Thermal NOx Research Articles

Investigation of important semi-empirical heat transfer models for a natural gas-fueled HCCI engine

Homogeneous charge compression ignition engine is a promising alternative to traditional internal combustion engines mainly due to its high thermal efficiency, low NOx, and soot emissions. Heat transfer from gases to the combustion chamber walls has a significant effect on the combustion, performance, and formation of pollutants in HCCI engines. This study used the zero-dimensional single-zone model coupled with detailed chemical kinetics to compare the accuracy of different semi-empirical heat transfer models In the single-zone model, the heat transfer models including, Annand, Woschni, Hohenberg, Assanis, and Hensel were evaluated in a wide working range of a natural gas-fueled HCCI engine. To the best of the author’s knowledge, the heat transfer has not been experimentally measured in an HCCI engine fueled with natural gas. Therefore, in this investigation, a three-dimensional computational fluid dynamics model with detailed chemical kinetics has been considered to study the heat transfer models. The validation results indicated that the 3D model could accurately estimate the engine-out parameters. Besides, the response surface method was employed to evaluate the impacts of the engine operating parameters, including the intake pressure (1, 1.25, and 1.5 bars), equivalence ratio (0.3, 0.5, and 0.7), and engine speed (800, 1100, and 1400 rpm) on the heat flux as a response factor. The results indicated that Assanis and Hohenberg heat transfer models had the best performance in estimating the heat transfer of an HCCI engine with an average error of 14.3% and 16.3%, respectively, compared with the 3D model.

CI engine performance and emissions with waste cooking oil biodiesel boosted with hydrogen supplement under different load and engine parameters

This research article deals with the variable parametric study on dual fuel compression ignition engine fueled with waste cooking oil biodiesel with hydrogen supplement at atmospheric condition. The parametric study include variation in engine speed (18–30 rev/sec), gaseous fuel flow rate (0–18.4LPM), pilot fuel flow rate (9.92–15.79Mlpm) and ignition timing (20–45° BTDC). The experiment was conducted on a four stroke, 0.5-liter single cylinder E6 Ricardo engine. From the experimentation, overall parametric variation of 4.15%, 64.7%, 76.61% and 57% in thermal efficiency, CO, NOX and opacity respectively was observed. However, with increase of hydrogen content resulted in increased engine performance, increased in NOx emission and reduction in CO emission with same WCO biodiesel flow rate.

Effect of plastic oil addition on performance and emission characteristics of biogas-diesel dual fuel engine using taguchi method and prediction of performance parameter using artificial neural network

Ever increasing usage of fossil fuels and dwindling natural resources led researchers to concentrate on investigating other sources which can satisfy our demands and reduce pollution levels. Present research work aims to investigate the performance and emission characteristics of plastic, diesel and biogas as fuel blend operated in a dual-fuel engine with biogas as a primary fuel and plastic oil – diesel blends as secondary fuel and also predict the output variable using artificial neural network. A modified four-stroke single cylinder CI engine was used for experiments conducted at varying load, percentage of plastic oil percentage in diesel and biogas flow rate. Based on the levels and factors a Taguchi L9 orthogonal matrix was designed to find the optimal combination of input indices. The signal to noise ratios in taguchi method were applied based on the desired output characteristics and according to the respective SNR ratios an ANOVA table was created to determine the major contributor effecting output parameters such as brake thermal efficiency, CO, HC NOx and smoke emissions. ANN model helped to predict BTE with same input parameters but with an increased set of sample data. Based on Gradient descent and Levenberg-Marquardt algorithm the ANN architecture was trained, validated and tested to predict the response with least error. The ANOVA calculated indicates load to be the prime factor effecting BTE and NOx emission

Performance and emission characteristics of biogas-bio diesel fuelled RCCI engine at various butanol-gasoline injection timings

Energy, a basic need of human life, has been playing significant role behind many technological developments. Most of the world’s commercial energy requirements are fulfilled by using fossil fuels. Combustion of fossil fuels releases toxic gases which in further turns as a source of pollution for the environment, globally. The present research work focused on minimizing the emissions that emerges during combustion in an IC engine through Reactivity Controlled Compression Ignition (RCCI) mode. The performance and emission characteristics of a single-cylinder CI engine are analyzed with 3 different fuels; biodiesel, butanol-gasoline (1:4 ratio), and biogas. The operational loads taken for the present study falls in the range from 5 N-m to 20 N-m at the engine speed of 1800 RPM. The influence of biogas on the emission characteristics is exclusively carried out with two different flow rates; 12lpm and 16lpm. The injection timings for butanol-gasoline blend are varied from 0 to 8ms. Fuel properties such as Viscosity, Vapor pressure, Density, Cloud point, Pour point, and Flashpoint are estimated. Engine parameters such as Brake Thermal Efficiency (BTE), Volumetric Efficiency (VE), HC, CO, NOx and smoke emissions, Peak pressure, Heat Release Rate (HRR), Ignition Delay, are analyzed. It is observed from the experiments that increasing injection time of pilot fuel - increases the HC and CO emissions; reduces the NOx emissions; decreases the smoke level with increase in biogas flow rate; and decreases the BTE, VE, and HRR

A preliminary numerical study on the use of methanol as a Mono-Fuel for a large bore marine engine

To use methanol as a mono-fuel in large bore marine engines, a distributed jets ignition combustion mode was applied on a 320 mm-bored engine, in which pre-chamber initiated jets were employed to ignite the in-cylinder lean mixtures and to enhance the flame propagation. A preliminary numerical study was carried out to investigate the effects of in-cylinder excess air ratio and ignition timing on combustion characteristics and performances of the engine. Conditions with excess air ratios ranged from 2.0 to 2.8 and ignition timings ranged from −8°CA ATDC to the top dead center were calculated. The numerical results show that, under the distributed jets ignition combustion mode, the in-cylinder lean methanol-air mixtures could be reliably ignited and the heat release rates showed a firstly slow and then rapid trend, resulting in high thermal efficiencies and low NOx emissions, which could meet for the IMO Tier III emission regulations without aftertreatment. Moreover, with the increase of the in-cylinder excess air ratio and the delaying of the ignition timing, the in-cylinder pressure, the peak pressure rising rate, the ringing intensity and the NOx emissions were continuously decreased. As the in-cylinder mixture becoming leaner, the combustion efficiency firstly kept constant and then rapidly dropped when the excess air ratio increased to 2.4, resulting in a peak value of the indicated thermal efficiency (49.2%) at this excess air ratio. According to the numerical results, a combustion control strategy was proposed: when the brake mean effective pressure was below 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.4 and coupled with an earlier ignition timing to obtain high thermal efficiency, and when the brake mean effective pressure was higher than 1.8 MPa, the in-cylinder excess air ratio was controlled at 2.1 and coupled with a later ignition timing, thereby to achieve high power density.

Numerical investigation of the effect of water vapor diluent injection on the formation of NOx pollutants

In this paper, the eddy dissipation model was used to predict the exact behavior of reacting flow in a round jet burner. The results were validated and verified with available experimental and numerical data. To this end, the turbulence and combustion equations were solved using the k-ε/EDM model and the PIMPLE algorithm by means of OpenFoam package. In addition, by modifying the reactingFoam solver, the thermal NOx equations were solved, and the equations of the P-1 radiation model were used to solve the radiation equations. After validating the numerical method, the effects of H2O diluent injection rate and its location were studied on the temperature distribution and NOx emission. The results revealed that as the injection rate of water vapor diluent increased, the temperature of the fluid decreased, and a decrease was observed in NOx emissions in proportion to the temperature reduction. Increasing the diluent injection velocity had a negligible effect on the similarity distribution of temperature and NOx mass fraction and the location of the maximum temperatures did not change much. The effects of diluent injection on reducing NOx pollution were also seen upstream. As the diluent injection velocity increased, the effect of the diluent on the NOx emission gradually were diminished.

Influence of H2 enrichment for improving low load combustion stability of a Dual Fuel lightduty Diesel engine

Dual Fuel (DF) combustion can help to reduce the environmental impact of internal combustion engines, since it may provide excellent Brake Thermal Efficiency (BTE) combined with ultra-low emissions. This technique is particularly attractive when using biofuels, or fuels with a low Carbon content, such as Natural Gas (NG). Unfortunately, as engine load decreases and the homogeneous NG-air mixture tends to become very lean, the high chemical stability of NG can be a serious obstacle to the completion of combustion. As a result, BTE drops and UHC and CO emissions become very high. A possible way to address this problem could be the addition of hydrogen (H2) to the NG-air mixture. In this paper, a numerical study has been carried out on an automotive Diesel engine, modified by the authors in order to operate in both conventional Diesel combustion and DF NG-diesel mode. A previous experimental characterization of the engine is the basis for the CFD-3D modeling and calibration of the DF combustion process, using a commercial software. The effects on combustion stability and emissions of different NG-H2 mixtures (six blends with 5%, 10%, 15%, 20%, 25%, and 30% by volume of hydrogen) are numerically investigated at a low load (BMEP = 2 bar, engine speed 3000 rpm). The results of the CFD-3D simulations demonstrate that NG-H2 blends are able to decrease strongly CO, UHC, and CO2 emissions at low loads. Advantages are also found in terms of thermal efficiency and NOx emissions.

Experimental studies on the effect of Carbon nanotube additives with Calophyllum Inophyllum biodiesel in CI engine

The rapid depletion of Non-renewable fuel sources coupled with environmental degradation, has led us further into the exploration of alternate energy resources. Biodiesels originating from non-edible feedstocks have garnered much attention in a span of few years. The current study focuses on the addition of Carbon Nanotubes in Tamanu oil biodiesel in a Diesel engine. In this study, parameters such as brake thermal efficiency, unburned hydrocarbon, carbon monoxide, and NOx emissions have been studied. The performance of these biodiesel-diesel blends were charted and results are compared with diesel. It is noted that the inclusion of nano-additives in dosages of 30 and 60 ppm enhances brake thermal efficiency, the drawback being increased specific fuel consumption. The emissions of HC, NOx and emissions show a favorable trend with addition of CNT but CO2 emissions were observed to be on the higher side. Also graphs were plotted revealing the relevant combustion characteristics of the test fuels. They are further discussed in detail and a comprehensive conclusion was made.

Study on CRDI engine for the various fuel injection pressures

The people in our society are highly depended on petroleum for their activities. The petroleum is a finite source and it produce several problems such as rising carbon dioxide level in the atmosphere. Around 75% of fuel produced is used for as an energy source for transportation, heat and electricity generation. This study was carried out to understand the effect of fuel injection pressure on the CRDI engine for the performance, combustion and emissions. This work has been done out on a four stroke, single cylinder diesel engine. The fuel injection pressure was varied from 400 bar, 500 bar and 600 bar by having the fuel injection angle as 20°bTDC. The collected data were analysed for various parameters such as brake specific fuel consumption (BSFC), brake thermal efficiency (BTE), CO, CO2, HC, NOx and Smoke emissions for diesel fuel. CO, HC and smoke emissions were reduced by increasing the fuel injection pressure. NO and CO2 emissions were increasing by increasing the fuel injection pressure. This is due to injected fuel droplets find smaller as the injection pressure increase, which leads to improve atomization of the fuel. The BTE and SFC were not much varying.

The Effect of Variable Air–Fuel Ratio on Thermal NOx Emissions and Numerical Flow Stability in Rotary Kilns Using Non-Premixed Combustion

One of the quickest ways to influence both the wall temperature and thermal NOx emissions in rotary kilns is to change the air–fuel ratio (AFR). The normalized counterpart of the AFR, the equivalence ratio, is usually associated with premixed flames and studies of its influence on diffusion flames are inconsistent, depending on the application. In this paper, the influence of the AFR is investigated numerically for rotary kilns by conducting steady-state simulations. We first conduct three-dimensional simulations where we encounter statistically unstable flow at high inflow conditions, which may be caused by vortex stretching. As vortex stretching vanishes in two-dimensional flow, the 2D simulations no longer encounter convergence problems. The impact of this simplification is shown to be acceptable for the thermal behaviour. It is shown that both the wall temperature and thermal NOx emissions peak at the fuel-rich and fuel-lean side of the stoichiometric AFR, respectively. If the AFR continues to increase, the wall temperature decreases significantly and thermal NOx emissions drop dramatically. The NOx validation, however, shows different results and indicates that the simulation model is simplified too much, as the measured NOx formation peaks at significantly fuel-lean conditions.

A Study on Water-Induced Damage Severity on Diesel Engine Injection System Using Emulsified Diesel Fuels

Diesel engine emissions contribute nearly 30% of greenhouse effects and diverse health and environmental problems. Amidst these problems, it is estimated that there will be a 75% increase in energy demand for transportation by 2040, of which diesel fuel constitutes a major source of energy for transportation. Being a major source of air pollution, efforts are currently being made to curb the pollution spread. The use of water-in-diesel (W/D)-emulsified fuels comes as a readily available (and cost-effective) option with other benefits including engine thermal efficiency, reduced costs, and NOx reduction; nonetheless, the inherent effects—power loss, component wear, corrosion, etc. still pose strong concerns. This study investigates the behavior and damage severity of a common rail (CR) diesel fuel injection system using exploratory and statistical methods under different W/D emulsion conditions and engine speeds. Results reveal that the effect of W/D emulsion fuels on engine operating conditions are reflected in the CR, which provides a reliable avenue for condition monitoring. Also, the effect of W/D emulsion on injection system components-piston, nozzle needle, and ball seat–are presented alongside related discussions.

Optimization of engine operating variables on performance and emissions characteristics of biogas fuelled CI engine by the design of experiments: Taguchi approach

AbstractBiogas obtained from renewable resources is a viable solution for solving energy scarcity and environmental degradation. A single‐cylinder 4‐stroke natural aspirated variable compression ratio research engine was fuelled with biogas as primary and diesel as a pilot injection in this work. Experiments were designed based on Taguchi L9 OA (orthogonal array) choosing biogas flow rate, compression ratio, and engine load as input factors, while brake thermal efficiency (BTE), BSEC, CO, HC, NOx, and smoke were targeted responses. The effects level of factors on responses was analysed by using MINITAB software. The higher value of raw data and S/N ratios for BTE was observed with low biogas flow rate, higher compression ratio, and full engine load. On the other hand, lower raw data and high S/N ratio analysis for emissions characteristics (CO, HC, NOx, and smoke) were achieved in the order of rank, that is, engine load > biogas flow rate > compression ratio. With the analysis of results, optimum levels of various factors were evaluated. These results showed that the Taguchi method design was an effective tool for optimizing the elements in terms of combustion performance and emissions characteristics.

Emission Characteristics of Hazardous Air Pollutants from Medium-Duty Diesel Trucks Based on Driving Cycles

Studies on the characteristics of hazardous air pollutants (HAPs) in the emissions of medium-duty diesel trucks are significantly insufficient compared to those on heavy-duty trucks. This study investigated the characteristics of regulated pollutants and HAPs, such as volatile organic compounds (VOCs), aldehydes, and polycyclic aromatic hydrocarbons (PAHs), and estimated non-methane hydrocarbon (NMHC) speciation in the emissions of medium-duty diesel trucks. Ten medium-duty diesel trucks conforming to Euros 5 and 6 were tested for four various driving cycles (WLTC, NEDC, CVS-75, and NIER-9) using a chassis dynamometer. In an urban area such as Seoul, CO and NMHC emissions were increased because of its longer low-speed driving time. NOx emissions were the highest in the high-speed phase owing to the influence of thermal NOx. PM emissions were almost not emitted because of the DPF installation. Alkanes dominated non-methane volatile organic compound (NMVOC) emissions, 36–63% of which resulted from the low reaction of the diesel oxidation catalyst. Formaldehyde emissions were the highest for 35–53% among aldehydes irrespective of driving cycles. By sampling the particle-phase of PAHs, we detected benzo(k)fluoranthene and benzo(a)pyrene and estimated the concentrations of the gas-phase PAHs with models to obtain the total PAH concentrations. In the particle portion, benzo(k)fluoranthene and benzo(a)pyrene were over 69% and over 91%, respectively. The toxic equivalency quantities of benzo(k)fluoranthene and benzo(a)pyrene from NIER-9 (cold) for both Euro 5 and Euro 6 vehicles were more than five times higher than those of NIER (hot) and NEDC. In the case of NMHC speciation, formaldehyde emissions were the highest for 10–45% in all the driving cycles. Formaldehyde and benzene must be controlled in the emissions of medium-duty diesel trucks to reduce their health threats. The results of this study will aid in establishing a national emission inventory system for HAPs of mobile sources in Korea.

NOx reduction of biodiesel engine using pongamia ester with oleic acid and optimization of operating conditions using particle swarm optimization

Biodiesel is comprised of 36–75% oleic fatty acid (OA) that has the molecular formula, C18H34O2 and is an excellent carrier of hydrogen and oxygen. OA has proven to have a positive effect in curbing NOx from biodiesel combustion. In this work, the effect of varying concentrations of OA in Pongamia ester is studied on a compression ignition engine that is again varied at different loads and compression ratios. Design of experiments is carried out with brake thermal efficiency and NOx emissions as responses. Regression equations for these responses are developed and optimized using multi-objective particle swarm optimization (MOPSO). It is found that the best operating regime for maximum efficiency and minimum NOx is by adding 10% OA, with a compression ratio of 17.5 running at an engine load of 81%. Experimental validation of the prediction made by the optimization model is also carried out.

Application of machine learning tools for constrained multi-objective optimization of an HCCI engine

Because of strict emission regulations, significant efforts are made by researchers to reduce the pollutants from internal combustion engines. Homogeneous mixture of fuel and air in Homogeneous Charge Compression Ignition (HCCI) engine results in lower amounts of thermal NOx while CO and HC emissions would be higher in this process. Besides, performance instability due to knock and misfire is another problem that HCCI engines are facing. In this paper, machine learning tools have been implemented to learn the behavior of a single-cylinder engine using three different fuels with the HCCI strategy. Changes in six objective functions with engine Inlet Valve Closing (IVC) temperature and air-fuel equivalence ratio are studied with the help of an Artificial Neural Network (ANN). Those objective functions are thermal efficiency, combustion efficiency, IMEP, together with NOx, CO, and HC emissions. A multi-objective optimization algorithm based on a decomposition method and genetic algorithm is used to identify the best operating condition of studied fuels. Results show that HCCI engine fueled with Ethanol and Methanol could produce significantly lower HC and CO emissions at their optimum point. However, the produced NOx would be higher in these cases comparing to the engine fueled with CNG. The genetic algorithm indicates that the optimum point of operation for CNG-fueled engine is TIVC ≈ 445 K while λ ≈ 2.25. In contrast, for the Ethanol-fueled case, this optimum point is located in the IVC temperature of ≈450 K and λ ≈ 2.75. The TOPSIS point is located in minimum air-fuel equivalence ratio and lower IVC temperatures (TIVC ≈ 420 K) when the engine is being operated with Methanol as fuel.

The similarity ratio effects in design of scaled model experiments for marine diesel engines

Marine diesel engines usually span a large range of bore diameters or power. While optimization of spray combustion system based on scaled model experiments would be beneficial to reduce the cost, energy consumption and project cycle of marine engine development, the similarity ratio effects on the design target parameters such as in-cylinder maximum pressure, indicated thermal efficiency, and NOx and soot emissions are rarely investigated. In this study, firstly, the three-dimensional computational fluid dynamics models are calibrated against the experiment data such as in-cylinder pressure and heat release rate evolutions, indicated thermal efficiency and NOx emissions, and the boundaries of similarity ratio determined by the limits of piston speed, engine speed and fuel injection pressure are clarified. Then, the effects of similarity ratio ranging from 0.8 to around 3 are studied under the different engine loads, engine types and scaling laws. The results show that the prediction accuracy of the scaled model experiments decreases with the increase of the bore diameter difference, and the exponential function can well describe the relationship between the design target parameters and similarity ratio. The results also reveal that the scaling laws should be properly selected for different design target parameters. The scaling law based on constant injection pressure exhibits great potential for predicting indicated thermal efficiency and maximum in-cylinder pressure, as the maximum difference of these parameters between the base engine and targeted engine is less than 1.2% with the similarity ratio up to 3.00.

Numerical and experimental investigation of natural gas injection effects on NOx reburning at the rotary cement kiln exhaust

Thermal NOx formation is very high in the rotary cement kiln due to high-temperature flame. Essentially all NOx emissions associated to the cement manufacturing are formed in cement kilns. In this paper, the effects of natural gas injection into calciner exhaust, i.e., rotary kiln inlet, on NOx reburning by CO and CH radicals is numerically and experimentally investigated. A 3D model of turbulent combustion flow to stimulate the NOX reburning on an industrial scale is developed by the finite volume method. The results show that the NOx reduction can be reached 30 % and 70 % by 950 m3/h and 2750 m3/h natural gas injection, respectively. Furthermore, by increasing natural gas injection flow rate and reaction time, NOx reduction rate is abruptly decreased. The experimental results imply 65 % NOx reduction by natural gas injection from walls of rotary furnace channel inlet where good agreement by numerical results is well proved. Obtaining results also prove that the NOx return in swirling region is highly increased and NOx concentration remarkably reduced.

Study of high-temperature oxygen combustion (HiTOx) and its heating performance using a laboratory-scale test furnace

Abstract High-temperature air combustion technology (HiCOT), which uses air preheated by heat recirculation, has had a great impact on reduction of CO2 and NOx emissions from combustion furnaces. In this study, a lab-scale test furnace was developed to examine the novel combustion method termed as high-temperature oxygen combustion, HiTOx. HiTOx uses combustion with a preheated mixture of oxygen and burned gas. Testing was conducted with liquefied petroleum gas. HiTOx has the following three characteristics because nitrogen is excluded from the working gas: (1) in principle, no thermal NOx is generated; (2) combustion gas is almost entirely water vapor and carbon dioxide, providing better heating performance because of its strong gas-phase radiation; and (3) the method has good compatibility with carbon dioxide capture, utilization and storage (CCUS) technologies because carbon dioxide can be separated easily from the combustion gas of HiTOx furnace by condensation of water vapor. Heating performance tests in a lab-scale test furnace were conducted using stainless steel rectangular rods as heating objects. Gas temperature, object temperature, and heat fluxes on the objects were measured. Compared to HiCOT, HiTOx enables stable operation with a lower flow rate of flue gas, better gas temperature uniformity in the furnace, faster heating, and higher heat flux. The heat flux of HiTOx was slightly higher than that of HiCOT (7%) when the furnace temperature was low (973 K) and the temperature difference between the gas and object was large (280 K). On the other hand, the heat flux of HiTOx was much higher than that of HiCOT (22%) when the furnace temperature was high (1323 K) and the temperature difference was small (60 K). Radiative heat transfer at high temperature was greater in HiTOx than in HiCOT at small temperature difference between the gas and object. A furnace body can be greatly downsized by the good radiation performance of combustion gas in HiTOx, resulting in a remarkable improvement in energy-saving performance.

Numerical Simulation of Coal Combustion in a Tangential Pulverized Boiler: Effect of Burner Vertical Tilt Angle

Understanding of the flow field and heat transfer in a boiler is important to meet with the often-conflicting objectives of efficient steam generation, safe operation and minimization of pollutant emissions. Steam generation requires high gas temperatures, which often lead to high NOx emissions. High gas temperatures inside the boiler may also lead to slagging and fouling problems, which adversely affect the heat transfer to the steam side. One of the principal ways of finding a compromise in tangentially fired pulverized coal (PC) boilers, which constitute the majority of the utility boilers, is through tilting the burners. The current work seeks to obtain a detailed understanding of the effect of burner tilt on the flow and heat transfer inside the boiler by utilizing numerical simulations. Computational fluid dynamics (CFD) simulations were performed on a 210 MWe tangentially fired pulverized coal boiler to understand the impact of two vertical burner tilt angles, − 15° and + 15°. The effect of burner tilt was investigated by analyzing the effect on gas flow, temperature distribution, coal particle trajectories and NOx emissions. The results suggest that a downward tilt of the burner (− 15°) has a significant effect on the particle trajectories and the residence time of the particle in the high temperature burner zone. The temperature of the exit gas was reduced by 33 K due to the downward tilt. NOx emissions were reduced by about 5.5% when the burners were tilted downward by 15° which be attributed to two factors, namely the relatively insignificant contribution of thermal NOx mechanism in utility boilers and the role of NOx reburning in reducing conditions.

Numerical Study of NOx Generation in a Trapped Vortex Combustor Fuelled by Kerosene Blended with Ethanol

The study of alternative fuels is of great importance, and the study of ethanol blended with kerosene is necessary. The trapped vortex combustor is a new type of combustor and NOx emissions are important in the study of trapped vortex combustors. In this article, the NOx generation rate of trapped vortex combustor was studied using kerosene blended with ethanol in different mass fractions as fuel. The results show that the thermal NOx is the main source of NOx in the combustor, which is mainly generated at the back of the combustor, and the thermal NOx generation rate decreases with the increase of ethanol mass fraction. The prompt NOx generation rate decreases with the increase of ethanol mass fraction. NOx is also easily produced near the sidewall of the combustor.