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The effects of pre-ignition chemistry on laminar flame speed in methane/n-heptane fuel blends are investigated numerically, leading to flame speed modelling accounting for these effects. The laminar flame speeds of fuel blends are important input parameters for turbulent combustion models needed to support design of dual-fuel engines. At the autoignitive conditions found in engines, pre-ignition reactions cause the speed of the reaction front to increase. Fuels that exhibit two-stage ignition behaviour, such as n-heptane, also exhibit a two-stage increase in the speed of the reaction front as the reactant residence time increases. There is a corresponding reduction in the flame thickness until the residence time approaches the ignition delay time, whereupon the deflagrative scaling of flame thickness breaks down. The analysis shows that the increase in flame speed is due to distinct contributions of heat release, reactant consumption, and enhanced reactivity ahead of the flame. Addition of methane to n-heptane-air mixtures retards and reduces the first-stage increase in flame speed, in part due to dilution of the more-reactive n-heptane fuel, and in part due to consumption of radical species by the methane chemistry. The effect of methane/n-heptane fuel blending on flame speed is described adequately by a linear mixing rule. The effect of pre-ignition chemistry can then be modelled as a linear function of the progress variable ahead of the flame-accounting for heat release, reactant consumption, and enhanced reactivity ahead of the flame. The flame speed model accurately describes the variation of flame speed across the full range of methane/n-heptane blends at engine-relevant conditions, up to the deflagration/ignition transition.

Information about the limits of flame propagation within streams of homogeneous gaseous fuel-air mixtures at atmospheric pressure is presented for both low velocity streams, in the presence of pilot jet flame ignition, as well as for high velocity streams when ignited by an electric spark of adequate and constant energy. In addition to methane, representing natural gas, other gaseous fuels were considered that included hydrogen and propane. The roles of the presence of varying concentration of the diluent gases, nitrogen and carbon dioxide, with the methane and changes in the intensity of turbulence were also investigated.

When air flows unsteadily in an internal combustion engine through its inlet pipe, chambers and valves, some effects such as friction and inertial forces have direct influence on the volumetric efficiency of the system. The work in this paper aims to investigate numerically and experimentally the pulsating phenomena present in an intake pipe of an internal combustion engine and to discuss the intake jet flow predictions through the novel implementation of a low Mach number preconditioned density-based method, including the three-dimensional modelling of the inlet valve, the inlet pipe and the pulsating effects. The inlet valve movement promotes moderate values of Mach numbers during its opening phase. After the inlet valve closes, the flow is abruptly restricted and a series of pressure waves propagate through the fluid at low Mach numbers. Although the low Mach number preconditioned density-based method is very attractive in this case, the study of the pulsating flow in the internal combustion engine intake systems has not been performed using this method, probably owing to robustness issues and simulation effort. The pressure-based methodology is widely used and, generally, the inlet pipe and pulsating effects are not included in the threedimensional fluid dynamics simulation. In order to verify the accuracy of the numerical solution, the results are compared with experimental data collected from a bench constructed specifically for this purpose. The numerical results were satisfactory for the amplitudes and the resonance frequencies in the air intake system. Also, different aspects of the jet flow inside the cylinder are shown and discussed.