Two-stroke Diesel Engine Research Articles

2행정 대형 디젤엔진의 성능향상을 위한 연료첨가제의 실험적 연구

In an effort to reduce the onset of global warming, the International Maritime Organization Marine Environment Protection Committee (IMO MEPC) proposed the reduction in ship speeds as a way of lowering the proportion of carbon dioxide (CO2 ) in the Green House Gas emissions from ships. To minimize fuel costs, shipping companies have already been performing slow steaming for their own fleets. Specifically, the slow steaming approach has been adopted for most ocean-going container lines. In addition, because of the increased marine fuel cost that is required to enable increased capacity, there is an urgent need for more advanced fuel-saving technologies. Therefore, in this present study, we propose a fuel-cost reduction method that can im- prove the performance of diesel engines. We introduce a predetermined amount (0.025% of the amount of fuel used) of fuel addi- tive (oil-soluble calcium-based organometallic compound). For improved experimental accuracy, as the test subjects, we utilize a large two-stroke diesel engine installed in land plants. The loads of the test engine were classified as low, medium, and high (50, 75, and 100%, respectively). We compare the engine performance parameters (power output, fuel consumption rate, p-max, and exhaust temperature) before and after the addition of fuel additives. Our experimental results, confirmed that we can realize fuel-cost savings of at least 2% by adding the fuel additive in low load conditions (50%). Likewise, the maximum combustion pressure was found to have increased. On the other hand, we observed that there was a reduction in the exhaust temperature.

Testing scuffing resistance of materials for marine 2-stroke engines – Difficulties with lab scale testing of a complex phenomenon

Optimising sliding materials of marine two-stroke diesel engine cylinders for reduced risk of scuffing is imperative because of the high costs associated with replacing the cylinder liner. But how can a complex and poorly understood phenomenon such as scuffing be tested? This study investigates the potential of material selection based on lab tests. Experience from ship operation is combined with analysis of lab scale scuffing tests to evaluate the possibilities of gaining applicable knowledge from scuffing testing. Two piston ring materials, a grey cast iron and a plasma sprayed cermet coating, both currently used in engines, were tested. Each of the materials was tested with two surface characters, achieved by run-in in a real engine and by fine grinding respectively. The ranking of the two materials proved to differ between the two surface characters. In the tests, scuffing could only be detected when all oil had become removed from the contact by being adsorbed by agglomerated wear debris and scraped away. This and other critical mechanisms behind scuffing in the tests are thoroughly discussed and compared to possible mechanisms taking place in the engine.

Analysis of Two Stroke Marine Diesel Engine Operation Including Turbocharger Cut-Out by Using a Zero-Dimensional Model

In this article, the operation of a large two-stroke marine diesel engine including various cases with turbocharger cut-out was thoroughly investigated by using a modular zero-dimensional engine model built in MATLAB/Simulink environment. The model was developed by using as a basis an in-house modular mean value engine model, in which the existing cylinder block was replaced by a more detailed one that is capable of representing the scavenging ports-cylinder-exhaust valve processes. Simulation of the engine operation at steady state conditions was performed and the derived engine performance parameters were compared with the respective values obtained by the engine shop trials. The investigation of engine operation under turbocharger cut-out conditions in the region from 10% to 50% load was carried out and the influence of turbocharger cut-out on engine performance including the in-cylinder parameters was comprehensively studied. The recommended schedule for the combination of the turbocharger cut-out and blower activation was discussed for the engine operation under part load conditions. Finally, the influence of engine operating strategies on the annual fuel savings, CO2 emissions reduction and blower operating hours for a Panamax container ship operating at slow steaming conditions is presented and discussed.

Scuffing resistance testing of piston ring materials for marine two-stroke diesel engines and mapping of the operating mechanisms

The incentive is strong for optimising sliding materials to reduce the risk for scuffing. In this study, scuffing tests were performed aiming towards finding new piston ring materials for greener marine diesel engines and also towards understanding scuffing mechanisms better. The tested ring materials where grey iron, Stellite 6, plasma sprayed cermet and high velocity oxy fuel (HVOF) cermet (both cermets with the same compounds: Cr-carbide, Ni, Cr, Mo). The Stellite 6 and HVOF cermet performed somewhat better than the other two materials. Microscopic and spectroscopic studies of failed sample surfaces revealed several characteristic features. It was clear that different mechanisms are active simultaneously, at different parts of the samples. Based on these results, we propose a hypothesis for a scuffing process involving several stages with distinctive mechanisms. Further studies are needed to strengthen this hypothesis and to relate these findings to actual deterioration mechanisms in the engine.

Modelling and simulation of a marine propulsion power plant with seawater desulphurisation scrubber

Exhaust gas scrubber is one of the options to comply with the new regulations for sulphur emissions in the shipping industry. This article presents a model-based approach to assess the energy and environmental performance effects from the installation of a seawater flue gas desulphurisation scrubber on a marine two-stroke diesel engine propulsion plant. A mathematical model was built that describes the governing physical and chemical behaviour of the integrated machinery system. The model was used to examine the impact of main scrubber design characteristics on the engine fuel consumption under different engine loads. The results indicate that the desulphurisation system causes an increase in the engine fuel consumption, for constant power output. This is due to the increased back-pressure to the turbocharging system caused by the pressure drops in the desulphurisation system. This effect can be partly mitigated by the installation of forced-draft fans after the desulphurisation system limiting the negative impact on the overall system efficiency to half of its initial value.

Application of a multi-zone combustion model to investigate the NOx reduction potential of two-stroke marine diesel engines using EGR

The most promising solution for propulsion of marine vessels currently and for the near future is the two-stroke low-speed diesel engines. Despite its advantages, as far as specific fuel oil consumption, power density and reliability is concerned, it suffers from increased NOx emissions mainly because of its low rotational speed. But the upcoming NOx emission legislation (Tier III) in the marine sector requires considerable reduction of NOx emissions towards levels which have not yet been commercially achieved using primary methods. This creates new challenges for the development and application of innovative techniques that could reduce engine’s NOx emissions with the lowest possible fuel penalty. This is important considering current and future fuel prices. The large size of the 2-stroke marine engine makes the use of experimental techniques, to investigate this potential, expensive and time consuming. Modelling can significantly contribute towards this effort and result to reduction of research and development cost. Among the most effective in-cylinder techniques for NOx reduction is EGR, a proven technology for smaller engines used in the transport sector. In the present study, it is investigated via modelling, the potential to reduce NOx emissions of two-stroke marine engines using EGR. Despite the technological difficulties resulting mainly from the use of Heavy Fuel Oil (HFO), which makes the application of conventional EGR techniques difficult, it is worthwhile investigating the NOx reduction potential, since significant progress has been achieved towards the development of new EGR gas cooling techniques and scrubber technologies for removal of sulphur species from the exhaust gas. The present investigation makes use of an existing well validated multi-zone combustion model, initially developed for high-speed DI diesel engines. The model has been successfully applied in the past, to investigate heavy duty diesel engine NOx reduction via EGR, providing favourable results. Currently it is modified and applied on a two-stroke marine diesel engine using EGR. Model evaluation is based on experimental data acquired from the international literature, due to lack of experimental data for 2-stroke engines. The analysis of derived results reveals model’s ability to predict both engine performance and NOx emissions but most important the ability to predict the overall effect of EGR on NOx emissions in a qualitatively correct way. The results also reveal the strong potential of EGR to control NOx emissions of 2-stroke engines with relatively low fuel penalty compared to alternative techniques.

Nonlinear Adaptive Control of Exhaust Gas Recirculation for Large Diesel Engines

A nonlinear adaptive controller is proposed for the exhaust gas recirculation system on large two-stroke diesel engines. The control design is based on a control oriented model of the nonlinear dynamics at hand that incorporates fuel flow and turbocharger speed changes as known disturbances to the exhaust gas recirculation. The paper provides proof of exponential stability for closed loop control of the model given. Difficulties in the system include that certain disturbance levels will make a desired setpoint in O2 unreachable, for reasons of the physics of the system, and it is proven that the proposed control will make the system converge exponentially to the best achievable state. Simulation examples confirm convergence and good disturbance rejection over relevant operational ranges of the engine.

Modeling of a Large Marine Two-Stroke Diesel Engine with Cylinder Bypass Valve and EGR System

A nonlinear mean value engine model (MVEM) of a two-stroke turbocharged marine diesel engine is developed, parameterized and validated against measurement data. The goal is to have a computationally fast and accurate engine model that captures the main dynamics and can be used in the development of control systems for the newly introduced EGR system. The tuning procedure used is explained, and the result is a six-state MVEM with seven control inputs that capture the main system dynamics.

舶用SCRシステムを搭載した大型ディーゼル機関の就航試験結果

The International Maritime Organization (IMO) has decided to implement a tighter limit for nitrogen oxide (NOx) emissions from ships operating in emission control areas (ECA) from 2016. Hitachi Zosen Corporation has developed a marine SCR system to denitrate exhaust gas of large two-stroke diesel engines in order to comply with the IMO regulation. Nippon Kaiji Kyokai issued a certificate attesting that certifies a large two-stroke diesel engine Hitachi-MAN B&W 6S46MC-C7 fitted with the SCR system achieved the NOx emission level required by the IMO regulation. The system was installed on a new-built vessel, and verification tests were carried out for a long period.In this paper, we will present a summary of the marine SCR system, and report on sea trial results of the marine SCR system installed on the new-built vessel, as well as those of a similar SCR system installed on a multi-cylinder test diesel engine in order to solve technical issues encountered during long-term service test.

Development of a model for the prediction of the fuel consumption and nitrogen oxides emission trade-off for large ships

The international regulations on fuel efficiency and NOx emissions of commercial ships motivate the investigation of new system layouts, which can comply with the regulations. In combustion engines, measures to reduce the fuel consumption often lead to increased NOx emissions and careful consideration of this trade-off mechanism is required in the design of marine propulsion systems. This study investigates five different configurations of two-stroke diesel-based machinery systems for large ships and their influence on the mentioned trade-off. Numerical models of a low-speed two-stroke diesel engine, turbochargers and an ORC (organic Rankine cycle), are used for the optimisation of the NOx and fuel consumption at design and part-load conditions, using a multi-objective genetic algorithm. Moreover, the effects of engine tuning and exhaust gas recirculation are investigated. The results suggest that increased system complexity can lead to lower fuel consumption and NOx. Fuel consumption reductions of up to 9% with a 6.5% NOx reduction were achieved using a hybrid turbocharger and organic Rankine cycle waste heat recovery system.

Effect of Cylinder Liner Oil Grooves Shape on Two-Stroke Marine Diesel Engine's Piston Ring Friction Force

The dimensions, area densities, and geometry of macroscale surface textures may affect the performance of hydrodynamic lubrication interface. Reported in this paper are the investigations of the effect of surface textures bottom shapes on the friction forces between piston ring and cylinder liner for two-stroke marine diesel engine, using numerically generated textures and average Reynolds equation. These textures are on the cylinder liner surface in the form of circumferential oil grooves with different aspect ratios and different area densities. The hydrodynamic pressure distribution is also calculated using Reynolds boundary condition. The results revealed that the bottom shape could positively affect the friction between moving surfaces, as it could provide a microwedge or microstep bearing that tends to enhance the lubrication condition between piston ring and cylinder liner.

Comparison of ship plant layouts for power and propulsion systems with energy recovery

Currently the increase in fuel costs and the need to reduce Carbon Dioxide (CO2) emissions have encouraged the search for even more efficient solutions to be adopted in energy conversion systems for ship installations. These systems generally include thermal prime movers consisting mainly of two-stroke or four-stroke diesel engines, a waste heat recovery (WHR) plant, a steam turbine and possibly a gas turbine, as well as electric machinery. These components may be used in various ways and through different plant configurations, whose optimization is under investigation by researchers and diesel engine manufacturers. In this paper four schemes of ship propulsion plants, using a two-stroke diesel engine equipped with waste heat recovery system are presented, analysed and compared by simulation. Some of the considered layouts can include also an electric motor to support the main engine in providing power to the propeller. On the other hand the electric power can be generated from both the diesel generators and the WHR plant. The considered propulsion plant schemes are compared in order to identify the configuration that meets in the best way the request of propulsive, electrical and thermal power of a 158000 dead weight tonnes (DWT) crude oil tanker ship, belonging to the Premuda Company, taken as a reference unit in this study. The comparison is carried out taking into account the payback time of the installation, the annual saving in the fuel outlay and the CO2 emissions. This last parameter is considered through the evaluation of the Energy Efficiency Design Index (EEDI).

Investigating the microstructures of piston carbon deposits in a large-scale marine diesel engine using synchrotron X-ray microtomography

The three-dimensional structures of carbon deposits on piston surfaces in a large-scale two-stroke marine diesel engine have been nondestructively investigated using synchrotron X-ray microtomography. The results indicate that the piston carbon deposit (PCD) has a flat bottom surface where many irregular structures accumulate. Based on the microtomography, cross sections of the carbon deposit sample can be obtained in the direction perpendicular to the piston surface. A uniform deposition is found on the bottom surface of piston, where many tiny pores appear, which implies that a liquid film first forms on the piston surface and subsequent nucleation boiling occurs due to the high surface temperature. A significant decrease in the PCD density is observed when the PCD thickness is below a threshold of approximately 150μm. However, the PCD density remains almost unchanged from 150 to 1800μm. This result suggests that there should be different dominant formation mechanisms at these two stages. The local morphology, especially the approximately circular structure and the smooth boundary on the PCD surface, indicates that condensation should be the major factor controlling the formation of the PCD surface. However, the internal pores and minimal swelling on the surface could result from other mechanisms.

Numerical modeling of lubrication of piston ring of two-stroke marine diesel engine considering the effect of multi-scale grooves on the cylinder liner

The method of lubrication for piston ring in some types of low-speed two-stroke marine diesel engines is completely different from those in medium- or high-speed diesel engines since the inner surface of cylinder liners are textured with elliptical grooves in macroscale and honing texture in microscale. In this paper, a numerical model has been developed to study the potential of use of cylinder bore surface texturing, in the form of circumferential oil grooves with different dimensions and densities, to improve the tribological properties of piston ring–cylinder liner tribosystem. The average Reynolds equation has been employed in the area of microscale texture and the effect of macroscale grooves has been incorporated to improve the currently lubrication model. The focus is put on cavitation formation condition and boundary condition in grooves within the area of lubrication, analysis of the effect of macrogroove dimension characters and distribution of grooves on the tribological performance of piston compression ring. The solution provides the hydrodynamic friction force, boundary friction force, coefficient of friction, and the total friction force. The results show that the cylinder liner oil grooves can efficiently be used to maintain hydrodynamic effect. It is also shown that optimum surface texturing may substantially reduce the friction losses between piston ring and cylinder liner.

Fault Tree Analysis in the Reliability of Heavy Fuel Oil Supply

Marine systems are complex and through the analysis of their reliability it is necessary to observe the reliability of their subsystems and components. With regard to the fact that the reliability is functionally dependent on faults, for the purpose of this study special attention has been given to possible faults on the heavy fuel oil supply pump of a two-stroke marine diesel engine MAN B&W 5L90MC. A deductive approach to reliability analysis, i.e. fault tree analysis method (FTA), has been used. By the use of this method it is simpler to identify the system’s weak link and it is shown that the method gives the basis for the ship’s system reliability analysis. Based on FTA analysis this paper suggests system parameters that require continuous monitoring in order to achieve reliability. The results show the behavior of the components in case of faults and this approach can help to create a plan of action in order to enforce timely corrective and preventive action and, accordingly, increase the rate of reliability of the entire ship’s systems.

MV “CRYSTAL STAR” Diesel Turbocharger Surge Cause Analysis and Troubleshooting

Currently shipping costs are increasing sharply due to the rising oil prices. In order to reduce shipping costs, most low-speed two-stroke diesel engines run at low speeds to reduce fuel oil consumption, and this measure might result turbocharger surge. For modern marine diesel engines, the exhaust gas turbochargers are becoming more and more important; their working conditions have a direct impact on the performance of diesel engines, consequently affecting the operation of the ship. Surge will fail a turbocharger to achieve the supercharging ratio, damage the turbocharger components and even lead to a damage accident of the whole turbocharger. Therefore, a good understanding of the reasons for marine diesel engine turbocharger surge will help to prevent and eliminate turbocharger surge in operation. This paper is to make an analysis on the special surge mechanism occurred to the turbocharger on MV "Crystal Star", and propose some appropriate supervisory and preventive measures against the problem.

Stress Analysis on a Connecting Rod Big End Bearing of Two-Stroke Marine Diesel Engine

In this paper, the multi-body dynamics software EXCITE was used to simulate the connecting rod big end bearing of two-stroke marine diesel engine. The result showed the stress analysis of connecting rod big end bearing. The purpose is to provide a theoretical basis for the actual conditions of connecting rod big end bearing, and to improve the design of the crankshaft structure.

Investigation on the microstructure and pore characteristics of carbon deposit on the piston top land of marine diesel engine using synchrotron X-ray microtomography

It is of significance that massive carbon deposit (CD) is observed in the combustion chamber of large-scale two-stroke marine diesel engine due to high thermal load, poor fuel quality, oil degradation and combustion and high particle emission. The structure and characteristics of CD have great influence on the engine performance and emissions. In this paper, we use synchrotron X-ray microtomography of Shanghai Synchrotron Radiation Facility to visualize the three dimensional structure of CD on the piston top land. Based on the quantitative image analysis, microstructure and pore characteristics of CD are investigated. The results show the CD thickness is around 1mm, half of clearance between cylinder liner and piston. However, the surface structure shows significant friction scratches, which suggests the oil film could be destroyed by the CD. The results of crackle distribution show that intensive crackle is located on the CD surface (inner and outer surfaces), while loosen crackle is found inside the CD. This implies that the crackle formation mechanism is different on the inner and outer surfaces. The analysis of pore connectivity indicated that most of cracks are connected, and the porosity is in the range between 10.9% and 12.8% in present experiments. In addition, small hole connected by cracks and the crackle could have impact on the absorption and desorption of unburnt emissions.

A comparison of advanced heat recovery power cycles in a combined cycle for large ships

Strong motivation exists within the marine sector to reduce fuel expenses and to comply with ever stricter emission regulations. Heat recovery can address both of these issues. The ORC (organic Rankine cycle), the Kalina cycle and the steam Rankine cycle have received the majority of the focus in the literature. In the present work we compare these cycles in a combined cycle application with a large marine two-stroke diesel engine. We present an evaluation of the efficiency and the environmental impact, safety concerns and practical aspects of each of the cycles. A previously validated numerical engine model is combined with a turbocharger model and bottoming cycle models written in Matlab. Genetic algorithm optimisation results suggest that the Kalina cycle possess no significant advantages compared to the ORC or the steam cycle. While contributing to very high efficiencies, the organic working fluids possess high global warming potentials and hazard levels. It is concluded that the ORC has the greatest potential for increasing the fuel efficiency, and the combined cycle offers very high thermal efficiency. While being less efficient, the steam cycle has the advantages of being well proven, harmless to the environment as well as being less hazardous in comparison.

Modal Analysis of Crankshaft for Two-Stroke Marine Diesel Engine Based on Block Lanczos Method

Modal analysis of crankshaft for two-stroke marine diesel engine is carried out on the block lanczos method. The finite element models of crankshaft is created in ANSYS. The crankshaft first 13 natural frequencies and mode shapes are shown as the result and lay the foundation for optimal design of the crankshaft and dynamic response.