Burn Rate Analysis of an Ethanol-Gasoline, Dual Fueled, Spark Ignition Engine

Abstract

An experimental study is performed to investigate the combustion characteristics of an ethanol-gasoline, dual fueled, single cylinder spark ignition (SI) engine. A dual fuel injection system with both Direct-Injection (DI) and Port-Fuel-Injection (PFI) is used in this work. The performance of PFI-E85 and DI-gasoline, and PFI-gasoline and DI-E85 systems is presented. E85 is a blend of 85% ethanol and 15% gasoline by volume. In each test, the percentage of E85 is varied from 100 (0% gasoline) to 0 (100% gasoline) to compare the various cases. PFI-gasoline and DI-gasoline (PFI & DI-gasoline) results are also presented to provide a baseline for comparison. The cycle-to-cycle variability is presented using coefficient of variation (COV) of indicated mean effective pressure (IMEP). Mass fraction burned (MFB) and burn duration are determined from the analysis of measured in-cylinder pressure data. The well known Rassweiler and Withrow method (Model 1), with a new linear model for the polytropic index, is used to obtain the MFB curves. The differences are presented for the net pressure method (Model 2) to evaluate the burn rates. It is found that combustion is faster with the increase in PFI percentage for all the three setups with dual fuel injection. The PFI-E85 and DI-gasoline system showed that the burn duration decreases significantly with the increase in PFI percentage; however, the PFI-gasoline and DI-E85 system showed only slight differences with the increase in PFI percentage. Model 2 showed good agreement with Model 1 at high load conditions; however, it predicts slower combustion at light load conditions.