Low-speed Two-stroke Marine Diesel Engine Research Articles

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 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.

An efficient approach to improve thermal efficiency on a low-speed two-stroke marine diesel engine

To increase the intensity of the swirl motion and further optimize the combustion characteristics, an efficient approach named cylinder gas recirculation (CGR) is proposed in this study. The effects of the CGR strategy on the swirl motion, process of fuel/air mixing, combustion characteristics, and energy distribution are investigated. Compared to the original case, the simulation results show that the CGR strategy can increase the swirl ratio with a 131.8 % increase at TDC, and the mass of cylinder recirculated gas only accounts for 3.65 % of the total mass of the charge in the cylinder. The enhanced swirl motion can improve the fuel/air mixing effect, and further optimize subsequent combustion characteristics. On the one hand, the STD value of the cases using the CGR strategy becomes smaller compared to the original case, showing the better mixing process of the fuel and surrounding charge in the cylinder. On the other hand, the enhanced swirl motion accelerates the combustion rate, specifically, the duration of CA50 ∼ CA90 of the CGR case and CGR-optimal case is reduced by 42.96 %, and 51.96 %, respectively. In the end, compared to the original case, the gross indicated work under the CGR and CGR-optimal case is increased by 0.61 % and 2.4 %, and the effective power output increases by 1.24 % and 4.84 %, respectively, which proves that the CGR strategy has great potential in improving thermal efficiency and reducing fuel consumption.

Modeling and performance analysis of diesel engine considering the heating effect of blow-by on cylinder intake gas

Recently, the stringent international regulations on ship energy efficiency and NOx emissions from ocean-going ships make energy conservation and emission reduction be the theme of the shipping industry. Due to its fuel economy and reliability, most large commercial vessels are propelled by a low-speed two-stroke marine diesel engine, which consumes most of the fuel in the ship. In the present work, a zero-dimensional model is developed, which considers the blow-by, exhaust gas bypass, gas exchange, turbocharger, and heat transfer. Meanwhile, the model is improved by considering the heating effect of the blow-by gas on the intake gas. The proposed model is applied to a MAN B&W low-speed two-stroke marine diesel engine and validated with the engine shop test data. The simulation results are in good agreement with the experimental results. The accuracy of the model is greatly improved after considering the heating effect of blow-by gas. The model accuracy of most parameters has been improved from within 5% to within 2%, by considering the heating effect of blow-by gas. Finally, the influence of blow-by area change on engine performance is analyzed with considering and without considering the heating effect of blow-by.

Numerical research of the injected exhaust gas recirculation strategy on a two-stroke low-speed marine diesel engine

To meet the stringent emissions legislation and higher fuel economy requirements of the low-speed two-stroke marine diesel engine, a new method named Injected Exhaust Gas Recirculation (IEGR) strategy was proposed in this paper. The effects of the IEGR strategy on the fuel/air mixture quality, combustion performance, and emission characteristics were numerically investigated. The simulation results show that the IEGR strategy could not only increase the in-cylinder swirl ratio but also achieve the distribution of EGR stratification. As a result, compared with the base case, both reduction of brake specific fuel consumption (BSFC) and NOx emissions could be realized by the IEGR strategy. Additionally, based on stratified EGR distribution, the NOx emissions could be further reduced by adjusting the fuel injection angle to control the main combustion area to be restricted to the high EGR rate region. Finally, on the premise of meeting the Tier III emission standards, the BSFC of the engine by using the IEGR strategy is reduced by 2.73% compared with the base case (Tier II emission standards). This study provides a new and reasonable solution for low-speed two-stroke diesel marine engines to meet the Tier III standards with better fuel economy.

Experimental and numerical study on the characteristics of a penetrating exhaust manifold for low-speed two-stroke marine diesel engine

Penetrating exhaust manifold systems are commonly used in low-speed two-stroke marine diesel engines owing to their potential for energy conservation. However, few studies in the literature have reported on this type of manifold system, and there are few guidelines for optimizing the configuration or predicting the performance via a mean-line model. This study investigates the loss characteristics and flow mechanism of the penetrating exhaust manifold of a low-speed two-stroke marine diesel engine using experimental and numerical methods. The loss is characterized by the entropy production, which indicates a decrease in the energy grade. The results show that the minimum loss can be achieved when the penetration depth and diffusion angle of the manifold are approximately 0.5 and 6°, respectively. Moreover, the loss coefficient is maximally reduced by 14.0 % with penetrating exhaust manifold. The flow field analysis shows that the trend of the flow loss is ‘decrease-increase’ owing to the interaction among three factors: the mixing loss due to the shearing of the injection flow with the main flow, the momentum loss due to the impingement on the bottom of the main pipe, and the separation loss in the branch pipe owing to the flow divergence. This investigation can provide guidance for the configuration optimization and loss modeling of the exhaust manifold for low-speed two-stroke marine engines.

Bench experimental research of cylinder oil on large marine diesel engines

To lower the risks of the real ship test of the cylinder oil of large marine low-speed two-stroke marine diesel engine, A 6S50ME marine diesel engine was selected to do bench test about cylinder oil. In the calibration condition, the test cylinder oil and the reference cylinder oil were compared. The test results show that the wear amount of cylinder liners, piston rings and piston-ring-grooves is consistent with the wear condition judged by the metal element content detected by the residual oil of the cylinder. At the same time, combined with the evaluation result of the detergency and dispersibility of the cylinder oil, it can effectively judge whether the oil product can be tested on the ship. Since wear volume of element Cr and Fe tends to the stabilization after 60 hours, so it is feasible to set the diesel engine bench test at 100 hours. In addition, special attention should be paid to the control of water outlet temperature and exhaust gas temperature in the test. The cylinder oil evaluated in the above way meets the requirements of OEM after the actual ship test. Thus, the assessment method of cylinder oil based on the bench test is feasible, and can greatly shorten the test time and reduce the test cost.

Impact of Pilot Injection on Combustion and Emission Characteristics of a Low-Speed Two-Stroke Marine Diesel Engine

Low-speed two-stroke marine diesel engines dominate the modern global long-distance transportation market; with the increasingly stringent regulations, the combustion and emissions of these engines is gaining intense interest. The primary objective of the present study was to understand the effects of air-fuel mixing by pilot injection strategy on the combustion and emission characteristics of the marine diesel engines through a numerical study. Specifically, a computational fluid dynamic (CFD) model was established and validated by experimental data for a typical low-speed two-stroke marine diesel engine. The combustion parameters under different stages were analyzed, including mean in-cylinder temperature and pressure, indicated thermal efficiency (ITE), indicated specific fuel consumption (ISFC), and distribution of fuel-air mixture. Results indicated that, due to the premixing effect, the pilot injection produced unburned soot from the main injection’s ignition as well as decrease the intervals between the middle and final stages of combustion, thus raising the in-cylinder temperature. The interaction between the reduction of soot particles resulted from the increased temperature, and the decrease of the stage intervals led to lower overall boundary heat loss, which improved the effective thermal efficiency. The pilot injection timing and quality, respectively, showed quadratic and linear impact modes on engine performance and emissions.

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.

EGR modeling and fuzzy evaluation of Low-Speed Two-Stroke marine diesel engines

Exhaust gas recirculation (EGR) can be widely used to reduce the oxynitride (NOx) pollution in Low-Speed Two-Stroke Marine Diesel Engines. In this paper, two EGR systems (HP EGR11HP EGR: high pressure EGR. and LP EGR22LP EGR: low pressure EGR.) were investigated in terms of the influence of different rates on the brake specific fuel consumption (BSFC) and the NOx emissions. As for this simulation, the exhaust gas cleaning water treatment was not concluded. Besides, Miller Cycle was used to determine the influence of its valve timing on BSFC and NOx emissions. The combination of Miller Cycle and HP EGR system decreased the NOx emissions, which could meet the IMO33IMO: international maritime organization. Tier III standard, 3.4 g/kWh. Moreover, the influence of the EGR cooling temperature was discussed. Finally, a fuzzy comprehensive evaluation model was developed to evaluate the two EGR systems. The results showed that when the HP EGR system and the LP EGR system were all operating at a maximum EGR rate, LP EGR system showed more advantages.

Combustion and Emissions Investigation on Low-Speed Two-Stroke Marine Diesel Engine with Low Sulfur Diesel Fuel

Abstract With the implementation and expansion of international sulfur emission control areas, effectively promoted the marine low sulfur diesel fuel (MLSDF) used in marine diesel engines. In this study, a large low-speed, two-stroke, cross-head, common rail, electronic fuel injection marine diesel engine (B&W 6S35ME-B9) was used for the study. According to diesel engine’s propulsion characteristics, experiments were launched respectively at 25%, 50%, 75%, 100% load working conditions with marine low sulfur diesel fuel to analyze the fuel consumption, combustion characteristics and emissions (NOx, CO2, CO, HC) characteristics. The results showed that: Marine diesel engine usually took fuel injection after top dead center to ensure their safety control NOx emission. From 25% to 75% load working condition, engine’s combustion timing gradually moved forward and the inflection points of pressure curve after top dead center also followed forward. While it is necessary to control pressure and reduce NOx emission by delaying fuel injection timing at 100% load. Engine’s in-cylinder pressure, temperature, and cumulative heat release were increased with load increasing. Engine’s CO2 and HC emissions were significantly reduced from 25% to 75% load, while they were increased slightly at 100% load. Moreover, the fuel consumption rate had a similar variation and the lowest was only 178 g/kW·h at 75% load of the test engine with MLSDF. HC or CO emissions at four tests’ working conditions were below 1.23 g/kW·h and the maximum difference was 0.2 or 0.4 g/kW·h respectively, which meant that combustion efficiency of the test engine with MLSDF is good. Although the proportion of NOx in exhaust gas increased with engine’s load increasing, but NOx emissions were always between 12.5 and 13.0 g/kW·h, which was less than 14.4 g/kW·h. Thus, the test engine had good emissions performance with MLSDF, which could meet current emission requirements of the International Maritime Organization.

APPLICATION OF THE OPTIMIZATION METHOD IN THE OBJECTIVES OF THE ANALYSIS OF THE WORKING PROCESS OF SHIP DIESELS

The article touches upon the possibility of using the method of gradientless n-parametric minimization of Powell'64 in tasks of monitoring the working process of marine diesel engines. There is given an example of finding a global minimum of the Rosenbrock test function. Using the Powell'64 method, the Least-squares functionals in the synchronization and modelling tasks of compression-expansion curves in the working cylinder are minimized. The calculation results of data synchronization for low-speed two-stroke and medium-speed four-stroke marine diesel engines are shown. The synchronization problem can be solved in terms of equation P' = 0 derived for the sector from compression starting to combustion starting in the cylinder. The selection of the boundary conditions for simulation is shown. The advantage of Powell’64 method is its high efficiency for quadratic functionals. As opposed to gradient methods, the Powell'64 method does not require calculating derivatives and is universal for minimizing complex nonlinear general functionals. The original author's algorithm of data synchronization by analyzing the indicator diagrams using the Powell'64 method has been applied in the latest versions of monitoring systems of D4.0H marine diesel engine.

МЕТОД БЕЗГРАДИЕНТНОЙ МИНИМИЗАЦИИ POWELL'64 В ЗАДАЧАХ МОНИТОРИНГА РАБОЧЕГО ПРОЦЕССА СУДОВЫХ ДИЗЕЛЕЙ

The article touches upon the possibility of using the method of gradientless n-parametric minimization of Powell'64 in tasks of monitoring the working process of marine diesel engines. There is given an example of finding a global minimum of the Rosenbrock test function. Using the Powell'64 method, the Least-squares functionals in the synchronization and modelling tasks of compression-expansion curves in the working cylinder are minimized. The calculation results of data synchronization for low-speed two-stroke and medium-speed four-stroke marine diesel engines are shown. The synchronization problem can be solved in terms of equation P' = 0 derived for the sector from compression starting to combustion starting in the cylinder. The selection of the boundary conditions for simulation is shown. The advantage of Powell’64 method is its high efficiency for quadratic functionals. As opposed to gradient methods, the Powell'64 method does not require calculating derivatives and is universal for minimizing complex nonlinear general functionals. The original author's algorithm of data synchronization by analyzing the indicator diagrams using the Powell'64 method has been applied in the latest versions of monitoring systems of D4.0H marine diesel engine.

A new coupling tribodynamic model of crosshead slipper-guide system and piston skirt-liner system of low-speed marine diesel engines

In this paper, considering the coupling effects of the crosshead slipper-guide system and the piston skirt-liner system, a new tribodynamic model is established for the low-speed two-stroke marine diesel engine. Firstly, a dynamic model including the crosshead slipper, the piston, the piston rod, and the crosshead pin is proposed. Then, considering the disciplinary coupling between the dynamic model and the lubrication models, the stiff and nonlinear tribodynamic model is solved with the modified extended backward differentiation formulae (MEBDF). Finally the tribodynamic performances of the crosshead slipper and the piston skirt are analyzed. The simulation results show that the crosshead slipper bears the thrust force and its friction power loss is obviously larger than that of the piston skirt.

Sensitivity Analysis of Heavy Fuel Oil Spray and Combustion under Low-Speed Marine Engine-Like Conditions

On account of their high power, thermal efficiency, good reliability, safety, and durability, low-speed two-stroke marine diesel engines are used as the main drive devices for large fuel and cargo ships. Most marine engines use heavy fuel oil (HFO) as the primary fuel, however, the physical and chemical characteristics of HFO are not clear because of its complex thermophysical properties. The present study was conducted to investigate the effects of fuel properties on the spray and combustion characteristics under two-stroke marine engine-like conditions via a sensitivity analysis. The sensitivity analysis of fuel properties for non-reacting and reacting simulations are conducted by comparing two fuels having different physical properties, such as fuel density, dynamic viscosity, critical temperature, and surface tension. The performances of the fuels are comprehensively studied under different ambient pressures, ambient temperatures, fuel temperatures, and swirl flow conditions. From the results of non-reacting simulations of HFO and diesel fuel properties in a constant volume combustion chamber, it can be found that the increase of the ambient pressure promotes fuel evaporation, resulting in a reduction in the steady liquid penetration of both diesel and HFO; however, the difference in the vapor penetrations of HFO and diesel reduces. Increasing the swirl flow significantly influences the atomization of both HFO and diesel, especially the liquid distribution of diesel. It is also found that the ambient temperature and fuel temperature have the negative effects on Sauter mean diameter (SMD) distribution. For low-speed marine engines, the combustion performance of HFO is not sensitive to activation energy in a certain range of activation energy. At higher engine speed, the difference in the effects of different activation energies on the in-cylinder pressure increases. The swirl flow in the cylinder can significantly promote fuel evaporation and reduce soot production.

Characterization of Particle and Gaseous Emissions from Marine Diesel Engines with Different Fuels and Impact of After-Treatment Technology

The International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) and some countries have gradually strengthened the laws regulating ship exhaust emissions. The aim of this paper is to estimate the impact of an after-treatment technology exhaust gas cleaning (EGC) system on marine diesel engine emissions and the cost advantage compared to using low-sulfur fuel oil. The emission characteristics of SO2 and particulate matter (PM) produced from high sulfur oil and low sulfur oil in a low-speed two-stroke marine diesel engine were also presented. The removal efficiency of SO2 has been tested and the PM removal efficiency was also predicted in this study. When using high sulfur oil, the emission factor of SO2 and PM were from 8.73 g/kWh to 11.6 g/kWh and 2.0 g/kWh to 2.7 g/kWh, respectively. These values are significantly higher than the emission values from using low sulfur oil. The fuel sulfur content (FSC) was the key factor affecting the emission factors of SO2 and PM. The fuel change could reduce the mass emission factor of PM, which is above 90% for the total particle emission with the two fuels. When using the EGC system, the desulfurization efficiencies were above 99%. The pH values at a 25, 39, 53, and 67% load were also stabilized to be around 7.5, 7.6, 7.7, and 8, respectively. The EGC system can also capture part of the primary PM and secondary PM formed from SO2. The EGC system was more effective for PM of the size larger than 1 μm. Thus, according to this study, the usage of low sulfur oil and EGC will also substantially decrease the emission of currently unregulated hazardous chemical species in the exhaust gas of ships in addition to satisfying future emissions regulations of ship. Furthermore, the EGC system also had a significant cost advantage compared to using low-sulfur fuel oil.

Research of NOx reduction on a low-speed two-stroke marine diesel engine by using EGR (exhaust gas recirculation)–CB (cylinder bypass) and EGB (exhaust gas bypass)

IMO Tier III, applied on 1 January 2016, forced that NOx emissions must not exceed 3.4 g/kWh for low-speed marine diesel engines (engine speed lower than 130 rpm) in NOx ECAs. And the best answer for propulsion of nautical ships presently and for the near decades is the low-speed two-stroke diesel engines. Any abatement technology that reduces NOx emissions to the expected point can be allowed. EGR is an effective technology that has been verified on automotive applications and marine diesel engines (high speed and medium speed). This paper provides an internal measure: EGR (exhaust gas recirculation) combined with CB (cylinder bypass) and EGB (exhaust gas bypass) to reduce NOx emissions. Combined with CB and EGB, the EGR system applied on the engine can reduce the NOx emissions under 3.4 g/kWh. To test the effects of the EGR system, three modes were set: non-EGR mode, low-EGR mode and ECA-EGR mode. The effects of different modes on NOx emissions, fuel consumption, engine power and emissions are investigated. As a result, it can be concluded when the engine run in the ECA-EGR mode, NOx emissions can meet the requirements of IMO Tier III.

The impact of the accuracy of indicator diagrams on the heat release characteristics calculation, used in the diagnosis of marine diesel engine

The paper analyzes the possibility to use the electronic type indicators in the diagnosis of marine engines. It has been shown that in-depth analysis of indicator diagrams would be useful – calculation of heat release characteristics. To make this possible, measuring indicated systems should meet a number of important requirements in or-der to ensure that they can be used for the diagnostic purposes. These includes: high precision sensors for the measurement of cylinder pressure, high speed and accuracy of measuring and recording of measured values. These also includes reliable determination of the top dead center piston (TDC). In order to demonstrate the impact of positional error TDC, simulation study was conducted in which indicated diagrams were used, obtained on a medium-speed four-stroke marine diesel engine type A25/30 and the low-speed two-stroke marine diesel engine type RTA76, Sulzer company.

Decreasing NOx of a Low-Speed Two-Stroke Marine Diesel Engine by Using In-Cylinder Emission Control Measures

The authors applied one-dimensional (1-D) simulation and 3-D Computational Fluid Dynamics (CFD) simulation to evaluate the potential of in-cylinder control methods on a low-speed 2-stroke marine engine to reach the International Maritime Organization (IMO) Tier 3 NOx emissions standards. Reducing the combustion temperature is an important in-cylinder measure to decrease NOx emissions of marine diesel engines. Miller-cycle and Exhaust Gas Recirculation (EGR) are effective methods to reduce the maximum combustion temperature and accordingly decrease NOx emissions. The authors’ calculation results indicate that with a combination of 2-stage turbocharging, a mild Miller-cycle and 10% EGR rate, the NOx emissions can be decreased by 48% without the increased Specific Fuel Oil Consumption (SFOC) penalties; with a medium Miller-cycle and 10% EGR, NOx can be decreased by 56% with a slight increase of SFOC; with a medium Miller-cycle and 20% EGR, NOx can be decreased by 77% and meet IMO Tier 3 standards, but with the high price of a considerable increase of SFOC. The first two schemes are promising to meet IMO Tier 3 standards with good fuel economy if other techniques are combined.