CPERI

The effect of adding hydrogen to methane and iso-octane–air premixtures has been investigated under both laminar and turbulent conditions. Five percent by mass of hydrogen was added the to base fuel. Measurements were performed at 5bar and the equivalence ratio was varied from the lean ignition limit to either the rich ignition or sooting/buoyancy limit. The laminar burning velocity, ul, increased for fuel lean and stoichiometric methane/hydrogen mixtures compared with pure methane. A doubling in ul was observed at the lean limit. There was no increase in ul for ϕ⩾1.2. Laminar hydrogen/iso-octane mixtures burned faster than those of pure iso-octane–air over the whole range of equivalence ratios investigated. For both methane and iso-octane, addition of hydrogen resulted in earlier onset of laminar flame instabilities and a reduction in the Markstein length (where measurement was possible). In the case of turbulent combustion, hydrogen addition (for both fuels), resulted in an approximate doubling of turbulent burning velocity at the lean limit. As the equivalence ratio was increased, the effect of adding hydrogen reduced until, at the rich ignition (methane) or sooting/buoyant (iso-octane) limit, no change in turbulent burning velocity was measured. The increased laminar burning velocity was primarily responsible for the increased turbulent burn rate with hydrogen addition. For lean iso-octane–air mixtures hydrogen addition resulted in further enhancement of the turbulent burning velocity over and above that expected on the basis of the laminar burning velocity. This was associated with a reduction of the flames sensitivity to strain rate, a result of the molecular mobility of H2.

ABSTRACT The prominent aim of this investigation was the examination of the in-principle feasibility of aluminum combustion under internal combustion engine (ICE)-like conditions. This study was performed in the framework of recent consideration of metallic nanoparticles as alternative fuels for ICE engines. Aluminum nanoparticles of different morphologies and sizes were studied with respect to their fundamental oxidation characteristics via thermogravimetric analysis under various nitrogen–oxygen environments and by spark-ignition of Al nanopowder “strips” under controlled airflow at ambient pressure. The ICE-like tests included measurements performed in two different arrangements; namely, a shock-tube setup and a constant-volume combustion vessel. A set of engine tests was also performed in a single-cylinder compression-ignition engine with a customized, single-shot aerosol injection system. Burned powder samples were, in all cases, examined via in situ and ex situ techniques for the identification of products and their morphologies. The results largely verified that combustion of aluminum particles in an engine environment is indeed feasible. Nonetheless, prominent differences, in terms of the products formed and their morphologies/structures, were identified among the various oxidation/combustion techniques employed.

ABSTRACT The present study addresses the feasibility to synthesize aluminium nanoparticles (NPs) from micron-sized aluminium powder with the use of a customized atmospheric plasma spraying (APS) technique. Using APS, nanoparticle synthesis can be achieved via rapid melting and vaporization of the initial micrometric particles and their subsequent re-nucleation. A custom mantle system was designed and developed with the aid of relevant simplified CFD simulations. The mantle provided the necessary inert environment (argon), at ambient pressure, in order to avoid any oxidation of the metal during plasma spraying while promoted rapid quenching of the gasified metal. The particles formed were collected with the aid of a quartz filter downstream of the plasma flame and the production rate achieved was 2 g min−1. Ex situ post-characterization of the particles via X-ray diffraction, specific surface area measurement (BET), transmission electron microscopy (TEM) coupled with energy dispersive spectrometry (EDS) and thermogravimetric analysis (TGA) under air revealed that the powders obtained primarily comprised of monocrystalline metallic aluminium nanoparticles of almost spherical shape. The NPs possessed a 2–5 nm oxide coating layer. By regulating the conditions inside the mantle, a variety of different size distributions were obtained.