High NOx Formation Research Articles

Hydrogen blending with natural gas for combustion efficiency improvement toward decarbonisation of power plants

Abstract The 12th Malaysia Plan highlighted Malaysia’s commitment to reduce Greenhouse Gas (GHG) emissions by 45% based on Gross Domestic Product (GDP) in 2030 and reach net zero by 2050. To achieve this target, Malaysia has to decarbonise the energy sector as it is the primary emission source, contributing up to 75% of GHG emissions in Malaysia. Hydrogen fuel is getting much attention globally, and it has been said that it can be a new renewable energy source to replace fossil fuels. Hydrogen combustion is clean and only produces water and energy. However, several studies have identified that hydrogen combustion could produce NOx, which is more harmful to the environment than CO2. Studies on hydrogen application in the energy sector in Malaysia are limited, and the implementation of total hydrogen fuel in power plants may not happen shortly. Hence, a fundamental study was proposed on co-firing hydrogen and natural gas fuel. This study aimed to examine co-firing characteristics such as temperature, pressure, and air-to-fuel ratio on GHG emission and energy release to find the optimum natural gas-to-hydrogen ratio. The model was developed using Aspen Plus, and hydrogen-natural gas blend percentages varied from 0% to 30%. The findings showed that increased operating temperature led to higher NOx formation, while varying pressures did not impact the CO2 and NOx formation. The pure natural gas combustion system was more sensitive towards air-to-fuel ratio changes, and an increase in air-to-fuel ratio to 1.5 led to 160% higher NOx formation due to an increase in nitrogen content. The combustion of the hydrogen blend led to lower CO2 formation but higher NOx formation. Lastly, the energy released by the hydrogen blending system was lower due to the formation of water that absorbed the heat released by the combustion.

Experimental evaluation on NOx formation and burnout characteristics of oxy-fuel co-combustion of ultra-low volatile carbon-based solid fuels and bituminous coal

Pyrolyzed semi-coke (SC) powder and gasification residual carbon are usually regarded as solid wastes, which feature high NOx formation amount and inferior burnout performance during burning process. Oxy-fuel co-firing of these ultra-low volatile carbon-based solid fuels (LVFs) with bituminous coal (BC) could reduce the NOx generation and realize the carbon capture to a large extent. However, the NOx formation and burnout features of oxy-fuel co-combustion of BC and LVFs are still unclear. Here, a two-staged drop-tube co-firing experimental system was employed to probe the oxy-fuel co-combustion characteristics of various blends. The experimental results show that the low ash melting temperature of coal-water-slurry gasification residual carbon yields an increase in Cfh with the temperature of burnout zone. The Cfh of BC/SC blend is decreased by 64.3% with the oxygen flow rate of primary air raised from 0.25 to 0.45 L min−1, which is the largest among all blends. The rise of difference between tube lengths in furnace of BC and LVF generates a decrease in NOx formation and an increase in Cfh. The present research could offer guidance for clean and efficient utilization of carbon-based solid wastes using oxy-fuel co-combustion technique, together with the encouraged development of carbon capture technology.

EXPERIMENTAL STUDY ON THE INJECTION CHARACTERISTICS OF HYDROTREATED VEGETABLE OIL IN A DIESEL ENGINE COMMON RAIL SYSTEM

The diesel combustion is primarily controlled by the fuel injection process. The start of injection therefore has a significant effect in the engine, which relates large amount of injected fuel at the beginning of injection to produces a strong burst of combustion with a high local temperature and high NOx formation. This paper investigated the impact of Hydrotreated Vegetable Oil (HVO) and blends of 10%, 20%, 30%, 50%, 80% by mass of HVO with commercial diesel fuel (mixed 7% FAME-B7) to injection process under the Zeuch’s method and compared to that of B7. The focus was on the injection flow rate in the variation of injection pressures, back pressures, and energizing times. The experimental results indicated that injection delay was inversely correlated to HVO fraction in the blend as well as injection pressure. At different injection pressures, HVO revealed a slightly lower injection rate than diesel that resulted in smaller injection quantity. Discharge coefficient was recognized larger with HVO and its blends. At 0.5ms of energizing time, injection rate profile displayed the incompletely opening of needle. Insignificant difference in injection rate was observed as increasing of back pressure.

Effect of injection timing on alcohol-biodiesel-diesel ternary blends in a CI engine

The major concerns of using Jojoba oil in CI engines is its high viscosity, low volatility, and high NOx formation. In this work, an analysis of the emission parameters and efficiency of a jojoba biodiesel-fuelled engine is carried out. This research study investigates the impacts of the addition of higher order alcohols with diesel fuel on the performance and emission parameters of CI engine working with diesel-jojoba oil methyl ester blend. 5% and 10% by volume of n-butanol is combined with B20 blend of jojoba oil methyl ester. The experiment is divided in two steps, firstly, the optimum combination of alcohol with biodiesel is evaluated based on the BTE and emission parameters. Secondly, the effect of varying the injection timing from 21°, 23° and 25° BTDC for the alcohol blends of diesel-biodiesel blends are studied. BTE increases by 4.5% for B20+10% butanol and NO emission decreases by 23%. Other emissions are facing a significant drop except HC emissions. Delayed injection timing of 21° BTDC reduces NO emission further by 18.4%. The findings prove that adding n-butanol, oxygenated fuel could enhance the viscosity issue of jojoba oil methyl ester and the mixtures as well resulting in an enhancement in their performance parameters.

Improvement of combustion and emission characteristics of a diesel engine working with diesel/jojoba oil blends and butanol additive

The main concerns of exploiting Jojoba oil in CI engines is that it has a high viscosity, low volatility, and high NOx formation. Therefore, this article purposes in endeavoring to improve the combustion and emission parameters of a CI engine working with diesel-jojoba oil blends and n-butanol additives under various engine loads. A 10% by volume of n-butanol is combined with 5%, 10%, 15%, 20%, 25, 30 and 35% of jojoba oil, and they are designated as DBJ5, DBJ10, DBJ15, DBJ20, DBJ25, DBJ30, and DBJ35, respectively. The experiments are divided into two steps, firstly, the viscosity of the fuel mixture is measured according to ASTM standards, and it is compared to ASTM D6751– 12 standers limits. Secondly, the jojoba oil with volume fraction up to 15% is tested in a CI engine to evaluate the combustion and emission developments. The results indicate that the addition of n-butanol with diesel-jojoba oil lowers the mixture viscosities by up to 85% compared to pure raw jojoba oil. The findings display that there is an increase in pmax. and HRR for DBJ5, DBJ10, and DBJ15 blends compared to pure diesel fuel, whereas the combustion duration and ignition delay are slightly reduced. The brake specific fuel consumption is enlarged. The NOx, CO, and UHC formations are reduced by 50%, 30%, and 40% respectively for diesel-jojoba oil-n-butanol mixtures. It can be deduced that combining high fractions of jojoba oil with n-butanol (DBJ15) have the feasible to accomplish low emission formations in the interim having high thermal efficiency level.