Since other factors, like air-density and the need for heat, also influence efficiency... who knows. Heck, even driving conditions change. So, we're all kind of stuck with a bad situation. It is fortunate that even in those conditions, Prius stills delivers better gas MPG than everything else out there.
For that matter, what is this "Winter blend" everyone talks about. When people complain of poor mileage in the cooler months and attribute it to the winter blend, they don't explain what it is, or why it would provide less energy per volume. Most of us here know that cold, dense air increases aerodynamic resistance, that engines and fluids take longer to warm up, and that the vehicle cools off faster when it's cool out. Tire pressures will be reduced in cooler weather if they aren't inflated, and running defrost (AC) reduces fuel economy. I would think all of these factors would decrease fuel economy more than winter blend fuel alone.
More Butane, so it is easier to start. (and butane is cheap) http://www.theoildrum.com/pdf/theoildrum_1776.pdf
This article has a reasonable discussion of summer and winter gasoline blends: A Primer on Gasoline Blending | EPRINC When I was doing gasoline studies many years ago I could see butane come out of solution in a graduated cylinder. Butane is used in winter gas when the cooler temperatures won't cause it to evaporate. Bob Wilson
OK I agree you may well observe that. Best you can do is refrigerate the sample to minimize vapor losses.
It was as if the gasoline sample had become a petroleum 'soda water.' I could see the small bubbles form in the middle of the column and grow as they floated to the top. After vigorous shaking, the bubble formation stopped. I wanted to find a non-combustion way to evaluate the energy content of a gasoline sample and was thinking the density of might give a correlation. My thought was the length of the molecular chains might provide a density gradient and provide a correlation . . . no luck. Organic chemistry does not reveal its secrets that easily. My thinking is a small, single burner, camp stove might provide a way to burn a known sample to heat or boil a known quantity of water. A pressed, metal-matrix might hold the sample; accurate scale for before and after weight and; a water container with multiple bends to transfer the heat. If sized so the water boils, a before and after weight would give a metric of how much energy was captured from burning the sample . . . hopefully with enough accuracy to determine relative energy content. But there is this 'open flame' issue and gasoline is not forgiving. Bob Wilson
One would think if we had the in-the-tank gaso density we could correlate to energy content pretty well. Problem is we don't have it except on a lab study.
