Experimental and numerical investigation of the ignition process in a large bore dual fuel engine

Dual fuel engines, powered by natural gas and ignited by a small quantity of diesel fuel, have emerged in marine and power generation sectors as extremely attractive solutions due to their low emissions and fuel flexibility. However, the stricter emissions regulations and the high demanding market requests for more efficient dual fuel engines require ever shorter time for engine development. Reliable phenomenological fast running 0D/1D combustion models can therefore be used as effective tools for reducing the time and cost of testing activities. Nevertheless, the simulation of the dual-fuel combustion process is particularly challenging, due to diesel/methane chemical interaction and combustion mode transition from diesel autoignition into premixed flame propagation. The correct simulation of the diesel injection, air entrainment and autoignition process is thus crucial for the combustion process prediction and for reliable estimations of the engine performance. The aim of the paper is therefore to investigate the ignition process in dual fuel engines through a detailed experimental analysis and to provide a suitable 0D predictive combustion model for the ignition process simulations. An ignition delay model was developed based on 0D detailed chemistry reactions mechanism and it was validated against experimental data from an extensive test campaign. Several diesel injection strategies in terms of injected quantity, injection pressure and duration and different in-cylinder conditions were considered. The proposed model was shown to be capable of providing reliable predictions of the ignition process with an error of ignition delay prediction limited on average in the +/− 1 crank angle degree.