What you need to know about Brake Specific Fuel Consumption

[Olympiadis]

Originally Posted by E4ODnut

I tune mainly for economy and reliability. Power output is important, but definitely not a priority. I also run open loop only. Some people may prefer to use closed loop but I agree with the camp that says you give up some control with closed loop, and it is often used as an excuse for sloppy tuning. I don't use EGR.
Tuning for best power is relatively easy, and I stress relatively. Best economy is a lot harder.
So far I've found that at loads under ~ 75 KPA MAP, EGTs are not an issue and it is almost impossible to induce detonation with any sane ignition timing. I tune for target AF ratios of between 16:1 and 17:1 below ~ 80 KPA. I reason that with pressures above that I am in need of some serious power and ramp up to ~ 13:1 at ~ 90 KPA and ~ 12:1 at 100 KPA. Some of my engines like it a bit richer, some a bit leaner, but not a whole bunch.

It sounds like we've learned a lot of the same things.
I almost always work in open-loop, and also almost always with factory ECMs. OLSD - Open Loop Speed Density is my preference.

It sounds as though, like me, you realized a long time ago that there is almost never a time during normal driving when 14.6:1 is the ideal AFR.
The reality is that it (14.6:1) is a window of predictable operation set in order to be able to guaranty that emissions can also be maintained within a certain window in order to satisfy the EPA requirement.
That fact that it is the stoichiometrically correct ratio for gasoline is for all practical purposes irrelevant.
In closed-loop, for at least 99% of your driving the burn speed of the air/fuel charge does not match the speed of the piston very closely. That's why a tuner can come in with an open-loop tune and make such huge improvements in both power and economy.

I also find economy tuning to be a bigger challenge than power tuning.

To tie this back to the subject of this thread, one problem with the BSFC maps that members here are using to guide their driving is that enough specifics aren't given with the maps to know what is actually going on there. The maps are plotted with load vs RPM, which is fine, but if you assume a constant AFR or spark lead, then the map becomes much less useful. If spark and AFR are optimized for each load cell, then they need to specify this. It's pretty obvious that a factory calibration could not hold an AFR of 14.6:1 at some of the higher loads on the map for any extended amount of time without having to adjust the spark due to cumulative heat build-up in the chamber. If the spark changes, then the adaptive fueling would also adjust via fuel trimming. They don't say the loading intervals or what engine management system was used to create the maps.
To me the BSFC map is almost useless.

Also, the idea about removing the throttle being a source for significant improvement in efficiency is false. I can understand people looking at everything in order to get the last bits of efficiency, but this situation is like tripping over dollars to look for a penny.
Variable valve control, in a very sophisticated form could allow removal of the throttle blade, but at that point the pressure differential and restriction is just shifted from the throttle to the intake valve.

And anyway, even if you could remove all the restriction, gasoline can not effectively burn over a wide range of AFRs that would be required. By effectively I mean that yes you can burn gasoline very lean, but you cannot then load the engine down. You can with diesel, but not gasoline.

The diagrams from the EPA should make it clear the small amount of efficiency that is listed under pumping loss. Once you find and quantify all of the sources of energy lost under this category, you would find several sources that dwarf the air-flow restriction caused by the throttle.
I'm not sure why this perspective has been completely lost in this discussion.

[user removed]

Olympiadis, I agree with your conclusion about throttle restriction. I would assume the reason why most here do not go the route of custom tuning and or running at higher than 14.7 to 1 ratios is the huge spike in NOX emissions you see when you go to more lean ratios.
That's what killed the 92-95 Civic VX as far as Honda continuing to use the lean burn system with AF ratios as high as 25 to 1, although they still made lean burn systems after 1995. In fact the original CVCC carbureted system was a type of lean burn, starting back in the 1970s.
Custom tuning is great and you are finding that there is definitely room for improvement over factory settings. Honda even went as far as to use primarily one of the two intake valves to increase swirl for better consistency in the air-fuel mix in the VX in lean burn mode.
Check out Homogenous Charge Compression Ignition for some more information. A lot of research has been done with some of the same apparent issues you have brought up about ultra lean mixtures and load sensitivity.
Open loop basically goes outside the paramters of factory design and most likely creates emission issues that are unresolveable today. That does not mean they will be unresolveable tomorrow, so keep up the good work. Just remember that there are legal issues with willful alteration of emission components, if that applies in your vehicle.
Not meant to be argumentive, you are just going to see a very small percentage of members here who consider emissions as secondary to function.

regards
Mech

[E4ODnut]

Here's a pretty good link on the subject of emissions

Tuning Your MegaSquirt-II™ (or MicroSquirt®)

[Olympiadis]

Originally Posted by Old Mechanic

Olympiadis, I agree with your conclusion about throttle restriction. I would assume the reason why most here do not go the route of custom tuning and or running at higher than 14.7 to 1 ratios is the huge spike in NOX emissions you see when you go to more lean ratios.

I would think more people don't use custom tuning because it's either too difficult (steep learning curve), and/or cost prohibitive.

Putting the NOx issue in perspective here,
a passing amount is in the range of 0.15% or a little over a tenth of one percent. Double that and you're up to three tenths of that same one percent.

Another important fact is that NOx goes back down as you approach the reasonable effective lean-limit of the engine at low loads. Low load means a necessarily lower combustion temp than when at high load. Even when you improve efficiency and combustion temp at low loads, you're still at a lower combustion temp than you are at higher loads. That means less total NOx is produced than the amount you are legally allowed to produce, because yes it is legal to drive at higher loads by climbing hills, carrying passengers, etc...

With a dynamic AFR tune, such as E4ODnut and myself are talking, the commanded AFR swings quickly from the lean-limit at low load to richer than stoich at higher loads. Not only is this more efficient, but NOx is also reduced lower than what would have been realized at 14.6:1 AFR.

At any rate, I do realize that there are emissions Nazis in every group ready to criticize individuals by spreading their misinformation and ignorance where it concerns their need to support a government controlled regulating body, and its associated very ill conceived legislation. That is unfortunate for us all.

http://www.legacygt.com/forums/attac...p;d=1268329060

Originally Posted by Old Mechanic

Open loop basically goes outside the paramters of factory design and most likely creates emission issues that are unresolveable today.

Yep, and many people are quite unaware of the other times and modes of operation where a 100% stock vehicle goes outside of the intended factory designed parameters, and also creates emission issues.
That's why the EPA peforms their emission test on a warmed up vehicle and measures average outputs over a range of relatively "mild" driving conditions during their driving simulation.

In order to meet ever stricter fuel mileage standards you will see auto manufacturers continue to increase the number of algorithms in the PCM, and also increase the amount of time that the engine runs outside of the 14.6:1 AFR window. Running at stoich is so inefficient that they will have no other choice but to do so.

The EPA has become an extremely corrupt arm of the government that has been used as justification to create economically destructive legislation.
For more than 20 years the EPA has required extra and expensive emissions equipment on our vehicles that was primarily designed to turn other combustion waste byproducts into CO2. Recently they have declared CO2 as a pollutant. They have legislatively backed themselves into a corner. Their way out of this conundrum is that they can legally place the responsibility of solving this problem squarely on the automotive manufacturers without enduring any of the responsibility themselves.

As far as being a mechanism to progress the improvement in fuel efficiency the EPA has been a complete and utter failure. If you look back over some of their published papers concerning engine analyzation and fuel economy tests they become downright embarrassing. As an example they were unable to find any fuel economy improvement on one vehicle when testing a set of under-drive pulleys that were submitted for their approval. The specifics of the test are all in print and it's absolutely atrocious, - the level of their incompetence.

I think what it boils down to, at least in part, is that government workers (the EPA) have no real desire to go out of their way to educate themselves, by at least reaching out to the automotive engineers to gain improved understanding of the engine management systems that they are tasked to test.

In a sense it is silly to expect more from such a government entity, but then again they wield a crippling power over us all.

[user removed]

Precisely. I always wondered why when emissions regulations began with PCV (1963) and air injection (1969) why they just didn't focus on efficiency that was integral with the engine design and fuel delivery system, but I guess that would make too much sense.

Instead we got the govt tail wagging the manufacturers dog, a certain recipe for disaster. Show me a govt bureaucrat who understands even the most basic engine technology. Even today you still have design by committee, which would not be so bad if the committee had any practical knowledge, and total allowable emissions were weighed as a sum of the parts, which would allow marginal designs to continue in development and refinement.

I knew lean burn under light loads resulted in lower peak temps. My 94 VX even today produced less CO2 than any current hybrid on the market.

Throttle control using egr volume would have come a long way as well.

regards
Mech

[user removed]

Heck we made lean burn modifications to the Datsun (pre Nissan) 280 Z beginning in 1975, first year of FI. In 75-76 Federal Z cars they had no cat, no egr, and that was emissions legal in 49 states. The FI cleaned up the engine.
You could increase the spring tension in the flap air flow meter, which made the engine run lean, then put a rheostat in the coolant temp circuit. With the rheostat mounted just above the console you could change the mixture just by rotating the knob on the rheostat.
Then we found out that it was a $2500 fine for violating emissions laws, so we just told the customers how to do it themselves, which was legal for them to do but not for us.

regards
Mech

[Olympiadis]

Originally Posted by Old Mechanic

but I guess that would make too much sense.

Yep, and that would be punishable by law that's there to protect us.

I do not tune professionally, or I would be quite unable to post the things that I have. My active contributions have been towards special projects only, and have mostly been limited to performance/track cars.
A track car also has a great interest in running lean at part-throttle to keep the plugs clean and unfouled when the time comes for WOT.

Factory tunes also introduce a level of inconsistency that many racers don't want, and the use of O2 sensors mean that race fuel with certain additives cannot also be used.

That explains the necessity for lean open-loop tunes.

I have used switchable potentiometers many times in order for a user to make temporary adjustments on the fly to either fuel, spark, or both.
It comes in very handy for many things from cold-starts, to using different home-blends of fuel.

[some_other_dave]

Originally Posted by George Tyler

there is a hydrogen powered V8 with no throttles, hydrogen can burn with a 5% ratio and power was controlled just be changing the amount of hydrogen injected.

Isn't that more or less how (older) diesel engines work?

-soD

[drmiller100]

Originally Posted by Olympiadis

For any given combustion event a falling average RPM of 2000 RPM will have a much slower piston speed than a rising average RPM of 2000 RPM.

kind of ok until here. you are missing the CAUSE.

the cause is if the rpm is slowing down, typically MAP is relatively low. If the RPM is rising, then MAP is high, and the driver is trying to accelerate.

The first case allows LOTS of spark advance, the second case much less spark advance.

In the cylinder, the spark ignites the air/fuel mixture. The rate of burn is measured in inches per second.

The time the piston has to hang out and wait for the burn is a function of RPM.

How fast the burn is going off is related primarily to cylinder pressure which is based in large part on heat, and when all done, MAP.

So. The lower the MAP (the higher the manifold vacuum) the slower the burn, so the more spark advance you need for "efficiency".

The higher the RPM, the more spark advance for efficiency.

If we lean the mixture out past 14.7 with high manifold vacuum, the flame burns much slower, so we need more spark advance.

As for HHO and nitrous, all of your comments are pointed towards making maximum horsepower, which implies wide open throttle. If we desire more power at part throttle, the EASY answer is to open the throttle more.

Nitrous has half of its effect due to the extra oxygen, the other half becuase NOS is COLD - it supercools the charge allowing more air molecules into the cylinder.

NOS makes no sense for better mileage. HHO makes no sense for better mileage, unless you are a unicorn salesman.

[drmiller100]

Ken,

I wrote my response before I read your response. It is interesting how we picked up on different things.

I didn't put together the idea HHO is supposed to oxidize anything. I agree with you - HHO is unicorn farts.

And I agree with you Ken there are not many opportunities for incremental improvements in playing with a modern fuel injection system.

But I think there are quantum jumps available - throwing away a paradigm, and getting out side the box.

So. back to the throttleing discussion.

Lets say we take a multi port fuel injection engine.

And we take the throttle body and wire it wide open.

Then we tell the computer to read a fly by wire throttle plate. And we shut off the injectors 98 percent of the time, but every once in a while we give a specific cylinder the "right" amount of fuel to run at WOT.

But most of the time the cylinders are not getting any fuel.

Then we determine "once in a while" to be decided by the throttle pedal - the more we push on the throttle, the more often a cylinder gets a shot of gasoline.

No pumping losses. Full efficiency of the cylinder. The engine can run at very efficient loads, and we can use the air pumping through the engine to be a pseudo carnot cycle.