Effect of biodiesel fuel properties and formation of NOx emissions: a review

Biodiesel is revealed as an environmentally friendly alternative fuel for a CI engine and it can palliate regulated and unregulated emissions. Biodiesel is substantially found to reduce the emissions of hydrocarbons, carbon monoxide, and particulate matter, but increasing (10–15%) oxides of nitrogen (NO_x) emissions compared with conventional diesel fuel. The accurate cause for NO_x emission is still vague. This paper reviews the effect of biodiesel properties and formation of NO_x emissions and it is classified in three sections. The first section bestows the NO_x formation mechanisms. The second edition deals with the influence of formation and biodiesel properties on NO_x emissions. Finally, a few prevailing conclusions are epitomised, and more researches are pointed out.     

Enhanced ignition of biomass in presence of NOx

Accumulation of combustible biomass residues on hot surfaces of processing machineries can pose fire hazards. In addition, the presence of nitrogen oxides (NO_x) from plant equipment alters the local conditions, aggravating the propensity for low temperature ignition risks. This study presents an experimental study on a relative effect of NO_x on ignition temperature of morpholine, an important surrogate of biomass, to reveal the sensitising role of NO_x in ignition of biomass fuels and to gain mechanistic insights into the chemical aspect of this behaviour in fire. The experiments employed a flow-through tubular reactor, operated at constant pressure and residence time of 1.01 bar and 1.0 s, respectively, and coupled with a Fourier-transform infrared spectroscope. For a representative fuel-rich condition (Φ=1.25), the concentration of NO_x as small as 0.06% lowers the ignition temperature of morpholine by 150 °C, i.e., from approximately 500 °C to 350 °C. The density functional theory (DFT) calculations performed with the CBS-QB3 composite method, that comprises a complete basis set, characterised the dynamics and energies of the elementary nitration reactions. We related the observed reduction in ignition temperature to the formation of unstable nitrite and nitrate adducts, as the result of addition of NO_x species to morphyl and peroxyl radicals. Furthermore, the reaction of NO_x with low-temperature hydroperoxyl radical leads to the formation of active OH species that also propagate the ignition process. The present findings quantify the ignition behaviour of biomass under NO_x–doped atmospheres. The result is of great importance in practical applications, indicating that safe operation of wood-working plants requires avoiding trace concentration of NO_x within the vicinity of biomass residues. This can be facilitated by proper (and separate) venting of engine exhausts.     

Development of De-NOx selective catalytic reduction catalyst using V2O5 –TiO2 supported on a ceramic filter candle

This study reports the development of a V₂O₅-TiO₂-based selective catalytic reduction (SCR) catalyst supported on alumina-silicate water filter candles for NO_x abatement. The synthesised catalysts have been characterised by thermogravimetry/differential scanning calorimetry, X-ray diffraction, scanning electron microscope and measurement of NO_x removal performance. The catalyst synthesised under optimal conditions shows NO_x reduction efficiency of >97%. SCR performance has been augmented using O₂ as a carrier gas. This simple, reproducible procedure can have wide applications in NOx abatement.     

Trends in NOx abatement: A review

Implementation of stringent regulations of NO_x emission requires the development of new technologies for NO_x removal from exhaust gases. This article summarizes current state of NO_x abatement strategy. Firstly, the influence of NO_x on environment and human health is described. The main focus is put on NO_x control methods applied in combustion of fossil fuels in power stations and mobile vehicles, as well as methods used in chemical industry. Furthermore the implementation of ozone and other oxidizing agents in NO_x oxidation is emphasized.     

Correlation of the ratio of non-methane hydrocarbon and nitrogen oxide concentrations in the atmosphere and outdoor environment

A correlation between atmospheric pollution due to the emission of volatile organic compounds (VOC) and the non-methane hydrocarbon/nitrogen oxide (NMHC/NO_x) ratio has been determined. We supposed the source of NMHC in a region using the NMHC/NO_x ratio without needing to consider diffusion and dilution due to meteorological conditions. At general measurement stations in Neyagawa and Higashiosaka cities in Osaka Prefecture, the NMHC/NO_x ratio was high in summer though the NMHC and NO_x concentrations were high in early winter. Conversely, measurements of the ratio at a traffic measurement station in Shijonawate did not have this pattern. That is, NMHC emission increased with the temperature in Neyagawa and Higashiosaka. It was concluded the waste plastic processing facility increased the NMHC/NO_x ratio by comparing the change in the annually averaged NMHC/NO_x ratio at Neyagawa and Higashiosaka with the developments of disposal and treatment facilities in Neyagawa. In the case of Neyagawa, ventilation is not suitable for improving indoor air quality, because the outdoor pollution level can be higher than that indoors. The NMHC/NO_x ratio is a useful index to evaluate the change in the regional environment due to VOC pollution, and it can judge whether outdoor air can improve indoor air quality by ventilation.     

Ozone precursors for the São Paulo Metropolitan Area

Ozone represents the main atmospheric pollutant in the São Paulo Metropolitan Area (SPMA). In this region, its concentration exceeds the national air quality standards for several days out of the year. Ozone is a secondary pollutant and is a product of VOCs, NO_x, and sunlight. Thus, it is very difficult to elaborate efficient strategies for its reduction. Computational simulations may provide an interesting alternative to evaluate the many factors that affect ozone formation. In this study, the trajectory model OZIPR was used together with the SAPRC chemical mechanism to determine the incremental reactivity scale for VOCs in the SPMA. VOC input data were obtained from two campaigns that were performed in the studied area in 2006. Values for CO, NO_x, and meteorological parameters were obtained by automatic monitors. Five base-cases were created to verify the variation in maximum ozone concentration and thus determine the ozone formation potential of each VOC. NO_x and VOC emissions were independently and simultaneously reduced by 5, 10, 20, and 30% to verify variations in ozone formation. With the simulator output data, ozone isopleths charts were generated for the city of São Paulo. Analysis of the obtained results shows that the most frequent compounds found among the ten main ozone precursors in São Paulo, using the reactivity scales created from the five base-cases, were: formaldehyde, acetaldehyde, propene, isoprene, cis-2-butene, and trans-2-butene, with formaldehyde being always the main ozone precursor compound. The simulations also show that an efficient strategy to decrease ozone concentrations in the SPMA would be to reduce total VOC emissions. The same strategy is not possible for NO_x, as the reduction of these pollutants would increase ozone concentrations.     

Detailed chemical analysis of regional-scale air pollution in western Portugal using an adapted version of MCM v3.1

A version of the Master Chemical Mechanism (MCM) v3.1, refined on the basis of recent chamber evaluations, has been incorporated into a Photochemical Trajectory Model (PTM) and applied to the simulation of boundary layer photochemistry in the Portuguese west coast region. Comparison of modelled concentrations of ozone and a number of other species (NO_x and selected hydrocarbons and organic oxygenates) was carried out, using data from three connected sites on two case study days when well-defined sea breeze conditions were established. The ozone concentrations obtained through the application of the PTM are a good approximation to the measured values, the average difference being ca. 15%, indicating that the model was acceptable for evaluation of the details of the chemical processing. The detailed chemistry is examined, allowing conclusions to be drawn concerning chemical interferences in the measurements of NO₂, and in relation to the sensitivity of ozone formation to changes in ambient temperature. Three important, and comparable, contributions to the temperature sensitivity are identified and quantified, namely (i) an effect of increasing biogenic emissions with temperature; (ii) an effect of increasing ambient water vapour concentration with temperature, and its influence on radical production; and (iii) an increase in VOC oxidation chain lengths resulting from the temperature-dependence of the kinetic parameters, particularly in relation to the stability of PAN and its higher analogues. The sensitivity of the simulations to the refinements implemented into MCM v3.1 are also presented and discussed.     

Impacts of motor vehicle inspection and maintenance on emission reductions in Southern California

The effectiveness of a proposed California mandatory annual vehicle inspection/ maintenance (I/M) program in reducing reactive hydrocarbon (RHC) and oxides of nitrogen (NO_x) emissions is evaluated in this report. Emission factors are derived from California in-use light duty passenger vehicle data by simple linear regression analysis for pre- and post-maintenance conditions. Percentage reductions in emissions are calculated, based on assumed vehicle fleet mixes, and compared with estimates from the California Air Resources Board (CARB) and the California South Coast Air Basin Air Quality Management Plan (AQMP). Future year estimates of RHC and NO_x emissions predict smaller RHC reduction than the CARB in both 1982 and 1987. NO_x reduction is underpredicted by the CARB in 1987. A comparison of reductions determined in this study with the South Coast Air Basin AQMP shows that the RHC reductions expected are equivalent; the AQMP NO_x reduction is significantly lower. These results have significance in meeting future air quality goals for Southern California, and point out the effectiveness of an I/M program in reducing total RHC and NO_x emissions from light duty passenger vehicles.     

Emission characteristic of hydrogen and gasoline blend in spark-ignited engine

Hydrogen is an energy carrier that can transform our fossil fuel-dependent economy into a hydrogen economy, which can provide an emission-free transportation fuel. Hydrogen-fuelled engines are known for several advantages, among which is the very low concentration of pollutants in the exhaust gases compared with internal combustion engines using traditional or other alternative fuels. Hydrogen-driven vehicles thus reduce both local and global emissions. It is an energy carrier that can be used in internal combustion engines or fuel cells producing virtually no greenhouse gas emissions when combusted with oxygen. The only significant emission is water vapour. The effect of blending of hydrogen with gasoline is analysed in this current paper. Both HC and NO_x concentration decrease with the increase in hydrogen fractions. The results were analysed by collecting data on different crank angles and at 5%, 10%, 15% and 20% of hydrogen introduction into combustion chamber along with gasoline as base fuel.     

Modeling residential indoor concentrations of PM2.5, NO2, NOx,and secondhand smoke in the Subpopulations and Intermediate Outcome Measures in COPD (SPIROMICS) Air study

Increased outdoor concentrations of fine particulate matter (PM_2.5) and oxides of nitrogen (NO₂, NO_x) are associated with respiratory and cardiovascular morbidity in adults and children. However, people spend most of their time indoors and this is particularly true for individuals with chronic obstructive pulmonary disease (COPD). Both outdoor and indoor air pollution may accelerate lung function loss in individuals with COPD, but it is not feasible to measure indoor pollutant concentrations in all participants in large cohort studies. We aimed to understand indoor exposures in a cohort of adults (SPIROMICS Air, the SubPopulations and Intermediate Outcome Measures in COPD Study of Air pollution). We developed models for the entire cohort based on monitoring in a subset of homes, to predict mean 2-week–measured concentrations of PM_2.5, NO₂, NO_x, and nicotine, using home and behavioral questionnaire responses available in the full cohort. Models incorporating socioeconomic, meteorological, behavioral, and residential information together explained about 60% of the variation in indoor concentration of each pollutant. Cross-validated R² for best indoor prediction models ranged from 0.43 (NO_x) to 0.51 (NO₂). Models based on questionnaire responses and estimated outdoor concentrations successfully explained most variation in indoor PM_2.5, NO₂, NO_x, and nicotine concentrations.     

Reduced NOx and PM10 emissions on urban motorways in The Netherlands by 80 km/h speed management

A speed limit of 80 km/h with “strict enforcement” has been introduced in 2005 on zones of urban motorways in The Netherlands with the aim to improve air quality of NO₂ and PM₁₀ along these motorways. Strict enforcement means speed control by camera surveillance over the whole trajectory of 2-4 km combined with licence plate recognition and automatic fining in case of exceeding the speed limit. Traffic data measured in Rotterdam and Amsterdam at the zones without and with speed management showed that traffic dynamics have been significantly reduced as a result of speed management with strict enforcement. Reduction of traffic dynamics results in more free-flowing traffic with relatively less NO_x and exhaust PM₁₀ emissions compared to congested traffic, i.e., stop-and-go traffic.The actual effect on NO_x and PM₁₀ emissions at these speed management zones was studied in the cities Rotterdam and Amsterdam. The study was performed in two different ways: firstly by measurements and by modelling the contribution to NO_x and PM₁₀ concentrations on both sides of the motorways, and secondly by estimating the change in traffic dynamics and the effect on emissions. From the results of both approaches in this study, it was concluded that in our case study in the Netherlands emission reduction by speed management is in the range of 5-30% for NO_x and 5-25% for PM₁₀. Actual emission reductions by speed management at a specific motorway mainly depend on the ratio of congested traffic prior and after implementation of speed management. The larger this ratio, the larger is the relative emission reduction. The impact on air quality of 80 km/h for NO_x and PM₁₀ is largest on motorways with a high fraction of heavy-duty vehicles.     

Experimental study on particulate and NOx emissions of a diesel engine fueled with ultra low sulfur diesel, RME-diesel blends and PME-diesel blends

Ultra low sulfur diesel and two different kinds of biodiesel fuels blended with baseline diesel fuel in 5% and 20% v/v were tested in a Cummins 4BTA direct injection diesel engine, with a turbocharger and an intercooler. Experiments were conducted under five engine loads at two steady speeds (1500 rpm and 2500 rpm). The study aims at investigating the engine performance, NO_x emission, smoke opacity, PM composition, PM size distribution and comparing the impacts of low sulfur content of biodiesel with ULSD on the particulate emission. The results indicate that, compared to base diesel fuel, the increase of biodiesel in blends could cause certain increase in both brake specific fuel consumption and brake thermal efficiency. Compared with baseline diesel fuel, the biodiesel blends bring about more NO_x emissions. With the proportion of biodiesel increase in blends, the smoke opacity decreases, while total particle number concentration increases. Meanwhile the ULSD gives lower NO_x emissions, smoke opacity and total number concentration than those of baseline diesel fuel. In addition, the percentages of SOF and sulfate in particulates increase with biodiesel in blends, while the dry soot friction decreases obviously. Compared with baseline diesel fuel, the biodiesel blends increase the total nucleation number concentration, while ULSD reduces the total nucleation number concentration effectively, although they all have lower sulfur content. It means that, for ULSD, the lower sulfur content is the dominant factor for suppressing nucleation particles formation, while for biodiesel blends, lower volatile, lower aromatic content and higher oxygen content of biodiesel are key factors for improving the nucleation particles formation. The results demonstrate that the higher NO_x emission and total nucleation number concentration are considered as the big obstacles of the application of biodiesel in diesel engine.     

Effect of TiO2 and nozzle geometry on diesel emissions fuelled with biodiesel blends

In this present study, the compression ignition engine was designed to run on CIME (Calophyllum inophyllum methyl ester) biodiesel with nanoparticles. The TiO₂ nanoparticle is added to the biodiesel in the form of nanofluid at concentration levels of 100?ppm whereas ethanox is added at levels of 100, 200 and 500?ppm. The nanoparticle and the ethanox are dispersed by the ultrasonication process. The addition of nanofluid reduces the particulate emission like nitrogen oxide (NO_x) at 100% load. The efficiency is better and emission is reduced owing to the influence of explosion of water molecules present in the biodiesel. We found ethanox to be a superlative nanofluid to reduce the emission of toxic gas at appreciable levels. We have witnessed a 20% reduction in emission of NO_x and 10% reduction of other particulate emission. In addition, the exit geometry of exhaust is modified from a circular shape to an elliptical one and the consequence of the geometry is calculated.     

In situ measurements of SO2, NOx, NOy, and O3 in Beijing, China during August 2008

The measurement of SO₂, O₃, NO, NO₂, and NO_y mixing ratios was conducted from Jul 28, 2008 to Sep 2, 2008 at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP, CAS) station, which is 2 km southwest to the Beijing National Stadium (Bird's Nest/Olympic Stadium). Photochemical pollution was detected during the measurement on Aug 2, 2008, and the maximum hourly average [O₃] reached 128 ppbv, caused by both the local photochemical reactions and regional transportation of pollutants. The NO_x Ozone Production Efficiency (OPE (NO_x)) values were 6.9 and 20.2 on Aug 2 and Aug 24, 2008 respectively, which were the two days with highest O₃ pollution. The OPE (NO_x) of 6.9 on Aug 2 was within a typical range in city area, and it implied that the high O₃ could be due to local sources. While OPE (NO_x) of 20.2 on Aug 24 was larger than the typical value in the region, but lower than that of the surrounding clean area during 2008 Beijing Olympics Closing Ceremony. It indicated that the pollution was because of regional transportation of pollutants. In addition, 60% of the extent of the Smog Production Model (SPM) data was less than 0.6 and the rest was slightly larger than 0.6, with maximum of 0.78. It indicated that the sensitivity of O₃ generated was volatile organic compounds (VOCs) control during the observation period. The SPM results also implied that O₃ product in high-O₃ day is a transition state from VOCs sensitivity to NO_x sensitivity. Lastly, the analysis of the wind direction and extent of SPM showed that the photochemical pollution of this region was mostly subject to the influence of southeastern air flow in the summer.     

Experimental exploration on NO x diminution by the combined effect of antioxidant additives with SCR in a diesel engine powered by neem biodiesel

ABSTRACT

The use of biodiesel in diesel engines leads to the reduction of tail pipe emissions; But, several researchers portray that the use of biodiesel produces more NO_x pollution than diesel-fuelled engines, which is an hindrance for the scope of biodiesel usage. In this work, an experimental investigation of the combined effect of antioxidant additive added in the fuel as a fuel modification technique and SCR (selective catalytic reduction) as after a treatment technique on NO _x reduction in a neem biodiesel-powered compression ignition engine has been conducted. Results show that the antioxidant additive combined with the SCR technique reduces the NO _x emission significantly by 82% and there was a slight increase in UBHC and CO emission due to the addition of oxidation-suppressing additives with neem biodiesel and aqueous urea solution injection at the exhaust without a major drop in BTE and fuel consumption.     

Experimental investigations of direct injection compression ignition engine by using Coconut,and Karanja biodiesel fuels with emulsions of microalgae based antioxidant

The Compression Ignition (CI) engines are playing vital role in the transportation sector; because of their lower maintenance cost even. The practice of Diesel or biodiesel is increasing Green House Gases (GHG) such as NO_x, particulate matter in the environment. Among all GHG emissions, NO_x is most harmful to human, environment. The use of additives in Diesel, biodiesel their blends in CI engine is very well practicing fuel modification technique to reduce GHG emissions. The higher cost of phenol, amine-based antioxidants are causing to increase CI engine operating cost. In this work, to investigate unmodified Direct Injection Compression Ignition engine characteristics. The Mixed culture Microalgae (MCM) biomass particles used as an antioxidant additive in pure Coconut, Karanja biodiesel. The brake thermal efficiency improved because of the explosion of MCM particles. The NO_x emissions reduced due to the absorption of heat from the combustion chamber by microalgae particle.     

Photocatalytic cement-based materials: Comparison of nitrogen oxides and toluene removal potentials and evaluation of self-cleaning performance

Using cement-based building materials as a matrix for nano-photocatalysts is an important development for the large scale application of photocatalytic technologies. Air pollution mitigation and self-cleaning surface are two major applications of photocatalytic building materials. In this study, a comparison was made to evaluate the performance of TiO₂ modified concrete surface layers for NO_x and VOC degradation. The self-cleaning performance of TiO₂ modified self-compacting mortars (SCM) developed for decorative applications was also evaluated. The results show that the photocatalytic conversion of toluene by the TiO₂ modified surface layer was not detected, although NO_x could be effectively removed under the same conditions. The presence of toluene did not influence the NO_x removal process. TiO₂ modified SCM were found to be effective in the discoloration of rhodamine B under UV and strong halogen light irradiation. The level of adsorption of the air contaminants onto the active sites of the cement-TiO₂ composite was identified to be the key factor determining the subsequent photocatalytic efficiency.     

Chemical and photochemical degradation of polycyclic aromatic hydrocarbons in the atmosphere

Results of studies on chemical and photochemical transformations of polycyclic aromatic hydrocarbons (PAH) are reviewed. Various parameters may modify the kinetics of these reactions, such as light intensity, concentration of gaseous pollutants (NO_x, SO_x, O₃), chemico-physical characteristics of particulates or substrates into which the PAH are adsorbed. Depending on these variables, the half-life of BaP varies from 10 to 104 300 min. The possibility of artefact formation during sampling is discussed. The necessity of clarifying mechanisms for these phenomena, in order to correctly evaluate the risks for exposed populations, is emphasized.     

Economic dualism and air quality in Italy: testing the Environmental Kuznets Curve hypothesis

The present work tests the Environmental Kuznets Curve hypothesis (EKC) in Italy for three air pollutants, namely CO₂, NO_x and SO_x, using an emissions data-set disaggregated at the provincial level. An empirical investigation, conducted through both a panel data and a cross-section approach, suggests the existence of the EKC at the national level for CO₂ and NO_x, but not for SO_x. Even more interestingly, the results achieved seem to be affected by the geographical dimension. When the data-set is split into two sub-samples of southern and central-northern provinces, the EKC is in fact found exclusively in the centre-north. This suggests that the inverted U-shaped relationship at the national level is mainly caused by the contribution of provinces that more than offset the environmental performance of their southern counterparts. The sub-sample estimation reveals that the geographical dimension also affects the inverted U-shaped relationship for SO_x and income, which is found exclusively in the southern provinces of the peninsula, although it does not contribute towards the EKC at the national level.