A Predictive Model for Knock in Dual Fuel Engines

A model is described for the prediction of the onset of autoignition and knock in compression ignition engines of the dual fuel type. The associated variations with time of performance parameters such as the energy release rate, cylinder pressure and charge temperature, power output and species concentrations can also be obtained. This is achieved through modelling in detail the chemical reaction rates of the gaseous fuel during compression and subsequently during diesel fuel pilot ignition and combustion. A comprehensive reaction scheme involving 105 reaction steps with 31 chemical species is employed for the purpose. The results are based mainly on methane or propane as the gaseous fuel while accounting for the contribution of pilot diesel fuel injection. Calculated data showed good general agreement with the corresponding experimental values.

The dual fuel engine offers flexible means for using conventional diesel engines while utilizing various gaseous fuel resources, without suffering significantly from exhaust particulate emissions (1)*. This is achieved through maintaining some liquid fuel injection for ignition purposes while the bulk of the energy release is obtained from the combustion of the gaseous fuel component. However, there is an acknowledged barrier to the widespread conversion to these engines, especially with some fuel mixtures, because of the incidence of knock. The effort to overcome this barrier is economically worthwhile, but is hampered by factors such as the diversity of diesel engine types available, the variety of the gaseous fuel mixtures that may need to be consumed, and the desire to maximize the use of the gaseous fuel relative to that of the liquid fuel.