Increased Heat Release Research Articles

Experimental study of flame extension lengths and fire pattern lengths induced by the turbulent jet fire impinging on inclined wooden boards

The safety of producing and transporting flammable gas may be compromised by the occurrence of jet fires resulting from pipeline leakage. During such incidents, combustible obstacles can impede the development of vertical jet fires, leading to impingement. Wood, a typical building material, was chosen as a combustible solid for the experiment due to its ability to produce regular fire patterns on its surface when heated, making it useful for fire investigation. A series of experiments were conducted to examine the flame extension length and fire pattern length resulting from a jet fire impinging on inclined wooden boards with different nozzle diameters, inclination angles, and heat release rates. This work showed that, unlike non-combustible boards, the rate of increase in flame extension length beneath a wooden board continues to rise as the heat release rate increases. Additionally, the boards' ability to absorb heat during the initial stages of combustion affects the flame extension length at low heat release rates. This work introduces a new correlation that can predict the length of flame extension under wooden boards, addressing a gap in research on jet fire impingement on combustible ceilings. For the regular fire patterns left by jet fires impinging on wooden boards, a new correlation of fire pattern length with flame extension length for different inclination angles of wooden boards is proposed. Considering the characteristics of turbulence, a novel model for fire pattern length is introduced, incorporating the Karlovitz flame stretch factor, nozzle inner diameter, and fire source-wooden board spacing.

A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine

Article A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine Qian Wang *, Botian Guo, Lixuan Cao, Xu Liu, Yi Jiang, and Jiawei Yao School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China * Correspondence: qwang@ujs.edu.cn Received: 8 November 2023 Accepted: 22 January 2024 Published: 30 January 2024 Abstract: This study investigates the combustion characteristics of hydrogen catalysed biodiesel (HCB) ignited gasoline in an optical engine using the Reactivity Controlled Compression Ignition (RCCI) combustion model. The experiment uses a single injection strategy to determine the optimum injection timing for gasoline ignition by varying the HCB injection timing (-30 to -15° CAATDC) and the ratio of high to low reactivity fuel energy (10% to 30%), to investigate the gasoline premix ratio, and to analyse the flame development characteristics. The results indicate that as the HCB energy ratio increases, the in-cylinder pressure and heat release rate increase significantly, and the in-cylinder combustion temperature improves significantly. As the injection timing is delayed, the combustion phase shifts back, and when the injection timing is close to the upper stop, the in-cylinder combustion pressure and heat release rate increase first increase and then decrease. Based on the results, it can be concluded that optimising the HCB injection timing and energy ratio can effectively control the distribution of the fuel-air mixture in the combustion chamber, thereby improving combustion efficiency and emission performance. By strategically adjusting the injection timing, an ideal balance between fuel stratification and flame propagation can be achieved, which ultimately improves the overall combustion process. The results of this study provide valuable insights for the further development of combustion control strategies and contribute to the development of more efficient and environmentally friendly engine technologies.

Multi-objective optimization of a pipe energy pile with heat exchanger pipes subjected to chaotic advection

Shallow geothermal energy extraction through an energy pile system relies on the constant temperature available below the earth's surface at shallow depths. The energy pile system transfers the heat stored in the earth to a place of utility for space heating and cooling through fluid circulation, thus extracting geothermal energy. In this study, a 3D energy pile model comprising a helical heat exchanger pipe (HHEP) was developed and validated with the existing experimental data using a FEM-based software package. Further, it was hypothesized that replacing HHEP with a chaotic configured helical heat exchanger pipe (CHEP) would enhance thermal performance. The numerical analyses supported the hypothesis, where there was about a 15 % increase in heat release rate for energy piles containing CHEP. The above results form a basis for exploring the simulation results through laboratory scale model tests. Thus, an experimental setup was fabricated to conduct geothermal energy tests on a scaled pipe energy pile (PEP) model. The investigation was carried out by considering three design-input parameters: flow rate, pitch, and inlet temperature at three different levels with water and ethylene glycol as heat exchanger fluid (HEF) in a 4:1 ratio. The heat release rate of the PEP (Qp), heat flux per unit length of HEP (qpl), soil excess temperature (θs), total thermal resistance (TTR), and energy consumed (EC) were analyzed. Furthermore, multi-objective optimization using the MO-Jaya algorithm and multiple attribute decision-making (MADM) R-method were used to predict an optimal set of design-input parameters. Finally, a confirmation test was conducted to test the competence of the predicted parameters. The percentage variation between the predicted design input parameters and the experimental values was below 10 %.

Assessment of Agent Avoidance Behavior in the Face of Fire Hazards

ABSTRACT An assessment approach is proposed to assess the injury consequences of evacuation in the face of fire hazards, taking into account the spatial-temporal distribution of fire hazards and the time-varying location of agents. In this study, the diffusion process of fire hazards is simulated first using the fire dynamics simulator (FDS version 6.7.7) software, and an assessment approach is proposed, when fire hazards including toxic gases, thermal radiation, high temperature, and extinction coefficient are considered. Then, a novel fire avoidance model based on the modified social force model is proposed, and the impacts of heat release rate and soot yield on the injury consequences are discussed. The results demonstrate that an increase in heat release rate leads to an increase in the temperature and radiation values near the fire source, which directly raises the injury consequences. Soot yield primarily affects environmental visibility and thus the agent’s evacuation speed, which in turn affects the exposure time in fire hazards and injury consequences. Finally, the proposed fire avoidance model is compared with the existing radiation repulsive force model and the interaction force model between agents and fire. It is concluded that the proposed fire avoidance model can present a more reasonable fire avoidance behavior with significantly less cumulative injuries than the existing fire avoidance models.

Energetic characteristics of highly reactive Si nanoparticles prepared by magnesiothermic reduction of mesoporous SiO2

In this study, highly reactive silicon nanoparticles (h-Si) were successfully prepared by an improved magnesiothermic reduction process with ∼ 100 nm mesoporous silica nanoparticles as templates. The prepared h-Si have an average particle size of 18 nm, an active content of 85 %, and a specific surface area of 69.2 m2/g. Meanwhile, the preparation process is simple, green (avoiding the use of HF), and shows a great improvement in the inhibition of side reactions. The energetic characteristics of h-Si were compared with those of commercially available silicon nanoparticles (c-Si) by using ultrasonically mixed KClO4 as the oxidizer. Thermal analysis indicates that h-Si/KClO4 has an advanced reaction onset temperature, increased heat release, and lower reaction activation energy. In constant-volume combustion tests, h-Si/KClO4 shows excellent ignition and combustion characteristics in the fuel-rich state. In addition, electrostatic discharge sensitivity tests indicate that the minimum ignition energy of stoichiometric h-Si/KClO4 exceeds 100 mJ, which is much more insensitive than that of n-Al/KClO4 (∼2 mJ). Overall, h-Si show enhanced reactivity and have attractive advantages in applications where suitable combustion properties and low electrostatic sensitivity are required.

Study on the Effect of High-Concentration Oxygen Enrichment on Engine Performance and Exhaust Emissions Using Diesel Fuel and Palm Biodiesel Substitute Fuel

Air pollution remains a big issue in many countries. One form of air pollution comes from the use of fossil fuels as the primary fuel in the power generating and transportation sectors. Diesel engines are employed in a variety of industries due to their dependability, durability, and efficiency. Enhancing the availability of oxygen within the combustion chamber is one technique for reducing exhaust gas emissions and optimizing diesel engine combustion. The aim of this study is to investigate how oxygen enrichment in diesel engines with diesel fuel and biodiesel affects their performance and emissions. The modeling in this research was carried out using AVL BOOST version 2011 software based on experimental results of the YANMAR TF 155 R-DI diesel engine at 1200 rpm with and without oxygen enrichment. Modeling was performed based on the baseline parameter of a diesel engine with gradual loads at 50%, 75%, and 100%. The oxygen concentration was increased to 30.6%, 37.8%, 45%, and 54% by mass. The results show an increase in the maximum heat release rate (HRR) and the mass fraction burned (MFB) up to 90% for both fuels. The peak heat release rate of biodiesel shifts around 6 J/degree and the brake-specific fuel consumption (BSFC) is up to 0.0035 kg/kWh higher than that of diesel fuel. When compared to diesel fuel, the thermal efficiency and BSFC of biodiesel usage are around 0.3% and 0.028 kg/kWh, respectively. NOx emissions increase due to higher combustion temperatures and more oxygen availability. Biodiesel emits 50% less NOx than diesel fuel, presumably due to a lower combustion temperature. As a result, while high-concentration oxygen enrichment improves combustion and lowers soot emissions, it raises NOx emissions. Soot emissions were reduced as a result of the enhanced combustion process, while NOx emissions rose due to higher combustion temperatures and increased oxygen availability.

Micron-sized iron particles as energy carrier: Cycling experiments in a fixed-bed reactor

Iron is a promising energy carrier with the potential to store substantial amounts of energy over extended time periods with minimal losses. For instance, the energy from green hydrogen sources can be used to reduce iron oxides, be stored or transported, and thus be regained by exothermic oxidation of the iron. This work explores the influence of oxygen partial pressure and temperature on the oxidation process in a fixed-bed reactor. Furthermore, the analysis extends to the reduction of oxidized iron particles at varying temperatures. The experimental findings highlight that both oxidation and reduction progress through the fixed-bed reactor as distinct reaction fronts. In the oxidation process, the speed of the reaction front increases with rising oxygen content and temperature, resulting in a higher reaction rate and a correspondingly increased heat release. Conversely, the reaction rate for reduction experiences a notable decrease for 600°C and 700°C. The reprocessability of the iron powder was validated for up to 16 cycles under the optimal reaction conditions established. Furthermore, it was demonstrated that the performance improves with an increasing number of cycles. This improvement is attributed to the formation of pores due to density changes and the subsequent creation of a larger surface area, mitigating the negative effects of sintering and agglomeration.

Longitudinal and azimuthal thermo-acoustic instabilities in an industrial gas turbine combustor operating at elevated pressure

This work numerically investigates longitudinal and azimuthal thermo-acoustic instabilities in the swirl-stabilised can-type industrial SGT-100 gas turbine combustor operated at elevated pressures of 3 and 6 bar. Previous experiments have shown that the combustor is susceptible to self-excited flame oscillations sustained by a thermo-acoustic feedback loop at specific operating conditions. In order to gain a better understanding of this feedback loop, a fully compressible large eddy simulation method is applied. The unknown sub-grid scale turbulence-chemistry interactions are modelled via a transported probability density function approach solved by the Eulerian stochastic fields method. First, the reaction zones and global flame topology at both operating pressures are analysed and compared to experimental images providing good qualitative agreement. Radial profiles of time-averaged and root-mean-square quantities furthermore demonstrate good quantitative agreement with the available measurement data. The applied simulation approach is capable of successfully reproducing self-excited thermo-acoustic instabilities in the longitudinal direction. The fundamental frequency of the predicted limit-cycle oscillation matches the experimentally measured frequency with high accuracy. Similar to the experimental observations, the fluctuation amplitudes of the pressure and global heat release rate increase significantly upon increasing the mean operating pressure from 3 to 6 bar. In addition to the dominant longitudinal mode, a high-frequency, low-amplitude azimuthal mode is also identified at both pressures. This azimuthal mode is periodically amplified and attenuated by the superposed longitudinal mode and induces small asymmetric (around the burner circumference) fluctuations of the local fuel and total mixture mass flow rates entering the flame region.

Varying Heat Release Rates per Unit Area – The Impact in Underground Mines

Abstract The fire behaviour and smoke behaviour of a fire in an underground mine will be largely dictated by the heat release rate of the fire. The heat release rate per unit area is generally the output from small-scale fire experiments and can be applied for larger objects with varying surface area. This paper studies the impact of varying heat release rate per unit area for fires in materials and substances typically found underground. Data from earlier fire experiments were analysed and discussed, and several different heat release rate curves and flame spread velocities for various fuel components were developed and discussed. It was found that the hydraulic hose presented the highest peak heat release rate per unit area of the solid fuel items, followed by the low-voltage cable, cab interior, and tyre in descending order. The increase in the peak heat release rate was highest for the highest incident heat flux levels, representative for scenarios underneath a mining vehicle. The heat release rate per unit area of pool fires underneath a vehicle is significantly higher than a corresponding free burning case - attributed to the higher incident heat flux – but a gravel surface underneath a pool fire will reduce the heat release rate considerably. Line fires in larger bundles of electrical cables were modelled and found to attain the peak flame spread velocity more rapidly compared with a fire in hydraulic hoses. This was caused by the higher heat release rate of the initial fire and ignited segments in the electrical cable case.

Evaluation of an integrated electric power generation system with natural gas engines operating in dual mode through heat recovery with thermoelectric devices for hydrogen production

In the present investigation, an environmental, thermal, economic, and social analysis of an integrated system is carried out, which has as its function the production of hydrogen through the recovery of residual thermal energy from exhaust gases. The proposed integrated system consists of a thermoelectric generator and a hydrogen production bench based on the water electrolysis process. For the development of the research, an internal combustion engine fueled with natural gas was used, operating under four load conditions (25%, 50%, 75%, and 100%). From the environmental assessment, it is demonstrated that the implementation of the integrated system allows a decrease of 12.30%, 6.26%, and 7.90% in CO, CO2, and HC emissions. However, the addition of hydrogen causes a 9.9% increase in NOx emissions. Additionally, the implementation of the integrated system allows a 4.9% decrease in brake specific fuel consumption and a 4.9% increase in engine thermal efficiency. The improvement in engine thermal performance contributes to the 7% reduction in engine operating costs. On the other hand, it demonstrates an 8.7% reduction in the environmental and social impact cost and a 9% reduction in the ecological cost. Additionally, the integrated system minimizes the cost of environmental and social impact, as well as the ecological cost of polluting gases CO, CO2, and HC. The mixture of natural gas and hydrogen allows for a 4.70% and 7.59% increase in pressure and maximum heat release rate. In general, the proposed integrated system is a way to harness the thermal energy of exhaust gases for hydrogen production. In this way, it is possible to obtain an auxiliary fuel that improves the efficiency of the combustion process of the natural gas engine. This allows for minimizing energy losses in self-generation activities in Colombia, achieving better energy management and a reduction in operating costs.

Effect of hydrogen addition on CO emission and thermo-chemical state near wall during head-on quenching of laminar premixed methane/air flame

A computational model for premixed methane-air flame under the flame-wall interaction was established based on CFD software and experimentally verified. The head-on quenching process of premixed methane-air flame under different hydrogen additions was simulated. The changes in CO emission, quenching distance, and the distribution of CO near the wall under different hydrogen additions were obtained. With the increase of H2 addition, the mass fraction of HCO and the generation of CO increase. Moreover, the consumption of OH in R79: OH+H2=H+H2O increases, resulting in the weakening of the oxidation of OH to CO in R94: OH+CO=CO2+H, and the EICO increases. With the increase of H2 addition, the heat release rate increases, the quenching distance decreases, and the Peclet number (Pe) increases. With the increase of hydrogen addition, the mole fraction of CO in Region A gradually decreases, the mole fraction of CO in Region B first increases and then decreases, and the mole fraction of CO in Region C increases. The temperature drops first and then rises. Near the wall (y < 0.3 mm), the convection term and diffusion term dominate, and the heat transfer time is less than the generation time and oxidation time of CO, and the generation branch and oxidation branch of CO move to the low-temperature region. Far from the wall (y ≥ 0.3 mm), the reaction source term dominates, the heat transfer time is greater than the generation time of CO, less than the oxidation time of CO, and the oxidation branch of CO moves to low temperature. With the increase of hydrogen addition, the chemical time scale of CO decreases, and the generation branches and oxidation branches of CO move to higher temperatures.

Numerical study on upstream smoke propagation and induced airflow velocity in a tilted channel under natural ventilation

A series of fire simulations were executed to explore the upstream smoke propagation characteristics and induced airflow velocity in tilted channels under natural ventilation. The channel slope ranging from horizontal to 58% (30°) and five heat release rates were used. Simulative results indicate that the airflow introduced by stack effect can enable the upstream smoke spread to reach sub-critical, critical and super-critical states without forced longitudinal ventilation. Meanwhile, taking the effect of fire heat release rate and height difference between the fire source and the upper portal into account, a piecewise function is developed to estimate the induced airflow velocity. It is found that when Ld∗·Q∗0.2 is less than or equal to 1.05, the airflow velocity increases exponentially with the variety of dimensionless elevation difference, but slowly rises logarithmically when Ld∗·Q∗0.2 is greater than 1.05. Besides, for scenarios in the sub-critical state, the relationship between the induced airflow velocity and the upstream smoke backflow length is revealed, which demonstrates that the dimensionless reverse flow length is in inverse proportion to the 1.5 power of dimensionless airflow velocity. For scenarios in the critical and super-critical states, there is still smoke backflow upstream of the fire source at the early period of a fire. And the disappearing time of smoke backflow reduces exponentially with the increase of heat release rate and elevation difference. Based on dimensional analysis and simulative data, a novel predictive model for the backflow disappearing time is proposed.

Experimental Study on the Impact of Hydrogen Injection Strategy on Combustion Performance in Internal Combustion Engines.

Hydrogen is an ideal alternative fuel for internal combustion engines due to its fast combustion rate and near-zero carbon emissions. To further investigate the impact of the injection strategy on combustion performance under various excess air coefficients and loads, experimental methods were employed to systematically study injection timing, injection pressure, and dual injection. The results demonstrate that appropriately delaying hydrogen injection timing can improve the thermal efficiency by up to 2.6% and reduce NOx emissions of equivalent combustion by nearly 88%. While increasing the hydrogen pressure to 8 MPa does not directly enhance the thermal efficiency and emissions, it can reduce the injection pulse width by approximately 75%, allowing for more flexibility in delaying the injection timing. Delaying the secondary end of injection (SEOI) leads to a reduction of over 47% in NOx emissions for λ (excess air coefficient) values of 1.5 and 1.0. The combustion duration and ignition delay initially increase and then decrease with the delay in SEOI, depending on the movement state of the fuel jet. With the increase in secondary injection proportion (SIP), brake thermal efficiency increases by no more than 1%, but NOx is reduced by more than 43% for λ values of 1.5 and 1.0. In the case of ultralean conditions (λ = 2.3), increasing the SIP from 0 to 30% results in a nearly 14% increase in the peak heat release rate (HRR) and a 19% reduction in combustion duration.

Enhancing physiochemical properties and reactivity of landfilled fly ash through thermo-mechanical beneficiation

This study investigates the impact of thermo-mechanical beneficiation techniques on the physiochemical characteristics and reactivity of landfilled fly ashes (LFAs) obtained from power plants in Wyoming and Colorado, USA. Thermo-mechanical beneficiation significantly improved the physiochemical properties of LFAs, leading to a decrease in loss in ignition (LOI) and an increase in fineness. The results revealed improvements in the strength activity index of all LFAs after beneficiation, surpassing the minimum requirement of 75% at 28 days. Beneficiation also enhanced heat release and calcium hydroxide consumption, indicating improved pozzolanic reactivity. The findings demonstrated that as beneficiation temperatures increased, there was a significant reduction in LOI, with levels falling below 3% at temperatures above 450 °C. The relationship between LOI and heat release indicated that reducing LOI could enhance the reactivity of fly ash. However, there was an inflection point at certain LOI thresholds, suggesting that further reductions in LOI may not significantly impact hydration kinetics. The results also showed that the specific surface area of LFA was correlated with heat release and calcium hydroxide consumption, emphasizing the importance of increased fineness for enhanced reactivity. The study also found associations between calcium hydroxide consumption, heat release, and early- and later-age strength activity indices. Higher calcium hydroxide consumption corresponded to increased heat release and reactivity, which in turn contributed to greater strength development over time, particularly at later.stages.

Study on using nano magnesium oxide (MNMgO) nanoparticles as fuel additives in terebinth oil biodiesel blends in a research diesel engine

ABSTRACT In this study, the effect of adding metal nano magnesium oxide (MNMgO) to a diesel-biodiesel blend on combustion and emissions was investigated. Firstly, Gas Chromatography-Mass Spectrometry (GC-MS) was used to determine that the unsaturated fatty acid content of Terebinth oil (TO) was 76.4%. Then, the free fatty acid value (%FFA) of TO was calculated to be 5.8%, indicating that the biodiesel production needed to be carried out in two stages. The conversion of triglycerides to methyl esters was confirmed using Fourier Transform Infrared Spectroscopy (FT-IR) at a wavelength of 1438.8 cm-1. The produced biodiesel and MnMgO were mixed with diesel fuel in certain proportions to prepare experimental fuels. The fuels were tested under variable loads and at a constant engine speed of 1500 rpm. The results obtained show that MNMgO reduced carbon monoxide (CO) emissions by an average of 10.23% and hydrocarbon (HC) emissions by 17.18%, but increased nitrogen oxide (NOx) emissions by 2.21%. Additionally, there was a 1.67% increase in cylinder pressure (%CP) and a 7.82% increase in the net heat release rate (%NHRR), while the mean gas temperature (MGT) value decreased by 0.52%.

Efficient decarburization modification of coal gasification fine ash by microwave field activation

The presence of residual carbon in coal gasification fine ash (CGFA) significantly impacts its subsequent processing and utilization. This paper proposes and investigates the use of microwave field heating to decarburize CGFA, exploiting its favorable microwave absorbing characteristics attributed to its composite structure comprising carbon, iron, and water. The experimental results demonstrate an 81% reduction in the required time and a 74% decrease in energy consumption (based on preliminary calculations) to achieve a decarburization rate of 95% compared to conventional thermal electric furnace calcination methods. The treated CGFA exhibits optimized mineral species, reduced electron binding energy, enhanced solubility, and increased heat release intensity during hydration, leading to improved reactivity of mineral phases in alkaline environments. Furthermore, when used as supplementary cementitious material, the activity index of CGFA shows a remarkable 21% increase in macroscopic performance testing.

Fire design approach for modern vehicles with combustion or electrical engine

AbstractDue to climate changes and environmental considerations, the current transportation changes to modern vehicles with different vehicles models and engine types. Especially vehicles with alternative types of drive, such as electrical vehicles, are increasing. This raises the question of whether modern vehicles, such as electric vehicles, lead to an increased fire risk as well as an increased heat release rate (HRR). In this article, a new fire design approach for modern vehicles is presented to evaluate the fire risk of electric vehicles compared to vehicles with combustion engines with respect to the fire resistance of the structural elements in open car parks. For this purpose, HRRs of different vehicles are analyzed and an approximated approach for modern vehicles is derived. The methodology can be used for performance‐based design, where the HRR plays a fundamental role. Furthermore, modeling approaches of the vehicle dimensions are presented, which are based on statistical data of the German Federal Motor Transport Authority. The vehicle dimensions are used to determine the fire spread time between vehicles using a parameter study. Based on the statistical data analyses and the parameter studies, this article provides a new fire design approach for modern vehicles in fire.

Understanding the Role of Sea Surface Temperature and Urbanization on Severe Thunderstorms Dynamics: A Case Study in Surabaya, Indonesia

AbstractWithin the period 2014–2017, five hail events were reported in the city of Surabaya in Indonesia. Although deep convection commonly develops over the Maritime Continent, severe thunderstorms triggering hail events develop less frequently as specific atmospheric conditions are required. The rapid urbanization in Surabaya might have led to increased heat release to the atmosphere and to the deepening of convection, which raises the question of whether urbanization is the culprit of the recent hail events in Surabaya. Hence, for a selected hail event, we used the high‐resolution Weather Research and Forecasting model to understand the storm dynamics and to explore the role of urbanization, sea surface temperature, and aerosol concentration on the storm dynamics with a total of 11 scenarios. The control simulation reveals that low‐level convergence induced by a sea breeze creates instability. At the same time, the urban heat release enhances the energy supply to induce hail formation and retain the storm's lifetime over the city. A factor separation method revealed that the urbanization (added anthropogenic heat flux, urban aerosol, and the rise in building height) and the sea surface temperature increase contribute to the storm enhancement over Surabaya, producing two times higher updraft velocity, doubling the maximum graupel mass mixing ratio and finally resulting in 15%–30% higher accumulated precipitation over Surabaya, compared to the control simulation.

Study on the Effects of the Hydrogen Substitution Rate on the Performance of a Hydrogen–Diesel Dual-Fuel Engine under Different Loads

Due to having zero carbon emissions and renewable advantages, hydrogen has great prospects as a renewable form of alternate energy. Engine load and hydrogen substitution rate have a considerable influence on a hydrogen–diesel dual-fuel engine’s efficiency. This experiment’s objective is to study the influence of hydrogen substitution rate on engine combustion and emission under different loads and to study the impact of exhaust gas recirculation (EGR) technology or main injection timing on the engine’s capability under high load and high hydrogen substitution rate. The range of the maximum hydrogen substitution rate was determined under different loads (30%~90%) at 1800 rpm and, then, the effects of the EGR rate (0%~15%) and main injection timing (−8 °CA ATDC~0 °CA ATDC) on the engine performance under 90% high load were studied. The research results show that the larger the load, the smaller the maximum hydrogen substitution rate that can be added to the dual-fuel engine. Under each load, with the increase of the hydrogen substitution rate, the cylinder pressure and the peak heat release rate (HRR) increase, the equivalent brake-specific fuel consumption (BSFCequ) decreases, the thermal efficiency increases, the maximum thermal efficiency is 43.1%, the carbon dioxide (CO2) emission is effectively reduced by 35.2%, and the nitrogen oxide (NOx) emission decreases at medium and low loads, and the maximum increase rate is 20.1% at 90% load. Under high load, with the increase of EGR rate or the delay of main injection timing, the problem of NOx emission increases after hydrogen doping can be effectively solved. As the EGR rate rises from 0% to 15%, the maximum reduction of NOx is 63.1% and, with the delay of main injection timing from −8 °CA ATDC to 0 °CA ATDC, the maximum reduction of NOx is 44.5%.

Heat release characteristics of ammonia flames in MILD conditions

Ammonia (NH3) combustion is an attractive energy source with zero carbon dioxide (CO2) emissions and a potential hydrogen-combustion enabler. In addition, the availability of ammonia and its amenability to transportation make it appealing to future energy supply. To provide fundamental insights into the heat release characteristics of ammonia in moderate or intense low oxygen dilution (MILD) combustion, one-dimensional laminar and two-dimensional turbulent premixed flames are studied numerically. In particular, the flame structure and heat release distribution of ammonia and ammonia-hydrogen premixed flames are examined under conventional and MILD, and preheated conditions, respectively. The results show that stoichiometric ammonia MILD flames differ from normal ammonia flames producing NH2 earlier, which results in the formation of a radical pool that shifts the chemical pathway towards hydrogen-related chemistry. The NH2 radical serves as a precursor for the ammonia flame and characterizes the reaction zone, and plays a crucial role in bringing the explosive nature into the system. For fixed ratios of the root-mean-square turbulent velocity fluctuation to the laminar flame speed and integral length scale to the laminar flame thickness, the flame surface wrinkling is comparable between the stoichiometric ammonia flame at MILD and non-MILD conditions. Furthermore, the hydrogen enrichment of the lean ammonia flame results in a significant increase in heat release rate due to the preferential diffusion effect. The study also examines chemical markers to identify heat-releasing regions of the flames and proposes the use of NH2 × O (on a mass fraction basis) as a suitable indicator of regions with high chemical activity and correlates well with the heat release for the MILD and non-MILD ammonia flames as well as ammonia-hydrogen flames at both laminar and turbulent conditions.