Low-speed Marine Diesel Engine Research Articles

Optimization and 4E analysis of integration of waste heat recovery and exhaust gas recirculation for a marine diesel engine to reduce NOx emissions and improve efficiency

This paper proposes an integration of waste heat recovery system and exhaust gas recirculation system to break the inherent trade-offs between oxynitride and carbon emissions of marine low-speed diesel engine. It is significant important to break these trade-offs, because Energy Efficiency Existing Ship Index may not be met, though Energy Efficiency Design Index and Tier III can be already achieved for old ships. The waste heat recovery system consists of supercritical carbon dioxide Brayton cycle and Kalina cycle, where the integration of supercritical carbon dioxide Brayton cycle and Kalina cycle is achieved in the parallel style. This paper uses the classical thermodynamics in terms of engineering approach to carry out the parameter analysis of combined system first. The optimization is conducted in terms of efficiency, energy density and techno-economy with the introduction of global optimal policy. The results showed that the highest efficiency of 52.32% at Tier III mode can be achieved, at which the net power, exergy efficiency, area per unit power output and levelized energy cost can be achieved by 1568.57kW, 45.75%, 0.589m2/kW and 0.114$/kWh at main engine load of 85%. Further, the net power output of waste heat recovery system can reach 1085.76 kW and 2043 kW at Tier II mode and Tier III mode, while the recovering rate of waste heat recovery system can reach over 5% at Tier III mode. Finally, the Energy Efficiency Existing Ship Index of a container ship equipping with such combined system can be reduced from 9.50 to 9.05.

Structural optimization of S-CO2 Brayton cycle compressor impeller based on evolutionary algorithm

As the critical components for marine low-speed diesel engine flue gas waste heat recovery (WHR) supercritical carbon dioxide (S-CO2) Brayton cycle system, the structure of the compressor impeller is optimized by the evolutionary algorithm (EA) based on the co-simulation of the CAESES, ANSYS CFX and Opti Slang. The law of impeller pressure ratio, efficiency and power consumption in S-CO2 Brayton cycle (SCBC) as a function of rotational speed, inlet temperature, pressure and impeller structural parameters are revealed, and the method of improving SCBC efficiency for marine low-speed diesel engine flue gas waste heat recovery is studied. The optimized impeller structure is greatly enhanced in aerodynamic performance and safety, and the isentropic efficiency is increased by 2.54%, the pressure ratio is increased by 35.64%, and the temperature rise is increased by only 4.6%. A 100kW S-CO2 compression cycle test bench was set up to verify the simulation-optimized impeller results. The final results show that the optimized impeller structure, aerodynamic performance and safety are greatly improved. It provides theoretical support for selecting and optimising compressor impellers for marine low-speed diesel engine flue gas waste heat recovery S-CO2 Brayton cycle.

Cam Profile Design of Low-Speed Marine Diesel Engine Based on the Grey Theory

The camshaft profile is one of the important parameters of the engine, the reasonableness or otherwise of its design directly influences the engine’s power output, fuel consumption, emissions, noise and reliability. However, most existing cam profile optimization designs are based on the basic software operation, profile parameter selection and tuning lack a scientific theoretical basis. In order to address this issue, this study establishes a single valve kinematic model of the gas delivery mechanism of diesel engines by using the AVL-EXCITE Timing Drive, and performs a model-based multinomial kinematic acceleration cam profile design. Subsequently, an orthogonal design method is employed to obtain the parameter combinations that can satisfy the dynamic requirements. The research investigates the influence of cam profile design parameters (C 4, p, q, r, and s) on valve fullness, maximum jerk, cam contact stress, and valve seating force through a systematic study. Lastly, based on the grey correlation theory, a thorough analysis of the performance indices of cams with different profile parameter combinations is conducted. The optimization problem of the profile parameters with multiple performance indicators is transformed into a single-objective grey relational optimization problem, resulting in the optimal cam profile parameter combination of C4 =0.1, p=14, q=20, r=28 and s=36. The optimal method proposed in the paper is straightforward to implement and is applicable to the optimum design of cam profiles of the engine, which is of great importance for the optimal design of cam fabrication processes.

Research and Optimization on the Exhaust Flow Characteristics Based on Energy-Splitting Method of the Low-Speed Marine Diesel Engine

Abstract In this study, an optimization scheme for exhaust flow characteristics based on the energy-splitting method is proposed. The low-speed marine diesel engine adopts the exhaust energy-splitting method during the exhaust process. Based on this, a one-dimensional calculation model, a three-dimensional calculation model, and a three-dimensional model of the gas collection box are established. After splitting, the vortex structure in the same phase of the gas collection box has a larger scale, higher flowrate, more significant entropy increase, and more severe turbulence dissipation. The length and diameter of the high-grade gas collection box are optimized. The results show that after optimization, the flow energy dissipation brought by the vortex structure is reduced, and the outlet pressure and flow velocity of the gas collection box are increased.

An Experimental Study of the Effects of Cylinder Lubricating Oils on the Vibration Characteristics of a Two-Stroke Low-Speed Marine Diesel Engine

Abstract Two-stroke, low-speed diesel engines are widely used in large ships due to their good performance and fuel economy. However, there have been few studies of the effects of lubricating oils on the vibration of two-stroke, low-speed diesel engines. In this work, the effects of three different lubricating oils on the vibration characteristics of a low-speed engine are investigated, using the frequency domain, time-frequency domain, fast Fourier transform (FFT) and short-time Fourier transform (STFT) methods. The results show that non-invasive condition monitoring of the wear to a cylinder liner in a low-speed marine engine can be successfully achieved based on vibration signals. Both the FFT and STFT methods are capable of capturing information about combustion in the cylinder online in real time, and the STFT method also provides the ability to visualise the results with more comprehensive information. From the online condition monitoring of vibration signals, cylinder lubricants with medium viscosity and medium alkali content are found to have the best wear protection properties. This result is consistent with those of an elemental analysis of cylinder lubrication properties and an analysis of the data measured from a piston lifted from the cylinder after 300 h of engine operation.

Design and research of a heavy load fatigue test system based on hydraulic control for full-size marine low-speed diesel engine bearings

As the power density design indicators of marine low-speed diesel engines gradually increased, resulting the loads of marine low-speed diesel engine bearings become increasingly complex. It's easy to cause crankshaft fatigue damage, leading to a very significant economic loss. Due to the maximum thrust loads of full-size-bearing is larger than 2000kN, the bearings performance tests are very expensive on a complete diesel engine. So, newly developed bearings must be verified on a specialized test rig. The research goal is to design a novel fatigue life test system (Bearing diameter: 300mm–520mm, Speed: 5r/min-200r/min, Thrust: 0kN–2800kN) that can simulate the working conditions of full-size low-speed marine diesel engine bearings. Adopting the advanced hydraulic-based control passive pressurization technology. Multi-platform joint simulation technology is used to make sure that the maximum thrust of the test rig is proportional to the eccentricity of the eccentric shaft. The final eccentricity of the shaft is determined by 3mm for test rig. The results based on 475mm×150mm bearing is published for the first time. The test load can be well enveloped in the load of the target diesel engine, with maximum load fluctuation less than 0.2%. The test rig can meet the performance testing requirements of full-size bearings.

Research on the characteristics of the exhaust energy splitting method for the two-stroke low speed marine diesel engine

Efficient waste heat recovery (WHR) is the key to improve the thermal efficiency of the marine diesel engine and reduce the cost. According to the characteristics of long stroke of low-speed marine diesel engine, the exhaust energy splitting (EES) method based on exhaust energy distribution is proposed in this paper. EES is a new method of improving waste heat grade by separating high temperature exhaust gas and low temperature scavenging air. Compared with other studies on increasing exhaust temperature, EES significantly increases exhaust temperature and improves waste heat recovery efficiency without negatively affecting engine performance. Moreover, due to the adjustable EES valve, the optimal performance of engine and WHR system can be achieved under various operating conditions by adjusting the exhaust splitting phase (ESP). The One-Dimension and Three-Dimension simulation models for a two-stroke low speed marine diesel engine with waste heat recovery system are established. The exhaust energy distribution and the splitting phase to be optimized are also explored synchronously. The results show that by using the exhaust energy splitting method, temperature after turbine can be increased by more than 100 K compared with the baseline of the original engine system. Using Organic Rankine cycle (ORC) as WHR system, the waste heat recovery efficiency can reach over 17 %. Compared with the original engine, the total output power of the optimized EES low-speed engine and ORC system Increase by 100.90 kW under 75 % load and 154.72 kW under 100 % load, and the NOx emissions can be reduced by 5 %.

Experimental Study of the Influences of Operating Parameters on the Performance, Energy and Exergy Characteristics of a Turbocharged Marine Low-Speed Engine

With appropriate strategy of EVC timing and fuel injection, the engine NOx emission could be reduced with acceptable deterioration of fuel consumption. However, for the mechanism of these favorable results, few studies focus on improving the fuel economy from the perspective of energy and exergy analysis, which could be helpful for providing a deeper comprehensive to researchers. Therefore, an experimental study for the combination of EVC timing and fuel injection strategy is conducted based on a marine low-speed engine with 340 mm bore, then the energy and the exergy analysis are separately carried out according to the obtained experimental results. The experimental results show that delaying the exhaust valve closing (EVC), complemented with an appropriate injection strategy, could improve the marine low-speed diesel engine brake specific fuel consumption (BSFC) with the NOx emission almost kept constant. The following energy balance analysis demonstrates that the losses from exhaust gas and heat transfer account for about 50% of total energy. However, from the perspective of exergy analysis, an opposite conclusion could be obtained; the proportion of exhaust gas and heat transfer exergy could reach about 15%, and the ratio of heat transfer could be higher relatively. The losses caused by irreversibility is the biggest source of all, and the irreversibility from combustion could takes about 70% of the total irreversibility. Finally, the reduction of total irreversibility could reach about 4% by optimizing the parameters of marine low-speed engines.

Significant impacts of injection parameters on marine diesel engines

Nowadays, over 90% of the shipping industry mainly relies on marine transportation. The ability of 2-stroke low-speed diesel engines to consume heavy fuel and even crude oil makes them occupy an important position in the main propulsion power market. Also, it is quite convenient for them to operate reversely, which is needed for the astern situation. Compared with other propulsion power sources such as gas turbines or electro-propulsion, low-speed diesel engines have relatively better part-load performance and long-time stability, making them stand out. Most importantly, their efficiency can reach up to 60% when combined with exhaust boilers and turbine-driven alternators. The majority of those advantages are gained from the delicately designed fuel injection system and the governor system. This article discusses 2-stroke low-speed marine diesel engines' fuel injection systems and how some important parameters influence engine performance. Future opportunities and key challenges in this exciting field are also highlighted.

Improving the Overall Efficiency of Marine Power Systems through Co-Optimization of Top-Bottom Combined Cycle by Means of Exhaust-Gas Bypass: A Semi Empirical Function Analysis Method

The mandatory implementation of the standards laid out in the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII) requires ships to improve their efficiency and thereby reduce their carbon emissions. To date, the steam Rankine cycle (RC) has been widely used to recover wasted heat from marine main engines to improve the energy-conversion efficiency of ships. However, current marine low-speed diesel engines are usually highly efficient, leading to the low exhaust gas temperature. Additionally, the temperature of waste heat from exhaust gas is too low to be recovered economically by RC. Consequently, a solution has been proposed to improve the overall efficiency by means of waste heat recovery. The exhaust gas is bypassed before the turbocharger, which can decrease the air excess ratio of main engine to increase the exhaust gas temperature, and to achieve high overall efficiency of combined cycle. For quantitative assessments, a semi-empirical formula related to the bypass ratio, the excess air ratio, and the turbocharging efficiency was developed. Furthermore, the semi-empirical formula was verified by testing and engine model. The results showed that the semi-empirical formula accurately represented the relationships of these parameters. Assessment results showed that at the turbocharging efficiency of 68.8%, the exhaust temperature could increase by at least 75 °C, with a bypass ratio of 15%. Moreover, at the optimal bypass ratio of 11.1%, the maximum overall efficiency rose to 54.84% from 50.34%. Finally, EEXI (CII) decreased from 6.1 (4.56) to 5.64 (4.12), with the NOx emissions up to Tier II standard.

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.

Simulation analysis and experimental verification of tribo-dynamics of reciprocating friction pairs in low-speed marine engines

ABSTRACT The performance of reciprocating friction pairs in low-speed marine diesel engines has an important impact on the economy, stability, and safety of the ship operation, which deserves special attention. However, the available research is very limited. In this paper, a new tribo-dynamics modeling method and an online measurement method for friction force are proposed. The friction force is simulated and verified by experiments. Based on the principle of multi-body dynamics and mixed lubrication theory, a tribo-dynamic model coupling the reciprocating friction pairs (piston assembly-cylinder liner, piston rod-stuffing box, and crosshead slipper-guide) is firstly established. The friction force and dynamics are theoretically analyzed. Then, a friction measurement method, which can measure the friction force of reciprocating friction pairs under engine firing conditions, is developed and used to verify the simulation. By comparison, it is found that the simulated friction is in good agreement with the experimental one. The results show that the crosshead slipper and piston assembly have obvious secondary motion, which will affect the vibration and noise of the engine. The friction force of the piston assembly is much higher than that of other reciprocating friction pairs. Improving the lubrication state near the top dead center of the piston assembly is of great significance to reduce the friction loss of the low-speed marine 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.

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.

Pilot diesel-ignited ammonia dual fuel low-speed marine engines: A comparative analysis of ammonia premixed and high-pressure spray combustion modes with CFD simulation

Decarbonization of global shipping plays an important role in avoiding the worst impacts of climate change, and ammonia is a promising sustainable and zero-carbon fuel in the maritime sector. The dual-fuel mode has the potential to compensate for the poor combustion property of ammonia, but the existing studies are mainly focused on automotive medium- and high-speed engines, researches on marine low-speed engines are rarely reported. In this paper, the numerical models of pilot diesel-ignited ammonia dual fuel engine under both the premixed and high-pressure spray combustion modes are established using a commercial low-speed marine diesel engine as the prototype, and verified against the experimental data of the spray mixture formation, ignition delay, in-cylinder pressure and pollutant emissions. Then, the engine performance and emissions of both two modes are studied and optimized. The results show that under the diesel replacement ratio of the commercial methane/diesel dual-fuel marine engine (i.e. around 98%–99%), both two modes can achieve an indicated thermal efficiency (ITE) of over 50%. At the optimized ammonia premixed combustion point, the ITE is increased by 5.1% owing to the significantly reduced cooling loss, but at the expense of 140.6% higher NOx emissions compared to the diesel-only mode. The optimized ammonia high-pressure spray combustion point can achieve a similar ITE and reduce the NOx emissions by around 47% compared to the diesel-only mode. For both the optimum points, the GHG emissions (i.e. CO2 + 300 × N2O) are reduced by around 97%, while the unburned NH3 emissions are negligibly small.

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.

Thermodynamic Analysis and Optimization for Exhaust Energy Splitting: An Innovative Method of Improving Exhaust Energy Grade for the Low-Speed Marine Diesel Engine

Abstract In this study, a method for improving the exhaust energy grade called exhaust energy splitting is proposed. During the exhausting process of a low-speed marine diesel engine, the exhaust energy splitting is used to split and recover the exhaust in the early stage and the sweeping gas in the late stage separately. GT-Power software and Flowmaster software are used to co-simulate and design the exhaust energy splitting system. Through exergy analysis of the exhaust piping system before and after the energy splitting, the exergy efficiency of the system increases by about 0.47–4.92%, and the optimal splitting phase is around −115 deg. At the same time, the exhaust splitting system is optimized from the perspectives of heat exergy and kinetic energy exergy, and the results show that the exergy efficiency of the optimized exhaust piping system improves by 0.2–2%. This paper demonstrates the feasibility of exhaust energy splitting through exergy analysis.

Finite Element Analysis of Piston of a Marine Low Speed Engine Based on Fluid-Thermal-Structure Coupling

The piston of low speed diesel engine works in bad environment and bears large thermal and mechanical load, so it is necessary to study the piston. In this paper, a Marine low-speed diesel engine piston as the research object, builds the piston component - crosshead assembly - connecting rod - crankshaft model, simulation of the piston in the working process of the actual working condition, through professional simulation software for fluid-thermal-structure coupling calculation, the temperature field and coupling stress field of piston assembly are obtained. In this paper, the convective heat transfer coefficient and fluid temperature on the surface of the piston cooling oil chamber are obtained by CFD simulation, the temperature field of the piston assembly is obtained by fluid-thermal coupling, and the coupling stress field and deformation of the piston assembly are obtained by fluid-thermo-solid coupling. Finally, the maximum temperature of the piston is 313.9°C, the maximum deformation is 1.03mm, and the maximum stress is 347.4Mpa, which meet the requirements.

Performance Modulation of S-CO2 Brayton Cycle for Marine Low-Speed Diesel Engine Flue Gas Waste Heat Recovery Based on MOGA.

(1) Background: the shipping industry forced ships to adopt new energy-saving technologies to improve energy efficiency. With the timing modulation for the marine low-speed diesel engine S-CO2 Brayton cycle, the waste heat recovery system is optimized to improve fuel economy. (2) Methods: with the 6EX340EF marine low-speed diesel engine established in AVL Cruise M and verified by the bench test data, the model of the S-CO2 Recompression Brayton Cycle (SCRBC) system for the low-speed engine flue gas waste heat recovery was developed in EBSILON, and verified by SANDIA experimental data. On this basis, the effects of injection timing and valve timing parameters on the comprehensive performance of the main engine and the waste heat recovery system were investigated. By optimizing the timing modulation parameters through multi-objective genetic algorithm (MOGA) and evaluating the flue gas waste heat recovery from the perspective of thermodynamic performance and emission reduction, the research on the performance modulation method of the S-CO2 Brayton Cycle for flue gas waste heat in marine low-speed engines has been completed. (3) Results: the SCRBC with waste heat modulation will further increase the total power and efficiency, which in turn brings about a reduction in the fuel consumption rate. The efficiency of the SCRBC system with the addition of waste heat modulation increases by 2.28%, 1.04% and 2.07% at 50%, 75% and 100%, respectively. After adding the residual heat modulation, the maximum annual CO2 emission reduction of 748.51 × 103 kg·a-1 occurred at 50% load; with the exergy analysis, the cooler has the largest system exergy loss of 165 kW, with the exergy loss efficiency of 2.06% under 100% load. (4) Conclusions: the research on the performance modulation method of S-CO2 Brayton cycle for flue gas waste heat in the marine low-speed engine has been completed, which further improves the efficiency of the system and can be extended to other engines.

Experimental evaluation of DPF performance loaded over Pt and sulfur-resisting material for marine diesel engines.

Different from vehicle engines, Diesel Particulate Filter (DPF) inactivation is an unavoidable issue for low-speed marine diesel engines fueled with Heavy Fuel Oil (HFO). This paper introduced a sulfur resisting material in Silicon Carbide (SiC)-DPF to improve DPF performance. The results of bench-scale experiments showed that the Balance Point Temperature of the modified DPF module was 300°C and DPF modules had a good filtration performance, with Particulate Matters (PMs) residual being less than 0.6 g per cycle. In pilot-scale tests, PMs emissions of unit power decreased with engine load going up, filtration efficiency of nucleation mode PMs being only 36% under 100% load, while DPF still had a good performance in accumulation mode PMs control, being 94.2% under the same load. DPF modules showed excellent regeneration durability in the 205h endurance test, with a regeneration period of 1.5-2h under 380°C. There was no obvious degeneration in the DPF module structure, with no cracks or breakage. Besides, the DPF module could also control gaseous emissions, total emissions decreased by 10.53% for NO and 57.19% for CO, respectively. The results suggested that introducing sulfur-resisting material in DPF could greatly improve the DPF performance of low-speed marine diesel engines fueled with HFO.