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This paper presents a Large Eddy Simulation (LES) study investigating jet flame ignition characteristics to achieve stable ammonia combustion for novel applications in gaseous ammonia/hydrogen-fueled engines with an active prechamber. The study investigated three cases with initial global equivalence ratios of 0.6, 0.8, and 1.0. Two main ignition modes were proposed, and five stages of coupled flame propagation processes were identified. The oscillation of supersonic hydrogen jet flame was investigated. The modes of flame-vortex interaction including vortex ring formation, along with the mechanism of highly reactive zone formation, were proposed. The effects of reactivity and turbulence transition on piloted ammonia flame were investigated to attain stable ammonia combustion and achieve a high heat release rate. The results showed that oscillations in the jet flame were strengthened at low global equivalence ratios with high hydrogen mass ratios. Enhancing propagation of initial and secondary vortex rings broadened highly reactive zones. Vorticity dissipated more rapidly at low equivalence ratios, leading to a stratified structure and enhanced piloted spherical flame. The Unsteady Flamelet Ignition Prediction (UFIP) sub-model of combustion was verified for the piloted ammonia flame, enabling a more comprehensive discussion of flame propagation tendencies. • The transient characteristics of jet flames ignited by H 2 /NH 3 mixtures were analyzed using LES. • The behavior of stratified flames at various equivalence ratios was investigated. • Various modes of turbulent jet flame ignition were proposed according to different stages. • The mechanism of vortex evolution to form the reactive zone and pilot flame was proposed. [ABSTRACT FROM AUTHOR]

Pre-chamber jet ignition is a key technology for future high-efficiency natural gas (NG) engines. It can achieve fast and stable combustion through excellent ignition performance. However, there are still some challenges, such as high combustion instability near the lean burn limit and the narrow engine operating range. Therefore, this paper investigates the combustion instability of a pre-chamber NG engine under ultra-diluted conditions by experimental method. At two engine loads, experiments are carried out with different jet ignition intensity schemes to study the effect of jet ignition intensity on the cyclic combustion variations. Then, the combustion instability characteristics of the pre-chamber NG engine are studied by cyclic variation analysis and phase space reconstruction. The results show that with the increase in the jet ignition intensity, the cyclic combustion variations decrease, and the cyclic variation coefficient of the indicated mean effective pressure decreases to below 2%. The lean burn limit of the pre-chamber natural gas engine is extended to an excess air ratio of 2.0. The operation instability of the pre-chamber NG engine is mainly due to cyclic variations in the ignition and combustion process. The nonlinear dynamic analysis shows that the combustion process in the lean burn pre-chamber NG engine behaves with chaotic characteristics under the operating conditions of low jet ignition intensity. As the jet ignition intensity increases, the combustion stability is improved and the cycle-to-cycle variations change from fairly deterministic to more stochastic behavior. The chaotic characteristics of the combustion process become weaker. In conclusion, it is of great importance to generate stable and high ignition intensity jets for reducing combustion instability and improving combustion efficiency in lean burn pre-chamber NG engines. [ABSTRACT FROM AUTHOR]

Water injection (WI) is a well-known technique to mitigate knocking phenomena, reducing the in-cylinder gas temperature with a high heat of vaporization and specific heat of water. In this study, the effect of WI directly into the cylinder on fuel efficiency was investigated using a 2.0 L naturally aspirated (NA), four-cylinder, port fuel injection (PFI)-spark-ignited (SI) engine. Spray visualization of water injection by a commercial gasoline direct-injection (GDI) injector was performed to elucidate the water evaporation characteristics. In engine experiments, combustion characteristics were analyzed by adjusting the WI timing and amount. Synergistic effects with other gas dilution techniques, such as EGR and Lean burn, were also investigated. The spray image of WI showed poor evaporation of water compared to gasoline, even at high fuel temperatures. The optimal timing of WI was advanced up to the early intake stroke due to the harsh conditions of NA engines for water evaporation compared to turbocharged engines. With the combination of EGR, the optimal WI timing was advanced by the compression stroke, and further fuel efficiency improvement was achieved. In lean combustion, WI can improve both combustion stability and fuel efficiency. [ABSTRACT FROM AUTHOR]

This experimental study investigates the palladium/rhodium based three-way catalyst (TWC) in a hydrogen-gasoline dual-fuel spark ignition (SI) engine under stoichiometric and lean conditions. The work focused on lean-burn engine operating conditions with the aim of reducing nitrogen oxides (NOx) emissions during the combustion process, where the TWC is not effective, while improving the thermal efficiency of the engine. Under these leanburn engine conditions, the combustion promoting properties of hydrogen allowed for maintained engine combustion stability as determined by the cycle-to-cycle variation (COVimep) values even up to ultra lean conditions (λ= 2.0). It was found that by reducing the combustion temperature through the application of lean conditions, engine-out NOx emissions could be reduced or even eliminated, while under these conditions the TWC was effective in reducing engine-out carbon-based gaseous emissions. [ABSTRACT FROM AUTHOR]

A direct injection (DI) CNG engine was developed and evaluated under stoichiometric and lean burn conditions, emphasising high compression ratios (CRs). A comparative analysis of PFI gasoline and PFI CNG engines was conducted to provide comprehensive insights. Results showed that the DI CNG engine exhibited a shorter combustion duration, indicating higher combustion speed, and enhanced combustion stability, particularly at low load and speed conditions, with a reduced coefficient of variation of indicated mean effective pressure (COVIMEP) below 1%. The DI CNG engine demonstrated a relative increase in net indicated thermal efficiency by 4–5% compared to the PFI CNG engine. Furthermore, CNG engines operating at a high compression ratio of 16 could run at high loads without encountering knocking issues. Lean burn operation, combined with high compression ratios, improved thermal efficiency while minimising emissions; however, challenges such as combustion instability and increased emissions under lean burn conditions were observed.

The shortage of fossil energy and the aggravation of environmental pollution have led to stricter requirements for energy conservation and environmental protection of automobiles. The development of new energy vehicles still needs time and space. The internal combustion engine is still the power source that automobiles will need to rely on in the future. Lean combustion is one of the key research directions for efficient and clean combustion technology for gasoline engines. In this paper, the effects of high-energy ignition coupling hydrogen blending on the combustion stability of lean-burn gasoline engines were studied by means of multi-point high-energy ignition and gasoline/hydrogen double direct injection. Through the combination of gasoline and hydrogen injection timing, a suitable stratified mixture can be formed in the cylinder. Combined with high-energy ignition, the fire core can be formed smoothly, and the flame spreads rapidly. The introduction of hydrogen increases the concentration of H in the reaction system, enhances the activity of the reaction system, and accelerates the oxidation process of fuel molecules. Compared with a pure gasoline engine, hydrogen blending can expand the lean burn limit by 66.2% and increase ITE (Indicated Thermal Efficiency) by 6.5%. NO x emission increases first and then decreases with the increase in excess air ratio, but when λ > 1.6, NO x emission is much lower than that of the equivalence ratio condition. HC (Hydrocarbons), CO, and CO 2 emissions are also lower than the equivalent ratio conditions. • Multi-point high-energy ignition with three spark plugs. • Gasoline and hydrogen double direct injection to achieve lean combustion. • Effects on combustion and emission of lean burn gasoline engine. [ABSTRACT FROM AUTHOR]

Lean combustion in gas turbines garners attention for emissions reduction, yet it faces stability challenges demanding careful design considerations. In this study, a novel CHAIRLIFT combustor concept, which integrates low swirl lean lifted spray flames known for substantial nitrogen oxides emissions reduction, into a Short Helical Combustors (SHC) arrangement, is investigated. A comprehensive experimental test campaign explores key parameters, including staggered arrangement offset, equivalence ratios, and air inlet temperature, to evaluate its performance. The results reveal exceptional stability in low swirl, lifted flames compared to moderate swirl flames with larger inner recirculation zones. The unwanted flow deflection of highly swirled flames in the SHC arrangement is effectively avoided with the investigated low swirl, lifted flames. The study emphasizes the significant influence of fuel droplet evaporation time on flame stability near the flame root under low air inlet temperatures. Furthermore, at high air inlet temperatures, the complex flame stability mechanism in inclined configurations is controlled by various parameters, including outer recirculation zone size, air inlet temperature, and additional vortices generated by pressure differences near the wall. OH∗ chemiluminescence results corroborate these stability mechanisms, showing that at lower temperatures, the flame stabilizes closer to the nozzle exit due to local rich pockets near the shear layer. Conversely, at the same tilt angle, higher air inlet temperatures lead to an increased flame lift-off height due to faster evaporation and enhanced mixing. Exhaust gas analyses confirm the potential of the investigated lean lifted spray flames in a multi-burner arrangement to achieve very low NOx emissions over a wide range of operating conditions for all investigated burner inclinations. These findings may facilitate the future development and optimization of lean combustion technology for aircraft engines.

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.

As a viable solution to meet rising energy costs and reduce greenhouse gases, alcohol fuels are considered the most promising renewable fuel and ethanol is a potential fuel for spark ignition engines. In the present study, experiments were conducted on a spark ignition engine modified from a diesel engine that uses an ethanol-gasoline mixture as fuel under lean operating conditions. The engine was operated at 1500 rpm at a high compression ratio of 10.5:1. The different proportions of ethanol namely 5 %, 10 %, 20 %, and 30 % with gasoline, were studied and compared. The throttle was set to 25 % to operate the engine at various equivalence ratios to study the performance and emissions. Experimental outcomes reveal that 10 % ethanol with gasoline enhances the brake thermal efficiency and brake power by 7 % and 4.5 % respectively, due to an enhanced compression ratio. Further, the gasoline lean limit is also extended from 0.74 to 0.70 equivalence ratios. In addition, ethanol blending with gasoline enhances the combustion characteristics and heat release rates. The influence of ethanol greatly decreases cycle-by-cycle variations and hydrocarbon emissions. Adopting a high compression ratio and lean-burn operation can effectively improve performance and decrease emissions in an ethanol-gasoline-fuelled spark ignition engine.

The effects of air and exhaust gas recirculation (EGR) dilution of a spark ignition engine fueled with methanol under different loads were studied by experiment in this paper. Such as ignition delay, combustion center (CA50), IMEP, break thermal efficiency (BTE) and other parameters were investigated to assess the combustion performance. And discussed in depth the balance between NOx emissions and economic performance represented by brake specific fuel consumption (BSFC). The results showed that combustion progress such as ignition delay, combustion duration and CA50 were more sensitive on the changes of EGR, introducing EGR under the same dilution rate prolonged combustion process. Air-EGR dilution showed the best improvement of IMEP and break thermal efficiency, except the optimal area, increasing EGR rate will decreased IMEP and BTE. Air-EGR dilution strategy showed the best improvement on BSFC than air dilution than EGR dilution. Under light load and high load, when the lowest BSFC was obtained, NOx emissions were less than 0.5 g/kWh with air-EGR dilution strategy. [ABSTRACT FROM AUTHOR]

In this study, the effects of piston shapes on in-cylinder flow characteristics and mixture formation in the lean condition was analyzed using the PIV method and CFD (CONVERGE v2.4). The four-piston geometries were concave, flat, convex, and base pistons, and the pistons were mounted on a GDI engine with transparent quartz. To quantify in-cylinder flow characteristics, the mean velocity, tumble ratio, turbulent kinetic energy, and tumble center were calculated. In addition, to analyze the effects of the difference in piston shapes in detail, the velocity fraction was calculated by dividing the cylinder area into three. In-cylinder flow was compared for the case without injection and the case with injection. There were four timed injections at C.A. 420°, 480°, 540°, and 600°, and the mixture characteristics were investigated in the cases of 480° and 600° injection. In the intake process and early compression process, there was no significant difference in the quantitative values for the shape of the piston regardless of the presence or absence of injection. However, the effects of the piston crown designs increased in the later compression process. As a result, the highest turbulent kinetic energy was found using a flat piston with a relatively high tumble ratio and swirl ratio in the absence of injection. The mixture formation was similar for all piston crown designs when injected at the crank angle of 480°. However, when the crank angle of 600° was injected, a stagnant fuel area was formed using the base-type piston, so it was difficult to secure sufficient fuel near the center of the cylinder. [ABSTRACT FROM AUTHOR]

Combustion diagnostics of highly diluted air fuel mixtures are of great importance for reducing the carbon footprint of various types of combustion systems. Flame detection techniques, such as ion sensing and optical diagnostics, have been reported for diagnosing combustion status. In this paper, a flame front detection technique based on active plasma probing is introduced and analyzed. Unlike the conventional ion sensing used in internal combustion engines, a separate electrode gap is used to detect the flame front arrival. Further, the voltage potential across the electrodes of the spark plug probe is modulated actively to be slightly below the breakdown threshold prior to flame arrival. At the arrival of the flame front, the ions in the flame tend to decrease the breakdown voltage threshold and trigger a breakdown event. An optically accessible constant volume combustion vessel is employed to investigate the efficacy of such active plasma probing for the detection of the flame front under quiescent and flow conditions. Three types of fuels are used in the tests, including methane, propane, and DME, with an air fuel ratio sweep (from stoichiometric to extremely lean) for each fuel. Efforts are made to characterize the probing criteria of minimum, yet adequate voltage to succeed in the detection of the arrival and departure of the flame front most sensitively and reliably, for all three types of fuels under various mixture strengths. For comparison, conventional ion current measurements are conducted under identical background conditions to benchmark the efficacy of flame detection. Results show that the active plasma probing can promptly detect the arrival and departure of the flame front, robustly regardless of the fuel type and excess air ratios. The precise control of the detecting voltage is key for reliable flame detection with high sensitivity. [ABSTRACT FROM AUTHOR]

This paper demonstrates a multiple-input multiple-output (MIMO) controller design framework and a controller switching algorithm for MIMO controllers in their state-space form, which together achieve robust, efficient control of turbocharged lean-burn engines over a wide operating space. The controller design framework requires a linearized plant model, and uses the μ -synthesis and DK-iteration algorithms while considering state and output uncertainties and actuator bandwidths to synthesize a robust H ∞ controller. A controller switching methodology using slow-fast controller decomposition and also incorporating hysteresis at switching points is utilized to smoothly transfer control authority between several MIMO controllers. The approach is applied to a high-fidelity truth-reference GT-Power engine model for a lean-burn natural gas-fueled engine to evaluate the closed-loop controller performance. The multi-tracking control problem targets engine speed, differential pressure across throttle as well as air-to-fuel ratio to achieve satisfactory engine performance and emissions without compressor surge. The engine response obtained using the robust MIMO controller is compared with that obtained using a state-of-the-art benchmark controller to evaluate the additional benefits of the MIMO controller. [ABSTRACT FROM AUTHOR]

This paper presents results obtained for the thermal and hydrothermal ageing of seven commercial precious metals-based catalysts for the combustion of methane. Experiments are performed in a large excess of oxygen representing lean conditions. Temperatures used are those typically found in lean burn compression ignition engines. The precious metals used were platinum, palladium and rhodium, present either singly or in combination. The most active catalyst contains a platinum and palladium mixture, with palladium being dominant. This catalyst was also the least affected by both thermal and hydrothermal ageing. The second most active catalyst contained only palladium, but this catalyst also demonstrated more susceptibility to ageing. The least active catalyst contained only platinum, although this catalyst was also the least affected by hydrothermal ageing. The addition of rhodium to either palladium or platinum–palladium catalysts caused a more rapid loss in activity at higher temperatures, although the loss in activity at lower temperatures was similar in magnitude to those catalysts without rhodium. In some cases, cycling the reactor temperature between high and low restored some activity to the catalyst. In all cases, the catalyst activity was observed to be lower in the presence of water, after both thermal and hydrothermal ageing. [ABSTRACT FROM AUTHOR]

Stringent environmental legislation demands development of internal combustion engines seeking higher thermal efficiency to reduce greenhouse gas emissions. Brazilian governmental programs like ROTA 2030 and RenovaBio drive the research and development of highly efficient engines fueled with biofuels, like sugarcane bioethanol, that has a near to zero carbon footprint. Some technologies such as gasoline direct injection, variable valve train, and turbocharging were implemented in downsized Spark Ignition (SI) engines in order to reach higher thermal efficiencies and decrease CO2 emissions. Homogeneous lean combustion in SI operation can improve fuel consumption and reduce exhaust gas emissions. However, it is limited by combustion instability and the three-way-catalyst (TWC) inability to work properly converting nitrogen oxides (NOx). With lean combustion the NOx emissions could be significantly reduced, enabling the use of lean NOx trap (LNT) as an effective lower cost after treatment system. To explore the limits of homogeneous lean combustion in SI engines, experimental tests were performed to investigate performance, efficiency, combustion, and emission parameters of a multi-cylinder Ford 1.0l Ti-VCT EcoBoost engine fueled with hydrous ethanol. Hydrous ethanol is a commercial Brazilian fuel which has greater laminar flame speed and higher dilution tolerance than gasoline, and thus can increase combustion stability. Different fuel direct injection strategies were explored at part load (below 8.0 bar IMEP) at engine speed of 1500 rpm. Air-to-fuel ratio was varied from stoichiometric (lambda 1.0) to lambda 1.5. The limit of stable homogeneous lean combustion (COVIMEP ≤ 3.0%) was achieved in lambda 1.4. The lowest indicated load of 2.1 bar IMEP was limited by combustion stability at lambda 1.3. The maximum indicated efficiency was 36.9% at indicated load of 8.0 bar IMEP and lambda 1.4. The NOx emissions dropped below 1.4 g/kWh at 4.0 bar IMEP and lambda 1.4. [ABSTRACT FROM AUTHOR]

Due to the depletion of conventional petroleum-based fuels and increasing environmental concerns, industries have been developing new combustion technologies with acceptable cost ranges and minimum system modifications for consumers. Among many approaches, the utilization of plasma ignition systems is considered as a promising pathway to achieve greener transportation while maintaining conventional internal combustion engine systems. Plasma contains highly reactive radicals, and those have a great potential of enhancing chemical reactions that are beneficial for reducing carbon emissions. The primary objective of this paper is to provide an overview of currently available plasma-assisted combustion systems including recent achievements in research and development, and technical challenges for successfully implementing a new ignition system. This review will introduce various plasma-assisted combustion approaches from worldwide projects, covering non-thermal and thermal plasma systems in internal combustion engines. [ABSTRACT FROM AUTHOR]

Ammonia exhibits significant potential as a carbon-free fuel; however, challenges such as ignition difficulty and slow combustion speed hinder its combustion process. Hydrogen, another carbon-free fuel, offers properties that complement those of ammonia and can augment its reactivity. The ammonia energy ratio (A R) and excess air coefficient (λ) wield considerable influence over performance in ammonia-hydrogen dual-fuel engines. However, a comprehensive comprehension of their mechanisms remains elusive. The experiment investigated for the first time the coupled effects of A R and λ on the combustion and emission characteristics under low-load conditions. Research indicates that elevating A R results in unstable combustion and prolongs the combustion duration. However, concurrently, it diminishes heat transfer losses and enhances brake thermal efficiency (BTE). The optimum range for the highest BTE is observed near λ = 1.4 and A R = 70% (where BTE surpasses 30.0%). In comparison with pure hydrogen, the BTE near λ = 1 (where BTE is less than 20.7%) exhibits an increase exceeding 9.3%. The lower concentration range of NO X is observed approximately between λ = 1.0–1.1 and A R = 45%–65%. Augmenting A R results in heightened emissions of unburned NH 3 and N 2 O. Unburned NH 3 and NO X emissions show a trade-off relationship in general. • Improved brake thermal efficiency at ammonia energy ratio 70% and lambda 1.4. • Brake thermal efficiency increased by 9.3% compared to pure hydrogen. • Optimal nitrogen oxide emissions between lambda 1.0 and 1.1. • Trade-off between unburned ammonia and nitrogen oxide emissions. • Increased N 2 O emissions with higher ammonia energy ratio. [ABSTRACT FROM AUTHOR]

Hydrogen fuel holds great promise for accelerating the energy sector's decarbonization efforts. However, hydrogen's unique properties pose challenges for hydrogen direct injection (HDI) engines, such as differences in airflow exchange capabilities for very low density and reduced combustion rates due to lean burn conditions. This study investigates the impact of combined variable valve timing (VVT) and split injection strategies on HDI engine combustion, efficiency, and emissions. Using Artificial Neural Network (ANN) models and experimental data, predictive models for Brake Thermal Efficiency (BTE) and Nitrogen Oxide (NOx) emissions were developed. Adjusting intake and exhaust valve timings improved BTE by up to 2.5 % and 1.8 %, respectively, while reducing NOx emissions by 48.9 % and 31.1 % under specific conditions. Optimizing split injection alongside VVT further increased BTE by 1.2 % and 0.9 %, but increased NOx emissions by 29.9 % and 26.5 %. The flexible application of VVT and split injection strategies aims to balance efficiency gains with emissions control. The ANN-based models demonstrated high accuracy (R2 > 0.974), proving reliable substitutes for real-engine testing in certain conditions. In conclusion, this research highlights the potential of VVT and split injection strategies to enhance HDI engine performance while mitigating environmental impact, supporting the transition to sustainable energy solutions. • Combined IVC and EVC timing control significantly improves BTE and NOx emissions. • Combined regulation of SEOI and SIF further increased BTE but worsened NOx emissions. • VVT + split injection strategies should be considered to balance efficiency and cleanliness. • ANN-based high-precision BTE and NOx emission prediction models were developed. [ABSTRACT FROM AUTHOR]

Turbulent jet ignition (TJI) technology has the potential to improve engine efficiency. To elucidate the influence of different factors (diameter and number of holes) affecting the nozzle's total cross-sectional area, internal structure of the pre-chamber, and nozzle angle on the combustion characteristics of the engine. A 3 × 3 orthogonal test was designed and machined. The experiments were carried out on a pre-chamber single-cylinder engine. The results show that the pre-chamber's internal volume ratio has a great effect on the combustion characteristics in the cylinder. While the volume ratio of top of pre-chamber, transition region, and pre-chamber throat is 1:1:1, the engine's peak heat release rate is the highest. The highest Indicated thermal efficiency (ITE) can reach 43.43 %, with an absolute increase of 1.24 %, and the lean burn limit can reach λ = 2.6. Too large or too small nozzle angle will worsen the combustion state in the cylinder. The aperture and Nozzle number, which are the factors influencing the nozzle's total cross-sectional area, have different effects on the ignition delay, CA10-CA50, and CA50-CA90 of the engine. Various factors affecting the nozzle's total cross-sectional area have no apparent influence on the changing trend of ITE, but the aperture greatly influences ITE. • 4 pre-chamber structure parameters on engine combustion are investigated. • Decoupling the 2 factors affecting the total nozzle cross-sectional area. • A new parameter describing the internal structure of the pre-chamber is presented. • Designed 3 × 3 orthogonal test to investigate the pre-chamber structural parameters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple ignition modes in pre-chamber have been systematically summarized. • Different jet ignition modes result in variations in ignition timing, ignition location, combustion speed, and lean combustion limits. • Higher initial density proves advantageous in augmenting the lean combustion limits of the pre-chamber jet ignition system. Optimizing boundary condition parameters is an effective means to substantially improve the combustion performance of methanol pre-chamber turbulent jet ignition systems. In this study, an optically accessible constant-volume combustion chamber was employed to delve deeply into the impacts of critical boundary condition parameters on the combustion performance of the pre-chamber jet ignition system. The findings suggest that adjusting the pre-chamber boundary condition parameters can lead to various jet ignition modes, including jet flame ignition, jet direct ignition, jet delayed ignition, jet wake ignition, and dual jet ignition. Different jet ignition modes result in variations in ignition timing, ignition location, combustion rate, and lean burn limits. Under identical initial temperature and pressure conditions, compared to jet flame ignition with the lowest combustion velocity and jet wake ignition with almost no lean burn capability, dual jet ignition can reduce the combustion duration by about 50% and elevate the lean burn limit by more than double. Unlike the patterns observed in traditional spark ignition systems, within the range of experimental tests, lowering the temperature and increasing the pressure significantly improved the lean combustion limit of the pre-chamber system and reduced the probability of jet wake ignition. This performance enhancement is attributed to the increase in the density of the mixture in the main combustion chamber. [ABSTRACT FROM AUTHOR]

Direct injection plus lean burn technology can effectively control combustion processes and reduce carbon emissions of hydrogen engines. Hence, hydrogen direct injection strategy optimization is a key means to improve engine performance and achieve low emissions. Thus, a three-dimensional transient calculation model coupled chemical reaction mechanism is established, and its reliability and accuracy are systematically evaluated using experimental data. Then, the effects of hydrogen direct injection strategies on the hydrogen-air mixing and combustion process are investigated. The results indicate that the ideal mixture stratification law is that the gas fuel concentration is gradually stratified from the ignition center to the periphery region. The maximum indicated work is obtained for the B-60° scheme which its injection position is near the intake side and 7.5 mm from the cylinder center on the X-axis. The optimal hydrogen injection angles vary with different injection positions by evaluating engine performance, specifically, 60° is optimal for injection position B, while 30° is best for injection position C which is between intake and exhaust and 40 mm from the cylinder center on the Y-axis. Finally, the achieved maximum thermal efficiencies of 41% and indicated power of 4.29 kW for the B-60° scheme, and its nitric oxide can meet the Europe V emission standards (7.5 g/kWh). This research can offer theoretical guidance for designing and optimizing fuel injection strategies for hydrogen energy engines, and it is relevant for promoting carbon neutrality and cleaner production. [ABSTRACT FROM AUTHOR]

Prechamber jet ignition can significantly enhance the progress of combustion and improve fuel consumption. Based on a single-cylinder gasoline engine and a small-volume prechamber, the prechamber local air-fuel equivalence ratio, ignition type, and compression ratio were examined under lean burn conditions. The results show that spray wetting the wall of the prechamber is inevitable. As the quality of the fuel injection increases in the prechamber, the quality of the spray wetting the wall also increases, and the particle number (PN) emissions increase significantly. A rich mixture in the prechamber can improve ignition and enhance the main chamber combustion process. However, an air-fuel equivalence ratio near 1 in the prechamber has a greater fuel saving potential and lower PN emissions. When the excess air coefficient in the main chamber is below 1.4, the gross indicated thermal efficiency (GITE) of the prechamber is lower than that of the spark plug ignition. When the excess air coefficient in the main chamber is above 1.4, the prechamber significantly improves the thermal efficiency of the lean burn. The prechamber achieves a maximum GITE of 48.5% when the excess air coefficient in the main chamber is 1.8. Moreover, a prechamber combined with a high compression ratio can further improve combustion and reduce fuel consumption in the lean burn engine. Prechamber ignition extends the lean burn limit to the excess air coefficient value of 2.1 in main chamber, and nitrogen oxides emissions are as low as 58 ppm. Furthermore, the higher the compression ratio, the more the mixture gas is pushed into the prechamber, which increases the prechamber ignition energy and enhances the combustion process of the main chamber. [ABSTRACT FROM AUTHOR]

Hydrogen is a carbon-free fuel that can be produced in many ways starting from different sources. Its use as a fuel in internal combustion engines could be a method of significantly reducing their environmental impact. In spark-ignition (SI) engines, lean hydrogen–air mixtures can be burnt. When a gaseous fuel like hydrogen is port-injected in an SI engine, working with lean mixtures, supercharging becomes very useful in order not to excessively penalize the engine performance. In this work, the performance of a turbocharged PFI spark-ignition engine fueled by hydrogen has been investigated by means of 1-D numerical simulations. The analysis focused on the engine behavior both at full and partial load considering low and medium engine speeds (1500 and 3000 rpm). Equivalence ratios higher than 0.35 have been considered in order to ensure acceptable cycle-to-cycle variations. The constraints that ensure the safety of engine components have also been respected. The results of the analysis provide a guideline able to set up the load control strategy of a SI hydrogen engine based on the variation of the air to fuel ratio, boost pressure, and throttle opening. Furthermore, performance and efficiency of the hydrogen engine have been compared to those of the base gasoline engine. At 1500 and 3000 rpm, except for very low loads, the hydrogen engine load can be regulated by properly combining the equivalence ratio and the boost pressure. At 3000 rpm, the gasoline engine maximum power is not reached but, for each engine load, lean burning allows the hydrogen engine achieving much higher efficiencies than those of the gasoline engine. At full load, the maximum power output decreases from 120 kW to about 97 kW, but the engine efficiency of the hydrogen engine is higher than that of the gasoline one for each full load operating point. [ABSTRACT FROM AUTHOR]

• The visualized experimental findings of glow plug ignition of ammonia were reported. • Glow plug ignition can ammonia ignition at lower temperature and leaner conditions. • The flame propagation and heat release under wide equivalent ratios were presented. • The hot surface ignition mechanism of ammonia for glow plug ignition was revealed. Ammonia has attracted wide attention in recent years as a carbon-free fuel. However, the low reactivity and combustion inertness of ammonia need to be solved by adopting a powerful ignition method. The glow plug can form a high temperature (1000 K or even higher) hot surface, which is capable of igniting of ammonia under certain conditions. To explore the potential of using a glow plug as a promising ignition method for ammonia engines, a series of experiments were carried out on a rapid compression machine to compare the combustion characteristics of glow plug ignition and spark ignition. The spark ignition used for comparison included single-spark plug ignition and dual-spark plug ignition. The lower limit of ignition temperature at stoichiometric equivalence ratio and the lean burn limit at 980 K were determined. Compared with spark ignition, glow plug ignition can cause ignition at lower temperatures and leaner conditions. The visualization results showed that under the stoichiometric equivalence ratio, the spark-ignited flame propagated spherically. In contrast, the glow plug ignition mode, exhibited the formation of a flame layer near the hot surface, subsequently spreading in an ellipsoidal shape. However, the flame experienced varying degrees of deformation under lean conditions. Heat release rate results indicated that at equivalence ratios of 1 and 0.7, the heat release of glow plug ignition was the fastest. Conversely, at an equivalence ratio of 0.4, the heat release of glow plug ignition was slower than that of dual-spark plug ignition after the middle stage of combustion. Notably, the phenomenon of ignition before the end of compression in glow plug ignition cases was observed. Finally, simulation results, unveiled the essence of glow plug ignition, highlighting that the heating effect improves the thermodynamic conditions of the local mixture near the hot surface, significantly reducing the ignition delay time. [ABSTRACT FROM AUTHOR]

Hydrogen internal combustion engine (H 2 ICE), heralded as the most promising application of hydrogen energy, represents an excellent pathway for achieving energy transformation and carbon neutrality objectives. However, constrained by the primary obstacles of H 2 ICE, including abnormal combustions and NO X emissions, the port fuel injection hydrogen internal combustion engine (PFI- H 2 ICE) exhibits some shortcomings in power output despite its relatively lower cost. In comparison, the direct injection strategy is unaffected by air displacement and can achieve stratified combustion by delaying the injection timing to organize the in-cylinder mixture, known as the Late Direct Injection (LDI), which further enhances power and economy. However, due to the stratified combustion, the NO X emissions of LDI increase significantly compared to the PFI. On the other hand, Exhaust Gas Recirculation (EGR), as the simplest strategy to implement, demonstrates robust effectiveness in balancing power and emissions, and reducing the risk of abnormal combustions. To alleviate concerns about emissions, the integration of EGR is one of the most promising directions for H 2 ICE. Therefore, this study compares and analyzes the effects and differences of PFI and LDI combined with EGR on combustion and emissions characteristics. The experimental results indicate that the PFI strategy characterized by a homogeneously mixed air–fuel mixture exhibits advantages in maintaining relatively high brake thermal efficiency (BTE) and reducing NO X emissions under low loads due to the implementation of lean burn. The addition of EGR slows down the flame speed and reduces the in-cylinder temperature, leading to a significant reduction in NO X emissions as the EGR rate increases, especially under high loads. On the other hand, due to the air displacement effect, the PFI strategy consumes part of the air entering the cylinder, resulting in a comprehensively lower cylinder pressure and heat release rate (HRR) than LDI, along with equally diminished overall levels in break mean effective pressure (BMEP) and NO X emissions. Nonetheless, when combining EGR and LDI's stratified combustion under high loads, not only an 84.4% reduction in NO X emissions is achieved, but also a comparable or even lower NO X emission level is reached compared to PFI under the same λ conditions, while maintaining relatively high BTE and BMEP. Therefore, the combination of EGR and LDI is more promising in balancing the power performance and NO X emissions of H 2 ICE. Moreover, Coefficient of Variation in Indicated Mean Effective Pressure (COV IMEP) are more significantly influenced by spark timing, with relatively minor effects attributed to EGR rates. Given the adoption of Minimum Spark Advance for Best Torque (MBT) and near-MBT in spark timing, the COV IMEP remains below 1.3% across most operational conditions. For H 2 emissions, generally increase with the rise in EGR rate and λ due to the decrease in flame speed and temperature. • EGR is one of the most effective strategies for balancing power output and NO X emissions in H 2 ICE. • The addition of EGR increases H 2 emission in most operating conditions. • Late direct injection has higher power, economy and emissions than port fuel injection due to stratified combustion. • Late direct injection combined with EGR can reduce NO X emissions at higher loads. [ABSTRACT FROM AUTHOR]

To achieve carbon neutrality goals, renewable alcohols and new technologies are receiving increased attention. Variable valve technology can effectively improve engine efficiency. However, there is limited research on valve strategies suitable for alcohol. To further promote the efficient and clean application of alcohol, this article studies the effects of intake valve timing and lift on performance of ethanol, n-butanol, and gasoline engines under stoichiometric combustion and lean burn. It is found that the combustion process of ethanol and n-butanol is prolonged by advancing intake valve timing, while gasoline is the opposite. Meanwhile, the improvement of equivalent brake-specific fuel consumption (ESFC) is the most significant when fueled with gasoline, improving by 6.9 %. The improvement of BSNOx is the highest when fueled with ethanol, improving by 42.07 %. Adjusting intake valve lift has a weaker impact on economy than valve timing. However, when adjusting the combination of throttle, valve lift and timing, the ESFC of ethanol, n-butanol, and gasoline can be reduced by 6.79 %, 4.35 %, and 10.98 %. Furthermore, combining valve timing and lean burn can further improve economy and emissions. The ESFC of ethanol, n-butanol, and gasoline can be decreased by 12.73 %, 6.87 %, and 11.96 %, while BSNOx decrease by 93.69 %, 74.86 % and 61.65 %. [Display omitted] • Variable intake valve adjustment strategies were achieved through a self-developed VVA mechanism. • Study the effect of intake valve strategy on high compression ratio SI engine fueled with ethanol, n-butanol, and gasoline. • N-butanol achieves the lowest BSNOx under the combination of intake valve timing and lean burn strategy. • Ethanol has the best combustion stability under the combination of intake valve timing and lean burn strategy. • Regardless of the strategy, ethanol maintains the fastest combustion rate. [ABSTRACT FROM AUTHOR]

The integration of direct water injection (DWI) with the lean burn (LB) process can significantly enhance engine performance. This study reveals that an increase in the water-fuel (W/F) ratio suppressed knocking by extending the ignition delay time. Specifically, the knocking of stoichiometric combustion was suppressed, while that of deeper LB (excess air ratio (λ) ˃ 1.5) was sensitive to a larger W/F ratio. The intensity of knocks during stoichiometric combustion decreased significantly (more than twofold) when the W/F ratio increased from 0.1 to 0.2. Under identical W/F conditions, a shorter ignition delay (CA0–10) and combustion duration (CA10–90) of the main combustion flame were identified as important factors for knocking when λ increased from 1 to 1.5. However, for λ values exceeding 1.5, CA10–90 emerged as the primary knocking determinant. Faster flame propagation and higher oxygen concentration caused by LB and an early spark promoted autoignition of the end-gas and increased the autoignition heat release rate, thus strengthening knock intensity (KI). Furthermore, a minimal amount of water (W/F ≤ 0.3) exerted negligible influence on the stoichiometric combustion stability. As the LB approached its limit, the average KI remained relatively consistent, with combustion stability emerging as the key factor in elevating the LB performance. A 0.3 W/F ratio and precise spark timing ensured that a balance exists between combustion stability and knocking, while simultaneously elevating λ to 2.0. • Stoichiometric combustion is more sensitive to increased water mass. • A DWI system was utilized for a high compression ratio engine. • DWI coupled with optimized spark timing breakthrough lean burn limitation. [ABSTRACT FROM AUTHOR]

In the previous studies on the effect of fuel composition on super lean burn (combustion with an excess air ratio of 2 or more), it was found that the lean limit will be significantly expanded by changing the fuel composition even for hydrocarbon fuels that do not contain oxygen or nitrogen. In this report, we focus on the ignition delay time and laminar burning velocity of hydrocarbon fuels on the expansion of the lean limit based on the experimental results. [ABSTRACT FROM AUTHOR]

Lean-diluted combustion can enhance thermal efficiency and reduce exhaust gas emissions from spark-ignited (SI) gasoline engines. However, excessive lean mixture with external dilution leads to combustion instability due to high cycle-to-cycle variations (CCV). The CCV should be controlled as low as possible to achieve stable combustion, high engine performance, and low emissions. Therefore, a stable combustion control function is required to predict the combustion phase with a low calculation load. A machine learning-based function is developed in this work to predict the 50 % mass fraction burn location (MFB50). Input parameters to the machine learning model consist of 1-, 2-, 3-, and 4-cycle from a three-cylinder production-based gasoline engine operated under stoichiometric to the lean-burn mixture. The results show that the MFB50 prediction model achieves high accuracy when 2-cycle data are used relative to 1-cycle data, which implies that the previous cycle data affects the predicted MFB50 of the next cycle. As a result, the neural network model can predict the cyclic MFB50 error within ± 3 °CA CCV and ± 5 °CA CCV with 70 % and 90 % accuracy, respectively. However, an increasing number of cycle data worsens the prediction accuracy due to model over-learning. [ABSTRACT FROM AUTHOR]

To explore a suitable combustion strategy for natural gas engines using jet ignition, lean burn with air dilution, stoichiometric burn with EGR dilution and lean burn with EGR dilution were investigated in a single-cylinder natural gas engine, and the performances of two kinds of jet ignition technology, passive jet ignition (PJI) and active jet ignition (AJI), were compared. In the study of lean burn with air dilution strategy, the results showed that AJI could extend the lean limit of excess air ratio (λ) to 2.1, which was significantly higher than PJI's 1.6. In addition, the highest indicated thermal efficiency (ITE) of AJI was shown 2% (in absolute value) more than that of PJI. Although a decrease of NOx emission was observed with increasing λ in the air dilution strategy, THC and CO emissions increased. Stoichiometric burn with EGR was proved to be less effective, which can only be applied in a limited operation range and had less flexibility. However, in contrast to the strategy of stoichiometric burn with EGR, the strategy of lean burn with EGR showed a much better applicability, and the highest ITE could achieve 45%, which was even higher than that of lean burn with air dilution. Compared with the most efficient points of lean burn with pure air dilution, the lean burn with EGR dilution could reduce 78% THC under IMEP = 1.2 MPa and 12% CO under IMEP = 0.4 MPa. From an overall view of the combustion and emission performances under both low and high loads, the optimum λ would be from 1.4 to 1.6 for the strategy of lean burn with EGR dilution. [ABSTRACT FROM AUTHOR]

Due to the depletion of conventional petroleum-based fuels and increasing environmental concerns, industries have been developing new combustion technologies with acceptable cost ranges and minimum system modifications for consumers. Among many approaches, the utilization of plasma ignition systems is considered as a promising pathway to achieve greener transportation while maintaining conventional internal combustion engine systems. Plasma contains highly reactive radicals, and those have a great potential of enhancing chemical reactions that are beneficial for reducing carbon emissions. The primary objective of this paper is to provide an overview of currently available plasma-assisted combustion systems including recent achievements in research and development, and technical challenges for successfully implementing a new ignition system. This review will introduce various plasma-assisted combustion approaches from worldwide projects, covering non-thermal and thermal plasma systems in internal combustion engines.

Due to the difficulty to directly study ammonia, the present work investigated the engine performance of lean iso-octane/air mixture to approximate ammonia combustion behaviour. The study was conducted using a single cylinder modified diesel engine that features a spark plug and glow plug in the sub-chamber. The investigations varied the engine speeds (1000 and 1500 RPM), glow plug voltages (6 and 10 volts), excess air ratios (1.4 to 1.8), and ignition timings (-2 to -5 °BTDC). The results suggested improved engine performances with a lower excess ratio and higher glow plug voltage due to more complete and stable combustion. By increasing the engine speed, the lean burn limit was extended and improved the engine performances. Because of the sub-chamber feature, delaying the ignition timing improved the engine performances. A larger excess air ratio was found to increase the sensitivity of the engine performances with the ignition timing. The brake mean effective pressure for all conditions has a coefficient of variation of less than 7%, indicating stable combustion. The results suggested that the current setup can be used to investigate ammonia blended fuel and direct ammonia combustion in future works.

[Display omitted] • A 3D hydrogen engine model coupled with chemical kinetics is built and validated. • Diverse hydrogen reaction mechanisms' feasibility for engine combustion is evaluated. • Hydrogen injection strategy effects on combustion and NO performance are studied. • Engine combustion and emission performance under HPI and HDI modes are compared. • Case6-HDI-100 is the ideal scheme with the indicated thermal efficiency of 40.52 %. With the proposal of "dual-carbon" goals and increasingly stringent emission regulations, hydrogen as a zero-carbon alternative fuel has great potential in engine applications. In the appliance of pure hydrogen engines, direct injection plus lean burn technology can effectively improve engine performance and reduce emissions. Therefore, this work establishes a three-dimensional (3D) simulation model of the pure hydrogen spark-ignition internal combustion engine (ICE) coupled with chemical reaction kinetics. Then, the applicability of different commonly used hydrogen simplified mechanisms to characterize the combustion process based on experimental data is evaluated, and the feasibility of the transient calculation model is verified. Then, the engine combustion and emission performance are compared by adopting hydrogen port injection (HPI) and hydrogen direct injection (HDI) strategies. Meanwhile, the effects of hydrogen injection timing (HIT) on flow, combustion and nitric oxide (NO) emission processes under direct injection plus lean burn mode are analyzed. The results show that: 1. For mixture distribution at ignition timing (IT), the hydrogen should be distributed near the spark plug and avoid its concentration being too rich since the richer mixture will lead to intense combustion and rapid heat release. 2. When using HDI mode, the engine combustion performance and power performance are better than that of the HPI mode. Delaying HIT, the power performance improves under HDI modes, while both the indicated thermal efficiency (ITE) and indicated mean effective pressure (IMEP) reached the maximum at Case6-HDI-100 with the values are 40.52 % and 0.498 MPa, respectively. 3. Considering the engine combustion, power and emission performance, Case6-HDI-100 (HIT at 100 °CA BTDC) is the preferred scheme. Its ITE and IMEP are 8.49 % and 37.33 % higher than that of Case1-HPI (HPI mode scheme) and 6.50 % and 14.95 % higher than that of Case4-HDI-220 (the lowest scheme under HDI mode), respectively, while nitrogen oxide (NO x) emissions meet the European Stage V non-road emission standards. This study provides some reference values for the combustion design of pure hydrogen ICEs. [ABSTRACT FROM AUTHOR]

Hydrogen is a carbon-free fuel that can be produced in many ways starting from different sources. Its use as a fuel in internal combustion engines could be a method of significantly reducing their environmental impact. In spark-ignition (SI) engines, lean hydrogen–air mixtures can be burnt. When a gaseous fuel like hydrogen is port-injected in an SI engine, working with lean mixtures, supercharging becomes very useful in order not to excessively penalize the engine performance. In this work, the performance of a turbocharged PFI spark-ignition engine fueled by hydrogen has been investigated by means of 1-D numerical simulations. The analysis focused on the engine behavior both at full and partial load considering low and medium engine speeds (1500 and 3000 rpm). Equivalence ratios higher than 0.35 have been considered in order to ensure acceptable cycle-to-cycle variations. The constraints that ensure the safety of engine components have also been respected. The results of the analysis provide a guideline able to set up the load control strategy of a SI hydrogen engine based on the variation of the air to fuel ratio, boost pressure, and throttle opening. Furthermore, performance and efficiency of the hydrogen engine have been compared to those of the base gasoline engine. At 1500 and 3000 rpm, except for very low loads, the hydrogen engine load can be regulated by properly combining the equivalence ratio and the boost pressure. At 3000 rpm, the gasoline engine maximum power is not reached but, for each engine load, lean burning allows the hydrogen engine achieving much higher efficiencies than those of the gasoline engine. At full load, the maximum power output decreases from 120 kW to about 97 kW, but the engine efficiency of the hydrogen engine is higher than that of the gasoline one for each full load operating point.

Advanced combustion strategies for gas turbine applications, such as lean burn operation, have been shown to be effective in reducing NOx emissions and increasing fuel efficiency. However, lean burn systems are susceptible to thermo-acoustic instabilities which can lead to deterioration in engine performance. This paper will focus on one of the common industrial techniques for controlling combustion instabilities, secondary injection, which is the addition of small quantities of secondary gas to the combustor. This approach has often been employed in industry on a trial-and-error basis using the primary fuel gas for secondary injection. Recent advances in fuel-flexible gas turbines offers the possibility to use other gases for secondary injection to mitigate instabilities. This paper will explore the effectiveness of using hydrogen for this purpose.The experiments presented in this study were carried out on a laboratory scale bluff-body combustor consisting of a centrally located conical bluff body. Three different secondary gases, ethylene, hydrogen and nitrogen, were added locally to turbulent imperfectly-premixed ethylene flames. The total calories of the fuel mixture and the momentum ratio were kept constant to allow comparison of flame response. The heat release fluctuations were determined from the OH* chemiluminescence, while the velocity perturbations were estimated from pressure measurements using the two-microphone method. The results showed that hydrogen was the most effective in reducing the magnitude of self-excited oscillations. Nitrogen had negligible effect, while ethylene only showed an effect at high secondary flow rates which resulted in sooty flames.

Lean burn spark ignition (SI) engines represent an effective solution for improving fuel economy and reducing exhaust emissions and can be implemented both in conventional and hybrid powertrains. On the other hand, lean operation increases cyclic variability with negative impact on power output, engine efficiency, roughness, and operating stability. Although this phenomenon has been widely investigated, the effects of flow field on the inception and development of flames in direct injection spark ignition (DISI) engines under lean burn conditions is not yet completely understood. In particular, the effect of spark plug geometry and electrode orientation with respect to tumble motion has been minimally investigated. For these reasons, two different spark-plug geometries (i.e., single- and double-ground electrode) and three different orientations (i.e., cross-, counter-, and uni-flow with respect to the direction of tumble motion) were investigated in an optically accessible DISI engine for understanding their influence on the initial phase of combustion. The relative air–fuel ratio (AFRrel) was changed from stoichiometric to lean burn (1.00 to 1.30) for different spark timings around the maximum brake torque setting at fixed engine speed (2000 rpm). An image processing procedure was developed for evaluating the morphological parameters of flame kernels and studying the effects of spark plug design on engine operating stability. With a focus on the correlation between the position where ignition occurs with the subsequent locations of the flame kernel during the first phases of the combustion process, the analysis allowed the gathering of a better understanding of the influence that the electrodes’ geometries and orientation can have on the first stages of combustion development.

Hydrogen and iso-butanol are notable potential alternative fuels. Hydrogen addition under air dilution conditions was investigated in this study in an attempt to enhance the thermal efficiency of spark ignition (SI) engines fueled with iso-butanol-gasoline (B33) at partial load. Hydrogen appears to have positive effect on combustion progress that is prolonged during air dilution. Under lean hydrogen-enriched mixture conditions, the brake thermal efficiency was increased by about 4% and combustion instability was reduced; the lean burn limit migrated from 1.4 to 1.8 for B33 engine after hydrogen addition. Under lean burn conditions, the durations of initial flame development and rapid burning were shortened markedly by hydrogen; both were extended by air dilution. After hydrogen addition, the unburnt HC emissions of iso-butanol-gasoline decreased markedly and carbon monoxide (CO) emissions decreased slightly. NO x emissions from hydrogen-enriched iso-butanol-gasoline increased as lambda grew near to 1.0, at a significant reduction with increasing excess air rate regardless of fuel type. The combination of hydrogen addition and air dilution exhibited a positive inhibition on particle matter (PM) emissions regardless particle in nucleation or the accumulation mode, and the particle surface concentration was reduced significantly. Finally, an improved combustion progress was observed after hydrogen addition during air dilution, as well as a higher brake thermal efficiency and wider lean burn limit with acceptable combustion stability. • H 2 causes an overall improvement of B33 burning behaviors during air dilution. • The lean burn limit of B33 migrates from 1.4 to 1.8 with acceptable COV IMEP. • Hydrogen has a positive impact on emissions and BTE during air dilution. • Lean burn and H 2 -enriched result in reduced PM emissions from B33 engine. [ABSTRACT FROM AUTHOR]

• Maximum BTE of 44.9% was achieved in a small bore spark-ignition passenger car engine. • Methanol direct injection extends lean burn flammability by only about 0.1. • Methanol direct injection and high CR increase CO and HC emissions at high dilution rate. • The main barrier to greater BTE for spark ignition MDI engine with high CR are extended combustion duration and increased incomplete combustion. The high octane number and high latent heat of vaporization of methanol are beneficial to suppress knock and consequently increase compression ratio (CR) of spark ignition engines, and thus improve the thermal efficiency. Few preious research on methanol engine combuston and performances have been conducted based on spark-ignition passenger car engines with a CR greater than 14. In this study, a 1.5-liter spark ignition passenger car engine with miller cycle was used to explore the potentials of high CR and methanol direct injection (MDI) on improving engine performances. First, the engine was tested under stoichiometric combustion using methanol and gasoline at BMEPs of 1.1 MPa and 1.5 MPa with CR11.5, CR13.8, and CR15.3. Then, the performances of the CR11.5 case with gasoline and the CR15.3 case with methanol were compared under lean burn combustion. The results show that for gasoline, increasing CR from 11.5 to 15.3 results in decreased fuel economy under stoichiometric combustion, whereas the exact opposite tendency is shown for methanol. Integrating a high CR of 15.3 and MDI improves brake thermal efficiency (BTE) to 43.3 % at an excess air/fuel ratio (λ) of 1.0, when compared with 37.4 % of gasoline at CR11.5. Applying lean burn can further improve the BTE of methanol at CR15.3 to 44.9 %. The main causes of the improvement of BTE by high CR and MDI are the reduced exhaust heat loss resulted from earlier combustion phasing. However, high CR and MDI also extend combustion durations at all specified λs, and emit more THC and CO emissions than low CR with gasoline at high λs because of higher surface/volume ratio and flame quenching. The extended combustion duration and the incomplete combustion are the main barriers to greater BTE for MDI sprak ignition engine with high CR. [ABSTRACT FROM AUTHOR]

Hydrogen energy in transport, particularly in the automotive internal combustion engine sector, is relevant for promoting carbon neutrality and cleaner production. In this study, effect of five mixture formation methods including Homogeneous charge, In-cylinder mildly stratified charge, In-cylinder severely stratified charge, Spark-plug mildly stratified charge, and Spark-plug severely stratified charge were studied on efficiency combustion, emissions, and energy distribution. The results show that equivalent combustion obtained the maximum hydrogen consumption and nitrogen oxide emissions exceeded 2900 ppm for all mixture formation methods. For light and medium lean burn conditions (λ = 1.6, 2.2, 2.7), Spark-plug severely stratified charge and In-cylinder severely stratified charge methods balanced combustion stability and thermal efficiency, but also maintained nitrogen oxide emissions to at least over 100 ppm. While at ultra-lean burn conditions (λ = 3.2 and 3.6), all methods limited nitrogen oxide emissions to less than 10 ppm. In addition, at λ = 3.62, Spark-plug mildly stratified charge method significantly reduced the coefficient of variation on P max by about 7 %. Compared to the In-cylinder severely stratified charge method with λ = 1, Spark-plug mildly stratified charge method with λ = 3.62 reduced hydrogen consumption by 75.8 g/(kW × h). The energy distribution proved that this reduction was attributed to the reduction of heat loss power from lean burn and a further limitation of exhaust power from Spark-plug mildly stratified charge method, which was considered to be the most promising method to achieve clean, efficient and stable combustion. • Five different mixture formation methods were implemented at different λ conditions. • The SMSC method could significantly reduce COV Pmax about 7 % at λ = 3.62. '. • The SMSC method obtained optimal hydrogen consumption 85.2 g/(kw × h) at λ = 3.62. • NOx emissions could be limited to less than 10 ppm at λ = 3.62. • The SMSC method achieved both high efficiency and near-zero emissions. [ABSTRACT FROM AUTHOR]

More efficient lean-burn, natural gas engines are limited by greenhouse gas emissions due to methane oxidation catalysts (MOC) that suffer from water inhibition and high temperature activation. Herein, we report that the addition of Mg to supported 1 wt% Pd MOCs improved hydrothermal stability even after severe hydrothermal aging. The superior methane oxidation activity compared to the corresponding Mg-free catalyst was attributed to (1) influence of Mg during surface roughening and restructuring at 700 °C on metal-support interaction, (2) reducibility of PdOx sites and (3) preferential stabilization of active Pd (1 0 0) facets in the sample as was evidenced by H 2 TPR and CO TPD characterization experiments. Methane conversion under synthetic exhaust conditions relevant to natural gas, lean-burn engines were investigated. BET, TPR, CO pulse chemisorption followed by TPD provided valuable insights into the surface area, pore volume, reducibility, Pd dispersion and Pd particle size of the selected catalyst samples. [Display omitted] • Mg modified Pd MOCs increase hydrothermal stability and inhibit PdOx agglomeration. • Mg presence during aging preferentially exposed CH 4 oxidation active PdOx facets. • Route of Pd and Mg introduction into SSZ-13 impacted catalyst activity. • Pd+Mg supported on Al 2 O 3 exhibited better low temperature activity than SSZ-13. • Increased TOF with PdOx particle size consistent with Mars-van Krevelen mechanism. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics is a fundamental tool to simulate the flow field and the multi-physics nature of the phenomena involved in gas turbine combustors, supporting their design since the very preliminary phases. Standard steady state RANS turbulence models provide a reasonable prediction, despite some well-known limitations in reproducing the turbulent mixing in highly unsteady flows. Their affordable cost is ideal in the preliminary design steps, whereas, in the detailed phase of the design process, turbulence scale-resolving methods (such as LES or similar approaches) can be preferred to significantly improve the accuracy. Despite that, in dealing with multi-physics and multi-scale problems, as for Conjugate Heat Transfer (CHT) in presence of radiation, transient approaches are not always affordable and appropriate numerical treatments are necessary to properly account for the huge range of characteristics scales in space and time that occur when turbulence is resolved and heat conduction is simulated contextually. The present work describes an innovative methodology to perform CHT simulations accounting for multi-physics and multi-scale problems. Such methodology, named U-THERM3D, is applied for the metal temperature prediction of an annular aeroengine lean burn combustor. The theoretical formulations of the tool are described, together with its numerical implementation in the commercial CFD code ANSYS Fluent. The proposed approach is based on a time de-synchronization of the involved time dependent physics permitting to significantly speed up the calculation with respect to fully coupled strategy, preserving at the same time the effect of unsteady heat transfer on the final time averaged predicted metal temperature. The results of some preliminary assessment tests of its consistency and accuracy are reported before showing its exploitation on the real combustor. The results are compared against steady-state calculations and experimental data obtained by full annular tests at real scale conditions. The work confirms the importance of high-fidelity CFD approaches for the aerothermal prediction of liner metal temperature.

The aircrafts are responsible for emitting several types of pollutants, especially the pollutants in the form of NOX, CO2, CO, UHC, SOX and Particulate Matter PM (smoke/soot). The impact of aviation emissions on the global is well known, where these emissions modify the chemical and microphysical properties of the atmosphere resulting in changes of earth’s climate system, which can ultimate in critical changes in our planet fragile ecosystem, also the pollutants produced by aircraft engines cause many health problems. This is why the International Civil Aviation Organisation (ICAO) is seriously seeking to control the emission levels by issuing new standards during the successive meetings of the Committee on Aviation Environmental Protection CAEP (CAEP/01 in 1986, CAEP/2, CAEP/4, CAEP/6, CAEP/8, etc). The new regulations include more stringent standards aimed to reduce emission levels, this led to increased interest in low emission technologies. In this paper, a comprehensive review of low emissions combustion technologies for modern aero gas turbines is represented. The current low emission technologies include the high Technologies Readiness Level (TRL) including RQL, TAPS, DAC and LDI. Also, there are advanced technologies at lower TRL including LPP, ASC and VGC.

• Ignition and combustion process of a lean burn engine was investigated. • A customized ignition system with 20 ignition coils was applied. • Lean limit was extended to excess air ratio of 2.1 with a discharge interval. • The longer discharge interval promoted the spark-shortening phenomena. • Repetition of spark-shortening phenomena promoted the formation of flame kernel. Lean combustion technologies have been investigated to decrease the heat loss of spark ignition engines. However, as the excess air ratio approaches the lean operation limit, the cycle-to-cycle variation of combustion becomes an obstacle to improving thermal efficiency. This paper discusses the influences of spark discharge characteristics, such as discharge current and spark-shortening phenomena, on the ignition and combustion process under lean conditions (excess air ratio (λ) of 1.8–2.3) to suppress the cycle-to-cycle variation of combustion and extend the lean operation limit. In this study, a customized inductive ignition system equipped with 20 conventional ignition coils was applied to enhance the ignition energy. The discharge interval between each coil unit was controlled to change the discharge current and duration. The results show that the in-cylinder discharged energy increased with the discharge interval. The cycle-to-cycle variation of combustion was minimized when the discharge interval was 0.4 ms, and consequently, the lean operation limit was extended to an excess air ratio (λ) of 2.1. The discharge waveforms indicated that the longer discharge interval could promote spark-shortening phenomena such as re-strike due to the lower discharge current. Finally, in-cylinder photographs of ignition and combustion process showed that the flame kernel formation could be promoted by the repetition of spark-shortening phenomena such as re-strike, as well as by the high elongation of the spark channel. [ABSTRACT FROM AUTHOR]