ARCHIVE

Michele Schiliro; Raghavendra Hegde; Iulian Vasile
Liebherr Machines Bulle SA, Bulle

Guoqing Xu
Liebherr Machines Bulle SA, Bulle/ETH, Zurich

Abstract
Manufacturers and customers of gas engines are constantly striving for improvements to comply with ever tightening emissions legislation and to achieve reductions in operating costs, increases in efficiency, improved reliability, extended maintenance intervals and lower maintenance costs. In order to adequately address this situation, Liebherr Machines Bulle SA (LMB) has developed the new G96 gas engine family over the last few years, investing considerable resources.

The targeted use of innovative virtual methods such as the 1D/3D simulation of thermodynamic processes, 3D FEM and multi-body analysis calculations, which was already carried out during the concept phase and in close connection with the engine design throughout the entire G96 project, has enabled the new development of a generally optimized crankshaft, a new valve train and a unit consisting of cylinder head and pre-chamber plug optimized in terms of their geometry, the use of which, together with the coordination of the software implemented on the LIEBHERR engine control unit, results in a considerable increase in gas engine efficiency.

Dr. Frederik Hahn*; Johannes Bauer; Udo Sander
MTU Friedrichshafen GmbH

Abstract
This article deals with the expansion of a high-speed map diesel engine that has been successfully in series production since 2007 to include the option of using gaseous fuels. The development of the retrofit kit presented is motivated both by the increasing importance of cost advantages when using gaseous fuels and by the potential to continue to deliver 100% power in diesel operation when they are not available. The requirements and concept, the technical description of the solution, the engine control and operating values are presented below. The developed product achieves maximum diesel savings while complying with emission limits and strict safety requirements, particularly in the partial load range, which is important for oil and gas applications. A wide variety of fuel qualities can be used, so that nothing stands in the way of the future use of e.g. low-processed associated petroleum gases.

Luc Mattheeuws*, Lieven Vervaeke
ABC Gent, Gent, BE

Abstract
Anglo Belgian Corporation (ABC) has over 100 years of experience in building internal combustion engines. ABC was founded in 1912 with the motto to build the strongest and most reliable engines. For many years, diesel or heavy fuel oil was used as the basic fuel for ships. In recent years, due to emission laws and our customers’ belief in green ship solutions, people have been looking for new concepts. Optimizing the standard diesel engine is one option, but fuel diversity (natural gas, methanol, …) is an alternative route that has become increasingly attractive. Since ABC has many years of experience with dual-fuel engines for land-based applications, it is ideal to extend the dual-fuel engines to marine applications.

ABC started with a specialized team to develop a dual-fuel engine for marine applications and focused on a specific concept that allows to achieve shorter response times than a pure diesel engine. Other topics included reducing the amount of ignition oil, obtaining class approval and developing a safety concept. This has made the newly developed dual-fuel engine available for the marine market.

The very good ignition response time of the engine together with the reliability and robustness have led to the first project in which two 12DZD engines were installed on board a ro-ro ferry from TESO, the Texelstroom. The Texelstroom is a hybrid ferry with solar panels and two dual-fuel engines powered by compressed natural gas as a clean fuel. The dual-fuel engines are installed as a generator set and used together with a large battery pack – which helps to reduce exhaust emissions during high peaks – as a hybrid propulsion system.

DEME was also interested in ABC’s dual-fuel engine concept and signed an agreement to build a green dredger. ABC had to supply two 16DZD engines and one 6DZD engine with liquefied natural gas as clean fuel, for the Minerva and the Scheldt River respectively. For the Minerva, the ABC engines had to power the drive train as well as the dredge pump and the AC machine. The ABC engine in the Scheldt River is an auxiliary engine to supply the AC machine.

All of these projects require high-quality control systems, adapted technology and the optimization of fuel consumption and emissions. This document describes these modifications and shows the installation of the dual-fuel engines in the ships.

N. Böckhoff*, D. Mondrzyk, S. Terbeck
MAN Diesel & Turbo SE, Augsburg, Germany

Summary
The demand for gaseous fuels continues to grow due to the increasing energy requirements and the search for alternatives to power generation using liquid fuels and nuclear energy. The MAN 51/60G can be used and optimized in many different ways. If the gas engine is used purely for power generation, it is designed for the highest possible efficiency on the output shaft. For base load applications, the gas engine is predominantly used in Europe in combined cycle or combined heat and power applications. The ability to reach full load within a very short time makes the gas engine an interesting option for balancing out fluctuations in renewable energy generation. Compared to conventional diesel power plants, gaseous fuels for energy generation are characterized by low primary emissions, especially of dust,_CO2 and _NOX. The new exhaust gas emission limits of the TA-Luft and the EU directive pose a challenge. In addition to other pollutants, the limit values for _NOX emissions have been more than halved. In order to ideally meet these market requirements, numerous optimizations have been carried out on the 51/60G.
This paper describes the further development of the 51/60G from MAN Diesel & Turbo.

Christian Trapp*, Robert Böwing, Andreas Birgel, Herbert Kope-cek, Wolfgang Madl, Albert Fahringer, Fabrizio Nota
GE Distributed Power, Jenbach

Abstract
Extending the performance limits of large gas engines to improve customer value continues to drive GE’s development of new technologies and set new standards. Large gas engines are increasingly being used for power generation around the world to meet the growing demand for electricity in developing countries and changes in power generation in industrialized countries. The demand for decentralized and flexible energy is increasing, driving the development of combustion engine technologies in terms of power density and efficiency as well as short start times and load shedding for grid stabilization. In 2013, GE launched the Jenbacher J920 FleXtra gas engine, a 20-cylinder 4-stroke gas engine in the 10 MW class developed from scratch. This engine utilizes the successful two-stage turbocharging technology of the Jenbacher J624 gas engine and represents a new milestone for a 10 MW engine with an engine speed of 1,000 rpm for 50 Hz applications. This design offers high power density, small dimensions, high electrical and thermal efficiency for cogeneration and great flexibility in application. This article highlights the major advances in performance, efficiency and operational flexibility of the Jenbacher J920 FleXtra gas engine, including a 10 percent increase in electrical output, 50.1 percent electrical efficiency demonstrated in a test environment, and greater operational flexibility under varying ambient conditions and gas compositions. GE has also invested significantly in its digital capabilities to combine advanced engine control and monitoring with big data analytics to take industrial plant operations with Jenbacher J920 FleXtra gas engines to the next level through predictive maintenance and optimization of plant and fleet utilization.

S. Zirngibl , M. Prager, G. Wachtmeister
Chair of Internal Combustion Engines (LVK), Technical University of Munich

Abstract
The combustion of natural gas and biogas in particular can be regarded as one of the key technologies on the way to a climate-neutral energy supply. Due to its wide availability, biogas already plays an important role in the German energy mix [1]. For example, in stationary power plant applications or modern combined heat and power (CHP) plants, the conversion of gaseous fuels is largely established. Particularly with large specific cylinder displacements, the gas/air mixture, which is usually formed with a relatively large excess of air to optimize efficiency, can also be ignited using pilot injection of liquid fuel, for example, in addition to conventional spark plug ignition. Apart from the fundamental aspects of combustion process development, such as the selection of the stroke-bore ratio and the subsequent optimization of the combustion chamber shape, or the definition of the valve timing, an additional, significant degree of freedom must therefore be taken into account with the definition of pilot injection.

The additional high-pressure fuel system required for pilot injection generally represents a further system expense. The additional complexity of the overall system must at least be compensated for by a consumption or efficiency advantage. This can be achieved in particular with comparatively large specific cylinder displacements and suitable adjustment of the pilot injection due to a significantly faster and therefore more efficient conversion of the gas/air mixture. Even in the combustion of gaseous fuels with a relatively high volumetric proportion of inert components, such as biogas, the significantly faster conversion of the cylinder filling could justify the additional expense of pilot injection, even with smaller combustion chambers. For this reason, the Chair of Internal Combustion Engines (LVK) at the Technical University of Munich (TUM) is investigating a biogas ignition jet combustion process for a small gas engine. On the one hand, this article describes the experimental investigations of pilot injection carried out to date. On the other hand, the mainly simulative adaptation and design of the individual subsystems is discussed. In addition to the pilot injection, the focus is therefore also on the valve timing, as well as the combustion chamber geometry and the geometric characteristics of the intake system with the resulting influences on the internal cylinder flow.

Björn Henke, Bert Buchholz*, Karsten Schleef, Christian Fink
Chair of Reciprocating Engines and Internal Combustion Engines, University of Rostock

Sascha Andree
Chair of Technical Thermodynamics, University of Rostock

Marius Wolfgramm, Robert Graumüller
Caterpillar Motoren GmbH & Co. KG

Abstract
With a view to analyzing various influencing variables on the dual-fuel combustion process, experimental investigations were carried out on a medium-speed 1-cylinder research engine with different injection strategies as part of the “LEDF concepts” research project. In addition to the injection start variation of a µ-pilot injection, the investigations include the analysis of the influence of a multiple-pilot injection with a first µ-pilot injection positioned in the compression phase and a second µ-pilot injection positioned in the typical time window before TDC. While the best values achieved for indicated efficiency, combustion stability and NOx/CH4 emissions for both injection strategies differ only insignificantly from each other, it can be determined on the basis of the results obtained that these parameters react significantly less sensitively to a change in injection timing with a multiple injection strategy than with a single injection strategy.

Dr. Christoph Redtenbacher*, DI Constantin Kiesling, DI Maximilian Malin
LEC GmbH, Graz

Prof. Dr. Andreas Wimmer
LEC GmbH, Graz / Graz University of Technology

Summary
In the gas operating mode of diesel-gas dual-fuel engines, the homogeneous gas-air mixture in the combustion chamber is ignited by injecting a small amount of diesel fuel. This diesel pilot injection has a significant influence on the performance of the combustion concept. Particularly for injection systems of fully flexible diesel-gas engines, which cover both the gas operating mode and pure diesel operation with just one diesel injector, good ignition of the lean mixture with simultaneously low NOx emissions is a challenge. The optimization of diesel pilot injection is therefore an important starting point for improving the diesel-gas combustion process in order to reduce the current performance deficits compared to monovalent gas engine concepts with gas-purged prechamber.

In this article, the diesel-gas engine concept is compared with the gas engine concept in order to show in which areas the dual-fuel combustion process must be optimized in order to bring efficiency and combustion stability closer to the level of the monovalent combustion process. Based on this, measures for diesel pilot injection are evaluated with regard to improving the diesel-gas combustion process. The analyses include influences of the variable injection parameters injection duration, injection start and rail pressure as well as influences of important nozzle parameters such as the number of nozzle holes. Since the achievement of a symmetrical spray pattern is associated with difficulties in the area of the small quantities of diesel required, the extent to which a nozzle with an asymmetrical spray pattern influences engine operation compared to a nozzle with a symmetrical spray pattern is also shown.

The findings are based on a series of tests on a high-speed single-cylinder research engine with a displacement of ≈ 6 dm³. The results of investigations in an optically accessible injection chamber and in an injection rate measuring device to characterize the injection process support the interpretation of the observable effects from the engine measurements. The combination of experimental methods and a detailed analysis of engine operating points using engine process calculation make it possible to derive the requirements for the injection process in order to achieve an efficient and low-emission combustion process. A final evaluation shows the extent to which the performance of the diesel-gas engine concept can be brought closer to that of the gas engine concept by optimizing the injection process.

Lukas Virnich*, José Geiger, Dirk Bergmann, Harsh Sankhla
FEV GmbH, Aachen

Avnish Dhongde
Chair of Internal Combustion Engines, RWTH Aachen University

Abstract
In the area of conflict between high thermal efficiency and operation with as little knocking as possible, while at the same time complying with the legally prescribed emission limits, the compression ratio is the key parameter for stationary large gas engines alongside the air ratio. Therefore, knowledge of the earliest possible combustion center of gravity position without the occurrence of knocking combustion (knock limit) is of decisive importance for the design of the optimum compression ratio of a gasoline engine combustion process. In addition to the compression and air ratio, the fuel used in particular has a decisive influence on the combustion delay and the combustion duration and thus on the thermodynamic state of the unburned air-fuel mixture. Furthermore, the fuel (the gas composition) determines the kinetic properties of the unburned air-fuel mixture and thus also the knock limit. The wide range of available gas qualities therefore makes it difficult to design an optimum compression ratio.

An ignition and knock model is being developed for a more precise analysis of the variables influencing the knock limit of a combustion process and for the simulation-based design of the compression ratio for widely differing fuel compositions. The critical states in the unburned air-fuel mixture before the flame progresses are identified with the aid of a detailed reaction kinetics simulation.

The reaction kinetic approach takes into account the influencing parameters compression ratio, air ratio and fuel composition. The interactions of the influencing parameters on combustion delay and combustion duration are taken into account via an entrainment model for flame propagation. Furthermore, the simulation of the cycle-individual fluctuations of the variables mentioned enables a distribution of knock intensities and occurrence probabilities corresponding to real engine operation.

A reaction mechanism suitable for engine operation is identified for the simulation of the reaction kinetics. This simulates the change in ignition delay time due to charge dilution and for different fuel compositions at the pressure and temperature conditions present in the combustion chamber.

D. Neher*, S. Fieg, W. Rieb, J. Bauer, M. Kettner
Engine Technology Research Department of the Institute of Refrigeration, Air Conditioning and Environmental Technology (IK-KU) at Karlsruhe University of Applied Sciences

H. Biermann, N. Albrecht
Eberhardt Hoeckle GmbH

Abstract
For combined heat and power plants in the output range up to 50 kWel, homogeneous lean-burn mixed-aspirated natural gas engines are predominantly used, which achieve low NOx emissions with satisfactory efficiencies. Although the NOx limit values introduced in 2018 can be complied with by further charge dilution, this is associated with a decrease in internal efficiency due to increasing carryover of combustion and increased cyclical fluctuations. In the naturally aspirated engine, the useful power also decreases, which increases the proportionate friction losses and consequently reduces the effective efficiency.

In this article, an alternative approach to mitigate the conflict of objectives between efficiency, NOx emissions and engine performance of a homogeneously lean-burn four-cylinder natural gas engine with mixed intake was investigated. Increasing the compression ratio to increase efficiency was the main measure, which initially led to a higher combustion temperature. The increase in NOx emissions was counteracted by the secondary measures of charge cycle optimization and cooled exhaust gas recirculation to reduce the process temperature before and during combustion.

The first step was to use 1D-CFD engine process calculation to optimize the timing to minimize the residual gas content. The determined valve lift curves were then designed using an MBS valve train simulation and examined on the test bench. To increase the compression ratio from 13.3 to 15.2, the piston geometry was modified and its influence on the charge movement was analyzed using 3D CFD simulations. Initial engine tests with increased compression were followed by tests with cooled exhaust gas recirculation, in which comparable NOx emissions were achieved and the effective efficiency was increased by 1.2 percentage points while maintaining the engine output.

M.Sc. F. Rosenthal*, Dr.-Ing. Heiko Kubach, Prof. Dr. sc. techn. T. Koch
Institute for Reciprocating Machinery (IFKM),
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Dr. Ulrich Arnold
Institute for Catalysis Research and Technology (IKFT),
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Abstract
Current developments in natural gas engines make use of further leaning or charge dilution with exhaust gas to reduce NOx emissions. Under these boundary conditions, the ignition of a single-cylinder research gas engine was investigated by pilot injection of ignition-ready fuels. Two ignition fuels (2-EEE, HVO) were determined by systematically selecting representatives of different substance groups with strongly increasing ignitability up to a cetane number of > 100 and their material properties were determined. These fuels were examined with regard to their suitability as ignition fuels and compared with diesel as a reference ignition fuel.

A higher ignition readiness reduces the combustion delay of the ignition injection and allows the proportion of ignition fuel to be reduced. A large proportion of nitrogen oxide emissions are attributable to ignition injection, which is why minimum ignition quantities are necessary to comply with emissions legislation. The minimum quantity injection of 2-EEE as an ignition-ready fuel enables lean operation with exhaust gas recirculation and low NOx emissions without any efficiency disadvantages.

1. Zirngibl , F. Günter, M. Prager, G. Wachtmeister
   Chair of Internal Combustion Engines (LVK), Technical University of Munich

Abstract
In view of increasing globalization and technological progress, the worldwide demand for energy is constantly growing. In addition, many countries are pursuing the goal of significantly increasing the proportion of renewable energy sources in their respective energy mixes. However, even with a fully renewable energy supply, a supply gap will remain due to climatic fluctuations. As efficient storage technologies are not yet available to an economically viable extent, fossil fuel power plants will continue to be integrated into the supply grid to cover the remaining residual load. One possible approach to covering the residual load using renewable energy sources is the use of biogenic gaseous fuels. In contrast to solar or wind energy, the gaseous fuel can be converted into electricity as required. This means that the combustion of gaseous fuels can potentially also contribute to covering the base load in addition to the aforementioned residual load. Even if the focus here is usually on the supply of electrical energy, the combustion of biogas also offers advantages in possible CHP applications. In order to maximize the efficiency of such systems, the processes for waste heat recovery from the combustion engine (e.g. from coolant, lubricating oil and exhaust gas) must also be optimized. For this reason, this article presents a simulative approach for investigating thermodynamic cycle processes in CHP applications. The source code developed in MATLAB enables any combination of the respective system components (such as heat exchangers and pumps as well as (steam) turbines and compressors) to be mapped in a cyclic process. In addition to the basic modelling approach, the article mainly describes the comparison of the Joule-Brayton and Clausius-Rankine processes as well as possible optimization potentials resulting from the dimensioning of the considered system components or the selected process control.

Wolfgang Fimml *, Jonathan Lipp, Michael Greil, Philippe Gorse
MTU Friedrichshafen GmbH

Christoph Mathey, Christoph Voser, Boris Willneff
ABB Turbo Systems Ltd

Abstract
Variable valve train technology offers new possibilities for improving the performance data of off-highway engines. In recent years, MTU Friedrichshafen GmbH has applied and successfully tested the fully variable valve train technology VCM® (Valve Control Management) from ABB Turbo Systems on Series 4000 engines.

A VCM® actuator for the intake side was developed and tested for this purpose. This article discusses the VCM® development methodology used and presents detailed results of the engine and endurance tests of stationary gas engines for the first time.

The engine tests concentrated on thermodynamic potential investigations with VCM® on a stationary large gas engine. The power control was realized via variable intake valve timing instead of conventional throttle valve control, whereby significant improvements in efficiency were measured: 0.65 percentage points for the single-stage turbocharged L64 engine and 1.5 percentage points for an emulated two-stage turbocharged stationary gas engine.

In addition to improving performance data, the reliability and robustness of new technologies for large engine applications are of the utmost importance. This article therefore presents the first endurance test results for 12 VCM® actuators, which were tested for more than 7,000 hours on a Series 4000 L64 CHP outdoor test vehicle under real conditions.

The installed VCM® actuators were monitored using measurement technology and subjected to regular component inspections. The results showed excellent drift stability, low cycle-to-cycle variations and very good wear behavior of the actuators.
The results obtained allow the conclusion that the VCM® technology is now ready for use on high-speed off-highway engines at any time.

Tobias Ehrler*, Manuel Cech, Titus Tschalamoff, Martin Wild
WTZ Roßlau gGmbH, Dessau-Roßlau, D

Summary
The use of CHP units as combined heat and power plants has a high overall efficiency in the generation of electrical and thermal energy. With the use of a heat-driven cooling system, the waste heat from the engine can also be used, e.g. for cooling buildings. This increases the running time of the combined heat and power plant, which increases the economic efficiency of the system. In addition to cooling buildings, another possible application is to use the cooling capacity generated to cool the charge air below ambient temperature. In the first stage of the project, the potential of low-temperature charge air cooling on a gas engine was investigated using engine simulation and an estimate of the potential was made with regard to the following target values:

• Reduction of _NOx emissions with constant efficiency to achieve future emission classes
• Increase in effective motor efficiency

In the subsequent test bench tests, the target variables were examined and the engine model validated. Further simulation calculations were carried out and the low-temperature charge air cooling was compared with the Miller process.

Dr. Hinrich Mohr*, Martin Abart, Ingo Koops, Dr. Rüdiger Teichmann
AVL List GmbH

Prof. Clayton Zabeu*, André Martelli, Roberto Salvador, Alexander Peñaranda, Glauber Ruy
Linhares Geração S.A.

Summary
Due to a lack of rain in Brazil in recent years, most of the thermal standby power plants have been put into continuous operation. In 2014, the Brazilian gas engine power plant operator Linhares Geração S.A. (LGSA) began a program to improve engine performance and increase reliability. With optimized operation, this should lead to improved economic efficiency of this 204 MW power plant with its 24 medium-speed gas engines. The implementation of permanent condition monitoring and closed-loop engine control were defined as relevant components for this. AVL was involved in the technical discussions as an independent engineering service provider and was finally contracted to develop and supply the necessary hardware and software to be integrated into the plant automation system for this application.

Two products from the AVL large engine portfolio were used as the basis for the technical concept: the proven condition monitoring system AVL EPOS™ and the services for the development of engine control systems. Both topics were bundled for this project, with the necessary requirements being jointly defined by AVL and LGSA. By incorporating the extensive knowledge of large engines, it was possible to achieve complete integration. This also allows the current engine status to be taken into account in the optimized engine control system.

The on-site implementation took place in several stages: first, an engine in the power plant was equipped with AVL EPOS™ hardware and software to demonstrate the possibilities of permanent condition monitoring. In the second step, this system was installed on all engines and integrated into the power plant automation system. The third stage involved converting the conventional engine control system to the closed-loop solution with a link to the AVL EPOS™ via hardware and software interfaces. This was done to test the functionalities and optimize the possibilities. Based on the results of this stage, a corresponding conversion of all remaining engines is planned.

The initial operating results are very promising. The integrated system is working very satisfactorily and sensitively. LGSA is now developing the potential of the new system as a basis for the optimized operating strategy.

Dr. M. Schultze*, C. Drexel
Caterpillar Energy Solutions GmbH, Mannheim, D

G. Kollias-Pityrigkas
Kaiserlautern University of Technology, D

Summary
In order to investigate the usability of hydrogen-containing gases, various gas mixtures consisting of the main species H2, CH4, CO, CO2 and N2 were tested on a modified TCG 2016 V08 gas engine. The engine was equipped with flame arresters in front of the intake ducts to prevent the spread of possible re-ignition into the intake tract. In addition to full indexing with high-pressure quartz crystals, the engine was equipped with additional low-pressure sensors and fiber optics in the receiver tube. During the tests, the same combustion focus was selected for all gases in order to ensure comparability. Operating parameters such as ignition timing, combustion air ratio, charge air temperature and pressure were varied.

As part of this work, it was investigated what output can be achieved with the various fuel gases at different operating parameters and what pollutant emissions can be expected depending on the fuel gas used. The knocking tendency of the various gases was also investigated. The extent to which knocking and self-ignition events differ with different fuel gas compositions is discussed.

Using the experimental data, a numerical model was developed and validated that allows a prediction of the usability of fuel gases with a different chemical composition. This model contains 0D and 1D simulations as well as detailed chemical reaction mechanisms.

Prof. Lars M. Nerheim*, Dr.-Ing. P. Koch, C.E. Harald Moen, B.Sc. Roger Aamot, M.Sc. Ørjan Høyvik
Bergen University College (HiB), Bergen, Norway

Summary
This article first summarizes the recent transition from Otto lean gas engine concepts to the l 1 process without or with EGR for Euro VI gas bus engines. It is concluded that further improvements, particularly with regard to CO2 emissions, will lead to gas-hybrid drive combinations.

In addition, comparative measurements between a city bus with a conventional Euro VI CNG drive and a serial CNC hybrid drive are reported. What was striking in this case was the much smoother operation of the hybrid drive, even in city traffic, which led to improved functioning of the TWC catalytic converter and thus to significantly reduced exhaust emissions. In contrast, it was not always possible to maintain the operating temperature of the TWC catalytic converter in the hybrid bus. Increased emissions were observed for short periods until the catalytic converter reached operating temperature again. It can therefore be concluded that the thermal management of this hybrid engine and its control strategy were still in need of improvement. It was also found that the contribution of the battery drive decreased in relative terms as the number of passengers increased, thus offsetting the improvements compared to the conventional drive.

Günther Gern, Managing Director WTZ Roßlau