New Quasi-Dimensional Simulation Model for Conventional Dual Fuel Combustion

This paper presents the development of a new quasi-dimensional cycle-simulation model for diesel fuel pilot ignited combustion of natural gas in a Diesel engine, so-called conventional dual fuel combustion. Dual fuel combustion has attracted a lot of attention as it is one of the options that can lead to a significant reduction of global (CO2) and local (soot and NOx) emission from conventional Diesel engine, which is a propellant of the modern industry. In dual fuel operation, two fuels that have different flammability limits are burnt together in a way that exploits advantages of each of them. High cetane diesel fuel is used as a high energy ignition device for the natural gas, which is a main energy source in this type of combustion. As diesel fuel releases 10000 times more energy compared to spark discharge in spark-ignited engines, ignition of lean premixed mixtures is enabled in this sort of operation. However, dual fuel combustion suffers from increased HC and CO emission due to flame extinctions and large crevice volumes, and knock or even preignition in the certain engine operating range. Therefore, in order to optimize the dual fuel engine performance in the conceptual development phase, new quasi dimensional cycle-simulation model has been developed and integrated in the existing cycle-simulation framework. Compared to detailed simulation models of computational fluid dynamics (CFD), cycle-simulations are time efficient. The developed quasi-dimensional combustion model is based on the two-zone modeling approach. The spray development and spray combustion are calculated with a modified AVL MZCM model which is based on the well-known Hiroyasu’s spray equations. The flame propagation through the premixed mixture is calculated with a modified fractal combustion model which takes into account combustion chamber geometry and in-cylinder turbulence effects on the combustion rate. In the paper, comparison between calculated and experimental results of conventional dual-fuel engine is presented.