ENGINES RESEARCH OVERVIEW
The research challenges to consolidate ethanol as the renewable substitute for gasoline are presented in two different time scales and technology bases. The first one, on a short to medium term (10 to 20 years), relates to the evolution of internal combustion engines. The other, on a long term, deals with fuel cells, Aviation fuels and applications.
The introduction of flex-fuel vehicles broke the paradigm of one specialized engine for one strictly specified fuel, as the vehicle has to be optimized for any ethanol and gasoline blends, thereby making the development issue a lot more complex. Only through an intensive use of on-board electronics has it been possible to tackle that problem and approach the development of “optimum” flex-fuel engines.
An “optimum” flex-fuel engine has to show the same performance, consumption, pollutant emissions and durability as the hypothetical engines that would have been optimized for each particular fuel blend on which the flex-fuel engine can run.
Flex-fuel engines still represent a trade-off between using C gasoline (gasoline with a 20-25% anhydrous ethanol addition) and using hydrous ethanol. The engine compression ratio is different than the optimum ratio for a gasoline engine and the optimum ratio for a hydrous ethanol one. In addition, before flex-fuel engines can start on cold days when using ethanol, the gasoline stored in an auxiliary reservoir needs to be injected.
The short term technological challenges, demanding innovation, are how to adjust the actual engine compression ratio, perhaps by changing the closing angle of intake valves or using turbo-charging, and how to solve the cold-starting problem when using only ethanol.
The technological evolution of spark ignition engines will, probably, include direct fuel injection together with port injection and turbo-chargers, in order to decrease fuel consumption and CO2 emission. The challenge here is to understand the role ethanol can play in this new engine configuration, and to study its compatibility with the after-treatment devices that will be used for emissions control.
Plenty of research is being carried out at universities, research institutions and automotive industries on the homogeneous-charge-compression-ignition (HCCI) process that, when kept under control, promises to combine high thermal efficiency with low NOx emission. The single substance characteristics of ethanol can imply some application advantages under this process.
The ever increasing price of fuel is reinforcing the advantages Diesel-cycle engines have over Otto-cycle ones. To develop ethanol or sugarcane products with physical-chemical properties adequate for compression ignition engines is another important medium term technological challenge and Develop aviation fuels.