Combustion Performance Research Articles

Simulation study on diesel-ignited ammonia/hydrogen mixture fuel combustion on engine combustion and emission performance

This study focuses on a diesel/ammonia/hydrogen premixed engine, which ignites an ammonia/hydrogen mixture introduced through the intake manifold via in-cylinder direct diesel injection. Simulations were conducted to examine the impact of different ammonia/hydrogen mixing ratios on engine performance. The goal was to identify the optimal mixing ratio for this premixed engine to enhance combustion and emission characteristics. The results demonstrated that with a hydrogen mixing ratio of H10, the maximum in-cylinder pressure increased by 5.8% compared to H0, power output decreased by 0.8%, and fuel consumption rate increased by 1.7%. Additionally, ammonia slip decreased by 86.3%, NOX emissions increased by 13%, CO emissions increased by 7.4%, N2O emissions decreased by 79.2%, and CO2 emissions remained unchanged. Soot emissions were improved, leading to an overall enhancement in engine performance with hydrogen blending. To achieve the carbon neutrality goal of net-zero carbon emissions, a small amount of diesel ignition, combined with ammonia pre-injection in the intake manifold and a 10% hydrogen blend, presents a more effective solution. The findings of this study contribute to the advancement of ammonia fuel in internal combustion engines and provide theoretical guidance for its practical application. Research aimed at optimising in-cylinder combustion processes and controlling emissions enhances our understanding of the impact of alternative fuels on greenhouse gases and harmful emissions, thereby contributing to the reduction of pollutant emissions.

Approaches to control primary zone equivalence ratio and its effect on combustor performance

Approaches to control primary zone equivalence ratio and its effect on combustor performance

Hydrothermal pretreatment for enhanced thermochemical or biochemical conversion of pharmaceutical biowastes into fuels, fertilizers, and carbon materials.

Pharmaceutical biowastes, rich in organic matter and high in moisture, are typical light industry byproducts with waste and renewable attributes. Thermochemical and biochemical conversion technologies transform these residues into value-added bioproducts, including biofuels, biofertilizers, and bio-carbon materials. Hydrothermal pretreatment effectively removes toxic substances and enhances feedstock for these processes. This review comprehensively examines its role in improving the formation of bioproducts from pharmaceutical biowastes, focusing on (i) upgrading and denitrogenating solid biofuels with better combustion performance; (ii) enhancing biodegradability and gaseous biofuel production via organic matter decomposition; (iii) enriching soluble carbon and nitrogen for liquid biofertilizer; (iv) eliminating antibiotic residues and reducing antibiotic resistance in solid biofertilizers; and (v) stabilizing carbon and nitrogen structures and optimizing pore characteristics for functionalized carbon materials. The review recommends a potential staged thermochemical approach to co-produce nitrogen-enriched liquid biofertilizers and porous carbon materials from pharmaceutical biowastes. Hydrothermal pretreatment emerges as a key technique for facilitating the migration and conversion of essential elements like carbon and nitrogen. This study reveals the potential of hydrothermal pretreatment to address the limitations of pharmaceutical biowastes and offers insights into their valorization.

Study on preparation of new solid fuel and its combustion performance from bio-oil and waste cooking oil mixture via vacuum distillation

Study on preparation of new solid fuel and its combustion performance from bio-oil and waste cooking oil mixture via vacuum distillation

Effect of cavity depth on air-breathing rotating detonation engine fueled by liquid kerosene

In our recent experimental investigation, the feasibility of a liquid-kerosene-fueled air-breathing/ramjet rotating detonation engine featuring a cavity-based annular combustor has been experimentally demonstrated. Achieving stable operation and organized detonation combustion within the rotating detonation combustor presents significant challenges that demand further investigation. Thus, this study aimed to deepen our understanding of the optimal geometrical configuration of a cavity-based annular combustor operating in air-breathing mode. Numerous experiments were conducted to evaluate the impact of varying cavity depths on combustion performance under a supersonic incoming flow with a total temperature of 860 K. The findings indicate that adequate cavity depth is essential for the generation of kerosene-fueled rotating detonation waves in air-breathing mode. Notably, a kerosene–air rotating detonation wave was achieved in combustors with cavity depths ranging from 10 to 30 mm while maintaining a supersonic heated air mass flow rate of approximately 1000 g/s and a minimum equivalence ratio of 0.77. However, at a cavity depth of 10 mm, both the propagation velocity and peak pressure of the rotating detonation waves were significantly lower compared to those at 20 and 30 mm, thereby suggesting that the depth of 10 mm may require optimization. Additionally, optical observations revealed that the detonation reaction zone was located further from the combustor head as cavity depth increased. This indicates that deeper cavity depths allow for longer mixing and preheating times of the combustible mixture before detonation, thereby enhancing detonation performance. This study clarifies how cavity depth influences liquid-fueled rotating detonation and provides guidelines for designing cavity-based annular combustors in air-breathing rotating detonation engines.

Large eddy simulation of spray evaporation characteristics of alcohol-based fuels based on modified evaporation model with UNIFAC

An accurate description of spray atomization and evaporation behavior is an important prerequisite for studying fuel spray's combustion performance and emission characteristics, especially for multi-component blended fuels (e.g., alcohol-based fuels). To improve the simulation accuracy, the large eddy model combined with a modified evaporation model with UNIFAC is proposed to investigate the spray evaporation kinetics of the mixtures of alcohol and alkane under gasoline engine conditions. The model accuracy is verified from multiple perspectives, including bubble point pressure, bi-component droplet and spray evaporation experiments. Then the modified evaporation model with the UNIFAC coupled LES method is used to study the spray evaporation of alkane/ethanol mixtures. The conclusions are as follows: 1) Asymmetric vortex structures in the spray lead to circumferential inhomogeneous distribution of evaporation characteristics. 2) The vapor mass fractions are significantly higher than those of Raoult's law for small proportions of the bi-component mixtures E10 and E85. 3) The E10-NH spray evaporation rate and total evaporated mass were higher than E10. In conclusion, the modified evaporation model with the UNIFAC-coupled LES method captures the tiny turbulent vortex structures during spray atomization, which further reveals the evaporation mechanism of two-component alcohol-based fuels by spray atomization.

A study on the co-optimization design method of diesel engine in-cylinder combustion performance and steel piston heat transfer characteristics: A new pit array combustion chamber structure

Steel pistons have become the optimal solution for high-performance engines. However, the efficient design and widespread application of steel pistons are constrained by physical parameters such as high density and low thermal conductivity. In this paper, a parameterized structure of pit arrays on the center, bottom, and top surfaces of the combustion chamber was set up by utilizing the high mechanical strength of steel pistons. Subsequently, the diesel engine in-cylinder combustion performance and steel piston heat transfer characteristics were co-optimized for the design. Ultimately, the structure of the researched design with indicated specific fuel consumption and thermal stress control was obtained. The study results show that the top surface mass of the researched design can be reduced by 8.32 g. The researched design can exhibit better combustion and emissions performance. Moreover, the pit structure can allow the fuel to touch the wall with less energy loss, thereby alleviating the problems of fuel accumulation on the wall and wall-adhered combustion. In addition, the maximum thermal stress in the researched design decreases by 15.68 MPa, or 3.93 %, while increasing the highest temperature by only 2.30 °C compared to the original design.

Study on mixing and combustion performance of hydrogen micro-mixing combustor

Study on mixing and combustion performance of hydrogen micro-mixing combustor

Effect of intake air conditions on combustion and emission performance of ammonia-diesel dual fuel engine

Effect of intake air conditions on combustion and emission performance of ammonia-diesel dual fuel engine

Impact of flue gas recirculation methods on NO emissions and flame stability in a swirling methane burner

This study investigates NOx emissions and flame stability using three flue gas recirculation methods: air-side recirculation (FGR), fuel-side recirculation (FIR), and combined recirculation (FGR + FIR). Experiments are conducted with varying combustion air inlet temperatures, recirculation ratios, and equivalence ratios for methane–air flames in a 2 kW swirl burner. Nonintrusive in-situ measurements of O2 and NO are performed using tunable diode laser absorption spectroscopy (TDLAS), an advanced measurement technology. Among the three methods, FGR exhibits the widest extinction limit, while FGR + FIR reaches similar extinction limits to FGR with the supply of preheated combustion air. FGR + FIR reduces NO emissions by up to 65 % at a lean equivalence ratio of 0.8.Numerical simulations conducted using Cantera offer valuable insights into the NOx formation mechanisms. The NO emission indices decrease by 50 % for both FGR + FIR and FGR at a recirculation ratio of 20 %. NO production primarily results from thermal NO and NNH mechanisms. Notably, reaction fluxes for the N2O-intermediate mechanism are the lowest in FGR + FIR. FGR + FIR demonstrates approximately 50 % reduction of NO emissions at a 20 % recirculation ratio under stable combustion conditions in both experiments and simulations. This study proposes FGR + FIR as the optimal recirculation method for low-NOx burners, offering effective NOx emission control and stable combustion performance.

Comparative analysis on the normal vector features of the conventional inverted flame and ultra-lean residual flame

Residual behavior often appears near the flammability limit for lean premixed flames. Insight into it is beneficial to improve the lean premixed combustion performance further. Identifying the normal vector of the residual flame front plays a key role in revealing its structure and evaluating the weights of some main effects quantitatively. For the present residual flame with a high curvature, as the polynomial curve fitting method causes a noticeable error due to the Runge phenomenon, a non-equidistant central difference method is proposed. Subsequently, the normal vectors of the bluff-body stabilized residual flame and conventional inverted flame of 40%H2–60%CH4–air are obtained accurately and their differences are compared quantitatively. It is found that there are significant differences in the normal vector and flow structure features between the conventional inverted flame and residual flame behaviors. The normal vector of the conventional inverted flame always points at the upstream direction. However, the normal vector at the middle section of the residual flame front is almost parallel to the horizontal direction, and it points at the downstream direction next to the residual flame tip. In addition, the flow structure around the residual flame front is revealed. This is the first time the normal vector of the residual flame has been accurately visualized and the difference in normal vector feature between the residual flame and conventional inverted flame revealed. This work provides a universal and accurate method to identify the normal vector of the flame front and new insight into residual flame dynamics.

Enhancing the Combustion Performance of Solid Propellants by External Magnetic Field

Enhancing the Combustion Performance of Solid Propellants by External Magnetic Field

Research and evaluation of turbulent jet ignition mode for improving combustion performance of ethanol rotary engine

Improving the combustion performance of ethanol rotary engine (ERE) is crucial for enhancing energy efficiency and reducing emissions, particularly in the context of global emission reduction efforts. Although the application of ethanol as a clean alternative fuel is growing, research on optimizing its combustion in rotary engines remains limited. The novelty of this work lies in the comparison of two ignition modes: the conventional spark plug ignition mode (CSPIM) and the turbulent jet ignition mode (TJIM). Experimental validation and numerical simulation methods were employed to evaluate the effects of these two ignition modes on in-cylinder flow field and combustion characteristics. The results indicate that, compared to the CSPIM, the use of the TJIM significantly improves turbulence intensity, increases peak pressure, reduces combustion duration, and expands the flame propagation area, leading to an average increase of 0.42 kW in the power output of the ERE. Furthermore, the use of the TJIM leads to a 130 % average increase in NO mass produced in the cylinder, while CO emissions are reduced by 40 % on average. These findings demonstrate that the TJIM has significant potential to improve the combustion performance of ERE, offering considerable advantages in both efficiency and emissions control.

Comparative study on synthesis processes on soot combustion performance of Co Ce O catalysts

Comparative study on synthesis processes on soot combustion performance of Co Ce O catalysts

Energy and combustion performance of Al/PVDF composite films: Vapor-grown carbon fiber as a new additive

Energy and combustion performance of Al/PVDF composite films: Vapor-grown carbon fiber as a new additive

Volumetric reconstruction of soot volume fraction through 3-D masked Tikhonov regularization

The ill-posed nature of the tomographic inverse problem for soot volume fraction reconstruction often creates artifacts and provides lower reconstruction accuracy, particularly when viewing angles are limited. In this study, a volumetric masked-based 3-D Tikhonov regularization method is proposed to reconstruct soot volume fraction in a purely absorbing flame. The 3-D Tikhonov regularization method addresses the ill-posedness by penalizing unrealistic variations in the soot volume fraction, thus enhancing the robustness of the reconstruction. Additionally, volumetric masking derived from light field ray-tracing refines the reconstruction by accurately defining the flame's boundaries and improving the soot volume fraction inversion accuracy. Numerical simulations were conducted on a bimodal asymmetric flame to analyze the effects of varying viewing angles and volumetric masking strategies. Experimental studies were also performed to reconstruct soot volume fraction under different combustion operating conditions. Both numerical simulations and experimental studies demonstrate that the proposed method not only works on a limited number of viewing angles but also mitigates the reconstruction artifacts and decreases the computational costs.

High‐Performance Bio‐Benzoxazine Resins Derived From Natural Renewable Vanillin: Synthesis, Characterization, and Properties of Their Thermosets

ABSTRACTIn this study, we used vanillin and furfurylamine from renewable resources as starting materials and successfully synthesized an innovative derivative of bisbenzoxazine (MH‐fa) using the Mannich reaction. We characterized the chemical structure of the newly synthesized bisbenzoxazine compound using high‐resolution mass spectrometry (HR‐MS) technology. The results of nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy analysis (FT‐IR) confirmed the successful synthesis of the target compound. The synthesis of the benzoxazine copolymer (MH‐fa‐co‐DDM‐BMI) was achieved by leveraging the reversibility of the Diels–Alder reaction between the MH‐fa monomer and 4,4′‐bismaleimide diphenylmethane (DDM‐BMI). In addition, the investigation into the polymerization behavior of benzoxazine monomer and its corresponding main‐chain copolymer was conducted employing differential scanning calorimetry (DSC) along with in situ FT‐IR. We studied the thermal stability and combustion performance of two samples using thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC). The results revealed that the bio‐based bisbenzoxazine exhibited excellent heat resistance and flame retardancy. Specifically, poly(MH‐fa) exhibits a Td10 value of 350°C and a Yc value of 62.3% at 800°C. Furthermore, the material exhibits an extremely low heat release rate (20.4 J g−1 K−1), highlighting its potential applications in the field of high‐efficiency flame retardant materials.

Experimental investigation of nano-enhanced Azolla biodiesel blends for improved diesel engine performance and emission mitigation

Abstract This study investigates the performance and emission characteristics of a diesel engine fueled with Azolla microphylla biodiesel blends and the effects of aluminium oxide (Al2O3) and copper oxide (CuO) nanoparticles as fuel additives. Azolla microphylla, an aquatic fern, was used to produce biodiesel through a transesterification process. Diesel fuel was blended with Azolla biodiesel in ratios of 10:90 (B10), 20:80 (B20), and 30:70 (B30). Engine performance parameters, including brake thermal efficiency (BTE), brake-specific fuel consumption (BSFC), and emissions of carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and smoke, were evaluated. The results showed that the B30 blend exhibited the highest BTE under maximum load conditions. To address the high viscosity and poor combustion performance of higher biodiesel blends, Al2O3 and CuO nanoparticles were added to the B30 blend at concentrations of 50 ppm and 100 ppm. The B30 blend with 100 ppm Al2O3 nanoparticles demonstrated the highest BTE and the lowest emissions of HC, CO, CO2, and smoke compared to the other test blends. The improved combustion and reduced emissions were attributed to the enhanced heat transfer and catalytic properties of the Al2O3 nanoparticles. These findings suggest that Azolla biodiesel, especially when combined with Al2O3 nanoparticles, can be a viable and sustainable alternative to conventional diesel fuel.

Effect of Selective Non-Catalytic Reduction Reaction on the Combustion and Emission Performance of In-Cylinder Direct Injection Diesel/Ammonia Dual Fuel Engines

Ammonia, as a hydrogen carrier and an ideal zero-carbon fuel, can be liquefied and stored under ambient temperature and pressure. Its application in internal combustion engines holds significant potential for promoting low-carbon emissions. However, due to its unique physicochemical properties, ammonia faces challenges in achieving ignition and combustion when used as a single fuel. Additionally, the presence of nitrogen atoms in ammonia results in increased NOx emissions in the exhaust. High-temperature selective non-catalytic reduction (SNCR) is an effective method for controlling flue gas emissions in engineering applications. By injecting ammonia as a NOx-reducing agent into exhaust gases at specific temperatures, NOx can be reduced to N2, thereby directly lowering NOx concentrations within the cylinder. Based on this principle, a numerical simulation study was conducted to investigate two high-pressure injection strategies for sequential diesel/ammonia dual-fuel injection. By varying fuel spray orientations and injection durations, and adjusting the energy ratio between diesel and ammonia under different operating conditions, the combustion and emission characteristics of the engine were numerically analyzed. The results indicate that using in-cylinder high-pressure direct injection can maintain a constant total energy output while significantly reducing NOx emissions under high ammonia substitution ratios. This reduction is primarily attributed to the role of ammonia in forming NH2, NH, and N radicals, which effectively reduce the dominant NO species in NOx. As the ammonia substitution ratio increases, CO2 emissions are further reduced due to the absence of carbon atoms in ammonia. By adjusting the timing and duration of diesel and ammonia injection, tailpipe emissions can be effectively controlled, providing valuable insights into the development of diesel substitution fuels and exhaust emission control strategies.

Investigation on Flow Features and Combustion Characteristics in a Boron-Based Solid-Ducted Rocket Engine

Numerical and experimental approaches are conducted to investigate the flow features and secondary combustion performance induced by different air–fuel ratios in a boron-based solid-ducted rocket engine. The results indicated that the afterburning chamber flow features become more complicated owing to the multiple nozzles of the gas injector, and a number of recirculation zones are generated. Because of this, the mixing of the fuel gas and incoming air is enhanced. When the air–fuel ratio decreases, the heat release in the afterburning chamber increases continuously, which causes the pre-combustion shock train to continue to propagate upstream in the subsonic diffuser of the inlet isolator, along with the boundary layer separation zone also moving forward, and the stability margin of the direct-connect inlet decreasing gradually. Furthermore, the direct-connect inlet works at a critical state with an air–fuel ratio of 11.5. As the mass flow rate of the fuel-rich gas rises gradually, the engine thrust gradually increases, and the number of vortexes in the afterburning chamber and the corresponding region affected by the vortexes generally decrease. Meanwhile, the mixing and combustion of the fuel-rich gas and incoming flow were not substantially changed. Additionally, the combustion efficiency and specific impulse are proportional to the air fuel ratio.