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This work compares the emissions and performance of two dual-mode reactivity controlled compression ignition (RCCI) combustion strategies under the World Harmonized Vehicle Cycle (WHVC), a chassis dynamometer version of the World Harmonized Transient Cycle (WHTC) test proposed by the EURO VI emission regulation for heavy-duty engines. The major difference between the two dual-mode combustion strategies investigated is that, while one of them relies on covering with conventional diesel combustion (CDC) the part of the map that cannot be covered by RCCI regime (RCCI/CDC dual-mode), the other does it relying on dual-fuel diffusion combustion (dualmode dual-fuel). The influence of the gear shifting strategy on the emissions and performance over the WHVC is discussed first. Later, both dual-mode concepts are compared considering the optimal gear shifting strategy. The results suggest that dual-mode dual-fuel concept allows reducing the specific fuel consumption by 7% in average versus RCCI/CDC concept. Moreover, NOx emissions are around 87% lower with dual-mode dual-fuel, meeting the EURO VI requirements without the need for an SCR aftertreatment system. In counterpart, HC and CO emissions are near 2 and 10 times greater, respectively, for dual-mode dual-fuel than for RCCI/CDC.

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a b s t r a c tThe use of ethanol as fuel has encouraged many countries to improve their production processes. However, costs related to its current production model have been occasionally mentioned as a disadvantage to the use of this biofuel. One of the main costs is the energy expenditure for an effective distillation of the fermented ethanol wort, to result a final product called hydrous ethanol (about 95% by volume of ethanol in water). A promising alternative is the use of ethanol fuel with high fractions of water (above 5% by volume), the so-called wet ethanol, which would reduce the energy cost of production during the distillation. Thus, this study proposes the development of a mathematical model that, along with experimental data, is able to predict the effect that the use of wet ethanol has on the performance of internal combustion engines. In order to do so, along with commercial hydrous ethanol, blends were prepared with the following volume fractions of water: 10% (E90W10), 20% (E80W20), 30% (E70W30) and 40% (E60W40). Tests were performed considering two engine operating conditions: (a) fixed ignition timing and (b) adjusted ignition timing for maximum engine torque. The model was able to successfully simulate the gradients of pressure and temperature in the cylinder and it showed good ability to predict engine performance based on the variations of power, torque, conversion efficiency, and specific fuel consumption. Except for the specific fuel consumption, where the estimated error for variations was greater than 20%, the estimates for the other performance parameter presented relative errors lower than 7%. For all tests, the relative error was lower than 13%. The gradual increase of specific fuel consumption was associated with the increasing water content. Among the fuels tested, E70W30 showed the best performance, followed by the E80W20 blend; both were more efficient than the commercial ethanol.

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