Just a thought - the comparison engine might be found in heavy duty fleet trucks with gas engines. Weren't they mostly free of emissions equipment for several years after the light duty trucks? There are lots of bare bones fleet trucks around that should be fairly comparable weight and engine spec-wise through several years.

Anyhow, would you knowledgeable gents be willing to give speculation on how much efficiency is lost to emissions? Percentage-wise. In general or for a particular motor. And to be more specific, I mean free of all emission equipment - this is all hypothetical after all.

 

The problem is that we are discussing current technology and all engines today are emissions controlled, including those over 8500lb GVWR. Comparing 1970's engines misses the point entirely. Also, there are no EPA mpg estimates published for heavy duty emissions vehicles.

 

1996 Ford F150, 302 engine, manual trans. I visit in North Texas a couple of times a year. 320 miles one way, mostly freeway. I set cruise at 65. Normal mileage is a little over 17mpg. I disconnect the DPFE when I make this trip, and mileage goes up to a little over 19mpg. jd

 

But is that "lean-o-peak" mixture is the one that provides peak efficiency? Methinks the answer is not. One would still need to go slightly lower than that.

Oh, and I forgot the 4th thing:
4) the extra restriction caused by the CAT(s) I know there are high-flow CATs, but I think most people stay with the factory installed, or an equivalent one.

 

I had to google for that: DELTA PRESSURE FEEDBACK EGR (DPFE) SENSOR

When did Ford start to use that? I have a '95 351W, and I don't remember this sensor.

 

If you go any leaner, misfire will occur, negating any fuel savings. As it is, high energy ignitions and more exotic spark plug designs are needed to fire the mixtures they have now. EGT of about 50F lean-of-peak is the most efficient. Note that 1/BSFC (at bottom of chart) is fuel efficiency. http://www.avweb.com/newspics/tcm_mixture_sweep.jpg

The next advance, which WV-Audi, Lexus, and maybe others are using on a few engines, but Ford isnt, yet, is direct cylinder gasoline injection. This allows gasoline engines to run almost like diesels. The compression can be higher, because only air is compressed without fuel, no preignition. Gasoline is injected at high pressure aimed directly at the spark plug near the top of the compression stroke. This allows a leaner mixture, but the main increase in mileage is from higher compression, still using ordinary unleaded gas. Ford experimented with "stratified charge" engines in the 1970's, but computer technology wasnt ready. The Honda CVCC system was an early version of stratified charge, but with a carburator, it was still crude.

Jim

 

Do you have the link for the article that goes with that picture? Also, any link to information showing to what production car engines are tuned?

 

There is a whole series of articles, but you have to register at the site, for free, to read them. They are about aircraft engines, as airplanes have manual mixture controls. Much of the terminology may be unfamiliar, but the basic combustion science is the same.

Here is the link. http://www.avweb.com/news/pelican/182179-1.html
The index is here. http://www.avweb.com/news/pelican/182146-1.html
I would recommend reading this one first. http://www.avweb.com/news/pelican/182084-1.html

I lost the link to automotive graphs of emissions pre and post cat, that I once had.

Jim

 

I did find a few words on what the Honda Insight did:
Honda Insight - GreenHybrid

 

just from what i've gathered in chats with other people, internet searches.

i'm guessing that to get less emissions, more heat is required to superheat the exhaust so less raw gas is getting into the atmosphere. but more heat means more gas is needed, lowering the fuel economy. but it seems better fuel economy would mean less emission. i have no scientific basis, so i could be completely wrong. i just feel the need to vent about what's going on with gas prices, etc.

 

IMO, engine technology has gotten to the point that there would be little to no difference in power or economy.

Case in point- the 2.0 Zetec in my car uses VCT cam timing to replace the usual EGR valve on most engines by retarding the exhaust cam. The ONLY other emissions part (other than the usual PCV and evap controls) is the cat, which in recent years will flow so close to no cat at all you would never notice.

Dyno tests have proven no difference in power by eliminating the VCT, and an average of 3-4 HP (at high RPM) from removing the cat. So basically power or efficiency (MPG) would not change at all.

Now '70-'80 cars and trucks are a different story. Auto makers were still trying to figure it all out.

 

Why guess? All this stuff is published by the various mfgs as to how they solved certain emissions issues.

Your point about getting less raw gas into the atmosphere:

With current emissions tech, the way you do that is:

--air/fuel management via electronic fuel injection

--high energy ignition

So far, not much extra heat. But high heat causes Nox emissions. To combat that, a little EGR or tricky valve timing as mentioned above to cool the combustion. In some engines, this also allows compression to move up.

If anything does get out, some engines still use the original method of burning off unburned fuel: The smog pump. A little fresh air into the hot exhaust and that unburned stuff burns off, with the remainder, if any, finished off good by the cat.

None of this costs much power or mpg, and in combination with better compression and fuel mgmt, results in more of both.

So don't let your anger about gas prices take you back to '60s/'70s think about emissions stuff. It is almost impossible to "take all the emissions crap" off a new engine, and if you did it wouldn't run because you would be removing major components engineered with emissions reductions in mind.

People do the "good old days" BS about how well cars ran in the old days. Well, some did, and some didn't. But a '66 Hi-Po Mustang--a great running car in the day--never saw 300 net hp, a 13.8 quarter on street tires, or 25+ mpg on the highway.

 

I think what we have determined here is that higher combustion temperatures mean more efficiency, and less HC and CO emissions at the same time. This matches what you would expect from basic thermodynamics. The only negative is higher NOX. So, the EGR system may reduce mpg, but all the other emissions equipment is a plus.

Jim

 

The trick is to get your compression and other factors up for efficiency, and then use EGR to reduce the combustion temp to ward off the nox. You may also ward off detonation at the same time...double bonus.

 

i'm not going to complain to be an expert on this. probably some of the stuff i've heard or read ends up merging with something else. i try to make valid points, but somehow it just seems to keep showing that i'm a moron.