CitationFigueroa-Labastida M, Badra J, Elbaz AM, Farooq A (2018) Shock tube studies of ethanol preignition. . Available: http://dx. AbstractUnderstanding premature ignition or preignition is of great importance as this phenomenon influences the design and operation of internal combustion engines. Preignition leading to super-knock restricts the efficiency of downsized boosted engines. To gain a fundamental understanding of preignition and how it affects an otherwise homogeneous ignition process, a shock tube may be used to decipher the influence of fuel chemical structure, temperature, pressure, equivalence ratio and bath gas on preignition. In a previous work by Javed et al.[1], ignition delay time measurements of nheptane showed significantly expedited reactivity compared to well-validated chemical kinetic models in the intermediate-temperature regime. In the current work, ethanol is chosen as a representative fuel that, unlike n-heptane, does not exhibit negative temperature coefficient (NTC) behaviour. Reactive mixtures containing 2.9% and 5% of ethanol at equivalence ratios of 0.5 and 1 were used for the measurement of ignition delay times behind reflected shock waves at 2 and 4 bar. Effect of bath gas was studied with mixtures containing either Ar or N2. In addition to conventional side-wall pressure and OH* measurements, a high-speed imaging setup was utilized to visualize the shock tube crosssection through a transparent quartz end-wall. The results suggest that preignition events are more likely to happen in mixtures containing higher ethanol concentration and that preignition energy release is more pronounced at lower temperatures. High-speed imaging shows that low-temperature ignition process is usually initiated from an individual hot spot that grows gradually, while hightemperatures ignition starts from many spots simultaneously which consume the reactive mixture almost homogeneously.

Shock tubes are used as homogeneous batch reactors to measure ignition delay times, reaction rate coefficients and species time-histories of a variety of chemical systems. Any non-ideality or inhomogeneity in the shock tube experiment would affect the quality and usefulness of measured data. Experimental and computational efforts have previously been carried out to characterize the regimes of ideal operation of shock tubes. High-speed imaging has proven to be a highly useful tool to assess ignition homogeneity. In this work, a dual-camera setup has been used with an optical end-section in a circular shock tube to obtain simultaneous high-speed images from the shock tube endwall and sidewall, thus providing visualization of the ignition phenomenon in three dimensions. Two case studies are presented herein to demonstrate the quality of data and insights that are obtained using this diagnostic technique to study the ignition modes of different fuels. The first is a comparison of the ignition of two alternative fuels, methanol and ethanol, and the second is a study of the ignition dependence on the fuel concentration of a representative paraffinic fuel, n-hexane. The unique dual-camera imaging diagnostic enabled deeper insights into the ignition homogeneity, with all fuels exhibiting localized ignition at low temperatures. Methanol showed a higher propensity than ethanol to ignite far from the endwall, and the high concentration of n-hexane led to inhomogeneous ignition.

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The presence of sulfates potentialize damage on cementbased materials, leading to structural failures. Therefore, structures must be designed to compensate for this effect. The mechanical properties of cement-chitin mixtures are investigated with different percentages of chitin (0.5, 1.3, and 2.1 wt.%) and aging of composite in a joint nanoscopic-and macroscopic-scale by experimental study. The objective is to increase the durability of concrete elements at coastal aquifers where concrete structures are in constant exposure to sulfate ions, chloride ions among others. Tapping mode AFM was used to characterize the surface structure and roughness of the cement pastes. To verify the chitin addition and the formation of sulfate-based aggregates Raman and IR spectra were recorded and are presented in this work. Then, force spectroscopy was used to obtain the nanomechanical properties at three different exposure times (1 day, 6 months, and 1 year) into water or a SO 4 À2 environment. Macroscopic parameters (e.g., compression strength of cylindrical probes) were assessed for comparison following standard guidelines. The results show a decrease of its mechanical properties as a function of the polymer concentration but more importantly, they correlate the elasticity and adhesion at the nanoscale with the behavior of the bulk material.

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