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Dual Fuel (DF) combustion concept has demonstrated to be a valid solution to ensure the utilization of diesel engines in heavy duty and naval applications. The substitution of part of diesel fuel with a cleaner gaseous one can reduce among others: carbon dioxides (CO 2), nitrogen oxides (NO x) and surely particulate matter (PM). Nevertheless, the difficulties encountered by the reduced pilot liquid jet to reach out the furthest areas of the combustion chamber, especially at partial load, lead to unburned emissions of the premixed charge. They can be a serious issue to overcome when the premixed fuel is represented by a carbonaceous fuel like natural gas (NG). For this reason, hydrogen, that is carbon-free, represents the new progression to clean mobility. This work aims at deepening the in-cylinder phenomena through a synergetic methodology that involves experimental optical diagnostics and 3D numerical investigations. The experimental activity is carried out on a single cylinder research engine (SCRE) equipped with an optical apparatus allowing the visualization of the combustion process, later processed via high speed visible (VIS) and infrared (IR) imaging. Several filters applied on the IR camera permit to detect specific species such as CO 2. Subsequently, these outcomes are used to validate numerical models, and in turn, the numerical results help to validate the species detected qualitatively via optical diagnostics and to identify which ones majorly affect the physical and chemical processes. Numerical simulations are performed with ANSYS Forte ® code on a geometry which accurately reproduces the shape of the combustion chamber. Combustion models include a turbulent-kinetic interaction model with a mechanism of 124 species and 660 reactions to deal with the autoignition phase and diesel surrogate oxidation, while to account for the flame propagation through the premixed charge the G-equation is considered. The reference test cases are characterized by two different engine speeds, 1500 and 2000 rpm, and a low load level, corresponding to 2 bar of brake mean effective pressure (BMEP) on light-duty vehicle. The hydrogen energy shares are between 83.2 and 81.8%. Results demonstrate that IR images and OH radical are key for the detection of ignition process of both diesel and hydrogen. The flame propagation in the air/H 2 charge can be observed with the help of CFD elaborations. Finally, emission levels are adequately predicted by the chosen oxidation models. • IR and VIS imaging are used to visualize the in-cylinder process in a diesel SCRE operating in DF mode supplied with H 2. • CFD is used to identify the species that better represent the oxidation process of both fuels. • IR imaging together with OH allows to identify the ignition phases of both diesel and H 2. • CFD flame front visualizations are necessary to overcome the limits of IR imaging for the representation of premixed flame. • The chosen kinetics well predict pollutant emissions. [ABSTRACT FROM AUTHOR]

Shipping is a highly energy-intensive sector, and fleet decarbonization initiatives can significantly reduce greenhouse gas emissions. In the short-to-medium term, internal combustion engines will continue to be used for propulsion or as electricity generators onboard ships. Natural gas is an effective solution which can be used to mitigate greenhouse gas emissions from the marine sector. Considered to be a transitional fuel, it can provide a potential reduction in CO2 emissions of around 20–30%, compared with conventional marine fuels. This work investigated the influence of diesel-injection strategies on the performance and emissions of a single-cylinder prototype compression-ignition engine for marine applications, retrofitted to run as a Low-Pressure Dual-Fuel Engine using natural gas. Two different injection systems were used: a mass flow controller enabling continuous-mode gas feeding, and a Solenoid-Operated Gas Admission Valve for marine applications, the latter allowing phased natural-gas injection. Experimental tests were focused on partial-load conditions, which are critical for dual-fuel engines, with a natural gas/diesel mass ratio of 4:1. Phased injection resulted in reductions in fuel consumption, compared to continuous mode, of up to 11%. Further experiments demonstrated reductions in fuel consumption of up to 20.7% (in equivalent diesel); on the other hand, the unburned hydrocarbon emissions which resulted were an order of magnitude larger than the reference values for full diesel, reducing the benefits in terms of greenhouse gas emissions, with a reduction in Global Warming Potential of only 3% compared to full diesel. [ABSTRACT FROM AUTHOR]

Because of their great capability and consistent quality, Diesel engines are commonly employed in Industrial regions, Transportation sectors, and Agricultural fields. The main disadvantage of this engine is the excessive amount of smoke and nitrogen oxide emissions. As a result, Mosambi Peel Pyro oil (MPO) was blended in varying quantities with straight diesel. Methanol enrichment was used to test D90MPO10 (10% MPO +90% Diesel), D90MPO10M21 (10% MPO +90% Diesel +21% Methanol), and D90MPO10M22 (10% MPO +90% Diesel +22% Methanol)Oil parameters.The ultimate, proximate, and FTIR analyses, as well as viscosity, density, flash point, and fire point, are estimated. D90MPO10, D90MPO10M21, and D90MPO10M22 are diesel engine fuels, and D90MPO10M22's combustion and emission performance are investigated. It was shown that using D90MPO10 as pilot fuel and methanol as an induction fuel in diesel engines resulted in lower smoke levels (3.5%) and increased thermal efficiency (2.5%) with no significant Performance Degradation. [ABSTRACT FROM AUTHOR]

Strict emission regulations together with reducing fossil fuels resources lead to more attention on new combustion strategies and alternative fuels such as biodiesel which is renewable, environmentally friendly and more cost-effective than other fuels. In this study, CONVERGE CFD software coupling with chemical kinetics mechanism is used to numerically investigation of natural gas (NG)/biodiesel dual fuel engine. The discussed biodiesel consists of 25% methyl decanoate (MD), 25% methyl-9-decanoate (MD9D) and 50% diesel. A comparative study of NG/diesel and NG/biodiesel fueled cases is performed to highlight the combustion characteristics of biodiesel. For all simulated cases, it is supposed that 5% of energy is supplied by high reactive fuel (i.e., Diesel or Biodiesel) and 95% is coming with low reactive fuel (i.e., Natural Gas). Results revealed that in full load condition, using biodiesel/NG led to 86% lower carbon monoxide (CO) and 91% unburned hydrocarbons (UHC). On the other hand, peak pressure and maximum in-cylinder temperature increased 5% and 83 K, respectively which led to 0.6% efficiency improvement. according to the results of different injection timing, when it was advanced from -4 to -20 crank angle degree after top dead center (CAD ATDC) for biodiesel/NG and diesel/NG, the indicated mean effective pressure (IMEP) and gross thermal efficiency (GTE) reached at their peaks 18.3 bar and 48.2% at -12 CAD ATDC, 18.05 bar and 47.7% at -8 CAD ATDC respectively. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this study, a fully optically accessible single-cylinder research engine is the basis for the visualization and generation of extensive knowledge about the in-cylinder processes of mixture formation, ignition, and combustion of alternative fuels for the dual-fuel combustion process. POMDME substitutes the fossil pilot fuel as a drop-in, non-sooting alternative to widely eliminate the NOx-PM tradeoff. Furthermore, an optimized ignition behavior, increased degrees of freedom in combustion phasing, and the pilot's energy content are expected. The flame luminosity transmitted via an optical piston was split in the optical path to record the natural flame luminosity simultaneously with an RGB high-speed camera. The second channel consisted of OH chemiluminescence recording, isolated by a bandpass filter via an intensified monochrome high-speed camera. To investigate the combustion process spectrally, spatially, and temporally resolved in more detail, selected operating points were re-recorded via a high-speed imaging spectrograph. POMDME is benchmarked against regular diesel oil, according to EN590. Synthetic natural gas is applied as the primary gaseous fuel. Experimental sweeps along the overall pilot's energy content (2%, 5%, 10%), injection pressure (500–1600 bar), and start of energizing (5–55 CAD bFTDC) are carried out. The given conditions result in decreased liquid-penetration length between 25% and 30% for the oxygenate, larger for earlier SOE and higher dilution. The lift-off length is nearer the liquid penetration length, increasing for higher rail pressures. The light-based ignition delay for EN590 is enlarged by 0.8 CAD after adding methane, while the oxygenate is not visibly retarded. Without methane, the oxygenate preceded EN590 by 0.6 CAD. The temporal and spatial position and extent of premixed, diffusive, and OH*, change significantly. RCCI operation at practically relevant 18.4 bar IMEP is demonstrated, highlighting the influence of the start of energizing variation with 51% decreased burn duration in the first half of combustion. [ABSTRACT FROM AUTHOR]

The effect of graphene oxide nanoparticles (50 ppm) and hydrogen enrichment on the Nerium oleander methyl ester-diesel blend is investigated in the present research study using a compression ignition engine in a dual-fuel mode. Biodiesel is derived from Nerium oleander oil, and 20% (v/v) is blended with 80% of diesel fuel. Following that, Novel carbon-based additives are dispersed in biodiesel–diesel blend and supplied as a piloted fuel. On the other hand, the variable volume flow rates (5 and 10 lpm) of hydrogen gas are supplied via the intake manifold as a secondary fuel. The effects of piloted fuel blends and secondary hydrogen fuel enrichment on overall combustion, performance, and emissions are explored by investigating the cylinder pressure, net and cumulative heat release rate brake thermal efficiency, brake-specific fuel consumption, exhaust gas temperature, carbon dioxide, carbon monoxide, hydrocarbons, nitrogen oxide, and smoke emissions. Combustion parameters, including cylinder pressure, net heat release rate, cumulative heat release rate, are improved by 16, 9.02, and 12.84%, respectively, for B20 + GO + 10H2 blend at maximum engine power when compared to biodiesel–diesel blend. The blend B20 + GO + 10H2 increases the brake thermal efficiency by 12.35% and decreases brake-specific fuel consumption by 15.15% at a maximum power output when compared to the biodiesel–diesel blend. The synergistic effect of B20 + GO + 10H2 decreases carbon monoxide, hydrocarbon, and smoke opacity emissions by 24.51, 27.04, and 7.5%, respectively, at a higher power output when compared to diesel. However, the carbon dioxide and formation of nitrogen oxide increased by 9.57 and 11.98% at a higher power output as compared to diesel. This is owing to the rapid flame speed of hydrogen, as well as the enhanced thermal conductivity and catalytic activity of a biodiesel–diesel blend, including graphene oxide nano-additions. [ABSTRACT FROM AUTHOR]

The current research focuses on the impacts of pine oil injection and hydrogen induction separately with hemp oil methyl ester (HOME) in the single cylinder diesel engine in dual fuel‐reactivity controlled compression ignition (DF‐RCCI) combustion mode. The engine was tested under a DF‐RCCI mode for the different energy shares of 10% pine oil with HOME (10P‐HOME), 30% pine oil with HOME (30P‐HOME), 3‐lpm hydrogen with HOME (3‐lpmH2‐HOME), and 6‐lpm hydrogen with HOME (6‐lpmH2‐HOME) separately at 345 °CA bTDC of low reactivity fuel (pine oil and hydrogen) and 23°C bTDC injection timing of high reactivity fuel (HOME). The results showed a higher Brake Thermal Efficiency (BTE) of 7.44%, 5.32%, 5.72%, and 2.46% for 6‐lpmH2‐HOME, 3‐lpmH2‐HOME, 30P‐HOME, and 10P‐HOME fuel shares, respectively, over the conventional diesel combustion (CDC) at full load. 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME fuel combinations recorded 4.08% 4.42%, and 5.69% lower brake specific fuel consumption (BSFC), respectively, at full load. When comparing DF‐RCCI combustion to CDC, an increase in the heat release rate (HRR) of 2.89%–26.50% and a rise in peak cylinder pressure of 0.77%–12.99% were observed. The 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME emit less smoke in DF‐RCCI combustion mode by 13.06%, 4.84%, and 7.26%, respectively at full load condition. When using 30P‐HOME the exhaust gas temperature (EGT) decreased by 3.50% at full load condition. At part and full load conditions, the 30P‐HOME fuel share reduced oxides of nitrogen (NOX) emissions by 3.93% and 5.26%, respectively. [ABSTRACT FROM AUTHOR]

Strict emission regulations together with reducing fossil fuels resources lead to more attention on new combustion strategies and alternative fuels such as biodiesel which is renewable, environmentally friendly and more cost-effective than other fuels. In this study, CONVERGE CFD software coupling with chemical kinetics mechanism is used to numerically investigation of natural gas (NG)/biodiesel dual fuel engine. The discussed biodiesel consists of 25% methyl decanoate (MD), 25% methyl-9-decanoate (MD9D) and 50% diesel. A comparative study of NG/diesel and NG/biodiesel fueled cases is performed to highlight the combustion characteristics of biodiesel. For all simulated cases, it is supposed that 5% of energy is supplied by high reactive fuel (i.e., Diesel or Biodiesel) and 95% is coming with low reactive fuel (i.e., Natural Gas). Results revealed that in full load condition, using biodiesel/NG led to 86% lower carbon monoxide (CO) and 91% unburned hydrocarbons (UHC). On the other hand, peak pressure and maximum in-cylinder temperature increased 5% and 83 K, respectively which led to 0.6% efficiency improvement. according to the results of different injection timing, when it was advanced from -4 to -20 crank angle degree after top dead center (CAD ATDC) for biodiesel/NG and diesel/NG, the indicated mean effective pressure (IMEP) and gross thermal efficiency (GTE) reached at their peaks 18.3 bar and 48.2% at -12 CAD ATDC, 18.05 bar and 47.7% at -8 CAD ATDC respectively.

This study investigates the ignition and combustion characteristics of intersecting diesel surrogate (pilot) and hydrogen (H 2 , main) jets under engine-relevant conditions. The experiments, performed in an optically accessible constant-volume combustion chamber (CVCC), utilised two converging single-hole injectors, with the pilot fuel accounting for 12% of the total injected fuel energy. This study investigated the effects of two key parameters on the ignition process: jet interaction angle (12° to 19°) and ambient O 2 concentration (10 to 21 vol.%). The results show that the presence of H 2 either advances or delays pilot ignition depending on whether the pilot n -heptane jet ignites before or after interacting with the H 2 jet, respectively. The pilot-main ignition transition period is influenced by both jet interaction angle and ambient O 2 concentration. Under identical ambient conditions, a smaller jet interaction angle results in a longer transition, while for a constant angle, lower ambient O 2 leads to a more prolonged transition. Under 10 vol.% O 2 conditions, flame kernels emerge upstream of the main flame body, before eventually merging with the reacting jet downstream, with this phenomenon observed to induce variation in heat and flame stabilisation characteristics. An explanation for the upstream kernel formation is offered based on the entrainment of residual pilot n -heptane-jet fuel into the upstream region of the still-injecting main jet, with the relative jet momentum a likely key contributor influencing this entrainment that impacts kernel formation. • Study of main H 2 and pilot diesel jet interactions in engine relevant conditions. • Studies on jet interaction angle, ambient O 2 and relative jet momentum effects. • Main jet interaction and pilot injection duration impact pilot ignition delay. • Jet overlap and ambient reactivity influence pilot-to-main jet ignition transition. • Interaction of H 2 jet and pilot remnants can impact flame stability and heat release. [ABSTRACT FROM AUTHOR]

The study was conducted to uncover the emission, combustion, and performance features of the blend of Water Hyacinth biodiesel and Mesua Ferrea seed oil biodiesel with Hydrogen addition on a diesel engine in dual fuel. Pilot fuel is a blend of 50% Water Hyacinth biodiesel and 50% Mesua Ferrea seed oil biodiesel. A single-cylinder compression ignition engine was modified to operate on dual fuel mode with hydrogen. Variations of engine operating parameters such as injection timing, and engine load were performed. The study was conducted with three pilot fuel injection timings (23, 26, and 29°bTDC) and variable engine loadings (20%–100% with an increment of 20%) at an injection pressure of 200 bar and compression ratio of 18. The results indicated that the maximum brake thermal efficiency of 28.11% and a replacement of liquid fuel by 85% was obtained for the WHMF blend powered dual fuel diesel engine at pilot fuel injection timings of 26°bTDC at 100% load. HC, CO, and smoke emissions are reduced with hydrogen due to faster combustion. On the other hand, there was a slight increase in NOx emissions noticed with hydrogen enrichment. [Display omitted] • Pilot fuel is a blend of 50% Water Hyacinth Biodiesel and 50% Mesua Ferrea Biodiesel. • Hydrogen is used with pilot fuel under dual fuel mode to improve combustion. • Hydrogen enrichment improves the brake thermal efficiency of the pilot fuel. • Emissions of CO and HC were reduced with hydrogen addition in the pilot fuel. • Liquid fuel replacement of 85% is achieved at an IT of 26⁰bTDC of the pilot fuel. [ABSTRACT FROM AUTHOR]

The combustion of diesel fuel in internal combustion engines faces challenges associated with excessive emissions of pollutants. A direct solution to this issue is the incorporation of cleaner energy sources. In this study, a numerical model was constructed to investigate the characteristics of ammonia–diesel dual-fuel application in a medium-speed diesel engine. Effects of ammonia–diesel blending ratios on engine performance and emissions were investigated. The results indicate that for this engine model, the optimal diesel energy ratio is about 22%. When the diesel energy ratio is less than 22%, the engine's output performance is significantly affected by the diesel energy ratio, while above 22%, the influence of the intake becomes more pronounced. When the diesel energy ratio is below 16%, the cylinder cannot reach combustion conditions. Diesel energy ratios below 22% can cause ammonia leakage. With increasing diesel energy ratio, the final emissions of carbon oxides increase. With a higher diesel energy ratio, NO emissions become lower. When the diesel fuel energy ratio exceeds 22%, the N2O emissions can be almost neglected, while below 22%, with poor combustion conditions inside the cylinder, the N2O emissions will increase. [ABSTRACT FROM AUTHOR]

Dual-fuel low-temperature combustion is a possible solution for alleviating the tradeoff between oxides of nitrogen and soot emissions in conventional diesel combustion, albeit with poor combustion stability, high carbon monoxide, and unburned hydrocarbon emissions at low engine loads. The present work compares emissions and combustion (heat release and other metrics) of both diesel and poly-oxy methylene dimethyl ether as high-reactivity fuels to ignite natural gas while leveraging spray-targeted reactivity stratification, which involved multiple injections of the high-reactivity fuels. The experiments included six parametric sweeps of: (1) start of first injection, (2) start of second injection, (3) percentage of energy substitution of natural gas, (4) commanded injection duration ratio, (5) rail pressure, and (6) intake pressure. The experiments were performed on a 1.8 L heavy-duty single-cylinder research engine operating at a medium speed of 1339 rev/min. Not-to-exceed limits for the indicated oxides of nitrogen emissions, maximum pressure rise rate, and the coefficient of variation of the indicated mean effective pressure were set to 1 g/kWh, 10 bar/CAD, and 10%, respectively. The indicated emissions decreased and combustion improved significantly for both fueling combinations when the experimental procedure was applied. [ABSTRACT FROM AUTHOR]

Modeling of in-cylinder combustion in internal combustion engines is still a complex issue. Further development studies are needed to accurately predict the performance, combustion regimes, and emission behavior of fuels other than conventional fuels such as gasoline or diesel. In this study, experimental data in full load diesel combustion regime were used to validate the numerical model using the 0/1-dimensional AVL Boost program. Vibe 2-Zone combustion model was used during the validation studies. As a result of the analysis, when the performance and emission values were examined, it was seen that there was close to 94% compliance. After numerical verification in the diesel combustion regime, the system was converted to a reactivity controlled compression ignition (RCCI) engine with the addition of an injector for propane injection to the intake port. Afterwards, the effects of the use of different propane ratios and different start of combustion times on the performance, combustion characteristics, and emission values of an RCCI engine were investigated by keeping the total fuel mass constant. As a result, with the use of 90% propane and 10% diesel fuel, an 11% improvement in performance was achieved, and it was observed that the use of catalytic exhaust equipment was not required for emission values. In addition, it has been determined that the best combustion start time for performance and emission values was -6 °CA ATDC. [ABSTRACT FROM AUTHOR]

Recently, the International Maritime Organization (IMO) introduced an initial strategy aiming to reduce and ultimately achieve net-zero greenhouse gas emissions by 2050. While various research projects on retrofitting have been conducted, there is a noticeable gap in detailed studies concerning emission reduction through liquefied natural gas (LNG) dual-fuel retrofit options. This study assesses the feasibility and environmental impacts of applying LNG dual-fuel retrofit to a 9196 gross tonnage training ship. It explores replacement scenarios of 20 %, 30 %, and 40 % LNG incorporation using life cycle assessment. Additionally, the study employs a life cycle assessment methodology to compare the global warming potential against both the life cycle assessment database and engine emission factors. Over 35 d of operation at a normal continuous rating of 85 % power load, replacing 20 %, 30 %, and 40 % of fuel with LNG resulted in a reduction of global warming potential by approximately 23.1 %, 32.7 %, and 42.3 %, respectively. These results indicate that LNG replacement cases significantly lower emissions related to global warming potential compared to conventional marine diesel oil (MDO) operations, with greater reductions observed at higher replacement percentages. Further investigation revealed significant differences between the results derived from the life cycle assessment database and engine emission factors. However, statistical analyses indicated that both sources exhibit a consistent trend, with p-values in all power load cases exceeding 0.05, indicating no significant interaction term. Despite notable differences, the utilization of life cycle assessment offers high reliability and ease of use, serving as a solid foundation for decision-making regarding sustainable options.

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.

The research aims to investigate the features of a dual-fuel mode diesel engine that runs on hydrogen gas and sapota seed biodiesel (SSB) blend. Using gaseous hydrogen in diesel engines is a practical solution for enhancing energy efficiency and reducing emissions. The use of sapota fruit waste seeds as a new and innovative source to produce biodiesel has been recognized. It is essential to mention that sapota seeds are only used for sowing purposes other than those considered wasteful. A comprehensive review of earlier research indicates that this study, which uses an SSB blend in addition to hydrogen in dual-fuel operation, is essential. The primary objective of this research is to analyze the impact of hydrogen in SSB dual-fuel mode in single-cylinder diesel engines. Hydrogen was introduced into the intake manifold via a port fuel injector at flow rates of 3 and 6 liters per minute (LPM), with SSB as the fuel. The hydrogen energy share for 3 LPM and 6 LPM at maximum brake power (BP) conditions is 16.17% and 31.07%, respectively. The results revealed that hydrogen induction 3 LPM and 6 LPM increased cylinder pressure by 17.26% and 21.03%, heat release rate (HRR) by 43.91% and 56.13%, brake thermal efficiency (BTE) by 6.29% and 14.62%, and decreased brake specific energy consumption (BSEC) by 21.73% and 39.13% than diesel at maximum BP. Moreover, hydrogen 3 LPM and 6 LPM reduced carbon dioxide (CO 2), carbon monoxide (CO), hydrocarbon (HC), and smoke emissions by 18.61% and 28.26%, 49.68% and 77.20%, 63.01% and 83.28% and 23.24% and 34.63% than diesel at maximum BP. Oxides of nitrogen (NOx) emissions were increased by 2.84% in biodiesel when compared to diesel; however, when hydrogen was added, NOx emissions increased by 9.40% and 16.15% compared to diesel at maximum BP. This study found that adding hydrogen to SSB increased BTE and decreased emissions with slightly increased NOx emissions. This research concluded that biodiesel and hydrogen induction can substitute diesel fuel in diesel engines. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Among alternative fuels, hydrogen has significant promise as both a fuel and a carrier of energy. Hydrogen is projected to be a key alternative fuel in the near future to meet stringent pollution standards. Internal combustion (IC) engines, gas turbine, and aerospace industries use hydrogen as a fuel because it is non-toxic, odorless with high calorific value (CV), and combustible across a wide temperature range while also being a long-term renewable and less polluting energy source. The objective of this study is to investigate the impact of using different hydrogen rations on combustion behaver, engine performance, and emission characteristics in a dual fuel compressed ignition (CI) diesel engine. The tests were performed at speeds of 1500, 2000, and 2500 rpm at difference operating conditions. Hydrogen was introduced at flow rates of 21.4, 28.5, 36.2, 42.8, and 49.6 L per minute for each load. The findings reveal that hydrogen flow rate of 21.4 l/min and 42.8 l/min gives significant impact to engine coefficient of variation (COV) and the performance of the engine. In addition, the emissions level of CO, CO 2 and smoke were improved at the same flow rate. Moreover, the break thermal efficiency (BTE) has shown significant improvement at 21.4 l/min of hydrogen flow rate due to the reduction in combustion length and the movement of the combustion phasing toward the ideal phase. The use of hydrogen as alternative energy has important role as a future green energy source. • Hydrogen Usage as a Dual Fuel in a Compression Ignition Engine. • Hydrogen Mixing and Energy Consolidation for better Brake Specific Energy Consumption BSEC. • Enrichment of Hydrogen is Analyzed for Efficiency. [ABSTRACT FROM AUTHOR]

Energy transition strongly leads researcher to find short-term alternative carbon-free fuels to be used in internal combustion engines. An interesting and transient solution can be the dual fuel (DF) technology. It can offer significant reduction of carbon dioxide and pollutant emissions. In this paper, DF operation was performed in an optically accessed research diesel engine running at a constant speed of 1500 rpm. Substitute fuels (methane or hydrogen) were injected in the intake manifold in front of the entrance of the tumble intake port. The objective was to compare the two DF modes using simultaneously Fast UV–Visible and Fast Infrared (IR) Imaging. We observed that IR camera was able to give deeper combustion information and allowed to grab the whole phenomenon for both DF hydrogen and methane, while identifying the combustion starting points. Also, IR acquisitions for premixed hydrogen evidenced an unpredictably behaviour of the mixture, demonstrating the necessity of a specific Diesel injection strategy to avoid hydrogen auto-ignition at higher engine load. Finally, a comparison of the measured emissions at the exhaust evidenced that in DF mode (both with CH 4 and H 2) a significant reduction of particulate matter is achieved with respect to conventional diesel operation. In addition, when hydrogen is used as primary fuel, a more efficient combustion is obtained drastically reducing HC and CO 2. • Dual fuel use for energetic transition. • Emission reduction. • E-fuel possibility use. • High potential for fast IR camera in engine studies. [ABSTRACT FROM AUTHOR]

This study investigates the ignition and combustion characteristics of interacting hydrogen (H 2) and diesel surrogate jets under simulated compression-ignition engine conditions. The experimental setup includes two converging single-hole injectors in an optically accessible constant-volume combustion chamber (CVCC). The parameters varied in the study are fuel injection durations and ambient O 2 concentrations (10 to 21 vol.%). The results show that a longer interaction between the diesel products and the H 2 jet is required to achieve ignition of the H 2 jet at lower O 2 concentrations. Once ignited, the flame stabilises near or at the nozzle, except under the lowest ambient O 2 condition of 10 vol.% where a lifted flame is observed. The lift-off response, however, is influenced by the relative injection duration of the fuels, with the interaction between the incoming H 2 jet and the diesel combustion recession products possibly playing a role. The interaction between the jets also affects the recorded intensity and the distribution of the diesel fuel jet soot zone. • Parametric study of H 2 -diesel jet combustion in engine-related conditions. • Energy share, via injection duration variation, and ambient O 2 concentration effects studied. • Longer jet–jet interaction required to cause H 2 ignition at lower O 2 ambient. • H 2 jet lift off response dependent on ambient O 2 concentration and jet–jet interaction. • Jet–jet interaction affects the characteristics of the diesel jet soot zone. [ABSTRACT FROM AUTHOR]

To realize a super-leanburn SI engine with a very-high compression ratio, it is required to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for stable combustion. Ethane shows a long ignition delay time at a low temperature close to that of methane, but a short ignition delay time at a high temperature close to that of gasoline. In the present study, the antiknocking effect of adding methane with the RON of 120, ethane with the RON of 108, or propane with the RON of 112 to a regular gasoline surrogate fuel with the RON of 90.8 has been investigated. Adding each gaseous fuel by less than 0.4 in heat fraction advances knocking limit in the descending order of SI timing advance of ethane, methane, and propane, and in the descending order of CA 50 advance of ethane, propane, and methane. Adding methane extends combustion duration slightly, but adding ethane or propane shortens it considerably. Shortening combustion duration has a negative effect on advancing knocking limit SI timing. The effect on advancing knocking limit CA 50 is dependent on not the RON's of the gaseous fuels, but the rates of OH removal by the gaseous fuels. The antiknocking effect of adding each gaseous fuel to a premium gasoline surrogate fuel with the RON of 100.2 has been also investigated. The effect on advancing knocking limit CA50 is not dependent on whether the liquid fuels have cool-flame reactions or not. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of the experimental results of direct hydrogen injection in a dual-fuel diesel engine. The test object is a four-cylinder, four-stroke ADCR engine. The parameters like: indicated mean effective pressure, peak pressure, angle of maximum pressure and released heat were analyzed. Statistical analysis of the obtained results was carried out for each cylinder separately for four different hydrogen doses. Both early and late direct hydrogen injection were analyzed. The significance of the differences for each of the analyzed parameters and type of injection was determined. The stability of the combustion process was evaluated using the coefficient of variation CoV(IMEP). [ABSTRACT FROM AUTHOR]

This study investigates the performance, emission and combustion characteristics of a stationary engine under diverse operating conditions. The research focuses on the impact of waste plastic oil (WPO) blends with and without biogas addition. WPO added in diesel at various proportions such as 20%, 35% and 50% by volume. Biogas is inducted through inlet manifold. Biogas flow rate was varied. This study introduces a pioneering approach by investigating the superior performance of WPO blends coupled with the unique exploration of biogas addition, revealing intricate relationships between fuel blends and combustion characteristics for enhanced stationary engine efficiency and reduced emissions. Notably, WPO with 80% diesel (WPO20) demonstrates superior Brake Thermal Efficiency (BTE), showcasing a significant increase compared to WPO35 and WPO50 across varying load conditions. The addition of biogas to WPO20 results in a measurable reduction in BTE due to incomplete combustion, insufficient excess air, and increased emissions. Hydrocarbon (HC) emissions increase with load for WPO blends, with WPO20 exhibiting the lowest HC emissions. Carbon monoxide (CO) emissions are influenced by WPO concentration, with WPO20–B12 and WPO20–B16 dual fuel mode showing varying trends. Nitrogen oxides (NOx) emissions decrease with the addition of biogas, indicating a 10% reduction for WPO20–B16 compared to WPO20–B12. Smoke emissions increase with higher WPO concentrations but decrease with the introduction of biogas, exhibiting a 20% reduction in smoke for WPO20–B16 compared to WPO20–B12.

Shipping is a highly energy-intensive sector, and fleet decarbonization initiatives can significantly reduce greenhouse gas emissions. In the short-to-medium term, internal combustion engines will continue to be used for propulsion or as electricity generators onboard ships. Natural gas is an effective solution which can be used to mitigate greenhouse gas emissions from the marine sector. Considered to be a transitional fuel, it can provide a potential reduction in CO2 emissions of around 20–30%, compared with conventional marine fuels. This work investigated the influence of diesel-injection strategies on the performance and emissions of a single-cylinder prototype compression-ignition engine for marine applications, retrofitted to run as a Low-Pressure Dual-Fuel Engine using natural gas. Two different injection systems were used: a mass flow controller enabling continuous-mode gas feeding, and a Solenoid-Operated Gas Admission Valve for marine applications, the latter allowing phased natural-gas injection. Experimental tests were focused on partial-load conditions, which are critical for dual-fuel engines, with a natural gas/diesel mass ratio of 4:1. Phased injection resulted in reductions in fuel consumption, compared to continuous mode, of up to 11%. Further experiments demonstrated reductions in fuel consumption of up to 20.7% (in equivalent diesel); on the other hand, the unburned hydrocarbon emissions which resulted were an order of magnitude larger than the reference values for full diesel, reducing the benefits in terms of greenhouse gas emissions, with a reduction in Global Warming Potential of only 3% compared to full diesel.

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.

This study is dedicated to improving the efficiency of the flamelet-generated manifold (FGM) tabulated chemistry combustion modeling approach for predicting the combustion process in diesel-ignited internal combustion (IC) engines. The primary focus is on reducing table generation time and memory requirements. To accurately predict dual-fuel combustion processes, it is important to model both premixed and non-premixed combustion regimes. However, attempting to include both regimes in a single FGM lookup table leads to significant increases in the table size and generation time. In response, this work proposes a dual-table configuration, with each table dedicated to a specific regime. The solution is then interpolated from these tables based on the calculated combustion regime indicator during the computational fluid dynamics (CFD) simulation. This approach optimizes computational efficiency while ensuring an accurate representation of dual-fuel combustion. Additionally, to establish a cost-effective and accurate 3D CFD simulation workflow, the dual-table FGM methodology is coupled with the partially averaged Navier–Stokes (PANS) turbulence model. The feasibility of the proposed FGM methodology is tested utilizing six chemical kinetics mechanisms with different levels of detail. The results of this study demonstrated that the dual-table approach significantly accelerates table generation time and reduces memory requirements compared to a single table that includes both combustion regimes. Furthermore, 3D CFD simulation results of the dual-fuel combustion process are validated against available experimental data for three engine operating points. The in-cylinder pressure traces and rate of heat release obtained from the 3D CFD simulations employing the FGM PANS methodology show good agreement with experimental measurements, confirming the accuracy and reliability of this modeling approach. [ABSTRACT FROM AUTHOR]

The exceptional properties of methanol, such as its high octane number and latent heat of evaporation, make it an advantageous fuel for efficient utilization in dual-fuel combustion techniques. The aim of this study is to investigate the effect of direct methanol injection timing on the combustion, performance and emission characteristics of a dual-fuel spark ignition engine at different injection pressures. We conducted four different direct injection pressure tests ranging from 360° ahead to 30° CA ahead at 30° CA intervals. The experimental results indicate that regardless of the injection pressure, altering the methanol injection timing from −360° to −30° CA ATDC leads to distinct combustion behavior and changes in the combustion phase. Initially, as the injection timing is delayed, the combustion process accelerates, which is followed by a slower combustion phase. Additionally, the combustion phase itself experiences a delay and then advances. Regarding performance characteristics, both the brake thermal efficiency (BTE) and exhaust gas temperature (EGT) exhibit a consistent pattern of first increasing and then decreasing as the injection timing is delayed. This suggests that there is an optimal injection timing window that can enhance both the engine's efficiency and its ability to manage exhaust temperature. In terms of emissions, there are different trends in this process due to the different conditions under which the individual emissions are produced, with CO and HC showing a decreasing and then increasing trend, and NOx showing the opposite trend. In conclusion, regardless of the injection pressure employed, adopting a thoughtful and well-designed injection strategy can significantly improve the combustion performance and emission characteristics of the engine. The findings of this study shed light on the potential of methanol dual-fuel combustion and provide valuable insights for optimizing engine operation in terms of efficiency and emissions control. [ABSTRACT FROM AUTHOR]

The present study aims on onsite production of hydrogen using electrolysis process in series and using temporary storage to store the gas and induce it at the required flow rate through the inlet manifold in a dual‐fueled engine along with injecting sapodilla oil through the fuel injector. Sapodilla oil biodiesel is prepared via conventional transesterification with standard operating conditions (65°C) reaction temperature, 3 h reaction time, 1.5% by wt. catalyst and 6:1 molar ratio). Diesel, B100 (100% biodiesel), B100 with two sets of hydrogen induction have been tested for its performance and emissions. Through this analysis it was found that the gas emission such as CO, HC, CO2 was greatly reduced compared to the diesel and sapodilla oil when hydrogen was induced but resulted in increase in NOx emission. There was improvement in parameters with increase in hydrogen induction. [ABSTRACT FROM AUTHOR]

Ammonia is considered one of the attractive alternatives for fossil fuels to realize carbon neutralization. However, low chemical reactivity limits its use in compression ignition (CI) engines. This study investigated dual-fuel combustion, involving the use of ammonia for port fuel injection (PFI) and diesel for direct injection (DI) in a heavy-duty engine. Unregular emissions, specifically HCN, were studied for the first time in an ammonia–diesel engine. The combustion and emission performance of the engine with pure diesel mode was also studied to reveal the influence on ammonia addition. The engine was consistently operated at a fixed condition of 0.556 MPa IMEP and 800 r/min. The findings reveal the successful achievement of stable dual-fuel combustion in the tested engine. The addition of ammonia led to delayed ignition and an extended combustion duration. Implementing early pilot injection timing (SOI1) strategies significantly improved ammonia combustion efficiency, elevating it from 74% to 89%. This enhancement could be attributed to the diesel injected during pilot injection, which facilitated ammonia decomposition. However, early pilot injection had adverse effects on emissions, including CO, THC, NOx, N2O, and HCN. Advancing the main injection timing (SOI2) within the early SOI1 strategies accelerated the oxidation processes for CO, THC, N2O, and HCN. Nevertheless, this adjustment resulted in increased thermal NOx emissions. The highest HCN emission detected in this study was 9.2 ppm. Chemical kinetics analysis indicated that HCN production occurred within the temperature range of 1000 K to 1750 K under fuel-lean conditions. Furthermore, H2CN played a significant role in HCN formation as temperatures increased. More HCN was formed by H2CN as temperature rose. Strategies such as increasing pilot injection fuel quantity, raising premixed gas intake temperature, or advancing combustion phases close to TDC could potentially reduce HCN emissions. [ABSTRACT FROM AUTHOR]

Cyclic variations in internal combustion engines are caused by various factors, including combustion mixture stratification, in-cylinder flows, local fluctuations in air-fuel ratio, etc. Cyclic variations have a profound impact on engine performance and emissions. In this study, cyclic variations in dual fuel combustion are analyzed, comparing diesel-natural gas (NG) and polyoxymethylene dimethyl ether (POMDME)-NG dual fuel combustion. Cyclic variability was initially quantified using the coefficient of variation of gross indicated mean effective pressure (IMEPg) computed from experimental cylinder pressure data. The cases analyzed in this study had a coefficient of variation (COV) of IMEPg greater than or around 5%, which was the lower limit of onset of instability for this engine. Experiments were performed at two fixed start of injection (SOI) of high-cetane fuel: 310 CAD and 350 CAD. For all experiments, a constant load of 5 bar IMEPg was maintained, and the intake boost pressure and rail pressure were fixed at 1.5 bar and 500 bar, respectively. For each case, 1000 cycles of cylinder pressure data were recorded, filtered, and processed using an in-house heat release analysis code for each cycle. A comparison between individual cycles and the "ensemble averaged cycle" was made for both diesel-NG and POMDME-NG combustion. For the early SOI of 310 CAD, the peak cylinder pressure fluctuations of individual cycle were found to be ± 15 bar for both fuel combinations, compared to the ensemble averaged cycle, and < 1/10th of the cycles had an IMEPg lower than 0.05 bar of the ensemble averaged cycle. However, the peak pressure fluctuations were found to be lower for POMDME-NG (±3 bar) than diesel-NG dual fuel combustion at 350 CAD SOI, indicating lower cyclic variations. The higher reactivity of POMDME helped reduce fluctuations in combustion phasing at the retarded SOI. The presence of cycles of deterioration and cycles of recovery were also observed with diesel-NG combustion for 310 CAD SOI, and the scatter in the IMEPg return map was similar for both fuel combinations. The IMEPg return map for POMDME-NG combustion was less scattered at the 350 CAD SOI. [ABSTRACT FROM AUTHOR]

In this study, experiments were conducted with a mixture of pure diesel and natural gas. In the experiments, a 6-cylinder heavy-duty diesel engine with an engine displacement of 11,670 cc was used and the engine speed was kept constant at 660 rpm The 386 Nm torque value was accepted as 100% and experiments were performed at torque ratios of 25, 50, 75 and 100%. In the experiments conducted with natural gas-diesel dual fuel, natural gas was injected into the intake manifold with 1.5 bar pressure and 1.29 g/sec mass flow. The present study aimed to investigate the diesel-natural gas dual fuel combustion characteristics in heavy-duty diesel engines with high emission values, such as maritime transportation. In addition, the feasibility of natural gas as a secondary fuel in existing heavy-duty diesel engines without making significant structural changes was investigated. The findings obtained in this study showed that the BTE value of a mixture of natural gas-diesel fuel decreased by 157, 89, 53, 53 and 28% at 25, 50, 75, and 100 torque values, respectively, compared to pure diesel. At maximum load, CO and UHC emissions were 4.42 and 4.5 g/kWh for pure diesel and 19.9 and 11.9 g/kWh for a mixture of natural gas, respectively. [ABSTRACT FROM AUTHOR]

This study focuses on the combustion timing control in hydrogen mixed combustion of a spark ignition gas engine. Especially, we examined the effect of hydrogen mixed ratio and air excess ratio on the combustion feature under same engine conditions. The 50% mass fraction burning timing (MFB50T) is within the specified range under MBT condition, independent of hydrogen mixed ratio and air excess ratio. We also examined the combustion phase estimation method using the existing sensor of the engine. The MFB50T can be estimated by the peak timing of angle speed.

Diesel pilot high-pressure direct injection (HPDI) natural gas technology has been noticed and applied in medium and heavy-duty engines due to its outstanding economy and power performance. However, the combustion of two kinds of fuels will involve more injection parameters, which increases the difficulty of designing injection strategy and calibrating injection parameters. This paper investigates comprehensively the effects of three key engine injection parameters (injection timing, injection duration of the pilot diesel, interval of injection between diesel and natural gas) on the engine ignition delay and cylinder pressure evolution using the experimentation method, which are utilized to guide the design of injection strategy and optimize injection parameters. Results show that the maximum in-cylinder pressure and its position are determined by the injection timing of natural gas, but little affected by the injection parameters of diesel. As the injection timing advances and the duration of diesel injection shortens, the ignition delay increases. To avoid rough combustion in the cylinder, it is necessary to optimize the injection timing, injection interval, and ignition diesel injection duration to ensure that the pressure rise rate does not exceed the threshold.

The combustion of diesel fuel in internal combustion engines faces challenges associated with excessive emissions of pollutants. A direct solution to this issue is the incorporation of cleaner energy sources. In this study, a numerical model was constructed to investigate the characteristics of ammonia–diesel dual-fuel application in a medium-speed diesel engine. Effects of ammonia–diesel blending ratios on engine performance and emissions were investigated. The results indicate that for this engine model, the optimal diesel energy ratio is about 22%. When the diesel energy ratio is less than 22%, the engine’s output performance is significantly affected by the diesel energy ratio, while above 22%, the influence of the intake becomes more pronounced. When the diesel energy ratio is below 16%, the cylinder cannot reach combustion conditions. Diesel energy ratios below 22% can cause ammonia leakage. With increasing diesel energy ratio, the final emissions of carbon oxides increase. With a higher diesel energy ratio, NO emissions become lower. When the diesel fuel energy ratio exceeds 22%, the N2O emissions can be almost neglected, while below 22%, with poor combustion conditions inside the cylinder, the N2O emissions will increase.

Dual-fuel low-temperature combustion is a possible solution for alleviating the tradeoff between oxides of nitrogen and soot emissions in conventional diesel combustion, albeit with poor combustion stability, high carbon monoxide, and unburned hydrocarbon emissions at low engine loads. The present work compares emissions and combustion (heat release and other metrics) of both diesel and poly-oxy methylene dimethyl ether as high-reactivity fuels to ignite natural gas while leveraging spray-targeted reactivity stratification, which involved multiple injections of the high-reactivity fuels. The experiments included six parametric sweeps of: (1) start of first injection, (2) start of second injection, (3) percentage of energy substitution of natural gas, (4) commanded injection duration ratio, (5) rail pressure, and (6) intake pressure. The experiments were performed on a 1.8 L heavy-duty single-cylinder research engine operating at a medium speed of 1339 rev/min. Not-to-exceed limits for the indicated oxides of nitrogen emissions, maximum pressure rise rate, and the coefficient of variation of the indicated mean effective pressure were set to 1 g/kWh, 10 bar/CAD, and 10%, respectively. The indicated emissions decreased and combustion improved significantly for both fueling combinations when the experimental procedure was applied.

Compression ignition engines will still be predominant in the naval sector: their high efficiency, high torque, and heavy weight perfectly suit the demands and architecture of ships. Nevertheless, recent emission legislations impose limitations to the pollutant emissions levels in this sector as well. In addition to post-treatment systems, it is necessary to reduce some pollutant species, and, therefore, the study of combustion strategies and new fuels can represent valid paths for limiting environmental harmful emissions such as CO2. The use of methane in dual fuel mode has already been implemented on existent vessels, but the progressive decarbonization will lead to the utilization of carbon-neutral or carbon-free fuels such as, in the last case, hydrogen. Thanks to its high reactivity nature, it can be helpful in the reduction of exhaust CH4. On the contrary, together with the high temperatures achieved by its oxidation, hydrogen could cause uncontrolled ignition of the premixed charge and high emissions of NOx. As a matter of fact, a source of ignition is still necessary to have better control on the whole combustion development. To this end, an optimal and specific injection strategy can help to overcome all the before-mentioned issues. In this study, three-dimensional numerical simulations have been performed with the ANSYS Forte® software (version 19.2) in an 8.8 L dual fuel engine cylinder supplied with methane, hydrogen, or hydrogen–methane blends with reference to experimental tests from the literature. A new kinetic mechanism has been used for the description of diesel fuel surrogate oxidation with a set of reactions specifically addressed for the low temperatures together with the GRIMECH 3.0 for CH4 and H2. This kinetics scheme allowed for the adequate reproduction of the ignition timing for the various mixtures used. Preliminary calculations with a one-dimensional commercial code were performed to retrieve the initial conditions of CFD calculations in the cylinder. The used approach demonstrated to be quite a reliable tool to predict the performance of a marine engine working under dual fuel mode with hydrogen-based blends at medium load. As a result, the system modelling shows that using hydrogen as fuel in the engine can achieve the same performance as diesel/natural gas, but when hydrogen totally replaces methane, CO2 is decreased up to 54% at the expense of the increase of about 76% of NOx emissions. [ABSTRACT FROM AUTHOR]

In the operation of SI engines, alternative biomass fuels such as rice husk can be utilized. This will contribute limit the consumption of fossil fuels. The dual-fuel approach can also be employed on SI engines. One of the solutions that can be employed in dual-fuel SI engines with gasoline is producer gas, a flammable gas created by biomass gasification. However, the numerous methods of incorporating gases into SI engines necessitate substantial investigation. In this study, producer gas and gasoline are combined and fed into an SI engine. The dual fuel is used to power the single-cylinder SI engine. The most optimal operation of the Y-shaped mixing chamber is investigated. Experiments were conducted to determine the optimal air-producer gas ratio values based on the SI engine's ability to operate in time at idle. Two variables were chosen as inputs: air producer gas ratio and fuel mixture percentage. According to the study's findings, an air-producer-gas ratio of 1.5:1 with 50% gasoline results in better mixing. The single-cylinder SI engine has been running smoothly and longer than other parameters without knocking. [ABSTRACT FROM AUTHOR]

The addition of Compressed natural gas as a complement to diesel in compression ignition engines in dualfuel combustion mode is a viable technology for increasing efficiency and lowering emissions. This work investigates the impact of a dual-fuel operating mode on the engine exhaust pollutant emissions of a diesel engine using compressed natural gas as the principal fuel and neat diesel as the pilot fuel. Compressed natural gas was injected into an intake manifold of a single-cylinder diesel test engine under different engine operating parameters, and up to 80% substitution was attained. And diesel fuel was injected after the compressed natural gas air mixture was compressed. The tests were carried out at five different compression ratios ranging from 13:1 to 15:1 in steps of 0.5:1. The experiment study revealed that injecting CNG into diesel engines via dual fuel combustion significantly impacted exhaust gas emissions compared to pure diesel combustion. The Carbon monoxide (CO) and hydrocarbon (HC) emissions were increased, while carbon dioxide (CO2), nitrogen oxide (NOX) and smoke opacity were decreased in dual fuel combustion compared to single diesel fuel. [ABSTRACT FROM AUTHOR]

In recent years, biomass fuelled engines have gathered major interest due to rapid depletion and rising price of conventional fuels. Biomass gasification has a better conversion efficiency compared to other conversion techniques. Also, Producer gas can be used directly in diesel engines without any modifications. In this study, the performance parameters of a variable compression ratio CI engine fuelled with diesel-producer gas combination derived from rice husk, coconut shell, and rubber shell have been experimentally and theoretically investigated. During experimentation, brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), brake specific energy consumption and biomass consumption (BMC) are obtained by varying compression ratio and brake power (BP). A new theoretical model based on the finite-time thermodynamics is developed and validated with experimental results. The experimental results show that rubber shell powered DF engine showed the maximum diesel savings of 48%. It is also observed that, among the three selected feedstock, the rubber shell-based dual fuel engine had the highest BTE of 19.80% followed by the coconut shell and rice husk as 19.44% and 19.13%, respectively. Similarly lowest BMC of 3.53 kg/h was observed for rubber shell driven engine. In addition, the rubber shell derived producer gas had a lower BSFC of 0.64 kg/kWh on dual fuel mode than rice husk and coconut shell. It is also predicted that the optimum BTE and diesel savings as 19.18% and 48% are obtained at the compression ratio and BP of 18 and 2.56 kW, respectively. [ABSTRACT FROM AUTHOR]

To realize a super-leanburn SI engine with a very-high compression ratio, it is required to design a new fuel which could have low ignitability at a low temperature for antiknocking, but high ignitability at a high temperature for stable combustion. Ethane shows a long ignition delay time at a low temperature close to that of methane, but a short ignition delay time at a high temperature close to that of gasoline, as well as having a higher laminar burning velocity than those of methane and gasoline. In the present study, the antiknocking effect of adding methane with the RON of 120 or ethane with the RON of 108 to a regular gasoline surrogate fuel with the RON of 90.8 has been investigated. Adding methane or ethane by 35 % or 25 % in heat fraction, respectively, shows the same knock limit SI timing as that of a premium gasoline surrogate fuel with the RON of 100.2. In the relationship between the heat fraction of the gaseous fuel and the advance of knock limit CA50, the effect of adding ethane is 1.9 times larger than that of adding methane. The effect of adding the gaseous fuel is dependent not on the RON of the gaseous fuel, but on the OH consuming rate of the gaseous fuel. The effect of adding methane or ethane to the premium gasoline surrogate fuel has been also investigated. The effect of adding ethane is 1.7 times larger than that of adding methane. The effect of adding the gaseous fuel is not dependent on whether the liquid fuel has cool-flame reactions or not. [ABSTRACT FROM AUTHOR]