High efficiency flex-fuel engines, a sustainable alternative for mobility 2018-36-0037
It can be said that the greatest engineering challenge of mobility it is not related to the energy shortage, but to its generation and sustainable use. In this context, the growing use of biofuels by high performance internal combustion engines represents a sustainable alternative from the economic, technological, social and environmental point of view. In some regions of the planet, the modern electric and hybrid vehicles may not be the most sustainable choice, since they face many obstacles regarding clean energy generation, reduced recharging station network, limited autonomy, expensive vehicle prices, and battery recycling.
In Brazil since its launching in 2003, the fleet of Flex-Fuel vehicles moved by either ethanol or gasoline is ever increasing. It is worth mentioning that the biofuel has physical and chemical properties that could make its use more efficient than it is nowadays. To take advantage of the anti-knocking properties of ethanol and to reduce significantly the fuel consumption it is also necessary to optimize the engine design. A successful way to achieve this goal is the employment of high volumetric compression ratio (CR), optimized for ethanol. However, that may be harmful to the engine when running on gasoline due to the knocking phenomena. To overcome this problem, engine research should focus on finding ways to reduce the temperature at the end of the compression stroke and thus allowing safe operation with gasoline. Among the most promising technologies are the exhaust gas recirculation, water injection and Atkinson/Miller cycles.
The objective of the work here described is to increase the efficiency of Flex-Fuel engines running on ethanol, without affecting the engine performance with gasoline. The influence of the volumetric compression ratio on the fuel conversion efficiency was investigated in comparative tests with CRs of 11.5 and 15:1 in a standard engine equipped with PFI injection system using E25 and E100. The VVT inlet system was modified in order to study the possibility of applying the strategy of late intake valve closing (LIVC), known as Atkinson cycle, to reduce the effective compression ratio and allow the safe engine operation with gasoline. The results have shown that the use of ethanol in high compression ratio (HCR) engines is a technological efficient alternative and very attractive from the sustainability point of view. That becomes more evident when the CO2 emission is taken into account during the complete fuel production life cycle (Well to Wheel), in line with the proposed goals of the RenovaBio policy.