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

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

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

Methanol is gaining traction in some regions, e.g. for road transportation in China and for marine transportation in Europe. In this research, the possibility for achieving higher power output and higher efficiency with methanol, compared to gasoline, is investigated and the influence of several engine settings, such as valve timing and intake boost control, is studied. At wide open throttle (WOT), engine speed of 1650 rpm, the brake mean effective pressure (BMEP) of the methanol-fueled engine is higher than on gasoline, by around 1.8 bar. The maximum BMEP is further increased when positive valve overlap and higher intake boost pressure are applied. Thanks to a lower residual gas fraction, and a richer in-cylinder mixture with positive valve overlap period, the engine BMEP improves by a further 2.6 bar. Because of higher volumetric efficiency with a boosted intake air, the engine BMEP enhances with 4.7 bar. The maximum BMEP for gasoline was found through a test matrix using the design of experiment approach. At that BMEP (16.3 bar), the efficiency when fueling the engine with methanol improves by 22.7% relatively with valve overlap control and by 25.75% with intake boost control. The BMEP of the methanol engine can increase to a higher value without knock when a higher boost pressure or a longer valve overlap duration is employed. Limitations are no longer engine knock, but excessive peak in-cylinder pressures, however, being over 100 bar. If the maximum pressure is limited to 100 bar, the downsizing potential with boost control is higher than with variable valve timing. The engine could be further downsized by ~10.7% with methanol by boosting the intake pressure.

Downsizing potential of methanol fueled DISI engine with variable valve timing and boost control

https://biblio.ugent.be/publication/8640449/file/8640450.pdf

Effects of molar expansion ratio of fuels on engine efficiency

Lean operation is a promising approach to increase the engine efficiency. One of the main challenges for lean-burn technology is the combustion instability. Using a high laminar burning velocity fuel such as methanol might solve that problem. The potential of lean-burn limit extension with methanol was investigated through a comparison with conventional gasoline. In this work, a direct injection turbocharged SI engine was operated at wide open throttle (WOT), with the load controlled by a lean-burn strategy. The amount of fuel was decreased (or lambda increased) until the combustion became unstable. For methanol, the lambda limit was about 1.5, higher than the lambda limit for gasoline which was only about 1.2. The brake thermal efficiency for methanol increased as lambda increased and reached its peak at ~41% in a lambda range of 1.2-1.4. Then, the efficiency decreased as lambda increased.
The increase of lambda also causes a change in the combustion process, e.g. prolonged flame development period (CA0-10). The relationship between the combustion characteristics and the combustion instability of methanol under lean-burn condition has not been reported previously. Values for the CA0-10 duration and the laminar burning velocity were searched for, able to define the combustion stability limit for the WOT operation with methanol. The laminar burning velocity was calculated using a previously developed correlation, with the unburned gas temperature and residual mass fraction derived from a three-pressure analysis simulation. A CA0-10 duration of 26.5 degree crank angle and a laminar burning velocity at ignition timing of ~0.4 m/s could be used to represent the combustion stability limit (5% coefficient of variance of indicated mean effective pressure). A longer CA0-10 and a smaller laminar burning velocity indicate an unstable combustion of methanol at WOT. At throttled conditions, those limits could not be employed to represent the instability limit for methanol combustion.

Combustion Characterization of Methanol in a Lean Burn Direct Injection Spark Ignition (DISI) Engine

The current work investigates the flame structure and the propagation of premixed laminar flame fronts for mixtures of diluted methanol–air enriched by fuel reforming products under spark ignition engine conditions. Two engine concepts were investigated: one with external fuel reforming (EFR) and one with reformed exhaust gas recirculation (R-EGR). Here, the fuel reformate (or syngas) is a mixture of H2, CO, and CO2 with a CO selectivity of 6.5%, which is used to represent the products of methanol steam reforming over a Cu–Mn/Al foam catalyst. The simulations were exercised over a wide range of dilution level and unburned gas temperature at 40 bar with a skeletal chemical kinetic mechanism using zero/one-dimensional codes. Two types of dilution—air and EGR—were compared at the same fuel-to-charge equivalence ratio (ϕ′). The results showed that the knock limit for spark-ignited operation is extended with rising dilution levels, especially when diluted by an R-EGR mixture. Syngas addition also leads to a re...

Duc-Khanh Nguyen

Papers

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

Downsizing potential of methanol fueled DISI engine with variable valve timing and boost control

Effects of molar expansion ratio of fuels on engine efficiency

Combustion Characterization of Methanol in a Lean Burn Direct Injection Spark Ignition (DISI) Engine

Computational Study of the Laminar Reaction Front Properties of Diluted Methanol–Air Flames Enriched by the Fuel Reforming Product