Low Temperature Combustion Research Articles

Low-temperature synthesis of binder with belite content

Sol-gel methods or hydrothermal treatment in combination with low-temperature burning are used for low-temperature syntheses of hydraulically active dicalcium silicate. The paper describes a two-stage preparation process without the use of an autoclave. In the first phase, the precursors of hydraulically active phases are prepared. In the second phase, burning up to 1000 °C takes place to form a C2S-based binder. Unlike commonly used procedures of the sol-gel method, solid raw materials and water are used. The main raw materials are quicklime and a source of SiO2 and then various activators. X-ray diffraction analysis and electron microscopy methods were used for the research. The resulting binders are similar to hydraulic lime, they achieve low initial strengths, the long-term strengths are satisfactory. It is suitable for the preparation of mortars and plaster mixtures.

Synthesis, Characterization and Investigation of Optical and Electrical Properties of Polyaniline/Nickel Ferrite Composites.

Nickel ferrite nanoparticles are prepared by using a low-temperature self-propagating solution combustion method using urea as fuel. The prepared nickel ferrite nanoparticles were doped with polyaniline in the three different weight ratios of 10%, 30% and 50% by using an in situ polymerization method and by adding ammonium persulfate as an oxidizing agent. The obtained samples were characterized by using XRD, FTIR, SEM and a UV-visible spectrophotometer. XRD examined crystalline peaks of ferrites and amorphous peak of polyaniline and confirmed the formation of the composites. FTIR examined the chemical nature of samples and showed peaks due to polyaniline and the characteristic peaks that were less than 1000 cm-1 wavenumber were due to metal-oxygen bond vibrations of ferrites. AC conductivity increased with frequency in all samples and the highest AC conductivity was seen in polyaniline/nickel ferrite 50%. DC conductivity increased in all samples with the temperature showing the semiconducting nature of the samples. Activation energy was evaluated by using Arrhenius plots and there was a decrease in activation energy with the addition of ferrite content. The UV-visible absorption peaks of polyaniline showed shifting in the composites. The optical direct and indirect band gaps were evaluated by plotting Tauc plots and the values of the optical band gap decreased with addition of ferrite in polyaniline and the Urbach energy increased in the samples with 10%, 30% and 50% polyaniline/nickel ferrite composites. The optical properties of these composites with a low band gap can find applications in devices such as solar cells.

Enhanced low-temperature catalytic combustion of toluene over Cu and Mn co-modified α-MnO2 with flower spheres

MnO2, MnO2-M and MnO2-CM were successfully obtained by one-pot hydrothermal method using different precursors, and were applied for the catalytic oxidation of toluene. A variety of characterization means were used to precisely define the physicochemical characteristics of these catalysts. The Cu and Mn co-modified MnO2-CM shows a nanosphere morphology which is made of worm-like particles. And it exhibits better low-temperature catalytic oxidation activity, long term activity stability and H2O resistance, in which the temperature of 90% toluene conversion is about 207 °C and the apparent activation energy of MnO2-CM is as low as 31.7 kJ∙mol−1. This is due to the strong interaction between Cu and Mn from the redox coupling reaction (Cu+ + Mn4+ ↔ Cu2+ + Mn3+) that contributes to produce more oxygen vacancies in MnO2-CM to enhance the gaseous oxygen activation and supplement of active oxygen species at low temperature, leading to stronger oxidation ability.

Tyre pyrolytic oil blends in a state-of-the-art compression ignition engine: Towards fuel-optimised combustion

The end-to-end efficiency and environmental impact of tyre pyrolysis oil (TPO) are currently high on the agenda of worldwide research. However, most knowledge regarding combustion and emissions of TPO fuels comes from legacy (pre-Euro standard) engine platforms, operating in non-optimal combustion conditions. The few tests on modern automotive engines have used factory, diesel-optimised calibration maps and focus on only small TPO admixtures to diesel fuel (DF). The present work aspires to tackle these knowledge gaps by testing higher TPO admixture diesel blends in a state-of-the-art research engine realising low nitrogen oxides (NOX), partially premixed compression ignition. Measurement campaigns focus on accuracy in establishing fuel-to-fuel differences in emissions, also with consideration of unlegislated species. A combination of thorough combustion analysis and accurate fuel property characterisation allows evaluation of a calibration strategy that harnesses multi-pulse injection and a fully controlled air-path to mitigate emissions. This strategy enables an engine fuelled with a 40% TPO blend to realise low-temperature combustion in a wider area of the calibration map than is possible with DF. The most favourable NOX/particulate matter (PM) mode is extended towards high exhaust gas recirculation and early injection regimes. Adopting this dedicated engine control for TPO allows best-point NOX/PM emissions of 1.22 g/kWh and 0.18 g/kWh respectively, while maintaining the baseline indicated thermal efficiency target of 42%. Carbon monoxide and hydrocarbons emissions are elevated, but in terms of current EU Non-road Mobile Machinery Stage V limits, differences between TPO and DF are insignificant. However, regardless of calibration, TPO's chemical make-up causes increased emissions of sulphur oxides and aromatic hydrocarbons.

Oxidation behaviors of Hongqian heavy crude oil characterized by TG-DSC-FTIR-MS within full temperature regions

To better understand in-situ combustion (ISC) theory and reveal the oxidation behavior and mechanism of Hongqian (HQ) heavy crude oil, the thermo-oxidative characteristics and kinetics of HQ heavy oil were studied under air conditions using TG-DSC-FTIR-MS technique. According to the TG/DTG-DSC curves, the oxidation reactions of HQ heavy oil can be divided into low temperature oxidation (LTO), fuel deposition (FD) and high temperature combustion (HTC) stages. The reaction mechanism for each reaction interval was comprehensively analyzed by online FTIR and MS analysis. In FTIR spectra, H2O, hydrocarbon, CO2, CO, –COOH, and aromatic ring were observed during the oxidation process, which are used to explain the occurrence of the possible decomposition/isomerization of hydroperoxides in the later stage of LTO and the important role of light hydrocarbons evaporation, thermal oxidative cracking and polycondensation for coke formation at FD stage, coke combustion at HTC stage, as well as the possible hysteresis of dehydrogenation and aromatization at FD and HTC stages. The strong variation of activation energy with conversion degree confirms the complex oxidation reactions. MS analysis of H2, CH4, H2O, CO, O2, and CO2 produced during oxidation process helps to verify these reaction mechanisms; and provide more information about the in-situ H2 generation and the conditions where H2 generation may occur as well as the generation of CO and its possible reaction mechanism in LTO reactions. These obtained data aid in a deeper insight into crude oil oxidation mechanism and provide reference for establishing accurate reaction scheme and reaction kinetic model for the precise simulation of ISC processes.

Numerical Investigation of a Heavy-Duty Compression Ignition Engine Converted to Ammonia Spark-Ignition Operation

Abstract Global decarbonization requires the increased use of zero-carbon fuels. Compared to hydrogen, ammonia is easier to store, transport, and produce. In addition, products of complete combustion of ammonia are water and nitrogen. Therefore, ammonia is an ideal green fuel for internal combustion engines. Drawbacks relate to the high ignition energy and low laminar flame speed of ammonia. This three-dimensional numerical study investigated the potential of converting existing diesel engines to ammonia spark ignition operation. Results indicated a slower kernel inception process, but the speed of the fully developed turbulent flame was enough to complete the bulk combustion process despite the lower laminar flame speed. The problem with pure ammonia operation was the reduced combustion efficiency and the high level of unburned ammonia emissions since the slow spark inception process can be compensated by a larger compression ratio. The results also suggested that emissions formation and subsequent oxidation were a more complex phenomenon. For example, lean ammonia combustion produced higher nitrogen oxides (NOX) concentrations due to the nitrogen in the fuel, despite the lower combustion temperature. Moreover, advancing spark timing reduced the NOX emissions, which was opposite to the traditional spark ignition engines. Additionally, the ammonia in engine crevices that escaped the late oxidation process was the main source of nitrous oxide (N2O) species in the exhaust gas that usually do not appear in traditional engines. Overall, all these results suggested that more fundamental research on ammonia combustion is needed to understand its use in efficient, decarbonized engines.

An Experimental Study of Operating Range, Combustion and Emission Characteristics in an RCCI Engine Fueled with Iso-Propanol/n-Heptane

Recently, studies have been carried out using environmentally sustainable technologies with more efficient energy conversion to fulfill emission requirements. One of these technologies, reactivity controlled compression ignition (RCCI), is a low-temperature combustion mode and has a dual fuel strategy. The controllability of combustion, high thermal efficiency and low nitrogen oxide (NOx) and soot emissions are some of the most prominent advantages of this combustion mode. In this study, the effects of the premixed ratio (PR) and intake air temperature (IAT) on the operating range, combustion characteristics and emissions were investigated experimentally. In the experiments, iso-propanol and n-heptane were used as fuels. The experiments were carried out for two different case studies. In the first case, the experiments were performed at a 50 °C intake air temperature and three different premix ratios (PR25, PR50, PR75). The minimum brake-specific fuel consumption (BSFC) was 268 g/kWh and the widest operating range was obtained with PR25. In addition, the lowest emission values in NOx, hydrocarbon (HC) and carbon monoxide (CO) emission formation were recorded with the use of PR25 fuel. In the other case, experiments were conducted at three different intake air temperatures (30 °C, 50 °C, 70 °C) with PR50. The minimum BSFC was measured as 268 g/kWh and the widest operating range was observed at a 70 °C intake air temperature. At the same time, the lowest NOx emission values were obtained at a 30 °C intake air temperature. The maximum HC emission was determined as 586 ppm at a 30 °C intake air temperature. In addition, the minimum CO emission was measured as 0.142% by volume at a 70 °C intake air temperature.

New insights into electronic structure effect of the SnMnOx nanorod catalysts for low-temperature catalytic combustion of o-dichlorobenzene.

For the catalytic combustion reaction of chlorinated volatile organic compounds (CVOCs), the electronic structure of the catalyst surface are important factors in determining the activity, selectivity, and chlorine-resistance stability. Herein, a series of SnMnOx catalysts for the catalytic combustion of CVOCs were prepared by the changing of Sn-doping way to regulate the electron valance state of Mn element, including reflux (R-SnMnOx), co-precipitation (C-SnMnOx) and impregnation (I-SnMnOx). It was discovered that the R-SnMnOx catalyst had better activity and chlorine resistance than the R-MnOx, C-SnMnOx and I-SnMnOx catalyst, and the doping ways of Sn in MnOx catalyst could regulate greatly the surface acidity, active oxygen species, the chemical state of Mn&+ species, and redox ability. Especially, the R-SnMnOx catalysts exhibit excellent water resistance, and the reasons were related to the strong interaction of Sn&+ and Mn&+, which could promote obviously the dispersion of active Mn species, form a large number of acid sites, provide the abundant lattice oxygen species, and own the excellent redox ability, which accelerate the rate of charge transfer between Sn&+ and Mn&+ (Sn4++Mn2+→Sn2++Mn4+) to produce the abundant active species and accelerate the rapid conversion of benzene and intermediates conversion.

Deep reinforcement learning to discover multi-fuel injection strategies for compression ignition engines

Over the past several decades, regulation of compression ignition engine emissions has become increasingly stringent as concern about the environmental and health implications of these emissions has grown. These changing constraints have led to a series of new, alternative fuel injection strategies that aim to maintain power output while reducing in-cylinder generated emissions by operating in the low-temperature combustion (LTC) regime. These advanced injection strategies are created and retuned for individual combinations of engine geometry, fuel, and emissions constraints. Deep reinforcement learning has been shown to be an effective alternative to traditional optimization approaches for highly combinatorial control problems, such as discovering the optimal injection schedules for compression ignition engines. In this study, we deploy a previously presented deep reinforcement learning framework to iteratively optimize a series of engine geometries over a range of increasingly strict NO x emissions regulations. We then examine the resulting injection schedules. We discuss the potential for using this deep reinforcement learning framework for fuel selection screening and for discovering unique injection strategies for different engine geometries and future emissions standards.

Role of Mg–O on phase stabilization in solution combustion processed rocksalt structured high entropy oxide (CoCuMgZnNi)O with high dielectric performance

High entropy oxide (CoCuMgZnNi)O with a phase pure rocksalt was synthesized using low-temperature solution combustion. The precursors were found to combust at 270 °C and 400 °C was considered to be the formation temperature. The high entropy rocksalt oxide (HERO) fully stabilized at 1000 °C shows a single-phase, fcc rocksalt structure with an Fm-3m space group. HERO displays one of its parent oxide Mg–O structural properties as both belong to the cubic family and had lattice parameters very close to each other. The lower cation systems exhibited a transition from spinel to rocksalt structure with the addition of Mg–O. Raman of HERO affirmed a completely disordered occupancy of various metal cations, the formation of HERO at 400 °C, and phase stabilization at 1000 °C. Dielectric measurements at room temperature showed high permittivity (κ) with magnitudes ∼1.9 × 103, 4.7× 101, and 0.9 × 101 at 100, 1k, and 100k Hz.

Experimental Characterization of Hydrocarbons and Nitrogen Oxides Production in a Heavy-Duty Diesel–Natural Gas Reactivity-Controlled Compression Ignition Engine

Reactivity-Controlled Compression Ignition (RCCI) combustion is considered one of the most promising Low-Temperature Combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. Due to the spontaneous combustion of a lean, nearly homogeneous mixture of air and low-reactivity fuel (LRF), ignited through the direct injection of a small quantity of high-reactivity fuel (HRF), RCCI (dual-fuel) shows higher efficiency and lower pollutants compared to conventional diesel combustion (CDC) if run at very advanced injection timing. Even though a HRF is used, the use of advanced injection timing leads to high ignition delays, compared to CDC, and generates high cycle-to-cycle variability, limited operating range, and high pressure rise rates at high loads. This work presents an experimental analysis performed on a heavy-duty single-cylinder compression ignited engine in dual-fuel diesel–natural gas mode. The objective of the present work is to investigate and highlight the correlations between combustion behavior and pollutant emissions, especially unburned hydrocarbons (HC) and oxides of nitrogen (NOx). Based on the analysis of crank-resolved pollutants measurements performed through fast FID and fast NOx systems under different engine operating conditions, two correlations were found demonstrating a good accordance between pollutant production and combustion behavior: Net Cyclic Hydrocarbon emission—cyclic IMEP variations (R2 = 0.86), and Cyclic NOx—maximum value of the Rate of Heat Released (R2 = 0.82).

Designing main-group catalysts for low-temperature methane combustion by ozone

The catalytic combustion of methane at a low temperature is becoming increasingly key to controlling unburned CH4 emissions from natural gas vehicles and power plants, although the low activity of benchmark platinum-group-metal catalysts hinders its broad application. Based on automated reaction route mapping, we explore main-group elements catalysts containing Si and Al for low-temperature CH4 combustion with ozone. Computational screening of the active site predicts that strong Brønsted acid sites are promising for methane combustion. We experimentally demonstrate that catalysts containing strong Bronsted acid sites exhibit improved CH4 conversion at 250 °C, correlating with the theoretical predictions. The main-group catalyst (proton-type beta zeolite) delivered a reaction rate that is 442 times higher than that of a benchmark catalyst (5 wt% Pd-loaded Al2O3) at 190 °C and exhibits higher tolerance to steam and SO2. Our strategy demonstrates the rational design of earth-abundant catalysts based on automated reaction route mapping.

Modulating the exposed facets of CeO2 nanorods by MoO42– inducing to promote low-temperature photothermocatalytic toluene combustion

Photothermocatalysis is a synergetic process with the participation of both thermal and light energies, and ceria is a promising candidate as photothermocatalysts for VOCs combustion. Nevertheless, how its exposed facets affect the photothermocatalytic activity remains dubious, since suitable facet control strategies are scarce. Herein, we exploit a “MoO42– inducing” method to modulate the exposed facets of CeO2 nanorods from (111) to (100) facet, and the effect of exposed facets on toluene combustion is systematically investigated. As compared to CeO2 nanorods with only the (111) facet, CeO2 nanorods with the (100) and (111) facets have more reducible Ce4+ and edge/corner defect-derived Ce3+ with stronger ability to capture O2, thereby leading to the higher thermocatalytic activity for toluene combustion; The Ce–O bonds at the (100) facet are more easily photoactivated, which is responsible for the more significant activity enhancement upon participation of both thermal and light energies. Additionally, in situ FTIR analysis shows that photothermocatalytic toluene combustion over ceria probably follows the process: toluene→ benzyl alcohol → benzaldehyde, benzoic acid, aliphatic aldehyde/acid→ anhydride → carbonate →CO2 and H2O. The work supplies new insight into correlation between ceria exposed facets and photothermocatalytic activity.

Investigations on reactivity controlled compression ignition combustion with different injection strategies using alternative fuels produced from waste resources

Reactivity-controlled compression ignition (RCCI) is a promising low-temperature combustion (LTC) strategy that results in low oxides of nitrogen (NOx) and soot emissions while maintaining high thermal efficiency. At the same time, RCCI leads to increased unburned hydrocarbon (HC) and carbon monoxide (CO) emissions in the exhaust, particularly under low loads. The current work experimented novel port-injected RCCI (PI-RCCI) strategy to overcome the high unburned emission limitations at low load conditions in RCCI. PI-RCCI is a port injection strategy in which low-reactivity fuel (LRF) is injected using a low-pressure injector, and the high-reactivity fuel (HRF) is injected through a high-pressure common rail direct injection (CRDI) injector. The low volatile HRF is injected into a heated fuel vaporizer maintained at 180°C in the intake manifold during the suction stroke. Modifying a single-cylinder, light-duty diesel engine with the necessary intake and fuel injection systems allows engine operation in both RCCI and PI-RCCI modes. Alternative fuels from waste resources such as waste cooking oil biodiesel (WCO) and plastic waste oil (WPO) are used as the HRF and LRF fuel in RCCI and PI-RCCI. To achieve maximum thermal efficiency in RCCI, the premixed energy ratio and the start of injection of the direct-injected fuel are optimized at all load conditions. The engine performance and exhaust emissions characteristics in PI-RCCI are compared with RCCI as a baseline reference. The results show a 70% and 48% reduction in CO and HC emissions, respectively, in PI-RCCI than in RCCI. Further, the brake thermal efficiency (BTE) was enhanced by around 20%, and the brake-specific fuel consumption (BSFC) was reduced by 13% in PI-RCCI. The NOx emissions decreased without any considerable changes in soot emission in PI-RCCI. The current study shows that fuels derived from waste resources can be used in RCCI and PI-RCCI modes with better engine performance and lower emissions.

CFD analysis of combustion and emission characteristics of biodiesel under conventional and late-injection based premixed combustion conditions

The simultaneous reduction in NOx and smoke emissions can be achieved with biodiesel under a late-injection based low temperature combustion (LTC) strategy. However, this occurs at the expense of a substantial increase in unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. It is worthwhile to understand the reasons behind the formation of these emissions, emphasizing comparison with conventional combustion, which is known to result in significantly low HC and CO emission levels, particularly with oxygenated biodiesel fuel. The present investigation attempts to examine the same with 3D CFD simulation. Experimental data were obtained from a light-duty diesel engine using biodiesel from non-edible Karanja oil. The unmodified engine with OEM low-pressure mechanical fuel injection system was utilized for conventional combustion operation. It is replaced with a modified common rail injection system for a late-injection-based LTC mode of operation. By combining retarded high-pressure injection with EGR, sufficient premixing was sustained to enable late injection-based premixed combustion (LI LTC). The combustion simulation was performed using CONVERGE CFD tool, utilizing a two-component surrogate of methyl butanoate (MB) and n-dodecane to represent biodiesel. A reduced chemical kinetic mechanism, developed and validated in an earlier investigation on biodiesel combustion, was utilized in the current study. The mechanism was solved using the SAGE Detailed CHEMKIN solver in CONVERGE. Validation was conducted at two engine operating conditions defining low and high loads for both combustion modes. The cylinder pressure and heat release rates were predicted with a maximum error of 1.5 and 13%, respectively. The validated CFD tool was employed to compare and analyze the equivalence ratio, in-cylinder gas temperatures, and HC and CO contours between conventional and LI LTC modes. Under LTC mode, the cylinder pressure and heat release rates were predicted with a maximum error of 10 and 15%, respectively. The comparison revealed fuel-rich regions concentrated near the bowl in conventional combustion, while the fuel was spread throughout the combustion chamber in LI LTC mode with over-rich and over-lean regions near the cylinder wall. The cylinder temperature is significantly higher for conventional combustion than LI LTC mode. The O and OH radical concentrations are higher for conventional combustion, corroborating with lower CO emissions, as they aid in CO oxidation. Fuel-rich regions contribute to increased CO emissions, whereas over-lean regions at a low-temperature result in high HC emissions, exhibited by the emission contours. Possible countermeasures to reduce high HC and CO emissions in LI LTC mode include maintaining higher coolant temperatures to enable HC and CO oxidation in the near-wall regions and fuel injection system modification to alter the air–fuel mixing.

Effect of compression ratio and Miller cycle on performance of methanol engine under medium and low loads

Considering the excellent anti-knock property of methanol fuel and the fact that passenger car engines typically operate at medium to low loads, this paper increasing the compression ratio and adopting the Miller cycle to improve the engine's efficiency, based on a methanol engine with compression ratio of 9.5:1. Experimental research is conducted to analyze the engine's combustion and emission characteristics under different operating conditions. The research shows that increasing the compression ratio to 12:1 can effectively reduce methanol consumption under medium to low loads, and applying the Miller cycle on the compression ratio of 12:1 can further improve fuel economy at low loads. Increasing the compression ratio raises the engine's cylinder pressure, maximum pressure rise rate, and cycle-to-cycle variation, thereby enhancing the tendency for knocking. However, the Miller cycle can effectively alleviate this situation while reducing engine pumping losses. From the perspective of emissions at medium and low loads, the high compression ratio reduces CO and HC emissions but increases NOx emissions due to high combustion temperature. The Miller cycle's shorter combustion duration and lower combustion temperature result in higher CO and HC emissions compared to an Otto cycle at the same compression ratio, but NOx emissions are improved.

Large-eddy simulation of dual-fuel spray ignition at varying levels of methane diluted ambient oxidizer using FGM

In the current work, the Flamelet Generated Manifold (FGM) method is applied with large-eddy simulation (LES) to investigate the effect of methane on dual-fuel (DF) spray ignition. The diesel surrogate n-dodecane is injected as the so-called pilot fuel into selected lean methane–air mixtures, ranging from ϕCH4=0 to ϕCH4=0.75, at engine relevant conditions. The operating conditions are those of the completely characterized Engine Combustion Network (ECN) Spray A configuration, for which the modeling approach adopted in the present study was extensively validated. The specific purpose of this study is to extend and validate the FGM approach for dual-fuel combustion. In order to understand the interplay of chemistry and mixing, the ignition behavior of selected cases is investigated. It is found that both low and high temperature combustion (LTC and HTC, respectively) are increasingly retarded by higher values of ϕCH4, while the induction time between LTC and HTC is relatively insensitive compared to the ignition delay time (IDT). Analysis reveals a more prominent role of mixing for increased ϕCH4. The development of LTC and HTC are quantitatively analyzed for different cases. The transition from LTC to HTC is found to be highly correlated with the evolution of lift-off length (LOL), which on its turn is seriously affected by ϕCH4. The local flame behavior is analyzed via chemical explosive mode analysis (CEMA), suggesting a clear flame propagation due to diffusion towards lean mixtures after the ignition of the pilot fuel. Besides, it is found that diffusion helps to stabilize the flame in leaner mixtures, which is more important in DF combustion. The results show FGM to be a promising tool in modeling the DF sprays.

Development and evaluation of a skeletal mechanism for EHN additized gasoline mixtures in large Eddy simulations of HCCI combustion

Advanced Low Temperature Combustion modes, such as the Sandia proposed Additive-Mixing Fuel Injection (AMFI), can unlock significant potential to boost fuel conversion efficiency and ultimately improve the energy conversion of internal combustion engines. This is a novel improved combustion process that is enabled by supplying small (<5%) variable amounts of autoignition improver to the fuel to enhance the engine operation and control. Common, diesel-fuel ignition-quality enhancing additive, 2-ethylexyl nitrate (EHN), is doped into gasoline to enable Sandia LTGC + AMFI combustion. This manuscript focuses on the development of a reduced sub-mechanism for EHN chemical kinetics at engine relevant conditions that is implemented into a skeletal mechanism for chemical kinetic studies of gasoline surrogate fuels. The mechanism validation utilized zero-dimensional numerical simulations and comparison to shock tube ignition-delay data of pure and EHN-doped n-heptane. Additional validation is presented with Homogeneous Charge Compression-Ignition (HCCI) engine data of pure and EHN-doped research-grade E10 gasoline. Then, the mechanism was deployed in a 3-D computational fluid dynamics (CFD) using Large Eddy Simulations (LES) to model the HCCI engine experiments of 0.4% vol EHN additized E10 gasoline at several equivalence ratios. Simulations showed a very good performance of the mechanism, and the model accurately reproduced (a) the ignition point, (b) combustion phasing, (c) combustion duration, and (d) the peak of the heat release rates of the engine experiments. The results show that EHN promotes Low-Temperature Heat Release, ultimately driving the gasoline to autoignite at thermodynamic conditions where the fuel would not otherwise ignite. Overall, this work demonstrates a viable reduced chemical-kinetic mechanism for EHN and shows that it can be combined with a skeletal gasoline mechanism for CFD-LES analysis of well-mixed LTGC that matches well with experimental results. The CFD-LES analysis also shows the spatial distribution of EHN-fuel interactions that control the autoignition throughout the combustion chamber.

High-Pressure-Limit and Pressure-Dependent Rate Rules for Intramolecular Cyclization Reactions of α,β-Hydroxyl Hydroperoxyalkyl Radicals

ABSTRACT The cyclization reaction class of hydroxyl hydroperoxyalkyl radicals is one of the crucial reaction classes in low-temperature combustion mechanism of alcohols and alkenes. However, there is a lack of reports on accurate high-pressure-limit rate rules and pressure-dependent rate rules for this reaction class in literature. In this paper, 108 reactions are selected and divided into different classes according to the type of hydroxyl hydroperoxyalkyl radicals, the ring size of the transition states, and the position of the OH group. The energy barriers of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are calculated by the isodesmic reaction method, and the high-pressure-limit rate constants and pressure-dependent rate constants of all reactions are calculated using the TST and RRKM/ME theory, from which a high-pressure-limit rate rule and pressure-dependent rate rule for each subclass are established. It found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the calculated rate constants of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are different from those of analogous reactions in alkanes, which indicates the necessity of establishing the rate rules for the cyclization reactions of hydroxyl hydroperoxyalkyl radical. There are large differences in energy barriers and rate constants among the whole reaction classes of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals, so it is necessary to divide the cyclization reactions class into subclasses, and it is also shown that the pressure has a significant effect on the rate constants. In summary, accurate high-pressure-limit rate rules and pressure-dependent rate rules for the cyclization of hydroxyl hydroperoxyalkyl radicals have been developed in this study, which is helpful for the automatic construction of higher accuracy combustion mechanisms for alcohols and alkenes.

Study on chemical kinetics and NO behaviors in pre-chamber jet-induced ignition mode with ammonia

Ammonia has been supposed to be an important carbon-neutral fuel for the applications in future engines. Its unique physical and chemical properties have great effect on engine combustion. The pre-chamber jet-induced ignition mode can yield very high turbulent jet ignition energy, which should be favorable for the ammonia combustion. To study the effects of key initial parameters in this combustion mode, the ammonia combustion and NOx formation processes were analyzed deeply in constant volume combustion chamber. A 3D CFD model was developed and validated with the visualization experiments, and the initial pressures (Pin) and temperatures (Tin) were numerically studied. The comparisons of different Pin for constant fuel mass (CFM) and constant equivalence ratio (CER) showed that Pin with CFM affects the combustion phase and burning rate more obviously. A higher Pin reduces the NOx emission slightly for CER but leads to higher NOx obviously for CFM, and a higher Pin for CFM also results in a slightly higher N2O emission due to the lower combustion temperature. The comparisons of different Tin showed that a higher Tin can enhance the combustion process greatly, while it also results in higher NOx due to high activity of OH and HNO for HNO + OH → NO+H2O.