Low-speed Two-stroke Diesel Engine Research Articles

Characteristics of Particulate Matter Emissions for Low-Sulfur Heavy Oil Used in Low-Speed Two-Stroke Diesel Engines of Ocean-Going Ships

Characteristics of Particulate Matter Emissions for Low-Sulfur Heavy Oil Used in Low-Speed Two-Stroke Diesel Engines of Ocean-Going Ships

Numerical Research on Effects of Variable Port Timing on Performance of Marine Low-Speed Two-Stroke Engine

Enhancing the effective expansion ratio to further improve the fuel consumption, this study implemented a kind of Variable Port Timing (VPT) by designing a vertically moving sleeve on the outside of the scavenging port of a low-speed two-stroke diesel engine with a 340 mm bore. A 3D Computational Fluid Dynamics (CFD) model was constructed and calibrated to investigate the influence of the VPT strategy on the engine performance and the internal gas exchange process. The results indicated that the VPT can reduce the negative work from the compression stroke and increase the expansion work from the expansion stroke, which effectively enhances the fuel economy. However, the reduction in the mass flow rate would lead to the severe deterioration of the turbocharging system’s performance. The related matching analysis between the sleeve and the scavenging ports revealed that the sleeve velocity had a minimal influence on the scavenging flow rate, while increasing the height of the scavenging port can restore a certain mass flow rate, but will decrease the in-cylinder swirl intensity, deteriorating the combustion in the cylinders. The optimal approach is to raise the position of the scavenging port, achieving a Scavenging Port Closing (SPC) at a 235°CA, which will restore the scavenging flow rate of the original level to 90.7% and improve the indicated fuel consumption by 2.9 g/kWh.

Development of a NOx Calculation Model for Low-Speed Marine Diesel Engines Based on Soft Measurement Technology

With the increasing level of intelligence of marine engines, there is an increasing demand for the online monitoring of engines, and marine NOx emissions have been of great concern. In this paper, a NOx simulation model is developed based on virtual measurement technology, which can calculate and predict NOx emissions based on the current operating state parameters of low-speed two-stroke diesel engines. First, the calibrated 3D simulation model is used to design the experiments to obtain the simulation experimental samples. Based on the NOx generation mechanism and diesel engine work-related parameters, the relevant factors were selected as alternative input parameters for the NOx emission model. The correlation analysis was then performed on the input parameters using the grey relational analysis correlation method and the Pearson correlation coefficient, and the principal component analysis method was used to reduce the dimensionality of the relevant factors by minimizing the loss of important information in reducing the complexity of the whole model. Then, the structure-related parameters of the backpropagation neural network (BPNN) were adaptively optimized using the group method of data handling (GMDH) to improve the accuracy of the NOx soft measurement model. Finally, the developed GMDH–BP model was validated with data and compared with the error evaluation index of BPNN and BPNN optimized by genetic algorithm (GA), and the developed NOx simulation model demonstrated high prediction accuracy under the same hyperparameter settings. The result provides technical support for the subsequent realization of the real-time online monitoring of NOx emissions from low-speed marine diesel engines without NOx sensors.

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.

NOx Emissions of N-butanol and Methane in Low-speed Two Stroke Diesel Engines

This article firstly structures a detailed combustion reaction mechanism including methane N-butanol nitrogen oxide. According to two-stroke low-speed diesel engine’s parameter with the characteristics of engine firing, homogeneous charge compression ignition is selected as simulation model. At the same the output power and the excess air coefficient is 1.5, by means of the simulation calculation and analysis of reaction path and reaction mechanism, when N-butanol and methane are mixed in different proportions, the exhaust temperature in the reactor reduces with the increase of methane proportion in reactants. At the same time NO mole fraction increases with the proportion of CH4 in the mixed fuel decreases, but the NO2 mole fraction will increase with the proportion of CH4 in the mixed fuel increases.

Experimental investigation of the high-pressure SCR reactor impact on a marine two-stroke diesel engine

The high-pressure selective catalytic reduction (HP-SCR) system arranged before the turbine is more suitable for high-power marine low-speed engines to reduce NOx emission. However, the HP-SCR reactor will cause an increase in engine exhaust back pressure, affecting its performance and brake-specific fuel consumption (BSFC). The 10WM marine low-speed two-stroke diesel engine and its HP-SCR system are taken as the research object in this paper. The engine performance and emissions in International Maritime Organization (IMO) Tier II and Tier III modes are tested by bench experiments. The effects of the HP-SCR reactor on engine performance parameters, emission characteristics, and pulse effect in exhaust pipe are obtained. The research showed that when the HP-SCR reactor is used, the BSFC of the engine will slightly increase, but the maximum will not exceed 1 g/kWh. The weighted specific emission of NOx is 2.09 g/kWh, which can meet Tier III emission regulations. In addition, under the Tier II mode, the engine exhaust pipe has a noticeable pulse effect. The exhaust gas temperature before the turbine is about 30 °C higher than that after the cylinder. However, under Tier III mode, the pulse effect in the exhaust pipe disappears completely. In addition to the fact that the HP-SCR reactor weakens the linear velocity of exhaust gas, the main reason is that the urea injection unit reduces exhaust gas temperature by 36 ∼ 47 °C.

Empirical Model of Uniflow Scavenging for Ultra-Long-Two-Stroke Marine Diesel Engines

_ Low-speed two-stroke diesel engines are widely employed in the marine industry, especially in tanks, owing to their advantages of fuel economy and reliability. However, with the emerging ultra-long-stroke trend, existing scavenging models, which are based on the configuration of cylinders with short strokes, are no longer applicable. In this study, we investigate the flow field and residual exhaust gas distribution in a cylinder using particle image velocimetry and computational fluid dynamics (CFD) simulations. The result shows a strong Burgers vortex structure upstream of the scavenger flow and dissipates gradually as it moves downstream. Furthermore, the scavenging process comprises three processes according to the detailed CFD analysis: displacement, mixing scavenging, and short circuit. Inspired by the results, a tailored empirical model of ultra-long-stroke uniflow scavenging comprising three sub-models is proposed. Specifically, a logarithmic relationship between the concentration level and scavenging deliver ratio is proposed to describe the mixing scavenging process. Finally, the model was validated against CFD results. The results demonstrate that the discrepancy in the scavenging efficiency curve predicted by this model and CFD is less than 1%, thereby demonstrating model reliability. Introduction Owing to the advantages of a large power range, high thermal efficiency, low fuel consumption rate, and good reliability, marine low-speed engines are widely used to provide power to civil ships (Heywood 1999). The market for low-speed engines is vast and is improving the performance of low-speed engines through research has great economic and environmental significance (Woodyard 2004). To meet the requirements of ship owners for lower fuel consumption and the IMO’s regulation of halving the greenhouse gas emissions of newly built ships, the ultra-long stroke of low-speed engines has become a trend (Lamas & Vidal 2012). With an ultralong stroke, the combustion speed of low-quality fuel oil is slow, and an ultra-long-stroke cylinder can prolong the expansion process, improve the combustion process, and reduce the fuel consumption rate (Fenghua 2014). The ultra-long-stroke diesel engine further creates fuel savings of 3.5–7% based on the original low fuel consumption. Previously, ultra-long strokes could not be achieved, limited by materials and manufacturing processes. However, in recent years, with the advancement of materials and processes, ultra-long strokes have been widely adopted as they have demonstrated superior competitiveness.

Modeling and Optimization of Ship Waste Heat Utilization System Based on Genetic Algorithm and Sensing

In order to solve the optimization problem of ship waste heat utilization system, the modeling and optimization method of ship waste heat utilization system based on genetic algorithm and sensing is proposed. The 6S50ME-C8.2 volume method model was established based on Matlab/Simulink simulation platform. According to the test data of the 6S50ME-C8.2 diesel engine, the simulation value is very close to the test value, which verifies the accuracy of the simulation model. The experimental results show that the thermal efficiency of high-power medium and low-speed two-stroke diesel engines is high, the exhaust temperature of the main engine is generally maintained at about 230°C, and the energy content of exhaust gas is relatively low. If no other measures are taken, the waste gas is directly channeled into the waste heat boiler, which cannot effectively recover the heat in the waste gas. Conclusion. The model can well simulate the actual working condition of the diesel engine, and the exhaust temperature has reached 298°C. The energy quality of waste gas at the inlet of the waste heat boiler is improved to meet the requirements of the waste heat recovery system.

Optimization of Marine Two-Stroke Diesel Engine Based on Air Intake Composition and Temperature Control

The influence of gas intake temperature, composition and the volume concentration of each gas component on diesel engine combustion, emission and the output power was studied by building a calculation model of the B&W 6S35ME-B9 marine two-stroke low-speed diesel engine, followed by a comprehensive optimization exploration. The results showed that under 295 K and 18.5% O2 of intake gas, the engine’s NOx emission is only 4.5 g/kWh and reduced to 58% from the normal air gas intake condition. Moreover, their power output is very similar. In addition, the effect of CO2 or H2O added into the intake of the diesel engine on the performance of the diesel engine can be compensated by reducing the intake temperature. At the intake temperature of 295 K, the engine’s NOx emission with 20.58% O2, 77.42% N2 and 2% H2O is 8.62 g/kWh, and 9.06 g/kWh under 20.79% O2, 78.21% N2 and 2% CO2. It is lower than 11.77 g/kWh, which is under normal intake conditions (315 K, 21%O2 and 79%N2). The power output is also similar to the normal intake condition. Therefore, the comprehensive optimization of gas intake temperature, composition and concentration can effectively optimize the diesel engine’s performance in terms of combustion, emission and power output. The research results have an important reference value for the optimization of diesel engine performance.

Design and performance evaluation of low-speed marine diesel engine selective catalytic reduction system

Selective catalytic reduction (SCR) systems are among the most effective methods used to reduce NOX emissions in internal combustion engines. SCR system performance is directly related to exhaust gas characteristics such as temperature and mass flow rate. Two-stroke engines commonly used in ships have different exhaust gas temperatures compared to four-stroke engines. In low-speed two-stroke diesel engines, the gas temperature drops after the exhaust gas expand in the turbocharger turbine, affecting SCR system performance. The main objective of this study is to determine performance parameters of marine SCR systems using computational fluid dynamics (CFD). The working processes of low-pressure SCR (LP-SCR) and high-pressure SCR (HP-SCR) systems were examined comparatively. The SCR system was modeled to include urea-water solution (UWS) decomposition and catalytic reduction reactions in the study. In the designed model, the amount of injected urea-water solutions (UWS), SCR bypass valve (RBV) opening, thermolysis and hydrolysis reactions, ammonia (NH3) slip and NOX reduction performances were investigated. In addition, pressure drop, velocity distribution and optimal catalyst length were determined on the model. The results showed that an increase in UWS reduces NOX emissions however increases the probability of NH3 slip. Increasing the RBV opening also reduced the pressure loss, which was beneficial to engine performance. However, the increasing RBV opening decreased the NOX reduction performance and increased the NH3 slip. The optimal SCR catalyst length was determined as 1200 mm. Furthermore, in the studies carried out under the same boundary conditions, the HP-SCR system meets the IMO Tier III standard, but it was observed that the LP-SCR system could not meet the standard due to the decreasing temperature in the turbine.

A study of smart thermal insulation coating on improving thermal efficiency in a marine two-stroke low-speed diesel engine

An advanced heat insulation coat, named Smart Thermal Coating (Smart TIC), was investigated in a marine low-speed two-stroke engine. Different with the conventional adiabatic engines that feature constant high temperature on combustion walls and low volumetric efficiency, the Smart TIC using low-heat-conductivity and low-heat-capacity materials can produce ''Temperature Swing'' (Temperature fluctuation) on the combustion chamber walls, reducing the heat transfer loss while increasing the volumetric efficiency and fuel efficiency. The performance of the Smart TIC with various thicknesses and thermophysical properties were evaluated through numerical simulations based on the ANSYS Software and CFD-code CONVERGE. The results show that the thinner Smart TIC can significantly increase the volumetric efficiency and thermal efficiency of the engine. The Smart TIC with the thermal conductivity of 0.1 W/((m*K)), the heat capacity of 20 J/(kg*K) and the thicknesses of 0.1 mm can increase the indicated thermal efficiency by up to 3.55% of the engine with little increases of NOx emissions. Furthermore, according to exergy analysis of exhaust gas, the engine with Smart TIC can improve exhaust energy available, which could improve fuel efficiency by waste heat recovery of engine. In addition, the potential of applying Smart TIC in a high-speed diesel engine was investigated in the last part, the results show the Smart TIC also can effectively improve the thermal efficiency of high-speed four-stroke engine. These results are believed to valuable reference for engine researchers and developers to further improve thermal efficiency of engine

Lubrication analysis of the piston ring of a two-stroke marine diesel engine considering thermal effects

Thermal deformation of the cylinder liner (TDCL) and the temperature–viscosity effect (TVE)of the lubricating oil are two common thermal effects which impact the lubrication properties of the piston-ring–liner tribological pair. In this study, the influence of these two thermal effects in a low-speed two-stroke diesel engine on piston ring lubrication performance are discussed in detail. For the TDCL, a steady-state heat-transfer model based on sequential fluid–solid coupling is used to solve for the heat-transfer coefficient and temperature on the coupling surface between the cylinder liner and the cooling water jacket. The boundary condition used to calculate the TDCL is the temperature distribution on the inner surface of the cylinder liner calculated empirically and verified experimentally. For the TVE, experimental data measured using capillary viscometers are used to determine the coefficients in four different empirical viscosity–temperature formulas, then the experimental and simulation results for TVE are compared using correlation coefficients and average absolute relative errors. Ultimately, the American Society for Testing and Materials (ASTM) model is selected to describe the viscosity–temperature characteristics of the lubricating oil used in this research. The results of the TDCL and the ASTM model are used in the lubrication model to analyze how the thermal effects influence the lubrication performance of the piston-ring–liner tribological pair.

Low-Speed Marine Diesel Engine Modeling for NOx Prediction in Exhaust Gases

Knowing the process of generating exhaust emissions and the determination of influential parameters are important factors in improving two-stroke slow-speed marine engines, particularly for further reductions in fuel consumption and stringent regulations on the limitation of nitrogen oxide emissions. In this article, a model of a marine low-speed two-stroke diesel engine has been developed. Experimental and numerical analyses of the nitrogen monoxide formations were carried out. When measuring the concentration of nitrogen oxides in the exhaust emissions, the amount of nitrogen dioxide (NO2) is usually measured, because nitrogen monoxide is very unstable, and due to the large amount of oxygen in the exhaust gases, it is rapidly converted into nitrogen dioxide and its amount is included in the total emission of nitrogen oxides. In this paper, the most significant parameters for the formation of nitrogen monoxide have been determined. Model validation was performed based on measured combustion pressures, engine power, and concentrations of nitrogen oxides at 50% and 75% of maximum continuous engine load. The possibilities of fuel consumption optimization and reduction in nitrogen monoxide emissions by correcting the injection timing and changing the compression ratio were examined. An engine model was developed, based on measured combustion pressures and scavenging air flow, to be used on board by marine engineers for rapid analyses and determining changes in the concentration of nitrogen oxides in exhaust emissions. The amount of nitrogen oxide in exhaust emissions is influenced by the relevant features described in this paper: fuel injection timing and engine compression ratio. The presented methodology provides a basis for further research about the simultaneous impact of changing the injection timing and compression ratio, exhaust valve opening and closing times, as well as the impact of multiple fuel injection to reduce consumption and maintain exhaust emissions within the permissible limits.

Effect of Engine Speeds and Dimethyl Ether on Methyl Decanoate HCCI Combustion and Emission Characteristics Based on Low-Speed Two-Stroke Diesel Engine

Abstract The combustion and emission characteristics of homogeneous charge compression ignition (HCCI) fuelled by methyl decanoate (MD) with different engine speeds and dimethyl ether (DME) mixing ratios are investigated in this work. Engine data of a MAN B&W 6S70MC low-speed two-stroke marine diesel engine were used for the reactor. The results show that a decrease of engine speed has little effect on the in-cylinder temperature and pressure of the engine at constant excess air coefficient of 1.5. Meanwhile, NOx emissions decrease with a decrease of engine speed in pure MD HCCI combustion. The results also indicate that NOx and CO2 emissions decrease significantly with an increase in the percentage of DME in MD and DME mixing combustion at a constant total mole fraction and engine speed of 85 revolutions per minute (r/min).

Modelling, performance improvement and emission reduction of large two-stroke diesel engine using multi-zone combustion model

The main energy source in marine industry is fossil fuel. Diesel engines are main power supply in sea transport at present times and will also be in the future. Energy conservation and environmental protection are the main problems that engine manufacturers are facing. Researchers have been making a lot of effort over the last decades to analyse energy conversion in large two-stroke engines. A 1-dimensional large two-stroke low-speed diesel engine model is developed, along with a multi-zone combustion model (MZCM), in which the losses of exchanging working medium and gas composition are calculated in the whole engine, unlike the preceding 0-dimensional and quasi-dimensional engine models that are only calculated in engine cylinder chamber. The model of a low-speed two-stroke marine diesel engine is calibrated and validated with experimental data and is used for simulation and analysis of the engine performance, combustion behaviour and emission of harmful exhaust gases. Large two-stroke marine diesel engines are problematic for modelling due to very few researches on this issue, due to the unsuitability of applying model on a low-speed two-stroke big diesel engines, large number of parameters that affect combustion behaviour, shape of ports and exhaust valves, working medium flow as well as because of shape of combustion chambers in these engines. For the reasons above, this research paper and its experiments contribute to better understanding large two-stroke low-speed marine diesel engine process. Analysis of engine characteristic was done by varying the most important parameters. Optimization of fuel injection characteristic and exhaust timing is achieved. The parameter of changing injection profile from classic to pre-injection was performed, and the effects on engine performance, NOx, CO and soot emissions were showed. With a pre-injection profile it is possible to reduce NOx emission by 9%, but a decrease in engine power is significant.

Simulation and economic assessment of using H₂O₂ solution in wet scrubber for large marine vessels

As emission regulation for marine vessels has become strict since 2016, a new emission control method is required. This paper proposes using the H₂O₂ solution in a wet scrubber for SOx and NOx removal for a conventional large marine vessel that uses a low-speed two-stroke diesel engine and a heavy fuel oil, and aims to evaluate the economic feasibility of this approach compared with other methods. Measurement data for the exhaust gas of the engine are incorporated in a process simulation based on physical properties and kinetics that relate H₂O₂ with emission materials. H₂O₂ consumption rate is determined to be 757.38 and 10.37 kg/h, depending on sailing in an emission control area or not. The parameters for techno-economic analysis are based on capital cost, operating cost, sailing information, and fuel cost in January 2018. The net present value of the proposed method is calculated to be 3.26% higher than other methods, and the proposed method is more economical than other methods when the sailing ratio in the emission control area is less than 75.98%. Based on these results, the proposed method can be utilized as an alternative emission control method for a marine vessel that considers retrofitting to satisfy strict emission regulations.

프로펠러 가진에 의한 저속 디젤엔진을 갖는 추진축계의 종진동

The axial vibration of propeller-induced excitation can be mostly seen in warships that have high-speed rotation propulsion shafting systems equipped with reduction gears. Coupled torsional and axial vibration is mainly focused on the excitation force that is induced by the cylinder’s gas pressure and the piston’s reciprocating mass in low-speed two-stroke diesel engines with seven or fewer cylinders; more complex vibration modes with one or more nodes can be seen in engines with eight or more cylinders. This thrust variation force caused by the axial vibration is the excitation force of the ship’s deckhouse in the longitudinal direction and has been researched extensively in the past. Recently, super-size containerships have been built that have more than 20 000 TEU. These ships have adopted low-speed diesel engines with 10 or more cylinders as their prime mover and the distance between the propeller and the main engine has increased significantly due to the streamlining of their hulls. As a result, there is the probability of resonance between the propeller’s axial excitation and the second node vibration. While this vibration frequency is rare, the possibility of resonance with the ship’s superstructure can create vibrations in the pipes and various accessories surrounding the main engine and stern tube. In addition, severe vibrations can occur if the natural frequency of these parts and that of the axial vibration are similar, which necessitates installing an additional damper on the intermediate shaft that resembles an axial vibration damper that is attached to the crankshaft free end. This paper intends to research the characteristics of axial vibration through theoretical analysis and measurement data with a focus on the 2nd order axial excitation of the propeller blade number in a propulsion shafting system with a 11G90ME engine as the research model.

Condition Diagnostic of Two-stroke Low-speed Diesel Engine using Acoustic Emission Sensor

Condition Diagnostic of Two-stroke Low-speed Diesel Engine using Acoustic Emission Sensor

Analysis of the Possibility of Using Low Speed Two-Stroke Dual-Fuel Engines for Propulsion of Sea-Going Vessels

Abstract The use of gas/LNG to supply marine engines in addition to tangible economic benefits is also a method of limiting emissions of harmful substances into the atmosphere and meeting strict environmental protection regulations, especially in special areas. The technology of supplying liquid and gas fuels (Dual Fuel) is most easily used in four-stroke engines but the highest thermal efficiency is ensured by combustion two-stroke piston engines. However, in the first two-stroke dual-fuel engines, the gas supply installation was more complicated than in the four-stroke engine. It resulted, among others from the necessity of compressing the gas to high pressures (15÷30 MPa), for which extremely energy-consuming multi-stage compression systems were needed. The complicated technical system is inherently prone to failures, which is why the dual-fuel low-speed two-stroke diesel engines remained for a long period in the design and experimental phase. In recent years, there has been a significant breakthrough thanks to the introduction of new solutions with the possibility of supplying two-stroke engines with low-pressure gas (less than 1.6 MPa). In recent years, many ships powered by two-stroke, dual-fuel internal combustion engines were commissioned. Some ship-owners owning a fleet of LNG carriers with two-stroke diesel engines that so far have been powered only by liquid fuels have decided to adapt them to gas combustion. This required the adaptation of the engine for gas combustion and the expansion of the supply gas fuel system. This paper is an attempt to analyse the legitimacy of introducing two-stroke, dual-fuel internal combustion engines into the propulsion system and adaptation of engines that are already used to burn gas in them. It presents the changes introduced on one of the LNG gas carriers consisting in adapting the engine to gas combustion through modification of the cylinder head and fuel supply installation. Parameter results of the modified engines obtained during sea trials have been presented. Both advantages and disadvantages resulting from gas combustion have been pointed out. Finally, the possibility of this solution application to other LNG carriers was assessed.

A Zero-Dimensional Mixing Controlled Combustion Model for Real Time Performance Simulation of Marine Two-Stroke Diesel Engines

The paper presents a performance prediction model of marine low-speed two-stroke diesel engines based on an advanced MCC (mixture controlled combustion) model coupled with a fuel injection model. Considering the time of real calculation, the so-called “concentrated exhausting gas” scavenging model and the working process model are used in the present work, and improved by introducing the ratio of pure combustion product over the total gas mass in the cylinder as an expression of the working medium components. The reaction rate model in the zero-dimensional MCC model is improved by introducing the fraction of combustion product in the fuel spray, and the relationship between the combustion model and scavenging quality is established. Meanwhile, the combustion model was simplified in the diffusion combustion phases and integrated with the fuel injection model in order to respond to the change of injection profile and injection timing. A large-scale low-speed marine diesel engine was used for a simulation. The results of the whole model are consistent with experimental data and the speed of calculation is fast enough for real time simulation of low speed and medium speed diesel engines. The prediction model can be used in the design and calibration of the electronic control system and performance optimization of the marine two-stroke diesel engine.