Investigation of the Effect of Hydrogen and Methane on Combustion of Multicomponent Syngas Mixtures using a Constructed Reduced Chemical Kinetics Mechanism

This study investigated the effects of H2 and CH4 concentrations on the ignition delay time and laminar flame speed during the combustion of CH4/H2 and multicomponent syngas mixtures using a novel constructed reduced syngas chemical kinetics mechanism. The results were compared with experiments and GRI Mech 3.0 mechanism. It was found that mixture reactivity decreases and increases when higher concentrations of CH4 and H2 were used, respectively. With higher H2 concentration in the mixture, the formation of OH is faster, leading to higher laminar flame speed and shorter ignition delay time. CH4 and H2 concentrations were calculated at different pressures and equivalence ratios, showing that at high pressures CH4 is consumed slower, and, at different equivalence ratios CH4 reacts at different temperatures. In the presence of H2, CH4 was consumed faster. In the conducted two-stage sensitivity analysis, the first analysis showed that H2/CH4/CO mixture combustion is driven by H2-based reactions related to the consumption/formation of OH and CH4 recombination reactions are responsible for CH4 oxidation. The second analysis showed that similar CH4-based and H2 -based reactions were sensitive in both, methane- and hydrogen-rich H2/CH4 mixtures. The difference was observed for reactions CH2O + OH = HCO + H2O and CH4 + HO2 = CH3 + H2O2, which were found to be important for CH4-rich mixtures, while reactions OH + HO2 = H2O + O2 and HO2 + H = OH + OH were found to be important for H2-rich mixtures

Complete Vaporisation of a Human Body

From the previous paper, we were able to determine, hypothetically, the approximate amount of energy required to completely vaporise a human skeleton. In this paper, we focused on vaporising the whole water constituent of the body and the remaining tissues of a human body by finding the total dissociation energy for each of this constituent. For simplification, we used dried pork to represent the remaining tissues of the body. Finally, we calculated the combined amount of energy required to completely vaporise a human body to be 2.99G

Chemical kinetics and CFD analysis of supercharged micro-pilot ignited dual-fuel engine combustion of syngas

A comprehensive chemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. The developed syngas chemical kinetics mechanism was validated by comparing ignition delay, in-cylinder pressure, temperature and laminar flame speed predictions against corresponding experimental and simulated data obtained by using the most commonly used chemical kinetics mechanisms developed by other authors. Sensitivity analysis showed that reactivity of syngas mixtures was found to be governed by H2 and CO chemistry for hydrogen concentrations lower than 50% and mostly by H2 chemistry for hydrogen concentrations higher than 50%. In the mechanism validation, particular emphasis is placed on predicting the combustion under high pressure conditions. For high hydrogen concentration in syngas under high pressure, the reactions HO2 + HO2 = H2O2 + O2 and H2O2 + H = H2 + HO2 were found to play important role in in-cylinder combustion and heat production. The rate constants for H2O2 + H = H2 + HO2 reaction showed strong sensitivity to high-pressure ignition times and has considerable uncertainty. Developed mechanism was used in CFD analysis to predict in-cylinder combustion of syngas and results were compared with experimental data. Crank angle-resolved spatial distribution of in-cylinder spray and combustion temperature was obtained. The constructed mechanism showed the closest prediction of combustion for both biomass and coke-oven syngas in a micro-pilot ignited supercharged dual-fuel engine

Reduced syngas-based chemical kinetics mechanisms for dual fuel engine combustion applications

The interest in sustainable and environmental friendly fuels such as syngas and their use in dual fuel engine applications, has intensified the research for an accurate and reduced chemical kinetics mechanism. The chemical kinetics mechanism should be applicable to simulate not only multicomponent syngas combustion but also NOx formation and the co-oxidation between the primary fuel (premixed syngas) and the pilot injected diesel based fuel. For the diesel based fuel n-heptane was used as a surrogate due to the fact that it has similar physical and chemical characteristics with the diesel and identical rate of heat release (ROHR). Despite the development of various chemical kinetics mechanisms for the simulation of syngas combustion and n-heptane oxidation, a robust and reduced chemical kinetics mechanism that includes full syngas and NOx chemistry and n-heptane chemistry remains elusive. Therefore, this thesis aimed to develop a reduced and robust chemical kinetics mechanism for multicomponent syngas combustion, NOx formation and syngas/n-heptane co-oxidation. This study is separated into three main sections: a) The development of a reduced syngas mechanism, b) development of a reduced syngas/NOx mechanism and c) development of a reduced n-heptane/syngas/NOx mechanism. The first section is the construction of a robust reduced chemical kinetics mechanism for multicomponent syngas combustion. Important chemical reactions were investigated by using sensitivity analysis and their rate constants were updated. By using sensitivity analysis, it was shown that the reactivity of syngas mixtures is governed by H2 and CO chemistry for H2 concentrations lower than 50% vol and mostly by H2 chemistry for H2 concentrations higher than 50% vol. Reactions responsible for the decomposition of H2O2 and the formation of high reactive OH species, found to play a key role in the combustion process during high pressure conditions and therefore their rate constants were updated. The constructed mechanism was validated against experimental results and simulated data obtained by using other well-validated chemical kinetics mechanisms, in terms of ignition delay and LFS. Finally, the new mechanism was implemented in a multidimensional CFD simulation for the prediction of syngas combustion in a micro-pilot-ignited supercharged dual-fuel engine. Results from the CFD were compared against experiments. However, while mixtures with H2 concentration > 50% vol used, the reactivity of the mixture increased due to the faster formation of OH and therefore some modification were adopted in the new mechanism in order to improve its accuracy. Modification such as the adaptation of new rate constants on important hydrogen reactions and the removal of reactions with very low sensitivity factor. At the end, a two-part mechanism was constructed for low and high H2 concentrations. The second section of this thesis was the optimization of the reduced mechanism for low H2 content proposed in Part 1, by updating the rate constants of important hydrogen reactions that were found to be very sensitive during high pressure conditions (10, 20 and 30 atm) and by incorporating a 12 reaction NOx pathway. The NOx sub-mechanism was selected after different NOx models available in the literature were tested and validated. The new reduced syngas/NOx mechanism was validated against experimental data as well as the simulated results by using other chemical kinetics mechanisms from the literature, in terms of LFS, ignition delay time, and NO concentration profiles, and showed very low error in all of the conditions. For LFS simulations the calculated absolute grand mean error for the developed mechanism was lower than 2%, for ignition delay times lower than 5% and for NOx formation profiles lower than 5%. Finally, similar to the first part of this study, the new mechanism was used in a multidimensional CFD simulation to predict the combustion of syngas in a micro-pilot-ignited supercharged dual-fuel engine. The final section of this research was the construction of a reduced n-heptane/syngas/NOx mechanism for modelling n-heptane/syngas co-oxidation, syngas combustion and NOx formation in a micro pilot-ignited dual fuel engine. For the construction of the reduced chemical kinetics mechanism, a comprehensive mechanism for n-heptane oxidation was reduced by using necessity analysis and was coupled with the reduced syngas/NOx mechanism developed in Part 2. The reduced mechanism consists of 276 reactions and was validated against experimental measurements for different fuel types obtained from the literature and numerical results by using other well validated mechanisms in terms of ignition delay time, LFS and NO concentration profiles. Moreover, a multidimensional CFD analysis was conducted for the prediction of syngas combustion in a micro-pilot-ignited supercharged dual-fuel engine. The reduced mechanism simulates accurately the experimental in-cylinder pressure and ROHR for all conditions except from the cases where 100% hydrogen was used

Reduced chemical kinetics mechanism for syngas combustion and NOx formation

Chemical kinetics and computational fluid-dynamics (CFD) analysis were performed to evaluate the combustion of syngas derived from biomass solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. For this analysis, a new reduced syngas chemical kinetics mechanism was developed and validated by comparing the ignition delay and laminar flame speed data with those obtained from experiments and other detail chemical kinetics mechanisms available in the literature. The reaction sensitivity analysis was conducted for ignition delay at elevated pressures in order to identify important chemical reactions that govern the combustion process. We found that H02+OH=H20+02 and H202+H=H2+H02 reactions showed very high sensitivity during high-pressure ignition delay times and had considerable uncertainty. The chemical kinetics of NOx formation was analysed for H2/CO/C02/CH4 syngas mixtures by using premixed laminar flame speed reactors. The new mechanism showed a very good agreement with experimental measurements and accurately reproduced the effect of the equivalence ratio on NOx formation. Finally, the new mechanism was used in a multidimensional CFD simulation to predict the combustion of syngas in a micro-pilot-ignited supercharged dual-fuel engine and results were compared with experiments. The mechanism showed the closest prediction of the in-cylinder pressure and the rate of heat release (ROHR)

Characterisation of DME-HCCI combustion cycles for formaldehyde and hydroxyl UV–vis absorption

We investigated time-resolved ultraviolet–visible (UV–vis) light absorbance to identify the formation behaviour of formaldehyde (HCHO) and hydroxyl (OH) within the wavelength range of 280–400 nm in a homogeneous charge compression ignition (HCCI) engine fuelled with dimethyl ether (DME). The time-resolved HCHO and OH profiles at different initial pressures showed that HCHO absorbance increased in the low-temperature reaction (LTR) and thermal-ignition preparation (TIP) regions and decreased gradually as the combustion approached the high-temperature reaction (HTR) region. At higher intake pressures, HCHO absorbance decreased and OH absorbance increased. The time-resolved absorbance spectra of HCHO, with peaks at 316, 328, 340, and 354 nm for all combustion cycles, were evaluated and it was found that average absorption at 328 nm was slightly higher than at 316, 340, and 354 nm. For knocking combustion cycles, the absorbance of HCHO in the LTR region was high for cycles with low knock intensity and low for cycles with high knock intensity, showing a high level of OH absorbance. Chemical kinetics analyses showed that for different fuel/oxidiser ratios, initial O2 concentration and intake temperature had no effect on in-cylinder temperatures in the LTR or TIP regions. However, they did have significant effects on HTR combustion. In-cylinder temperature in the LTR region had less effect on HCHO and H2O2 formation than pressure

Aerodynamic design of wind turbine blades considering manufacturing constraints

The present paper investigates the aerodynamic design of wind turbine blades while considering manufacturing constraints. Blade topologies achieved by unconstrained optimisation methods are likely to lose optimality after manufacturing simplifications are applied. The present paper proposes and evaluates the performance of an optimisation method for wind turbine blades while considering manufacturing constraints. The optimal solution achieved this way is manufacturing-ready. In addition, integrating manufacturing design knowledge into the optimisation is shown to significantly reduce the design space, and therefore the time taken by the optimisation algorithm. While the proposed method herein is described for a standalone aerodynamic optimisation, it can also be used for aero-structural optimisations

Chemical Kinetics and Computational Fluid-Dynamics Analysis of H2/CO/CO2/CH4 Syngas Combustion and NOx Formation in a Micro-Pilot-Ignited Supercharged Dual Fuel Engine

A chemical kinetics and computational fluid-dynamics (CFD) analysis was performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. For this analysis, a reduced syngas chemical kinetics mechanism was constructed and validated by comparing the ignition delay and laminar flame speed data with those obtained from experiments and other detail chemical kinetics mechanisms available in the literature. The reaction sensitivity analysis was conducted for ignition delay at elevated pressures in order to identify important chemical reactions that govern the combustion process. We have confirmed the statements of other authors that HO2+OH=H2O+O2, H2O2+M=OH+OH+M and H2O2+H=H2+HO2 reactions showed very high sensitivity during high-pressure ignition delay times and had considerable uncertainty. The chemical kinetics of NOx formation was analyzed for H2/CO/CO2/CH4 syngas mixtures by using counter flow burner and premixed laminar flame speed reactor. The new mechanism showed a very good agreement with experimental measurements and accurately reproduced the effect of pressure, temperature and equivalence ratio on NOx formation. In order to identify the species important for NOx formation, a sensitivity analysis was conducted for pressures 4 bar, 10 bar and 16 bar and preheat temperature 300 K. The results show that the NOx formation is driven mostly by hydrogen based species while other species, such as N2, CO2 and CH4, have also important effects on combustion. Finally, the new mechanism was used in a multidimensional CFD simulation to predict the combustion of syngas in a micro-pilot-ignited supercharged dual-fuel engine and results were compared with experiments. The mechanism showed the closest prediction of the in-cylinder pressure and the rate of heat release (ROHR)