A PREDICTIVE MODEL FOR GAS FUELED SPARK IGNITION ENGINE APPLICATIONS 1999-01-3482
A predictive procedure for establishing the performance parameters of spark ignition engines fueled with a range of gaseous fuels and their mixtures is described. The incidence of knock and its relative intensity are also accounted for. The two-zone model incorporates a procedure for deriving an estimate of the effective duration of combustion and the associated mass burning rate for various operating conditions and gaseous fuels.
The preignition chemical reaction activity of the unburned end gas zone and its consequences on cylinder pressure development is evaluated while using detailed chemical kinetics. The onset of autoignition and knock is established via a parameter that monitors the incremental pressure increase solely due to the preignition reaction activity per unit of mean effective combustion pressure. This knock parameter corresponds also to the specific energy release within the end gas due to the preignition reaction activity relative to the total energy released by combustion per unit of initial cylinder volume. For normal knock-free combustion the value of this parameter remains throughout very low, while for knocking combustion its value exceeds a certain acceptable limit. The more intense the knocking the earlier this value is reached.
It is to be shown that this relatively simple model can be used to predict many aspects of engine performance parameters including the incidence of knock and account for cyclic variations as well as to be used in analytical optimization procedures.
Experimental results obtained in a CFR engine for different fuels that include methane, hydrogen, ethane, propane and their mixtures yield satisfactory agreement with the corresponding predicted values.