I have been playing around with lean areas on the map around cruse. I so far have gone as far as lambda 1.1. I know the engine can take 1.2, but im not to sure about going that far for one reason. That is, I was on the understanding that lean conditions will start melting stuff, bad!, however, why is this so, when, looking at Cliff's calibration guide you can see in the charts that both combustion temps and EGTs drop off with leaner mixtures, so how will this melt stuff? In a way I can understand that an oxygen rich flame is hotter ( oxy acetylene cutting) but as long as the cooling system is up to it, it will remove the extra heat? At the same time I am confused with that theory against the charts in Cliffs calibration guids mentioned above. That leads me to the thinking that if the combustion temps and the EGTs are indeed lower, that if anything was to melt, it is as a result of one of two things, perhaps. First is that because the leaner mixtures require more ignition advance, meaning that the hot gasses ( but not as hot as a rich mixture) are in the combustion chamber longer, the combustion chamber picks up more heat than it would normaly? Secondly stuff melts with lean mixtures as a result of too much advance bringing on pre ignition?
Lots to think about.
I have read alot about lean burn and spoke to engine testing technicians at Shell Research. I understand the theory behind the lean burn. It is not the fact that you run the engine lean to save the fuel, but rather running lean causes a reduction in torque requiring more throttle input to increse the torque thereby reducing the pumping losses, which is what saves the fuel :D
Take that into consideration, I am in the process of fitting larger throttle bodies. This should give me more air for the same throttle opening. Another way of looking at it is that it will move the lean area on the map down, giving me a bit more room at the top for expanding out into the richer areas. At the moment the lean cruse area is in the middle of the map, and the smooth out to the rich area is getting tight. Obviously running lean needs very smooth blending into the richer areas so that it is not noticeble.
so what am I prattling on about :D well, what I need to be sure of is that I do not melt anything going up to lambda 1.2 at cruse part throttle ;D
Remember that your talking about cruise,
it´s never going to be similar as running lean under high load.
If anything stick to Cliffs calibration guide. It´s good stuff.
Ultimately you´d like to run 100kpa all the time and throttle for fuel enrichment to make it go faster , that
way you get the least pumping losses. Like a Diesel non turbo :)
You can always look at your EGTs to see what the combustion temperatures are like.
I've been round this loop twice now with the TVR (two different specs of engine) Lean burn works pretty well and plotting the EGTs out, I found that it didn't get very hot at all - in fact rather the opposite - I was getting good combustion with EGTs of 250 to 350C. Full load got to 700C+.
It's good for keeping the torque sane on the TVR, otherwise it would be impossible since it's now more than 350 ftlbs over most of the rev range. (Which makes it kill diffs and tear diff mounts apart... but that's another story.)
Cool
I'll have a play around and let you know what happens, but not until I fit the larger throttles and re calibrate the lower end of the map. I am aiming for lambda 1.2 at cruse ;D
I never went as lean as 1.2. I started to get misfires at 1.15 which I thought was due to charge robbing. (age old wild cammed v8 problem...)
Quote from: dnb on January 29, 2009, 04:52:40 AM
I never went as lean as 1.2. I started to get misfires at 1.15 which I thought was due to charge robbing. (age old wild cammed v8 problem...)
Yeh. I have seen logs for this engine where I have seen 1.2 lambda without missfire, we shall see how I get on. I could open up the plug gap and increase the dwell to help I would have thought?
If theres just not the charge in the cylinder theres nought you can do to light it.
Dave Visard recons he's had 25:1 from one of his test engines at cruse conditions on a 5 port A series :D People told him it couldnt be done, but he did it. He managed 20:1 on occasions on his across the USA tour in the late 70s, so I dont think 17:1 is going to be a problem. Mind you the crap we have for fuel these days could be a problem.
Thats another thing, and one reason I went to 1.1.44 firmware with switching config. Theres an E85 pump 12 miles from me ;D
You can run really lean on E85, I've tried 1.2 even on more load then cruise and it seams to work..
No misfire or so.
But it's very engine dependent, on my friends BMW M10 turbo we couldn't run leaner than 1.08 without getting misses.
E85 is nice but you need to go to the pump all the time..
Quote from: Ascona 400 on January 30, 2009, 03:00:56 AM
E85 is nice but you need to go to the pump all the time..
Yes, and the Mini only has a 32 litre tank :D and with a very thin spread of 85 pumps around the UK at the moment, I wouldnt get very far :D Infact I dont think I would actualy arrive at the next pump they are that far apart :D
I like the idea of a 60 year old design engine running sequential injection, wideband closed loop fueling, coil on plug ignition,lean burn E85 and a catalytic converter. The air the engine breathes will almost be dirtier than the exhaust gasses :D I wonder what VOSA would say to that :D
Quote from: Sprocket on January 30, 2009, 04:11:13 AM
The air the engine breathes will almost be dirtier than the exhaust gasses :D I wonder what VOSA would say to that :D
Not necessarily the case with lean burn - the reason that the technology died a death (anyone remember Ford's "Clover leaf" piston crown design?) was because of the huge NOx emissions problems.
You'll have to get way past the lambda 1.1 peak:
(http://franzh.home.texas.net/images/afr.gif)
The article that explains that diagram is here: http://franzh.home.texas.net/lean.html
Looking at that graph, at 1.2 lambda the NOx is less than at stoich and with a cat, the NOx is reduced further
just as long as it doesnt missfire, i'll be happy :D
Does it cause any harm to head-gasket or exaust valves?
Sounds like you are going to have a good time learning some interesting stuff, but I think you've got your wires crossed a little bit on a couple of things...
The definition of 'lean' is not necessarily lambda > 1, but simply a lambda that is more lean than the engine can tolerate at that particular condition. All the scare stories about 'I upped the boost and the engine ran lean and melted the piston' don't refer to the engine running at lambda 1.2, probably still < lambda 1 - just too lean for the particular condition, and hence too hot at that point.
At low load conditions, running at lambdas>1 is not an issue and will not melt anything. (Of course, the definition of 'low' is relative to your engine and car)
As the load increases the problem with running on the lean side of lambda 1 is that you are in the less efficient region - i.e. you are not using all the air you pump into the engine, so you need to move across to the 'rich' side, and the (roughly) optimum lambda of 0.85 - but in moving from 1.2 to 0.85, you move through the hottest part of the lambda region, so you need to be careful to do this at a load that is low enough for the temperatures not to become an issue.
Alternatively, you may choose to always stay on the lean side of lambda 1. the problem here is that your operating window is much narrower, i.e. lambda 1 is too hot so you have to go leaner, but the engine starts to misfire around 1.25, 1.3, whereas on the rich side you can go all the way to about 0.6 before you start to misfire, giving you much more headroom.
Another issue with running leaner than 1, linked in with the last point, is that engine response tends to be reduced and fuelling control during transients needs to be much better controlled, again due to the reduced operating window.
Also, as Rob pointed out, the major reason for modern engines operating in the lambda 1 and richer area is the requirement to meet emissions legislation, regarding HC, CO and NOx. This is achieved by using a catalyst, which operates most effectively in a narrow regions around lambda 1, and also by minimising the feedgas concentration in the first place. Therefore at cruise we need to run around lambda 1 to keep the catalyst working and avoid saturation of any of the gasses, and running lean of lambda 1 and even moderate loads significantly increases NOx concentrations, and can quickly saturate the cats leading to breakthrough and a test failure. On the other hand On the other hand, allowing the lambda to wander slighly to the rich side of lambda 1 is less of a problem.
Last point - you are quite right in that its not the fact that you use less fuel when running leaner than lambda 1, as the torque drops off - its the fact that you open the throttle more to get back to the same torque point, and therefore reduce pumping losses. The improved pumping efficiency is slightly greater than the reduced thermal efficiency, so on balance you're up. However, as has been hinted at, the leaner mixture is less willing to burn. One way of helping counter act that may be advancing the ignition timing, but also increasing the compression ratio and improving the charge preparation and mixing will help. Unfortunately your idea of fitting bigger throttle bodies is directionally the wrong way here - larger diameter ports will mean slower moving air so worse charge preparation. Assuming you haven't opened out the inlet ports in the head it probably won't make much difference, so my advice is don't bother with the different throttle bodies for the sake of trying to run leaner than lambda 1.
As an interesting, related footnote, GDI (Gasoline Direct Injection) was re-discovered and developed (initially by Mitsubishi but then others) in order to allow the fuel to be injected as a 'stratified' cloud around the spark plug, so that the localised mixture is actually at a sensible lambda, but the overall cylinder lambda is very lean. At the extreme the throttle can remain completely open and the load controlled by injected fuel quantity - just like dirty oil burning truck engines! When running stratified some very impressive fuel economy improvements can be seen. But this technology suffers the basic problem of NOx emissions (caused by the fact that the cloud inevitably has a boundry region which encounters lean combustion), which requires additional NOx trap systems. Since these are not continuously reducing systems, they require periodic 'regeneration' which is achieved by - you guessed it - running rich for a while! therefore the real world fuel economy improvements of stratified gasoline engines are only of the order of a few percent, while the control strategies, calibration effort and extra hardware required to operate the system make the production cost significantly higher. Basically, its just not worth the effort.......
On my car i get lowest consumption at lambda 1.07-1.09. So far i made more than 30 000km on lean mixture(crusing on lean and rich on wot). My eco test(i set lamda 1.00 becouse of law) was veary good(0.00% CO, HC less than 10ppm). I think that is good for 18 years old car.
Cliff, all very interesting stuff and I am learning as I go ;D
Going back to the throttles. The original K1200 bike head used the 38mm throttles that I intend to fit. The bore is the same as the bike engine, but the stroke is longer, giving me just over anothr 100cc resulting in the 1275cc. I am running the 34mm throttles from the K1100 bike engine at the moment. The way I see it is that if BMW though it wise to fit 38mm throttles on the K1200, that should be the way I go with this engine. after all, I spent a lot of time and effort to get the cylinder head and bores to line up as if it were the Bike engine ;D The ports in the head a standard and the same whether K100, K1100 or K1200, the heads are pretty much all the same, although the K1200 uses 5mm stem valves as oposed to the 6mm stems
Currently the cruse point is around 14% at 30mph and around 20% at 60mph. Maybe its just the throttle break points but that is the middle of the map, which leaves me little room to traverse to the rich load points and have enough of them at the top of the map. I would hope for the same throttle % that the larger throttles will provide more air but lower down the map, so I can move the lean spot down and away from the rich load points. Its going to be a suck it and see matter, excuse the puhn ;D
I have the idle tuned for Lambda 1 and the fast idle set for 1.02, while I dont yet have the cat fitted, it will be going back on when I can get the link pipe welded up.. Everything above the 5000rpm mark in the cruse area is lambda 1, and blending from low rpm to the 5000rpm is smooth, as it is going from part throttle to full throttle, but i would like to drop the full throttle 0.86 lambda down a line or two. I have raised the compretion ration half a point from the standard 11:1, I run V power all the time and I have increased the part throttle ignition advance to 38 degrees with 30/ 32 at full throttle. we never managed to get the ignition map tuned due to issues unknown causing a retard of advance going into the engine compared to what was actualy in the map.
I dont think there will be much of a problem loosing some torque off the bottom of the map requiring more throttle input, the engine puts out over 100bhp at full throttle and the car only really needs 18bhp to keep it moving. so if by opening the throttle and leaning off i can get the torque back to the reuired level at a point in the map that is not too high up the map to affect the transition from part throttle lean to full throttle rich, I think there is some gains to be had in there some where.
One of the other reasons I went for firmware 1.1.44 was the better acceleration enrichments. Hopefully I can tune these to take into consideration the lean spot on the map.
This lean area is purely for cruse and nothing else. The engine revs to 8500rpm and is a bit of an animal at full throttle when it comes on can around 4000rpm
I am never going to get the results manufacturers do, I just cant afford the dyno time :D so a comprimise will always be on the front foot
No harm in trying, and is easy to get back to a lambda 1 map as long as there is no damage to the engine as a result :D
Hi,
Maybe a switch to 14x16 tables will give more room to fit everything in?
You've probably already done that and I'm about a week behind! :-[
Cheers,
Gavin :)
I see what you are trying to achieve, and there is certainly no harm in experimenting :) I'm working in generalisations, and as you know how different engines respond to things can vary wildly depending on many factors, so in the end experimentation is the only way to really find out what works for you.
I hear what you are saying about the throttle bodies, but remember that they are sized based on the engine's peak mass flow on a time basis - i.e. how many kg/hour of air does the engine move. You may be using the same head and have an extra 100cc's, but what is your rev limit compared to the bike engine? Does your engine actually achieve the same air mass flow as the original? That may well be the case - and you may even benefit from bigger bodies at peak power (less pressure loss across the butterflies and spindles) - but that doesn't change the basic physics that the same mass flow through a bigger tube will move slower, so at your low load point where the enine is still consuming the smae amount of air, it will be moving more slowly through the throttles, and this may lead to worse charge preparation, maybe.....
Also, it sounds like you are basically changing a major engine component because the ECU has a lack of functionality (in this case, the possibility to adjust the breakpoints to where you need them) - I guess you'd have to take that up with the developers. Would there be a way of adjusting the signal instead to make it non linear (though I realise that is a bit of a bodge)?
In any event, you've clearly thought it through and want to give it a go, and it would be great if you can get it to work nicely - I look forward to following your progress ;)
Peak power of the K1200 is 130bhp at 8750 rpm.
So par with a mixed cam set ( lower duration inlet cam) I managed 107 at 7300rpm. That is without igniton at MBT and cam timing different to that of the bike.
I have since fitted a matching pair of cams, and set the time to match the bike, and it does feel quite happy to rev to 8000rpm. I have an hour on the dyno next friday to resolve the ignition map and to fine tune the VE map for the new cam settings. As you say, its all in the testing. We will have to wait and see ;D
The larger throttles can wait until I have pulled the engine to fix the oil pressure problem, but thats after the dyno shoot out next Saturday. Which should be the biggest collection of the most powerfull A series engines in the world in one place !! ;D
Quote from: cliffb75 on February 01, 2009, 03:19:06 AM
Also, it sounds like you are basically changing a major engine component because the ECU has a lack of functionality (in this case, the possibility to adjust the breakpoints to where you need them) - I guess you'd have to take that up with the developers. Would there be a way of adjusting the signal instead to make it non linear (though I realise that is a bit of a bodge)?
I'm not sure what you're saying, with the 16x14 map you can set the breakpoints where ever you please. Which signal are you trying to make non-linear?
Err, I'm not trying to do anything....... :-[
I was inferring from Sprockets comments that he had a problem with the cruise point being halfway up the map - i.e. he felt he was lacking resolution between the cruise point and WOT to make the transition from lean side to rich side fuelling.
If he is able to adjust the TPS breakpoints (presumably by switching to a different firmware?) then all will be well ;D
It's a good job you are here to keep and eye on things Rob ;)
:oCliff, I'm not coming over all moderator with hammers - I was trying to quantify what was being said, and if a problem with the implementation had been identified then we could define it and feed it into the developers TODO list...
The TPS/MAP breakpoints can be adjusted where ever needed with any firmware.
Thank-you for your kind words regarding my attendance on this forum, its less of a hobby, and more of a calling ;)
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