Influence of Injection Timing on the Engine Efficiency and Emissions in a SI PFI Engine Using Ethanol-Gasoline Blends with Several Water Content Levels 2017-36-0147

The need to reduce greenhouse gas emissions by the automotive sector has demanded an increase in the efficiency of internal combustion engines as well as the use of renewable fuels, with ethanol being one of the most promising fuels. In SI PFI engines, the quality of the air-fuel mixture formed during the injection event is dependent on several factors, such as: physical-chemical properties of the fuel (density, viscosity, surface tension, latent heat of vaporization), interaction between fuel spray and gas flow / pipe walls / back surfaces the intake valves. To better understand the impact caused by some of these characteristics in the formation of the mixture - and in the efficiency / emissions - of a PFI engine, tests were performed at the Engine and Vehicle Division of Mauá Institute of Technology on a 3 cylinder, 1.2l displacement engine, tests in which the opening and closing times of the needle of the injectors were varied as a function of the crankshaft angle, keeping other parameters of the engine unchanged. These tests were conducted in five engine operating regimes that represent more than 30% of the fuel consumption in the fuel consumption and emissions test cycle in Brazil (NBR 6601) and five fuel blends were used in the tests: hydrous ethanol (E95h), anhydrous ethanol (E100), 85% ethanol+water (E85h), pure gasoline (E0 R95) and gasohol (E27). The results indicated that there was a maximum reduction in the order of 0.4 to 1.0% in the specific consumption when the end of the injection event occurs soon after the opening of the intake valves. However, if the end of the injection event occurs later in the intake stroke, there is a considerable decrease in the energy conversion efficiency, as well as a considerable increase in the levels of UHC and CO, as already reported in the literature. This mechanism can be better utilized to aid in the mixture formation in PFI engines at low loads, mainly when low volatility fuels such as ethanol (at various water contents) is employed.