该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。Developers of lean burn natural gas engines have made dramatic improvements to engine performance in the last three decades. This includes nearly doubling the achievable power density and reducing fuel consumption by 25% while operating on a clean, plentiful and low cost fuel source. These developments, which have greatly benefited end users and society in general, have been achieved in conjunction with dramatic reductions in engine emissions. Potential future regulations intended to limit the emissions of unburned hydrocarbons from natural gas engines are a new challenge that is only beginning to be addressed by heavy-duty natural gas engine manufacturers. Emissions of non-methane hydrocarbons from many sources, including natural gas engines, are becoming more strictly regulated due to their contribution to local air quality issues. Increased natural gas engine utilization has the potential to reduce greenhouse gas emissions substantially, but this benefit requires exhaust methane emissions to be contained. Also of significant importance is the loss of engine efficiency that results from the failure of a given combustion system to convert between 1% and 4% of the supplied fuel energy. The challenge of unburned hydrocarbons is further exacerbated by the fact that technologies which reduce NOx emissions and increase thermodynamic efficiency often decrease combustion efficiency. This paper describes research work aimed at understanding the sources of unburned hydrocarbons from lean burn engines and identifying technology to mitigate these emissions. An overview of all potential sources of unburned hydrocarbon emissions, as described in the literature for spark-ignited engines, is provided. For a sub-set of these potential sources, test results from a single cylinder medium speed engine are coupled with zero and one-dimensional cycle simulation analysis to provide a quantitative perspective of unburned hydrocarbon emissions in lean burn gas engines. Engine test data and basic simulation results are provided which quantify the impact of the piston top land crevice on engine out hydrocarbons. Data for a variety of top land geometries and compression ratios is presented. Crank angle resolved exhaust port hydrocarbon measurements and cycle simulation results are used to quantify the impact of fuel short-circuiting during valve overlap in port-injected gas engines. The impact of flame extinction at combustion chamber surfaces is investigated using flame quench thickness relationships available from the literature. Based on this analysis an estimate of the potential contribution of wall quenching to unburned hydrocarbons is given. Finally, measured variations in total heat released per cycle, as extracted from cylinder pressure data, demonstrates the tendency towards bulk flame extinction near the lean limit for a given engine. The in-cylinder conditions that contribute to flame extinction and thus high emissions of unburned hydrocarbons are investigated. The relative importance of these sources of unburned hydrocarbons is compared and various approaches for reducing each source is discussed and, where possible, demonstrated.

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。More stringent emission legislations will increase the pressure on conventional propulsion systems like diesel engines operated with HFO. On the other hand, large gas engines with lean air/fuel-mixture are becoming an interesting alternative, particularly if the combustion process is flexible with respect to the methane number of the fuel gas. However, the combustion efficiency of large gas engines is strongly limited by the self-ignition of the endgas (knock) depending on the gas quality. As a consequence, it is an important goal for future gas engine development to optimise the combustion process for different gas qualities and compositions. Due to the complexity of the kinetically controlled processes of the irregular combustion (knock) and emission formation these investigations were carried out experimentally in the past, what is time and cost consuming and does not allow a full understanding of the processes involved. Therefore, a numerical method was developed to model the knocking combustion and the formation of nitric oxides for a large gas engine in dependency of the fuel gas chemistry. With this approach optimal operating parameters were investigated for a given fuel composition and methane number. A comprehensive simulation approach based on a 0D-2-Zone combustion model was enhanced for theseinvestigations. The burn rate was predicted with a phenomenological combustion model. The knocking combustion and nitric oxide emissions for different fuel compositions were modelled with detailed reaction chemistry. Therefore, a suitable CH4/C3H8-mechanism was chosen, validated and reduced by means of a sensitivity analyses. Since the knocking combustion is related to the fast burning cycles, an empirical cycle-to-cycle model was implemented. All models were calibrated with measurements of a large gas engine with pre-chamber spark plug. A good correlation of the simulation results with the measured burn rates, NOx concentrations and knock intensities could be observed. With this thermodynamic approach detailed studies were carried out for fuel gas with methane numbers between 65 and 100 in order to identify the impact of engine parameters like the compression ratio, inlet valve closing, EGR-rate and the boost pressure on fuel efficiency. The boundaries for these investigations were the knock limit of the combustion process and the legislation for the nitric oxide emissions. Detailed investigations were carried out for IMO TIER III, TA Luft and TA Luft ½ and the impact of the mentioned engine parameters is discussed. In an additional step, the thermodynamic model was combined with a metaheuristic optimisation method in order to achieve optimal results for the process efficiency and a given limit of the NOx-emissions by searching the best combination of spark timing, compression ratio, boost pressure, equivalence ratio and miller timing in the multiparameter space. The optimization results are presented in dependency of the fuel gas quality, too. The impact of different fuel parameters like the methane number and the fraction of inert gases (N2, CO2) on the engine process are described with respect to the burn rate, the knock limit and the NO-formation. The impact of the fuel quality on the engine design is documented. The numerical method based on 1D-simulation and detailed chemistry is regarded as new and innovative. The discussion of different fuel gas qualities and emission limits provides a detailed understanding of the thermodynamic process of large gas engines

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。At Caterpillar Motoren GmbH in Kiel, Germany major emission reduction technologies have been investigated in the recent years. This will build a solid base for the development path towards IMO Tier 3 emission legislation. One ofmthese technologies is the exhaust gas recirculation, already established in passenger car and truck engines to reduce nitrogen oxide emissions of Diesel engines. However, deploying exhaust gas recirculation onto a medium speed Diesel engine for marine applications is not just copying existing concepts. The specific definition of nitrogen oxide emission limits inside and outside of the emission control areas as well as the compliance with different sulfur emission limits were the main drivers for a concept that is tailored to the needs of marine applications. Following a general concept selection phase a technology demonstrator engine was built at Caterpillar Motoren, based on the proven M32C Diesel engine. The chosen concept is highly flexible with regards to emission limits and fuel quality, thus enabling a cost optimized operation depending on shipping routes. To fulfill these criteria a new charge air path architecture was realized by rebuilding an existing IMO 2 compliant 6M32C Diesel engine in the lab. But not only the engine’s air path had to be redesigned completely. As one of the major principle penalties of exhaust gas recirculation is an increased smoke emission, also the fuel injection equipment had to be upgraded to the latest state-of-the-art technology. This gives the opportunity to optimize the combustion process to enable invisible smoke emission under all operating conditions. As a result, the lab engine is capable to fulfill IMO Tier 3 emission limits with activated exhaust gas recirculation by burning low sulfur MDO. The operation mode can be switched to an IMO Tier 2 compliant and cost optimized HFO burning operation mode outside the emission control areas. The following paper describes the concept architecture, summarizes the main test results of the lab engine and describes the positive aspects as well as the challenges of the chosen concept.

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。The new limits for NOx emission in ECA countries for large-bore engines in effect since 2016 bring the law values close to zero. Since NOx are mainly formed in high temperature zones, the research has been oriented towards reducing the combustion temperature by low compression temperature or using gas fuels. However, exhaust gas recirculation has been adopted with success for a few decades in high-speed diesel engines. This study describes the application of exhaust gas recirculation in a single-cylinder large-bore medium-speed research engines: the system permits to cool the exhaust gas and mix them with the charge air in the intake manifold, likewise in smaller engines. Tests were carried out with exhaust gas rate up to 30% at engine load ranging from 10 to 20 bar, as indicated mean effective pressure. All the tests were run at constant speed of 900 rpm. In addition, two injection pressure levels were tested. The results showed that exhaust gas in the mixture charge reduced the combustion temperature, abating NOx up to 95%. However, this implied longer combustion duration worsening the engine fuel economy. To improve the fuel economy, Miller cycle was applied and exhaust gas rate reduced. The outcomes claimed more favorable NOx-fuel consumption trade-off to meet the law limits, which can be optimized by tuning the injection pressure and timing.

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。After a long-term use of a power machinery, the rubber portion of the elastic coupling might change in someway and deviate from the parameters or characteristics designed. Due to this deviation, the inherent parameters of the power set will change, which might cause the unstable adjust of the speed control system and the occurrence of malfunctions. Thus, it is extremely essential estimating the actual parameters of a elastic coupling stiffness after a period of running. In order to solve the severe wear of the timing gears of a certain type diesel engine set, the torsional vibration calculation of the engine shafting has been done, which shows that the stiffness of the coupling has a maximum effect to the whole shaft by the first vibration mode. Hence, the coupling is highly concerned,in the meantime,a torsional vibration test on site has been done. The natural frequencies of the test were compared with the theoretical calculation using the parameters designed, which illustrates an error of 9% at most. The torsional-vibration equivalent simulation model was established to calculate the high-elastic coupling stiffness which is 0.54MNm/rad based on the test results. With this stiffness, the error of the natural frequencies has been decreased to 1.1%. Since the original stiffness of the coupling is 0.36MNm/rad, the actual coupling stiffness is no longer meet the designed one. Obvious crack damages can been observed from the coupling unloaded. These results indicates that the abrasion of the gears was might caused by the change of the power set inherent figures through the deviation stiffness of the coupling, which leads to the instability of the speed control system. After the replacement of the new coupling, a test has been done on board again. The stiffness of the new coupling has been calculated with the same method, which is 0.42MNm/rad. This result is basically consistent to the stiffness 0.44MNm/rad obtained from a dynamic torsional performance test station, which verified the effectiveness of this method. This paper presents a reverse estimation method calculating the real-time dynamic stiffness of the couplings by shafting torsional vibration test of the power unit on site and establishing an accurate torsional-vibration simulation model of a power shaft which is corrected by the test results. Using this method, it can not only be learned of the realtime dynamic stiffness of the couplings, but also has been used to discover crack damages of a high-elastic coupling on a diesel set, which prevented the occurrence of an unnecessary accident. In this way, this estimation methodprovides a new idea of diagnosis and can be applied to fault diagnosis of a power machinery.

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。Ship emissions are anticipated to increase with the expected rise in commercial shipping, particularly in the Arctic, if preventive actions are not implemented. Shipping represents 9% of the global SOx emissions and 18-30% of the global NOx emissions. Share of shipping in the global black carbon (BC) emissions is less than 2%, however, in the north of 70° latitude BC mostly originate from shipping [1, 2]. BC increases global warming and ice melting through deposition on ice and snow. The international maritime organisation (IMO) limit for BC is anticipated, and work is launched to establish definition and methodology for BC. BC measurements and its definition are known to be challenging. For example, results from different experimental techniques, absorptive, refractive and thermal, differ from each other, but only a few studies provide detailed insight on the BC emissions from ships. This work on BC measurement techniques is realised within the “SEA-EFFECTS BC” project in co-operation with research organisations and industrial partners. BC emissions were measured with Wärtsilä Vasa 4R32 marine engine at VTT’s laboratory by using IMO relevant measurement methods, for example OC/EC, MAAP, FSN, MSS and PAS. In-depth analysis of other emissions in parallel to BC measurements were used to increase understanding of the results obtained with different techniques, which is a prerequisite for further development. Tested fuels with sulfur contents ranging from 0.1% to 3.5% were used in order to generate different exhaust gases from marine engine in realistic conditions. Preliminary analysis of the results by using different techniques to measure BC emissions from ships are shown. Future work will focus on the on-board validation of measurement methods, and in-depth evaluation of the results to increase understanding of applicability of the methods. Other aspects of the “SEA-EFFECTS BC” project deal with on-line monitoring and business opportunities in the field of emission measurements. References 1. Winther, M. et al. Emission inventories for ships in the arctic based on satellite sampled AIS data. Atmospheric Environment 91, 2014, 1-14. 2. AMAP. The Impact of Black Carbon on Arctic Climate, 2011. By: P.K. Quinn et al. Arctic Monitoring and Assessment Programme (AMAP), Oslo. 72 pp.

该论文已在芬兰赫尔辛基举行的第28届CIMAC大会上发表。论文的版权归CIMAC所有。Combustion engine power plant related technologies play a significant role in the energy industry. Today, global challenge over whole energy field is to reduce greenhouse gas emissions to combat climate change. This can be achieved by increasing energy efficiency, and by finding alternative and renewable options instead of conventional fossil energy sources. Work on fuel flexibility was conducted within the Future Combustion Engine Power Plant programme (FCEP) of the Cluster of Energy and Environment (CLEEN) in Finland. A number of fuel options, including challenging liquid biofuels and their treatment, as well as gaseous fuels, were explored for different engine concepts. LNG was found to be potential solution to oncoming environmental requirements in shipping. Biogas was studied as regards upgrading technologies, particularly siloxane removal, which is a weak spot for biogas from wastewater and landfills. Mediumspeed engine was tested by using different fuels. Some of the fuels were challenging, and therefore pre-treatment methods for difficult fuels were developed to enable their use in medium-speed engines. Combustion properties of various fuels were studied with special ignition test unit, with a medium-speed and with a high-speed engine. Some fuels yielded promising results when engine performance and emissions are considered. A special task devoted to development of a diesel-ignited dual fuel ethanol high-speed engine for non-road machinery. The developed engine can be switched from diesel to diesel-ethanol operation at any load without noticeable change in engine operating point. Work on fuel flexibility within the FCEP programme took steps towards increased fuel flexibility, and consequently, towards better energy security in Finland. In addition, the demand for lower environmental impact of the current combustion engines was sought for. The structure and form of FCEP programme supported close cooperation of the industrial and research partners. This kind of cooperation and further development in the field of fuel flexibility is still needed.

该论文已在赫尔辛基举行的第28届CIMAC大会上发表，论文的版权归CIMAC所有。ABSTRACT In the late 1980’s the International Maritime Organisation (IMO) started work on reducing air pollution from ships. Since then in a parallel movement to automotive application, the introduction of further legislation and emission regulations have seen the introduction of low sulphur fuels (0.1% sulphur limit inside Emission Control Areas, meaning an unprecedented increase in MGO consumption) and common rail diesel injection equipment. Increasingly marine grade fuels are nearing the specification of that seen in the automotive industry, such as the potential introduction of FAME into ISO specs. As in the automotive industry, injection equipment manufacturers are also moving to increased pressure and temperature common rail systems. It can be noted that large two stroke engines are now also using Common Rail systems; however these are relatively low pressure at the rail (1000 Bar) and are often designed to operate on both MGO and HFO. Common rail engines not only offer improvement in emissions but are also more efficient and allow more operational flexibility than their predecessors. It is anticipated that next generation medium speed engines will increase the pressure at the rail and will continue to run on both HFO and MGO. High pressure common rail diesel engines are currently seen on MGO only vessels such as high speed Naval or Coastguard vessels.

该论文已在赫尔辛基举行的第28届CIMAC大会上发表，论文的版权归CIMAC所有。ABSTRACT Wärtsilä has performed full-scale engine tests with advanced Miller timing and 2-stage turbocharging on diesel engines in the Engine Laboratory since year 2006. The main objective was to explore the potential of advanced Miller timing as a means to reduce NOx emissions and fuel consumption and also to explore the potential for increased power density. Totally eight test engines of different types, including a single-cylinder research engine, have been tested since then at an overall pressure ratio (PIC) of up to 13 and brake mean effective pressure (BMEP) of up to 36 bar. The total operating time of these engines was 11400 hours, and most of the operation was on heavy fuel. With gas engines, both spark-ignited gas (SG) engines and dual fuel (DF) engines testing started in 2011. The main objective with these tests was to explore the potential for an increased BMEP through a widened operating window between knock and misfiring limits. Considerably higher engine efficiency was also expected. Totally six test engines of different type and size, including a single-cylinder research engine, have been tested. The total operating time of these test engines is 6500 hours. A BMEP of up to 32.5 bar was reached without facing problems with self-ignition and knocking. The highest overall PIC run on the gas versions is ca 9.0.

该论文已在赫尔辛基举行的第28届CIMAC大会上发表，论文的版权归CIMAC所有。ABSTRACT With increased awareness of environmental issues and regulations, developments for middle and high speed engines are progressing towards engines with low fuel consumption and low harmful substances such as NOx in the exhaust gas. As one of the methods to solve a problem, these engines have improved the combustion efficiency by increasing the internal cylinder pressure. Due to this improvement, middle and high speed engine bearings are required high-temperature strength by higher load and higher temperature around shaft. On the other hand, bearing alloy is requiring conformability and corrosion resistance, it becomes necessary to develop a bearing alloy having higher strength without losing conformability and corrosion resistance. Conventionally, Al-Sn-Si alloy bearing have been used in these engines. This material has both strength and conformability, its properties are contradictory. And Al-Sn-Si alloy also has corrosion resistance. Sn phase disperse in the aluminum alloy matrix, it gives not only conformability but also good sliding properties to bearing alloy. Si particles disperse same as Sn, it prevent to seizure between bearing alloy and shaft to scrape off aluminum alloy attached on the shaft. About aluminum matrix, bearing strength depends on aluminum matrix strength and its strong oxide layer prevents corrosion.