Excess NOx Emissions Research Articles

Effects of sub-atmospheric pressure on appearance and pollutant formation of inverse diffusion flame within a confined space

Gas-fired boilers operating at high-altitude regions often suffer from inadequate output, decreased thermal efficiency, and excessive NOx emissions. The effect of sub-atmospheric pressure on flame appearance and pollutant formation is the main reason for those problems, and thus needs to be clarified particularly under furnace combustion conditions with a fixed excess air coefficient. Inverse diffusion is a widely employed fuel–air configuration in burners of gas-fired boilers, and therefore the flame appearance, CO generation, and NO generation were experimentally investigated in this paper by adopting a low-pressure quartz tube reactor. Results show that the flame is elongated from reducing pressure under fuel-lean conditions, mainly due to the reduced oxygen mass concentration and the elevated jet velocity. Under fuel-rich combustion conditions, however, the flame is shorted at sub-atmospheric pressure from the suppressed soot formation. The reduced pressure leads to an increase in the global strain rate, making the flame more prone to uplift. With decreasing pressure, the increased air–fuel mixing and flame length facilitate the gas burnout, thus decreasing CO generation. The sub-atmospheric pressure could evidently reduce the NO generation under fuel-rich conditions, but slightly increase it under fuel-lean conditions. Under fuel-lean conditions, the NO major pathways (prompt, thermal, NNH, and N2O) are promoted which leads to an increase in NO generation with decreasing pressure. Under fuel-rich conditions, however, NO formation is suppressed from the decreased rate of reaction N2+CH↔HCN+N.

Model construction and multi-objective performance optimization of a biodiesel-diesel dual-fuel engine based on CNN-GRU

To tackle the challenges of low efficiency and excessive NOx emissions in biodiesel-diesel dual-fuel engines, this paper presents an optimization method using the Pareto-multiple objective snake optimizer (Pareto-MOSO) to drive a convolutional neural network-gated recurrent unit (CNN-GRU). In the Pareto-MOSO, brake specific fuel consumption (BSFC), NOx, Soot, and CO are optimized by changing the engine control parameters, including injection timing (Tinject), engine speed (n), biodiesel blending ratio, torque (Ttorque), exhaust gas recirculation (EGR rate), intake pressure (Pin), and rail pressure (Prail). The experiment generates training data for CNN-GRU and verifies the accuracy of the Pareto-MOSO optimization results. The findings suggest that the optimized engine exhibits a balanced correlation between economy and emissions under propulsion characteristics. Furthermore, the NOx emissions are all in accordance with the IMO Tier III emission regulations. Under the rated condition, Scheme 2 demonstrates a significant reduction of 76.57 % in NOx emissions. However, this optimization has resulted in a 1.63 % increase in BSFC compared to its pre-optimized state. Therefore, the adoption of suitable control strategies proves advantageous in addressing the trade-off between economy and emissions of engines.

Hybrid rich- and lean-premixed ammonia-hydrogen combustion for mitigation of NOx emissions and thermoacoustic instabilities

The large-scale direct utilization of two carbon-free fuels, ammonia and hydrogen, is currently attracting significant interest in the context of the development of new gas turbine combustion technologies, with paying close attention to the reduction of nitrogen oxides and unburned ammonia emissions. Motivated by recent observations that rich-premixed conditions tend to mitigate excessive NOx emissions from ammonia combustion, and that uniformly blended ammonia-hydrogen fuel/air mixtures tend to increase NOx production exponentially, here we propose a hybrid configuration of hydrogen-doped rich-premixed ammonia-air flames (inner stage) and lean-premixed pure hydrogen-air flames (outer stage) in a radially stratified primary reaction zone. This fuel staging scheme offers a possible mechanism for chemical kinetics-controlled NOx abatement and asymmetry-induced thermoacoustic instability suppression. The relevance and feasibility of the unconventional premixing approach are rigorously evaluated based on detailed measurements of exhaust gas concentrations and self-excited pressure fluctuations, in conjunction with OH*/NH2*/NH* chemiluminescence and OH PLIF imaging measurements. We observe that drastically different non-homogeneous reaction regions can be stably established in a comparatively compact combustion volume without producing negative flame stabilization effects – such as blowoff of less reactive ammonia flames and flashback of more reactive hydrogen flames. As compared with the uniform-blend baseline condition, the hybrid staging method is shown to significantly mitigate total nitrogen oxides emissions, from 7764 to 310 ppmvd (96 % reduction), and achieving an approximately two-fold reduction in dynamic pressure amplitude. Interestingly, hydrogen-enriched rich-premixed ammonia flames are revealed to exhibit anomalous oscillatory states originating from the preferential diffusion of hydrogen molecules and reaction rate-dependent separation of reactive layers, enabling interacting non-homogeneous reaction zones with markedly different characteristic time scales to resist the growth of intense pressure perturbations.

The impact on passenger car emissions associated with the promotion and demise of diesel fuel

The promotion and growth in the use of diesel fuel in passenger cars in the UK and Europe over the past two decades led to considerable adverse air quality impacts in urban areas and more widely. In this work, we construct a multi-decade analysis of passenger car emissions in the UK based on real driving emissions data. An important part of the study is the use of extensive vehicle emission remote sensing data covering multiple measurement locations, time periods, environmental conditions and consisting of over 600,000 measurements. These data are used to consider two scenarios: first, that diesel fuel use was not promoted in the early 2000s for climate mitigation reasons, and second, that there was not a dramatic decline in diesel fuel use following the Dieselgate scandal. The strong growth of diesel fuel use coincided with a time when diesel NOx emissions were high and, conversely, the strong decrease of diesel fuel use coincided with a time when diesel vehicle after-treatment systems for NOx control were effective. We estimate that the growth in diesel car use in the UK results in excess NOx emissions of 721 kt over a three decade period; equivalent to over 7 times total annual passenger car NOx emissions and greater than total UK NOx emissions of 681.8 kt in 2021 and with an associated damage cost of £5.875 billion. However, the sharp move away from diesel fuel post-Dieselgate only reduced NOx emissions by 41 kt owing to the effectiveness of modern diesel aftertreatment systems.

Co-combustion strategy of waste energetic materials with pine sawdust for efficient NOx emissions reduction

Excessive NOx emissions during incineration of waste energetic materials (EMs) is harmful to the environment. Co-combustion technologies with biomass have demonstrated remarkable advantages in reducing NOx emissions. Herein, the co-combustion characteristics and NOx emission behaviors of waste double-base propellant (DP) and pine sawdust (PS) were investigated via thermogravimetric (TG) and fixed-bed experiments firstly. Meanwhile, the general full factorial design (GFFD) was performed to explore the effects of different factors on the NOx emissions of co-combustion. The interaction mechanism between DP and PS was discussed as well. Moreover, the interaction of three other typical waste EMs (RDX, TNT, and triple-base propellant) co-combustion with PS in NOx emissions was studied utilizing orthogonal experiments. The kinetics under air atmosphere indicated that the mixing of PS slightly diminished the combustion reactivity of DP, conversely, the remaining residue of DP combustion promoted the combustion of PS. Oxygen concentration, temperature and mixing ratio all had significant effects on NOx emissions of co-combustion between DP and PS, the degree of effect decreased in turn. Overall, the mixing of PS all suppressed the NOx emissions with significant synergistic effects, optimal synergistic effect at 20 wt% of PS mixing. The synergistic effect in oxygen environment was lower than that in oxygen-free environment. Meanwhile, increasing temperature contributed to enlarging the synergistic effect. Additionally, there was synergistic effect of TNT and PS co-combustion, whereas RDX, TP exerted inhibition effect of co-combustion with PS. Therefore, the co-combustion strategy of waste EMs with PS provides reliable data support and guidance for the control of NOx emissions during the incineration of waste EMs.

Effects of compression and mixing ratio on NH3/H2 fueled Si engine performance, combustion stability, and emission

• NH 3 /H 2 are attractive alternative fuels for the worldwide decarbonization movement. • H 2 is an excellent ammonia additive because it eliminates the cold start problem. • The combustion of ammonia/hydrogen reduces fuel waste while increasing BP. • There are no greenhouse gas emissions from ammonia/hydrogen combustion. • As a result, it appears that fuel NOx predominates over thermal NOx. Carbon-free fuels for the worldwide decarbonization movement are ammonia and hydrogen. The experiment is conducted under WOT conditions with a constant ignition timing of 24°CA BTDC to evaluate performance, combustion stability, and emissions with varying CR (12 to 15), hydrogen energy fractions (5 to 21%), and engine speeds between 1500 and 1700 RPM. BP increased by 31.2% at 1700RPM and BTE increased by 39.0% at 1500RPM, despite a 9% decrease in volumetric efficiency at 1700RPM, from 5% hydrogen fraction at CR12 to 21% hydrogen fraction at CR15.The combustion process is sped up by the effect of hydrogen fraction and CR, causing the flame development and propagation period to shorten. NOx emission was increased significantly with hydrogen and CR, with an increase of 42.34% from 5% hydrogen at CR12 to 21% hydrogen at CR15 at 1700 RPM. Excessive NOx emissions are a drawback that can be successfully controlled by installing after treatment or exhaust gas recirculation technologies. Ammonia is another important key element used to reduce NOx emissions from vehicles because it is used in SCR.

Evolution of N2O production at lean combustion condition in NH3/H2/air premixed swirling flames

In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures.

Application and Development of Selective Catalytic Reduction Technology for Marine Low-Speed Diesel Engine: Trade-Off among High Sulfur Fuel, High Thermal Efficiency, and Low Pollution Emission

In recent years, the International Maritime Organization (IMO), Europe, and the United States and other countries have set up different emission control areas (ECA) for ship exhaust pollutants to enforce more stringent pollutant emission regulations. In order to meet the current IMO Tier III emission regulations, an after-treatment device must be installed in the exhaust system of the ship power plant to reduce the ship NOx emissions. At present, selective catalytic reduction technology (SCR) is one of the main technical routes to resolve excess NOx emissions of marine diesel engines, and is the only NOx emission reduction technology recognized by the IMO that can be used for various ship engines. Compared with the conventional low-pressure SCR system, the high-pressure SCR system can be applied to low-speed marine diesel engines that burn inferior fuels, but its working conditions are relatively harsh, and it can be susceptible to operational problems such as sulfuric acid corrosion, salt blockage, and switching delay during the actual ship tests and ship applications. Therefore, it is necessary to improve the design method and matching strategy of the high-pressure SCR system to achieve a more efficient and reliable operation. This article summarizes the technical characteristics and application problems of marine diesel engine SCR systems in detail, tracks the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions. Results showed that low temperature is an important reason for the formation of ammonium nitrate, ammonium sulfate, and other deposits. Additionally, the formed deposits will directly affect the working performance of the SCR systems. The development of SCR technology for marine low-speed engines should be the compromise solution under the requirements of high sulfur fuel, high thermal efficiency, and low pollution emissions. Under the dual restrictions of high sulfur fuel and low exhaust temperature, the low-speed diesel engine SCR systems will inevitably sacrifice part of the engine economy to obtain higher denitrification efficiency and operational reliability.

Prediction of NOx Concentration at SCR Inlet Based on BMIFS-LSTM

As the main energy source for thermal power generation, coal generates a large amount of NOx during its incineration in boilers, and excessive NOx emissions can cause serious pollution to the air environment. Selective catalytic reduction denitrification (SCR) selects the optimal amount of ammonia to be injected for denitrification based on the measurement of NOx concentration by the automatic flue gas monitoring system. Since the automatic flue gas monitoring system has a large delay in measurement, it cannot accurately reflect the real-time changes of NOx concentration at the SCR inlet when the unit load fluctuates, leading to problems such as ammonia escape and NOx emission exceeding the standard. In response to these problems, this paper proposes an SCR inlet NOx concentration prediction algorithm based on BMIFS-LSTM. An improved mutual information feature selection algorithm (BMIFS) is used to filter out the auxiliary variables with maximum correlation and minimum redundancy with NOx concentration, and reduce the coupling and dimensionality among the variables in the data set. The dominant and auxiliary variables are then fed together into a long short-term memory neural network (LSTM) to build a prognostic model. Simulation experiments are conducted using historical operation data of a 300 MW thermal power unit. The experimental results show that the algorithm in this paper reduces the average relative error by 3.45% and the root mean square error by 1.50 compared with the algorithm without auxiliary variable extraction, which can accurately reflect the real-time changes of NOx concentration at the SCR inlet, solve the problem of delay in NOx concentration measurement, and reduce the occurrence of atmospheric pollution caused by excessive NOx emissions.

A novel vortex combustion device: Experiments and numerical simulations with emphasis on the combustion process and NOx emissions

Experimental and numerical studies of combustion process in a vortex flow device have been developed. The modelling part of the study has been performed by means of ANSYS Fluent package. Fuel droplet trajectories and the flow pattern on their motions have been modeled by the function ?injection?. The combustion process utilized the k-? turbulence model. A special trend on the effect of the vortex generator blade orientation on the gross process has been developed. It has been established that optimal process performance (high air excess ratio and low NOx emissions) could be attained with an angle of the vortex generator blade orientation, especially with respect to the minimization of NOx emissions.

Selective catalytic reduction failure of low NH3-NO ratio

An insufficient amount of NH3 (ammonia) will reduce the conversion efficiency of NOx, which may lead to excess NOx emissions, resulting in NH3-SCR failure. In this article, SCR failure caused by a low NH3- NOx ratio is studied systematically by experiments. The main reasons for a low NH3-NOx ratio in SCR include insufficient urea injection, hydrothermal aging of catalysts and urea crystallization. It was found from an insufficient urea injection experiment that with the increase of NH3- NOx ratio, the NOx conversion efficiency of the SCR system increased, but the ammonia leakage also increased. The main influencing factors of NOx conversion efficiency are different under different NH3- NOx ratios. A flow reactor system was used in the catalyst hydrothermal aging experiment to investigate the effect of hydrothermal aging on catalyst activity. After a 24 h hydrothermal aging experiment at 800 °C, the NOx conversion efficiency of the copper-based zeolite catalysts decreased significantly at the boundary of medium and low temperature regions. And the NO2- NOx ratio in the mixture had a significant effect on the catalytic performance. Thermogravimetry coupled to Fourier transform infrared spectroscopy (TG-FTIR) was used to analyze the composition of urea deposits in a urea deposits analysis experiment. It was found that the main components of urea deposits were urea and isocyanic acid (HNCO). Preventing HNCO polymerization, especially the formation of CYA, can decrease the formation of urea deposits.

On-road detection of trucks with high NOx emissions from a patrol vehicle with on-board FTIR analyzer

Technological advances in heavy-duty vehicle engines, allowing them to reach NOx emissions comparable to European diesel passenger cars per km driven, are being compromised by aftermarket defeat devices such as selective catalytic reduction (SCR) emulators, many of which can be quickly deactivated by the driver. In a pilot study, the prevalence of trucks with excess NOx emissions on Czech motorways was evaluated using an ordinary Customs Administration patrol vehicle temporarily fitted with a portable fast-response Fourier Transform Infra Red (FTIR) analyzer, acting as an impromptu chase vehicle. The Euro emissions category of the truck was provided from the motorway toll collection transponders. A total of 222 unique trucks were measured during a one-week pilot project. Of these, 66% were Euro VI, 25% were Euro V, and 9% were older categories. NO/CO2 ratios were calculated as a ratio of numerical integrals of the peaks of measured concentrations, as a ratio of maximum measured concentrations, and by linear regression, with the regression approach yielding most realistic results and mean calculated error of 0.2 g/kWh NO. At assumed 85% NO in NOx and 634 g/kWh mean CO2 emissions, the mean emissions of the cleanest 83% of Euro V and cleanest 63% of Euro VI trucks were within the corresponding NOx limit (2 g/kWh for Euro V, 0.46 g/kWh for Euro VI) multiplied by a factor of 1.5. Providing for some allowance for legitimate occurrences of high NOx emissions, about 10–15% of Euro V and about 10–25% of Euro VI trucks are believed to be excess emitters, with no SCR functionality on about 10–15% of Euro VI trucks. The portable FTIR, temporarily mounted on a law enforcement vehicle, can be readily used as a screening tool, identifying vehicles to be stopped for additional inspection, but also during roadside emissions inspections.

Investigation on regenerative heat exchanger with novel low-leakage system for flue gas denitration in steel industry

In order to counter the excessive NOx emissions caused by the leakage of regenerative rotary gas-to-gas heater (GGH) in the denitration system of steel industry, a new low-leakage system was proposed. An analytical model based on local thermal non-equilibrium was developed and the corresponding calculation program was built to analyze and compare the characteristics of the GGHs with and without the low-leakage system. As circulated flue gas mass flow rate increases, the increasing rate of the scavenge flow is far greater than that of the purge flow, due to the much higher resistance of the purge flow. The temperature distributions of matrix and flue gas were obtained for the GGH with and without the low-leakage system. The scavenge flows can greatly affect the flue gas temperature distribution but has little effect on that of matrix temperature. The effects of matrix height, hydraulic diameter, porosity and rotating speed on the leakage rate and thermal efficiency were examined. The low-leakage system can greatly reduce the leakage rate by up to 66.5% and save up to 12.26 kW fan power in operation, though it could also cause a reduction of the heat exchanger effectiveness of GGH by less than 2.2%. The circulated mass flowrate should not be too large, otherwise the leakage rate cannot be further decreased and the saved fan power would even be reduced.

Sliding-mode control of automotive selective catalytic reduction systems with state estimation

A sliding-mode controller for an automotive selective catalytic reduction system is designed to drive its ammonia surface coverage ratio to the target level. The proposed controller only requires NOx, temperature and air flow sensor measurement installed on most mass production vehicles. Selective catalytic reduction systems have been widely equipped on diesel-powered ground vehicles to remove excessive NOx emissions. The tradeoff between NOx removal efficiency and ammonia slip poses a control challenge on regulating the ammonia surface coverage ratio to a proper level in the presence of disturbance. In this study, a sliding-mode controller is designed with explicit consideration of measurement noise and actuator saturation. The finite time convergence of tracking error is proved by a Lyapunov approach. For implementation purpose, an observer of ammonia surface coverage ratio and ammonia slip is also designed to provide states feedback and fault diagnostic information. The closed-loop controller performance is evaluated under an urban driving scenario based on an experimentally validated model. Results demonstrate the robust tracking performance and estimation accuracy against bounded uncertainties. The overall NOx efficiency is maintained with an acceptable ammonia slip level during the transient test cycle FTP75.

Application of Variable Valve Actuation Strategies and Direct Gasoline Injection Schemes to Reduce Combustion Harshness and Emissions of Boosted HCCI Engine

The present study investigates various measures to reduce pressure rise rates (PRRs) in a residual-affected homogeneous charge compression ignition (HCCI) engine. At the same time, the impact of those measures on efficiency and emissions is assessed. Experimental research was performed on a single cylinder engine equipped with a fully flexible valve train mechanism and direct gasoline injection. The HCCI combustion mode with exhaust gas trapping was realized using negative valve overlap (NVO) and fuel reforming, achieved via the injection of a portion of fuel during exhaust recompression. Three measures are investigated for the PRR control under the same reference operating conditions, namely: (i) variable intake and exhaust valve timing, (ii) boost pressure adjustment, and (iii) split fuel injection to control the amount of fuel injected for reforming. Variable exhaust valve timing enabled control of the amount of trapped residuals, and thus of the compression temperature. The reduction in the amount of trapped residuals, at elevated engine load, delays auto-ignition, which results in a simultaneous reduction of pressure rise rates and nitrogen oxides emissions. The effects of intake valve timing are much more complex because they include the variability in the amount of intake air, the thermodynamic compression ratio, as well as the in-cylinder fluid flow. It was found, however, that both early and late intake valve openings (IVOs) delay auto-ignition and prolong combustion. Additionally, the reduction of the amount of fuel injected during exhaust recompression further delays combustion and reduces combustion rates. Intake pressure reduction has by far the largest effect on peak pressure reduction yet is connected with excessive NOX emissions. The research successfully identifies air-path and injection techniques, which allow for the control of combustion rates and emissions under elevated load regime.

Real world CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars

In this study CO2 and NOx emissions from 149 Euro 5 and 6 diesel, gasoline and hybrid passenger cars were compared using a Portable Emissions Measurement System (PEMS). The models sampled accounted for 56% of all passenger cars sold in Europe in 2016. We found gasoline vehicles had CO2 emissions 13–66% higher than diesel. During urban driving, the average CO2 emission factor was 210.5 (sd. 47) gkm−1 for gasoline and 170.2 (sd. 34) gkm−1 for diesel. Half the gasoline vehicles tested were Gasoline Direct Injection (GDI). Euro 6 GDI engines <1.4ℓ delivered ~17% CO2 reduction compared to Port Fuel Injection (PFI). Gasoline vehicles delivered an 86–96% reduction in NOx emissions compared to diesel cars. The average urban NOx emission from Euro 6 diesel vehicles 0.44 (sd. 0.44) gkm−1 was 11 times higher than for gasoline 0.04 (sd. 0.04) gkm−1. We also analysed two gasoline-electric hybrids which out-performed both gasoline and diesel for NOx and CO2. We conclude action is required to mitigate the public health risk created by excessive NOx emissions from modern diesel vehicles. Replacing diesel with gasoline would incur a substantial CO2 penalty, however greater uptake of hybrid vehicles would likely reduce both CO2 and NOx emissions. Discrimination of vehicles on the basis of Euro standard is arbitrary and incentives should promote vehicles with the lowest real-world emissions of both NOx and CO2.

The potential health, financial and environmental impacts of dieselgate in Ireland

ABSTRACTThe transportation sector is the greatest contributor to air pollution. With the booming demand for transportation, reducing the pollution has become one of the main concerns of researchers. EPA emission standards are designed to protect air quality and human health. Diesel Euro 5 NOx has become a matter of disquiet since it has been found that NOx emissions are significantly exceeding the standard limit. This paper presents a study to estimate the disparity in real-world NOx emission levels resulted from all diesel Euro 5 passenger cars (PC) and light commercial vehicles (LCV) that are present in Ireland. NOx emission levels calculated based on laboratory test results, on-road measurements and the COPERT 4 model were compared. Additionally, NOx emission levels from the defective Volkswagen models have been calculated to quantify the effect of the Volkswagen scandal on Ireland. Impacts of excess NOx emissions on health and cost have also been presented.

Impact of excess NOx emissions from diesel cars on air quality, public health and eutrophication in Europe

Diesel cars have been emitting four to seven times more NOx in on-road driving than in type approval tests. These ‘excess emissions’ are a consequence of deliberate design of the vehicle’s after-treatment system, as investigations during the ‘Dieselgate’ scandal have revealed. Here we calculate health and environmental impacts of these excess NOx emissions in all European countries for the year 2013. We use national emissions reported officially under the UNECE Convention for Long-range Transport of Atmospheric Pollutants and employ the EMEP MSC-W Chemistry Transport Model and the GAINS Integrated Assessment Model to determine atmospheric concentrations and resulting impacts. We compare with impacts from hypothetical emissions where light duty diesel vehicles are assumed to emit only as much as their respective type approval limit value or as little as petrol cars of the same age. Excess NO2 concentrations can also have direct health impacts, but these overlap with the impacts from particulate matter (PM) and are not included here. We estimate that almost 10 000 premature deaths from PM2.5 and ozone in the adult population (age >30 years) can be attributed to the NOx emissions from diesel cars and light commercial vehicles in EU28 plus Norway and Switzerland in 2013. About 50% of these could have been avoided if diesel limits had been achieved also in on-road driving; and had diesel cars emitted as little NOx as petrol cars, 80% of these premature deaths could have been avoided. Ecosystem eutrophication impacts (critical load exceedances) from the same diesel vehicles would also have been reduced at similar rates as for the health effects.

Public health impacts of excess NOx emissions from Volkswagen diesel passenger vehicles in Germany

In September 2015, the Volkswagen Group (VW) admitted the use of ‘defeat devices’ designed to lower emissions measured during VW vehicle testing for regulatory purposes. Globally, 11 million cars sold between 2008 and 2015 are affected, including about 2.6 million in Germany. On-road emissions tests have yielded mean on-road NOx emissions for these cars of 0.85 g km−1, over four times the applicable European limit of 0.18 g km−1. This study estimates the human health impacts and costs associated with excess emissions from VW cars driven in Germany. A distribution of on-road emissions factors is derived from existing measurements and combined with sales data and a vehicle fleet model to estimate total excess NOx emissions. These emissions are distributed on a 25 by 28 km grid covering Europe, using the German Federal Environmental Protection Agency’s (UBA) estimate of the spatial distribution of NOx emissions from passenger cars in Germany. We use the GEOS-Chem chemistry-transport model to predict the corresponding increase in population exposure to fine particulate matter and ozone in the European Union, Switzerland, and Norway, and a set of concentration-response functions to estimate mortality outcomes in terms of early deaths and of life-years lost. Integrated over the sales period (2008–2015), we estimate median mortality impacts from VW excess emissions in Germany to be 1200 premature deaths in Europe, corresponding to 13 000 life-years lost and 1.9 billion EUR in costs associated with life-years lost. Approximately 60% of mortality costs occur outside Germany. For the current fleet, we estimate that if on-road emissions for all affected VW vehicles in Germany are reduced to the applicable European emission standard by the end of 2017, this would avert 29 000 life-years lost and 4.1 billion 2015 EUR in health costs (median estimates) relative to a counterfactual case with no recall.

Stability maps of non-premixed methane flames in different oxidizing environments of a gas turbine model combustor

Oxy-fuel combustion provides a promising solution to the problem of excessive NOx emissions generated by air-based combustion systems; NOx is potentially eliminated in the absence of air-based nitrogen. However, severe temperatures are reached if fuel is burned in pure oxygen. Dilution by CO2 is thus implemented to control the flame temperature. The addition of CO2, however, was found to retard chemical-kinetics rates and negatively affect the laminar burning velocity and combustion efficiency. This study thus set out to examine oxy-fuel combustion and compare it to oxygen-enriched air-fuel combustion based on flame stability and appearance. Experiments were conducted on a swirl-stabilized model gas-turbine combustor to determine the ranges of stable operation of methane flames in different oxidizer environments, including CO2-diluted oxy-combustion and oxygen-enriched air-combustion. Based on that, two sets of experiments were conducted over ranges of oxidizer Reynolds number, equivalence ratio, and oxygen fraction in the oxidizer mixture. The first set of experiments considered CO2-diluted oxy-combustion, while the second set considered oxygen-enriched air-combustion. For both sets, the results showed that the stability map widens as the oxygen fraction is increased in the oxidizer mixture. This can be attributed to higher flame speeds, which assist flame stabilization under lean operation. For the same oxygen fraction and Reynolds number, the oxy-combustion flames were found to stabilize at higher equivalence ratios and fuel flow rates when compared to the oxygen-enriched air flames. This difference in flame stability magnifies at smaller oxygen fractions and gradually diminishes as the oxygen fraction is increased.