Two-stroke Marine Diesel Engine Research Articles

A full-scale CFD model of scavenge air inlet temperature on two-stroke marine diesel engine combustion and exhaust emission characteristics

Most ships in the maritime transport sector are equipped with large two-stroke marine diesel engines in their propulsion systems. Therefore, ensuring stable and long-term operation of these engines is crucial to maintaining freight transportation. The design of the ship's machinery, particularly the diesel engine, is a crucial step in achieving this goal. Computational Fluid Dynamics (CFD) tools can be used to achieve this goal. This article presents a full-scale CFD study on the effect of different scavenge air inlet temperatures (300, 312, 330 and 340 K) on the combustion process and generation of exhaust emissions in a two-stroke marine diesel engine using ANSYS Forte software. Regarding the cylinder pressure, the presented model agrees well with experimental data. The maximum cylinder pressure decreases as the scavenge air inlet temperature increases, whereas the maximum cylinder temperature increases as the scavenge air inlet temperature increases. The maximum NOX, CO and UHC emission values are calculated to be 2256.5, 20375.8 and 3743.9 ppm, respectively, at a scavenge air inlet temperature of 340 K. Due to the higher combustion temperature caused by the increasing scavenge air inlet temperature, it is observed that the exhaust emission levels increase.

Exergy analysis under consideration of operational parameters by numerical approach in a two-stroke marine diesel engine

This paper presents a numerical approach of the influence of operational parameters on the exergy terms in a two-stroke marine diesel engine. Operational parameters are introduced as different start of injection (-4, -2, 0 and 2 °CA) and scavenge air inlet temperature (300, 312, 330 and 340 K) values. The energy analysis is conducted within a closed cycle by using a three-dimensional computational fluid dynamics code. The simulation results are compared with the corresponding experimental pressure data in the literature and show good agreement. Also, the exergy analysis is performed by a developed in-house computational code. Various exergy rates and cumulative exergies are detected and computed separately at operational parameters. The study reveals that varying the start of injection timing from −4 to 2 °CA at full load condition results in a decrease in exergy efficiency from 43.45 % to 41.36 %. Furthermore, an increase in scavenge air inlet temperature from 300 K to 340 K leads to a reduction in exergy efficiency from 42.83 % to 41.44 %. These findings underscore the critical influence of injection timing and scavenge air temperature on the exergy performance. In light of these results, this paper gains more insight into the impact of design parameters of a two-stroke marine diesel engine on exergy efficiency and presents a preliminary data for marine diesel engine manufacturers in the design of a two-stroke marine diesel engine that uses energy efficiently.

Modeling and simulating axial vibrations on the crarkshaft of the large two-stroke marine diesel engine

The axial vibration is the strong vibrated phenomenon occurring on the main propulsion using a large two-stroke marine diesel engine. This article researches to build a mathematical model of the axial stiffness coefficient and force generated by the geometric configuration of the crank pin-crank web assemblies and the combustion gas force. The numerical simulation is performed by finite element method, using ANSYS software, applied to the main engine MAN B&W 6G70ME. Keywords: Axial stiffness; crank pin–crank web set; axial force; diesel crankshaft; large two-stroke marine diesel engine; Axial vibration simulation.

Design assessment of the range of permissible operation modes of a marine two-stroke diesel engine

In the practice of operating marine diesel engines, as a limiting characteristic for mechanical stress, a characteristic corresponding to a constant effective torque, which is proportional to the average effective pressure, is used. There is no such unambiguity regarding the restrictive characteristics of thermal intensity. Limitations on the thermal stress of a diesel engine depend on its design features and the efficiency of the cooling system of the cylinder-piston group. At the diesel engine design stage, it is important to assess in advance whether the operational characteristics correspond to the technical specifications.
 The work carried out computational and theoretical studies of the operational parameters of the main marine two-stroke diesel engine operating according to the screw characteristic, which affect its mechanical and thermal stress, and determined the expected limiting characteristics of the mechanical and thermal stress. The studies were carried out for wide ranges of changes in the weight coefficient of the screw characteristics and the relative power of the diesel engine. The estimated design ranges of diesel operating modes are given, excluding its mechanical and thermal overload, and an assessment of the permissible weighting of the screw characteristics is given. The results obtained were compared with the characteristics of a marine four-stroke diesel engine.

Effects on of Blended Biodiesel and Heavy Oil on Engine Combustion and Black Carbon Emissions of a Low-Speed Two-Stroke Engine

Abstract The effects of heavy fuel oil and biodiesel blends on engine combustion and emissions were studied in a marine two-stroke diesel engine. The engine was operated under propeller conditions using five different fuels with biodiesel blends of 10% (B10), 30% (B30), 50% (B50), and sulphur contents of 0.467% low sulphur fuel oil (LSFO) and 2.9% high sulphur fuel oil (HSFO). Tests have shown that using a biodiesel blend increases the engine fuel consumption due to its lower calorific value. Heavy fuel oil has a high Polycyclic aromatic hydrocarbons (PAH) content, which leads to higher exhaust temperatures due to severe afterburning in the engine. A comparison of engine soot emissions under different fuel conditions was carried out, and it was found that the oxygen content in biodiesel promoted the oxidation of soot particles during the combustion process, which reduced the soot emissions of biodiesel. Compared to HSFO, B10, B30, B50 and LSFO, the soot emission concentrations were reduced by 50.2%, 56.4%, 61% and 37.4%, respectively. In our experiments, the soot particles in the engine exhaust were sampled with a thermal float probe. Using Raman spectroscopy analysis, it was found that as the biodiesel ratio increased, the degree of carbonisation of the soot particles in the exhaust became less than that in the oxygenation process, resulting in a decrease in the degree of graphitisation.

Investigation of Seasonal Effects on Two-Stroke Marine Diesel Engine Performance Parameters and Emissions

Investigation of Seasonal Effects on Two-Stroke Marine Diesel Engine Performance Parameters and Emissions

Simulation of ammonia injection system for a compression ignition engine

Ammonia in anhydrous and aqueous forms, are attractive carbonless fuels for future marine diesel engines. The aim of this study was to determine if these fuels could be injected into a two-stroke marine diesel engine using a unit injector system. In this study, existing in service injector hardware was used to develop a dynamic numerical injector model. The results of the simulation were then validated against injector performance literature obtained for an engine, using conventional diesel fuel oil. Using the developed numerical model, the injection performance of anhydrous and aqueous ammonia solutions could then be investigated. The study found good correspondence between the model and the pressure trace found in literature. In terms of fuel injection performances, it was found that both fuels were injectable with a unit injector, however the correct volume and mass required were not achieved. Furthermore, injection timing and duration were affected marginally. For aqueous ammonia, with the higher bulk modulus, injection was advanced by 0.21 CA degrees and for anhydrous ammonia with a lower bulk modulus; it was delayed by 0.21 CA degrees. Overall proper operation of the injection system was observed. This outcome is promising, especially in shifting the maritime industry towards zero carbon ammonia engines.

Lubrication analysis of the piston ring for the two-stroke marine diesel engine based on modified radial tension

As the piston ring is inserted into the bore, it is forced against the liner by radial tension, thereby creating a seal. Radial tension not only affects the piston ring’s seal, but also significantly influences its tribological properties. To investigate the effect of non-uniform radial tension of piston ring on the lubrication properties, a contact finite element model of piston ring and cylinder liner tribo-pairs is constructed in this study. The contact pressure distribution between the tribo-pairs is determined based on this model. The obtained pressure is then regarded as the non-uniform radial tension of the ring, which is fitted to a formula. The formula is validated in two ways. Firstly, its generality is verified by simulating several different piston rings using the contact model and comparing their results with the formula. Second, a test rig was designed and set up to measure the piston ring’s circumferential tension. To verify the formula’s accuracy, an equivalent principle model of distributed pressure and concentrated force was proposed. This formula is used as an initial force to modify the piston ring mixed lubrication model. Based on this model, the lubrication performance of the piston ring with uniform radial tension and non-uniform radial tension into consideration is investigated. The findings demonstrate that the piston ring radial tension is of significance to its lubrication performance and can be modified to lessen local friction and wear issues, particularly those related to the piston ring gap, and thus improve the dependability of the piston ring.

Experimental Study of Identifying Emission Sources of Acoustic Signals on the Cylinder Body of a Two-Stroke Marine Diesel Engine

In this paper, an experimental method was utilized to investigate acoustic emission (AE) characteristics and to identify emission sources of the nonlinear AE signal on the cylinder body of a large low-speed two-stroke marine diesel engine in real-working conditions on the sea in misfiring and normal firing modes. Measurements focused on the AE signal acquired in a transverse direction in low-frequency (20–80 kHz), medium-frequency (100–400 kHz) and high-frequency (400–900 kHz) ranges. The collected signals were analyzed on the crank angle and crank angle-frequency domains. The results showed that all potential sources of the nonlinear AE signal could be mapped in the low-frequency range. However, only the AE signal caused by the combustion process at around the top dead center could be well-observed in the medium-to-high-frequency range. The findings also revealed that in normal firing conditions, the AE energy radiated by friction in the down-stroke period was smaller than in the up-stroke process due to gas-sealing forces. Moreover, the AE energy in the misfiring condition was higher than in the normal firing state. These outcomes considerably contributed understandings to characteristics of friction and wear around the mid-stroke area of the cylinder on a two-stroke marine diesel engine.

Development of multi-component surrogate fuel for marine diesel considering fuel physical-chemical properties

Herein, as an alternative to heavy fuel oil (HFO), a multi-component surrogate fuel was developed, consisting n-tetradecane (6.36 %), n-hexadecane (4.25 %), i-hexadecane (20 %), n-eicosane (15 %), decalin (17 %), toluene (4.45 %), naphthalene (13 %), and phenanthrene (19.94 %). The proportions of the components of the surrogate fuel were determined by studying the chemical and physical characteristics of HFO. The surrogate fuel was optimized by matching the cetane number (CN), density at 20 °C, lower heating value (LHV), and hydrogen-carbon (H/C) ratio. The developed skeletal surrogate mechanism constituted 128 species and 375 reactions. It was extensively validated using various fundamental experiments based on its single components and HFO performance under relevant engine conditions. The predicted ignition delay time in shock tubes and the concentrations of primary species in jet stirred reactors and flow reactors were in good agreement with the previously measured values. The predicted laminar flame speed in counterflow configuration was close to the experimental data. The flame spray and combustion characteristics were found to be well produced by the proposed mechanism in a fuel ignition analyzer and a two-stroke marine diesel engine. The proposed skeletal mechanism exhibited reliable overall performance for combustion behavior, indicating that it can be used for modeling HFO in realistic engine applications.

Data-driven condition monitoring of two-stroke marine diesel engine piston rings with machine learning

ABSTRACT Maintaining the condition of a vessel and its equipment guarantees the scheduled completion of voyages and the safety of the crew. This paper presents condition monitoring techniques for early detection of faults related to piston rings in remote cylinders of two-stroke marine diesel engines. Operational sensor data from the main engine of a container ship are provided by a shipping company. A graphical approach complimented by correlation heatmaps and feature importance from gradient boosting trees are used for feature selection. Support Vector Machine, Random Forest and Extreme Gradient Boosting Trees are tested for residual generation from the nominal behavior. The residual time series gives a good indication of the degradation of the system and can be used for alarm raising under strict rules. It is proven that the proposed method could alert the engine crew of a change in the condition of the piston rings much earlier than existing methods.

Fault Diagnosis for Marine Two-Stroke Diesel Engine Based on CEEMDAN-Swin Transformer Algorithm

Fault Diagnosis for Marine Two-Stroke Diesel Engine Based on CEEMDAN-Swin Transformer Algorithm

A fluid-structure coupled transient mixed lubrication model for piston ring lubrication property analysis with CMFF method

The bore's circumferential cross-section is not always a perfect circle, due to manufacturing errors, installation, and the influence of high-temperature and high-pressure gas, especially for a cylinder liner of the two-stroke marine diesel engine. This non-axisymmetric feature significantly impacts the lubrication properties of the piston ring and cylinder liner tribo-pair. To study the tribology and lubrication properties of the tribo-pair, a fluid-structure coupled transient mixed lubrication model is developed, which incorporates the piston ring curved beam model and mixed lubrication model. The key challenge lies in integrating the interface contact issue between the piston ring and bore with the structural deformation, requiring a multi-scale modeling strategy. To address this challenge, a method of coupling mesh between the finite difference method and the finite element method (CMFF) is proposed. The approach achieves the requirement for a fine mesh for the interface contact solution while maintaining the accuracy of the curved beam model for the structural response of the piston ring. Based on the model, the lubrication performance and deformation behavior of the piston ring in an elliptical bore are comprehensively analyzed. The results are compared with those of the rigid ring model to explore the overall differences. Results reveal that the current model predicts the friction is mostly caused by asperity contact between solids at the top dead center, whereas the rigid ring model predicts viscous shearing of the lubricant. The discrepancy is mainly due to the reduction of the oil film thickness between the piston ring and the cylinder liner following the consideration of ring deformation. Moreover, the minimum clearance exhibited at the piston ring end gap demonstrates the thorough consideration of the local and global lubrication performance of piston rings in the proposed model. This is significant for the resolution of local friction and wear problems of piston rings in engineering applications. Based on the work, a new framework is established for the study of the coupled performance of piston ring dynamics and tribology.

Development of a Zero-Dimensional Model for a Low-Speed Two-Stroke Marine Diesel Engine with Exhaust Gas Bypass and Performance Evaluation

Most large commercial vessels are propelled by low-speed two-stroke diesel engines due to their fuel economy and reliability. With increasing international concern about emissions and the rise in oil prices, improvements in engine efficiency are urgently needed. In the present work, a zero-dimensional model for a low-speed two-stroke diesel engine is developed that considers the exhaust gas bypass and geometry structures for the gas exchange model. The model was applied to a low-speed two-stroke 7G80 ME-C9 marine diesel engine and validated with engine shop test data, which consisted of the main engine performance parameters and cylinder pressure diagrams at different loads. The simulation results were in good agreement with the experimental data. Thus, the model has the ability to predict engine performance with good accuracy. After model validation, the variations in compression ratio, fuel injection timing, exhaust gas bypass valve opening portion, exhaust valve opening timing, and exhaust valve closing timing effects on engine performance were tested. Finally, the influence level of different parameters on engine performance was summarized, which can be used as a reference to determine the reasons for high fuel consumption in some cases. The developed engine performance model is considerable in digital twins for performance simulation, health management, and optimization.

Hierarchical Multiscale Fluctuation Dispersion Entropy for Fuel Injection System Fault Diagnosis

Abstract Marine electronically controlled (ME) two-stroke diesel engines occupy the highest market share in newly-built ships and its fuel injection system is quite different and important. Fault diagnosis in the fuel injection system is crucial to ensure the power, economy and emission of ME diesel engines, so we introduce hierarchical multiscale fluctuation dispersion entropy (HMFDE) and a support matrix machine (SMM) to realise it. We also discuss the influence of parameter changes on the entropy calculation’s accuracy and efficiency. The system simulation model is established and verified by Amesim software, and then HMFDE is used to extract a matrix from the features of a high pressure signal in a common rail pipe, under four working conditions. Compared with vectorised HMFDE, the accuracy of fault diagnosis using SMM is nearly 3% higher than that using a support vector machine (SVM). Experiments also show that the proposed method is more accurate and stable when compared with hierarchical multiscale dispersion entropy (HMDE), hierarchical dispersion entropy (HDE), multiscale fluctuation dispersion entropy (MFDE), multiscale dispersion entropy (MDE) and multiscale sample entropy (MSE). Therefore, the proposed method is more suitable for the modelling data. This research provides a new direction for matrix learning applications in fault diagnosis in marine two-stroke diesel engines.

Influence of Macro-Scale Cylinder Liner Partial Surface Texturing on the Tribological Behavior of Two-Stroke Marine Diesel Engine Piston Ring

In this paper, the influence of cylinder liner partial surface texturing in the top and bottom dead centers proximities was investigated. That influence was compared to full stroke surface texturing in order to evaluate the function of texturing on the surface of cylinder bore of low-speed marine diesel engine to improve the tribological performance of ring-liner pairs. Cylinder liner texturing has been designed in the form of macro-scale circumferential parabolic bottom shape oil grooves, with different depth-to-width ratios and area coverage density. Average Reynolds equation has been applied considering the oil flow factors through the micro asperities. Oil grooves has been numerically represented through the oil film configuration between piston ring and cylinder liner. The solution provides the cyclic average values of friction force of hydrodynamic lubrication, boundary lubrication, and total friction force. Results showed that the partial surface texturing has the superiority in improving tribological behavior of piston ring rather than that associated with full surface texturing.

Investigation on diesel spray flame evolution and its conceptual model for large nozzle and high-density of ambient gas

To reveal the theory behind the ignition phenomenon of large nozzle diameter spray and better organize the combustion of two-stroke marine diesel engine, in this article, the numerical simulation has been made by CONVERGE to study the developing process of large nozzle spray and flame in constant volume combustion chamber. Spray and flame characteristics for different nozzle diameters 0.5 mm, 0.625 mm and 0.875 mm are compared to investigate the effect of nozzle diameter on spray and flame characteristics. Then the ambient pressure is increased and a swirl is added to discuss the spray and flame characteristics under high-density of ambient gas and swirl. It was shown that for large nozzle led spray heads, there would be several stripping processes of the spray head periphery under air-dragging work. The first stripped fuel remains on the periphery of the spray upstream, evaporating and igniting. The flame propagates through the stripped fuel evaporation path from the ignition position to the spray tip. Flame propagation stops after nearly reaching the spray tip due to the lack of the combustible mixture but the presence of unevaporated liquid fuel, which was caused by the large nozzle diameter slowing down the spray tip evaporation. The liquid fuel at the spray tip then evaporates and mixes with the air. Then flame begins to propagate through the vapor fuel path, enveloping the entire spray. Increasing ambient pressure accelerates spray break-up and evaporation. The flame can directly envelop the spray through the combustible mixture in the spray tip. Adding swirl pushes the separated swirl-facing side-periphery fuel to the spray tip. Ignition occurs in the spray tip and mid-part of spray leeside then flame propagates in the direction of each other direction.

Study on the Design Stage from a Dimensional and Energetic Point of View for a Marine Technical Water Generator Suitable for a Medium Size Container Ship

The purpose of this study is to provide an overview of the development of the modern low-speed marine two-stroke diesel engine from the point of view of the technical water cooling plant, taking into account and starting from the market requirements for power and speed, with information and design options relevant to the entire shipping industry. Thus, through the ideas of this project, we analyze notions and relevant aspects of systems related to marine slow turning engines, including the basic thermodynamic structure of the technical water system designed for a marine engine. This study also presents the design criteria that define the size and design concept of the engine structure components, with a focus on the technical water cooling installation. The concepts for the main engine hot parts served by the technical water cooling installation play a vital role in the marine technical water generator. The choices the engine designer must make regarding basic auxiliary systems, such as fuel injection and exhaust valve actuation, are important factors to keep in mind when installing a technical water generator onboard a ship. The automation and control systems that govern the modern electronic engine, which drive the supply pump of the technical water cooling system can provide a simplified view of the engine development process. In order to point out the contributions of this study, it is important to focus on the calculations used to determine the main parameters of a technical water generator especially designed for a midsized container ship.

Study on the Emission Characteristics in Renewable Energy Combustion under Different Working Conditions of Marine Two-Stroke Diesel Engine

In this paper, MAN 6S35ME-B9 two-stroke diesel engine is taken as the research object. By constructing a detailed combustion reaction mechanism including CH4, C4H10O, nitrides and other substances, CHEMKIN-PRO is used to simulate the same fuel mixing ratio and excess air coefficient. Under the condition of 1.5, the temperature, NO mole fraction and NH3 mole fraction in the reactor change and study the factors affecting the pollutant emission of marine diesel engine with the crank angle under different working conditions. The simulation shows that with the decrease of diesel engine speed, the maximum temperature of combustion reaction and the temperature at exhaust opening are obviously reduced. At the same time, mole fraction of NO and NH3 decreases with the decrease of rotational speed, and there is no nitride production in the combustion reaction at 25%.

Ignition improvers for aqueous ammonia as marine fuel

The potential of three molecules NH4NO2, H2O2 and O3 to ignite aqueous solutions of ammonia (25% by mass) as fuel, was investigated using chemical kinetic simulations at conditions representative of a two-stroke marine diesel engine. The purpose was to address two of the most prominent issues with making ammonia a practical fuel for marine applications: the difficulty of igniting ammonia, and the safety concerns regarding its volatility and toxicity. The ignition simulations carried out to this end used a two-zone reactor model of the engine, representing the ignition zone into which fuel was injected, and the bulk cylinder gases, respectively. The results suggested that all three ignition improving molecules were able to ignite aqueous ammonia reliably and at high combustion efficiency with acceptable levels of NO, N2O and NH3 emissions. Among the three fuel formulations investigated, H2O2 as 12% aqueous solution by mass, promised the lowest emissions of NO and N2O in the exhaust gases. This ignition improver in aqueous solution added in a mole fraction of 0.15 to a mole fraction of 0.85 aqueous ammonia having an ammonia fraction of 25% by mass promised to be the most practical solution, since it is stable and can be stored safely in a separate tank until injected into the engine.