Ignition phenomena of ethanol under IC-engine-like conditions: Shock-tube experiments and kinetics modeling
Final Report Abstract
In the current discussion of biomass-derived fuels, ethanol has gained significant importance. The properties of alcohol-containing fuels are, however, not comparable to those of conventional hydrocarbon fuels. On one hand, ethanol increases the knock resistance of fuels and thus seems to be suited for engines with supercharging and high compression ratio and thus increased efficiency. This project aimed at providing chemical mechanisms for the ignition of ethanol and ethanol-containing fuel blends. Also the effect of the affinity of ignition of ethanol on surface was studied in shock tube. For this, a new methodology was developed to study hot-surface ignition of fuel/air mixtures in a shock tube at high pressure (40 bar) and temperatures between 750–1050 K by placing a hot glow plug (1200 K) in the shock tube directly in contact with the reactive mixtures. The new concept can be used to study hot-surface ignition for a large variety of parameters such as gas composition, pressure, surface temperature and temperature of the surrounding gas. The progress of the reaction near the hot surface was followed by high-repetition-rate chemiluminescence imaging. The optical method was used to temporally and spatially monitor the development of the ignition process behind the incident and reflected shock wave. In case of ethanol, the results show that the ignition on the hot surface appears in a narrow range of conditions. Ethanol as well as Ethanol/PRF blends were found to be insensitive to surface ignition for glow-plug temperatures below 1000 K and gas temperatures higher than 900 K. With increased surface temperature, the ignition is obviously seen near the surface. Chemiluminescence as a result of surface reactions on the hot surface was visualized after the arrival of the shock wave. The geometric perturbation of the plug (unheated) did not induce any ignition although the simulation predicts conditions that are favorable for it. For surface temperatures above the shock-heated gas temperature, surface ignition is initiated close to the heated plug only behind the reflected shock wave. In addition, a hot spot created by the heated plug is swept away by the gas flow following the incident shock wave towards the endwall. Numerical simulations were used to reconstruct the shock procedure and simulate gas dynamic effects decoupled from chemistry. For heated glow plug the gas-dynamic effects in the simulation explained the observed moving gas clouds and the shock heating of the cloud itself while the pressure slightly relativizes this effect concerning ignition delay times. For the unheated case the simulation could not be validated by the experimental observations because the heated gas emits no light and does not ignite earlier compared to the unheated surrounding. Also, the pyrolysis and ignition of ethanol have been intensively studied in different apparatuses using different diagnostics such as time-of flight mass spectrometry and laser absorptions. The data served to constrain different mechanisms from the literature. The ignition of diethylether – which was proposed to index the pre-ignition behavior of ethanol has been intensively (shock tube and RCM) studied. This permits to develop a new model that covers low temperature and high pressure.
Publications
- Experimental study of the kinetics of ethanol pyrolysis and oxidation behind reflected shock waves and in laminar flames, Proc. Combust. Inst. 35 (2015) 393-400
M. Aghsaee, D. Nativel, M. Bozkurt, M. Fikri, N. Chaumeix, C. Schulz
(See online at https://doi.org/10.1016/j.proci.2014.05.063) - Ignition delay times of diethyl ether measured in a high-pressure shock tube and a rapid compression machine, Proc. Combust. Inst. 35 (2015) 259-266
M. Werler, L. R. Cancino, R. Schiessl, U. Maas, C. Schulz, M. Fikri
(See online at https://doi.org/10.1016/j.proci.2014.06.143) - Ignition delay times of primary reference fuels dopedwith diethyl etherat high pressureand intermediate temperatures in: Proc. of 25th International Colloquium on the Dynamics of Explosions and Reactive Systems, Leeds, 2015; Leeds, 2015
M. Fikri, J. Herzler, O. Welz, Y. Sakai, C. Schulz
- Experimental and numerical study of the ignition delay times of primary reference fuels containing diethylether in: Proc. of the 26th International Colloquium on the Dynamics of Explosions and Reactive Systems, Boston, 2017
M. Fikri, Y. Sakai, J. Herzler, C. Schulz
- Methodology for the investigation of ignition near hot surfaces in a high-pressure shock tube, Review Sci. Instrum. 89 (2018) 055111
P. Niegemann, M. Fikri, I. Wlokas, M. Röder, C. Schulz
(See online at https://doi.org/10.1063/1.5017275) - Ignition of individual droplets in a reactive fuel/air mixture behind reflected shock waves, JSAE 20199110 (2019)
P. Niegemann, M. Fikri, S.A. Kaiser, C. Schulz
(See online at https://doi.org/10.4271/2019-01-2162)
