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This study investigates the efficiency and combustion characteristics of a hydrogen port fuel injection (PFI) spark ignition (SI) engine under various load levels, excess air ratios and intake pressures. Experiments were conducted on a single-cylinder research engine to evaluate the effects of throttle opening and supercharging on pumping work and combustion parameters. The key findings indicate that abnormal combustion events are more closely related to the relative air-fuel ratio (λ) than to load, further limiting load increases during de-throttled operation. Additionally, combustion variability compromised mixture enleanment in both naturally aspirated and supercharged conditions. The gross indicated efficiency was approximately 40.7% across the range of 2.2 < λ < 3.5 with minimal variation. Efficiency gains were linked to reduced heat transfer losses in lean conditions, as validated by computational heat transfer, thermodynamic and fluid dynamic models on Gamma Technologies GT-ISE software. Moreover, nitrogen oxides (NO x) emissions were nearly zero for all test conditions when λ was above 2.2. These findings provide crucial insights into optimizing hydrogen engine performance under various intake pressures, highlighting the potential for achieving high efficiency and low emissions. • Wide-range excess air ratios sweep from 1.3 to 4.0 and IMEP from 2.5 to 12.9 bar. • Best founded net indicated efficiency of 38.7% with de-throttling. • Efficiency sweet spot at near λ = 2.2 under supercharged operation. • Near-zero indicated specific NO x emissions above λ = 2.2. [ABSTRACT FROM AUTHOR]

This article presents the first practical engine system using ammonia (NH 3) as a mono-fuel. To address the low flammability and distinctive odor, the system incorporates a four-cylinder spark ignition engine with an onboard reformer applying autothermal reforming to generate hydrogen as a combustion promoter, a three-way catalyst (TWC), and selective catalytic reduction (SCR) catalyst as an NH 3 adsorbent. The system successfully reduced nitrogen-based exhaust emissions during cold starts, which was a challenge, by controlling the air-fuel ratio (λ). Nitrogen oxides were suppressed by rich combustion until the TWC became active, while NH 3 passing through the TWC was adsorbed by the SCR catalyst. After TWC activation, simultaneous purification of NH 3 and nitrogen oxides was achieved by controlling λ at 1. The adsorbed NH 3 was subsequently purified along with nitrogen oxides via the SCR reaction by lean operation, regenerating the adsorption capacity and achieving near-zero emissions. • An NH 3 mono-fueled engine system with a reformer and an adsorbent was proposed. • Successful cold start-up was achieved with suppressed NH 3 , NO x , and N 2 O emissions. • Rich combustion reduced NO x and N 2 O until a three-way catalyst is activated. • Adsorbed NH 3 was purified with NO x by lean operation using SCR reactions. • Production of N 2 O on TWC was reduced avoiding lean and low temperature conditions. [ABSTRACT FROM AUTHOR]

Safety of using hydrogen as fuel in aerospace applications is closely connected with hydrogen explosion safety during its transportation and stockpiling at launch places. In this paper, preventing the detonation propagation in the mixtures of hydrogen with air due to accidental hydrogen releases is studied in numerical experiments. Another fuel - hydrocarbon propylene – is studied as an optional inhibitor to be added in a small volume quantity to hydrogen-air mixture. The dependence of detonation wave cellular structure on the content of inhibitor is studied for different fuel-air ratios. The results make it possible determining the content of inhibitor sufficient for preventing the detonation onset or destroying the existing detonation wave. • Preventing the detonation propagation in the mixtures of hydrogen with air is studied numerically. • Another fuel - hydrocarbon propylene – is studied as an optional inhibitor. • The dependence of detonation wave cellular structure on the content of inhibitor is studied for different fuel-air ratios. • The content of inhibitor sufficient for preventing the detonation onset or destroying the existing detonation wave. [ABSTRACT FROM AUTHOR]

The ignition of spray flames is a process of stochastic nature, especially relevant to the high-altitude relight of aeroengines. The present work aims to quantify the role of spray inhomogeneities in a realistic droplet-laden ignition set-up through Direct Numerical Simulations (DNS). Computations of the ignition process of weakly turbulent ethanol spray flows are performed using complex chemistry, a realistic energy deposition model and a polydisperse description of the spray. A good qualitative agreement of the flame radius evolution is found between the DNS and experiments, and both long-time failure and ignition modes are recovered with comparable radii, hence reproducing the experimentally-observed range of behaviour of ignition kernels. In contrast to experiments where the presence of large droplets at the spark impact both the actual energy deposited in the flow and the local fuel-air equivalence ratio, the effect of both parameters on the ignition outcome are assessed independently in this work by carefully choosing ignition locations in the flow representative of time-wise fluctuations. The minimum ignition energy (MIE) representative of the global flow condition is then evaluated using results from the DNS simulations and flow and spark characteristics. In order to understand the origin of the ignition stochasticity observed experimentally, local values of the fuel-air equivalence ratio $ \Phi _t $ Φt and turbulence level $ u' $ u′ at the spark plug are measured in the simulations using an averaging in volumes of size $ \Delta _b $ Δb. It is found that $ \Phi _t $ Φt best correlates to the MIE at three different locations in the domain for a size around 4 mm, which corresponds approximately to the kernel size at 0.1 ms, that is, the typical time scale of plasma processes and right when the flame becomes toroidal. The results give support to the experimental conjecture that stochasticity is largely due to the spatial fluctuations of $ \Phi _t $ Φt induced by polydispersity and in a lesser extent to those of $ u' $ u′. [ABSTRACT FROM AUTHOR]

Knock combustion has become the main barrier in the development of hydrogen internal combustion engine (ICE). This study investigated the factors (engine speed, spark timing, injection timing, and injection pressure) influencing knock combustion based on the data of a bench test and a 1D simulation model on GT-Power. And the Taguchi-Grey method was applied to rank the four factors. Results showed that knock combustion occurs under lower relative air-fuel equivalence ratio, the percentage of the knock cycle in 100 continuous cycles decreased from 45.8% to 0 when λ raised from 2.47 to 3.37. The advancement of injection timing and the decreasing of injection pressure, along with higher engine speed, facilitate the occurrence of knock. However, the knock tendency increases first and then declines with the advancement of spark timing. Among all the factors considered, engine speed has the greatest influence on knock combustion, whose contribution rate is 50.64%. • Injection timing and pressure, spark timing, and engine speed can affect knock. Engine speed has the largest impact on knock. • The advancement of spark timing makes the knock tendency increase first and then decline. • Engine speed has the largest contribution on knock combustion through the Taguchi-Grey method. [ABSTRACT FROM AUTHOR]

The effect of small fractions of acetaldehyde (CH3CHO) on the ignition delay time of methane (CH4) was examined at high pressure. Measurements are reported for the ignition delay time obtained in a rapid compression machine (RCM) at a compression pressure (Pc) of ∼60 bar and temperatures after compression (Tc) in the range 750–900 K for fuel‐air equivalence ratios ϕ in the range 1–4. The results show that mixtures of 2%–5% CH3CHO in CH4 ignite under conditions at which pure methane does not ignite experimentally. The efficiency of acetaldehyde as a promoter seems to be comparable to that of other oxygenated fuels like alcohols and ethers. For comparison with the experimental results, ignition delay times are computed using an updated reaction mechanism and two mechanisms from the literature for CH3CHO oxidation. For most conditions, the simulations using the current mechanism agree with the measurements to within a factor of two. The ignition profile shows a pre‐ignition temperature rise and two‐stage ignition similar to that previously observed in low fractions of dimethyl ether in ammonia; both phenomena are captured by the simulations. Analysis of simulations at constant volume indicates that CH3CHO is oxidized much more rapidly than CH4, producing reactive species that initiate the oxidation of CH4 and generates heat that accelerates oxidation toward ignition. The low‐temperature chain‐branching reactions of CH3CHO are important in the early oxidation of the fuel mixture. Additional simulations were performed for equivalence ratios of ϕ = 1 and 4, at a compression pressure (Pc) of 100 bar and Tc = 750–1000 K. The simulations indicate that CH3CHO has a strong ignition‐enhancing effect on CH4, with small fractions reducing the ignition delay time by up to a factor of 100, depending on the temperature, as compared to pure CH4. [ABSTRACT FROM AUTHOR]

In order to explore effects of coal-based oxygenated fuels polyoxymethylene dimethyl ether (PODE) and methanol on pollutant emissions of diesel engines, in-cylinder combustion numerical model was developed by coupling PODE/methanol reaction mechanism with CONVERGE software. The influences of exhaust gas recirculation (EGR) and nozzle angle on in-cylinder combustion and pollutant generation of PODE/methanol blends were studied. Results show that with the increase of EGR ratio, the fuel-air equivalence ratio increases, the in-cylinder pressure decreases, and the ignition delay period is prolonged. The generation range and rate of NOx gradually decrease, and the final NOx generation decreases by 85.1% at EGR = 20%. However, the peak soot generation rate and the final soot generation increase. With the increase of nozzle angle, the peak in-cylinder pressure and the overall heat release rate increase. When the nozzle angle is adjusted from 148° to 164°, the rich area of fuel-air equivalent ratio in the piston pit decreases, the high temperature area in the piston pit almost disappears. The final in-cylinder NOx generation has been reduced by 29.3%. The soot distribution gradually moves to the upper layer of combustion chamber, and the peak soot generation rate decreases, while the final soot generation increases by almost 49.5%. [ABSTRACT FROM AUTHOR]

Intake parameters are essential factors that are often overlooked, but can easily change the direct internal reforming solid oxide fuel cell (DIR-SOFC) performance. A three-dimensional model is developed to simulate the effects of intake parameters on the performance of an anode-supported flat-plate DIR-SOFC. The two primary chemical reactions, water gas shift reaction (WGSR) and methane steam reforming reaction (MSR), as well as the electrochemical oxidation of H 2 and CO, are considered in this model. It was found that the aspect ratio corresponding to the peak current density decreases as fuel increases. A moderate air flow rate makes the fuel-to-air ratio (FAR) corresponding to the drastic change in current density relatively small and wide-ranging, resulting in more desirable temperature distribution and fuel utilization. Under the operating conditions of this paper, adjusting the steam-to-carbon ratio (S/C) to between 1.5 and 2 results in both excellent electrical performance and good temperature uniformity. Additionally, adjusting the flow rate by changing the inlet area or velocity has its own advantages in terms of temperature distribution or current density, which must be taken into account when adjusting the flow rate. This study provides a valuable reference on inlet settings of DIR-SOFC, which would help to promote the development of high-performance SOFCs. • A three-dimensional flat-plate DIR-SOFC model has been developed. • Oxidation reaction of CO is included in the mode. • Different flow rates would change the effects of the aspect ratio and S/C. • Impacts of the fuel-air ratio are analyzed fully in terms of both fuel and air sides. • Changing the flow rate by altering the area or speed can make differences. [ABSTRACT FROM AUTHOR]

The minimum ignition equivalence ratio of the strut stabilizer is an important parameter in the design of integrated afterburners. The ignition location significantly affects the ignition equivalence ratio and flame propagation, and therefore, it should be deeply studied. The ignition equivalence ratio and flame propagation at different axial ignition locations downstream of the strut stabilizer are studied in this paper. When the ignition distance is approximately the bluff body trailing edge width, a lower ignition equivalence ratio is required for ignition, and the flame propagates faster through the entire combustion chamber. For different ignition locations, the generated flame kernel at different locations all first propagates to the shear layer. Subsequently, the unilateral flame rapidly extends, ultimately igniting the entire combustion chamber. The flame propagation trajectory depends on the ignition location controlled by the non-reacting flow field and the distribution of kerosene concentration. The flame propagation trajectory mainly includes three paths: (1) the flame kernel is directly downstream the shear layer when the ignition location is close to the tail edge of the stabilizer, (2) the flame propagates upstream into the shear layer in a U-shape when the ignition location is far from the stabilizer but still in the recirculation zone, and (3) the flame propagates upstream into the recirculation zone and shear layer in a U-shape when the ignition location is outside the recirculation zone. In addition, the time for flame propagation to the shear layer is directly related to the ignition performance when the ignition location is within the recirculation zone. If the flame reaches the shear layer in a longer time, there will be more energy loss during the flame propagation process, and the ignition performance will deteriorate. The speed of the flame-trailing edge extension is directly related to the ignition fuel-air ratio, and the downstream extension of the flame is mainly affected by the turbulence velocity in the shear layer. [ABSTRACT FROM AUTHOR]

In order to improve the real-time performance of the aero-engine Component-Level Model (CLM) while ensuring accuracy, a method for the Calculation of Thermodynamic Parameters of Working Fluids (CTPWF) based on a Neural Network and Newton Raphson (NN-NR) is proposed. In this method, the enthalpy or entropy under different fuel-air ratio and humidity conditions is mapped to temperature by a neural network, and the mapping output is used as the initial solution of Newton Raphson (NR) iteration. Then, a high-precision solution can be obtained through a few iterations, which avoids the shortcoming that the traditional method uses a fixed initial solution that leads to too many iterative steps. This effectively reduces the number of iterative steps and improves the calculation efficiency. This method is applied to the aero-thermodynamic calculation of each component of an engine CLM, which improves the accuracy and real-time performance of the CLM. The simulation results show that, compared to the traditional method, the proposed method improves the accuracy of the CTPWF and can reduces the single aero-thermodynamic calculation time by 25 % when humidity is not considered and by 47 % when humidity is considered. This effectively improves the real-time performance of the CLM. [ABSTRACT FROM AUTHOR]

A new numerical procedure is presented to enable a hydrogen-fuelled two-stroke resonating free-piston generator target ideal Otto cycles to provide tracking paths for feedback control to maximise efficiency. Piston trajectories and design parameters are obtained for specified power, compression-ratio, and air-fuel-ratio. These parameters include scavenge port locations, heat release position, equivalent bottom-dead-centre position, and an electrical machine constant which is generally power-switched to take two values within a cycle. The main objectives of the paper are to develop the numerical procedure, and to demonstrate its use in finding a generator with maximum efficiency, and a generator with a single electrical machine constant, avoiding in-cycle power switching. To develop the procedure, a multi-physics generator model provides kinematics to an energy equation, culminating in a novel two-stage procedure. Stage-1 involves iteration and minimisation; Stage-2 just involves minimisation. Testing by simulation involves a 14-kW generator case study with compression ratio of 9, lean air-fuel equivalence ratio of 0.4, plus friction and electrical machine losses. An overall maximum generator efficiency of 54.9% is obtained using the procedure, compared to 51.3% without power switching. Computationally, the two-stage procedure proves highly efficient, typically taking around 11 min in total to complete on a desktop computer. The novelty of the procedure is its ability to optimally design and operate a hydrogen-fuelled resonating free-piston generator to meet a target specification, thereby offering a potentially inexpensive way to decarbonize transport, particularly in heavy duty applications. • Resonating free-piston generator is ideal energy converter for use with hydrogen. • New two-stage procedure able to target maximum efficiency. • Key cylinder positions and electrical machine constant easily found. • Planned Otto trajectories provide ideal two-stroke tracking paths. • New procedure tested on 14-kW generator maximises efficiency to 55%. [ABSTRACT FROM AUTHOR]

In internal combustion engines, adjusting the air-fuel ratio is essential to control the speed and minimize the burnt fuel. The throttle opening is the actuator to control the air-fuel. A better design for the used/conventional controller can give a better response without additional cost. In this work, the proposed controller gains of the proportional-integral (PI) controller are tuned to enhance the speed in constant and variable drive cycle modes. The tuning process is conducted based on two of the most efficient performance indices used in this field. The performance indices are integral absolute error (IAE) and integral time absolute error (ITAE). The optimization problem is solved using three reliable stochastic optimization algorithms to ensure mature convergence of the solutions, to avoid local optima solutions, and to ensure effective shrinking of the search space. The optimization algorithms are teaching-learning-based optimization (TLBO), particle swarm optimization (PSO), and genetic algorithm (GA). Different simulations are conducted to validate the results. The results are compared with conventional tuning methods regarding the system's time response. [ABSTRACT FROM AUTHOR]

An experimental investigation was performed to study the effect of the central air flow on the turbulent inverse diffusion flame height. The study conducted a series of experiments using two coaxial burners with different nozzle sizes in the atmospheric environment. The experimental results show that the central air flow influences the mixing process between the air/fuel jets and the flame morphology. The inverse diffusion flame height decreased with the increase in air flow rate under the same heat release rate due to the strengthening of air/fuel mixing. The flame height decreases sharply when the air flow is turbulence flow. The air–fuel momentum ratio was found to estimate the inverse diffusion flame height. The momentum flux and buoyancy flux of inverse diffusion flame have been analyzed. Considering the combinational effect of momentum flux and buoyancy flux on the inverse diffusion flame, a new correlation between the inverse diffusion flame height, air flow rate, and heat release rate has been established which provides a valuable resource for designing the inverse diffusion flame burners. [ABSTRACT FROM AUTHOR]

The impact of inlet fuel temperature on the performance and emission characteristics of a 406 cc, single‐cylinder, air‐cooled, 4‐stroke, direct injection (DI) diesel engine was investigated to determine the suitable temperature of fuel for the best conditions of the engine in lean and ultra‐lean mixture combustion mode. B20 palm oil biodiesel‐diesel blend fuel (B20 POBD), as common renewable fuel and favorite biodiesel blend ratio used in the research, was provided and injected in the engine at varying temperatures in the range of 10–40°C and the engine parameters including the output power, specific fuel consumption (SFC), thermal efficiency, flue gas heat recovery efficiency and CO and NOx pollutant emissions were measured at different air–fuel ratios corresponded to lean and ultra‐lean mixtures. The results showed that there is an optimum temperature for fuel (about 20°C) in which maximum thermal efficiency and minimum SFC and CO emission are obtained. The minimum SFC and CO emission were 0.45 Kg/kWh and 610 ppm at the optimum temperature and output power of 1.5 kW, respectively. The effect of fuel temperature on SFC and CO increases as the output power decreases and for all fuel temperatures, the output power is inversely related to the air–fuel ratio. In addition, the elevated output power reduces the CO emission in all inlet fuel temperatures. Furthermore, an ultra‐lean mixture (very high A/F ratio) can dramatically decrease the thermal efficiency of diesel engines at all fuel temperatures, such that at the inlet fuel temperature of 17°C, increase in A/F ratio from 51 to 108 decreases the thermal efficiency from 16.8% to 0.12%. Finally, low engine output power leads to low levels of NOx emission, such that decrease in output power from 1.5 to 0.5 kW reduces the NOx emission from 522 to 204 ppm, respectively. [ABSTRACT FROM AUTHOR]

Past research has mostly concentrated on the utilization of hydrogen or biodiesel in various proportions when blended with diesel fuel. Despite considerable research conducted on the utilization of fuel blends consisting of hydrogen and biodiesel. Currently, there is a lack of research that has conducted a comparative analysis regarding the impact of air-fuel ratio on the performance of diesel fuel blended with Hydrogen and FAME. This research article examines three fuel blends to determine four critical diesel engine parameters (BTE, Brake Torque, NO x concentration, and BMEP) at five distinct air-fuel ratios spanning from 14 to 65. The present study aims to enhance the comprehension of the intricate characteristics of air-fuel mixtures, specifically rich, stoichiometric, and lean, by conducting an extensive analysis. Additionally, the investigation focuses on the impact of the exhaust gas recirculation technique on the NO x concentration. This article presents a mono-cylinder diesel engine model developed in the Ricardo wave program, simulated in three cases: I) Diesel only, II) B50(Blend of 50 % Diesel and 50 % FAME), and III) H50(Blend of 50 % Diesel and 50 % Hydrogen) at a compression ratio 21 with an rpm ranging from 500 to 2500. Fair agreement with peak results deviating in a few percent revealed that H50 significantly enhances brake thermal efficiency (BTE) measured to Diesel and B50, with improvements of up to 5.6 % and 5 %, respectively. When Hydrogen is mixed with Diesel, the combustion process quickens and becomes more complete, and ultimately, an improved combustion quality is achieved. H50 generates 13 % and 12 % higher levels of NO x in comparison to Diesel and B50, respectively. Increased engine speed triggers the in-cylinder temperature to rise, promoting NO x generation. The heat release rate is a significant parameter for assessing combustion efficiency. Diesel releases more heat than B50 at a particular crank angle. However, from 15-64° CA, B50 keeps generating more heat than Diesel. Thereby, B50 releases more heat than the Diesel overall. The Brake torque and BMEP decrease with the increase in AFR for each case. In conclusion, H50 and B50 generate higher BTE than Diesel. Meanwhile, this comes at the cost of a rise in NO x concentration. When the exhaust gas recirculation is applied at 25 %, the NO x concentration is reduced drastically, and it is further deduced that the rate of change of EGR is inversely proportional to the NO x concentration. • Hydrogen blended diesel fuel showcases an improvement in brake thermal efficiency. • Implementing five cases to find a relation between air-fuel ratio and brake thermal efficiency. • Heat release rate is a significant parameter for assessing combustion efficiency. • The Brake torque and brake mean effective pressure decreases with the increase in air-fuel ratio. • The rate of EGR change is inversely proportional to the NOx concentration. [ABSTRACT FROM AUTHOR]

The increasing trend towards global carbon neutrality is driving interest in ammonia fuel as a potential zero-carbon solution for transportation. However, due to the non-ideal combustion characteristics of ammonia, it is necessary to mix it with hydrogen to achieve better engine performance. While generating hydrogen from ammonia on-board is a key technology, there has been limited research in this area, which is hindering the introduction of ammonia engines to the market. This paper proposes an initial study on the feasibility of thermochemical fuel reforming (TFR) technology for generating hydrogen from ammonia fuel-rich operations. A zero-dimensional engine model, validated against experimental results, is used to assess the potential of the TFR approach and identify any barriers to implementation. The results indicate that the optimum air-fuel ratio for hydrogen generation is an equivalence ratio of two, as it maximizes hydrogen production rates while minimizing operational complexities. Moreover, increasing intake temperature, pressure, and compression ratio enhances hydrogen generation from the ammonia-rich mixture. However, owing to the limited reactivity of the ammonia fuel, the rate of hydrogen production remains relatively small (less than 1%/cycle), significantly falling short of the demand. Additionally, the combustion of the fuel-rich mixture in the TFR cylinder results in approximately 20%/cycle of hydrogen in the emitted gases, potentially enhancing the efficiency of working cylinders, but it also poses the risk of engine component failures due to the high pressure rise rate. In conclusion, the use of solely ammonia to produce hydrogen in the TFR cylinder proves to be inefficient, warranting further investigations into the potential benefits of incorporating additives to promote hydrogen production. Alternatively, if a catalyst is utilized to promote hydrogen production from ammonia, a separate electrically heated hydrogen generation system independently of the engine system proves to be more effective, allowing continuous hydrogen production, unlike the intermittent high-temperature environment provided by TFR technology. • Hydrogen production using in-cylinder thermochemical ammonia reforming is evaluated. • An air-ammonia ratio of ϕ = 2.0 is identified as optimal for hydrogen production. • Unfired conditions produce less than 1% of hydrogen in the exhaust per cycle. • Fired conditions can produce ∼20% of hydrogen in the emitted gases per cycle. • Extremely high pressure rise rates are implementation barriers for fired conditions. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulation methods are adopted to explore the influencing factors of a Ceramic Catalytic Turbine (CCT) for reduced exhaust pollution from vehicles during the warm-up stage. Also, an analysis is conducted regarding the potential effects of turbulence on the catalytic reaction mechanism and the sensitivity of relevant parameters to the Arrhenius equation. It is found out that the air-fuel ratio inside the engine has a considerable effect on the reactions of CCT, with the conversion efficiency of each emission species sharply reduced under fuel-rich conditions. At 600K, the conversion efficiency declines by 11.3% for C3H6, 12.26% for CO, and 3.64% for NO. At 700K, the conversion efficiency is reduced by 6.7% for C3H6, 11.56% for CO, and 6.44% for NO. Despite increasing the concentration of reaction gas components, a high flow rate makes little difference to the reaction itself. At the same rotational speed of the turbine, the conversion rate of harmful components drops with an increase in flow rate due to the increase in space velocity. When the flow rate is constant and the temperature is kept in the control zone of chemical kinetics, the conversion efficiency of the catalytic reaction is enhanced at a higher rotational speed. Differently, when the temperature is in the control zone of mass transport and the flow rate is constant, the conversion efficiency decreases as the turbine accelerates. In practical terms, reducing activation energy within a controllable range is equivalent to further reducing the light-off temperature of the catalyst. Meanwhile, this may disrupt the convergence of numerical calculations because the catalytic reactions could occur at around the light-off temperature. [ABSTRACT FROM AUTHOR]

Heavy-fuel engines are widely used in UAVs (Unmanned Autonomous Vehicles) because of their reliability and high-power density. In this study, a combustion model for an in-cylinder direct injection engine has been implemented using the AVL FIRE software. The effects of the angle of nozzle inclination on fuel evaporation, mixture distribution, and combustion in the engine cylinder have been systematically studied at 5500 r/min and considering full load cruise conditions. According to the results, as the angle of nozzle inclination increases, the maximum combustion explosion pressure in the cylinder first increases and then it decreases. When the angle of nozzle inclination is less than 45°, the quality of the mixture in the cylinder and the combustion performance can be improved by increasing the angle. When the angle of nozzle inclination is greater than 45°, however, the mixture unevenness increases slightly with the angle, leading to a deterioration of the combustion performances. When the angle of nozzle inclination is between 35° and 55°, the overall combustion performance of the engine is relatively good. When the angle of nozzle inclination is 45°, the combustion chamber's geometry and the cylinder's airflow are well matched with the fuel spray, and the mixture quality is the best. Compared with 25°, the peak heat release rate increases by 20%, and the maximum combustion burst pressure increases by 5.5%. [ABSTRACT FROM AUTHOR]

The present study deals with the flow structure and mixing characteristics of liquid fuel injected laterally into a supersonic crossflow. The geometry, with a cavity downstream of the injector, mimics a supersonic combustor with a cavity flame holder. A variety of injection schemes and cavity configurations were investigated by means of high-speed schlieren photography. A reflected shock tunnel was employed to generate a Mach 2 air flow and to simulate the high-temperature environment in the combustor. JP-4 liquid fuel was injected at different jet-to-crossflow momentum flux ratios upstream of and from the front wall of the cavity. Results showed that in direct injection into the cavity adjusting the injection angle has significant effect on the local fuel-air ratio. Upstream injection far from the leading edge of the cavity yielded more effective fuel mixing and shorter dissipation length (Ld) than closer injection, due to the development of a vortex on the lee side of the jet core. These results suggest that a combination of upstream injection far from the leading edge of the cavity and inclined direct injection into the cavity may be beneficial for effective mixing in a supersonic combustor cavity flame holder. [ABSTRACT FROM AUTHOR]

Material treatment in pulsation reactors (PRs) offers the potential to synthesize powdery products with desirable properties, such as nano-sized particles and high specific surface areas, on an industrial scale. These exceptional material characteristics arise from specific process parameters within PRs, characterized by the periodically varying conditions and the resulting enhanced heat and mass transfer between the medium and the particulate material. Understanding flame behavior and the re-ignition mechanism is crucial to controlling the efficiency and stability of the pulse combustion process. In order to accomplish this objective, an investigation was conducted into flame behavior within the combustion chamber of a Helmholtz-type pulsation reactor. The study was focused on primarily analyzing the flame propagation process and examining flame velocity throughout the operational cycle of the reactor. Two optical methods—natural flame luminosity (NFL) and particle image velocimetry (PIV)—were applied in related experiments. An analysis of the NFL measurement data revealed a correlation between the intensity of light emitted by the pulsed flame and the air-fuel equivalence ratio (range from 0.89 to 2.08 in this study). It is observed that a lower air-fuel equivalence ratio leads to higher flame luminosity in the PR. In addition, in order to study the parameters related to system stability and energy transfer efficiency, this study also focuses on the local velocity field measurement method and an example of a fluid flow result in a combustion chamber by using a phase-locked PIV measurement system upgraded from a classic PIV system. The presented results herein contribute to the characterization of flame propagation within a pulsation reactor, as well as in pulsatile flows over one working cycle in a broader context, with flow velocity in the center of the combustion chamber ranging from 1.5 m/s to 5 m/s. Furthermore, this study offers insights into the applicable experimental methodologies for investigating the intricate interplay between flames and flows within combustion processes. [ABSTRACT FROM AUTHOR]

A multidimensional numerical model was developed to simulate the operation of one cylinder of a 1.4-liter flex-fuel spark-ignition engine. Hydrous ethanol with 4.3%, 7.5%, 10%, 15%, and 20% water volumetric contents were the considered fuels for the engine. The full load engine operating point was analyzed at 3,875 rpm with a relative air-fuel ratio of 0.9 and a fixed ignition delay. A Grid Convergence Index study was conducted to guarantee the accuracy of the obtained numerical solutions. A six consecutive mechanical cycle simulation was performed for hydrous ethanol with 4.3% water content, and experimental data were used for validation purposes. Turbulent flame speeds were also evaluated and analyzed. Numerical results showed that 10% water content led to the highest engine-generated power output and flame propagation speeds and to the lowest CO and unburned ethanol emissions among the tested fuels. The flame shape and encompassed volume were also analyzed. The results also showed that the high swirl in the in-cylinder flow affects the initial development of the flame for all water contents considered. Fuels leading to lower flame distortions early after ignition showed higher reaction rates and better performance. [ABSTRACT FROM AUTHOR]

In the current study, an onboard dry cell electrolyzer was built to produce an oxyhydrogen (HHO) flow rate of 0.5 L/min by water electrolysis. The objective is to show the impact of oxyhydrogen introduction on engine exhaust gases, combustion characteristics, and engine performance related to gasoline. The experiments were carried out in a petrol engine at a fixed engine speed of 3000 rpm and variable engine loading. When comparing HHO gasoline dual fuel to standard gasoline fuel, the maximum improvements in volumetric efficiency, thermal efficiency and air-fuel ratio were determined as 7.5%, 8% and 11%, respectively. In the case of HHO addition, the highest reductions in specific fuel consumption and exhaust gas temperature were 9% and 6.5%, respectively, compared with conventional gasoline fuel. The highest reduction in CO, HC, NOx, and CO 2 concentrations was observed as 18%, 9%, 15%, and 11%, respectively, for HHO-gasoline dual-fuel mode compared to gasoline fuel. The peak cylinder pressure and HRR improvements were 1.5% and 4.5%, respectively, at 100% engine load. Oxyhydrogen gas is highly recommended as a substitute fuel since it significantly enhances engine performance and combustion characteristics as well as reducing exhaust pollutants. • An on-board dry cell electrolyzer was used with an HHO flow rate of 0.5 L/min. • Experiments were carried out in SI engine at 3000 rpm and variable engine loading. • Maximum improvement in BTE was 8% about the reduction in BSFC was 9%. • HHO-gasoline dual-fuel mode found reduction in CO, HC, NOx, and CO 2 emission. [ABSTRACT FROM AUTHOR]

This article explores the flow characteristics and fuel mixing in a premixed tube leading to the combustion chamber, focusing on hydrogen fuel. A CFD simulation utilizing a discrete phase model (DPM) was conducted to investigate the impact of spray angle, spray pressure, and fuel-to-air ratio on fuel atomization, fragmentation, and fuel-air mixing efficiency. The findings highlight the critical role of the spray angle in fuel atomization and breakup. Increasing the spray angle enhances atomization, resulting in smaller fuel droplet sizes and improved fuel-air mixing. The particle diameters ranged from 165 μm to 117 μm for spray angles of 15°–60°, respectively. Additionally, spray pressure significantly influences particle diameter, velocity, and turbulent kinetic energy. Higher spray pressures promote efficient atomization, fragmentation, and smaller particle sizes, enhancing fuel dispersion and mixing. The fuel-to-air ratio also plays a crucial role, with lean mixtures (0.0003 kg/s of fuel flow rate) facilitating increased fuel-air mixing and smaller droplet sizes. Furthermore, the swirl motion induced by airflow and lower fuel-to-air ratios enhances fuel atomization and breakup, resulting in finer spray characteristics. These insights contribute to optimizing spray angle, pressure, and fuel-to-air ratio, ultimately improving fuel injection systems, combustion efficiency, and emissions reduction across various applications. • Investigated flow characteristics & fuel mixing in premixed tube for hydrogen fuel. • The particle diameters decreased from 165 μm to 117 μm at spray angle of 60°. • Higher spray pressure promotes efficient atomization & smaller particle sizes. • Particle diameter of 98 μm was obtained at pressure of 2 MPa. • Swirl motion & lower fuel-air ratio of 0.3 g/s enhance breakup & fuel-air mixing. [ABSTRACT FROM AUTHOR]

In the current study, a fixed‐bed downdraft gasifier was used, in addition to gas cleaning and treatment units, to evaluate hydrogen production from the waste from a date molasses factory. Date pits and pomace were gasified at a temperature of 800°C with oxygen‐rich air and standard air as the gasifying agents. Simulations were performed using the Cycle‐Tempo simulation tool. The impact of many process parameters (air–fuel ratio, gasification temperature, moisture content, oxygen concentration and temperature of the water–gas shift) on gas composition was investigated. The economic evaluation of hydrogen production is also discussed in this paper. Depending on the operating conditions, the results indicate that gasification of biomass in oxygen‐rich air improves hydrogen yield compared with air gasification of biomass. Over the range of operating conditions examined, the maximum hydrogen production reached 45.86% for pits and 35.81% for pomace from gasification with oxygen‐rich air while the H2 content reached 36.71 and 28.72% respectively for air gasification of pits and pomace. The cost analysis for the date waste gasification unit showed that the hydrogen production cost is $3/kg for date pits and $4/kg for pomace. The production of hydrogen from date molasses manufacturing waste helps to lessen reliance on fossil fuels and is an environmentally beneficial alternative source of renewable energy. [ABSTRACT FROM AUTHOR]

Gas motion in the engine cylinder plays a critical role in diesel engines' air-fuel mixing and combustion processes. Moreover, it influences the engine's performance, emissions, and heat transfer. The intake air motion regulates the main phases of the flow in the cylinder, which is characterized by swirl, squish, and turbulence. Inducing swirl and tumble in the intake process provides high turbulence levels at ignition, resulting in more effective flame speeds and better combustion for lean air-fuel ratios or with EGR. Computational fluid dynamics (CFD) software is used to enhance in-cylinder flow characteristics. In this study, a cold flow simulation of a naturally aspirated, direct injection diesel engine was conducted with different piston bowls using AVL Fire M R2022.2. Swirl, tumble, and TKE parameters were investigated to make a detailed analysis of the in-cylinder flow for the relevant engine. Contrary to the expectation, the swirl ratio for the Piston B configuration is less than that for the original piston configuration. It causes a decrement of swirl ratio compared to the initial piston geometry and the maximum decrement is about 19%. In both cases, the second peak of TKE corresponding to the reverse-squish is around at the -30 CA and the difference between the curves is about ±8%. [ABSTRACT FROM AUTHOR]

The current study aimed to measure real-world emissions of three-wheeled autorickshaws powered by CNG and parameters (such as speed, acceleration, air-fuel (A/F) ratio, and rpm) influencing 3-wheeler emission rates. Test vehicles manufactured under Bharat Standards BS-III and BS-IV were monitored for exhaust emissions in Delhi city using a portable exhaust emission measurement system (AVL Ditest Gas 1000). The average emission rates of CO, HC, and NO gases for on-road autorickshaws were found to be 0.015 ± 0.017, 0.003 ± 0.0017, and 0.007 ± 0.005 g/s, respectively. Further, the highest emission factor values of 3.98 g/km and 3.93 g/km were estimated for CO and HC+NO gases, respectively. These values were found to be 1.4–3.2 times higher than the respective BS emission norms (BS III-CO =1.25 g/km, HC+NO = 1.25 g/km; BS-IV-CO = 0.94 g/km and HC+NO = 0.94 g/km). In this study, it was observed that the driving pattern and emissions were affected by traffic characteristics, driver behavior (constant acceleration and deceleration), and vehicle characteristics. The air-fuel ratio (A/F) was found to correlate highly with emission rates, followed by acceleration/deceleration and speed. Further analysis found that more than 70% of the aggregated emissions were due to acceleration and deceleration, which contributed to nearly 70% of the travel time. This was followed by the breakdown of speed and emissions into different bins, which found that 20–30 kmph has a higher emission rate and 40–50 kmph bin has a lower emission rate. [ABSTRACT FROM AUTHOR]

Aiming to improve the stabilization of unstable swirling turbulent premixed flames, an actively controlled swirler and electrical hardware and control software are developed, implemented, and tested in the present study. Stereoscopic particle image velocimetry is performed to calculate the swirl number and study the flame stabilization. A mixture of methane and air with a mean bulk flow velocity of 5.0 m/s and a fuel–air equivalence ratio of 0.6 is examined. This test condition, along with an original swirler vane angle of 30°, led to the initial anchoring of an unstable premixed flame at the burner exhaust. The developed actuation mechanism allows for changing the swirler vane angle from 30° to 60° and back to 30°. Increasing the vane angle from 30° to 60° increases the swirl number to relatively large values, which leads to the formation of a recirculation zone, a downward velocity along the burner centerline, and, as a result, the stabilization of an M-shaped flame. After the vane angle is reduced to 30°, the swirl number decreases but remains relatively large compared to its original value. As a result, the recirculation zone is present at the end of the actuation process and a V-shaped flame is stabilized. Improving the stabilization of the swirl flames is made possible because of the control apparatus and the method developed in the present study. The apparatus and technique designed and tested in this study facilitate the development of robust tools for improving the stabilization of swirling premixed flames in gas turbine combustors. [ABSTRACT FROM AUTHOR]

Poor fuel–air mixing of the diesel spray in low ambient temperature and pressure or thin air leads to intricate fuel breakup mechanism near the nozzle, which still remains worth of study. In this study, a pressure-based modified multiphase lattice Boltzmann flux solver (MLBFS) is proposed to accommodate the fuel spray breakup characteristics of multiphase, multicomponent, and large density ratio, in which the source terms of governing equation are modified emphatically for high injection pressure. Therefore, the characteristics of microscopic diesel spray breakup induced by Rayleigh–Taylor instability are investigated, including spray penetration, spray area, and spray arc length. It is revealed that the spray penetration is increased exponentially with the fuel–air density ratio Rρ. Influenced by air resistance and circulation interference, the roll-up vortex, droplet size, and spray area increase with the decreasing of Rρ (corresponding to high ambient pressure). Affected by entrainment and Rayleigh–Taylor instability, the development of the spray arc length experienced three stages: rapid growth, peak, and violent fluctuation, in which the lower Rρ facilitates development. It is concluded that Rayleigh–Taylor instability is favorable for stimulating the spray internal circulation of spray to enhance entrainment with surrounding air, while improving roll-up and breakup in the spray tail region. Such investigation is conductive to better understanding the micro-breakup mechanisms of fuel spray in the spray-induced internal combustion engine. [ABSTRACT FROM AUTHOR]

Liquefied natural gas (LNG) is widely regarded as the midterm solution toward zero-carbon transportation at sea. However, further applications of gas engines are challenging due to their weak dynamic load performance. Therefore, the comprehension of and improvements in the dynamic performance of gas-engine-based power systems are necessary and urgent. A detailed review of research on mechanisms, modeling, and optimization is indispensable to summarize current studies and solutions. Developments in engine air-path systems and power system load control have been summarized and compared. Mechanism studies and modeling methods for engine dynamic performance were investigated and concluded considering the trade-off between precision and simulation cost. Beyond existing studies, this review provides insights into the challenges and potential pathways for future applications in decarbonization and energy diversification. For further utilization of clean fuels, like ammonia and hydrogen, the need for advanced air–fuel ratio control becomes apparent. These measures should be grounded in a deep understanding of current gas engines and the combustion characteristics of new fuels. Additionally, the inherent low inertia feature of electric power systems, and consequently the weak dynamic performance when adopting renewable energies, must be considered and studied to ensure system reliability and safety during transient conditions. [ABSTRACT FROM AUTHOR]

Recently, the environmental problem has become a global issue. The air to fuel ratio (AFR) in the combustion of thermal power plants directly influences pollutants and thermal efficiency. A research result was published showing that the AFR control performance of thermal power plants can be improved through supplementary control using dynamic matrix control (DMC). However, online optimization of DMC needs an extra computer server in implementation. This paper proposes a practical AFR control with one-step ahead control which does not use online optimization and can be implemented directly in existing distributed control system (DCS) of thermal power plants. Closed-loop transfer function models at three operating points are independently developed offline. Then, an online transfer function using interpolation of offline models is applied at each sampling step. A simple one-step ahead control with online transfer function is applied as a supplementary control of AFR. Simulations with two different type power plants, a 600 MW oil-fired drum-type power plant and a 1000 MW ultra supercritical (USC) coal-fired once-through type power plant, are performed to show the effectiveness of the proposed control structure. Simulation results show that the proposed supplementary control can effectively improve the conventional AFR control performance of power plants. [ABSTRACT FROM AUTHOR]

This paper presents results from the Sydney inhomogeneous burner for two gaseous hydrocarbons: methane (CH4) and propane (C3H8). These different hydrocarbons enable the exploration of fuels with significantly different stoichiometric air-fuel ratios (A/F) and hence mixing requirements in the burner. Stability limits of blow-off velocities vs. fuel jet recession, identify that both fuels exhibit improvement due to inhomogeneity, albeit occurring at different equivalence ratios. For CH4, the largest improvement due to inhomogeneity, compared to the homogeneous limit, was close to φ = 4.76, which corresponds to VA/VF = 2. For C3H8, the peak stability occurred at φ = 12, which interestingly also corresponds to VA/VF = 2. Rayleigh imaging at 10 Hz, performed at the burner exit plane, was used to identify the mixing profiles of the two fuels for different equivalence ratios. It was verified that the optimal recess distance coincides with the most stoichiometric samples contacting the pilot, with the samples augmenting the pilot heat release. The addition of N2 further reduced the inhomogeneous improvement, verifying that mixing and the mixture near the pilot controls the inhomogeneous stability. [ABSTRACT FROM AUTHOR]

Traditional incinerators achieve the thermal requirements through heat transfer and heat radiation. However, the early recovery of flue gas preheats the air and yields nitrogen oxide (NOx) to rise in the combustion of overoxygen. The operation of an incinerator inevitably implies the release of greenhouse gases and emissions of NOx harmful to the human health. The administrator of one laboratory incinerator in Taiwan sought to optimize the operation conditions such as temperature or oxygen level of the combustion products within the combustion chamber to minimize the release of pollutants and maximize the efficiency of combustion. In this phase, air-fuel ratio control and air volume control are regarded as the first priority. A numerical model of the laboratory-scale plant in southern Taiwan is established by using enhanced wall treatment and coupling the thermochemical conversion of volatile waste to the gaseous combustion of the released syngas. The model allows users to characterize the temperature and retention time of the combustion products for the verification of the fulfillment of the existing regulation for NOx and oxygen level in incineration plants. It shows trade-off relationship between combustion efficiency of fuel and emissions (NOx and CO) in surveying cases of air-fuel ratio (AFR) ranges from 1.5∶1 to 14.4∶1 according to numerical results. Increasing the air volume enhances this trend. In this study, it shows the lowest emissions of NOx in case of AFR=1.5∶1 , but worse combustion efficiency. Meanwhile, to increase the air volume by 1.15 times suppress most CO and about 28% NOx, but increases by 6% the residual fuel. The averaged distribution of retention time of particles in this study ranged from 30 to 50 s, and is provided for further improvement of geometry in the next phase. [ABSTRACT FROM AUTHOR]

Spurred by the world's attention to pollution emissions from commercial aeroengines, the International Civil Aviation Organization (ICAO) has made more stringent emission regulations for civil aircraft engines, especially the NOx emission. This paper develops a Five-Point lean direct injection (LDI) combustor with three swirler schemes to reduce the emissions of commercial aircraft engines. The flowfield of the combustor is studied numerically. Moreover, the combustion efficiency and gaseous emissions in different inlet conditions and fuel ratios of the main stage (α) are studied experimentally. The corresponding results reveal that, under a fuel-air ratio (FAR) between 0.0130 and 0.0283 and an a value between 30% and 60%, the combustion efficiency is 99.18%, 98.83%, and 99.03% when the pilot stage works alone, and 99.69%, 99.23%, and 99.75% when the pilot and main stage work simultaneously. Furthermore, the experimental results suggest that the NOx emission decreases as α increases, demonstrating that the convergent swirler has a tremendous advantage in reducing NOx emissions over Venturi. [ABSTRACT FROM AUTHOR]

In a global scenario, the exhaust emissions of automobiles need to be regulated. These emission regulations are met by maintaining the air-fuel ratio resulting in improved automobile performance like better engine torque and fuel economy. The air-fuel ratio of Spark Ignition (SI) engines needs to be maintained at a stoichiometric value of 14.7:1. To maintain this ratio, the estimation of the in-cylinder mass airflow rate is highly significant. One of the important parameters that influence the mass airflow rate is Manifold Absolute Pressure (MAP). The conventional methods that make use of MAP sensors have oscillations at engine firing frequency and poor dynamic response. This research paper uses an Unscented Kalman Filter (UKF) for the estimation of MAP in SI engines. The complete system consisting of the engine model and UKF algorithm has been simulated in Matlab/Simulink. With Root Mean Square Error (RMSE) as the performance metric, the accuracy in the estimation of MAP with UKF is higher than the Extended Kalman Filter (EKF). Hence, the UKF algorithm works out to be a better estimator for the efficient fuel injection in an engine management system. [ABSTRACT FROM AUTHOR]

Controlling the air-fuel ratio system (AFR) in lean combustion spark-ignition engines is crucial for mitigating emissions and addressing climate change. In this regard, this study proposes an enhanced version of the Aquila optimizer (ImpAO) with a modified elite opposition-based learning technique to optimize the feedforward (FF) mechanism and proportional-integral (PI) controller parameters for AFR control. Simulation results demonstrate ImpAO's outstanding performance compared to state-of-the-art algorithms. It achieves a minimum cost function value of 0.6759, exhibiting robustness and stability with an average ± standard deviation range of 0.6823±0.0047. The Wilcoxon signed-rank test confirms highly significant differences (p<0.001) between ImpAO and other algorithms. ImpAO also outperforms competitors in terms of elapsed time, with an average of 43.6072 s per run. Transient response analysis reveals that ImpAO achieves a lower rise time of 1.1845 s, settling time of 3.0188 s, overshoot of 0.1679%, and peak time of 4.0371 s compared to alternative algorithms. The algorithm consistently achieves lower error-based cost function values, indicating more accurate control. ImpAO demonstrates superior capabilities in tracking the desired input signal compared to other algorithms. Comparative assessment with recent metaheuristic algorithms further confirms ImpAO's superior performance in terms of transient response metrics and error-based cost functions. In summary, the simulation results provide strong evidence of the exceptional performance and effectiveness of the proposed ImpAO algorithm. It establishes ImpAO as a reliable and superior solution for optimizing the FF mechanism-supported PI controller for the AFR system, surpassing state-of-the-art algorithms and recent metaheuristic optimizers. [ABSTRACT FROM AUTHOR]

A reliable combustion monitoring system is essential to satisfy global carbon neutrality trends. As the concentrations of emissions and flame stability are associated with the air–fuel ratio, the equivalence ratio should be continuously evaluated. In this study, a deep neural network- (DNN-) based regression model is proposed to predict the equivalence ratio of turbulent diffusion flames. Chemiluminescence signals from the OH ∗ , CH ∗ , and C2 ∗ radicals were acquired as input features. In addition, three different optical sensing views were applied to consider the future general measurement conditions. Furthermore, a loss function comparison for model training and hyperparameter tuning techniques, such as random search and Bayesian optimization, were used to improve the prediction performance. Consequently, the enhanced DNN model showed reductions in the mean absolute error and root mean square error of ~17.84% and ~12.06%, respectively, compared with the initial model. In addition, a mean absolute percentage error and R -squared value of ~3.61% and ~0.9311, respectively, were obtained. Thus, a novel sensing method has been proposed for flame monitoring systems to realize future digital transformations in the combustion industry. [ABSTRACT FROM AUTHOR]

The air–fuel ratio (AFR) system helps reducing the rate of harmful pollutants in lean combustion spark-ignition engines and achieving optimal fuel consumption, thus, has a significant role in terms of protecting the environment and the consumer's budget. The AFR system includes time delays and presents uncertainties due to existing subsystems and requires an effective control method. Therefore, in this study, a feedforward (FF) compensated proportional-integral (PI) control method based on the enhanced weighted mean of vectors algorithm (En-INFO) is proposed for more effective control of the AFR system. The developed En-INFO algorithm was used to optimally determine the coefficients of the PI + FF controller. The initial performance of the En-INFO algorithm was tested against benchmark functions comparatively and its superiority was confirmed. To achieve optimal tuning of PI + FF controller, a modified integral of squared error objective function was also proposed. The AFR system control was performed using the optimal controller coefficients calculated by the En-INFO algorithm. The performance of the developed control structure was comparatively demonstrated using several analyses such as transient response, tracking performance, disturbance rejection and Padé approach techniques. The results revealed that the PI + FF control method based on the proposed En-INFO algorithm can be used as an effective method for the AFR system control. [ABSTRACT FROM AUTHOR]

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This paper considers optimizing the performance of high-temperature combustion chamber of an aero-engine based on a concentric and hierarchical model. First, sample data for the design variables are obtained based on Latin hypercube sampling method, and a one-dimensional program is used to obtain the true values of combustion efficiency and total pressure loss corresponding to each group of variables. The obtained data are then pre-processed to establish a dataset. Second, a multi-layer artificial neural network (ANN) architecture is designed and a surrogate model of the combustion-related performance of the combustor is established using a data-driven method. The results of global sensitivity analysis based on variance show that ratio of fuel flow to air flow (fuel–air ratio) and the total inlet pressure are the most important factors influencing the two objective functions. Finally, we optimize the multi-objective combustion-related performance of the surrogate model by applying the particle swarm optimization algorithm to it. The results of experiments show that the ANN-based model could accurately predict the efficiency of combustion and total pressure loss of the chamber, yielding root mean-squared errors of 0.0107 and 0.3032%, respectively. It also had better generalization ability than the cubic polynomial surrogate model. Compared with the cubic polynomial model, it generated an optimal Pareto solution set as prediction that had higher values in both objective functions. The proposed model might require better data that can be obtained using intelligent sampling methods so that deeper neural networks can be designed to reduce error and improve its optimization design. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of hydrogen-fueled, spark-ignited, single-cylinder Cooperative Fuel Research using experimental and numerical approaches. This study examines the effect of the air–fuel ratio on engine performance, emissions, and knock behaviour across different compression ratios. The results indicate that λ significantly affects both engine performance and emissions, with a λ value of 2 yielding the highest efficiency and lowest emissions for all the tested compression ratios. Combustion analysis reveals normal combustion at λ ≥ 2, while knocking combustion occurs at λ < 2, irrespective of the tested compression ratios. The Livenwood–Wu integral approach was evaluated to assess the likelihood of end-gas autoignition based on fuel reactivity, demonstrating that both normal and knocking combustion possibilities are consistent with experimental investigations. Combustion analysis at the ignition timing for maximum brake torque conditions demonstrates knock-free stable combustion up to λ = 3, with increased end-gas autoignition at lower λ values. To achieve knock-free combustion at those low λs, the spark timings are significantly retarded to after top dead center crank angle position. Engine-out NOx emissions consistently increase in trend with a decrease in the air–fuel ratio of up to λ = 3, after which a distinct variation in NOx is observed with an increase in the compression ratio. [ABSTRACT FROM AUTHOR]

Predicting engine efficiency for environmental sustainability is crucial in the automotive industry. Accurate estimation and optimization of engine efficiency aid in vehicle design decisions, fuel efficiency enhancement, and emission reduction. Traditional methods for predicting efficiency are challenging and time-consuming, leading to the adoption of artificial intelligence techniques like artificial neural networks (ANN). Neural networks can learn from complex datasets and model intricate relationships, making them promise for accurate predictions. By analyzing engine parameters such as fuel type, air-fuel ratio, speed, load, and temperature, neural networks can identify patterns influencing emission levels. These models enable engineers to optimize efficiency and reduce harmful emissions. ANN offers advantages in predicting efficiency by learning from vast amounts of data, extracting meaningful patterns, and identifying complex relationships. Accurate predictions result in better performance, fuel economy, and reduced environmental impacts. Studies have successfully employed ANN to estimate engine emissions and performance, showcasing its reliability in predicting engine characteristics. By leveraging ANN, informed decisions can be made regarding engine design, adjustments, and optimization techniques, leading to enhanced fuel efficiency and reduced emissions. Predicting engine efficiency using ANN holds promise for achieving environmental sustainability in the automotive sector. [ABSTRACT FROM AUTHOR]

The ignition reliability of combustor is related to the safety of the whole machine, especially the high-altitude ignition and combustion stability, which are the common requirements of the combustor. In this paper, the simulated altitude test facility was introduced. And the ignition performances of a linear combustor with five burners were carried out under the simulated altitude of 0–8 km, including the ignition boundary and flame propagation between burners. The process of flame propagation was recorded by a high-speed camera. The results indicate that the fuel-air ratio increases with the increase of altitude at the same pressure drop, and it decreases with the increase of pressure drop. For the period of ignition delay, the evaporation of droplets and the chemical delay process are mainly affected with the increase of altitude. At the altitude of 6 km to 8 km, flame propagates from burner to burner in an axial pattern, and the influence of altitude on flame propagation is mainly manifested in ignition delay and initial flame propagation. The key to improve the reliability of high-altitude ignition is to improve the fuel atomization and evaporation characteristics. The contribution of this article is to explore the mechanism of altitude on ignition characteristics and propose two methods to improve the high-altitude ignition characteristics. [ABSTRACT FROM AUTHOR]

Natural gas, which is also referred to as eco-friendly fuel, is being seen as a potential solution to challenge the decline of crude oil resources and the deteriorating air quality in urban areas. This fuel has been verified to emit less CO, HC, and PM compared to other fuels. A potential approach to reducing NOx and soot emissions while also achieving low fuel consumption is the low temperature combustion process. In this study, internal combustion engines were simulated under various conditions. The objective was to investigate the effect of different operating variables on the low temperature combustion mode. To begin with, a natural gas powered engine was modeled using complex chemical kinetics software. The outcomes of the simulation were then compared to experimental data, demonstrating a high level of agreement. Subsequently, the impacts of key variables, including the air-fuel ratio, compression ratio, and engine speed, were analyzed using a cycle simulation code. Increasing the compression ratio improves engine performance, and the specific fuel consumption decreases. However, it leads to a significant increase in NOx emissions until a certain value. Thereafter, it changes the trend. Engine speed indirectly affects performance by increasing fuel consumption and changing ignition timing. A leaner air fuel ration may be used to produce more power and keep the temperature of combustion below a certain value (low-temperature combustion), ensuring low NOx emissions. [ABSTRACT FROM AUTHOR]