Quote :

"Dirty gas (Shell...) can really gunk up your lines."

no offense but you have no idea what you are talking about. i make shell gas ok. actually shell gas is quite clean as most shell refineries run very sweet crude. in other words, our sulfur content is usally quite low.

comment was made concerning the P/L and that all gas is the same. that isn't really accurate. each company "rents" time. and they run diesel and jet fuel on the same line. but of course you don't have diesel in your gas now do you? no. that is because it is a plug flow operation. as in there is very very little mixing.

ok so say refinery A ships 200,000bbls of diesel. then refinery B ships 300,000Bbls of gasoline. the gas pushes any diesel left in the line. flow calcs are so precise, they know exactly when the products arrive and when to divert diesel to diesel tank and gas to gas tanks. that little bit at the ends that does mix is sent to diversion tanks and is later sent off for processing or sold, whatever. the vast majority of the time, there are no back to back gas shipments. most of the time, it is ref A gas, ref A jet, ref A diesel, ref B gas, ref B jet, etc. but even when there are back to back ref A and B gasoline shipments, those same flow calcs are used to segregate exxon from shell gas, etc. they are stored usually in separate tanks at the terminals. if they are mixed, it is because exxon sold shell gas or vice versa.

ok, now sometimes you do have exxon gas at a racetrack or shell gas at a BP. it depends on the sales. all gasoline has to meet a minimum spec period. that is govt required. BUT what you find is that the gas that major companies supply their own stations versus what they supply to third parties can vary. you will always send your best stuff to your own stations. so if you have a batch of 87 octane that really is 87.5 (this actually happens alot), you are going to send it to your own station. the batch that just meets requirements will go to third parties. not always the case but MOST of the time it is. also your additive packages vary greatly... major companies such as exxon, shell, bp, etc have great packages. i don't particularly like chevron's typical gas... they run a higher sulfur crude and the combination of their recipes and the techron produces a smell i don't trust (smells too sulfur-y to me).

a little more info on gasoline that you may or may not care about. gasoline varies greatly... depending on what units your refinery has and what types of crude you run. typical components include: ligh and heavy cat cracked naphtha, butane, alkylate, reformate, toluene, c5 and c7 hydrotreated gasoline, straight run gasoline, straigh motor base, MTBE, hydromate, natural gasoline, and others. the recipe changes on any given day based on inventories and what part of the country you are blending for (i.e. Atlanta 25ppm low sulfur). there have been days that we can beldn only two of those components for a batch and then another day where we had 9 components. just depends. components are chosen based on octane, gums, RVP, haze, and various other properties.

ok that is enough of that. i'll gladly explain more if needed.

good comments on saving fuel. we are having to do it down here in louisiana due to simple supply... there isn't any. (my refinery and our sister refinery down the road are presently coming up so that will be something like 6-7% of the US supply back up).

-definitely carpool if possible
-keep you car running below 2500rpm. my car (4cyl) gets significantly better mileage at 65mph than it does at 85mph. sucks a little but it really only adds a couple of minutes to the commute
-keep your tires inflated
-keep the general condition of you car in good shape... oil changes, spark plugs, etc.
-buy the minimum octane gas before you hear knocking. a lot of car manuf. tell you to buy a higher grade than you really need. i did a 9 tank test with my car at constant speed and the same route... got only slightly better mileage with 92 than 87 but definitely not enough to justify the $0.20/gal difference
-make lists of stuff you need and plan your path before you go out... that way you don't have to keep going out for items you forgot and you don't have to backtrack and consume needless gas.
- use your car's momentum when possible and don't accelerate needlessly.

[Edited on September 12, 2005 at 2:37 PM. Reason : oh yeah, and i made it through the hurricane & am now trying to crank out more gas]

9/12/2005 2:36:08 PM

Maybe I should use more discretion before posting stuff from memory nowadays, however lower octane gas should result in increased efficiency in any engine that doesn't require more detonation resistance.
Ahmet

9/12/2005 2:42:07 PM

so how do we get that gas with jet fuel mixed in with it?

9/12/2005 2:44:57 PM

I am not new to EFI. It would surprise me that the injector pulse width/duty cycle would reach zero in drop throttle situations. Air is still entering the cylinders, so accordingly fuel must also be injected, although the mixture is most likely leaned out considerably. From the data pulled from the Motec M4 on the FSAE race car (not a production car, so not exactly apples to apples, I know) the lowest pulse width was around 1.2ms, and effective pulse width was 0.7ms at 5% duty. This was at a sudden drop throttle situation, like you describe.

I've also had my truck fuel pump fail while driving on I40 and the resultant engine braking from no fuel was more than just a drop throttle situation alone. I can't argue that the Bosch systems don't completely turn off the injectors because I don't know anything about them, but every other form of EFI and engine management I have dealt with do not.

9/12/2005 3:19:34 PM

"Air is still entering the cylinders, so accordingly fuel must also be injected, although the mixture is most likely leaned out considerably."

Air is indeed entering the cylinders however no power output is being asked from the engine. This is why Bosch systems cut off the fuel. I would like to think that this is more widespread than just european engines running Bosch fuel management systems, but obviously I don't have any non-bosch concrete data.

I will say one more time with absolute certainty that some (I would've said most, but let's keep that on the side for now) Bosch fuel injection systems until recently (not counting "fuel injection" systems that use a non pulsing injector), did cut fuel 100%.
Ahmet

9/12/2005 3:59:19 PM

just a question.. regarding k-jetronic/CIS. are you familiar with that?

ok.. from what i understand, the air entering the intake pulls that plate open. this, in turn, causes the fuel distributor to send fuel to the injectors. am i wrong? i guess the ecm overrides the signal at zero-throttle?

or is this not "modern fuel injection" since it is like dinosaur technology?


[Edited on September 12, 2005 at 4:15 PM. Reason : maybe i just need to read that book...]

9/12/2005 4:14:14 PM

You're correct, the air causes the plate to open (more air, plate moved farther). This plate acts on a valve (plunger). Farther the plunger moves, more air comes in. K-jetronic started getting somewhat complex with electronic control units, idle enrichment, etc.

I would not consider K-jetronic "modern", it's more like precise carburation at very high pressure. Technically it qualifies as fuel injection, but I won't consider it that modern without a knock sensor, a real built in oxygen sensor analization/adaptation capability, and electronically pulsed fuel injectors. This should be calculated using many factors such as load, rpm, all the whille actively shooting for a stoichiometric ratio. Ofcourse full built in ignition control as well. That would be my definition, these models started appearing in the mid to late 80s, and became common place by the mid 90s (at least on European vehicles).
Ahmet

9/12/2005 5:16:06 PM

The above should read "farther the plunger moves, more fuel comes in, or is injected".
Ahmet

9/12/2005 5:17:32 PM

Quote :

"-keep you car running below 2500rpm. my car (4cyl) gets significantly better mileage at 65mph than it does at 85mph. sucks a little but it really only adds a couple of minutes to the commute"

See, the comments about rpm and efficiency gains per speed confuse me a little. My car only turns about 1700 rpm in overdrive at 65, to hit a steady 2500 I'd probably be doing well over 90 mph. I wonder if the difference in economy is comparable though? Or does each different engine have a spot where economy tends to drop off noticeably?

9/12/2005 5:55:10 PM

depends on application

9/12/2005 6:04:39 PM

ahmet, you may have been correct. i havent done any logging yet, but it registers "-.--mpg" while in-gear & off-throttle. i was mistaken, but the drive home reminded me.

[Edited on September 12, 2005 at 6:45 PM. Reason : -]

9/12/2005 6:44:28 PM

Good to know I'm not going crazy. Now if I could just remember random things for my classes, I'd be all set...
Ahmet

9/13/2005 6:57:33 AM

yeh i was going to say. if go into neutral and glide i get a fairly high MPG reading (same VW MFA as beethead), but if i leave it in gear and coast i get the --.- which i assume it does when its really super high or dividing by 0.. which i interpret as little to no FI activity.. but either way its better than when coasting in neutral

[Edited on September 13, 2005 at 1:00 PM. Reason : hhgh]

9/13/2005 1:00:23 PM

ahmet are you saying that when you let off the throttle that no fuel is entering the engine at all?

9/13/2005 6:48:30 PM

In many cases, that's absolutely correct.
Ahmet

9/13/2005 7:23:19 PM

is power not asked of the engine to drive the accessories even when off throttle? are you saying these accessories are driven by the remaining momentum of the crank?

9/13/2005 7:28:52 PM

Quote :

"In many cases, that's absolutely correct."

no. nothing else to be said about it, except that the above statement is never correct. never.

Quote :

"is power not asked of the engine to drive the accessories even when off throttle? are you saying these accessories are driven by the remaining momentum of the crank?"

the first couple of worms from the can he just opened.

9/13/2005 7:34:16 PM

Quote :

"saying these accessories are driven by the remaining momentum of the crank"

was wondering about that too

[Edited on September 13, 2005 at 7:35 PM. Reason : .]

9/13/2005 7:34:17 PM

9/13/2005 7:35:36 PM

When you're in gear, and decelerating off throttle, the drivetrain keeps the engine turning.

I will say this one last time, not only have I observed this first hand (wideband 02 output, injector pulsewidth observation AND tuning), but I've read it from no less than 5 sources, including the 3 I've cited, Porsche design manuals, and the factory workshop documentation. If you're telling me I'm wrong, I am unable to reason with you any further.
Ahmet

9/13/2005 8:15:37 PM

What happens in an automatic? How does the fuel injection know when you clutch? The Bosch systems you talk about aren't very advanced for fuel injection. How high does your lambda go on drop throttle? Most lambda sensors only go to 1.2 lambda, which is pretty lean, but there's still fuel. The f-car goes to 1.2 on drop throttle, but the injectors never turn off completely. I might understand momentarily dropping the pulse width to zero for the instant the throttle is dropped, but it might last for a millesecond or two at most. If the the injectors do not inject fuel, turn off the key while you are coasting down, and there won't be any difference.

9/13/2005 9:24:51 PM

Quote :

"If the the injectors do not inject fuel, turn off the key while you are coasting down, and there won't be any difference."

a good start

ill be back in a little while

9/13/2005 10:06:23 PM

I am going to speculate about the automatic issue. Torque converter uses driveline speed to induce coupling force. This should happen when the vehicle is moving. I'm talking about Motronic systems in general starting with the L-jectronic. If memory serves me correctly, internal Bosch designation for the current engine control units are still derived from the earliest motronic versions. They're considered related, but more sophisticated.

I feel silly saying this one more time... Injectors completely shut off. I've not only tuned several cars this way myself, I've seen the factory fuel injection tables. Most oxygen sensors will stop registering a value. All of that should be a moot point as the Bosch design manuals clearly state motronic (what they call modern in their latest editions) to completely cut fuel. One more data point, as if this isn't enough, EGTs will also register ambient, given enough time in coasting. Indeed, if you turn off the key while coasting, there will not be ANY difference other than electrical accessories turning off.

I understand this concept does not seem intuitive to you guys, but I've shared facts with you, and posted clear references for you to look them up. I cannot sit here and defend verifiable facts any longer.

I can seperately talk to you about your F-car if you wish but I simply will not debate typical Bosch motronic behaviour any longer. What kind of fuel injection does it utilize? We're not talking about a 308 or anything are we?
Ahmet

9/13/2005 10:07:15 PM

Quote :

"and posted clear references for you to look them up"

out of curiosity i tried to find something from your clear refrence (pictures of books) but couldn't find anything

9/13/2005 10:15:15 PM

Quote :

"Most oxygen sensors will stop registering a value."

you think that means that there is no fuel? in case you think i have no experience with these, i can assure you i have tinkered quite a bit with them in the past. one of the things i used to do quite frequently was adjust the plunger screw in order to pass inspection because the idle emissions were too high.

please explain how injector pulsewidth is determined on these bosch systems. please tell us does it utilize an idle air control circuit.

[Edited on September 13, 2005 at 11:05 PM. Reason : k]

9/13/2005 11:03:56 PM

Cutting fuel completely sounds counterintuitive to me. We use a Motec M4 on the race car, write all the maps and set everything ourselves on a 35 year old water brake engine dyno. The highest lambda reads is 1.2, and it'll read that in ambient air as well as in drop throttle situations, but there is still fuel present in combustion. The torque converter doesn't work well transferring torque in the opposite direction, so I don't see how an automatic is to keep running in these drop throttle, no fuel situations. What happens if the clutch is depressed while the engine is getting no fuel?

[Edited on September 13, 2005 at 11:14 PM. Reason : ]

9/13/2005 11:12:04 PM

John, I'm not sure if you're being sarcastic or not. If you mean it in seriousness, you can look it up yourself. It's in there.

optmusprimer, neither how injector pulsewidth is determined nor idle air control circuitry has any relevance to the topic at hand. I will have to ignore your post, when also coupled with your earlier umbrella statement "no. nothing else to be said about it, except that the above statement is never correct. never. " which is plain incorrect.

Poe, "The torque converter doesn't work well transferring torque in the opposite direction", they do in the Volvo and Honda automatics I have experience with. These are not the ECUs that I claim to shut injectors however, so I will not speculate there. " What happens if the clutch is depressed while the engine is getting no fuel?", the rpms drop to a pre determined rpm level before fuel injectors are "softly" brought back online (forexample in a batch, -->skip revolution--> batch, -->fire every time). The RPM for injectors to come back online is usually a few hundred above idle. You're programming the Motec, if you want you could map it to inject no fuel when the throttle is closed at higher rpm, and introduce fuel back say 300rpm above idle speed, to be at "regular" mixure by idle. You'd want to interpolate the fueling between this value and the idle. Perhaps you'd have to go a bit richer than normal for a small rpm range to "catch" the engine properly.

I have just described you how to mimic the engine management system's behaviour in a VW, BMW, Porsche, etc. when coasting in gear, or when backing off the throttle in neutral. In short, when the engine is revving down with no "load" (closed throttle).
Ahmet

9/13/2005 11:32:58 PM

what you are talking about is the trip down from a high engine speed back to idle, no load on engine. that is the only time fuel is cut 100%. what poe87 and i both mistook you for stating was that at idle (which is what some of us american boys call "let off the throttle") all fuel is cut. now of course, being form durham we has never heard of this german bosch super perpetual motion mechanical fuel injection and we thank you for clarifying.

9/13/2005 11:47:32 PM

can we all have makeup sex?

9/14/2005 12:43:48 AM

i swear to christ, ahmet posts in such a manner that i believe every word he says.

thats never happened on tww before.

9/14/2005 12:59:21 AM

Quote :

"John, I'm not sure if you're being sarcastic or not. If you mean it in seriousness, you can look it up yourself. It's in there."

i was being serious, i couldnt find anything online

9/14/2005 6:18:34 AM

I can only think of one way to do that with the motec, it would be with a throttle position compensation, but I couldn't make it do the whole soft re-supply of fuel. I don't really see why I would do that though. It is set up with accel and decel tables, so when the efficiency point drops at a given rate, fuel is scaled back by a clamp value and returns to the main fuel map values over a set decay time. What happens when you get back on the throttle? Does it skip a revolution then too? Automatics will send some torque back to the engine on coast down, but not as much as a manual.

[Edited on September 14, 2005 at 8:58 AM. Reason : ]

9/14/2005 8:54:24 AM

9/25/2005 7:27:42 PM