Single spark plug housings
12-30-11, 07:16 AM
#26
"Elusive, not deceptive!”
As in other thread, even with timing advanced to reach MBT, it would be poor, as majority of air fuel mixture is pushed to the leading side, no matter if rotor recess is MDR or LDR design. Maybe it could work "ok" if you had rotor with trailing deep recess, but still, it won´t match dual plug system.
I would highly speculate on lower chance of detonation in leading only design. As the burn rate is even worse than normaly, for same output from same airflow (which won´t even happen) it would call for more advanced timing, which on its own defeat its purposse. From above graph we can also see that leading only has higher blowdown pressure so higher EGTs without making good power.
Still there are some thing which I don´t understand. Like a fact that zero split is fine even in high boost engine in spite of opinions that it would cause annihilation of human race but trailing firing just small bit ahead at high load will cause immediate engine death.
I would highly speculate on lower chance of detonation in leading only design. As the burn rate is even worse than normaly, for same output from same airflow (which won´t even happen) it would call for more advanced timing, which on its own defeat its purposse. From above graph we can also see that leading only has higher blowdown pressure so higher EGTs without making good power.
Still there are some thing which I don´t understand. Like a fact that zero split is fine even in high boost engine in spite of opinions that it would cause annihilation of human race but trailing firing just small bit ahead at high load will cause immediate engine death.
Some people do this in the idle and no boost range.
Barry
12-30-11, 11:04 AM
#27
Let me add this to the conversation.
Since I am doing the ignition timing and split testing I thought I would revisit Mazda's papers on the subject. My favorite is the somewhat confusing chart on flame front. I think it is time to decipher it better. (See Attached)
At first it makes little sense because the legend's symbols and traces are not well marked and seem to be mislocated. One symbol in the legend had to be interrupted as -15 degrees (or ATDC) for trailing plug to make the chart work correctly.
It also helps to know that the actual ignition point is about 5 degrees before the points that were initially shown ( I added extension lines to the actual location).
Now you know how I like to color.... it helps to simplify it for me.
It looks like the biggest split burns the fastest because it allows the leading plug to spread furthest before the collision with the trailing flame front.
What thoughts do you guys have?
Since I am doing the ignition timing and split testing I thought I would revisit Mazda's papers on the subject. My favorite is the somewhat confusing chart on flame front. I think it is time to decipher it better. (See Attached)
At first it makes little sense because the legend's symbols and traces are not well marked and seem to be mislocated. One symbol in the legend had to be interrupted as -15 degrees (or ATDC) for trailing plug to make the chart work correctly.
It also helps to know that the actual ignition point is about 5 degrees before the points that were initially shown ( I added extension lines to the actual location).
Now you know how I like to color.... it helps to simplify it for me.
It looks like the biggest split burns the fastest because it allows the leading plug to spread furthest before the collision with the trailing flame front.
What thoughts do you guys have?
Another big factor here are overlap and exhaust pulse interference effects. This is going to depend on engine speed, port timing, and exhaust manifold design (twin scroll should have little interference between the two rotors). I have been studying exhaust pulse interference effects on piston engines, specifically 4 cylinders and the current Ford Coyote 5.0 which has an oddball firing order. On those engines, overlap and exhaust pulse interference contributes to the amount of residual exhaust gas blown back into the cylinder. This affects combustion phasing, pumping work, and the tendency to knock. Ford has published an extensive analysis of 5.0 twin turbo prototypes that deals with this issue.
I have not seen full details of the various tests you have been doing. I know you have been using some kind of pressure transducer equipment. Have you generated indicator diagrams from your tests? Do you have specs on peak combustion chamber pressure and indicated mean effective pressure?
Raymond, are you going to DGRR this year? I would to talk with you and some of our other thinkers.
12-31-11, 11:35 AM
#28
"Elusive, not deceptive!”
The color does help but it's still a very crude diagram with a lot going on. It appears to be hand sketched, as was typical back then. All the newer literature uses 3d solid modeling and visualization which is much easier to understand. I don't have a whole lot to add about that diagram. As I mentioned in an earlier post, I would like to see statistics on combustion phasing--crank angle at which 10, 50, and 90% of mass fraction is burned. Then we could benchmark it to known piston engines.
The program does combustion burn rate. I usually compare runs at the 70% point.
It also does peak pressure and location, max rate increase pressure and burn location, horsepower, torque, and IMEP.
Getting clean data is essential for the comparisons. I try to get air, water, and oil temps the same for each run. This requires driving for about 5 miles after each stop to check logged data, and then adding a new map for the next test.
The real problem is that after a 3rd gear run to 8000 rpm I may or may not have good data. I would estimate my success rate at only about 20%.
We think that my old PCIA card equipped computer is the problem.
Another big factor here are overlap and exhaust pulse interference effects. This is going to depend on engine speed, port timing, and exhaust manifold design (twin scroll should have little interference between the two rotors). I have been studying exhaust pulse interference effects on piston engines, specifically 4 cylinders and the current Ford Coyote 5.0 which has an oddball firing order. On those engines, overlap and exhaust pulse interference contributes to the amount of residual exhaust gas blown back into the cylinder. This affects combustion phasing, pumping work, and the tendency to knock. Ford has published an extensive analysis of 5.0 twin turbo prototypes that deals with this issue.
I have not seen full details of the various tests you have been doing. I know you have been using some kind of pressure transducer equipment. Have you generated indicator diagrams from your tests? Do you have specs on peak combustion chamber pressure and indicated mean effective pressure?
The program does combustion burn rate. I usually compare runs at the 70% point.
It also does peak pressure and location, max rate increase pressure and burn location, horsepower, torque, and IMEP.
Getting clean data is essential for the comparisons. I try to get air, water, and oil temps the same for each run. This requires driving for about 5 miles after each stop to check logged data, and then adding a new map for the next test.
The real problem is that after a 3rd gear run to 8000 rpm I may or may not have good data. I would estimate my success rate at only about 20%.
We think that my old PCIA card equipped computer is the problem.
Another big factor here are overlap and exhaust pulse interference effects. This is going to depend on engine speed, port timing, and exhaust manifold design (twin scroll should have little interference between the two rotors). I have been studying exhaust pulse interference effects on piston engines, specifically 4 cylinders and the current Ford Coyote 5.0 which has an oddball firing order. On those engines, overlap and exhaust pulse interference contributes to the amount of residual exhaust gas blown back into the cylinder. This affects combustion phasing, pumping work, and the tendency to knock. Ford has published an extensive analysis of 5.0 twin turbo prototypes that deals with this issue.
I have not seen full details of the various tests you have been doing. I know you have been using some kind of pressure transducer equipment. Have you generated indicator diagrams from your tests? Do you have specs on peak combustion chamber pressure and indicated mean effective pressure?
Barry
12-31-11, 05:38 PM
#29
so in the above screenshot I am seeing 50% mass fraction burnt at about 50 degrees ATDC? That does seem to be occurring late compared to some of the numbers I have seen on piston engines, but those tests are all done on engine dynos. What are the pressure units here? It says IMEP 251... 251 psi? That's about 1.73 mPA/17bar which passes a sanity check at least.
I'm not completely clear what the arrow is pointing to.
I'm not completely clear what the arrow is pointing to.
12-31-11, 09:59 PM
#34
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Most piston engines have highest burn rate around TDC - its logical, very compact and dense space - very short distance for flame to travel. Also burn rate itself has much higher value. Consequently, peak pressure is much higher and much better positioned to make work. 90% of mass fraction is usually burned before 40° ATDC or earlier...
We can fiddle with timing, but it still will be poor. Direct injection and stratification of charge is way to go. Or fuel which burns ridiculously fast and is not practical at all - hydrogen
12-31-11, 10:13 PM
#35
talking head
puts hand up
have been running leading only wastespark HEI ignition system daily for several years
i idle at lambda , i cruise at lambda and at wot under medium boost i run low 13 AFR
so would be suffice to say my engine efficiency is UP with single leading plug
there is a mitigating factor----
fuel of choice is LPG propane/butane vapour ,, and lambda is 15.7:1
so why is it i am the only rotary i know of that idles at lambda ?
and why am doing so with a supposedly lesser single location ignition system ?
here is the curveball ---
homogeneous mixture charging
-something LPG vapour does naturally that petroleum does not-
it has a positive effect on flame propogation and burn efficiency
,, burning more completely with stability at lambda ,,, even in the long narrow chamber
what happens when i put back in that trailing spark?
-nothing positive in terms of running mixtures , still idles and cruises at the same lambda
- under medium ( up to 15 psi ) boost with hot soaked inlet manifold with a NGK 10 plug the trailing spark will introduce a light preignition
timing revision is then required to push back that preignition threshold
quite a lot,, more than 5 degrees off the total timing when done on the microtech
( the dizzy proving a little crude to quantify and the microtech was installed to test various ignition configs )
my current daily config is back to the modded dizzy,, with BIM024 modules with HEC 715 coils and leading only wastepark
have been running leading only wastespark HEI ignition system daily for several years
i idle at lambda , i cruise at lambda and at wot under medium boost i run low 13 AFR
so would be suffice to say my engine efficiency is UP with single leading plug
there is a mitigating factor----
fuel of choice is LPG propane/butane vapour ,, and lambda is 15.7:1
so why is it i am the only rotary i know of that idles at lambda ?
and why am doing so with a supposedly lesser single location ignition system ?
here is the curveball ---
homogeneous mixture charging
-something LPG vapour does naturally that petroleum does not-
it has a positive effect on flame propogation and burn efficiency
,, burning more completely with stability at lambda ,,, even in the long narrow chamber
what happens when i put back in that trailing spark?
-nothing positive in terms of running mixtures , still idles and cruises at the same lambda
- under medium ( up to 15 psi ) boost with hot soaked inlet manifold with a NGK 10 plug the trailing spark will introduce a light preignition
timing revision is then required to push back that preignition threshold
quite a lot,, more than 5 degrees off the total timing when done on the microtech
( the dizzy proving a little crude to quantify and the microtech was installed to test various ignition configs )
my current daily config is back to the modded dizzy,, with BIM024 modules with HEC 715 coils and leading only wastepark
Last edited by bumpstart; 12-31-11 at 10:15 PM.
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