Marine Dual-fuel Engine Research Articles

Numerical investigation on the effects of pilot fuel and natural gas injection pressures on methane slip in a large marine dual-fuel engine

Numerical investigation on the effects of pilot fuel and natural gas injection pressures on methane slip in a large marine dual-fuel engine

Strategies to improve ammonia combustion in a dual fuel marine engine by using CFD

Maritime transportation is currently responsible for delivering most of the world trade, and it still plays a major role in the global economy and pollutant emissions. Due to their heavy loads and long distances, full electrification is generally assumed as an unsuitable pathway, leaving combustion engines as the dominant technology in the marine sector. For a long time, these engines have benefited from the low costs of heavy oils produced from oil refining, but these fuels present a difficult combustion and are associated with significant pollutant emissions and greenhouse gases. Today, carbon-free fuels such as hydrogen and ammonia are gradually getting a foothold in the shipping market.In the present paper, an investigation on several strategies to improve the oxidation of ammonia is carried out for a dual fuel (DF) medium speed marine engine. A CFD analysis using ANSYS FORTE® code is performed on an improved and more realistic bowl geometry by varying the premixed fuel according to methods validated in previous studies and introducing adequate kinetic mechanisms from the literature. Results show that the sole use of ammonia to replace natural gas, as premixed fuel, leads to incomplete combustion; the increase of diesel fuel can only mitigate this condition, but it cannot be considered as viable solution. Therefore, several blends of ammonia/hydrogen are tested to examine combustion development and pollutant emissions. The addition of hydrogen above 10% to the premixed charge composition demonstrates to promote the oxidation of ammonia and to effectively reduce CO2 emissions of 84% without a dramatic increase in nitrogen oxides. On the contrary, hydrogen percentages lower than 10% feature a worsening of the combustion of the premixed charge. Finally, the use of a fuel containing nitrogen promote a slight formation of NOx emissions.

Numerical Study on Optimization of Combustion Cycle Parameters and Exhaust Gas Emissions in Marine Dual-Fuel Engines by Adjusting Ammonia Injection Phases

Decarbonizing maritime transport hinges on transitioning oil-fueled ships (98.4% of the fleet) to renewable and low-carbon fuel types. This shift is crucial for meeting the greenhouse gas (GHG) reduction targets set by the IMO and the EU, with the aim of achieving climate neutrality by 2050. Ammonia, which does not contain carbon atoms that generate CO2, is considered one of the effective solutions for decarbonization in the medium and long term. However, the concurrent increase in nitrogen oxide (NOx) emissions during the ammonia combustion cycle, subject to strict regulation by the MARPOL 73/78 convention, necessitates implementing solutions to reduce them through optimizing the combustion cycle. This publication presents a numerical study on the optimization of diesel and ammonia injection phases in a ship’s medium-speed engine, Wartsila 6L46. The study investigates the exhaust gas emissions and combustion cycle parameters through a high-pressure injection strategy. At an identified 7° CAD injection phase distance between diesel and ammonia, along with an optimal dual-fuel start of injection 10° CAD before TDC, a reduction of 47% in greenhouse gas emissions (GHG = CO2 + CH4 + N2O) was achieved compared to the diesel combustion cycle. This result aligns with the GHG reduction target set by both the IMO and the EU for 2030. Additionally, during the investigation of the thermodynamic combustion characteristics of the cycle, a comparative reduction in NOx of 4.6% was realized. This reduction is linked to the DeNOx process, where the decrease in NOx is offset by an increase in N2O. However, the optimized ammonia combustion cycle results in significant emissions of unburnt NH3, reaching 1.5 g/kWh. In summary, optimizing the combustion cycle of dual ammonia and diesel fuel is essential for achieving efficient and reliable engine performance. Balancing combustion efficiency with emission levels of greenhouse gases, unburned NH3, and NOx is crucial. For the Wartsila 6L46 marine diesel engine, the recommended injection phasing is A710/D717, with a 7° CAD between injection phases.

NOx generation in marine dual-fuel engines: Effects of ammonia blending ratio and spark ignition timing

Ammonia application in marine engines can effectively mitigate greenhouse gas emissions. However, engines powered by ammonia produce considerably higher levels of NOx emissions compared to conventional fuel engines. In the present study, a combustion model for the marine dual-fuel engine fueled with natural gas and ammonia has been established using the CONVERGE software. The nitrogen element-tracking method is employed in the engine combustion simulation. This study aims to investigate the effects of ammonia blending ratio (XNH3 = 0% ∼ 50%) and spark ignition timing (SIT = −20 °CA ATDC ∼ −40 °CA ATDC) on the emission characteristics and spatiotemporal distribution of nitrogen-based pollutants under lean-burn and stoichiometric-burn conditions. The results indicate that as the XNH3 increases, total NOx emissions decrease at stoichiometric-burn conditions, while it initially increases and then decreases at lean-burn conditions, reaching a peak of 3760 ppm at XNH3 = 30%. Besides, fuel NO emissions are predominant at lean-burn conditions, whereas at stoichiometric-burn conditions, thermal N*O emissions are predominant. Additionally, as the SIT advances, total NOx emissions initially decrease and then remain unchanged, reaching a minimum at −35 °CA ATDC, and it gradually increases at lean-burn combustions. Furthermore, the spatial distribution of NO at CA50 illustrates that fuel NO is primarily concentrated at the flame front, while thermal N*O predominates in the high-temperature burned region. N2O is observed in the low-temperature region near the cylinder wall during the expansion stroke. Moreover, fuel NO is primarily produced by ammonia's decomposition with OH radicals. There are three dominant reactions for the formation of NO: HNO→NO, NH→NO, and N→NO. The coupling mechanism of carbon and nitrogen elements is achieved by H2CN and HCN radicals.

Cybersecurity risk assessment of a marine dual-fuel engine on inland waterways ship

Cybersecurity risk assessment of a marine dual-fuel engine on inland waterways ship

Experimental Optimization of Natural Gas Injection Timing in a Dual-Fuel Marine Engine to Minimize GHG Emissions

Phased injection of natural gas into internal combustion marine engines is a promising solution for optimizing performance and reducing harmful emissions, particularly unburned methane, a potent greenhouse gas. This innovative practice distinguishes itself from continuous injection because it allows for more precise control of the combustion process with only a slight increase in system complexity. By synchronizing the injection of natural gas with the intake and exhaust valve opening and closing times while also considering the gas path in the manifolds, methane release into the atmosphere is significantly reduced, making a substantial contribution to efforts to address climate change. Moreover, phased injection improves the efficiency of marine engines, resulting in reduced overall fuel consumption, lower fuel costs, and increased ship autonomy. This technology was tested on a single-cylinder, large-bore, four-stroke research engine designed for marine applications, operating in dual-fuel mode with diesel and natural gas. Performance was compared with that of the conventional continuous feeding method. Evaluation of the effect on equivalent CO2 emissions indicates a potential reduction of up to approximately 20%. This reduction effectively brings greenhouse gas emissions below those of the diesel baseline case, especially when injection control is combined with supercharging control to optimize the air–fuel ratio. In this context, the boost pressure in DF was reduced from 3 to 1.5 bar compared with the FD case.

Evaluation of Control Strategy on Operation Range Expansion of High-Pressure Ammonia Direct Injection Marine Dual-Fuel Engine

Evaluation of Control Strategy on Operation Range Expansion of High-Pressure Ammonia Direct Injection Marine Dual-Fuel Engine

Optimization of PID control parameters for marine dual-fuel engine using improved particle swarm algorithm

This study presents a comprehensive investigation into the optimization of PID control parameters for marine dual-fuel engines using an improved particle swarm algorithm. Through the development of a Matlab/Simulink simulation model, the thermodynamic behavior of the engine and the functionality of its control system are analyzed. The PID control parameters for air–fuel ratio control and mode switching control systems are fine-tuned utilizing the improved particle swarm algorithm (PSO). Simulation results demonstrate that the proposed improved PID-PSO approach outperforms traditional PID and traditional PSO-PID control methods in terms of reduced overshoot, minimized steady-state error, faster response times, and improved stability across various operating conditions and response modes. In comparison to traditional PID and PSO-PID controllers, the improved PSO-PID controller reduces the response time by 0.47 s and 0.21 s, the maximum overshoot by 98.43% and 96.05%, and decreases the absolute errors by 87.42% and 90.55%, respectively, in air–fuel ratio control using the step response method. The study's findings offer valuable insights into enhancing the performance and efficiency of marine dual-fuel engines through advanced control strategies.

Research on the Ignition Strategy of Diesel Direct Injection Combined with Jet Flame on the Combustion Character of Natural Gas in a Dual-Fuel Marine Engine

In large-bore two-stroke diesel/nature gas dual-fuel marine engines, a certain quantity of diesel is injected into the cylinder to satisfy the full-power output engine rated power of the gas mixture. However, the ignition and flame propagation process based on the injection strategy of diesel direct injection combined with diesel jet flame on the ignition and combustion of natural gas is unclear, which directly affects the power and the thermal efficiency of engine and emissions. Therefore, this work numerically investigates the flame propagation characteristic under the strategy of the main and pilot diesel modes. The influence of the injection timing and proportion of diesel on combustion and emission performance are further analyzed. The results show that the influence of the injection timing of main diesel (MDIT) on the combustion process and emission performance is more obvious than that of the injection timing of pilot diesel (PDIT). The results indicate that the MDIT increased from −2°CA to −8°CA, the power increased by 316 kW, and the thermal efficiency improved by 1.5%. However, the CO2 emissions increased by 10.5 g/kWh, and the NOx emissions increased by 0.7 g/kWh. Additionally, an early PDIT is not conducive to the rapid organization of combustion, resulting in decreased engine power and thermal efficiency. Furthermore, it was found that the power improved by 50 kW and the thermal efficiency improved by 0.6%, with a decrease in the main diesel ratio (MDR) from 100% to 90%. Meanwhile, the CO2 emissions decreased by 4 g/kWh, although there was no obvious change in NOx emissions with the advance of MDR.

Impact of pilot diesel injection timing on performance and emission characteristics of marine natural gas/diesel dual-fuel engine

In diesel-ignited natural gas marine dual-fuel engines, the pilot diesel injection timing (PDIT) determines the premixing time and ignition moment of the combustible mixture in the cylinder. The PDIT plays a crucial role in the subsequent development of natural gas flame combustion. In this paper, four PDITs (− 8 °CA, − 6 °CA, − 4 °CA, and − 2 °CA) were studied. The results show that the advancement of PDIT increased the engine's power, thermal efficiency, and natural gas flame spread velocity, and increased NO emissions and CH4 emissions of the marine engine. The PDIT affected the ignition delay period and the rapid combustion period to a greater extent than the slow combustion period and the post combustion period. With each 2 °CA advancement of PDIT, the engine's power increased by 69.87 kW, thermal efficiency increased by 0.42%, radial flame spread velocity increased by 2 m/s, axial flame spread velocity increased by 1.7 m/s, NO emissions increased by 6.1%, and CH4 emissions increased by 3.75%.

Effects of split injection strategy on combustion characteristics and NOx emissions performance in dual-fuel marine engine

In order to address environmental concerns and promote sustainable development, the maritime industry is facing a demand to reduce emissions from ship engines. To address this, a growing trend in the development of diesel natural gas dual-fuel marine engine involves implementing more flexible diesel injection strategies, with the aim of enhancing performance and minimizing harmful emissions. This study utilized a numerical investigation based on the Large Eddy Simulation (LES) method to examine pilot diesel injection strategies in a dual-fuel marine engine operating at a high degree of natural gas substitution rate. Specifically, the analysis focused on the start of injection (SOI) in the single injection strategy and the first start of injection (SOI1) in the split injection strategy for pilot diesel. The findings highlight distinct trade-off relationships between these two injection strategies regarding their impact on indicated specific fuel consumption (ISFC) and NOx emissions. Compared to the optimized single injection strategy (Case A: SOI = -15°CA ATDC), the optimized split injection strategy (Case B: SOI1 = -60°CA ATDC, SOI2 = -10°CA ATDC) increases thermal efficiency by 0.77 % while reducing NOx emissions by 36.3 %. The split injection strategy induces low-temperature reactions of n-heptane in the squish region, resulting in the generation of active free radicals such as CH2O and OH, thereby accelerating the propagation speed of the flame in the squish region. Meanwhile, the split injection strategy diminishes pilot diesel accumulation in the piston bowl region, narrows the distribution range of high-temperature areas surpassing 2400 K, consequently leading to a reduction in NOx emissions.

Optimization of Combustion Cycle Energy Efficiency and Exhaust Gas Emissions of Marine Dual-Fuel Engine by Intensifying Ammonia Injection

The capability of operational marine diesel engines to adapt to renewable and low-carbon fuels is considered one of the most influential methods for decarbonizing maritime transport. In the medium and long term, ammonia is positively valued among renewable and low-carbon fuels in the marine transport sector because its chemical elemental composition does not contain carbon atoms which lead to the formation of CO2 emissions during fuel combustion in the cylinder. However, there are number of problematic aspects to using ammonia in diesel engines (DE): in-tensive formation of GHG component N2O; formation of toxic NOx emissions; and unburnt toxic NH3 slip to the exhaust system. The aim of this research was to evaluate the changes in combustion cycle parameters and exhaust gas emissions of a medium-speed Wartsila 6L46 marine diesel engine operating with ammonia, while optimizing ammonia injection intensity within the limits of Pmax, Tmax, and minimal engine structural changes. The high-pressure dual-fuel (HPDF) injection strategy for the D5/A95 dual-fuel ratio (5% diesel and 95% ammonia by energy value) was investigated within the liquid ammonia injection pressure range of 500 to 2000 bar at the identified optimal injection phases (A −10° CAD and D −3° CAD TDC). Increasing ammonia injection pressure from 500 bar (corresponding to diesel injection pressure) in the range of 800–2000 bar determines the single-phase heat release characteristic (HRC). Combustion duration decreases from 90° crank angle degrees (CAD) at D100 to 20–30° CAD, while indicative thermal efficiency (ITE) increases by ~4.6%. The physical cyclic deNOx process of NOx reduction was identified, and its efficiency was evaluated in relation to ammonia injection pressure by relating the dynamics of NOx formation to local combustion temperature field structure. The optimal ammonia injection pressure was found to be 1000 bar, based on combustion cycle parameters (ITE, Pmax, and Tmax) and exhaust gas emissions (NOx, NH3, and GHG). GHG emissions in a CO2 equivalent were reduced by 24% when ammonia injection pressure was increased from 500 bar to 1000 bar. For comparison, GHG emissions were also reduced by 45%, compared to the diesel combustion cycle.

Diesel Substitution with Hydrogen for Marine Engines

Zero-carbon fuels are expected to catalyse the decarbonisation of the maritime industry, with hydrogen being considered a long-term solution. This study aimed to investigate the feasibility of using hydrogen as a secondary fuel in marine diesel engines. A marine four-stroke engine with a nominal power output of 10.5 MW at 500 rpm was investigated, whereas the hydrogen injection at the engine port was considered. A CFD model was set up in CONVERGE for both diesel and the diesel-hydrogen operating modes to investigate the effects of 20% hydrogen fuel fraction (by energy) on engine performance, emissions, and combustion characteristics. This model was validated against experimental data for the diesel operating mode. Based on a parametric study, the mesh characteristics were selected to compromise between the prediction error and the computational effort. The impact of 20% hydrogen energy fraction on the heat release rate (HRR) and NOx emissions is comparing with the diesel mode. The results demonstrate that despite the reduction in carbon emissions when using hydrogen, the NOx emissions increase by 2.5 times, whereas the lower compression ratio allows for engine free-knock operation. This study contributes to the identification of efficient and reliable combustion conditions for diesel-hydrogen dual-fuel marine engines.

Thermo-economic optimization of an ORC system for a dual-fuel marine engine

The Organic Rankine Cycle (ORC) is one of the most promising systems to recover the waste heat sourced from internal combustion engines. In this study, thermodynamic, economic and environmental analyses of the scavenge air cooling water-driven Waste Heat Recovery System (WHRS) based on the organic Rankine cycle are conducted for a dual-fuel marine engine integrated with exhaust gas recirculation (EGR) system. Zero ozone-depleting and low global warming potential working fluids; R245fa, R236ea from hydrofluorocarbons, R600a, R601a from hydrocarbons, R1234ze and R1234yf from hydrofluoroolefins are selected for the low-grade WHRS. In addition to the thermal analyses, the mass and volume of the system along with the safety factors of the working fluids are evaluated to judge the physical applicability of the system for ships. Thermo-economic performances of the fluids are analyzed, optimized and compared under various engine loads, Tier II and Tier III modes to reveal the effects of different engine operating conditions on the parameters. According to the results, scavenge air has a significant amount of waste heat at medium and heavy loads and switching the engine mode remarkably affects the performance of the WHRS. R601a shows the best thermo-economic performance, however, considering the applicability of the system R236ea is the most suitable working fluid for the ORC WHRS. The overall thermal efficiency of the power generation system can be increased by about 2.8%.

Effect of flexible camshaft technology on dual-fuel engine performance using phenomenological combustion model

AbstractThe objective of the current study is to investigate the effect of tunable valve timings on the performance and emissions of a dual-fuel marine engine. A simulation model was developed in MATLAB to simulate the valvetrain mechanism. The model generates different valve lift curves depending on the input conditions, and after that, it tests them against any possible collision with the piston. The valid valve lift curves were exported to a two-zone combustion model in AVL CRUISE-M platform. The combustion model depends on the fractal principle and aims to predict the in-cylinder parameters. In addition, it contains sub-models to calculate the ignition delay and emissions formation. Model results were compared against experimental data, as the latter were obtained from a heavy-duty, medium-speed, single-cylinder research engine, which employs natural gas as a main fuel. The results showed good agreement and the model was used for further investigations with other cam pairs. It has been found that the fractal combustion model can effectively represent the combustion behavior in the dual-fuel engine. Furthermore, valve timing has a significant influence on the engine performance and exhaust emissions. Results also revealed that applying Miller cycle can reduce the nitrogen oxides emissions, while the higher valve overlap period had a negative effect on methane slip.

Numerical simulation of methane slip from marine dual-fuel engine based on hydrogen-blended natural gas strategy

This study examines the effect of a hydrogen-blended natural gas strategy on methane slip in two-stroke marine engines using numerical simulation. A combined simulation model, integrating a 1-D engine model from GT-POWER and a 3-D CFD model from CONVERGE, was developed and validated with experimental data. Subsequently, the effects of hydrogen molar fraction and energy fraction on methane slip were investigated. It was demonstrated that an appropriate hydrogen doping ratio in natural gas can effectively reduce methane slip. The methane slip decreased with an increase in the hydrogen molar fraction. The maximum reduction in methane slip was 26.76% when the molar fraction of hydrogen was 40% and the equivalent CO2 emission decreased by 142.78 g/kWh. Furthermore, with an enhanced energy fraction of hydrogen, a decrease in methane slip from 10.00 g/kWh to 5.83 g/kWh was observed. The CO2 emission was reduced by 143.86 g/kWh, and the equivalent CO2 emission (CO2 + 36 × CH4) was reduced by 293.80 g/kWh. However, there was a slight increase in indicated specific fuel consumption by 0.03 g/kWh and a decrease in power output by 54.6 kW. The findings offer theoretical guidance and technical suggestions for mitigating methane slip in marine dual fuel engines.

Performance research and optimization of marine dual-fuel engine based on RSM and NSGA-II

ABSTRACT In order to improve the economic efficiency of the ship when sailing and reduce the engine optimization cost. We propose the Response Surface Methodology (RSM) combined with NSGA-II to optimize the engine parameters. First, a simulation model of a marine four-stroke dual-fuel engine is established in AVL-BOOST software. Then, control parameters such as engine speed, exhaust valve opening (EVO) and compression ratio (CR) are planned by design of experiments. The response surface model was established in Design-Expert software. The significant influence of control parameters on performance parameters was studied by analysis of variance (ANOVA). Finally, with the output power, indicated fuel consumption rate and nitrogen oxide emissions as the optimization objectives. Non-dominated Sequential Genetic Algorithm (NSGA-II) is used to optimize the parameters to improve engine performance and reduce emissions. The results show that the established response surface model has good prediction accuracy. The response surface model visualizes the mathematical relationship between the control parameters and the optimization targets. The ANOVA results show that engine speed, EVO and CR have significant effects on engine performance and emissions. The optimization results show that the engine speed is 793 rpm, the EVO is 145°CA, and the CR is 12.3. Compared to standard settings, the optimized data shows a 3.4% increase in power, a 0.3% reduction in ISFC, and a 6.2% reduction in nitrogen oxide (NOx) emissions. The combination of response surface analysis and NSGA-II algorithm to optimize engine performance and emissions is thereby a feasible method.

Techno-Economic Comparison of Dual-fuel Marine Engine Waste Energy Recovery Systems

Techno-Economic Comparison of Dual-fuel Marine Engine Waste Energy Recovery Systems

Performance and emission characteristics of an ammonia/diesel dual-fuel marine engine

This study explores the challenges and possibilities of using ammonia (NH3) as a carbon-free fuel for marine propulsion in a Wärtsilä ammonia/diesel dual-fuel engine using a reactivity-controlled compression ignition (RCCI) concept. The main issues in ammonia RCCI engines are high ammonia slip and high emissions of nitrogen oxides and nitrous oxide. A joint experimental and computational investigation was conducted to understand the combustion process, pollutant and greenhouse gas (GHG) formation mechanisms, and the effects of injector configuration and injection timing on engine performance. A comparative assessment between the ammonia/diesel RCCI engine and a baseline natural gas/diesel RCCI engine showed that, upon replacing premixed natural gas with ammonia and maintaining the same energy share of diesel (8.5% of the total energy from diesel), the engine yielded considerably poor combustion efficiency. Increasing diesel usage to 24% share of the total energy allowed a successful engine operation, cutting GHG by 70%. However, higher diesel usage increased CO and CO2 emissions. N2O emission was attributed to the slow premixed ammonia/air flame propagation and near-wall flame quenching. The primary sources of NO emissions in ammonia/diesel RCCI engines were identified as fuel-NOx from premixed ammonia oxidation and thermal NOx in the diesel flame region. A recommendation was put forth for enhancing the operating conditions and injection strategies of ammonia RCCI engines. The proposed operation and injection strategy results in a 45% reduction in CO emission, a 60% reduction in total GHG emissions, and, notably, an 89% decrease in CO2 emissions compared to the LNG/diesel engine.

Efficiency of fuel gas supply on LNG-fueled vessels

The widespread use of LNG as a fuel for marine internal combustion engines makes to pay attention to the quality of gas fuel supply systems and its specifics. The objective of this paper is to review modern gas fuel supply systems and analyze their efficiency. The goal is to determine the most important parameters of gas fuel that affect the stability of the working process of marine dual-fuel engines and ways to maintain them within the specified limits. Evaluation of the gas fuel preparation efficiency is carried out on the basis of operational data obtained on the gas carrier vessel board. Data collection is carried out under non-standard operating conditions, which makes it possible to evaluate the quality of the resulting gas fuel with a time-varying composition of the initial natural gas. To analyze the obtained data, modern software, which is used by leading developers of marine diesel engines, is used (Wartsila Methane Number Calculator, AVL BoostTM and Python 3 statistic libraries). The analysis results are approximated for gas fuel supply systems for gas-fueled vessels, but not being gas carriers. This approximation is made taking into account the design features of gas fuel supply systems, since the specificity of the design imposes certain restrictions on the applicability of the conclusions obtained as a result of the previous analysis. Also, attention is paid to the accumulation of residual heavy hydrocarbons in bunker tanks, the excess of which can adversely affect the quality of gas fuel. Since there is no universal way to solve this problem, only general assumptions about possible ways to dispose of them have been made.