https://biblio.ugent.be/publication/8589931/file/8609217.pdf

Methanol as a fuel for internal combustion engines

Fuel reforming in internal combustion engines

Energy Independence and Security Act of 2007 Lighting Mandate Analysis

Abstract A large set of experimental data was accumulated for hydrogen combustion: ignition measurements in shock tubes (770 data points in 53 datasets) and rapid compression machines (229/20), concentration–time profiles in flow reactors (389/17), outlet concentrations in jet-stirred reactors (152/9) and flame velocity measurements (631/73) covering wide ranges of temperature, pressure and equivalence ratio. The performance of 19 recently published hydrogen combustion mechanisms was tested against these experimental data, and the dependence of accuracy on the types of experiment and the experimental conditions was investigated. The best mechanism for the reproduction of ignition delay times and flame velocities is Keromnes-2013, while jet-stirred reactor (JSR) experiments and flow reactor profiles are reproduced best by GRI3.0-1999 and Starik-2009, respectively. According to the reproduction of all experimental data, the Keromnes-2013 mechanism is currently the best, but the mechanisms NUIG-NGM-2010, OConaire-2004, Konnov-2008 and Li-2007 have similarly good overall performances. Several clear trends were found when the performance of the best mechanisms was investigated in various categories of experimental data. Low-temperature ignition delay times measured in shock tubes (below 1000 K) and in RCMs (below 960 K) could not be well-predicted. The accuracy of the reproduction of an ignition delay time did not change significantly with pressure and equivalence ratio. Measured H2 and O2 concentrations in JSRs could be better reproduced than the corresponding H2O profiles. Large differences were found between the mechanisms in their capability to predict flow reactor data. The reproduction of the measured laminar flame velocities improved with increasing pressure and total diluent concentration, and with decreasing equivalence ratio. Reproduction of the flame velocities measured using the flame cone method, the outwardly propagating spherical flame method, the counterflow twin-flame technique, and the heat flux burner method improved in this order. Flame cone method data were especially poorly reproduced. The investigation of the correlation of the simulation results revealed similarities of mechanisms that were published by the same research groups. Also, simulation results calculated by the best-performing mechanisms are more strongly correlated with each other than those of the weakly performing ones, indicating a convergence of mechanism development. An analysis of sensitivity coefficients was carried out to identify reactions and ranges of conditions that require more attention in future development of hydrogen combustion models. The influence of poorly reproduced experiments on the overall performance was also investigated.

Comparison of the performance of several recent hydrogen combustion mechanisms (proceedings)

Parametrization of the temperature dependence of laminar burning velocity for methane and ethane flames

The current work provides a quasi-dimensional model for the combustion of methanol–gasoline blends. New correlations for the laminar burning velocity of gasoline and methanol are developed and used...

A quasi-dimensional combustion model for spark ignition engines fueled with gasoline–methanol blends

Methanol fueled spark ignition (SI) engines have the potential for very high efficiency using an advanced heat recovery system for fuel reforming. In order to allow simulation of such an engine system, several sub-models are needed. This paper reports the development of two laminar burning velocity correlations, corresponding to two reforming concepts, one in which the reformer uses water from an extra tank to produce hydrogen rich gas (syngas) and another that employs the water vapor in the exhaust gas recirculation (EGR) stream to produce reformed-EGR (R-EGR). This work uses a one-dimensional (1D) flame simulation tool with a comprehensive chemical kinetic mechanism to predict the laminar burning velocities of methanol/syngas blends and correlate it. The syngas is a mixture of H2/CO/CO2 with a CO selectivity of 6.5% to simulate the methanol steam reforming products over a Cu-Mn/Al catalyst. The simulation was exercised over syngas contents in the blend, fuel-air equivalence ratios, pressures, unburned gas temperatures and EGR ratios ranging respectively from 0% to 50%, 0.5 to 1.5, 10 to 85 bar, 550 to 800 K and 0% to 30% (by mass). The developed correlations are ready to be implemented into engine simulation tools as well as computational fluid dynamic codes. Based on the developed correlations, optimal control strategies and dilution methods have been studied. The engine is able to work with the same mass burning rate at leaner mixtures or lower intake charge temperatures with an onboard fuel reformer. If the engine is operated at stoichiometric condition, at the same mass fraction of methanol to the catalyst and the same EGR, the R-EGR concept is recommended because it provides a faster laminar burning velocity and does not require an extra tank of water for fuel reforming.

Development of Laminar Burning Velocity Correlation for the Simulation of Methanol Fueled SI Engines Operated with Onboard Fuel Reformer

Using the simplest alcohol – methanol – as a fuel for spark ignition (SI) engines, enables an increase of thermal efficiency compared to gasoline. Additionally, with the enrichment of hydrogen rich gas from methanol reforming (syngas) using exhaust heat, the efficiency can be further improved. The complexity of optimizing such an arrangement asks for numerical support. However, there is no research that publishes the effect of unburned mixture temperature and equivalence ratio on the laminar burning velocity of methanol-syngas blends, which is needed for developing an engine cycle code to simulate methanol fueled SI engines with syngas addition from exhaust gas fuel reforming. The influence of temperature on the laminar burning velocity of methanol-syngas blends is investigated in this study using CHEM1D. The simulation shows that the flame speed increases dramatically with the enrichment of syngas, especially at lean and rich conditions. The effect of syngas ratio on the improvement of burning velocity is less important at higher temperatures, and there is almost no influence at stoichiometry. Some well-known mixing rules are then examined. In general, the Hirasawa mixing rule shows the best fit with the numerical data. For blends with high syngas content, the Le Chatelier’s mixing rule is recommended. The temperature power exponent α is calculated and compared to other correlations. It shows that the published correlations are unable to predict the influence of temperature on laminar burning velocity accurately enough for the combustion of methanol, syngas and their blends in air.

https://biblio.ugent.be/publication/8108048/file/8108064.pdf

The temperature dependence of Laminar burning velocities of methanol-syngas-air flames

Methanol is a promising fuel for spark ignition engines because of its high octane number, high octane sensitivity, high heat of vaporization and high laminar flame speed. To further boost the efficiency of methanol engines, the use of waste heat for driving fuel reforming was considered. This study explores the possibility of the reformed-exhaust gas recirculation (R-EGR) concept for increased efficiency of methanol engines. A simple Otto cycle calculation and a more detailed gas dynamic engine simulation are used to evaluate that potential. Both methodologies point to an enhancement in engine efficiency with fuel reforming compared to conventional EGR but not as much as the increase in lower heating value of the reforming product would suggest. A gas dynamic engine simulation shows a shortening of the flame development period and the combustion duration in line with the expected behavior with the hydrogen-rich reformer product gas. However, the heat loss increases with the presence of hydrogen in the reactants. The improvement of brake thermal efficiency is mainly attributed to the reduction of pumping work. The R-EGR concept is also evaluated for ethanol and iso-octane. As the reforming fraction increases, the efficiency of ethanol and iso-octane fueled engines rises faster than for the methanol engines due to a higher enhancement of exergy in their reforming products. At high reforming fractions, the efficiency of the ethanol engine becomes higher than with methanol. However, if the impact of optimal compression ratio for different fuels are considered, the methanol engine is able to produce a higher efficiency than the ethanol engine.

https://biblio.ugent.be/publication/8575734/file/8575739

Exploring the potential of reformed-exhaust gas recirculation (R-EGR) for increased efficiency of methanol fueled SI engines

Using methanol as an alternative fuel for gasoline engines can reduce CO2 emissions. Engines and fuel technology are scalable, compact and can be produced in a sustainable way. Methanol is the simplest liquid synthetic fuel, therefore has production advantages compared to more complex fuels. The CO2 emissions can be further decreased with a waste heat recovery system for fuel reforming. Thanks to a high hydrogen to carbon ratio and low reforming temperature, methanol was considered as the most promising fuel for onboard hydrogen production. The aim of this research was evaluating the efficiency improvement of methanol fueled spark-ignition engines with on-board fuel reforming. The research shows that the use of methanol produces a significant increase in engine efficiency compared to gasoline. With the addition of fuel reformates, engine efficiency further increases. However, the improvement is not as much as the increase in the heating value of the reforming product would suggest.

Duc-Khanh Nguyen

Papers

A quasi-dimensional combustion model for spark ignition engines fueled with gasoline–methanol blends

Development of Laminar Burning Velocity Correlation for the Simulation of Methanol Fueled SI Engines Operated with Onboard Fuel Reformer

The temperature dependence of Laminar burning velocities of methanol-syngas-air flames

Exploring the potential of reformed-exhaust gas recirculation (R-EGR) for increased efficiency of methanol fueled SI engines

Diluted combustion of methanol in spark-ignition engines with on-board fuel reforming