How to get 100 mpg from your car

[Brian]

This is the title of an article in Engineering & Technology (E&T) magazine Vol 3 Issue 2 9-22 Feb. 2008, accessible only to members.

It describes how the author added an extra Li-ion battery to obtain a claimed 100 mpg plus. However, because the battery characteristics do not match those of the original NiMH, he used the power from the Li-ion only to charge the NiMH when it was running low. The power to charge the Li-ion came from the power grid, not from the engine.

This is a cheat, pure and simple, by making the car a plug-in, because he counts only the energy he uses in the fuel to get his 100 mpg, ignoring the fuel burnt in the power station. This is like saying that an electric vehicle gets a fuel consumption of 0 l/100 km or infinity mpg. His battery required about 12 kWh to charge, requiring typically about 40 kWh of fuel at the power station. This is equivalent to about 4 litres of petrol (gasoline). The author doesn't say what his actual performance improvement is, in real figures. However, he does say the NiMH would take the car one mile at 31 mph, with a capacity of 1 Ah. The battery he used was 50 Ah at 200 V, which he had to step up to 240 V, giving an effective 40 Ah at 95% converter efficiency, so he could get an extra 40 miles per charge or roughly 40 mpg, which is worse than using the Prius normally. Assuming the power station was powered with fossil fuels, there would be a net loss in terms of emissions (and pollution).

So, what would be gained? Because UK petrol is heavily taxed and electricity isn't, he would gain a mite in running costs, but anyone whose family can run two Prius cars and can afford the cost of hyper-expensive Li-ion batteries, cannot be short of money, bearing in mind that such batteries have a short lifetime (whether they are used or not). I suggest that all he can gain is the satisfaction of seeing 99.9 mpg on his display on relatively short runs, while defeating the purpose of buying a Prius in the first place.

In other words, his 100 mpg smells of male bovine excrement.

[jams002]

yah how to get an 100mpg to a car?? :?maybe your speed not like that to fast!!





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[Darin]

So, what would be gained? Because UK petrol is heavily taxed and electricity isn't, he would gain a mite in running costs, but anyone whose family can run two Prius cars and can afford the cost of hyper-expensive Li-ion batteries, cannot be short of money, bearing in mind that such batteries have a short lifetime (whether they are used or not).

Depends on the chemistry. Lithium Cobalt? Sure! Lithium Iron Phosphate and co? Probably not.

That said, I can't disagree, especially when ordinary cars can break 100mpg at lower speeds w/ a bit of driver know-how.

[Brian]

In this day and age, the car should perhaps not be judged on mpg or l/100 km but on holistic ("well-to-wheels") GHG emissions as CO2-equivalent. This would have to include methane emissions from coal mines and NG exploitation where these fuels are indirectly used to charge batteries. Of course, some assumptions would have to be made, such as using the global average emissions for all kinds of electricity generation, so that you would include the proportions of both "dirty" countries (e.g., China, Australia, USA, etc.) and "clean" ones (e.g., France, Switzerland etc.). I think NO2 should also be factored in, because this may be the counter to ultra-lean engines.

As for your article, the guy achieved exceptional results under exceptional conditions, using his so-called P&G technique (which is illegal here, BTW: the engine or driving force must be engaged at all times while the vehicle is in motion). "This was possible only because I was virtually alone on the road, unmolested by other drivers - and it was nearly all rural driving." I would challenge him to do the return journey from my house to Nicosia with his Metro driven legally on the crowded highway! If he drove P&G on ordinary roads in the UK I could pretty well guarantee that he would have a black eye or worse within the first hour, as road rage is rife there!

[Darin]

I think that emissions should be associated w/ the local electricity emissions profile. If I have an EV and generate as much electricity via solar panels as I use, then that could reasonably be associated w/ very low Carbon emissions. If I live in the south eastern U.S. and get all my electricity from an old coal plant, then it would be fairly high Carbon electricity, and if I live where I live right now and get the bulk of my electricity from wind turbines and a bit from the LADWP's generating mix, then my Carbon emissions would reflect that profile.

The individual I linked has averaged ~80mpg over the last 90 days during a Canadian winter, so even w/o perfect conditions I think that a smaller (~2000lbs) aerodynamic vehicle w/ a manual trans and 1-2L engine could see nearly 100mpg w/ judicious driving habits. We have similar laws regarding a car being in gear but only on downgrades, and they are mostly meant for tractor trailers. I've never heard of someone driving a passenger vehicle getting a ticket for it unless they flat out told a cop what they were doing during a stop. Ironically enough we have had legal vehicles w/ freewheeling transmissions, and EVs don't require any effective form of "engine braking" so simply being in N w/ no power flow from the engine/motor doesn't constitute something illegal.

I can't speak for the other driver, but I wouldn't be worried about driving a bit slower on UK roads in terms of physical assault. My friend and I clock in at ~240kg/3.8m. It would take a very brave or very stupid "road rager" to do something IME.