Wiebe function parameter determination for mass fraction burn calculation in an ETHANOL-GASOLINE fuelled SI engine

The Mass Fraction Burn (MFB) and Heat Release Rate (HRR) reflect the amount of fuel burned and the rate of burning throughout the combustion process in an internal combustion engine. These parameters play a crucial role in research and development endeavours focused on engine efficiency, emissions, and overall operating performance. Analytically in a Spark-Ignition (SI) engine, these parameters are often modelled with the Wiebe function, a well known mass fraction burn formulation, which is a function of "a" (efficiency parameter), "m" (form factor), crank angle, and the duration of combustion. This function is a simple but powerful correlation model that is well suited for zero and one dimensional engine cycle simulations. In this work, the Wiebe function parameters are determined over a range of fuel compositions and compression ratios by fitting the Wiebe function curve to the experimentally obtained MFB data from a single-zone HRR analysis. The Wiebe function parameters are determined using a curve fitting model by finding the minimum of a scalar function of several variables. This functionality has been built into the single-zone mass fraction burned model. Experiments with five ethanol-gasoline fuel blends: E0 (gasoline), E20, E40, E60, and E84 were conducted on a SI Cooperative Fuels Research (CFR) engine while holding a constant load of 330 kPa Net Indicated Mean Effective Pressure (Net IMEP). There were five methods introduced to fit the Wiebe function parameters, which utilized a combination of least square method and direct algebraic solution. This paper details the process used to determine the Wiebe function parameters, and compare the results obtained using these methods for the ethanol-gasoline mixture concentrations.