Combustion Period Research Articles

An innovative automatic dynamic target species selection technique for skeletal chemical reaction mechanism development for various fuels

In skeletal reduction of large chemical mechanisms, graph-based reduction methods such as directed relation graph with error propagation (DRGEP) are widely utilized. For the graph-based reduction methods, it is a common practice to pre-select a static set of target species for graph searching process. However, such practice faces some major challenges. The first one is that the reduction performance is strongly dependent on the selection of target species, a proper selection of which requires abundant experience and expertise. The second one is that some of the species in the static set can be consumed entirely and thus no longer important during some combustion period. In addition, a limited number of species in the pre-selected set of target species may not satisfy all sampled chemical states, which has the risk of missing some essential species as target species at certain sampled chemical states. In this study, an automatic dynamic target species selection (ADTSS) technique was proposed to replace the traditional pre-selection of target species and incorporated with DRGEP. After that, extensive validations against the detailed mechanisms and comparisons with utilizing static target species were conducted. It has been found that the ADTSS technique is reliable and significantly improves the reduction capability. Another great benefit of the ADTSS technique is that it removes the need of manually pre-selecting target species and their cut-off threshold on mass fraction, which makes it possible to obtain a good skeletal mechanism for researchers without much experience and expertise in mechanism reduction.

Fire Diurnal Cycle Derived from a Combination of the Himawari-8 and VIIRS Satellites to Improve Fire Emission Assessments in Southeast Australia

The violent and persistent wildfires that broke out along the southeast coast of Australia in 2019 caused a large number of pollutant emissions, which seriously affected air quality and the global climate. The existing two methods for estimating combustion emissions based on burned area and fire radiative power mainly use a medium resolution imaging spectrometer (MODIS) on the Aqua and Terra satellites. However, the low temporal resolution of MODIS and insensitivity to small fires lead to deviation in the estimation of fire emissions. In order to solve this problem, the Visible Infrared Imaging Radiometer Suite (VIIRS) with better performance is adopted in this paper, combined with the fire diurnal cycle information obtained by geostationary satellite Himawari-8, to explore the spatio-temporal model of biomass combustion emissions. Using this, a high-spatial- and -temporal-resolution fire emission inventory was generated for southeastern Australia from November 2019 to January 2020, which aims to fully consider the highly dynamic nature of fires and small fires (low FRP) that are much lower than the MODIS burned area or active fire detection limit, with emphasis on dry matter burned (DMB). We found that during the study period, the fire gradually moved from north to south, and the diurnal cycle of the fire in the study area changed greatly. The peak time of the fire gradually delayed as the fire moved south. Our inventory shows that the DMB in southeast Australia during the study period was about 146 Tg, with major burned regions distributed along the Great Dividing Range, with December 2019 being the main burning period. The total DMB we calculated is 0.5–3.1 times that reported by the GFAS (Global Fire Assimilation System) and 1.5 to 4 times lower than that obtained using the traditional “Burned Area Based Method (FINN)”. We believe that the GFAS may underestimate the results by ignoring a large number of small fires, and that the excessive combustion rate used in the FINN may be a source of overestimation. Therefore, we conclude that the combination of high-temporal-resolution and high-spatial-resolution satellites can improve FRE estimation and may also allow further verification of biomass combustion estimates from different inventories, which are far better approaches for fire emission estimation.

Study on the combustion behavior and soot formation of single coal particle using hyperspectral imaging technique

This paper proposes a hyperspectral imaging technique for capturing radiative images at a high temporal–spatial resolution, for the purpose of spectrally visualizing the instantaneous combustion behaviors of single coal particles. We initially use a hyperspectral imaging device to record the combustion processes of two types of single pulverized coal particles on a McKenna flat-flame burner. From the snapshot images captured by the device, we observe the combustion processes, ignition characteristics, flame morphologies, and sizes of the two single coal particles. The observations indicate that the two single coal particles undergo volatile release/combustion and char ignition/oxidation during the luminous combustion process; moreover, both particles exhibit homogeneous ignition characteristics under the experimental conditions. Furthermore, based on the spectral radiative intensity images obtained via the device, the soot temperature and volume fraction images of the two single coal particles in the envelope flame are obtained at different burning times. Thereafter, the influences of the combustion behaviors and soot formation mechanisms on the distribution rules of the soot temperature and concentration at different combustion periods are discussed. Finally, the temperature and apparent spectral emissivity values of the two single char particles during the char oxidation process are also calculated to analyze their combustion behaviors. The results show that the temperature changes within a relatively narrow range with respect to the burning time during the oxidation stage, whereas the spectral emissivity continues to increase with the oxidation of chars and subsequently decreases.

Impact of biomass induced black carbon particles in cascading COVID-19

We explore the association of biomass-induced black carbon aerosolized virus with COVID-19 in one of the top-ranked polluted hot spot regions of the world, Delhi, at the time when other confounding factors were almost stable and the pandemic wave was on the declining stage. Delhi was worst affected by COVID-19. However, when it was fast returning back to normal after about 6 months with minimum fatalities, it suddenly encountered a reversal with a 10 fold increase in infection counts, coinciding with the onset of the stubble burning period in neighbouring states. We hereby report that the crop residue burning induced lethal aged Black carbon-rich particles which engulfs Delhi during the post-monsoon months of October–November are strongly associated with COVID-19 and largely responsible for the sudden surge. It is found that the virus efficacy is not necessarily related to any particulates but it is more of source-based toxicity of its component where the virus is piggybacking. We conclude that the aged biomass BC particles tend to aggregate and react with other compounds to grow in size, providing temporary habitat to viruses leading to the rapid increase in COVID-19 cases which declined after the crop burning stopped.

Prediction of Size Distribution and Mass Concentration of Smoke Particles on Moisture Content and Combustion Period from Para Rubber Wood Burning

The size distribution and total particle mass concentration (TPMC) of smoke particles from para rubber wood (Hevea brasiliensis) combustion in the ribbed smoked sheet (RSS) process were studied. In this experiment, temperature data values of para rubber wood combustion were recorded at 500 mm above the base of the fire by K-type thermocouples. The wood moisture content and wood combustion period were used to find and improve an equation of smoke particle size distribution (SPSD) and TPMC by the response surface method (RSM). An eight-stage Andersen air sampler and a high-volume sampler were used to measure and calculate SPSD and TPMC, respectively. Resulting data in this experiment showed that TPMC ranged from 3.12 to 77.42 mg/m3. SPSD was single mode in which MMAD, mass median aerodynamic diameter, ranged from 0.64 to 1.27 microns for para wood with moisture content ranging from 31.5 to 89.7% dry weight basis. The combustion period and moisture content of para wood have a direct effect on the change of temperature data above the base of the fire and the TPMC and MMAD values. For predicting TPMC and MMAD values by the para wood moisture contents in each combustion period, the results found that the second-degree model was a better plot than the first-degree model, confirmed by higher values of the coefficient of determination (R2).

An experimental evaluation of the equivalence ratios in tests apparatus used for fire effluent toxicity studies

SummaryAn experimental evaluation was conducted on the bench‐scale test methods most commonly applied for generating data for fire toxicity assessments. The test methods evaluated were ISO/TS 19700, ISO 5660‐1 with the controlled atmosphere box, and ISO 5659‐2. Toxic gases were quantitatively analyzed using Fourier transfer infrared spectroscopy. Tests were made with 11 different insulation materials and polymethylmethacrylate as a reference material. The evaluation made was on the combustion conditions in the test apparatus, not generally on the precise yields measured. The evaluation focused on the ventilation conditions created in flaming combustion tests. It was seen that ISO/TS 19700 currently offers the best means among the three test methods evaluated for conducting tests at pre‐determined and controlled equivalence ratios. The controlled‐atmosphere cone calorimeter does not give a prolonged steady flaming combustion period for most materials and the influence of vitiation was difficult to predict and limiting in achieving higher equivalence ratios, with the test settings applied. ISO 5659‐2 generally accumulates a mixture of gases from periods of both flaming and nonflaming combustion in a test, and the yields measured do not, in those cases, represent any specific combustion stage. For materials not showing flaming combustion, for example, mineral fiber products, the influence on the test conditions regarding oxygen consumption and heat generation from the material itself is limited compared to burning materials. However, there were specific properties and limitations of the different test methods observed that are important to consider.

Effects of ethanol on the evaporation and burning characteristics of palm-oil based biodiesel droplet

Palm biodiesel-ethanol blends could be the better automotive fuel over palm biodiesel alone owing to the high oxygen content and high volatility of ethanol. The evaporation and burning characteristics of palm biodiesel with 10%, 20%, and 30% ethanol by volume concentration respectively, were investigated by using the droplet experiment. Rapid bubble growth and bubble explosions during the heating stage were observed to be substantial for the palm biodiesel droplet added with 30% volume of ethanol (BE30). Adding ethanol in palm biodiesel increased the ignition delay and burn-rate constant by up to 38.6% and 23.2%, respectively whereas, the evaporation duration and burning period decreased by up to 20.6% and 22.5%, respectively. Overall, the relatively shorter evaporation duration and higher burn-rate found for the BE30 droplet could promote high thermal efficiency and has the potential to achieve ultra-low carbon monoxide (CO) and unburned hydrocarbons (UHCs) emissions in diesel and gas turbine engines.

A study on the working characteristics of free piston linear generator with dual cylinder configuration by different secondary injection strategies

Aiming at the dead center change of free piston linear generator with dual-cylinder configuration(FPLGDC), this paper proposes stratified combustion technology and studies the influence of secondary injection timing and injection ratio on the formation and combustion characteristics of stratified mixture. The results show as the secondary injection timing was advanced from 16oCABTDC to 36oCABTDC, local over-concentrated mixture in-cylinder was diluted, and the overall uniformity of the mixture was improved. Further, the overall evaporation increased from 89% to 97%. More, as secondary injection ratio decreased from 20% to 10%, the fuel evaporation ratio increased from 14% to 16%, and the stratification of the in-cylinder mixture at the ignition time was more obvious. Therefore, advancing the time of secondary injection and reducing secondary injection ratio can make the mixture more properly stratified, shorten the rapid combustion period, and improve combustion quality. Further, compared with the secondary injection ratio was 20% for secondary injection time at 16oCABTDC, the peak pressure in the cylinder increased by 14%, and the peak pressure position increased by about 2oCA when the secondary injection ratio was 10% at a secondary injection time of 36oCABTDC. Thus, reasonable control the injection strategy can significantly improve the dynamic performance of FPLGDC.

Effect of Impregnation with Boron Compound Doped Rosin to the Combustion Resistance of Oriental Beech Wood (Fagus orientalis Lipsky)

In this study, investigation of the combustion properties of Oriental beech wood (Fagus orientalis Lipsky) impregnated with boron compound (borax (Na2B4O710H2O), boric acid (H3BO3) doped rosin (C19H29COOH) was aimed. For this purpose, Oriental beech wood samples were prepared according to ASTM E 160-50 and impregnated with boron compound doped rosin by the method of medium-term dipping (24 hours) according to ASTM D 1413 and producers’ definition. Combustion properties of samples after impregnated process were determined according to ASTM E 160-50. As a part of the research, 6 different combination and contents of impregnation materials have been used in order to especially investigate resistance against combustion of wood material treated with boron compounds in different concentrations. As a result of the study, retention performance and leaching resistance of boron compounds can be increased through rosin addition. Consequently, impregnation materials with rosin decreased the flame sourced combustion (Fsc) temperatures depending on kind of impregnation material, extended combustion period and decreased weight loss ratio of the test samples in comparison to the control samples. On the contrary, weight loss ratios were affected negatively in Oriental beech test samples up to 3% when compared with samples which were impregnated with borax. Meanwhile, combustion periods increased in test samples up to 30%. Rosin, in terms of its combustion performance, can be preferred in impregnation with boron compounds depending on kind of wood and using area.

What are the effects of portable air cleaners with a high-efficiency particulate air filter on aerosol removal in dental surgeries?

Design Volumetric air flow was measured in a number of dental surgeries to calculate the air change rate per hour (ACHvent). In each surgery, measurements of aerosol removal by ventilation alone, and then with ventilation provided by a high-efficiency particulate air filter (PAC), were completed. The concentrations of aerosol particles of various sizes were recorded at baseline, after an initial period of incense burn, and then after 30 minutes of observation with and without the use of the PAC or ventilation system.Sample selection Ten dental surgeries with differing baseline ventilation rates had the concentrations of 0.3, 0.5 and 1.0 μm aerosol particles measured at 0 minutes, after 5 minutes of incense burn and then after 30 minutes of observation, firstly without the PAC system in operation and then with the PAC system in use.Data analysis For the 0.3 μm particles, velocities of aerosol removal were assessed by analysing the concentration decay constants with ventilation alone and ventilation with the PAC. Aerosol removal velocities were assessed by the time needed to reach 95% and 100% removal of accumulated aerosol particles.Results ACHvent in the ten different surgeries varied from 3-45. The concentration decay constants for the 0.3 μm particles with ventilation alone and ventilation with the PAC were correlated to the mechanical ventilation rate and combined respectively. For rooms with ACHvent of less than 15, accumulated aerosol particles could not be removed by ventilation alone in 30 minutes. The PAC accelerated aerosol removal and reduced aerosol accumulation, and with the use of the PAC in addition to ventilation, accumulated aerosols were removed completely in 4-12 minutes. The PAC was shown to be more beneficial in rooms with poor ventilation and the added effectiveness of the PAC in aerosol removal was inversely correlated with the ACHvent by ventilation.Conclusions Although the air change rate differed considerably among dental surgeries, this study suggests that the addition of the PAC with a HEPA filter significantly increased aerosol removal and lessened aerosol accumulation, particularly in rooms with low ventilation rates.

Stubble Burning and its Impact on Air Quality in Delhi NCT: A Case Study

Stubble burning is now considered to be one of the major activities affecting air quality because it is one of the major sources of aerosol as well as gaseous pollution. There are two main reasons for biomass burning, first one is that there is a very short window of time between the harvesting and the wheat sowing of the wheat. The second being, removing the paddy residue that has remained on the field is a time-consuming job. The time period from harvesting to sowing being very low and the labor is either very expensive or unavailable this leads to the only easiest option that the farmer has i.e. burning the residue right on the field after harvest so that the farmers can quickly prepare the land for the next sowing. This method is very cheap and takes less time that’s why farmers use this method. For this specific reason with the onset of winter, stubble fires become rampant in north India. Stubble-burning emissions contain toxic chemicals which cause respiratory problems as well as diseases. The paper aims to examine the environmental impacts associated with stubble burning over the NCT of Delhi. The paper performs both qualitative and quantitative analysis on the statistical data pertaining to crop burning. The monthly variation for particulate matter (PM10 and PM2.5) and trace gases (NOx, CO, and SO2) during the stubble burning period (Sep-Nov) has also been studied and analyzed for 5 years (2015-19), and a noticeable increase in pollutant levels.

Experimental investigation of the influences of Miller cycle combined with EGR on performance, energy and exergy characteristics of a four-stroke marine regulated two-stage turbocharged diesel engine

In order to explore the technical route to meet the Tier III emission regulations, the experimental study of the influence of Miller cycle combined with EGR on the performance, energy and exergy of a four-stroke marine regulated two-stage turbocharged diesel engine was achieved by redesigning the camshaft and EGR system. The results shown that Miller cycle combined with EGR increased the peak HRR of premixed combustion period, decreased the peak HRR during the main combustion period, and delayed the crank angle corresponding to the peak HRR, resulting in longer combustion duration and a later 50% combustion position. In the 75% load, the combination of medium Miller timing and medium EGR rate can not only meet the NOx emission requirements of Tier III, but also far superior to only high EGR rate in terms of fuel economy, opacity performance and COVIMEP. As the EGR rate increased, heat transfer energy to coolant, BTE and ITE dropped significantly, while exhaust energy and combustion loss increased significantly. The change trends of exergy terms with EGR rate and Miller timing were similar to their corresponding energy. It should be noted that the exhaust energy was about 2.5 times larger than the exhaust exergy while the heat transfer energy to coolant was about 8 times larger than the heat transfer exergy to coolant, which indicated that the recoverable potential of heat transfer energy to coolant is much smaller than exhaust energy.

Combustion of hazelnut shell-lignite blends in poly-particulate beds

In this study, combustion behaviours of blends prepared from 2.18 mm mean size lignite and hazelnut shell particles in specific proportions were investigated using a vertical pre-heated furnace system through which air was flowing upwards by natural convection. The results revealed that the ignition time of the blends approached those of hazelnut shell with temperature and showed certain interactions of the two materials during the volatiles combustion period. Combustion time generally complied with volatiles and carbon combustion rates of the two materials and their blends. Carbon combustion time decreased with temperature and hazelnut ratio, and implied some interactions of the materials. Although any effect of initial furnace temperature and hazelnut ratio of the blends on the NOx emissions was not clearly seen, SO2 emission levels depended on these factors.

Effects of methane ratio on MPDF (micro-pilot dual-fuel) combustion characteristic in a heavy-duty single cylinder engine

In this study, the characteristics of micro-pilot dual-fuel combustion with respect to the fuel mixture ratio in a single cylinder dual-fuel engine have been investigated. In order to analyze the characteristics of micro-pilot dual-fuel combustion, a metal engine and an optical single cylinder dual-fuel engine were used. The fuel mixture ratio was varied for experimental purposes; the diesel was directly injected into combustion chamber and the methane gas was supplied via intake port. The present study reports that increasing the methane mixture ratio from 0 to 97.67% changes the diesel combustion to pre-mixed combustion. As a result, the peak cylinder pressure was increased from 184 to 198 bar, and the rate of heat release was greatly advanced. In the MPDF condition, the nitrogen oxides emissions were reduced by about 90%p, and the fuel conversion efficiency increased about 5%p because of the low combustion temperature of pre-mixed combustion. However, for the same reason, the hydrocarbon emissions were increased about 95%p. The fastest combustion speed was found form the results of methane mixture ratio between 40 and 80%. In the condition of diesel combustion and micro-pilot dual-fuel combustion, the combustion periods of middle and initial were increased, respectively, resulting in the low combustion speed. The standard deviation of peak cylinder pressure, which represents the combustion variation, was correlated with initial combustion period. While the condition of methane gas mixture ratio between 40 and 80% shows the lowest combustion variation, the highest combustion variation was occurred by MPDF condition. Through the optical engine experiment, it can be found that the cycle to cycle combustion variation is ascribed to the turbulent flow and the variation of ignition position. The combustion images show that the unpredictable characteristics of the ignition position and slow flame propagation speed caused the combustion variation in micro-pilot dual-fuel combustion.

Impact of crop residue burning in Haryana on the air quality of Delhi, India

Crop residue burning (CRB) over northern India is a major air quality and human health issue. The present study assesses the impact of PM10, PM2.5, NO2 and SO2, emitted during CRB activities in Haryana on the air quality of Delhi. The transition from pre-burning to burning period, in both rabi and kharif seasons, shows considerable increase in pollutant concentrations. PM10 and PM2.5 concentrations exceeded NAAQS limits by 2–3 times, while NO2 and SO2 stayed within the limits. MODIS fire observations used to estimate CRB fire counts (confidence ≥80%) shows that rabi (burning period) fires in Haryana are ~3 times higher and more intense than in kharif. Furthermore, backward trajectories shows air mass movement from Haryana, Punjab and Pakistan. Thus, pollutants emitted reach Delhi via air masses, deteriorating its air quality.Meteorological conditions influence pollutant concentrations during both seasons. Frequent dust storms in rabi, and Dusshera and Diwali firework celebrations in kharif season exacerbate air pollution. In rabi, PM10 and PM2.5 have a significant negative association with (relative humidity) RH and positive association with (air temperature) AT. High AT during pre-monsoon, accompanied by low RH, loosens up soil particles and they can easily disperse. Stronger winds in rabi season promote NO2 and SO2 dispersion. In kharif, lower AT, higher RH and slower winds exist. Both PM10 and PM2.5 have a negative association with AT and (wind speed) WS. With lower temperature and slower winds during winter, pollutants are trapped within the boundary layer and are unable to disperse. As expected, NO2 has a significant negative association with AT in Haryana. However, in case of Delhi, the association is significant but positive, and could be due to the odd-even scheme imposed by the Delhi government. More research is needed to determine the health effects of Haryana's rabi CRB activities on Delhi.

Effects of split ratio of diesel spray injection on mixture formation and combustion process

The effects of the split ratio on the mixture formation and combustion process of a diesel spray in a constant-volume chamber were experimentally investigated. A commercial seven-hole injector was used in this experiment. The effects of the mass-dependent split ratio and dwell time were observed when the total fuel injection was 5.0 mg/hole. Three split ratios were considered: 3:7, 5:5 and 7:3, while the dwell time of 120 µs was fixed for every condition. A laser absorption-scattering technique was adopted to examine the formation of mixtures with regarding to the equivalence ratio. A high-speed video camera was used to observe natural flame luminosity, and a two-colour pyrometer system was employed to evaluate the temperature and soot concentrations in the flame. Among the distribution ratios tested in this study, the 7:3 split ratio exhibited the best performance for the lean mixture formation considering the overall equivalence ratio distribution. The air entrainment wave at the end of injection timing of the first injection caused the fuel near the nozzle to lean at a rapid rate. The soot formation process for the 3:7 and 5:5 split ratios was observed because the second injection fuel caught the flame of the previous injections; this deteriorated the combustion region and influenced soot formation. The result also revealed that for the 7:3 split ratio, accelerated the soot deduction rate to the cycle of soot oxidation during the combustion period.

Preliminary Study on Pelletization of Oil Palm Empty Fruit Bunches (EFB)/Spent Activated Carbon (AC): Effect of Mixing and Adhesive Ratio

Non-renewable resources such as fossil fuels could be combusted for energy and electricity to human kind. The demand of fossil fuel energy had reached an exponential growth which caused disasters and catastrophic damages on the environment; thus, renewable resources should be implemented to protect the environment. One of the natural resources was biomass waste. In this study, spent activated carbon (AC) was co-pelletized with biomass waste, oil palm empty fruit bunches (EFB). The effect of EFB, AC and adhesive (tapioca) mixing ratio in the pellet was evaluate through physical and thermal properties. The raw materials were grinded and mixed together at different AC/EFB/tapioca ratio. The mixed raw materials were compressed at 130°C and 7 MPa for 10 minutes. The densified products were characterized by using Thermogravimetric Analysis (TGA). For the thermal characteristics, sample with 0% waste AC, 90% EFB and 10% starch had the highest mass loss rate (570 µg/min) followed by sample with 10% of waste AC, 60% of EFB and 30% of starch which was 420 µg/min. Besides, sample with 0% waste AC, 90% EFB and 10% had the highest burn out temperature (802.6 °C) followed by sample with 30% of waste AC, 60% of EFB and 10% of starch which was 792.85 °C. In conclusion, sample with 0% waste AC, 90% EFB and 10% starch had an easiest ignition and longest combustion period since it had the highest mass loss rate and burn out temperature.

Spray, Combustion, and Air Pollutant Characteristics of JP-5 for Naval Aircraft from Experimental Single-Cylinder CRDI Diesel Engine

This study was performed to analyze the spray, combustion, and air pollutant characteristic of JP-5 fuel for naval aircraft in a spray visualization system and a single-cylinder CRDI diesel engine that can be visualized. The analysis results of JP-5 fuel were compared with DF. The spray tip penetration of JP-5 showed diminished results as the spray developed. JP-5 had the highest ROHR and ROPR regardless of the fuel injection timings. The physicochemical characteristics of JP-5, such as its excellent vaporization and low cetane number, were analyzed to prolong the ignition delay. Overall, the longer combustion period and the lower heat loss of the DF raised the engine torque and the IMEP. JP-5 showed higher O2 and lower CO2 levels than the DF fuel. The CO emission level increased as the injection timing was advanced in two test fuels, and the CO emitted from the DF fuel, which has a longer combustion period than JP-5, turned out to be lower. NOx also reduced as the fuel injection timing was retarded, but it was discharged at a higher level in JP-5 due to the large heat release. The images from the combustion process visualization showed that the flame luminosity of DF is stronger, its ignition delay is shorter, and its combustion period is longer than that of JP-5.

Experimental Investigation of Combustion Characteristics on Opposed Piston Two-Stroke Gasoline Direct Injection Engine

The combustion characteristics of an opposed-piston two-stroke gasoline engine are investigated with experiment. The energy conversion and exergy destruction are analyzed and the organization method of the combustion process is summarized. The effects of phase difference, scavenging pressure, injection timing, ignition timing, and dual spark plug ignition scheme on the combustion process and engine performance are discussed, respectively. The heat release rate of the opposed-piston two-stroke gasoline engine is consistent with the conventional gasoline engine. With the increase of opposed-piston motion phase difference, the scavenging efficiency decreases and overmuch residual exhaust gas is not beneficial to the combustion process. Meanwhile, the faster relative velocity of the opposed-piston near the inner dead center enhances the cylinder working volume change rate, which leads to the rapid decline of in-cylinder pressure and temperature. The 15 °CA of opposed-piston motion phase difference improves the scavenging and combustion process effectively. When scavenging pressure is 0.12 MPa, the scavenging efficiency and heat release rate are improved at medium-high speed conditions. With the delay of injection timing, the flame developing period decreases gradually, and the rapid burning period decreases and then increases. The rapid burning period may reach the minimum value when the injection advance angle is 100 °CA. With the delay of ignition timing, the flame developing period increases gradually, and the rapid combustion period decreases and then increases. The rapid combustion period may reach the minimum value when the ignition advance angle is 20 °CA. Notably, the flat-top piston structure should be matched with the dual spark plug, which the ignition advance angle is 20 °CA at medium-high load conditions.

Using TROPOspheric Monitoring Instrument (TROPOMI) measurements and Weather Research and Forecasting (WRF) CO modelling to understand the contribution of meteorology and emissions to an extreme air pollution event in India

Abstract. Several ambient air quality records corroborate the severe and persistent degradation of air quality over northern India during the winter months, with evidence of a continued, increasing trend of pollution across the Indo-Gangetic Plain (IGP) over the past decade. A combination of atmospheric dynamics and uncertain emissions, including the post-monsoon agricultural stubble burning, make it challenging to resolve the role of each individual factor. Here we demonstrate the potential use of an atmospheric transport model, the Weather Research and Forecasting model coupled with chemistry (WRF–Chem) to identify and quantify the role of transport mechanisms and emissions on the occurrence of the pollution events. The investigation is based on the use of carbon monoxide (CO) observations from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor satellite and the surface measurement network, as well as the WRF–Chem simulations, to investigate the factors contributing to CO enhancement over India during November 2018. We show that the simulated column-averaged dry air mole fraction (XCO) is largely consistent with TROPOMI observations, with a spatial correlation coefficient of 0.87. The surface-level CO concentrations show larger sensitivities to boundary layer dynamics, wind speed, and diverging source regions, leading to a complex concentration pattern and reducing the observation-model agreement with a correlation coefficient ranging from 0.41 to 0.60 for measurement locations across the IGP. We find that daily satellite observations can provide a first-order inference of the CO transport pathways during the enhanced burning period, and this transport pattern is reproduced well in the model. By using the observations and employing the model at a comparable resolution, we confirm the significant role of atmospheric dynamics and residential, industrial, and commercial emissions in the production of the exorbitant level of air pollutants in northern India. We find that biomass burning plays only a minimal role in both column and surface enhancements of CO, except for the state of Punjab during the high pollution episodes. While the model reproduces observations reasonably well, a better understanding of the factors controlling the model uncertainties is essential for relating the observed concentrations to the underlying emissions. Overall, our study emphasizes the importance of undertaking rigorous policy measures, mainly focusing on reducing residential, commercial, and industrial emissions in addition to actions already underway in the agricultural sectors.