The truth about the economy (Ok, maybe borderline soapbox)
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Mike Mullikin wrote:
have lesser emissions standards and that adds significantly to the equation.
That I think is the case as well. Don't the American's also have slightly different fuel to what we have over hear. I remember Clarkson mentioning something that if you run a Koenignseggyywhatsit on European fuel you'll get another 60bhp compared to what the American's can. Of course wait until everyone cottons onto bioethanol[^] then things will get more interesting. I love that Nemesis will out accelerate Aston Martins (so goodbye to almost all American muscle cars) and is exempt various charges because it's ecofriendly, yet still averages about 10mpg :cool: Can't wait to see how that stacks up in the Dakar, apparently Bowler have been the most consistent competitor in the Dakar and this is shaping up to annihilate the competition from what "experts" are saying. Which isn't bad for two British brothers up against multi-national organisations.
I doubt it. If it isn't intuitive then we need to fix it. - Chris Maunder
Uncomparable numbers again. The US use Anti-Knock Index rather than Research Octane Number, used in the UK. The AKI number is four to five points lower than RON (source[^]). So US "87 octane" is about 91-92 "octane" UK. That said, the 'octane rating' is a measure of the compressibility of the fuel, not of the energy content. The higher output of performance engines is due to higher compression leading to more energy from combustion. Sticking higher-octane fuel into the same engine gives very little or no benefit. Putting lower-octane fuel into a car with a high compression ratio will cause knocking (detonation rather than controlled combustion) and the engine computer will adjust the timing to avoid that happening, at the cost of decreased power. Ethanol compresses well giving more energy per cycle (if compressed more heavily) but has less energy per litre than petrol. When put into regular petrol as an additive fuel economy falls. The problem with ethanol is where do you get it from? UK bioethanol comes from 'waste' sugarbeet, what's left after crystal sugar has been refined. There's only so much of this stock available and producing more would require redirecting growing land from some other crop. In addition, the energy return on energy invested is poor enough even if you totally discount the energy cost of growing the sugar beet in the first place, counting the energy used to plough and plant the stuff, and the energy content of the petrochemical fertiliser, against the refined sugar and not the ethanol. It works better in Brazil, as they use cane sugar without much extra energy investment through mechanized cultivation (much is still cultivated and cropped by hand), although fertilization is often done chemically. Still, their ethanol only caters for less than 50% of demand, and some analysis (e.g. here[^]) suggests that when all inputs are taken into account, the ethanol produces less energy once burnt than if the fossil fuel inputs were burnt directly.
DoEvents: Generating unexpected recursion since 1991
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Disclaimer up front, I've bought a Toyota Prius and I'm getting about 60mpg (imperial). Whenever you have a discussion between US and UK drivers on fuel consumption, you have to remember we're not working with the same units. We (UK) quote fuel economy in miles per (imperial) gallon, they (US) quote it in miles per (US) gallon. One US gallon is 3.785 litres, one Imperial gallon is 4.546 litres, making the UK gallon 1.2 times larger, so you'd expect 20% more miles per UK gallon than US. My consumption compares favourably with that of a US driver getting 45mpg from his Prius (54mpg Imperial). The models are not, however, completely identical. You also have to remember that the quoted figures are based on a standard test procedure which is performed on a rolling road and is therefore not subject to wind resistance. This makes the quoted figures unachievable in practice. In addition the EU test is done in temperatures between 20 and 30 degrees Celsius, something that very rarely happens in the UK. (That said, on a nice day a few weeks back I did get a reported 65.1mpg for the day's commute, although drivers report that the Prius on-screen consumption display can be quite inaccurate.) The emissions standards are based on the different test procedures between the US and EU and are therefore not really comparable. Ultimately the undesirable emitted compounds come from incomplete combustion and non-hydrocarbons in the input. The ideal combustion formula reacts (burns) hydrocarbons with oxygen to produce carbon dioxide and water, but insufficient oxygen/too rich fuel produces carbon monoxide (CO) instead of CO2, while too much oxygen/too lean mix causes some nitrogen in the air to react with the excess oxygen to produce nitrogen oxides (NOx). The catalytic converter turns the undesirable NOx back into nitrogen gas (N2) and oxygen (O2), adds oxygen to CO to produce CO2, and burns off any unburnt hydrocarbons to produce CO2 and water (ideally). As a proportion, the EU standards appear to allow more NOx to CO than the US standard, but this may be an artifact of the different test cycle rather than an actual difference in output. California's LEV (Low Emission Vehicle) standard allows 3.4 grams per mile of CO (source[^]) while the EU permits only 1.0g/km (1.6 g/mile) (
Mike Dimmick wrote:
You also have to remember that the quoted figures are based on a standard test procedure which is performed on a rolling road
Oh I know that's the typical one but for example the RR Sport figure which I quoted was from a magazine which tested it over 300 miles with Motorway, Dual-Carridge Way, Normal A-Road, Country lanes, Green lanes, serious off-road and included a 2-mile stretch in a river so I don't think you can get much fairer than that. I mean what Prius is going to average 65mpg (Imperial) when driving in a metre of water? Not one I would think ;P Where as the TDV8 did average 25mpg including the section through the river.
I doubt it. If it isn't intuitive then we need to fix it. - Chris Maunder