Abstract
Using alcohols for fueling spark ignition (SI) engines can significantly contribute to the reduction of green house gas emissions. However, this category of renewable fuels presents several challenges when used in unmodified engines. Isobutanol, like shorter chain alcohols such as methanol or ethanol, features a higher latent heat of vaporization compared to gasoline. This leads to difficult cold starts during cold weather. Also, as it contains an increased quantity of oxygen, fuel flow needs to be increased in order to maintain the same relative air-fuel ratio as for gasoline operation. A significant advantage of isobutanol compared to shorter chain alcohols is that it is fully compatible with the materials used in gasoline fuel systems.
The paper presents an experimental study of engine performance and fuel system behavior of a port injection engine. Measurements were conducted on a chassis dynamometer using a passenger car powered by a SI engine. As well as fueling the engine with gasoline, 50% and 70% volumetric concentrations of isobutanol mixed with the conventional fuel were used. During the initial electronic control unit’s learning period, right after switching the conventional fuel to gasoline–isobutanol blends, a significant power loss was observed at full load and a slightly erratic engine behavior in transient conditions. While the fuel system fully adapts to the 50% concentration and practically no loss of power was observed after a few minutes of operation, 70% isobutanol mixed with gasoline was found to be right at the upper limit of the electronic control unit’s learning range. As a result, the fuel system has to be modified in order to obtain the same full load performance with high concentrations of isobutanol, compared to gasoline operation. Also, a slightly lower fuel conversion efficiency was observed during part load operation with gasoline-alcohol blends compared to using the conventional fuel alone.
KEYWORDS: spark ignition engines, port injection, fuel system performance, biofuels, isobutanol