High Efficiency Flex-Fuel Engines and the End of the 70% Paradigm 2017-36-0162
Recently many government Acts (Inova Energia, Inovar-Auto, RenovaBio) [1, 2, 3] have been implemented in order to expand the use of biofuels in Brazil. Besides the fulfillment until 2030 of the commitment assumed at the COP21 to reduce in 43% the gas emission contributing to the greenhouse effect, the expansion of the use of biofuels is important to assure regularity in the supply of fuels to the automotive sector in the next 15 years.
In this context, it is worth mentioning a special characteristic of the Flex-Fuel engines that equip the majority of the automobiles in Brazil since their launching in 2003. The maximum compression ratio of these engines depends on the knocking characteristics of the gasoline, but usually an intermediate value, nearer to the ideal value for gasoline, is a compromise. In any case, the energy conversion efficiency of the engines is not optimal, especially for ethanol, since the lower compression ratio required by the gasoline does not allow the full benefits of ethanol´s anti-knocking properties at higher compression ratio .
Aiming to reduce the fuel consumption of Flex-Fuel engines, the influence of the volumetric compression ratio on the fuel conversion efficiency of a single cylinder research engine was investigated. In this article the experimental results of engine tests using E22 and E100, with PFI and DI injection systems, varying the compression ratio from 11.5 to 15:1, and optimizing the flow structure (tumble and swirl) for different internal EGR, will be reported. The experimental results showed good correlation with the numerical simulation, which is part of this research and presented on another article.
Both the numerical simulation and the experimental tests confirmed the theory that higher compression ratios will result in better fuel consumption ratio between ethanol and gasoline, with advantages for the biofuel due to its anti-knocking properties. It also became clear that high compression ratios, associated to internal EGR and optimized flow structures, allow relevant fuel consumption reductions, especially of ethanol at medium and high loads.