Final NOx Research Articles

Exploiting synergies between sustainable ammonia and nitric acid production: A techno-economic assessment

The decarbonization of the fertilizer industry is an important step towards a climate-neutral society. Nitric acid produced via the Ostwald process is a key precursor to nitrogen-based fertilizers, with the production of ammonia representing an important intermediate step. This work focuses on the search for synergies between the sustainable production of ammonia feedstocks – hydrogen and nitrogen – and nitric acid production in the Ostwald process: Oxygen a by-product of sustainable hydrogen and nitrogen production was considered for injection in the Ostwald process at 4 points. A techno-economic assessment was performed to identify the technical and economic potential of this air enrichment. In addition, the safety implications of applying a higher oxygen concentration in the ammonia combustion step of the Ostwald process was evaluated based on explosion limit simulations. The techno-economic assessment was based on a mono-pressure nitric acid plant with a plant capacity of 700t/d of pure nitric acid at a concentration of 60wt% in water. The investigations of injecting oxygen at four different points of the plant show that daily nitric acid production can be increased by 0.31% and final NOx concentration of the absorption column can be reduced by up to 43.6% by enriching the main air pipeline with oxygen. Optimal oxygen injection could reduce the capital costs by 0.41M€. Nevertheless, the operating costs dominated the final cash flow analysis with ammonia costs accounting for ca. 60% of the total operating costs. The CO2 price would need to increase to at least 233€/t to compensate for the higher green ammonia price and equalize the minimum selling price. As the oxygen injection at the main air line comes with safety risks due to the ammonia explosion limits, we evaluated the effect of O2-enrichment on the explosion limits of NH3-O2-N2 mixtures. The foreseen oxygen enrichment reduced the lower explosion limit only marginally. For a medium pressure plant at 5.8bar the lower explosion limit is reduced to 10.3% for the highest considered oxygen injection case, which is close to the applied ammonia concentration.

Simulation Investigation on the Effects of EGR Ratio and Nozzle Angle on In-Cylinder Combustion and Pollutant Generation of PODE/Methanol Blends

ABSTRACT In order to explore effects of coal-based oxygenated fuels polyoxymethylene dimethyl ether (PODE) and methanol on pollutant emissions of diesel engines, in-cylinder combustion numerical model was developed by coupling PODE/methanol reaction mechanism with CONVERGE software. The influences of exhaust gas recirculation (EGR) and nozzle angle on in-cylinder combustion and pollutant generation of PODE/methanol blends were studied. Results show that with the increase of EGR ratio, the fuel-air equivalence ratio increases, the in-cylinder pressure decreases, and the ignition delay period is prolonged. The generation range and rate of NOx gradually decrease, and the final NOx generation decreases by 85.1% at EGR = 20%. However, the peak soot generation rate and the final soot generation increase. With the increase of nozzle angle, the peak in-cylinder pressure and the overall heat release rate increase. When the nozzle angle is adjusted from 148° to 164°, the rich area of fuel-air equivalent ratio in the piston pit decreases, the high temperature area in the piston pit almost disappears. The final in-cylinder NOx generation has been reduced by 29.3%. The soot distribution gradually moves to the upper layer of combustion chamber, and the peak soot generation rate decreases, while the final soot generation increases by almost 49.5%.

Is Europe on the Way to Sustainable Development? Compatibility of Green Environment, Economic Growth, and Circular Economy Issues.

The challenges imposed by climate change and the limited nature of resources generate paradigm shifts at the level of economic, social, and environmental policies and strategies. Promoting the principles of sustainable development and the circular economy is a priority worldwide. Thus, the motivation of this research is to explore the European countries' path toward sustainable development by analysing the relationship between green environment, economic growth, and circular economy issues. In order to explore this relationship in the case of European countries, the analysis takes into consideration specific variables: final energy consumption, GDP, capital gross fixed capital formation, greenhouse gas emissions, SOx emissions, NOx emissions, and generation of municipal waste per capita. This study is focused on the period 2009-2020 for 31 European countries, with data being provided by Eurostat and World Bank databases. The panel data analysis was used in order to examine the relationship between a green environment, economic growth and a circular economy. The results of the study suggest that gross fixed capital formation and total greenhouse gas emissions lead to decreasing generation of municipal waste; instead, final energy consumption, GDP, SOx emissions and NOx emissions generate an increase in the generation of municipal waste. The novelty of our paper consists of associating green environment, economic growth, and circular economy in the case of European countries, the results allowing the proposal of economic policy measures to favor the green transition process considering the potential of the circular economy.

Simulation Research of the n-Butanol Proportion Influence on HCCI Combustion of Free-Piston Diesel Engine Generators

For researching the influence of n-butanol proportion in diesel fuel on homogeneous charge compression ignition (HCCI) combustion of the free-piston diesel engine generator (FPDEG), a three-dimensional (3D) moving mesh computational fluid dynamics (CFD) simulation model of a FPDEG prototype was developed. A detailed chemical reaction mechanism of diesel fuel was selected as the HCCI combustion mechanism and coupled in the established HCCI combustion simulation model of the FPDEG prototype. The validity of the established HCCI combustion simulation model is proved by comparing the simulation and experimental pressure curves under the condition of pure diesel fuel. The simulation results of different n-butanol proportions in diesel fuel showed that as the n-butanol proportion increased from 0 to 60%, the maximum heat release rate decreased to 59.6 J/deg, the calculated indicated thermal efficiency augmented to 4.6%, the calculated indicated mean effective pressure increased to 0.057 MPa, and the final NOx and CO content decreased to 0.239 and 0.57 g/kg fuel, respectively, but the final soot content increased to 0.000562 g/kg fuel. Therefore, the n-butanol proportion of diesel fuel played a vital role in combustion and emission progress of the FPDEG.

Study on NOx emission from an improved wood stove

Aiming at the problem that the NOx emission of civilian biomass wood stoves is difficult to meet the ultra-low emission requirements and the widespread use of biomass fuels, on the basis of traditional wood stoves, the stove structure is improved and a biomass pyrolysis device is added to make the stove have a reducing atmosphere. The final NOx emission mass concentration is reduced to below 150 mg/m3, which meets the emission standards for civilian wood stoves.

The effects of particle size on flameless combustion characteristics and NOx emissions of semi-coke with coal preheating technology

The experiments of the effect of particle size on flameless combustion characteristics and NOx emissions of Shenmu semi-coke were launched on a bench-scale coal preheating combustion test rig. The results revealed that the difference of fuel particle size greatly influenced the yield of each component in high-temperature coal gas and the reactive activity of coal char, thus subsequently affecting the final combustion process and NOx emissions. The specific surface area and pore volume of Shenmu semi-coke were both significantly increased after preheated, leading to a better reactivity and the improved combustion performance, especially when d50 (the mean particle size) = 163.84 μm, where the temperature of the down-fired combustor reached the highest. The different particle size of Shenmu semi-coke resulted in different preheating temperature, which further affected the content of each component in the high-temperature coal gas. During the self-preheating process, most volatile matter and fuel bound N were separated out and the released N was mainly converted to N2 and NH3, besides the conversion rate of each component (C, H, N and V) was the highest when d50 = 100.17 µm. Additionally, all experimental conditions achieved flameless combustion, with a transparent combustion area, but no flame front visible to the naked eye, and the highest combustion efficiency was 98.23% when d50 = 163.84 µm with the brightest flame image. It was discovered in this experimental that there was a critical value (d50 = 198.54 μm) of Shenmu semi-coke particles. When the particle size was lower than or higher than the critical value, NOx generated by combustion would decrease. The lowest NOx emission was 89.46 mg/m3 (@6% O2) when d50 was 35.34 μm.

Experimental study of NH3 transformation in the CO/O2/CO2 system at 1073–1773 K

NH3 is an important N-containing intermediate in solid fuel combustion, an efficient NO reducing agent and a carbon-free fuel. The transformation of NH3 is fairly complex in furnace and dominates the final NOx emission level. In this work, the effect of the CO/O2/CO2 system on NH3 transformation was researched in a self-designed flow reactor in a wide temperature range, 1073-1773 K. A small amount of NO net formation was detected in both the CO/NH3 and CO2/NH3 systems, while the mechanisms are different. The reaction between CO and NH3 is complex at low and intermediate temperatures, while the effect of CO2 is limited in the elevated temperature range. Significant amounts of NO forms in the O2/NH3 system, but the net formation of NO depends on the competition between NH3 oxidation by O2 and NO reduction by NH3. With CO oxidation included, the transformation of NH3 is dramatically enhanced. However, due to the rapid chemical reaction in the presence of O2 or CO oxidation, the mixing process in the front end of the reaction tube strongly influence the reaction results, leading to a fairly low conversion ratio of NH3 to NO at elevated temperatures.

Characteristics of Preheating Combustion of Power Coal with High Coking Properties

Yankuang coal with the high coking property is difficult to use through direct combustion. The main purpose of this paper is to study the combustion characteristics and NOx emissions of this type of coal using preheating combustion technology. The experimental results show that after the pulverized coal is preheated, the char residue characteristic is significantly reduced from 5 to 1. During the preheating process, the preheating temperature is stable at about 910°C, and the particle size of char after preheating is reduced, and the pore structure and specific surface areas are increased. The combustion temperature of preheated fuel is stable at around 1100°C, and the combustion efficiency can reach more than 99% under different conditions. Changing the structure of the secondary air nozzles during the preheating combustion process can influence the characteristics of emissions. The NOx emission of the central nozzle is about 112 mg/Nm3 lower than that of the annular nozzle. Changing the tertiary air distribution modes can reduce the final NOx emissions to 215 mg/Nm3 (@6%O2), and the corresponding conversion ratio of fuel N to the final NOx is 4.2%. The results of this experiment prove that the Yankuang coal can achieve stable combustion by preheating combustion technology, and this proposed a new way for the utilization of Yankuang coal.

NOx Emissions and Nitrogen Fate at High Temperatures in Staged Combustion

Staged combustion is an effective technology to control NOx emissions for coal-fired boilers. In this paper, the characteristics of NOx emissions under a high temperature and strong reducing atmosphere conditions in staged air and O2/CO2 combustion were investigated by CHEMKIN. A methane flame doped with ammonia and hydrogen cyanide in a tandem-type tube furnace was simulated to detect the effects of combustion temperature and stoichiometric ratio on NOx emissions. Mechanism analysis was performed to identify the elementary steps for NOx formation and reduction at high temperatures. The results indicate that in both air and O2/CO2 staged combustion, the conversion ratios of fuel-N to NOx at the main combustion zone exit increase as the stoichiometric ratio rises, and they are slightly affected by the combustion temperature. The conversion ratios at the burnout zone exit decrease with the increasing stoichiometric ratio at low temperatures, and they are much higher than those at the main combustion zone exit. A lot of nitrogen compounds remain in the exhaust of the main combustion zone and are oxidized to NOx after the injection of a secondary gas. Staged combustion can lower NOx emissions remarkably, especially under a high temperature (≥1600 °C) and strong reducing atmosphere (SR ≤ 0.8) conditions. Increasing the combustion temperature under strong reducing atmosphere conditions can raise the H atom concentration and change the radical pool composition and size, which facilitate the reduction of NO to N2. Ultimately, the increased OH/H ratio in staged O2/CO2 combustion offsets part of the reducibility, resulting in the final NOx emissions being higher than those in air combustion under the same conditions.

Effects of moisture and its input form on coal combustion process and NOx transformation characteristics in lignite boiler

Effects of moisture content in lignite (MCL) and its input form (IFMC), i.e. liquid water or water vapor, on coal combustion behavior and NOx transformation characteristics were studied in this paper. For this, 6 cases were numerically investigated within a previously validated 660 MW lignite-fired pulverized boiler model, where coal properties were defined by simplified coal compositions method. Among cases, MCL and IFMC were artificially altered while the relative contents of other coal components remain unchanged. Results show that when MCL is increased as H2O(l), coal combustion process deteriorates heavily and thus results in decreases in combustion temperature and fuel utilization rate. Meanwhile, the weakened in-furnace reductive atmosphere leads to a monotonic increase of NOx emission with liquid MCL increasing. Besides, IFMC is found to greatly affect NOx emission, and an increased proportion in water vapor tends to significantly lower the final NOx emission. Based on this, the operating cost of pre-drying system is correlated to that of the post-furnace denitrification process. Considering the potential widespread use of high moisture lignite in future power plants, these findings can be of great theoretical help in guiding the practical operation of lignite boilers.

Influence of Nanoseconds Pulsed Discharges on the Composition of Intermediate and Final Combustion Products in the HCCI Engine

The composition of combustion products depending on the method for the organisation of combustion in the HCCI engine (with and without a non-equilibrium discharge in misfiring conditions) for equivalence ratios ϕ = 0.33 and 0.5 has been investigated for a propane–air mixture. The qualitative composition of the combustion products is generally not dependent on considered values of ϕ. Quantitatively, the combustion products depend on the specific energy deposited in a small mass of fuel–air gas treated by the discharge for a short time, and whether ignition occurred or no. The kinetic analysis was carried out to identify the leading reactions in the formation of phenol, propadiene, diacetylene and other products. The non-thermal NO formation in the mass treated by the discharge and influence of it on the final NOx concentration in the exhaust was also considered.

NOX reduction in a 40 t/h biomass fired grate boiler using internal flue gas recirculation technology

A decoupled numerical modelling method is developed in this study to simulate the whole combustion process of biomass in a grate firing boiler, which includes the thermochemical conversion of biomass in the fuel-bed and gaseous combustion in the freeboard. With the aid of this modelling method, the objective of this study is to explore the NOX reduction mechanism as well as to investigate the potential of internal flue gas recirculation technology (IFGRT) on the combustion process and emissions formation in a 40 t/h biomass-fired grate boiler. Computational fluid dynamics (CFD) modelling results show that IFGRT can be realized in the grate boiler by establishing intense flue gas recirculation within the boiler, which allows for lower peak combustion temperatures and smaller flame kernel sizes, while improving the overall average gas temperature. Consequently, NOX emission can be reduced mainly via the thermal formation route in comparison with the conventional combustion case. More specifically, the parallel over-fired air (OFA) burner configuration is suggested for implementation to produce even lower NOX emission compared to the staggered OFA burner configuration. To further understand the reasons behind the NOX reduction, NOX formation and destruction mechanisms are also examined through reduced order modelling (ROM) with the help of detailed reaction chemistry. It is revealed that flue gas recirculation inhibits NOX formation from thermal, NNH and N2O routes. Although NOX destruction rate through reburning is suppressed, the net NOX production rate is found to be decreased under the condition of IFGRT. Moreover, as the flue gas recirculation ratio increases, final NOX emission shows a decreasing trend.

Effect of char gasification on NOx formation process in the deep air-staged combustion in a 20 kW down flame furnace

Deep air-staged combustion tests of Datong (DT) bituminous coal were carried out in a 20kW down flame furnace (DFF) with the burner stoichiometric ratio (SR) ranging from 1.200 (unstaged) to as low as 0.696 (deep staged). The experimental results shown that the concentration of CO reach as high as 120,000ppm (12vol.%) and the NOx decrease to nearly zero in the reducing zone under deep staging conditions of SR=0.696, which was never observed before. Thus, the extent of CO formation (i.e. char gasification) and the NOx reaction mechanism under deep staging condition were studied in order to understand the combustion process of coal. This paper presents a refined numerical simulation for reproducing the profiles of CO and NOx along the DFF under deep staging condition. The comparison between simulation and experimental results prove the reasonability of refined kinetic parameters of char gasification. The enhancement of char gasification by CO2 is proposed and validated. With the simulated CO profile in the DFF confirmed by experiment, the NOx profile could be further analyzed. The discrepancy of simulated NOx profile in the reducing zone (i.e. fuel-rich zone) indicates that there are some undetected nitrogenous species and undiscovered NOx transfer mechanism regardless of the consistence of final NOx emission between simulation and experiment. It is supposed by us that a majority of NOx immersing in high level of CO in the reducing zone is mainly transferred into undetected nitrogenous species (excluding HCN and NH3) which is then rapidly oxidized into NOx once the remaining oxygen is injected into the DFF.

Combustion, cofiring and emissions characteristics of torrefied biomass in a drop tube reactor

The study investigates cofiring characteristics of torrefied biomass fuels at 50% thermal shares with coals and 100% combustion cases. Experiments were carried out in a 20 kW, electrically heated, drop-tube reactor. Fuels used include a range of torrefied biomass fuels, non-thermally treated white wood pellets, a high volatile bituminous coal and a lignite coal. The reactor was maintained at 1200 °C while the overall stoichiometric ratio was kept constant at 1.15 for all combustion cases. Measurements were performed to evaluate combustion reactivity, emissions and burn-out.Torrefied biomass fuels in comparison to non-thermally treated wood contain a lower amount of volatiles. For the tests performed at a similar particle size distribution, the reduced volatile content did not impact combustion reactivity significantly. Delay in combustion was only observed for test fuel with a lower amount of fine particles. The particle size distribution of the pulverised grinds therefore impacts combustion reactivity more.Sulphur and nitrogen contents of woody biomass fuels are low. Blending woody biomass with coal lowers the emissions of SO2 mainly as a result of dilution. NOX emissions have a more complex dependency on the nitrogen content. Factors such as volatile content of the fuels, fuel type, furnace and burner configurations also impact the final NOX emissions. In comparison to unstaged combustion, the nitrogen conversion to NOX declined from 34% to 9% for air-staged co-combustion of torrefied biomass and hard coal. For the air-staged mono-combustion cases, nitrogen conversion to NOX declined from between 42% and 48% to about 10%–14%.

Remote sensing of NO2 emission from the central urban area of Shanghai (China) using the mobile DOAS technique

The mobile DOAS technique was used to quantify the NOxvehicle emission of the central urban area, enclosed by the Inner Ring Viaduct Road (IRVR), of Shanghai, China. Three field measurement campaigns were performed during the pre‐EXPO period in October 2009, the EXPO opening ceremony, and the closing ceremony period in 2010. The spatial and temporal distributions of NO2 Vertical Column Densities were derived, and the effects of traffic and wind conditions were studied. The averaged NO2 emissions rates from the IRVR area were determined to be 2.1 ± 0.9 ton/h, 2.8 ± 1.4 ton/h and 2.7 ± 1.4 ton/h for these three campaigns. The annual vehicle NOx emissions for the central urban area were estimated to be (2.3 ± 1.0) × 104 ton in 2009 and (3.0 ± 1.5) × 104 ton in 2010, and those for the whole city were (13.4 ± 5.9) × 104 ton in 2009 and (17.6 ± 8.4) × 104 ton in 2010, by considering a typical NO/NO2 ratio, NOx lifetime, as well as the traffic emission share of central urban area with respect to the entire city. The vehicle NOx emissions quantified by mobile DOAS were found to exhibit an increasing trend in the central urban area of Shanghai, by 1.6 times and 2.1 times from 2006 to 2009 and 2010. Due to wind field variations, unknown NOx chemical transformation, and uncertainties in AMFs, the systematic derivation of the final NOx emission rates obtained was about 55% for averaged several consecutive days.

Numerical study of hydrogen addition to DME/CH4 dual fuel RCCI engine

In this study, the effect of hydrogen addition to DME/CH4 dual-fuel RCCI (Reactivity Controlled Compression Ignition) engine is investigated using three dimensional calculations coupled with chemical kinetics. A new reduced DME (Dimethyl Ether) oxidation mechanism is proposed in this study. With the addition of H2, the ignition time is advanced and the peak cylinder pressure is increased. The addition of hydrogen has a greater effect on the beginning stage of combustion than the later stages of combustion. The CH4 emission is reduced with the addition of H2. However, as the flame does not propagate throughout the charge, the CH4 emission is still high. The CO emission is reduced and most of the remaining CO is produced by the combustion of the premixed CH4. With the addition of hydrogen, NO emission is increased. The simulation shows that the final NOx emissions are significantly determined by the injection strategy and quantity of the pilot fuel during dual fuel operation conditions.

The Fate of Ammonia and Hydrogen Cyanide during Flameless Combustion of Low Calorific Value Gases

In this paper, the review of the experimental investigations on the fuel-NO x formation during flameless combustion is presented. The first series of experiments described in the paper were conducted using ammonia doped synthetic gases with different compositions. During these experiments, the influence of gas composition on the conversion of ammonia (NH 3 ) to NO x is investigated. In the second part, experiments, in which product gas generated in fluidized bed gasifier is subsequently combusted in FLOX ® -Burner are presented. These results show the dependences between the gasifier operating parameters, product gas composition and final NO x emissions. Moreover, the concentrations of the ammonia and hydrogen cyanide (HCN) in the product gas were measured in order to calculate the conversion ratios of these compounds to NO x . The results show a significant influence of the gas composition and the gasifier process parameters on the final fuel-NO x emission. In particular, the hydrocarbon content influences the ammonia to NO x conversion. Lowest NO x emissions and therefore lowest conversion ratios were measured when burning gases with lower hydrocarbons content. An increase in hydrocarbon concentration of the gas corresponded to a rapid increase in the conversion ratios. In this paper, a review of the experimental investigations on the fuel-NOx formation during flameless combustion is presented. The first series of experiments described in the paper were conducted using ammonia doped synthetic gases with different compositions. During these experiments, the influence of gas composition on the conversion of ammonia (NH3) to NOx is investigated. The second series of experiments were conducted using product gas generated in a fluidized bed gasifier. These results show the dependencies between the gasifier operating parameters, product gas composition and final NOx emissions. Moreover, the concentrations of the ammonia and hydrogen cyanide (HCN) in the product gas were measured in order to calculate the conversion ratios of these compounds to NOx. The results show the significant influence of the gas composition and the gasifier process parameters on the final NOx emissions. In particular, the hydrocarbon content influences the ammonia to NOx conversion. The lowest NOx emissions and therefore the lowest conversion ratios were measured while burning gases with a low hydrocarbon content. An increase of the hydrocarbon concentration in the gas corresponded to a rapid increase in the conversion rati-->In this paper, a review of the experimental investigations on the fuel-NOx formation during flameless combustion is presented. The first series of experiments described in the paper were conducted using ammonia doped synthetic gases with different compositions. During these experiments, the influence of gas composition on the conversion of ammonia (NH3) to NOx is investigated. The second series of experiments were conducted using product gas generated in a fluidized bed gasifier. These results show the dependencies between the gasifier operating parameters, product gas composition and final NOx emissions. Moreover, the concentrations of the ammonia and hydrogen cyanide (HCN) in the product gas were measured in order to calculate the conversion ratios of these compounds to NOx. The results show the significant influence of the gas composition and the gasifier process parameters on the final NOx emissions. In particular, the hydrocarbon content influences the ammonia to NOx conversion. The lowest NOx emissions and therefore the lowest conversion ratios were measured while burning gases with a low hydrocarbon content. An increase of the hydrocarbon concentration in the gas corresponded to a rapid increase in the conversion ratios.

Fundamental Study on NOx Formation Characteristics in Spray Combustion under Supercharged Conditions

Effects of ambient conditions and fuel injection parameters on diesel combustion under supercharged conditions have been investigated using a constant volume vessel. NOx formation process has been investigated using a total gas-sampling device. The results indicate that it is possible to realize entirely diffusion combustion in this experiment like what seen in highly supercharged engines. Elevating injection pressure increases the NOx formation rate during heat release, however reduces final NOx mass per released heat. Nevertheless, there is no remarkable change in final NOx level. Lowering oxygen concentration shows significant reduction in NOx formation rate and final NOx concentration.

Effects of Fuel-Air Mixing on NOx Formation in Simulated Direct-Injection PCCI Combustion Using a Constant Volume Vessel

The effects of fuel injection parameters, such as injection pressure and nozzle hole diameter, on NOx formation in direct-injection Premixed Charge Compression Ignition (PCCI) combustion were investigated using a constant volume vessel and a total gas-sampling device. The results show that promotion of fuel-air mixing reduces final NOx mass accompanying delayed hot flame. In this case, the NOx reduction trend is enhanced by lowering oxygen concentration. Under a fixed nozzle hole size condition, final NOx mass is reduced with increasing injection pressure, and smaller nozzle hole size promotes this effect. Enhanced mixing and reduced oxygen concentration provide longer mixing periods leading to lower NOx mass per released heat NOx/qt, while promotion of mixing hardly affects NOx/qt when the quantity of injected fuel exceeds a certain level.

Repetitively pulsed plasma remediation of NOx in soot laden exhaust using dielectric barrier discharges

The removal of NOx from diesel exhausts is being investigated using a variety of repetitively pulsed plasma sources. Soot particles influence NOx densities in the gas phase of these devices through heterogeneous reactions on the soot surface. In repetitively pulsed devices, such as dielectric barrier discharges, the starting gas composition of any given pulse depends on the homogeneous and heterogeneous chemistry occurring during previous pulses. In this regard, we have computationally investigated the consequences of repetitive discharge pulses and heterogeneous chemistry on remediation of NOx and soot oxidation. In the absence of soot, a series of discharge pulses results in increased conversion of NO to NO2 compared to depositing the same energy in a single discharge pulse. With soot, single pulses result in an initial gas phase oxidation of NO to NO2, followed by heterogeneous conversion of NO2 to NO on the soot. With multiple pulses and soot, due to the larger gas phase density of NO2, there is an increased flux of NO2 to the soot surface, resulting in increased soot oxidation and larger rates of heterogeneous conversion of NO2 to NO. With both single and multiple discharge pulse formats, the proportion of NOx removed, both in the presence and absence of soot, is about the same. The composition of the NOx depends on the soot. With 107 cm−3 of 40 nm soot particles, the final NOx was primarily NO2, whereas, with 109 cm−3 of 200 nm soot particles, the NOx was mainly NO.