How Far Can We Take Advantage of Combustion Characteristics of Fuels?

Abstract

How far can we take advantage of combustion characteristics of fuels? It depends on how well we know about the combustion properties of fuels. The effect of modifying or changing fuels on the SI combustion has been investigated in terms of the fundamental combustion properties calculated by detailed kinetic models. Several previous studies suggested that the lean limit of SI combustion is significantly improved by the additives like nitromethane and by using high octane sensitivity fuels. The effects of the addition of nitromethane to methane and butane have been investigated based on the extinction flame stretch rate as well as the well-known properties including ignition delay time and laminar flame propagation velocities. The results suggested that the addition of nitromethane or the increase of octane sensitivity expands the lean and stretch extinction limit of early flame propagation. Also, recent experimental works have identified ethanol as a fuel with extended lean limit for SI combustion due to improved anti-knock and initial flame propagation. However, a part of reason may be in the smaller molecular weight and size which decrease Lewis number. For the elucidation of the effect of this Lewis number on the flame stretch-extinction behavior, numerical calculations have been performed by artificially modifying the collision diameters of the fuel molecules. The results indicate that both Lewis number and chemistry affects the extinction limit in the same order of magnitude.