Lean burn with negative split timing
04-04-2012, 11:52 PM
#176
I'd like to believe that negative split would allow the trailing plug to ignite the rich pocket at the trailing edge of the chamber and act like a pilot for the main combustion event.
However everything I've read suggests that the flame front around the trailing plug does not propagate forward, and suffers substantial quenching. Generally, it doesn't seem to do much at light loads, except it can get in the way at idle if it is retarded along with leading.
So, I'm clueless, but it is fun to think about.
Thought I'd add this paper, just in case anyone understands post-graduate engineer-jargon Japanese.
However everything I've read suggests that the flame front around the trailing plug does not propagate forward, and suffers substantial quenching. Generally, it doesn't seem to do much at light loads, except it can get in the way at idle if it is retarded along with leading.
So, I'm clueless, but it is fun to think about.
Thought I'd add this paper, just in case anyone understands post-graduate engineer-jargon Japanese.
Last edited by oltmann; 04-05-2012 at 03:07 AM. Reason: Add nihongo paper
04-05-2012, 07:37 PM
#179
Well that one was a bridge too far. Started hearing knock around 1k-2k rpm also lost a small amount of power top end. Backing off now to rev 11, keeping advance in cruise and leaning out further this will be rev 13 and should start showing results if there are any to find.
04-06-2012, 10:59 AM
#183
Think I may have figured out something. There comes a point, it actualy comes very quickly, where the ammount of heat lost to the coolant caused by the longer duration of burn is of higher consequence then the extra efficiency caused by a more complete and longer burn. Maybe going leaner will help, but if I see no more positives I'm gonna start from scratch and tune the other way with a neg split and go richer. I'm starting to think that MM was right, he just didn't know why and therefore couldn't explain it.
OD: Yeah I think a third spark plug would help. Anything that helps light off the fuel faster can help both economy and power if tuned right.
OD: Yeah I think a third spark plug would help. Anything that helps light off the fuel faster can help both economy and power if tuned right.
04-06-2012, 12:03 PM
#184
Only problem with this is finding a way to actually fire it in a meaningful manner
And given the fact that the trailing plugs do very little for power in the first place....it is unlikely that there will be much gained with a huge insrease in complexity
04-07-2012, 03:48 PM
#186
Well here is what I've learned so far.
Anything you can do to a NA Renesis engine that slows combustion is bad for fuel economy.
Water injection, steam injection, donkey **** injection. Or even using high octane fuel. Also running a colder thermostat is in this category. Unfortunately running a water free coolant is also in this category, since it maintains better heat transfer in the engine at all times. I would have figured this out sooner had I properly tuned my engine first and then worked on crazy FE projects.
Running lean also goes into this category, although if you can keep enough heat in the engine such as with a hotter thermostat, or possibly even conventional coolant (although that will be reducing the margin to det to nil, and I'm not gonna try it) you can get gains.
Running rich can add to fuel economy once you have exhausted the limits of effective timing. Since from +45 to -45 there is very little movement of the combustion pocket, you can advance within this range without losing efficiency; however the effect of timing is minimal within this range too. Once you start going farther you run into two things, the combustion pocket is traveling a greater distance along the housing which leads to greater losses to coolant, and the engine is well within the compression phase which can cause det. However, running rich quickly drops fuel economy due to unburned fuel, so there is a balance just rich of stoich with advanced timing.
This all goes out the window with FI however, you can use the extra pressure to speed up the burn and allow both good fuel economy and acceptable power with lean burn. The only limitation seems to be overburdening the coolant system.
Using neg split to light the rich fuel first is a great way for improving dynamic compression. It should cause the lean fuel mass to burn quicker and give better gains, but I've had limited success with it. I'm either at the limits of the compression of my engine, and/or at the limits of heat loss to the coolant system. Either way I'm showing no more gains. I am however slowly showing equivalent gains with a near stock fuel map and increased timing.(Btw increasing the Min afr to 12.5 gave me quite a kick in the pants boost in power!)
I have no doubt Mazda found great emissions benefits with a lean burn system. The decreased burn speed and temp is perfect for minimizing everything in the exhaust, but without special engine coatings and a torque based ECU I don't think it's doable on a NA engine for fuel economy.
So I'm gonna drop out of this research until my turbo build, but I'm keeping the neg split timing.
Anything you can do to a NA Renesis engine that slows combustion is bad for fuel economy.
Water injection, steam injection, donkey **** injection. Or even using high octane fuel. Also running a colder thermostat is in this category. Unfortunately running a water free coolant is also in this category, since it maintains better heat transfer in the engine at all times. I would have figured this out sooner had I properly tuned my engine first and then worked on crazy FE projects.
Running lean also goes into this category, although if you can keep enough heat in the engine such as with a hotter thermostat, or possibly even conventional coolant (although that will be reducing the margin to det to nil, and I'm not gonna try it) you can get gains.
Running rich can add to fuel economy once you have exhausted the limits of effective timing. Since from +45 to -45 there is very little movement of the combustion pocket, you can advance within this range without losing efficiency; however the effect of timing is minimal within this range too. Once you start going farther you run into two things, the combustion pocket is traveling a greater distance along the housing which leads to greater losses to coolant, and the engine is well within the compression phase which can cause det. However, running rich quickly drops fuel economy due to unburned fuel, so there is a balance just rich of stoich with advanced timing.
This all goes out the window with FI however, you can use the extra pressure to speed up the burn and allow both good fuel economy and acceptable power with lean burn. The only limitation seems to be overburdening the coolant system.
Using neg split to light the rich fuel first is a great way for improving dynamic compression. It should cause the lean fuel mass to burn quicker and give better gains, but I've had limited success with it. I'm either at the limits of the compression of my engine, and/or at the limits of heat loss to the coolant system. Either way I'm showing no more gains. I am however slowly showing equivalent gains with a near stock fuel map and increased timing.(Btw increasing the Min afr to 12.5 gave me quite a kick in the pants boost in power!)
I have no doubt Mazda found great emissions benefits with a lean burn system. The decreased burn speed and temp is perfect for minimizing everything in the exhaust, but without special engine coatings and a torque based ECU I don't think it's doable on a NA engine for fuel economy.
So I'm gonna drop out of this research until my turbo build, but I'm keeping the neg split timing.
04-07-2012, 07:55 PM
#189
I have no direct proof that water free coolant is keeping internal temps lower because I don't have a control run or any internal instrumentation.
What I do know is this:
My idle vac is much higher than it should be. (Better Vacuum.)
My EGTs are much hotter than they should be, but go down the hotter I can get the coolant.
Edit: And my engine should have gone off like a hand grenade with some of the timing I pushed if it wasn't cooler on the inside.
Internal housing temp should directly effect both Vac and combustion speed, (as should compression.) So it's not that big a leap to say I have lower internal temps. Low compression alone would cause slower combustion speed with lower idle vac.
Also the coolant passages are horizontal, this allows steam to collect and blanket the inside top of the channel. This steam layer doesn't have to be thick (in fact it's pretty thin) but when it happens it removes surface area for heat transfer.
http://en.wikipedia.org/wiki/Nucleate_boiling
Tried to find a video, but no such luck.
The point is that with the high amount of heat transfer to only a couple of coolant passages in an engine with a high power density to begin with is just begging for departure from nucleate boiling. In fact I think rotaries do it at idle. At high rpms the flow should strip most of the steam film away (until heat flux gets high enough.) but at idle there just isn't the flow.
The biggest question I have involves the exhaust ports. Most of the housing is shielded by the boundary layer preventing direct contact of the hot gasses. The exhaust ports kinda lose this benefit as the exhaust has to snake into/through them. So... since side seal failure is a big cause of engine failure, and exhaust port heat is the smoking gun... Is this also coolant related? I think it might be. I doubt Mazda ever dropped a camera into the coolant passages of a running engine, but maybe they did embed some thermocouples.
Sorry for a bit of a ramble. To sum it up, Evans NPG is pretty much the same as yellow Prestone, just more expensive, but the fundamental theory is sound.
Sauce: I've tried lower octane. Runs slightly better. Maybe I should toss in a gallon of diesel fuel every fill up. Also I really don't have much of a clue what I'm doing, I'm just flying by the seat of my pants until I crash and burn or fly. I can give you advice, but I really only take chances with my own car.
Gonna post a diy alignment thread now.
What I do know is this:
My idle vac is much higher than it should be. (Better Vacuum.)
My EGTs are much hotter than they should be, but go down the hotter I can get the coolant.
Edit: And my engine should have gone off like a hand grenade with some of the timing I pushed if it wasn't cooler on the inside.
Internal housing temp should directly effect both Vac and combustion speed, (as should compression.) So it's not that big a leap to say I have lower internal temps. Low compression alone would cause slower combustion speed with lower idle vac.
Also the coolant passages are horizontal, this allows steam to collect and blanket the inside top of the channel. This steam layer doesn't have to be thick (in fact it's pretty thin) but when it happens it removes surface area for heat transfer.
http://en.wikipedia.org/wiki/Nucleate_boiling
Tried to find a video, but no such luck.
The point is that with the high amount of heat transfer to only a couple of coolant passages in an engine with a high power density to begin with is just begging for departure from nucleate boiling. In fact I think rotaries do it at idle. At high rpms the flow should strip most of the steam film away (until heat flux gets high enough.) but at idle there just isn't the flow.
The biggest question I have involves the exhaust ports. Most of the housing is shielded by the boundary layer preventing direct contact of the hot gasses. The exhaust ports kinda lose this benefit as the exhaust has to snake into/through them. So... since side seal failure is a big cause of engine failure, and exhaust port heat is the smoking gun... Is this also coolant related? I think it might be. I doubt Mazda ever dropped a camera into the coolant passages of a running engine, but maybe they did embed some thermocouples.
Sorry for a bit of a ramble. To sum it up, Evans NPG is pretty much the same as yellow Prestone, just more expensive, but the fundamental theory is sound.
Sauce: I've tried lower octane. Runs slightly better. Maybe I should toss in a gallon of diesel fuel every fill up. Also I really don't have much of a clue what I'm doing, I'm just flying by the seat of my pants until I crash and burn or fly. I can give you advice, but I really only take chances with my own car.
Gonna post a diy alignment thread now.
Last edited by Harlan; 04-07-2012 at 08:00 PM. Reason: addition
04-07-2012, 10:28 PM
#190
I think Mazda has tested/modeled all of this stuff in every way we can imagine and a couple dozen we can't. Unfortunately their engineers are tasked with entirely different priorities than ours.
Setting timing is certainly the tricky bit. The tuner method is simply to advance until you get knock and then back it off a little. This works if the engine happens to be knock limited, otherwise it become a huge PITA unless you are equipped to do spark sweeps.
Setting timing is certainly the tricky bit. The tuner method is simply to advance until you get knock and then back it off a little. This works if the engine happens to be knock limited, otherwise it become a huge PITA unless you are equipped to do spark sweeps.
04-09-2012, 08:39 AM
#193
Mark has a lot of experience with water free coolant and I am on the fence about it. Maybe he can share? I concur that I think there is a cooling problem at idle and very low rpms. I have my own findings. Its hard for me to explain them.
Based on my personnel experiences and beliefs, I am actually torn between doing evans or an electric water pump. I dont want to do both and I have my reasons.
I have a thought concerning the exhaust ports--that is, the airspace between the actual insert and the iron. The coolant passage doesnt touch the insert due to this space. So obviously the coolant cannot have as good of an affect. Since so many of us now run with out the air pump ot the cat--this may be an area worth some attention? I wish I had the tools to do more with it --but I dont.
Based on my personnel experiences and beliefs, I am actually torn between doing evans or an electric water pump. I dont want to do both and I have my reasons.
I have a thought concerning the exhaust ports--that is, the airspace between the actual insert and the iron. The coolant passage doesnt touch the insert due to this space. So obviously the coolant cannot have as good of an affect. Since so many of us now run with out the air pump ot the cat--this may be an area worth some attention? I wish I had the tools to do more with it --but I dont.
04-09-2012, 10:19 AM
#194
I have a thought concerning the exhaust ports--that is, the airspace between the actual insert and the iron. The coolant passage doesnt touch the insert due to this space. So obviously the coolant cannot have as good of an affect. Since so many of us now run with out the air pump ot the cat--this may be an area worth some attention? I wish I had the tools to do more with it --but I dont.
Unless you are talking about porting, then that is a completely different discuission
Last edited by stinksause; 04-09-2012 at 10:57 AM.
04-09-2012, 12:24 PM
#195
Well, I'm tired of being in the dark. Gonna do some logs with a stock tune then convert to 50/50 and see what happens. I've done much more work for much less usefull data. I'll let y'all know how it turns out. I hope I'm right, but if I'm wrong it gives me a reason to rebuild.
04-09-2012, 06:35 PM
#196
Just to be clear, I'm not arguing that Mazda knows all and therefore stock is best. Their engineers face many constraints that we just don't care about.
They say that Henry Ford once sent his engineers to junkyards to study how all of the Model T's had failed. When they came back with the results, they expected him to have them improve the parts that failed the most. Instead he instructed them to weaken the parts which never failed.
So, the point I was trying to make was that Mazda probably knows exactly how much boiling goes on in the coolant passages. Any CFD package can model it quite well, and I think they've measured it every which way. The cost-effective design got built in the end.
They say that Henry Ford once sent his engineers to junkyards to study how all of the Model T's had failed. When they came back with the results, they expected him to have them improve the parts that failed the most. Instead he instructed them to weaken the parts which never failed.
So, the point I was trying to make was that Mazda probably knows exactly how much boiling goes on in the coolant passages. Any CFD package can model it quite well, and I think they've measured it every which way. The cost-effective design got built in the end.
04-10-2012, 09:31 AM
#197
They did redisign the coolant channels around the sparkplug area--but it was not enough obviously. Modifications to the coolant passageways by some builders have proved to be an improvement. However engine cooling is a complicated discussion and there is not a single answer for everyone.
Waterless coolant may be a great option for some--I am still trying to find data concerning how the hotter normal operating temperatures it brings affects the oil temeratures. But, that is another subject and I dont want to derail this thread.
An axialary small electric water pump plumbed to the heater side may be in the future? This could increase flow ( and cooling) during the lower rpms. Volkswagon had a problem with low speed cooling and had to fix some warped cyclinder heads as a result. They solved the issue with a small axiallary ewp. BMW , Toyota and Mercedes all have this now. They advertize it as a heater booster pump, but those in the know, know the real reason it is there.
Very interesting thread--keep it going.
Waterless coolant may be a great option for some--I am still trying to find data concerning how the hotter normal operating temperatures it brings affects the oil temeratures. But, that is another subject and I dont want to derail this thread.
An axialary small electric water pump plumbed to the heater side may be in the future? This could increase flow ( and cooling) during the lower rpms. Volkswagon had a problem with low speed cooling and had to fix some warped cyclinder heads as a result. They solved the issue with a small axiallary ewp. BMW , Toyota and Mercedes all have this now. They advertize it as a heater booster pump, but those in the know, know the real reason it is there.
Very interesting thread--keep it going.
04-10-2012, 01:20 PM
#198
At least from first principles, higher operating temps should increase heat rejection and improve efficiency. Evans would seem to help here.
Loss of lubrication is a concern, but for me the apex seals are a bigger ?? That is where rotaries fail. Personally, my omp table is pretty liberal, and I'm running a Sohn adapter.
If waterless coolant can really keep the oil film from breaking down around around the exhaust ports, it seems like a win on all fronts. I'm still researching as well.
Loss of lubrication is a concern, but for me the apex seals are a bigger ?? That is where rotaries fail. Personally, my omp table is pretty liberal, and I'm running a Sohn adapter.
If waterless coolant can really keep the oil film from breaking down around around the exhaust ports, it seems like a win on all fronts. I'm still researching as well.
04-10-2012, 07:47 PM
#199
i dont think it is the oil film breaking down around the exhaust ports? The side seals from what I know are not showing abnormal wear, which they would if the lubrication was compromised? Again from what I understand it's the side seal springs that are failing not the seals.
04-10-2012, 09:06 PM
#200
The point is that with the high amount of heat transfer to only a couple of coolant passages in an engine with a high power density to begin with is just begging for departure from nucleate boiling. In fact I think rotaries do it at idle. At high rpms the flow should strip most of the steam film away (until heat flux gets high enough.) but at idle there just isn't the flow.
The biggest question I have involves the exhaust ports. Most of the housing is shielded by the boundary layer preventing direct contact of the hot gasses. The exhaust ports kinda lose this benefit as the exhaust has to snake into/through them. So... since side seal failure is a big cause of engine failure, and exhaust port heat is the smoking gun... Is this also coolant related? I think it might be. I doubt Mazda ever dropped a camera into the coolant passages of a running engine, but maybe they did embed some thermocouples.
Sorry for a bit of a ramble. To sum it up, Evans NPG is pretty much the same as yellow Prestone, just more expensive, but the fundamental theory is sound.
The biggest question I have involves the exhaust ports. Most of the housing is shielded by the boundary layer preventing direct contact of the hot gasses. The exhaust ports kinda lose this benefit as the exhaust has to snake into/through them. So... since side seal failure is a big cause of engine failure, and exhaust port heat is the smoking gun... Is this also coolant related? I think it might be. I doubt Mazda ever dropped a camera into the coolant passages of a running engine, but maybe they did embed some thermocouples.
Sorry for a bit of a ramble. To sum it up, Evans NPG is pretty much the same as yellow Prestone, just more expensive, but the fundamental theory is sound.
I implemented it because I wanted to avoid boiling around the exhaust passages because I had read about engines losing the water seal in that area as well as my reading of Evans coolant in racing from about twenty years ago. Evan NPG is pretty much straight propylene glycol with NPG+ and NPGR being propylene glycol with a certain amount of ethylene glycol mixed in to adjust viscosity.