A question about fuel economy to all the boy geniuses..and girls

[Michael Gibbons]

... Do you think we have tapped all the energy available in a drop of gas? I'm far from an engineer but I have heard that for every 100 lbs you remove from a vehicle you gain about 5 hp which would probably get you more MPH. So all the car companies have to do now is lighten the cars without sacrificing safety, correct??.. BTW, at what speed do they test vehicles to come up with the gas mileage ratings on the window sticker??

[Brian Willan]

... Do you think we have tapped all the energy available in a drop of gas? I'm far from an engineer but I have heard that for every 100 lbs you remove from a vehicle you gain about 5 hp which would probably get you more MPH. So all the car companies have to do now is lighten the cars without sacrificing safety, correct??.. BTW, at what speed do they test vehicles to come up with the gas mileage ratings on the window sticker??

Not even close to tapping all the energy in a drop of gas. The internal combustion engine is about 15% efficient according to http://www.fueleconomy.gov/FEG/atv.shtml. Diesel engines are more efficient than gas. Still nowhere close to using all of the energy available.

A gallon of gas has about 35KWh of energy. Now if you want to talk about efficient motors, electric is the way to go. Most electric motors are well over 85% efficient.

Cheers

Brian

[Larry Edgerton]

The formula that you heard is baloney. It would have to change continually with the weight of the car as the percentage of difference would be changing as the car became lighter and lighter. For example at 2000 pounds a 100 pound loss would be a 5% decrease in weight. At 200 pounds it would be a 50% decrease in weight. So for your theory to work it would have to consider that variables, not just weight but efficiency, wind resistance[CD], etc. and so on. I would not add 5 hp anyway, but would rather require less HP to move the same distance. It would however increase the speed of acceleration, not MPH. Top speed is governed more by aero than weight. For example to double the top speed requires four time the HP.

That sounds like one of those things tossed around in the same conversation with the 75mpg carburetor.


Less weight is a viable way to improve performance. I spent most of my life wasting my money racing one thing or another, and development to make it handle better and go faster is the fun part for me.

[Paul Ryan]

Guys I am an ex master auto mechanic. I had been at it for 17 years untill I quite last year. There are lots and lots of veriables that goes into fuel mileage. I bigest thing effecting fuel milage right now is the emission requirements. You may not believe this but today's fuel injected motors must burn more fuel to meet emission requlation. That is baloney you might say. Think about it this way. The very 1st car I owned was a 1969 plymouth barracuda. It had a 318 with a 2 barrel carb. I got consistantly 20 mpg on the highway. I increased that to 28 mpg in the summer when I could lean out the carb. But this car did not have a cataylitic converter or oxygen sensors. In order for todays vehicles with cat converters to clean up the NOX emissions they have to get hot 800-1100 degrees. In order to get that hot they have to have fuel in the cat. So the oxygen sensors along with you map or maf sensor adjust the fuel mix to get the cat to "light off" once this happens the NOX emissions are cleaned up enough to meet regulations. But if is gets too hot then the carbon emissions are out of wack, and the cat will burn up. We all have seen the dreaded check engine light. But most know unless it starts flashing you can continue to drive the car until you can get it serviced. The only reason the light will start flashing is because you have a hard miss fire. And this is allowing to much unburndt fuel to get to the cat and make it get really hot, like red hot. If this happens the cat will burn up and be wrecked. I am not against clean emissions but the auto companies are facing consumers that want lots of power for towing and pleasure, but also the government saying the emissions need to be cleaner. You could much better fuel enconomy out of todays fuel injected engines if you could just lean them out. But if that happens then the emissions would be out of wack. We also have ac and ps systems taking power away from the engine that wasn't the case in the past. But gasoline is not a very efficent fuel to begine with. There is double the BTU's of heat in a gallon of diesel then in gas. But the future is not fossile fuels because they release horrible gases and solids into the atmosphere. Hopefully it will be electricity and then soon after fuel cells. I could write forever about mileage and emissions but who would want to listen. That is my .02.

[Karl Brogger]

NOBODY is willing to pay for the technology and research it would take to make a vehicle really fuel efficient. Just adding a turbo boosts economy drastically, using wasted energy to pump more air into the engine. Volumetric effieciency is one of the most important factors to squeazing the most energy out of fuel, whether its alcohol, gasoline, or diesel.

The easiest way to raise effeciency is to lower the load on the engine, as in drag from valve train, and windage from oil. Use a drysump engine, getting the oil out of the crankcase will allow lower engine temps, (smaller water pump/less drag), plus the crank doesn't need to dip through the oil every revolution. Overhead cams did alot to reduce drag on the engine, but they are still driven by the engine. Switching to a system of electic solenoids, or running the valve train off of compressed air would be a good way to go. The added benifit would be that a computer would be able to control the cam timing and duration for essentially any RPM or load. You could go from a mileage setting to a performance setting at the push of a button. But no one is willing to pay for what is basically a Formula One engine. I always got a kick out of the Nascar folks, 800hp out of a 5.8L V8 engine, while F1 is getting 945hp from a twin turbo'd 1.8L V12 turning 22k rpm or better.

The absolute best engines that we have, as far as economy goes, is train engines. 2-stroke, w/ valves, supercharged, and turbo charged. The train companies wouldn't use them if there was something better.

[Greg Cuetara]

Paul,
I for one would want to listen to more so please keep going if you have more to say. I am an engineer by trade but know nothing about cars. I hate to take my car into the shop because I know I am getting duped everytime I go in.

When I was living in CO they increased the ethanol in gas during the winter months and I always saw a decrease in fuel economy. I always questioned that because the ethanol was supposed to make the emissions better but you used more gas to get from point A to B so in the end you would be putting the same amount of emissions into the air. Not sure if this is correct but this is what I always thought and questioned.

Greg

[Karl Brogger]

The biggest thing effecting fuel milage right now is the emission requirements.

Look at new diesel pickups, I've got a 2001 Cummins, before the switch to Ultra Low Sulphur Diesel (ULSD), I was consistantly getting 21mpg with a 4wd, 7400# pickup. With the switch to ULSD I'm struggling to get 18 mpg. The new super clean diesels, post 2007, struggle to get 12mpg. Plus they have MAJOR mechanical issues. Some guys are removing the EGR valve, and the scrubber and instantly seeing a 5-6 mpg increase. If they get caught they're in a world of trouble though. I think the fine starts around $20k.

[Jim Becker]

BTW, at what speed do they test vehicles to come up with the gas mileage ratings on the window sticker??

It used to be 50 or 55 mpg, but the new EPA rating system is supposed to be much closer to how folks drive in the real world. That's why all the sticker ratings dropped a year or so ago.

While it's true that saving weight will generally improve fuel economy it's still a balancing act. In order to save weight and also satisfy folks with all the features they want in a vehicle, a lot more has to be done with alternative materials, etc...many of us are just not willing to give up the toys!

[Dennis Peacock]

I noticed that when we got gasoline with 10% ethanol in it, my fuel mileage immediately dropped by 10%. My minivan went from 25 MPG to just shy of 23 MHP and even my Honda Shadow motorclcye dropped from 51 MPG to just barely 46 MPG.

I can't quiet figure it out.......I pay the same for fuel, I get the same amount of fuel, but I get less mileage out of that same gallon of gas....so I'm buying MORE. just doesn't make good sense to me.

[Karl Brogger]

I noticed that when we got gasoline with 10% ethanol in it, my fuel mileage immediately dropped by 10%.

This is why ethanol is such a cruel joke. Supposedly you get almost a 1.3 return by volume. You put 1 gallon of diesel into the production of the corn, and you get 1.3 gallons of ethanol. Great! but as far as energy goes, we've lost. It takes almost twice the amount of alcohol, which is more or less what ethanol is from an power producing standpoint, to generate the same amount of HP. In certain applications it is a good thing, but that is only when the fuel is used as a way to reduce temperatures in the cylinder. Ethanol is really hard on anything rubber, if the fuel system is designed for it, fine. If you're dumping that fuel into something older it will eventually dry rot many of the seals gaskets and hoses.

No easy solutions.

Give me a flat out electric car! No batteries like the hybrids. Just a generator, and electric motor. I like the idea of having the same amount of power at any given rpm.

[Jim Becker]

Give me a flat out electric car! No batteries like the hybrids. Just a generator, and electric motor. I like the idea of having the same amount of power at any given rpm.

What runs the generator? (My mind is seeing Fred Flintstone... LOL )

[Ben Rafael]

Not even close to tapping all the energy in a drop of gas. The internal combustion engine is about 15% efficient according to http://www.fueleconomy.gov/FEG/atv.shtml. Diesel engines are more efficient than gas. Still nowhere close to using all of the energy available.

A gallon of gas has about 35KWh of energy. Now if you want to talk about efficient motors, electric is the way to go. Most electric motors are well over 85% efficient.

Cheers

Brian

If used in a fission reaction a gallon of gasoline would produce approximately 12 megajoules of energy(If I remember my physics correctly). So if we were really serious about energy efficiency we need automobiles to have fission engines. 1 gallon of gas is all you would need to run your car for your lifetime.
The oil companies would never allow fission engines in cars, it would kill their business.

[Joe Chritz]

What runs the generator? (My mind is seeing Fred Flintstone... LOL )

Seriously it is likely coal.

Gasoline engines will get the advancements they need when the market forces them to do so. That is one of the cool things about supply and demand and the open market. Some government interference is needed (emissions, safety standards, etc) but some just hurt everyone.

Ethanol is a great alternate fuel source when we stop producing it from corn and start using easier to produce crops. The biggest advantage is that the infrastructure is already in place to distribute it.

It is coming but it is likely to get painful before it gets here.

Joe

[Neal Clayton]

I can't quiet figure it out.......I pay the same for fuel, I get the same amount of fuel, but I get less mileage out of that same gallon of gas....so I'm buying MORE. just doesn't make good sense to me.

it does if you're an oil conglomerate.

Seriously it is likely coal.

Gasoline engines will get the advancements they need when the market forces them to do so. That is one of the cool things about supply and demand and the open market. Some government interference is needed (emissions, safety standards, etc) but some just hurt everyone.

Ethanol is a great alternate fuel source when we stop producing it from corn and start using easier to produce crops. The biggest advantage is that the infrastructure is already in place to distribute it.

It is coming but it is likely to get painful before it gets here.

Joe

people have been saying "it's coming" for decades, we have less efficient versions of the same engines in everything detroit produces than we had a decade ago.

there is no open market. 2/3 of the oil market is controlled by a cartel. the US government selectively tariffs competing vehicles at detroit's behest to make sure "it's coming" never comes. if you think there are advancements in oil production and consumption drive to texas city sometime.

[Mitchell Andrus]

The gasoline driven cars we know and drive today will be around for 15 - 20 years. Changes come slowly, and used cars don't get scrapped as blithely as they used to. So, the cars we're driving today will be here in great numbers til 2030 or longer.

Hybrids are a joke of an excuse for innovation. At 100,000 miles they won't be worthy of spending any money for a replacement battery. When the government of Japan stops the subsidies, new batteries will be unavailable for older models. spend $2,500.00 for a 10% increase in gas milage???? Right! At about 75,000 miles and a 15% efficient battery, you're pretty much back to driving a gas powered car like everyone else.

Hybrids are the automotive bridge to nowhere.

Fuel cell cars are DOA. The infrastructure changes required to deliver the fuel, not to mention the cost of production of the hydrogen and the cost to maintain the cars's systems put this off the table. Interesting college project, not gonna happen. The low cost to deliver electricity and the low cost to buy the power for charging a battery has already killed this concept.

All-electric drives will be showing up 3 years, super big-time in about 8 years - but as econo-boxes only. You'll see some bigger stuff like pick-ups and vans in about 12 years. We'll plug them in where we can, the rest of the time, they'll charge via a constant RPM gas engine turning a generator. Go the mall, restaurant, grandma's house? - The gas engine will run while you park if you tell your car the trip home is beyond the battery's range. It'll take about 3 hours of charge time to get you 1 hour of drive time. Gas engine efficiency about doubles when it only runs at it's optimum speed and is designed for a set load, as is the case with all-electrics.

Our driving habits will change substantially. The week-long road trip will be a distant memory. So will towing a boat and warming up the car in the middle of January.

Nuclear power plants and wind farms will need to be built to avoid running our cars on coal/electric not to mention the 50% increase in the county's population by 2070. So, NIMBY is gonna go away.

If we're going to change - we're gonna change a lot of stuff.