Increase In NOx Emissions Research Articles

Enhancement of combustion, performance and emission characteristics of diesel engines fuelled with jatropha-karanja biodiesel using EGM and TGME as additive

The oxygenated additives can improve the physical properties of biodiesel blends to achieve enhanced characteristics of a diesel engine. The present work has investigated ethylene glycol monoacetate (EGM) and tri-ethylene glycol mono-methyl ether (TGME) as potential additives for the jatropha-karanja dual blended biodiesel for improved characteristics of diesel engines. The experiments have been conducted with a single cylinder four stroke diesel engine operating at constant speed of 1500 rpm. The performance, emission and combustion parameters of the engine were investigated with pure diesel, jatropha-karanja dual blended biodiesel having 20 % of methyl ester and the biodiesel added with 2, 4, and 6 % of both the additives respectively. The doping of additives improved the brake thermal efficiency by 4.1 and 4.7 % with brake specific fuel consumption dropped by 0.18 and 0.2 kg/kWh. The additives reduced the hydrocarbon emission by 29.8 % and carbon monoxide by 40 % with a slight increase in NOx emission by 5.2 %. The cylinder pressure attained value near to pure diesel while the heat release rate increased by 12.6 % indicating proper fuel combustion inside the engine cylinder. Thus, the oxygenated additives can suitably be adopted as performance improvers in biodiesel fuels for automotive engines.

Greenhouse gas reduction in a medium-duty compression ignition engine with optimization for B20

Soy-based biodiesel can reduce well-to-wheels greenhouse gas (GHG) emissions per unit energy (i.e., gCO2e/MJ) by 66%–72% as compared to the petroleum-based diesel fuel with currently adopted agricultural and industrial practices. Biodiesel can reduce particulate matter and carbon monoxide emissions with a manageable degree of increase in NOx emissions. From the perspective of GHG emissions reduction per unit travelling distance (i.e., gCO2e/mile), the application of B20 in compression ignition engines without the adjustment in engine control unit (ECU) settings will not extract the best carbon emissions reduction that B20 could achieve. Optimizing the engine control settings permits re-calibration to achieve the maximum brake fuel conversion efficiency (BFE) based on comprehensive understanding on the impact of both “fuel” and “ECU calibration” on BFE and other criteria pollutant emissions. The maximum GHG emissions reduction with B20 application is experimentally measured with the optimized ECU calibration, thus providing the understanding of the combined impact of biodiesel fuel and calibrations on engine performance and emissions. Six steady operating modes were considered, that can be combined to estimate the US federal test procedure BFE and emissions over the Federal Test Protocol (FTP) 75 cycle. Combined with the weight factors to simulate the EPA FTP 75 cycle from these 6 “mini-map” test points, 0.53% improvement in the energy requirement per unit traveling distance (i.e., MJ/mile) is achieved for B20 with the final ECU calibration, in addition to the degree of GHG emissions reduction on a “gCO2e/MJ” basis from the use of B20 blend of soy biodiesel of ∼12.5% reduction in gCO2e/MJ, for a total GHG emissions reduction of 13%.

Influence of baffle height on the in-cylinder mixing and performance characteristics of a gasoline direct injection engine - a CFD investigation

In modern GDI engines, in-cylinder flows play a crucial role in the performance and emission characteristics. Adding baffles to the cylinder head is one way to enhance these flows, as baffle effectiveness is linked to its height. This study aims to investigate the influence of baffle height on the in-cylinder flows and its impact on the performance and emission characteristics of a four-stroke, four-valve, spray-guided GDI engine using computational fluid dynamics (CFD) analysis. The maximum baffle height is determined based on the geometry of the engine. Throughout the analysis, the engine operates at a constant speed of 1000 rev/min., under part-load conditions. From the results, the baffle heights of 2 mm and 3 mm significantly improve mixture stratification compared to the base engine. Furthermore, the indicated mean effective pressure (IMEP) for the engine with 2 mm and 3 mm baffle height improves by about 3% and 4%, respectively, compared to the base engine. In addition, with the increase in the baffle height, there is a significant reduction in the HC emissions with a marginal increase in NOX emissions.

A novel concept of active pre-chamber engine with a single injector – The passive main chamber approach

The pre-chamber spark ignited combustion is recognized as one of the most promising concepts utilizing a lean burn combustion approach towards the increase of efficiency and reduction of NOx emissions in spark ignited engines. Numerous investigations indicate the possibility to reduce the engine-out NOx emissions under the regulation limits by using active pre-chamber at very high dilution levels. Regardless of the dilution approach, one of the main challenges is to achieve the proper mixture formation and scavenging of the pre-chamber from residual gases to ensure stable engine operation without misfires. Recent investigations imply that the auxiliary air injection in the pre-chamber might be necessary to ensure stable operation at such highly diluted mixtures, especially if an EGR dilution approach is utilized, further increasing the complexity of such a concept. In this work, a new approach is investigated which can be described as a passive main chamber approach and relies on a single fuel injector supplying both the pre-chamber and the main chamber. Contrary to the passive pre-chamber systems, the injector in this approach is mounted in the pre-chamber, while the main chamber is supplied indirectly through the pre-chamber nozzles. To verify the feasibility and the potential benefits of such an approach, a numerical framework consisting of 3D-CFD and 1D/0D models is applied. The performed study included different pre-chamber variants, previously investigated on an experimental gasoline-fuelled engine, to verify the applicability of such a concept regardless of the pre-chamber geometry. The performed study showed that the proposed concept is a feasible option and, despite the inability to directly control the excess air ratio in the pre-chamber, results with the desired values of λPC ≈ 0.8 at the MBT optimized spark timings. At very lean mixtures (λglobal > 2.0), the average residual gas concentration in the pre-chamber and around the spark plug at the ignition timing is reduced from 10 % and 13 % respectively to 2.5 %, along with a 1.4 percent point increase of indicated efficiency when compared to normal operation. When compared to the reference gasoline fuelled cases, a highest efficiency of 37.7 % is achieved at moderately lean mixture (λglobal ≈ 1.6) and MBT optimized spark timing with NOx levels of 1.41 g/kWh, which represents a 0.7 percent point increase in indicated efficiency but 75 % increase of NOx emissions. At NOx optimized spark timing however (NOx < 0.4 g/kWh), an identical indicated efficiency of 34.7 % is obtained. Overall, the results indicate that with the proposed concept, it is possible to achieve the same scavenging effect as with auxiliary air injection while eliminating the need for both the main chamber injection system and the pre-chamber auxiliary air supply system and without sacrificing the overall performance.

Effect of Water Injection on Combustion and Emissions Parameters of SI Engine Fuelled by Hydrogen–Natural Gas Blends

Technologies used in the transport sector have a substantial impact on air pollution and global warming. Due to the immense impact of air pollution on Earth, it is crucial to investigate novel ways to reduce emissions. One way to reduce pollution from ICE is to use alternative fuels. However, blends of alternative fuels in different proportions are known to improve some emissions’ parameters, while others remain unchanged or even worsen. It is therefore necessary to find ways of reducing all the main pollutants. For SI engines, mixtures of hydrogen and natural gas can be used as alternative fuels. The use of such fuel mixtures makes it possible to reduce CO, HC, and CO2 emissions from the engine, but the unique properties of hydrogen tend to increase NOx emissions. One way to address this challenge is to use port water injection (PWI). This paper describes studies carried out under laboratory conditions on an SI engine fuelled with CNG and CNG + H2 mixtures (H2 = 5, 10, 15% by volume) and injected with 60 and 120 mL/min of water into the engine. The tests showed that the additional water injection reduced CO and NOx emissions by about 20% and 4–5 times, respectively. But, the results also show that water injection at the rate of 120 mL/min increases fuel consumption by between 2.5% and 7% in all cases.

Investigation of the effect of injection rate shaping on combustion and emissions in heavy-duty diesel engine under steady and transient conditions

The fuel injection rate (ROI) is a crucial factor that affects the combustion and emissions of diesel engines. This study focuses on the injection pressure in a common rail system, which is divided into a high-pressure section and a low-pressure section. A control-oriented ROI shaping (ROIs) model is developed based on the switching strategy between high and low injection pressure. Three types of ROI were generated, namely ROIB (conventional ROI), boot-ROI (low followed by high injection pressure), and anti-boot-ROI (high followed by low injection pressure) respectively. The 1-D and 3-D numerical simulations are conducted to analyze the impact of the shaped ROI on combustion and emissions for steady condition and transient condition. In terms of overall results, boot-ROI shows significant advantage among the three types of ROI. For the steady condition, the boot-ROI was able to increase the IMEP (indicated mean effective pressure) (1.57 bar) at high load conditions with almost unchanged NOx emission. For low load conditions with delayed SOI (start of injection), the exhaust temperature is close to that of the ROIB with a reduction of 0.51 g/kW·h in NOx emissions. For transient condition, the boot-ROI also shows its advantage. It was found to improve the BSFC (brake specific fuel consumption) with almost unchanged NOx emission during load-down process. And in load-up process, the BSFC and soot emission also could be improved with slightly increase in NOx emission through advance of SOI when boot-ROI was adopted. The one-dimensional model using boot-ROI reduces fuel consumption by 2 g/kW·h in experiment with WHTC cycles, with slightly higher soot emission and similar NOx emission.

The Combustion and Emission Characteristics of Corn Oil Biodiesel with Titanium Oxide (TiO2) Nano-additive

This experiment produced biodiesel from corn oil through transesterification. Fuel mixture proportions were changed to assess engine performance and reduce fossil fuel emissions. This study examined brake power, mean effective pressure, mechanical efficiency, brake thermal efficiency and indicated thermal efficiency, and emissions such as hydrocarbons, carbon monoxide and NOx. 20% of corn oil was blended with diesel to make biodiesel. The fuel characteristics of the corn oil methyl ester matched ASTM standards. Experimental results were obtained by operating a single-cylinder four-stroke diesel engine under various load conditions. Titanium oxide nanoparticles in the biodiesel reduced HC and CO engine emissions whereas, there was an increase in CO2 and NOx emissions. Combustion parameters such as cumulative net heat release rate and fuel line pressure decreased whereas, cylinder pressure and net heat release rate increased; the sample BD20 + 100 ppm TiO2 sample exhibited appreciable results.

Exploring the efficiency and emission characteristics of hydroxy-boosted canola biodiesel in comparison to traditional diesel fuels

In this research, we experimentally examined how incorporating HHO into blends of 20% canola biodiesel with 80% diesel and 40% canola biodiesel with 60% diesel impacts the engine’s performance and its emission traits. Canola oil, widely used in Europe, served as the biodiesel base. The addition of HHO, recognized for its potential to improve combustion efficiency and reduce emissions which were deteriorated by biodiesel addition. The findings revealed decrement on fuel consumption as 5.74% and 4.43% and rise in thermal efficiencies as 3.92% and 3.97% with HHO addition compared to B20 and B40, respectively. Besides that, CO emissions were reduced significantly up to 35.43%, while CO2 emissions decreased moderately up to 14.93% compared to diesel fuel. On the other hand, biodiesel and HHO addition increased NOx emissions as 49.80%. Utilization of biodiesel and HHO in diesel engines offers a straightforward way to reduce emissions and enhance fuel efficiency, addressing environmental issues and promoting sustainable transportation.

The effects of ammonia addition on the emission and performance characteristics of a diesel engine with variable compression ratio and injection timing

Ammonia, future of the carbonless marine fuel, presents significant potential in achieving zero-emission targets within maritime transportation. In this context, this study explores the use of an ammonia/diesel fuel mixture in a diesel engine, employing both experimental and numerical methods. We focus on the impact of injection timing and compression ratio to optimize the engine while using ammonia/diesel mixture in terms of both engine performance and exhaust emissions. The results show a decrease in engine power with an increasing content of ammonia, reaching the lowest power of 4.53 kW at 60% ammonia content. On the other hand, the increase in compression ratio generally enhances engine power. Thermal efficiency shows an increase up to 40% ammonia content, followed by a decline. CO2 emissions significantly reduce with an increase in ammonia content, reaching the lowest level, especially at 60% ammonia content. NO emissions rise with increasing ammonia content up to 40%. Furthermore, increasing the compression ratio reduces CO2 emissions and contributes to an increase in NOx emissions. These findings have assessed the potential usage of ammonia-diesel fuel mixture with regards to environmental impacts and energy efficiency in internal combustion engines.

Effect of flue gas recirculation on combustion instability and emission characteristics of premixed CH4/NH3/air flame

The hydrogen carrier ammonia is considered a prominent carbon-free alternative fuel. This paper examines the impact of flue gas recirculation (FR) on combustion instability and emission behavior of premixed CH4/NH3/air swirl flame at different equivalence ratios (Φ) and ammonia mole fractions (χNH3). Experimental results show that FR is beneficial to suppressing the self-excited pulsating pressure and pulsating heat release rate of CH4/NH3/air flame, and the pulsating frequency decreases monotonically with the increase of FR. Under fuel-lean and stoichiometric conditions, FR is beneficial to suppressing NOx formation but will increase CO and NH3 emissions. Under fuel-rich conditions, FR reduces CO emissions but increases NOx emissions. The NO emissions obtained from the chemical reactor network simulation are in qualitative agreement with the experimental results. The results show that the elementary reactions related to HNO and NHi radicals play a crucial role in the influence of FR on NO formation.

Combustion and emission characteristics of a gasoline/ammonia fueled SI engine and chemical kinetic analysis of NOx emissions

Mitigating climate change involves the greater adoption of carbon–neutral and renewable energy sources within the transportation sector. Ammonia (NH3), as a carbon-free and sustainable fuel, has garnered growing interest in recent years. The present study aims to investigate the impact of NH3 blending on combustion and emission characteristics of a stoichiometric spark-ignition gasoline engine, with a particular emphasis on nitrogen-based emissions. The experimental investigation was complemented by chemical kinetic calculations. The results showed that NH3 blending could effectively suppress engine knock, optimize combustion phase and improve thermal efficiency. For pure gasoline, advancing the spark timing resulted in increased NOx emissions. However, when NH3 was blended, NOx emissions decreased with advancing spark timing, indicating a negative correlation with pressure. The NH3 emission was attributed to the ‘crevice mechanism’ as well as the absorption/desorption in the lubricant oil film on the cylinder wall. Chemical kinetic analysis revealed that the NOx emission from NH3 blended combustion is closely related to reactive radicals such as OH, H and O. The reduction in NOx emissions under high-pressure conditions was primarily attributed to the consumption of these reactive radicals via three-body reactions. Interestingly, NOx emissions initially increased with increasing NH3 blending ratio but eventually followed a decreasing trend. This can be attributed to the lower combustion temperature, lower concentration of reactive radicals, and enhanced de-NOx reactions.

Effects of injection timing on mixture formation, combustion, and emission characteristics in a n-butanol direct injection spark ignition engine

The impact of injection timings on the in-cylinder flow field intensity, mixture formation process, combustion, and emission characteristics are analyzed. The range of injection timing is set between −320°CA and −260°CA. The research results indicate: Delaying the injection timing causes the spray plumes increasingly align with the tumble direction, consequently enhancing the in-cylinder tumble intensity and the turbulence near the spark timing. The mixture homogeneity is influenced by both the formation time and the in-cylinder flow field intensity. Moreover, combustion performance is linked to the homogeneity of the mixture and turbulence intensity near the spark timing. Despite the fact that postponed injection may augment both turbulence intensity and the equivalent ratio around the spark plug at the moment of spark, achieving higher explosion pressure, but the higher viscosity of n-butanol impedes droplet break-up, and its low volatility decelerates the evaporation rate, leading to poorer mixture homogeneity, reduced BMEP, and increased CO and soot emissions. However, at −300°CA start of injection, the extended mixing time optimizes the fuel-air mixture homogeneity, thus improving combustion quality and reducing CO, soot, and HC emissions, albeit leading to increased NOx emissions.

Experimental investigation of hydrogen enriched natural gas combustion with a focus on nitrogen oxide formation on a semi-industrial scale

Combustion of hydrogen-enriched natural gas is a valuable short-term strategy for reducing CO2 emissions from high temperature industrial heating. This paper presents several experiments on combustion characteristics and the formation of nitrogen oxides. The experiments included hydrogen contents up to 100% and fuel heat inputs up to 75 kW. Water-cooled lances were used to influence the furnace temperature. The analysis includes the distribution of furnace temperatures, the composition of flue gas, the cooling capacity of the lances under steady-state operating conditions, and OH*-chemiluminescence imaging of the near burner region. The presented results demonstrate the dependence of furnace conditions and NOX formation on various factors, such as different air inlet fluxes, furnace temperature, and fuel composition, for constant heat inputs. Efficiency increased by up to 5.5% and significant changes in flame shaped along with a maximum increase in NOX emissions when comparing natural gas to hydrogen was measured at 167%.

Stratified premixed combustion optimization of a natural gas/biodiesel dual direct injection engine

The natural gas (NG) stratified premixed combustion mode (NSPC) demonstrates significant potential for improving thermal efficiency and lowering emissions when compared to the NG mixing-limited combustion mode (NMLC). In this study, the NSPC for a NG/biodiesel dual direct injection engine was optimized through numerical simulation. The initial evaluation of biodiesel as the pilot fuel reveals its capacity to reduce soot and CO emissions while simultaneously increasing thermal efficiency in comparison with pure diesel. The subsequent examination delved into the effects of the injection timing of biodiesel and natural gas on mixture distribution, combustion, and emissions characteristics. The findings indicates that a well-balanced combination of moderate injection timing of natural gas and slightly delayed injection timing of biodiesel results in significantly lowered CO and soot emissions while maintaining high thermal efficiency, but with a trade-off of increased NOx emissions. The engine performance was further refined through the integrated application of exhaust gas recirculation (EGR) and pilot fuel pre-injection. Achieving a high thermal efficiency of 42.5%, minimal CO emissions at 1.5 g/kWh, soot emissions below 1 × 10−4 g/kWh, and NOx emissions less than 2 g/kWh, is achieved by configuring the start of injection for natural gas and biodiesel at −56°CA ATDC and −10°CA ATDC, respectively, with a biodiesel pre-injection ratio of 30%, and an EGR rate of 36%.

Multi-objective optimization of emission parameters of a diesel engine using oxygenated fuel and pilot injection strategy based on RSM-NSGA III

In this work, a diesel engine fueled with PODE3/n-butanol/diesel blends at high altitudes was optimized using the RSM-NSGA III hybrid optimization methodology to achieve a reduction in emissions. The target parameters of the optimization were soot, NOx, and HC emissions, and the decision variables were the mass ratio of pilot injection (MRPI), pilot injection timing (PIT), mass ratio of PODE3 (MRP) and mass ratio of n-butanol (MRB). Firstly, a three-dimensional simulation model of the CI engine was built in CONVERGE, and the model was verified through experiments. Secondly, the effects of the pilot injection strategy, also known as the pre-injection strategy, on the combustion characteristics of the CI engine were analyzed. Then, an experimental design based on Box-Behnken Design (BBD) was conducted and a mathematical model of the target parameters was obtained using RSM. Finally, the mathematical model of RSM was optimized using NSGA III to obtain the Pareto frontier, and the optimal solution was selected from the Pareto frontier using TOPSIS. The results showed that a suitable pilot injection strategy helped alleviate the problem of low cylinder pressure (CP) and high soot and HC emissions from the CI engine at high altitudes. The soot and HC emissions exhibited a decreasing and then increasing trend as the PIT advanced. As MRPI increased, both soot and HC emissions decreased. The NOx emissions showed the opposite trend. Compared with the non-optimized results, at an altitude of 2000 m, the optimized engine exhibited a 65.29% decrease in soot emissions, a 24.7% increase in NOx emissions, and a 74.94% decrease in HC emissions. Compared with the non-optimized results, at an altitude of 4000 m, the optimized engine demonstrated a 54.70% decrease in soot emissions, a 15.71% increase in NOx emissions, and a 65.78% decrease in HC emissions. This research will contribute to the application of oxygenated fuels in plateau diesel engines and the optimization of plateau diesel engines.

Sustainability of flameless combustion mode with hydrogen addition to liquid kerosene fuel at high-intensity conditions

The application of hydrogen for fuel enrichment and blending has recently gained importance. The sustainability and performance enhancement through hydrogen addition in flameless combustion mode for liquid fuels needs further investigation to enhance our understanding. Therefore, the present study reports the effect of hydrogen addition on the flameless combustion of a kerosene-fired 30 kW swirl combustor with hydrogen addition. A divergence-shaped conical combustor with tangential air injection and asymmetric fuel injection scheme is adopted. The liquid fuel was injected using a solid-cone swirl nozzle with 34 μm Sauter Mean Diameter. The hydrogen addition was varied from 0 to 20% on a thermal input basis, and the thermal input of liquid fuel was maintained at a 30 kW level. Computational studies helped understand the flow physics behavior within the combustor volume. The hydrogen addition was observed to improve the reactant dilution ratio (Rdil). The maximum values of the Rdil increased from 4.47 to 5.44 with hydrogen addition. Hydrogen addition further helped extend the flameless combustion regime to φ = 0.3 without any air preheating. A uniformly distributed reaction with a reduced-temperature gradient is observed with extended combustion stability limits. A marginal increase in NOx emissions was observed with hydrogen addition, albeit within permissible limits, accompanied by ∼8–20 dB reduction in acoustic emissions.

Techno-Economic Analysis of Cement Decarbonization Techniques: Oxygen Enrichment vs. Hydrogen Fuel

The Paris Agreement aims to limit global warming, and one of the most polluting sectors is heavy industry, where cement production is a significant contributor. This work briefly explores some alternatives, recycling, reducing clinker content, waste heat recovery, and carbon capture, discussing their advantages and drawbacks. Then, it examines the economic viability and benefits of increasing oxygen concentration in the primary burning air from 21 to 27 vol.%, which could improve clinker production by 7%, and the production of hydrogen through PEM electrolysis to make up 5% of the fuel thermal fraction, considering both in a cement plant producing 3000 tons of clinker per day. This analysis used reference values from Secil, an international company for cement and building materials, to determine the required scale of the oxygen and hydrogen production, respectively, and calculate the CAPEX of each approach. It is concluded that oxygen enrichment can provide substantial fuel savings for a relatively low cost despite a possible significant increase in NOx emissions. However, hydrogen production at this scale is not currently economically viable.

Review on Performance and Emissions Characteristics of Compression Ignition Engine Fueling Non-Edible Vegetable Oil

The tremendous exhaustion of resources, a surprising price increase of petroleum fuel and worldwide ecological issues implement to find renewable fuel for compression ignition engine. Non-edible vegetable oils have proven consensus to opt as a replacement for diesel fuel due to comparable properties and less-pollutant characteristics. Using Unmixed Untreated Non-edible Vegetable Oil (UUNVO) in the CI engine matches the needs of a sustainable future and restricts the intensifying cost involved in biodiesel production. This paper aims to review the influence of various UUNVO (Karanja, Jatropha, Neem, Linseed, Mahua and Rubber Seed etc.) on the important performance parameters and emission level of diesel engine. UUNVO can be fuelled to the unmodified CI engine. However, the viscosity of UUNVO is reasonably higher compare to diesel fuel at room temperature, which deteriorates the engine performance and exhaust emission. Minor changes in the injection line for preheating the UUNVO and operating parameters are the way to improve it. It can clearly understand here that preheated UUNVOs typically increase NOx emissions and decrease PM, HC, and CO emissions level compared to standard diesel. UUNVO can substitute diesel fuel completely for short-duration operation. With the long-duration operation, UUNVO produces problems like poor engine performance, injector chocking, and erosion of piston crown, rings, cylinder liner, and other internal parts, and degradation of the lubricant. Problems raised due to durability can be minimized by controlling operational parameters.

Experimental study on the effects of ammonia cofiring ratio and injection mode on the NOx emission characteristics of ammonia-coal cofiring

Ammonia (NH3) cofiring is a promising approach to reduce the CO2 emissions from coal-fired power plants. However, the potential drastic increase of NOx emissions may inhibit the wide implementation of NH3 cofiring. To explore the potential NOx control strategies, the effects of NH3 cofiring ratio (RNH3), NH3 injection mode and overfire air (OFA) rates on the NOx emission characteristics of NH3/coal cofiring are studied in a test furnace that allow for flexible control of the injection positions and combustion environment of NH3. The results show that when NH3 is injected with coal stream (top mixing mode), the NOx emissions increase and then decrease with the increase of RNH3 under all OFA rates. However, when NH3 is fed through the side port of furnace separately (side mixing mode), the NOx emissions exhibit distinct trends under different OFA rates. Under lower OFA rates, the NOx emissions show monotonical decrease with the increase of RNH3, while under higher OFA rates the NOx emissions first decrease and then increase with the increase of RNH3. Consequently, higher OFA rates could produce higher NOx emissions than lower OFA rates. This indicates that air-staging is not always effective in the NOx reduction of NH3 cofiring. Thus, although the side mixing mode of NH3 cofiring exhibits overall better performance in NOx control, caution is needed to accommodate the OFA rate with NH3 cofiring ratio. Although a variety of trends of NOx emissions were observed in this study, the results demonstrate that all these trends are in fact governed by the same mechanism – the competition between the NO-formation and NO-reduction reactions of NH3 in the varying O2 environment in the furnace. By creating appropriate O2 environment in the furnace, the NOx emissions of NH3/coal cofiring could be substantially lower than that of pure coal combustion. The findings of these paper are instrumental in the design and operation of NH3 cofiring system in full scale coal-fired boilers to achieve effective NOx control.

A numerical study of NOX and soot emissions in ethylene-ammonia diffusion flames with oxygen enrichment

Blending ammonia with hydrocarbon fuels is gaining interest due to its potential to significantly reduce carbon emissions from the combustion of these blends. Additionally, studies have provided strong evidence of oxygen enhanced combustion to reduce soot emissions and improve flame stability. The present work attempts to leverage the benefits of both strategies, ammonia doping and oxygen enhanced combustion, by considering ethylene diffusion flames. Simulations are performed using the CHEMKIN-Pro software. A reaction mechanism with 372 species and 13,847 reactions is developed by combining gas phase chemistries for ethylene, NH3 and NOX, along with a detailed soot mode. The mechanism is extensively validated for a range of fuel blends in terms of flame structure, intermediate hydrocarbons, soot precursors and soot. Oxygen enrichment is achieved by removing certain amount of nitrogen from oxidizer stream and adding it to fuel stream, and thereby maintaining a nearly constant flame temperature. Extensive analysis is carried out to characterize the chemical and dilution effects of ammonia doping on flame structure, soot precursors, soot, and NOX in ethylene flames with varying levels of oxygenation. Further, dominant reaction pathways for several soot precursors and NOx are identified through detailed rate of production analyses. Results indicate that ammonia doping in ethylene flames leads to substantial increase in NOX emissions, while oxygenation has negligible influence on NOX emissions. In contrast, both NH3 doping and oxygenation provide significant reduction in the formation of soot precursors and soot. Oxygenation achieves this reduction through both hydrodynamic and flame structure effects, as the flame shifts from oxidizer side to fuel side. On the other hand, NH3 doping reduces the rates of important reactions for the formation of soot precursors, as the concentrations of relevant species (C2H2, C3H3, C3H3-P, C3H3-A etc.) decrease due to their consumption through reactions with species like NCO and CN formed from NH3. Moreover, the effectiveness of NH3 doping is further enhanced when combined with oxygenation. Hence, NH3 doping and oxygenation are found to be effective and synergistic strategies in reducing soot emissions, and their proper combination could provide near zero soot emissions.