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Two fuel strategy
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Post Two fuel strategy 
So why not run 87 and directly inject water/methanol controlled by engine management.

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At part loads below 8 bar BMEP, the engine OctaneNumberRequirement is quite low, below 90 RON. The vast majority of driving time is at light load implying that the fuel octane is wasted. A new solution is to separate tank fuel into low octane and high octane components, like separating E10 into E3 and E50. The fuel separator stores the lower volume high octane fuel and uses the low octane fuel directly. The high octane fuel is used only as needed but the relative volumes of fuel used will depend on the drive cycle requirement. Honda compared a 1.5L engine with 12.5 CR using the twofuel system to a 1.8L engine with 10.5 CR and found very large benefits in fuel economy of ~25%. Some of this benefit is due to the use of Atkinson cycle on the 12.5 CR engine.


While octane benefits starting at a base engine with 10.5 to 11CR are reasonable, the benefits decline with increasing CR. Average engine CR has been increasing continuously for the last 30 years and new technologies suggest that they will increase by 1.5 to 2.0 CR from 2010 to 2025. This implies decreasing value of octane in the future. Octane waste at part load suggests that the fuel splitting solution into low and high octane components, if proven, may provide engine designers more flexibility without having to introduce new high octane fuels.

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