legatia

Hey guys

Is there anyone out there running single spark plug housings on their engines?

I just bought one of a member on this forum. And Im wondering a little about tuning it, is there anything I need to do differently than if I was running regular housings with leading and trailing?

arghx

iTrader: (3)

You might be referring to the "anti detonation" mod that some have done. It basically deletes the trailing plug. In contrast, all the old Audi/NSU rotaries ran on trailing plugs only (believe it or not).

I don't have firsthand experience with tuning these but I would expect a decrease in fuel economy at the very least.

RENESISFD

iTrader: (13)

Arghx check this out,

https://www.rx7club.com/3rd-generation-rx-7-1993-2002-parts-99/stage-3-ported-motor-dowell-pinned-balanced-coated-oil-coolant-mods-3mm-polished-966223/

In the description Allrotor93 claims single spark plug housings. I guess they do exist



John

legatia

Renesisfd nailed it. That engine is currently on the way over the pond (to Norway).

Arghx, trailing plugs only?? This one is the other way around. Leading only.

jaggermouth

iTrader: (1)

Interested in this as well since I don't want to run my giant trailing coil pack (FC ignition)

arghx

iTrader: (3)

Running leading-only could prevent detonation in modified turbo applications. That's really the only potential benefit. There's nothing else to gain from running it, and the engine will lose some efficiency.

I just double checked some stuff. The NSU KKM 502 engine used a single trailing plug. This was a single rotor, peripheral ported engine found in the Wankel Spider which was the first production rotary-powered vehicle. At the time NSU found that running dual spark plugs was superior but they couldn't figure out an affordable way to do it.



Here's some data from their early tests. The crude triangle-looking plots are from the experimental 2 plug system, and circle plots are from the trailing-only system used in the KKM 502. You can see that specific fuel consumption ("SFC") is lower, the mixture is leaner (lambda is a higher value), and engine load/output (brake mean effective pressure, BMEP) is higher with the two-plug system.

Later Audi/NSU switched to a dual plug system in the KKM 612 engine, which was a 2 rotor peripheral ported configuration found in the Audi Ro80 luxury car. The dual-plug system didn't need as cold of a heat range so the plugs lasted longer.

Mazda investigated leading-only, trailing-only, and dual spark plugs when they were developing the 10A engine. They used combustion chamber pressure sensors to generate the pressure-volume indicator diagrams commonly used in engine development:



The problem with running leading-only plugs is that the flame must work against the gas flows traveling along the trochoid path of the rotor. The problem with trailing-only is that the flame can encounter quenching effects. The dual spark plug system has superior output. Mazda used 3 spark plugs per rotor on the R26B 4 rotor engine in the 787B LeMans race car:

arghx

iTrader: (3)

In actual day-to-day use, it is certainly conceivable that deleting the trailing plugs reduces detonation. The reason why it reduces detonation is because most detonation typically occurs in the trailing portion of the combustion chamber due to the squish flows. Squish flows are concentrated pockets of air/fuel mixture that are also found on piston engines.





When you eliminate the trailing plugs there's much less flame propagation into the trailing portion of the chamber, thus the chance of knock in that area naturally decreases. There are legitimate reasons why it works, but overall engine efficiency will undoubtedly decrease even if it's not obvious on the dynojet at Billy Bob's Mustang Shop.

RIX-7

iTrader: (2)

So would running 3 plugs help prevent det and give more power ?

Rix

arghx

iTrader: (3)

Theoretically yes (at least on the power part, not sure about detonation) but how many sets of 3 plug housings are out there? To my knowledge only the R26B had them, and those housings were meant for a peripheral ported n/a race engine application.

legatia

Nice, your like the encyclopedia of rotary.
Hopefully the loss of efficiency will be outweighed by the benefit of less detonation. Im using a t88 34d and aiming for 500+rwhp.

I was thinking of buying some mercury IGN-1A coils, looks like they are the bees knees these days. Although i have been considering msd 6 or 7 series ignitors with coils.

RIX-7

iTrader: (2)

Going off topic, sorry op.

Raymond, I think I need to get my dad to get his drill and tap set out .
Easy to drill and tap a third hole. Time for some R&D I think.
Did you pull any info on the wiring for a third plug.

Bryan Jacobs

iTrader: (66)

I think rx7specialties can modify for a 3rd spark plug.

j9fd3s

iTrader: (3)

Revolution sells 3 plug housings, http://revo-tune.jp/catalogue/detail.php?id=98 although i'm not really sure if that makes it available, and B i have no idea what ecu would run that

RIX-7

iTrader: (2)

Thankyou,

Rix

RotaryEvolution

iTrader: (30)

i'd be curious about trailing only if it was timed correctly. ran a TII on the dyno which wound up having a incorrectly installed leading coil pack that was put on afterwards. i know the timing was correct before so i didn't recheck it.

the car made about 247whp with trailings only but came up about 50 horsepower with the leadings working with a different leading coil pack.

of course the trailing timing is severely retarded in comparison to the proper leading timing. many people have ran with just 1 plug per housing in the leading position and have had decent results but probably could have had better with both functioning.

allrotor93

iTrader: (126)

When I spoke to Adam(rx7specialties) he said that these housings are uber rare and were used in rotary generators

RotaryEvolution

iTrader: (30)

got any pics of these 1 plug housings?

Liborek

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

Barry Bordes testing so far shown that burn rate in rotary engine is without excuse sh*t and peak pressures are extremely delayed resulting in poor HP/airflow and high EGTs. Making it worse by running leading only?

arghx

iTrader: (3)

There are lots of things done by OEM's and research labs that make most of us scratch our heads. For example, lots of engines run what we would consider to be stupid lean under boost from the factory, even ones without direct injection. They can often make it work because they have really good software and equipment to do sophisticated testing.

I haven't seen a comprehensive overview of his testing. Normally when testing burn rate there are a few metrics used, such as the crank angle at which 50% of the mass in the combustion chamber is burnt.



Speaking of burn rate...

I know we're jumping around a little bit here, but if you're wondering how combustion phasing/burn rate is measured in engine development see the above data from a study on a prototype Ford Ecoboost V6 engine. The engine was used to evaluate E85 injection. E85 was sprayed through direct injectors while E0 pure gasoline was sprayed in the conventional port configuration. In this case Ford engineers were trying to tweak the timing and the amount of E85 injection. The whole point was to find a balance between spark retard and E85 use for purposes of good torque output without too much E85 consumption.

Looking at the graph I boxed, you can see a combustion phasing plot. Y axis is the degrees ATDC at which 50% of the mass in the cylinder is burnt. X axis is load. As load increases, spark is retarded, and the mixture burns later. The ratio of E85 to gasoline decreases and the mixture richens up to keep the exhaust temps from getting too high.

RotaryEvolution

iTrader: (30)

i don't doubt it, which is why i always run the stock 2 plug system.

j9fd3s

iTrader: (3)

i think the porting matters too. on a side port, the trailing doesn'tt do much. on the Peripheral port the trailing plugs do more. to the point where it won't idle without the trailings, but if the leadings aren't working you'd never notice. off idle its the same, but max power is still made with both plugs

the NSU is a P port too....

Liborek

Very nice, as always
Their burn rate must be really fast, so low EGTs at stoichiometric AFR (granted its partly due to E85). On rotary it would be over 1000°C

Well, I´m going by some common sense and conclusions from several NASA research papers which clearly indicates that prolonged burn rate is major hurdle in efficiency of rotary engine. These papers have all kinds of graphs but unfortunately they have poor image quality. When you compare combustion pressure graphs from Barry´s testing to usual piston engines, you can clearly see that pressure rise is slow and to late. Main problem with burn rate in rotary is establishment of large flame front and consequent high heat release in early crank angles. Conventional ignition system is not enough.

Mazda did research of "pilot flame ignition system". Whole paper is called "Research and Development of a Direct Injection Stratified Charge Rotary Engine with a Pilot Flame Ignition System"

Todays development seems like joke compared to what these folks were doing decades ago

Barry Bordes

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?

Raymond, are you going to DGRR this year? I would to talk with you and some of our other thinkers.

Barry

ksu-chewie

iTrader: (14)

When I first bought my rx7 it had the anti-det mod done by KDR. My arm was twisted by several folks so I took out the faux plugs, added a coil pack, & re-tuned. I still have the faux plugs & pfc map if anyone is interested.

Liborek

I think that we can´t draw such conclusion from this graph. Total advance itself is different, we don´t know what load and internal flow was taking the place etc. Its no wonder that blue trace has quickest burn rate when leading advance is so much bigger. Even from numerous published papers, I still can´t draw some concensus. Leading timing is pretty straightforward, but with trailing, its so complicated... Non colliding flame fronts are maybe nice, but ultimately it just about generating heat and pressure at right place and time, and so far, small to zero split with adjusted overall timing is still most efficient. But its only my opinion