Dual-fuel Engine Research Articles

Experimental investigation of the effects of energy ratio and combustion chamber design on engine performance and emissions in a hydrogen-diesel dual-fuel CRDI engine

In compression ignition engines, the use of hydrogen-diesel dual fuel mode has a positive impact on engine performance and emissions. To enhance the impact of hydrogen in dual-fuel mode, it is crucial to properly adjust the energy ratio and design the combustion chamber for dual-fuel mode. This study focuses on these two situations. The study conducted a literature review and designed and manufactured two combustion chambers (Natural Gyration 1, Natural Gyration 2) suitable for dual fuel mode. Using the original combustion chamber and the manufactured combustion chambers, at a constant engine speed of 1850 rpm, at five different loads (3, 4.5, 6, 7.5, and 9 Nm), and at three different hydrogen injection times (1.6, 1.8, and 2.0), tests were performed. Engine performance and emission data obtained as a result of the tests were examined. Tests revealed that at a load of 9 Nm and with a hydrogen energy ratio of 12%, the Natural Gyration 1 combustion chamber increased the internal cylinder maximum pressure by 1.41%, reduced the specific energy consumption by 2.29%, and reduced particulate emissions by 8.82%. On the other hand, it was determined that the Natural Gyration 2 combustion chamber reduced the maximum cylinder internal pressure by 1.98%, increased the specific energy consumption by 2.66%, and soot emissions by 5% at the same load and hydrogen energy ratio.

Effects of different ammonia energy ratio on soot formation and oxidation in an ammonia diesel dual-fuel engine

Due to environmental pollution and energy crises, zero‑carbon fuel ammonia (NH3) has attracted extensive attention as an alternative fuel for engines. In this paper, the effects of ammonia energy ratio (AER) and injection strategy on particulate emission characteristics of an ammonia diesel dual-fuel engine were examined by merging experimental and simulation results; additionally, soot formation and oxidation mechanism were investigated. Results showed that the reduction in particulate emission was substantially higher than the increase in AER. When AER increased to 60 %, the reduction in particulate mass concentration reached 97.5 %. The initial soot formation area gradually moved to the bottom of the piston bowl with increasing AER. When the piston reached the top dead center, the high-soot-concentration area was shifted to the center of the piston bowl as AER increased. The contents of acetylene (C2H2) and methyl (CH3) reduced considerably, which restricted the formation of soot precursors. With AER increasing, the contents of nitric oxides (NOx) and other nitrogen-containing species increased and reacted with CH3 and other carbon-containing species, which effectively reduced the number of C in soot formation pathway, thereby lowering particulate emissions. As AER increased, hydroxyl (OH) involved in soot formation gradually decreased, and only 14 % of OH was involved in the oxidation of n-heptane at 60 % AER, which was favorable for reducing the soot formation rate. Furthermore, OH is a substantial species in soot oxidation. The introduction of ammonia caused an increase in OH, which facilitated the removal of soot. The decrease in hydrogenium (H) hindered the hydrogen–abstraction–acetylene–addition (HACA) reaction, further limiting the soot surface growth. By optimizing the injection timing and AER, particulate emission was lowered to 4.31 × 10−5 μg/cm3, and particle size was reduced by 64.2 % when AER was 60 %, injection timing was −20° CA ATDC, and injection pressure was 60 MPa.

Study on fuel injection stability improvement in marine low-speed dual-fuel engines

Pressure waves within the fuel injection system exert a significant influence on the fuel injection process. This study investigated the impact of pressure waves on injection quantity stability. To quantify the influence of pressure waves on injection quantity stability, the relative standard deviation (RSD) was introduced as a metric. Through computational analysis under various operating conditions, the following results were obtained: when the target rail pressure is constant, the RSD tends to diminish as the injection quantity increases. The elevated RSDs observed during small injection quantities are predominantly attributed to the short power-on period of the solenoid valve. Subsequently, parameter optimization and structural improvements were carried out on the injector to address this problem. The results indicate that optimizing structural parameters alone has a limited effect on reducing RSD. However, by adding a block in the control chamber above the needle to improve the structural layout of the injector, the maximum RSD has been reduced from 21.08% to 4.58% under the action of pressure waves caused by fuel injection, and from 29.24% to 6.67% under the action of given random high-frequency pressure waves. The proposed improvement idea for existing injectors enhances injection stability across the entire operating condition range, thereby improving fuel utilization efficiency.

Diesel direct injection and EGR optimization for a syngas-diesel dual-fuel generator operating at constant load

Diesel generators are widely used to produce electricity and heat in remote communities. However, their use contributes to harmful pollutant and greenhouse gas (GHG) emissions, negatively impacting the environment and public health. Syngas, which is a sustainable fuel, can play an important role in the transition from petroleum to renewable fuels. When used in dual-fuel diesel engines, it can contribute to reducing GHG emissions and the cost of transporting diesel, especially for rural and remote communities. This study investigates the effects of optimizing the diesel direct injection (DI) and exhaust gas recirculation (EGR) strategies on the combustion and emission performance of a syngas-diesel dual-fuel generator at constant load. The experiments were conducted using a 30-kW generator with a four-stroke, four-cylinder, turbocharged, and electronically controlled direct-injection diesel engine. The intake manifold of the engine was modified to allow introducing syngas upstream of the turbocharger. The syngas was simulated using individually controlled flow rates of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), and nitrogen (N2). The syngas flow rate was adjusted to replace 40% of the energy provided by diesel fuel while optimizing the diesel DI parameters such as the pilot injection timing, main injection timing and diesel direct injection rail pressure, as well as the EGR rate. The findings of this study reveal that optimizing diesel injection strategy and appropriately raising the EGR rate have a positive impact on the engine performance and emissions.

Modelling the evaporative cooling effect from methanol injection in the intake of internal combustion engines

Renewable methanol is one of the most promising alternative fuels for internal combustion engines. However, its much higher latent heat of vaporization compared to traditional fossil-based hydrocarbon fuels poses new challenges. On both spark-ignition (SI) engines and dual-fuel (DF) engines, methanol can be introduced through injectors installed in the intake path, with its evaporation then causing a cooling effect to the intake air flow. While this is beneficial in mitigating knock with both SI and DF operations, it could potentially lead to cold-starting issues in SI engines and incomplete combustion in DF engines. To properly model the in-cylinder behaviour, the mixture temperature after methanol injection needs to be accurately predicted. A simple yet effective methanol evaporation model based on the liquid droplet and film evaporation mechanisms is thus proposed here to quantify the evaporative cooling effect from methanol injection. The model first treats the methanol spray as a group of droplets with identical size, and after reaching the wall the model assumes that the remaining methanol forms a thin liquid film. The evaporation rates and the consequent temperature drops of these two modes are calculated separately. The calculation results indicate that only a negligible amount of methanol evaporates as droplets, with the predicted temperature drops agreeing well with the validation datasets when taking only the film evaporation into account. The key factor for this good agreement is that the balance between the heat and mass transfer needs to considered when evaluating the surface temperature of a liquid methanol film. The proposed model also suggests that the droplet evaporation can be greatly improved with an injection angle nearly parallel to the air flow, or a finer initial droplet size. Both measures are more effective than increasing the air temperature before injection.

Implementation of various injection rate shapes in an ammonia/diesel dual-fuel engine with special emphasis on combustion and emissions characteristics

As the problem of global warming continues to intensify, carbon-free fuel ammonia is crucial for internal combustion engines, and a potential ammonia combustion route is dual-fuel mode. The impact of various injection rate shapes (trapezoid, wedge, slope, triangle, and rectangle) on engine combustion and emissions performance with 0 %, 20 %, and 40 % ammonia energy fractions were estimated. Under the identical ratio of the ammonia-doped schemes, the fuel injection gross mass and fuel injection duration are the same. The results indicate that the triangle injection rate shape can make the mixture of diesel and ammonia gas more uniform, leading to combustion in the combustion chamber closer to homogeneous combustion. When the injection shape is the triangle, the indicated mean effective pressure in the cylinder is the highest at 10.29 bar, which is 4.04 % higher than that of the pure diesel original injection shape. The triangle injection shape makes the ammonia-diesel dual fuel burn more concentrated, resulting in lower unburned ammonia loss and higher thermal efficiency. Under the 40 % ammonia energy fraction and triangle injection shape, the highest thermal efficiency reaches 40.57 %, 1.58 % higher than the pure diesel original injection shape. Additionally, it significantly reduces unburned ammonia emissions. The injection rate shapes have a minor impact on CO2 emissions. The rapid increase in-cylinder average temperature can substantially reduce N2O emissions, thereby lowering total greenhouse gas emissions. Among them, the total greenhouse gas emissions of 40 % ammonia energy fraction and triangle injection shape are the lowest, at 81619 ppm, which is 11.3 % lower than that of pure diesel original injection shape. On the contrary, it will increase NOx emissions. Conversely, the slopes exhibit the lowest NOx emissions at 220.8 ppm, representing an 88 % reduction compared to the pure diesel original injection shape.

Impact of injection pressure on a dual-fuel engine using acetylene gas and microalgae blends of chlorella protothecoides

The amount of fossil fuel usage in compression ignition (CI) engines is greatly reduced when biodiesel is used. The primary disadvantage of using biodiesel is that, due to its high viscosity, which causes fuels to remain unburned during the premixed combustion stage, leads to lower brake thermal efficiency (BTE). Gaseous fuels predominantly reducing emissions in CI engines due to its complete burning without leaving any carbon traces. Fuel injection pressure (FIP) is one of the factors which is influencing the combustion phase because they are used to optimize fuel particle atomization. The current study examines engine parameters for a dual fuel engine that runs on biodiesel blends made from 20 % methyl ester of chlorella protothecoides micro algae (B20MEOA) and acetylene gas under variable Fuel injection pressure (FIP) ranging from 200 bar to 240 bar with 10-bar steps. According to the experimental results, when 3 LPM of acetylene gas is supplied along with the intake air and B20MEOA supplied at a FIP of 240 bar, the emissions such as smoke opacity, hydrocarbon (HC), and carbon monoxide (CO) are reduced by 16.9 %, 8.3 %, and 15.4 %, respectively, whereas the oxides of nitrogen (NOx) increases by approximately 7 % when compared to B20MEOA alone operation.

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.

Shape/penetration analysis and comparisons of isolated spray plumes in a multi-hole Diesel spray

Fuel injection systems significantly impact the combustion process and play a key role in reducing harmful exhaust emissions in internal combustion engines. For dual-fuel (DF) engines operating in gas mode, ignition of the main fuel is typically controlled by directly injected liquid pilot fuel. Liquid pilot fuel’s initial penetration and total mass considerably impact exhaust emissions and combustion stability. We investigated the spray morphology of a multi-hole diesel fuel injector within a constant-volume spray chamber using high-speed shadowgraphy and Mie-scattering measurements. Two methodologies were employed. The first one utilized a nozzle equipped with a thimble structure to isolate a single plume. The second methodology known as plume-blocking, involved sealing the orifices of the multi-hole nozzle to generate a single-spray plume. Our findings revealed that the plume-blocking approach demonstrated greater penetration than the thimble-equipped nozzle. The rapid penetration of this method may restrict its applicability to single-spray studies. Sprays generated from this partially sealed nozzle exhibited noticeable disparities compared to an unblocked nozzle, whereas a nozzle equipped with a thimble produced similar outcomes to the standard nozzle. The orifices when sealed, modify the flow distribution within the sac volume, which consequently affects the spray characteristics. In summary, this research provides insights into the impacts of various plume isolation methods on spray morphology, thereby enhancing the understanding of spray behaviour in transient conditions by comparing plume variations and disturbances under various fuel pressure and ambient conditions.

Synergistic effect of hydrogen induction on the performance, combustion and emission phenomenon of dual-fuel CI engine with Chlorella vulgaris algae oil and its methyl ester

The present work aims to investigate the cumulative effect of hydrogen enrichment with the fuels of diesel, Neat chlorella vulgaris oil (NCVO), and Chlorella vulgaris methyl ester (CVME) in a mono-cylinder CI engine. The performance, combustion, and emission parameters of diesel, NCVO, and CVME are analyzed and compared to the findings obtained with hydrogen induction in the intake manifold under dual fuel configuration. With the effect of hydrogen infusion, the metrics of performance, combustion and emission parameters are improved. Under maximum load condition, the induction of hydrogen escalates the BTE from 32.74%, 28.01%, and 23.02%–35.39%, 31.40%, and 28.12% with diesel, CVME, and NCVO at maximal hydrogen share energy of 14.38%, 11.50% and 9.61% respectively. Alongside, the enrichment of hydrogen declines the carbon monoxide (CO) from 4.13, 10.38, and 19.24 g/kWh to 3.16, 8.02, and 15.26 g/kWh, unburned hydrocarbons (UHC) from 0.51, 0.71, and 2.02 g/kWh to 0.36, 0.50, and 1.64 g/kWh, smoke opacity from 55%, 75%, and 85%–43%, 67%, and 71% with diesel, CVME, and NCVO respectively. However, the hydrogen's significant flame velocity and immense calorific value confect to an elevated combustion temperature and subsequent rise in heat release rate (HRR) to, cylinder pressure, and emission of nitrogen oxide (NO). Among the tested fuels, diesel posses maximum HRR and cylinder pressure of 80.46 J/0CA and 88.67 bar respectively. Maximum specific NO emission was observed with CVME having 10.80 g/kWh, whereas diesel and NCVO has 9.49 g/kWh and 4.93 g/kWh respectively.

Effect of ammonia energy ratio and load on combustion and emissions of an ammonia/diesel dual-fuel engine

Ammonia is receiving increasing attention as a zero-carbon fuel. However, it is difficult to use alone because of its high auto-ignition temperature. Therefore, in this paper, the effects of four ammonia energy ratios (15 %, 30 %, 45 %, and 60 %) on the combustion and emission characteristics of the engine at different loads were studied by using the ammonia/diesel dual-fuel strategy. The results indicated that the presence of ammonia lowered the combustion temperature at all loads, thereby lowering the cylinder temperature and cylinder pressure. In addition, the HRR first increased and then decreased as the ignition delay increased with the increase in ammonia energy ratio. In terms of emissions, at 100 % load, the CO2 and NO of the D40A60 were 65.5 % and 88.14 % lower than that of the D100. The decrease in CO2 was due to more carbon-based fuels being replaced by ammonia. The decrease in NO was due to the decomposition of NO by the thermal deNOx reaction resulting from the lower combustion temperature. The emissions of N2O produced by partial ammonia oxidation offset the greenhouse gas emission reduction effect caused by the reduction of carbon dioxide emissions. Further optimization of the engine combustion strategy is still needed in the future.

Study on the active regeneration characteristics of DPF in diesel-methanol dual-fuel engine under different exhaust oxygen concentrations

This study proposes a method to control exhaust oxygen (O2) concentration by adjusting the intake throttle valve, achieving intake throttling, and reducing intake airflow. The impact of exhaust O2 concentration at the inlet of the diesel oxidation catalyst (DOC) the diesel particulate filter (DPF) performance during active regeneration in diesel engines is investigated. Experiments are conducted under methanol substitution rates (MSR) of 0% and 20% to investigate how different exhaust O2 concentrations affect the performance of the DOC and DPF during active regeneration. A comparative analysis of fuel consumption and cumulative CO2 emissions during DPF active regeneration under different exhaust O2 concentrations is performed. Research results indicate that decreasing exhaust O2 concentration reduces exhaust flow, raising DOC inlet temperature. This enhancement improves catalytic conversion efficiency, accelerating the rise in DPF inlet temperature. The average conversion efficiency of DOC to unburned methanol exceeds 98.07%. After initiating DPF active regeneration, O2 concentration sharply drops, leading to elevated CO2 emissions. As soot combustion advances, the required O2 diminishes, resulting in a gradual rise and eventual stabilization of O2 emissions. Economically and environmentally, irrespective of MSR (20% or 0%), there exists an optimal exhaust O2 concentration that minimizes effective regeneration time during DPF active regeneration, achieving minimal fuel consumption and the lowest CO2 mass emissions. This study offers theoretical support for optimizing energy-saving and emission-reduction processes during DPF active regeneration.

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.

Biogas as a sustainable and viable alternative fuel for diesel engines: A comprehensive review of production, purification, economic analysis and performance evaluation

Economic and environmental concerns have propelled alternative fuel research in the last few decades. Numerous research initiatives have been undertaken to optimize energy demand by exploring alternative fuels. This comprehensive review presents an in-depth analysis of the current and future prospects of biogas production, filtration and engine applications. To evaluate the performance and emission characteristics of biogas in compression ignition engines, its impact has been extensively analyzed. The study finds that using biogas as an alternate fuel in a dual-fuel mode engine leads to a degradation of 5–27% in performance parameters such as brake thermal efficiency, while brake-specific fuel consumption increases by up to 33%. A subsequent study of emissions reveals a 25–65% reduction in nitrogen oxides and smoke emissions. In contrast, the dual-fuel engine showed a 31% increase in hydrocarbon and carbon monoxide emissions when compared to a conventional diesel engine. In conclusion, biogas has emerged as a promising alternative fuel for diesel engines due to its sustainable nature and potential for reducing emissions. While there are certain trades-offs in terms of performance parameters, the reduction in harmful emissions makes it a viable option for future research and development.

Decarbonization strategies in the maritime industry: An analysis of dual-fuel engine performance and the carbon intensity indicator

This study is based on detailed data from 11 sea voyages over three years to determine the impact of liquefied natural gas (LNG) use on the decarbonization pathway in maritime transportation. The research detailed the vessel's daily fuel consumption, CO2 emission inventories, and Carbon Intensity Indicator (CII). The decision tree method used to evaluate this complex dataset highlights the possible contributions of LNG to maritime energy efficiency and sustainability. While the findings show that LNG reduces CO2 emissions by around 30 %, it is insufficient to meet the International Maritime Organization's (IMO) 2050 targets. The study concludes that LNG should be an important transition fuel until the mid-2030s. However, the maritime sector needs multi-pronged strategies such as technological innovations, stringent regulations and sectoral collaborations to achieve a decarbonized future. This research provides a comprehensive analysis assessing the potential of LNG to achieve the IMO 2050 targets in the context of maritime decarbonization strategies.

Investigation of the impacts of regeneration temperature and methanol substitution rate on the active regeneration of diesel particulate filter in a diesel-methanol dual-fuel engine

Methanol (CH3OH), a sustainable fuel derived from many renewable resources, simultaneously reduces nitrogen oxides (NOx) and particulate matter (PM) in diesel-methanol dual-fuel engines. This study systematically investigated the effects of regeneration temperature and methanol substitution rate (MSR) on the performance of diesel oxidation catalyst (DOC), diesel particulate filter (DPF), and the temperature characteristics of DPF substrate during active regeneration. The experimental results show that the DOC catalytic oxidation of unburned CH3OH has a conversion rate of more than 97.5 % across various MSR. DPF inlet temperature rose faster with higher MSR. Elevated regeneration temperature reduced effective regeneration times and diesel equivalent consumption. Within active regeneration conditions with MSR increases, both effective regeneration times and diesel equivalent consumption initially decreased and then increased as the MSR rose. At MSR = 30 %, the duration of effective regeneration times during DPF active regeneration was minimized, and diesel equivalent consumption at MSR = 30 % experienced an improvement of 22.52 % compared to MSR = 0 %. The highest DPF substrate temperatures across various MSR levels are consistently observed at T6 position within the DPF. This study can provide a theoretical basis for the active regeneration of DPF in methanol-diesel dual-fuel mode.

Optical engine investigation of ammonia combustion enhancement with polyoxymethylene dimethyl ethers (PODE₃) as pilot fuel

Ammonia, gaining attention as a carbon-free fuel amid declining fossil fuel reserves, faces challenges like combustion instability and misfiring in its application in internal combustion engines. In this study, polyoxymethylene dimethyl ethers (PODE3), a clean, renewable, and electrically synthesized fuel with high cetane number and oxygen content, is evaluated as a pilot fuel for ammonia in dual-fuel engines. The study, performed in a dual-fuel optical engine, investigates the use of PODE₃ compared to diesel as direct injection fuels for ammonia combustion, focusing on the impact of PODE3 injection timing and dwell (the interval between dual-stage injections) on the ignition characteristics of ammonia. The results demonstrate that, compared to diesel, using PODE3 enhances ammonia combustion in dual-fuel engines. This is evident from increased in-cylinder pressure, higher apparent heat release rate (AHRR), advanced combustion phases, and improved indicated mean effective pressure (IMEP), enhancing overall stability. PODE3 also effectively minimizes soot generation, evidenced by a 71.5 % reduction in spatially integrated natural luminosity (SINL), accompanied by a 16.9 % increase in peak flame area. Adjusting PODE3 injection timing is crucial; initial retardation improves combustion performance, marked by higher in-cylinder pressure and AHRR, as well as expanded flame area. However, over-delaying injection timing reduces these gains. The optimal performance is achieved under the SOI-25 condition, balancing combustion and flame development, though some areas remain unburnt. In a dual-stage injection strategy using PODE3, where the second injection timing remains fixed at −25 °CA ATDC, the critical adjustment of advancing the first injection timing to −35 °CA ATDC markedly enhances combustion performance compared to a single injection condition. This setting reduces ignition delays, increases peak in-cylinder pressures, and improves stability, which collectively contribute to a significant 20.4 % increase in the peak flame area, particularly between adjacent fuel jets. Expanding upon this, advancing the first injection timing further to −45 °CA ATDC leads to a decrease in peak in-cylinder pressure and AHRR, accompanied by a notable 40.3 % reduction in the peak flame area. This research affirms the advantages of PODE3 over diesel in ammonia-powered dual-fuel engines, markedly enhancing combustion performance and environmental sustainability, where the injection strategy of PODE3 emerges as a crucial element.

Piston ring and cylinder liner scuffing analysis in dual-fuel low-speed engines considering liner deformation and tribofilm evolution

The piston ring and cylinder liner (PRCL) system in larger-bore low-speed marine engines frequently experiences scuffing failures, which significantly decrease the engine reliability. To understand this failure mechanism, a scuffing failure model subjected to the PRCL system was developed considering multidisciplinary coupling effects that integrate asperity contact, hydrodynamic lubrication, tribochemistry reactions, thermal effects, friction, and surface wear. The impacts of large-scale deformation and gas-combustion mode on the scuffing performances of the PRCL system were examined. The key findings indicate that the larger-scale liner deformation can markedly reduce oil film thickness and exacerbate local asperity contact, influencing the evolution of the tribofilm by increasing the removal process. Under gas-combustion mode, the oil film thickness is even lower, and the asperity contact pressure further increases due to a more starved lubrication state and higher combustion temperature. This leads to tribofilm breakdown and severe wear near the ring opening area, which are aligning with the full-scale experimental results with scuffing failure.

Effect of ammonia energy ratio and diesel pilot-injection strategy on the performance of ammonia-diesel dual fuel engine

ABSTRACT The combustion strategy under a higher ammonia energy ratio (AER) is expected to improve the combustion performance of ammonia-diesel dual-fuel (ADDF) engines, leading to additional reductions in greenhouse gas (GHG) emissions. In order to meet the engine’s performance requirements while achieving the low carbon emissions, this study utilized CFD numerical simulations to analyze the combustion and emission characteristics for an ADDF engine at AER levels from 0% to 90%. It focused primarily on evaluating the effectiveness of diesel pilot-injection strategy in reducing GHG emissions at AER50%. The obtained results showed that the unburned NH3 and N2O emissions exhibited an upward trend with the increment of AER, leading to a degradation in the indicated thermal efficiency (ITE), while GHG emissions were more significant than in the original diesel-only combustion mode. Based on AER50%, the ITE exhibited a trend of initially rising and then falling with the increment of diesel pilot-injection ratio (DPR) from 0% to 60%, reaching a maximum value of 47.1% at DPR 40%. At this point, the unburned NH3 emission decreased by 42.4% compared to the DPR0%, and no longer declined after the DPR exceeded 40%. Based on AER 50% and DPR 40%, ITE peaked at 48.1% with the optimal timing for diesel pilot-injection, which represented a 1.6% rise in ITE relative to the original diesel-only combustion mode, while GHG emissions decreased by 35%, and NO emissions increased by 25%.

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%.