Low Temperature Combustion Research Articles

A Double-Wiebe Function for Reactivity Controlled Compression Ignition Combustion Using Reformate Diesel

AbstractReactivity controlled compression ignition (RCCI) combustion has previously been proposed as a method to achieve high fuel conversion efficiency and reduce engine emissions. A single-fuel RCCI combustion strategy can have decreased fuel system complexity by using a reformate fuel for port fuel injection and the parent fuel (diesel) for direct injection. This paper presents a one-dimensional computational model of a compression ignition engine with single-fuel RCCI. A Wiebe function is used to predict the combustion process by representing the mass fraction burned (MFB) on a crank angle resolved basis. One single-Wiebe function (SWF) and two double-Wiebe functions(DWFs) were fitted to experimentally derive MFB data using the least-square method. The fitted results were compared with MFBs calculated from experimental data to verify the accuracy. The SWF did not fully capture the MFB curve with high fidelity while the detailed DWF captured the MFB curve within a root mean square error of 1.4%. The reduced double-Wiebe function (RDWF) also resulted in a predicted combustion profile with similar accuracy. Hence, the RDWF was used in a GT-power thermodynamic study to understand the effects of the low-temperature heat release (LTHR) fraction and combustion phasing on combustion characteristics. At optimum phasing of 5–10 crank angle degree after the top dead center, increasing the LTHR fraction from 20% to 60% resulted in the fuel conversion efficiency increasing from 39.5% to 41.1%, thus suggesting that the reformate fuel-based RCCI strategy is viable to unlock improved combustion performance.

A systematic study of the influence of 1-pentanol as the renewable fuel blended with diesel on the reactivity controlled compression ignition engine characteristics and Trade-off study with variable fuel injection pressure

Compared to conventional CI engines, the analysis on the advanced low-temperature combustion technologies like RCCI engines produces better thermal efficiency with a simultaneous reduction in smoke and oxides of nitrogen emissions. The purpose of this study is to examine the reactivity-controlled compression ignition (RCCI) engine characteristics using diesel as the high reactivity and 1-pentanol as low reactivity fuel. To analyse the influence of operating parameters (i.e., fuel injection pressure (FIP) (500, 750, and 1000 bar), an experiment was performed on a water-cooled single-cylinder engine (modified) for brake mean effective pressure (BMEP) of 2 and 4 bar at a constant speed of 2000 rpm. During the initial suction stroke, 1-pentanol (10%, 20%, and 30% energy share) is injected into the port. Tests were conducted at varying proportions (energy share) to calculate the optimum proportion of diesel and 1-pentanol. The findings were analyzed and mapped under the same working conditions as diesel fuel, and a 2.5% gain (max) in thermal efficiency is observed while utilizing a 1-pentanol blend in contrast to diesel. Smoke opacity (7.82%) and oxides of nitrogen (NOx) (3.42%) emissions were also lowered while employing the 1-pentanol/diesel blend. The ideal combination for minimizing emissions is the D70A30 blend at BMEP of 4 bar with a FIP of 1000 bar. According to this study, standard fossil fuel can be efficiently substituted with a 1-pentanol/diesel fuel combination in an RCCI engine.

Influence of 1-pentanol as the renewable fuel blended with jatropha oil on the reactivity controlled compression ignition engine characteristics and trade-off study with variable fuel injection pressure

Compared to conventional compression ignition (CI) engines, the analysis on the advanced low-temperature combustion technologies like reactivity-controlled compression ignition (RCCI) engines produces better thermal efficiency with a simultaneous reduction in smoke and oxides of nitrogen (NOx) emissions. Instead of petroleum-based fuels, biofuels obtained from jatropha oil are anticipated to be employed in the current research. The purpose of this study is to examine the RCCI engine characteristics using Jatropha oil as the high reactivity and 1-pentanol as low reactivity fuel. To analyze the influence of operating parameters (i.e., fuel injection pressure (FIP) (400, 500, and 600 bar), an experiment was performed on a water-cooled single-cylinder engine (modified) for medium load and full load operations at a constant speed of 2000 rpm. The biodiesel (B20) obtained from jatropha oil is inducted into the chamber directly which is produced by transesterification. During the initial suction stroke, 1-pentanol (10%, 20%, and 30% energy share) is injected into the port. Tests were conducted at varying proportions to calculate the optimum proportion of biodiesel and 1-pentanol. The findings were analyzed and mapped under the same working conditions as diesel fuel, and a 2.5% gain (maximum) in thermal efficiency is observed while utilizing a 1-pentanol-biodiesel blend in contrast to diesel. Smoke opacity (7.82%) and NOx (3.42%) emissions were also lowered while employing the 1-pentanol-biodiesel blend. The ideal combination for minimizing emissions is the BD70P30 (70% biodiesel + 30% 1-pentanol) blend at maximum load with a FIP of 600 bar. According to this study, standard fossil fuel can be efficiently substituted with a 1-pentanol-biodiesel fuel combination in an RCCI engine.

Soot emission reduction in n-hexadecane/cycloalkane mixtures combustion with the addition of Borane-dimethyl sulfide

Soot is carbonaceous particulate produced by incomplete combustion of hydrocarbon fuel, reducing the efficiency of energy utilization and affecting the environment and people’s health adversely. Naphthenic hydrocarbons are essential components in diesel and kerosene, generating great quantities polycyclic aromatic hydrocarbons (PAHs) and subsequently soot particles in the combustion process at high temperature. In this study, a new strategy of cycloalkane combustion at low temperature is developed to reduce the formation of the PAH soot-precursors in the combustion process to decrease soot emission. Borane-dimethyl sulfide (BDMS) and n-hexadecane were employed to promote the low-temperature ignition of cycloalkanes and the reduction of soot emission. By adding of 5% BDMS, the ignition temperature of hybrid fuel 10 (10 vol% n-hexadecane, 90 vol% cyclohexane) decreased drastically from 570 °C to 213 °C and PAH formation was reduced by 87%. In the flame development stage of the combustion process, the flame of BDMS/hybrid fuel 10 appears green in color and is larger than the blue flame in the stage of flame reduction, indicating the complete combustion of cycloalkane fuels. By this strategy of low-temperature combustion, the generation of PAH during combustion of cyclohexane decreases, thereby reducing the generation of soot and improving hydrocarbon fuels utilization.

Study on control-oriented emission predictions of PPCI diesel engine with two-stage fuel injection

Model predictive control (MPC) is an effective technology used to improve the control accuracy of low temperature combustion engines. The main purpose of this study is to establish a control-oriented emission prediction model based on fuel injection parameters, which provides the basis for the development of MPC controller for PPCI engines. In this study, the combustion model and backpropagation (BP) neural network emission prediction model of a partially premixed compression ignition (PPCI) diesel engine were established, through which the real-time combustion and emissions can be realized by inputting two-stage fuel injection parameters. The Wiebe function linearization method was proposed for the combustion model to achieve high-precision reconstruction of combustion at different fuel injection parameters. The nitrogen oxide (NOx) and particulate matter (PM) emissions were predicted using the combustion characteristics calculated by the combustion model. The results show that the established combustion model can accurately reconstruct the heat release rate and cylinder pressure of PPCI combustion, and the maximum error between the calculated and test values of the combustion parameters is less than 9%. The three-layer BP neural network can achieve high-precision predictions of NOx and PM emissions, with a prediction accuracy greater than 95%. Under the 300th continuous transient seconds, the cumulative prediction error of NOx was 2%, and the cumulative prediction error of PM was 4.9%, indicating high accuracy. This provides the basis for developing MPC controllers for PPCI engines.

Development and Validation of an EHN Mechanism for Fundamental and Applied Chemistry Studies

<div class="section abstract"><div class="htmlview paragraph">Autoignition enhancing additives have been used for years to enhance the ignition quality of diesel fuel, with 2-ethylhexyl nitrate (EHN) being the most common additive. EHN also enhances the autoignition reactivity of gasoline, which has advantages for some low-temperature combustion techniques, such as Sandia’s Low-Temperature Gasoline Combustion (LTGC) with Additive-Mixing Fuel Injection (AMFI). LTGC-AMFI is a new high-efficiency and low-emissions engine combustion process based on supplying a small, variable amount of EHN into the fuel for better engine operation and control. However, the mechanism by which EHN interacts with the fuel remains unclear. In this work, a chemical-kinetic mechanism for EHN was developed and implemented in a detailed mechanism for gasoline fuels. The combined mechanism was validated against shock-tube experiments with EHN-doped n-heptane and HCCI engine data for EHN-doped regular E10 gasoline. Simulations showed a very good match with experiments.</div><div class="htmlview paragraph">EHN chemistry fundamentals were also studied. Under LTGC-AMFI engine conditions, EHN generates NO<sub>2</sub>, formaldehyde and a combination of ~85% 3-heptyl and ~15% 1-butyl radical and butoxy diradical. Results show that the 3-heptyl and 1-butyl radicals are responsible for the autoignition-enhancing effect of EHN. Each mole of these radicals rapidly generates 2 moles of OH, which accelerate the low-temperature chemistry of the fuel, increasing its reactivity. The effects of the operating conditions on the effectiveness of EHN to increase the autoignition reactivity of the fuel were also studied. EHN’s effectiveness for increasing the autoignition reactivity is highest in the low-temperature regime, and it decreases as the temperature increases. EHN’s effectiveness to increase autoignition reactivity decreases with the combination of intake-pressure boost and EGR for typical engine operation. The effect of EHN on autoignition reactivity increases as equivalence ratio increases, enhancing the fuel’s φ-sensitivity. Therefore, with fuel stratification, EHN’s larger enhancement of autoignition reactivity for richer regions makes stratification techniques more effective.</div></div>

Reliability Analysis of Pyrotechnic Igniter for Hydrogen-Oxygen Rocket Engine with Low Temperature Combustion Instability Failure Mode

To evaluate the functional reliability of the pyrotechnic igniter in the failure mode of unstable combustion at low temperature, a reliability and reliability sensitivity analysis method based on the combination of an interior ballistic model and Kriging reliability method is proposed. Through the deterministic interior ballistic simulation, the failure mode of low temperature unstable combustion of the pyrotechnic igniter is examined, while the random variables are introduced to establish the ignition nonlinear implicit function of the pyrotechnic igniter. The ignition display function of the pyrotechnic igniter is established by the Kriging model, which avoids the repeated calculation of true limit state function values. This study provides an efficient approach to evaluate the ignition reliability of the pyrotechnic igniter and compared with the traditional Monte Carlo method to verify the accuracy of the results. Finally, reliability-based sensitivity indices are presented to quantify the significance of random parameters. It is shown that the influence of the uncertainties can be precisely described, and the diameter of the nozzle plays a dominant role in ignition reliability. Additionally, ignition experiments of nozzles with different diameters were performed to verify the result of sensitivity. This can further support the detailed design of the pyrotechnic igniter.

A numerical study on fuel film and emissions formations during cold start in a diesel engine using an improved spray-wall impingement model

Understanding the physical process such as fuel film formation during cold start is essential to reduce engine emissions. In this study, an improved spray-wall impingement model was applied to the cold-start simulation of a diesel engine. The fuel film and emissions formations during cold start were studied in depth. The effects of injection strategies were investigated by the use of various designed injection schemes. The results showed that a certain amount of fuel film is deposited on the wall surface due to the poor spray evaporation caused by the adverse thermal atmosphere in the cylinder. The low combustion temperature, insufficient oxygen, and the deposited fuel film are the primary causes for high HC, CO and soot emissions. The NOx emissions are relatively low because of low combustion temperature and oxygen content. A double injection strategy can reduce the deposited and remaining fuel film by 13% due to improved mixing, which benefits the reduction of HC and CO emissions, while it has a negligible effect on NOx and soot emissions. The percentage of first injected fuel has little impact on the amount of the remaining fuel film and emissions in the studied range. Increasing engine speed can inhibit the formations of fuel film, HC, CO, and soot emissions, which is due to the improved fuel evaporation, better flow motion, and thermal environment in the cylinder. Double injection allows a smaller amount of injected fuel to obtain a stable ignition. Decreasing the injected fuel mass can suppress the formation of fuel film and improve mixing, thus reducing HC, CO, and soot emissions. This work expands the application scenarios of the newly developed spray-wall impingement model. The new model has been successfully applied to investigate the cold start process of diesel engines in detail. The results provide insights into the fuel film formation and its effect on emissions, which can guide the development of a cold-start emission control strategy.

Shock tube experimental studies on the ignition delay of n-heptane/ethanol fuel blends with acetaldehyde (CH3CHO) and oxynitride (NO/NO2) additives

In recent studies around low-temperature combustion (LTC) engines, it has been found that the incomplete oxidation products (IOP) within exhaust gas recirculation (EGR) presents non-negligible chemical effects. However, IOP generally has complex ingredients, and little literature available conducts quantitative and comparative studies on the effects of these ingredients. In this paper, CH3CHO, which is considerably abundant, and NO, which is most active, are selected as typical ingredients of IOP, and their effects on ignition delay times of n-heptane/ethanol fuel blends are studied experimentally in a shock tube covering the equivalence ratios of 0.5, 1, 1.5, temperature range of 900–1200 K, and pressure of 10 atm. Experimental results show that both CH3CHO and NO/NO2 (part of NO is inevitably converted to NO2) promote ignition, and the promoting effect of NO/NO2 is stronger than CH3CHO . It is consistent for both CH3CHO and NO/NO2 that the higher the concentration or, the lower the equivalence ratio, the greater the promoting effect. The difference is that the promoting effect of CH3CHO weakens with temperature increasing, while the promoting effect of NO/NO2 strengthens. Besides, the promoting effect of NO2 is weaker than that of NO, and NO2 even begins to inhibit ignition at temperatures below 960 K. In addition, it follows chemical kinetic analysis that both CH3CHO and NO/NO2 accelerate the decomposition of fuel by producing more OH radicals during the ignition stage. Although the additives are in trace amounts, the OH produced by their early involvement in reactions can effectively accelerate the ignition, which indicates the non-negligible chemical effects of IOP in EGR.

Thermo-kinetic multi-zone modelling of low temperature combustion engines

Many researchers believe multi-zone (MZ), chemical kinetics–based models are proven, essential toolchains for development of low-temperature combustion (LTC) engines. However, such models are specific to the research groups that developed them and are not widely available on a commercial nor open-source basis. Consequently, their governing assumptions vary, resulting in differences in autonomy, accuracy and simulation speed, all of which affect their applicability. Knowledge of the models´ individual characteristics is scattered over the research groups´ publications, making it extremely difficult to see the bigger picture. This combination of disparities and dispersed information hinders the engine research community that wants to harness the capability of multi-zone modelling.This work aims to overcome these hurdles. It is a comprehensive review of over 120 works directly related to MZ modelling of LTC extended with an insight to primary sources covering individual submodels. It covers 16 distinctive modelling approaches, three different combustion concepts and over 60 different fuel/kinetic mechanism combination. Over 38 identified applications ranging from fundamental-level studies to control development. The work aims to provide sufficient detail of individual model design choices to facilitate creation of improved, more open multi-zone toolchains and inspire new applications. It also provides a high-level vision of how multi-zone models can evolve.The review identifies a state-of-the-art multi-zone model as an onion-skin model with 10–15 zones; phenomenological heat and mass transfer submodels with predictive in-cylinder turbulence; and semi-detailed reaction kinetics encapsulating 53-199 species. Together with submodels for heat loss, fuel injection and gas exchange, this modelling approach predicts in-cylinder pressure within cycle-to-cycle variation for a handful of combustion concepts, from homogeneous/premixed charge to reactivity-controlled compression ignition (HCCI, PCCI, RCCI). Single-core simulation time is around 30 minutes for implementations focused on accuracy: there are direct time-reduction strategies for control applications. Major tasks include a fast and predictive means to determine in-cylinder fuel stratification, and extending applicability and predictivity by coupling with commercial one-dimensional engine-modelling toolchains. There is also significant room for simulation speed-up by incorporating techniques such as tabulated chemistry and employing new solving algorithms that reduce cost of jacobian construction.

Optimization of magnetic properties of BaTiO3/Li0.5Fe2.5O4 multiferroics prepared via modified low-temperature combustion

Multiferroic (x)BaTiO3/(1 − x)Li0.5Fe2.5O4 (0.0 ≤ x ≤ 1) perovskite/spinel nanocomposite was synthesized using a modified citrate auto-combustion method. Both BaTiO3 (BTO) and Li0.5Fe2.5O4 (LFO) phases along with their composites were successfully characterized using X-ray diffraction, Fourier transformation infrared spectroscopy, and X-ray absorption fine structure spectroscopy. The nanoscale, morphology, and magnetic properties were imaged and acquired using high resolution transmission electron microscopy, atomic force microscopy, and vibrating sample magnetometer. Synchrotron radiation-based elemental selective XAFS technique was performed around Fe K-edge to obtain the selective and the detailed local structural information of Li0.5Fe2.5O4 nanoparticles (NPs). The main remarkable result in this work is the enhancement in the coercivity (HC) of LFO NPs after compositing with BTO particularly at x = 0.6, and at x = 0.8. Based on the collected results, BTO/LFO nanocomposite can be seen as a good candidate for different technological applications including magnetically modulated piezoelectric, safety rechargeable batteries, and multilayer ceramic capacitor.

Combustion Performance and Low NOx Emissions of a Dimethyl Ether Compression-Ignition Engine at High Injection Pressure and High Exhaust Gas Recirculation Rate

Dimethyl ether (DME) is a promising alternative to diesel for compression-ignition (CI) engines used in various industrial applications. However, the high nitrogen oxide (NOx) emissions of DME combustion have restricted its use. The primary cause of high NOx emissions is a high combustion temperature. In this study, a high exhaust gas recirculation (EGR) rate was used when testing a common-rail direct injection CI engine suitable (with minor modifications) for a passenger car. A modified fuel supply system created high injection pressure during evaluation of combustion performance. The physical and chemical properties of DME were the principal determinants of the ignition delay, combustion speed, and heat release rate. Although a high injection pressure accelerated formation of the fuel-air mixture and the combustion speed, combustion performance deteriorated with increased NOx emissions. An increased EGR rate affected combustion and the NOx concentration. A high EGR rate effectively reduced NOx formation and emission under low-temperature combustion conditions. Also, the good DME combustion characteristics were maintained when the EGR rate was high, unlike for an ultra-low sulfur diesel engine.

Limits of sustaining a flame above smoldering woody biomass

ABSTRACT Smoldering is slow, low-temperature, and flameless burning of porous fuel, and it is also an emerging method for energy conversion and waste removal. However, smoldering combustion is an incomplete combustion process, so the pollutions resulted from smoldering emissions are significant concerns. This work explores the flaming of emission gases from the smoldering wood chips (200 kg/m3) under different oxidizer flow velocities (4 mm/s-24 mm/s) and oxygen concentrations (14%-21%) through porous media. Once ignited on the top, the smoldering front first propagates downward (1st stage, opposed) to the bottom and then propagates upward (2nd stage, forward). We found that during the 1st-stage downward smoldering propagation, a stable flame of smoldering emissions could be piloted and sustained. The critical smoldering burning rate for maintaining a stable flame remains constant at 10–12 g/m2∙s. To reach such a minimum smoldering burning rate, the required opposed flow velocity increases from 6 to 24 mm/s, as the oxygen concentration decreases from 21 to 14%. A simplified heat transfer process is proposed to reveal the limiting conditions for the co-existence of flaming and smoldering. This work enriches strategies for the clean treatment of smoldering emissions and promotes an energy-efficient and environment-friendly method for biowaste removal.

Comparison of efficiency and emission characteristics in a direct-injection compression ignition engine fuelled with iso-octane and methanol under low temperature combustion conditions

Gasoline and methanol are highly recommended for low temperature combustion (LTC) engines due to their high research octane number. However, engines fuelled with these fuels suffer from high unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions at low loads, which can be improved by controlling the level of mixture stratification. This paper reports on the experimental and numerical comparison of the emission characteristics and engine performance of methanol and iso-octane in a heavy-duty direct-injection compression ignition engine operating in HCCI and PPC regimes. Overall, methanol requires a higher intake temperature, compared with iso-octane, to counter the high heat of vaporization. The onset of ignition is from the relatively fuel-lean regions resulting in lower CO emissions. This is due to the methanol ignition delay times being less sensitive to the fuel/air mixture and the larger temperature gradient of the equivalence ratio. Methanol achieves lower charge stratification because of its low stoichiometric A/F ratio, which extends the SOI window with ultra-low NOx emissions. However, methanol suffers from higher UHC emissions in the HCCI regime due to fuel trapped in the crevice region. Three cases include HCCI, PPC with low and high mixture stratification were detailed investigated. Of these cases, PPC with low mixture stratification case shows the highest engine thermal efficiency and the lowest emissions. Methanol has more advantages operating in the PPC regime in the aspect of emissions.

An experimental investigation into the soot particle emissions at early injection timings in a single-cylinder research diesel engine

Engine experiments were performed to examine the effect of early-injection on smoke emissions and engine performance under typical low temperature combustion (LTC) and reactivity controlled compression ignition (RCCI) operating conditions. On that basis, the influence of exhaust gas recirculation (EGR), intake pressure, fuel properties and fuel injection strategy on the engine-out soot emissions at early injection timings was also assessed. At last, the morphology, nanostructure characteristics of exhaust soot particles were analyzed. The test results showed when the injection timing was advanced before −30° crank angle after top dead center (CA ATDC) and earlier, the fuel spray impinged onto the piston crown surface, and a part of fuel entered into the squish zone and expanded to reach the cylinder liner wall and entered into the crevice volume, leading to a continuous increase in soot emissions, the peak smoke emission was found to occur at −55° CA ATDC. By adopting fuels with high volatilities and a RCCI fuel delivery strategy, soot emissions can be effectively reduced at early timings. Most of the high-resolution transmission electron microscopy (HRTEM) images of the sampled soot particles showed small spherical particles with a wide range of size distribution connected, and “onion-like” fringe arrangement was found in most of the images. As the fuel injection timing was retarded from −55° to −35° CA ATDC, the samples exhibited more highly organized carbon nanostructures; the fringe tortuosity and separation distance increased, while the fringe length decreased. The formation of more ordered arrangement of graphene layers led to significant resistance to oxidation.

Oxygen Vacancy-Mediated Selective H2S Oxidation over Co-Doped LaFexCo1−xO3 Perovskite

Compared to the Claus process, selective H2S catalytic oxidation to sulfur is a promising reaction, as it is not subject to thermodynamic limitations and could theoretically achieve ~100% H2S conversion to sulfur. In this study, we investigated the effects of Co and Fe co-doping in ABO3 perovskite on H2S selective catalytic oxidation. A series of LaFexCo1−xO3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) perovskites were synthesized by the sol-gel method. Compared to LaFeO3 and LaCoO3, co-doped LaFexCo1−xO3 significantly improved the H2S conversion and sulfur selectivity at a lower reaction temperature. Nearly 100% sulfur yield was achieved on LaFe0.4Co0.6O3 under 220 °C with exceptional catalyst stability (above 95% sulfur yield after 77 h). The catalysts were characterized by XRD, BET, FTIR, XPS, and H2-TPR. The characterization results showed that the structure of LaFexCo1−xO3 changed from the rhombic phase of LaCoO3 to the cubic phase of LaFeO3 with Fe substitution. Doping with appropriate iron (x = 0.4) facilitates the reduction of Co ions in the catalyst, thereby promoting the H2S selective oxidation. This study demonstrates a promising approach for low-temperature H2S combustion with ~100% sulfur yield.

Long-Term and Seasonal Changes in Sources of Urban Atmospheric Particulates in the Western Pacific

To reduce atmospheric pollutants, the sources need to be identified. To this end, combustion-derived particulates (Pc) in atmospheric suspended particulate matter (TSP) in ten Western Pacific cities from 1997 to 2018 were analyzed using the NP method, which we have recently developed. The method separates Pc into particulates originating from high-temperature (Ph) and low-temperature (Pl) combustion sources. Using this method, ten cities in the Asia-Pacific region were separated into three classes. Class 1: commercial cities whose major contributor to Pc was from vehicles, and which showed lower [Pc] values with larger [Ph]/[Pc] ratios. Sapporo, Kanazawa, Tokyo, Sagamihara (Japan), Shanghai (China), and Busan (Korea) were contained in this class. Class 2: cities whose main source of Pc was from coal heating, and which showed much higher winter [Pc] with larger [Pl]/[Pc] ratios. Beijing, Shenyang (China), and Vladivostok (Russia) were contained in this class. Class 3: steel manufacturing city which showed lower [Pc] with larger [Pl]/[Pc] ratio. The low [Pc] appeared to be due to elimination of Pl from coke oven plants. Only Kitakyushu was contained in this class. This study has elucidated the contribution of sources to urban atmospheric TSP in the Western Pacific that was previously unknown. Overall [Pc] was decreasing in this region, mainly due to the decreasing contribution of vehicles to Pc, but not due to a decrease in coal combustion.

Thermally Conductive Cellulose/Coper Composite Rods for Tailoring the Characteristics of Cigarettes

A new style of low temperature combustion cigarettes was prepared by implanting a thermally conductive cellulose/coper composite rod (TCCR) in the cut tobacco section, so as to explore the application feasibility at the low temperature environment. The burning temperature of the cigarettes was investigated by thermocouple to study the influence of the implanted TCCRs. The emission of conventional components and seven harmful components in mainstream smoke were also carried out to study the effect of TCCRs. The results show that implantation of TCCRs could reduce the burning temperature of cigarettes effectively, which decreased over 100 °C. In compared with conventional cigarettes, the amount of nicotine and nicotine-freed dry particulate matter (NFDPM) in mainstream smoke of TCCRs implanted cigarettes changed little, while the release of harmful components such as CO, HCN, NNK and phenol decreased over 20%. Moreover, the TCCRs, which made of copper paper with 2 g / 18 g weight ratio of pulp and copper, and 5 mm interval perforating, could reduce the burning temperature of cigarettes by 145 °C and the hazard index by 2.01.

Thermal energy simulation safety model of wupaolong fireworks based on Friedman method

The performance of firecrackers and fireworks in the dance, artillery and dragon competitive activities enhances appreciation and entertainment of wupaolong. Wupaolong has the meaning of dispelling evil spirits and eliminating disasters. With the development of fireworks preparation technology, wupaolong powder throwing technology also puts forward the requirements of low ignition point, rich color and low combustion and explosion temperature. In this paper, the effects of water content and environmental humidity on the thermal decomposition characteristics of pyrotechnic agents were studied by thermal analysis method. The thermal decomposition kinetic parameters of red pyrotechnic agents were determined by Friedman method. The effects of water content and environmental humidity on their thermal decomposition characteristics were summarized and analyzed. The thermal safety model studied in this paper can play a key role in improving the theory and technology of fireworks material components. And it creates the data micro-control processing of naked grain ignition time, ignition delay period, ignition temperature and ignition position of fireworks at different ambient temperatures. Experiments show that the optimized model scheme in this paper can analyze the thermal decomposition dynamics of different component grains and has high application value for improving the thermal safety of propellant.

Dynamic measurement with in-cycle process excitation of HCCI combustion: The key to handle complexity of data-driven control?

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion technique with a high potential for reducing emissions while simultaneously improving fuel consumption. However, the high sensitivity to changing boundary conditions and low combustion stability at the edges of the operating range has lead to implementation challenges. Additionally, cyclic coupling through internal exhaust gas recirculation causes cyclic variations of the process, resulting in incomplete combustion, or even misfiring. Thus, consecutive cycles must be decoupled to increase the process stability. To achieve an accurate description of the coupling effects on a cycle-to-cycle and an inner-cyclic timescale, a novel measurement methodology is presented to generate data with a high variance. For this purpose, an active process excitation is performed to capture all relevant interactions between operating and feedback variables to enable modeling of the coupling effects on both timescales. To demonstrate the potential of the methodology, the generated data is used to design multiple input, multiple output (MIMO) models for both cyclic and inner-cyclic timescales. Artificial neural networks are then utilized to address the highly nonlinear process by taking advantage of the large amount of training data. Inverse process models are then used to implement a pure cycle-to-cycle and a multiscale MIMO closed-loop controller. Compared to state-of-the-art rule-based control approaches, the process stability and its thermodynamic efficiency are significantly improved. For the multiscale MIMO controller, a reduction of the standard deviation of the indicated mean effective pressure and the combustion phasing of more than 65% is achieved. In particular, the additional inner-cyclic feedback loop achieves a remarkable reduction of the standard deviation of approximately 35% and a 1.2% higher indicated efficiency compared to the cycle-to-cycle MIMO controller. The dynamic measurement with active in-cycle process excitation has proven to be an enabler for data-driven MIMO control of HCCI on multiple timescales.