JAMES EMPSON PETERS, Purdue University


An ignition model for liquid fuel sprays with particular emphasis on gas turbine applications is developed and tested. The ignition model is cast in the form of the characteristic time model and states that for ignition to occur, the energy of a spark must heat up an initial volume such that the heat release rate within that volume is greater than the heat loss rate. Heat generation is limited first by a droplet evaporation time and then a kinetic time; heat loss (for gas turbine applications) is due to turbulent diffusion and, hence, is controlled by a mixing time. The model is verified by an examination of data in the literature from a simplified, experimental test rig and good agreement is found between the model and ignition data with a wide range of variations of drop size, equivalence ratio, velocity, pressure and fuel type. To provide an additional check on the model ignition limits for a previously untested fuel, JP-10, were predicted. An experimental rig was constructed to test the fuel and a description of the rig and operating procedures are included. The experimental results confirm the validity of the model and provide evidence of the utility of the model as a predictive tool. The application of the ignition model to gas turbine engines is illustrated with ignition data from three different engines, tank, helicopter and jet. The model correlates the ignition data which include cold start, altitude relight and thirty fuels from these engines with a single ignition limit curve. The key to applying the model to engine data is the estimation of drop sizes and equivalence ratios at the spark gap. The single most critical factor for ignition in gas turbines is the evaporation of the fuel and consequently combustor or fuel changes which affect evaporation can strongly influence ignition. Finally, the additional applications of the model to homogeneous ignition and lean blowoff are briefly illustrated.



Subject Area

Mechanical engineering|Energy

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