Reactive Fuels Research Articles

Investigation of NO emissions and chemical reaction kinetics of ammonia/methane flames under dual-fuel co-combustion mode at elevated air temperature conditions

Utilising ammonia, which is one of the most promising carbon-free fuels, comes with the challenge of stable combustion due to its low reactivity. Therefore, advanced strategies are needed, including blending ammonia with highly reactive fuels or implementing innovative combustion techniques. For this reason, the present study proposes an ammonia-methane dual-fuel co-firing combustion mode. The second focus is to analyse the effect of preheating the main swirl air on NO emissions and examine the chemical kinetic reactions. Experimentally, chemiluminescence imaging was conducted to analyse OH* and NH2* emissions to evaluate the flame structure and reaction zones. Numerically, simulations were performed using a chemical multi-reactor network model to examine kinetics. By comparing the fully premixed combustion to the dual-flame co-burning mode, the NO emissions decreased by 80% in the latter case at T = 473K and ϕ = 0.6. The NH3 reaction pathway analysis shows a significantly higher percentage reduction of NO and NH2 reactions in dual flame mode compared to premixed flames. Preheating the main air impacts NO reactions in the dual flame mode, allowing for lower NO emissions.

Assessment of reactive-control compression ignition engine performance and emissions using spirulina microalgae biodiesel in conjunction with methanol as low-reactive fuel

AbstractDue to their numerous uses and great fuel economy, diesel engines have been around for millennia. Despite these benefits, diesel engines have been found to pollute the environment severely. Most of the problems were caused by these engines' combustion processes, engine loads, and exhaust particles. The RCCI engine used in the experiment has 20% lower fuel and 80% high reactive fuel. In this research, methanol, and algae biodiesel blends with dimethyl ether acted as lower and higher reactive fuels, respectively, and these fuels were used to analyze the performance and emission in the RCCI engine. Among the 80% of high reactive fuel, blends contain different proportions of algae biodiesel and diethyl ether such as 32B, 28B4ME, 24B8ME, 20B12ME, and 16B16ME. A single-cylinder, four-stroke RCCI engine with a speed of 1500 rpm is used for the experiment. In the tests, the brake power is varied from 1 to 5 kW with an interval of 1 kW. In the results, BTE, BSFC, and EGT engine performance as well as NOX, HC, CO2, and smoke emissions. According to the experimental findings, the fuel properties of 16B16ME show a calorific value of 34.7 /MJ kg-1 and BTE shows improvement for all additive added fuel and 16B16ME shows higher BTE of 32.5% than other fuel blends, Similarly NOx emission also reduced for 628 ppm for 16B16ME than other fuel blends. Therefore 16B16ME is a suitable blend than other blends in RCCI engine based on the experimental results achieved in the present research.

Study on the microscopic characteristics of pentanol/highly active fuel spray based on high-speed droplet tracking velocimetry technology

Pentanol blending with highly reactive fuels for internal combustion engines holds considerable promise. The atomization of sprays closely influences the efficiency and combustion characteristics of the system. Based on Particle Tracking Velocimetry and high-speed shadow imaging technology, we propose a method termed High-speed Droplet Tracking Velocimetry for analyzing spray particle size. Prior to conducting our study, we validated the reliability of High-speed Droplet Tracking Velocimetry through comparisons with the Malvern and Phase Doppler methods. This study utilized long working distance micro high-speed shadow imaging technology in a visualized constant volume combustion chamber to investigate the spray micro-characteristics of pentanol blended with highly reactive fuels, including Fatty Acid Methyl Ester, Hydrogenated Catalytic Biodiesel, and Diesel. The results indicate that under all operating conditions, the droplets of P20H80 (the volume fraction of 20 % n-pentanol mixed with 80 % Hydrogenated Catalytic Biodiesel) are smaller and more uniformly distributed, demonstrating the minimum Sauter Mean Diameter, characteristic diameter, and width of droplet size distribution. The droplet velocities of P20H80 are the lowest, followed by P20Di80 (the volume fraction of 20 % n-pentanol mixed with 80 % Diesel), and P20B80 (the volume fraction of 20 % n-pentanol mixed with 80 % Fatty Acid Methyl Ester) exhibits the highest velocities. These velocity differences among the three fuels generally remain within 10 %-20 % across various injection pressures. P20Di80 shows the highest Reynolds and Weber numbers, followed by P20H80, with P20B80 having the smallest values due to its intermediate physical properties. The gaps between each fuel type range from 20 % to 30 %.

A comparative study of effects of methane and hydrogen on ammonia combustion in air via reactive molecular dynamics

Ammonia (NH3) is a promising substitute for fossil fuels to achieve the net-zero emission targets. To improve the combustion performance of NH3, reactive fuels are added to the NH3 combustion. In the present study, the combustions of NH3, CH4/NH3, and H2/NH3 in air conditions were simulated using a reactive molecular dynamics method. Results suggest that whether the addition of CH4 and H2 could accelerate the consumption of NH3 and reduce NOX emissions depends on the fuel ratio of the reactive gas (CH4/H2) and NH3 molecules. The acceleration of NH3 consumption is significant at low H2/NH3 fuel ratios and high CH4/NH3 fuel ratios, as the addition of H2 and CH4 lowers the activation energy for NH3 combustion. NOX emissions are mitigated at low H2/NH3 and CH4/NH3 fuel ratios but increase at high fuel ratios. The pathways for NOx generation and de-NOx reactions were identified. This study unveiled the mechanism via which the reactive fuels affect the NH3 combustion performance from an atomic perspective. The findings will be useful for the design of high-efficiency and low-emission combustion chambers in ammonia-powered energy systems.

Shock tube and comprehensive kinetic modeling study of ammonia/diethyl ether (DEE) mixtures

Ammonia (NH3) is a promising alternative clean fuel due to its carbon-free and high hydrogen content, along with the well-established infrastructure for storage and distribution. To overcome the issue of the low reactivity of NH3, a feasible strategy is co-burning ammonia with highly reactive fuels. Diethyl ether (DEE) is considered a promising alternative and biomass-oxygenated clean diesel substitute. Therefore, the NH3/DEE blend is also a promising carbon neutral alternative fuel. In this work, we measured the ignition delay times (IDTs) of NH3/DEE mixtures with DEE fractions (XDEE) of 0.05, 0.10, 0.30, and 1.00 at equivalence ratios of 0.5, 1.0, and 2.0, pressures of 1.75 and 10 bar, and temperature ranges from 1102 K to 1673 K in a shock tube. The DEE-NH3 model was proposed in this work, which included the DEE sub-model, NH3 sub-model, and some new cross-reactions between N-containing species and C-containing species. The DEE sub-model from Shrestha et al. (Fuel Communications, 2022) was modified in this work, NH3 sub-model was from our previous work (Reaction Chemistry & Engineering, 2023). The DEE-NH3 model was extensively validated by the IDTs, laminar flame speeds (LFSs), and species profiles (SPs) of NH3/DEE mixtures as well as pure DEE and NH3. The comparison of the prediction performance between the DEE-NH3 model and the Shrestha model was conducted for the ignition, flame propagation, and NH3 consumption. The effects of the cross-reactions on the NH3/DEE ignition and combustion were studied in detail.

Ignition characteristics of ammonia-methanol blended fuel in a rapid compression machine

Ammonia has attracted wide attention in recent years as a carbon-free fuel. However, the low reactivity and combustion inertness of ammonia pose challenges to its applications in engines. Adding highly reactive fuels, such as renewable carbon–neutral methanol, offers a potential solution. To investigate the ignition characteristics of ammonia-methanol blended fuel, ignition delay time measurement and fast gas sampling under stoichiometric conditions with four ammonia blending ratios (20 % ammonia, A20; 40 % ammonia, A40; 80 % ammonia, A80; 95 % ammonia, A95) were carried out on a rapid compression machine under engine-relevant conditions. The effective thermodynamic conditions were 15–25 bar and 810–970 K. The concentrations of fuels NH3, CH3OH, and intermediate species N2O, CO, as well as products N2, CO2 were detected using gas chromatography. Chemical analysis was performed based on simulations using five ammonia-methanol reaction mechanisms. The ignition delay time results showed that the addition of methanol shortened the ignition delay time, with only a little change in ignition delay time beyond 20 % methanol content. Methanol significantly promoted the production of OH radical, leading to the enhancement of the overall mixture reactivity. The sampling results showed different consumption patterns of ammonia and methanol during the ignition process at different mixing ratios. For A80, methanol was consumed from the early stage of the ignition process, while ammonia consumption was negligible in the early stage. Conversely, for A95, ammonia consumption began in the early stage. This suggests that methanol and its intermediate species inhibited the consumption of ammonia, however, ammonia promoted the consumption of methanol. Chemical analysis further revealed that the inhibitory effect of methanol on ammonia consumption was weakened with the decrease of methanol proportion.

Combustion Efficiency of Carbon-neutral Fuel using Micro-Combustor Designed for Aerospace Applications

Recent advancements in the field of micro combustor research are growing for achieving high-performance systems in micro power generation and microelectromechanical devices. To mitigate the hazardous emissions from carbon fuels, as an alternative, zero-carbon-free fuels ammonia, and hydrogen are being explored in micro combustion processes. The distinctive feature of a micro combustor lies in its significantly higher area to volume ratio in comparison with traditional combustion systems, leading to accelerated combustion reaction rates. However, the small size of micro combustors poses a challenge in achieving efficient mixing of highly reactive fuels like hydrogen and ammonia with oxidizers. The unique properties of micro combustors can lead to differences in the combustion behavior of hydrogen and ammonia compared to larger-scale combustion systems. Hence, examining the performance of carbon-free fuels in micro combustors is crucial for the advancement of clean energy combustion systems. A numerical investigation on a Y-shaped micro-combustor was carried out to identify the aspects of non-premixed combustion of ammonia/air and hydrogen/air. The findings reveal that in the case of hydrogen combustion, stable flames were reached, even at low equivalence ratios. Therefore, the distinct combustion properties of hydrogen and ammonia result in varying NOx emissions, with hydrogen generally leading to higher NOx levels due to its higher flame temperature and increased thermal NOx production.

Effects of PODE substitution rate and fuel injection timing on combustion, emission characteristic and energy balance in PODE-gasoline dual direct-injection engine

Dual direct injection (DDI) mode allows two kinds of different reactivity fuels to be flexibly injected into the cylinders and offers lower pressure rise rate (PRR), CO and HC emissions than Reactivity Controlled Compression Ignition (RCCI) mode. Thus, a single-cylinder engine was modified to adopt two direct-injection systems to inject PODE and gasoline respectively in this paper. Due to high oxygen content and high cetane number, PODE was selected as a high reactivity fuel to replace diesel in the experiments. The effects of different PODE substitution rates(PSR), PODE injection timing(injP) and gasoline injection timing(injG) on the combustion, emission characteristics and energy balance were studied. The results concluded the using PODE-gasoline mode could increase the indicated thermal efficiency(ITE) and reduce exhaust losses compared to the diesel-gasoline mode. As PSR increased, it led to the increased ITE and effective power, decreased CO, HC emissions. Compared to the PODE late injection mode, the effective power and ITE were higher, and CO, HC emissions were lower in the PODE early injection mode. The coefficient of variation of IMEP(COVIMEP) for the DDI combustion was also in an acceptable range. Furthermore, an early injG could lead to higher ITE, lower COVIMEP, CO and HC.

Predicting the effects of direct-injected fuels co-powered by high-CO2 biogas on RCCI engine emissions using kinetic mechanisms and multi-objective optimization

High inert gas content in biogas resulted in poor burning and emissions attributes, though scarcely investigated in reactivity controlled compression ignition (RCCI). Established kinetic mechanisms were combined with multi-objective optimization to investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The work examined the impact of direct-injected high reactivity fuels (HRF) and port-injected Biogas at various inert gas (carbon dioxide, CO2) rates (25 – 45% vol), biogas fractions (40 – 70%), speeds (1600 – 2000 rpm), and loads (4.5 – 6.5 bar IMEP) on emissions of RCCI engine, experimentally. The findings revealed that while engine speeds greatly decreased CO (carbon monoxide) and NOx (nitrate oxide) emissions with rising unburned hydrocarbon (UHC) regardless of HRF employed, higher engine load significantly reduced UHC emissions. Diesel-biogas reduces NOx emissions and performs better in reducing CO and UHC emissions at lower speeds than B5-biogas, except in low-level loads. Although increasing CO2 impact led to a reduction in UHC and CO emissions, the biogas proportion was the most significant variable. The main factor influencing increased NOx emissions was engine load, which is inversely correlated with reduced NOx and increased particulate emissions owing to high CO2 content and biogas proportion. The premixed mode's optimisation outcome confirms the trade-off reduction at 5.5 bar IMEP, 35.586% CO2, and 50% fraction. As a result, running the RCCI engine with direct-injected diesel co-powered in equal proportion with high-CO2 biogas cuts the emissions trade-off dramatically, limiting the environmental repercussions of the emissions.

Laminar flame stability analysis of ammonia-methane and ammonia-hydrogen dual-fuel combustion

In recent years, dual-fuel combustion of ammonia blended with reactive fuels like methane or hydrogen has gained attention for reduced carbon emissions. This study investigates the stability of NH3-CH4 and NH3-H2 laminar propagating flames, utilizing experimental and numerical methods. It covers an extensive span of equivalence ratios (0.7–1.6), fuel compositions, and a variety of initial temperatures (300–600 K), as well as pressures ranging from 1 to 5 bar·NH3-CH4 blends exhibit stability across all equivalence ratios, with Markstein lengths of 0.02–2.49. In contrast, NH3-H2 flames display significant variations in Markstein lengths, ranging from 3.73 to −3.36 at an equivalence ratio of 0.7, particularly destabilizing fuel-lean flames due to heightened preferential-diffusional instabilities. Increasing ammonia content stabilizes fuel-rich flames but destabilizes fuel-lean ones. As ammonia content rises, both NH3-CH4 and NH3-H2 flames become more hydrodynamically stable due to flame thickening, although this can exacerbate flame instabilities when preferential-diffusional instabilities dominate. Additionally, preheating destabilizes both ammonia-methane and ammonia-hydrogen flames hydrodynamically, while pressure affects NH3-CH4 and NH3-H2 mixtures oppositely, destabilizing the former and stabilizing the latter due to reduced flame thickness. The addition of diluents stabilizes NH3-CH4 flames but destabilizes NH3-H2 flames, influencing Le and Ze numbers. Diluent addition significantly reduces the flame temperature gradient (up to 64 %), resulting in thicker flames and enhanced hydrodynamic stabilities. This research provides insights into the complexities of ammonia-blended dual-fuel combustion and its impact on flame stability under various conditions.

Coupling experimental and modeling approaches for understanding diethoxymethane low-temperature oxidation at high pressure

Diethoxymethane (DEM) has attracted significant attention as a potential renewable alternative fuel. The lack of detailed product species distributions for DEM oxdation led to insufficient exploration of its low-temperature oxidation chemistry. In this study, the low-temperature oxidation reactions of DEM were conducted using a jet-stirred reactor (JSR) coupled with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) under conditions of 10 atm, an equivalence ratio of 0.5, and temperatures ranging from 470 to 850 K. Identification and quantification of various oxygenated species were performed. Additionally, complementing our previous kinetic theoretical studies for low-temperature oxidation of DEM radicals, previously calculated rate constants were incorporated into an earlier DEM combustion model, accompanied by additional adjustments to the rate constants of hydrogen abstraction reactions by C˙2H3 radicals. The modified model exhibits good agreement between the predicted and experimentally obtained product mole fraction distributions. Remarkably, a relatively weak negative temperature coefficient (NTC) was observed under the studied conditions, highlighting differences in the self-ignition behavior of DEM compared to other highly reactive fuels. Analyzing the rates of production (ROP) in the modified model indicates that the use of oxygenated fuels might elevate the production of small-molecule oxygenated pollutants while reducing the formation of carbon soot precursors and consequently curbing soot generation. Moreover, keto-hydroperoxides (KHPs) were detected during the experimental process. This study lays a foundation for further detailed exploration of the DEM oxidation mechanism, aiding in untangling its intricate reaction processes.

Toward Zero Carbon Emissions: Investigating the Combustion Performance of Shaped Microcombustors Using H2/Air and NH3/Air Mixtures

The research effort in the microcombustor field has recently increased due to the demand for high-performance systems in microelectromechanical and micro power generation devices. To address rising concerns about pollutants from fossil sources, zero-carbon fuels such as hydrogen (H2) and ammonia (NH3) have been considered as an alternative in microcombustion processes. In a microcombustor, the surface area-to-volume ratio is much higher compared to conventional combustion systems, resulting in faster heat transfer rates and more intense combustion reactions. However, achieving efficient mixing of fuel and an oxidizer in a microcombustor can be challenging due to its small size, particularly for highly reactive fuels like H2. For NH3, challenges in microcombustion involve a low reactive, high ignition temperature (923 K vs. 793 K of H2) and high concentration of NOx combustion products. Therefore, studying the performance of these fuels in microcombustors is important for developing clean energy technologies. In this paper, to explore features of non-premixed NH3/air and H2/air combustion in micro-scale combustors, an Ansys Fluent numerical investigation was conducted on a Y-shaped microcombustor. Results show that for combustion with H2, stationary flames can be achieved even at lower equivalence ratios. Additionally, the pollutants generated from H2 in the flame are generally twice those of NH3. The overall efficiency of the microcombustor is two times greater for NH3 conditions than for H2 conditions.

Effect of Fuel Reactivity and Operating Conditions on Flame Anchoring in the Premixing Zone of a Swirl Stabilized Gas Turbine Combustor

Abstract Flashback with subsequent flame anchoring (FA) is an inherent risk of lean premixed gas turbine combustors operated with highly reactive fuel. The present study has been performed to characterize flame stabilization in the premixing zone of a lean premixed swirl stabilized burner and to identify critical combustion characteristics. An optically accessible burner was used for experimental investigations under atmospheric pressure and elevated preheat temperatures. The air mass flowrate, global equivalence ratio and preheat temperature were systematically varied to identify critical operating parameters. Hydrogen-natural gas mixtures with hydrogen mass fractions from 15 to 100% were studied to evaluate the impact of fuel reactivity. The air-fuel mixture was ignited with a focused single laser pulse to trigger FA in the premixing zone during steady operation. High speed imaging with OH*-chemiluminescence were applied to observe flame characteristics and evaluate flame anchoring propensity. Flame anchoring limits (FAL) are reported in terms of the minimum global equivalence ratio at which the flame was blown out of the premixing zone within a critical time period. A comparison of characteristic time scales at FAL shows that the main impact during flame anchoring is given by the fuel reactivity and to some ex tent by preheat temperature. A Damköhler criterion is derived from the FAL that allows prediction of FA propensity based on operating conditions and 1-D reacting simulations.

The relationship between fuel reactivity and exergy features in combustion process

Fuel reactivity is a flexible and feasible method to control combustion, thus reactivity-controlled compression ignition (RCCI) has the potential to achieve lower emissions and higher thermal efficiency. However, the exergy loss during combustion hinders the further exergy-work transform, which limits the thermal efficiency further improvement. The present work focuses on the relationship between fuel reactivity and exergy which contains exergy loss (EL) and thermomechanical exergy (Exthermo due to the temperature and pressure imbalance between system and reference state). By varying the reactivity of primary reference fuels (PRFs) with different initial boundary conditions, it is found that different PRFs could not reduce EL and change Exthermo under same condition but could change the exergy loss rate as well as the EL structure by influencing low-temperature combustion. In terms of boundary conditions, both high temperature and lean mixture could improve Exthermo but with different mechanism: high temperature saving EL into Exthermo, lean mixture recovering incomplete combustion exergy (Exincom) into Exthermo. By contrast, equivalence ratio more easily affects EL and Exthermo. In three-dimensional situation, it is found that decreasing reactivity of PRFs leads more in-cylinder area below equivalence ratio 1.0 which benefits for the Exthermo improvement, but it would cause Exthermo structure mutation which is unfriendly for the smooth output of work near top dead center. The conversion of fuel exergy to final useful work is indirect, and there exist two sub-processes: fuel exergy to thermomechanical exergy then thermomechanical exergy to useful work. The final exergy-work transform efficiency is influenced by both processes. Therefore, using low reactivity fuel as PRF90 in engine is favor of the exergy from fuel transforming into Exthermo by more lean mixture, adopting high reactivity fuel as PRF0 is favor of the Exthermo sequential structure which is benefit for the combustion control and useful work extract near top dead center. Therefore, there is potential to further improve the thermal efficiency by using a dual-fuel combination, with the low reactivity fuel creating a low equivalence ratio region to improve the thermomechanical exergy, and the high reactivity fuel achieving precise phase control during the combustion.

Probing the effect of fuel components on the auto-ignition behavior of ammonia/natural gas blends: A case study of ethane addition

Ammonia (NH3) is carbon-free and is known as a promising renewable fuel to achieve carbon reduction and carbon neutrality. However, ammonia presents much lower fuel reactivity compared to hydrocarbon fuels. Thus, ammonia is often blended with high reactivity fuels in practical combustion facilities, and natural gas is a good candidate due to its low carbon emissions and massive reserves. Methane is often used to represent natural gas in previous experimental and simulation studies, while the larger alkanes in natural gas can affect the fuel reactivity of ammonia/natural gas blends. This study aims to explore the effects of fuel components on the auto-ignition behaviors of ammonia/natural gas blends. As methane and ethane are the most important species in natural gas, a blend of 90 % methane and 10 % ethane by volume is used to represent natural gas in this study. A low-pressure shock tube was used to measure the ignition delay times (IDTs) of ammonia/methane, ammonia/ethane, and ammonia/natural gas blends in ‘air’ mixtures, with different ammonia blending ratios, at stoichiometric condition, at 1 atm and over the temperature range 1200 – 1800 K. The experimental results show that the IDTs of fuel blends increase with ammonia blending ratios. Meanwhile, 10 % ethane in natural gas can influence the fuel reactivity of ammonia/natural gas blends. A detailed kinetic model proposed in our previous study is used to simulate these new IDTs in addition to experimental data available in the literature. Overall, the kinetic model can predict well the auto-ignition behavior of ammonia/methane, ammonia/ethane, and ammonia/natural gas blends over a wide range of experimental conditions. The simulation and sensitivity analyses results show that the interaction reaction between ammonia and ethane, C2H6 + ṄH2 〈=〉 Ċ2H5 + NH3, is important for predicting the fuel reactivity of ammonia/ethane blends below 1600 K at the studied conditions.

Fuel reactivity stratification assisted jet ignition for low-speed two-stroke ammonia marine engine

Ammonia (NH3) has gained much attention as a carbon-free fuel due to its great potential to reduce carbon emissions in the shipping industry. However, ammonia is difficult to use directly in existing marine engines due to its low flame propagation speed and high auto-ignition temperature. In this work, a new combustion mode for low-pressure injection low-speed two-stroke ammonia marine engines: Reactivity Stratification Assisted Jet Ignition (RSAJI) is proposed and explored. The results of the study show that the RSAJI mode is very promising. Especially at low and medium loads, the peak pressure can be increased by 27.3%, and NH3 and N2O emissions in the exhaust gas can be reduced by 87.1% and 99.7%. Two key parameters: direct injection timing and ammonia substitution rate (ASR) determine the reactivity stratification in the main-chamber, which directly affects the jet ignition effect and turbulent flame speed. A thorough analysis of engine performance shows that the injection timing should be appropriately far from the Top Dead Center (75°CA BTDC & 86.4°CA BTDC). Further increases in ammonia substitution rates (ASR = 90%, 95%) will result in a reduction in power performance gains but will improve the indicated thermal efficiency (>50%).

Experimental investigation on the effect of injection timing and injection duration of low reactive fuels on RCCI mode of combustion operated with plastic pyrolysis oil

The goal study is to investigate the effect of low reactive fuels (LRFs) injection timing and duration of injection on a reactivity-controlled compression ignition (RCCI) engine. The diesel, mixtures of Karanja oil methyl ester (KOME), plastic pyrolysis oil (PPO) and ethanol are used as LRFs. The examined LRFs have the injection timings (ITs) of 40°ATDC, 45°ATDC, and 50°ATDC. Additionally, the influence of different LRFs injection durations (IDs) of 3, 6, and 9 ms, on the RCCI mode of combustion is included in the present work. The entire experimental process is performed at 75% of the rated power. According to the findings, at IT of 45°ATDC and ID of 6 ms, the Diesel-Gasoline mixture has the highest brake thermal efficiency (BTE) of all the ITs and IDs examined. Nitric oxide (NOx) emissions are higher for all ITs and IDs but smoke, carbon monoxide (CO), and hydrocarbon (HC) emissions are lower for the Diesel-Gasoline mixture compared to other fuel mixtures. Diesel-Gasoline produces a greater peak pressure rise (PPR) compared to other test samples at all ITs and IDs.

Ammonia/syngas MILD combustion by a novel burner

Ammonia has received increasing attention as one of the most attractive energy carriers because of its carbon-free nature and the established reliable and economic infrastructure for its storage and distribution. However, the low burning velocity and nitrogen-containment of pure NH3 can cause some challenges for its combustion control such as flame instability and large NOx emissions. To overcome these issues, strategies of co-burning NH3 with highly reactive fuels such as CH4 or H2 have been developed and applied. Syngas, which can be produced from biomass pyrolysis, is a promising alternative fuel in the transition from carbon-based fuels to carbon-free fuels. Therefore, comparing to co-firing NH3 with CH4, co-firing NH3 with syngas is a better environmentally friendly option to improve the NH3 combustion property. However, co-firing NH3 with syngas faces severer combustion instability, NOx emissions and NH3 leakage due to the low heating value of syngas. To the best of the authors’ knowledge, the NH3/syngas combustion with low NOx emissions and zero NH3 leakage has not been achieved in a lab-scale combustor. In the present study, NH3/syngas MILD combustion was carried out in a novel burner developed in our previous work. In the novel burner, the high-temperature and diluted air produced by the lean premixed syngas combustion is the key to accomplish the MILD combustion of NH3. The impact of the temperature and O2 mole fraction of the HTDA on the emissions of NO, NO2, N2O, NH3, and CO was experimentally investigated with varying equivalence ratios and NH3 flow rates. The chemical reactor network was employed to analyze the experimental observation from the chemical kinetic aspect.

Model predictive control of mixing controlled compression ignition operation for low reactivity fuels

Using gasoline or other low reactivity fuels with a pilot injection or port fuel injection in a compression ignition engine has shown great potential in reducing NOx emissions while keeping high thermal efficiency compared to diesel. However, excessive combustion noise is caused by a high maximum pressure rise rate in the cylinder due to the higher fractions of premixed charge of the low-reactivity fuel. This noise can result in structural damage to engine components and as such, combustion noise limits the range of the operating parameters and makes the control of such engines challenging. In this study, a simulation environment was built up in MATLAB/Simulink leveraging a physics-based zero-dimension combustion model to capture the in-cylinder pressure time traces as well as metrics relevant to thermal efficiency and combustion noise. In order to also facilitate the control of emissions, machine learning models were investigated to capture NOx emissions. A kernel-based extreme learning machine (K-ELM) performed best and had a coefficient of correlation (R-squared) of 0.998. The combustion and NOx emission models are valid for not only conventional gasoline fuel but also oxygenated alternative fuel blends at three different pilot injection strategies. In order to track key combustion metrics while keeping noise and emissions within constraints, a model predictive control (MPC) was applied for a compression ignition engine operating with a range of potential fuels and fuel injection strategies. The MPC is validated under different scenarios, including a load step change, fuel type change, and injection strategy change, with proportional–integral (PI) control as the baseline. The simulation results show that MPC reduces about 26% of ringing intensity in the transient process and 17% at the steady state for E30. Generally, MPC can optimize the overall performance through modifying the main injection timing, pilot fuel mass, and exhaust gas recirculation (EGR) fraction.

Ignition and Emission Characteristics of Waste Tires Pyrolysis Char Co-Combustion with Peat and Sawdust

The pyrolysis processing of waste tires is a promising technology for obtaining products with high marginality. One of the possible methods of solid pyrolysis product utilization is its combustion for energy production, but this is complicated by poor reactivity and sulfur emissions. The combustion of char together with more reactive fuels could solve this problem. The current study is devoted to the combustion characteristics of waste tires pyrolysis carbon residue mixed with biomass: pine sawdust and peat. The oxidation characteristics in thermal analyzer conditions were found to change insignificantly. In contrast, 15 wt% of peat and sawdust additives was found to decrease ignition delay times in realistic conditions of combustion at 800 °C by 42 and 78%, respectively, while the SO2 emissions also dropped by 73 and 52%, respectively. The extra sulfur was found to be contained in ash residue in the form of CaS and CaSO4. While increasing peat concentration from 5 to 15 wt% was found to have almost no effect, the same increase for sawdust resulted into an almost proportional decrease in ignition delay times. The results obtained could be used for the integration of waste tires pyrolysis char mixtures with peat or sawdust into the energy sector.