EPA - Cars LESS Fuel Efficient Than In The 80s!

[drees]

Originally Posted by priusenvy

I stand by my statement that the reduction in fuel economy compared to the '80s is due to cars being heavier and more powerful.

I did not (and still do not) question that portion of your post.

Originally Posted by priusenvy

Also, my statement that current emission standards are not significantly impacting fuel economy is partially based on the following correspondence which appeared in a recent issue of R&T.

Please read R&T's response again.

They clearly state that the close coupled cat reduces peak power by about 10%. Which I do not disagree with. But they do not say anywhere that the cat also reduces fuel economy by 10% and in fact, only make very vague references to efficiency and instead concentrate on the power aspect along with throttle response.

Which is what I expect from a publisher like R&T, who has historically been an entity enthralled with the love and joy of driving vehicles and not a group which concentrates on improving fuel economy.

So I'll say it again: In order to keep emissions low (in particular, NOx emissions), you must keep air/fuel ratios within a very tight range, meaning 14.7/1 or slightly richer. This has a significant affect on fuel economy, because you could significantly lean out the air/fuel ratio in most light load situations and open the throttle body slightly, make the same power but do it more efficiently - at the expense of NOx emissions.

The Prius (and other cars using the Atkinson cycle) work around this by holding the intake valve open longer and allowing the engine to spit air back out the intake valves, thus reducing the amount of air sucked in to the engine and allowing wider throttle body angles which improves efficiency because the throttle body when nearly closed presents large pumping losses to the engine (it's not easy to suck air past a nearly closed metal plate). The Atkinson cycle has the drawback of significantly reduced peak power output, but this can be somewhat alleviated by using variable valve timing.

Another approach which was popular in the 80s to reduce pumping losses and NOx emissions was EGR (Exhaust Gas Recirculation). By recirculating air in to the cylinders from the exhaust (which will have just about all the oxygen burnt off) you also reduce the amount of fresh air required while still being able to maintain 14.7/1 air fuel ratios, thus allowing wider throttle openings and an reduction in pumping losses.

Recently EGR has seen an upsurge in popularity as automakers look for any way possible to improve fuel economy without affecting peak power output.

[priusenvy]

Originally Posted by drees

So I'll say it again: In order to keep emissions low (in particular, NOx emissions), you must keep air/fuel ratios within a very tight range, meaning 14.7/1 or slightly richer. This has a significant affect on fuel economy, because you could significantly lean out the air/fuel ratio in most light load situations and open the throttle body slightly, make the same power but do it more efficiently - at the expense of NOx emissions.

I understand that but 20% improved fuel economy from reduced pumping losses due to a slightly wider throttle opening seems very optimistic.

[drees]

Originally Posted by priusenvy

I understand that but 20% improved fuel economy from reduced pumping losses due to a slightly wider throttle opening seems very optimistic.

I said 10-20%, which is what Mitsubishi has proven possible.

From: Lean burn - Wikipedia, the free encyclopedia

Mitsubishi says air/fuel ratios of up to 25:1 are possible with its lean-system powerplant. The single-overhead-cam 1,468-cc 4-cylinder boasts a 10-20% gain in fuel economy (on the Japanese 10-mode urban cycle) in bench tests compared with its conventional MPI powerplant of the same displacement. The vertical vortex engine has an idle speed of 600 rpm and a compression ratio of 9.4:1 compared with respective figures of 700 rpm and 9.2:1 for the conventional version.

[cwerdna]

Per Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2007 - Executive Summary | Cars and Light Trucks | US EPA peak US gas mileage was in 1987.

Minicars? I don't See No Stinking Minicars - Column/Csaba Csere - The Steering Column/C/D Staff/Columns/Features/Car and Driver - Car And Driver
also has some info that many might not be aware of/noticed.

[LenS]

Boy,

1973 average fuel economy was 13mpg and but 2007 it was about 20mpg. In 1987 it was 22mpg average. Note that over the same period that average fuel economy was going up the 0 to 60 times were really dropping! 1987 had going for it was less vehicle weight (not many light duty trucks yet) and lower hp.

Modern fuel injection and computer controls ARE GREAT. The draw back has been that the U.S. auto manufactures have been using the technology gains to get more horse power and faster cars (and JUST meeting the CAFE standards) rather than improving fuel economy. The only time fuel economy sells cars is during periods of gas price shock.

[PriuStorm]

Originally Posted by dr_d12

The car manufacturers are responding to consumers. They're producing the one thing that the consumer is willing to pay more for: horsepower.

Funny how only some car manufacturers respond to the other thing consumers are willing to pay more for: fuel economy.

Speaking of fuel economy... My 1986 Mitsubishi Mirage regularly got 40 to 45mpg. Sure, it was a small car, a stick shift, and no A/C, but still... That, and the VW Rabbit were staple vehicles amongst my young adult friends who didn't have a lot of money but needed to get around.

[ranchogirl]

I don't remember MPG on my first car (1987), but I do remember it had a 15 gallon tank and gas was 99 cents a gallon. It cost me less than $15 to fill up my car. I usually got a free drive-in car wash with a fill up too.

Ah, those were the days....

[LenS]

I think as far as gas prices are concerned we are now paying about the same percent of disposable income per gallon as we did in the early 1960's. The big difference is that the very cheap gas of the 70's and 80's made it possible for people to move out of the cities away from there jobs and into the new suburbs. So, miles REQUIRED to drive by 'our' current life styles does consume large amounts of gasoline.

My dad used to sell gas for 8 gallons for a dollar. Sounds cheap but the 1940's dollar is not the same thing as the 2007 dollar.