How much does emissions kill MPG?
 

Thought someone here may give me a general idea. Wife and I got in to a discussion because of an environment class she's in. I tried to do a search on this forum, but couldn't seem to narrow it down.

So, how much are emission equipment lowering the MPG of vehicles? I wonder how the lowered emissions due to less fuel usage without the smog stuff would compare to emissions equipped lower mpg? Get the idea? Less fuel usage means less byproduct. Are emissions equipment doing more harm than good keeping pollutants down? Marginally better?

I commented to my wife how my father had a 79 Accord that got 30-40 mpg new. So what has offset tech advances in economy that the mpg haven't increased since? The only answer I could think of is emissions. Safety I suppose also...

My guess would be that for smaller econoboxes that were mpg monsters of yesteryear, is that the once low price of oil and market demands in America, made them concentrate on more horsepower and a better ride to grab and gooble more market share. So the MPG stayed about the same, but the ride, reliability, comfort, and horsepower all got better.

The story that I hear often enough from others, is that essentially the same model of car being offered in the American and whatever other market has vast differences in mpg by at least 10 or 20% difference. I don't know how true that it is but that is what i hear often enough from different people.

I do know that emissons equipment and ULSD did castrate these newer Ford diesels. Just look at the price of the newly double refined tree hugger diesel formula and all the mileage complaints on the Ford trucks about abbysmal milage for overprice fuel.

For gasoline burners, it's the NOx rules that make them really suck. In the late 80's / early 90's, one model of the Honda Civic (CRX HF) had an EPA highway rating of 45/52 mpg!! That was on an alcohol free gasoline, and it was a measly 62 HP I4 engine, but still. So my guess would be in the range of 20% - 40%, depending on a few things.

I'm not familiar enough with the diesel emission systems, so I can't comment on those.

Its not emissions, its WEIGHT. Every generation of car/truck model gets heavier. Part of it is safety features, but also luxuries, like more soundproofing, bigger wheels, power everything. The market has also demanded more horsepower and acceleration.

That Honda Civic HF was how heavy and had how much power? In England today, you can buy a 60 mpg turbodiesel Ford car, but not here. Ford wont sell it here because "Americans dont want ...., Americans demand..., etc". They are right. How well did the Fiesta sell here? I owned one, but Ford didnt promote or support it well, so the Civic took over the market.

Jim

I saw on a Honda Hybrid or MPG forum an argument of the reasoning being the horsepower and acceleration differences between the old models and the recent. Also the EPA testing procedure of that era, some people claimed gave strangely skewed numbers which were highly underivable in reality.

And they can sell those cars for significantly more.

Weight also plays a role, but the question wasn't about weight.


Here's the specs page for all '91 Civics: http://autos.msn.com/research/vip/Spec_Glance.aspx?year=1991&make=Honda&model=Civic& trimid=-1

Or because the much stricter emission rules in the USA.

Or the Civic was simply a much better car...

Those 1991 Civic HF specs prove my point.
Curb weight 1967lb
Hp 62
EPA mpg 49/52

2008 Honda Fit
Curb weight 2432lb
Hp 109
EPA mpg 28/34

European rules, safety and emissions are quite strict, but gas prices are 2-3 times higher so that the market demands cars with much better mileage.

Jim

I think you'll have a hard time linking emissions equipment to decreases in fuel milage in gasoline engines. Two things remain constant with vehicles as we know them, it takes more fuel to make more power and a heavier vehicle needs more power to get around. All the newer generation of vehicles are heavier and have more powerful engines so they won't get the milage an earlier version would. And since the widespread implementation of catalytic converters the CO, NOx and Hydrocarbon emissions have been reduced to nil compared to the pre-cat cars, the only time the older motors produced less emissions is when they were not running.

I don't think so, but lets do the math on weight:
The Fit is about 20% heavier, yet it gets 34% worse mileage.

Weight factors in heavily into city mpg, but not so much into highway mpg
when you drive at a steady highway speed. And you don't need the extra HP at a steady speed either.

I think it was VW that exported lots of 2006 diesels, then no 2007 diesel because their 2007 mode wouldn't meet the 2007 EPA requirements.

Cats can definitely take care of HC and CO, but I don't think they do much with NOx. (I need to do some reading on that, though) NOx is partly (mostly?) taken care of with EGR, and guess what EGR does to efficiency....

OK, nil would be hard to makeup for, and I see it is hard to not compare apples to oranges with this topic. So, my questions narrow down to how much economy is lost to emissions. To be more specific (to keep the thread from wandering too far!) if two same model engines were built and tuned for emissions and no emissions, but the same hp and torque, what would be the difference in economy (mpg)? Any real world examples?

You need to be more specific in your question, that is, differentiate between HC, CO, and NOx. The former two are only loosely tied to efficiency (unless an engine is running overly rich), but the NOx is coupled much more closely, especially in high compression, or in diesel engines. Also, there will be HP and torque changes.

A better exercise would be to have the exact same engine tuned to:
a) peak efficiency (regardless of enission)
b) tuned to emission compliance (except NOx) without any use of a CAT
c) tuned to emission compliance for all 3 without a CAT
(might need to use 80's or 90's limits for b) and c))
d) tuned to b) but with a help of a CAT
e) tuned to c) but with a help of a CAT

Here are two relevant pages about CATs and NOx:
http://en.wikipedia.org/wiki/Catalytic_converter (read Three-way catalytic converters)
http://en.wikipedia.org/wiki/NOx_Adsorbers

And BTW, I did give you one estimate. :)
Whether that's correct or not, that's a different issue. }> (I believe it is, unfortunately :()

Diesel engine emissions are an interesting topic, but add too much complexity to this discussion. I think the topic starter meant gasoline engines.

All recent gasoline engines have three-way cats that address HC, CO and NOx. The only emissions-related control that I agree for sure decreases mpg is mandatory E10 fuel.

Asking for real world comparisons of the same late-model car with and without emissions certifications is impossible, because no one manufactures one without emissions controls. Full-race off-road vehicles get terrible mileage, so that wont work for this discussion.

My Honda Fit example is as close a comparison as I could find. Remember, 1991 cars still had HC, CO and NOx requirements, just not quite as stringent as today. The difference in mpg/weight may due to the 22 lb/hp of the Fit vs 32 lb/hp for the HF, and there is some difference in 2008 EPA test methodology that would bring the 1991 model down a couple of mpg.

Jim

1. Because of the 3-way CAT, the mixture isn't as lean as it could be for maximum efficiency. (to burn most of the HC and CO in the engine instead of having the CAT burn up the leftovers)
2. EGR (even though it's not used al the time)
3. E10 (though it's not exactly an engine control :))
So my count is 3.

I'm actually thinking about playing with my O2 sensor to report a slightly richer mixture, so the engine would run slightly leaner. Plus I'd like to disable EGR w/o any bad side effects.

Except at WOT, gasoline engines are calibrated for lean-of-peak mixtures once they go into "closed loop" operation. If you go much leaner, you will get lean misfire, which causes HC to go up, but wont help mileage. Also, because it is not running peak EGT, less NOx is produced, which is why fewer engines have EGR systems than in the past. Cats are more to cleanup during engine warmup and WOT conditions, when computer controls are not optimum.

The only thing that might increase both mpg and emissions is more spark advance. But, you will need higher octane fuel, the cost of which may negate your savings from better mileage.

Jim