-unbounded fuel like propane must be at disposal.

At the last 2 lectures of the conference, the application of gas engines in vehicles stood at the foreground. Like Ernstwendelin Bach, FH Dresden, explained, CNG-driven cars or industrial vehicle can contribute a part for the reduction of emissions of the increasing road traffic, because series-produced engines fulfills the request of the EURO IV-standard today. Significant barricades for a wide market launch in Germany exists inspite of the lower natural gas taxation, because of the economy and the thin natural gas station network.

The lack of infastructure is to be solved through bivalent propulsions. Ernst Sperling, FH Saarbrücken, stressed at his essay that higher octane number of natural gas should be used partly by using bivalent propulsion optimized for a RON of 98 and catalysators adapted to natural gas. Overall a coefficiency rise of 2 or 3% during reduced HC- and CO-emissions could be achieved, but higher values of nitrogen oxide must be accepted.

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