Stratified Charge
05-25-06, 10:17 AM
#1
Stratified Charge
My question is, why aren't the rotary engines being produced for the RX-8 employing the stratified charging technology?
The following information is my understanding of the system. Please correct it if it's wrong.
Stratified charge engine:
This system combines the advantages of both a pre-mixed combustion system and a diesel combustion system. The basic principle is that the fuel can be injected directly into the compressed air charge at or near TDC, rather than introduced as a fuel air mixture thereby increasing engine fuel consumption and decreasing emissions. This would come from a combination of the unthrottled intake system and the introduction of fuel only as required rather than trying to "fill the entire combustion chamber" with an ignitable fuel/air mixture. The quantity of fuel injected is determined by the load requirements on the engine.
SC allows for a multi-fuel use platform. It could use gas, metahnol, diesel fuel, and jet fuel without any engine adjustments. Additionally, it can produce a lower misfire levels, more stable combustion and higher combustion speed.
The following information is my understanding of the system. Please correct it if it's wrong.
Stratified charge engine:
This system combines the advantages of both a pre-mixed combustion system and a diesel combustion system. The basic principle is that the fuel can be injected directly into the compressed air charge at or near TDC, rather than introduced as a fuel air mixture thereby increasing engine fuel consumption and decreasing emissions. This would come from a combination of the unthrottled intake system and the introduction of fuel only as required rather than trying to "fill the entire combustion chamber" with an ignitable fuel/air mixture. The quantity of fuel injected is determined by the load requirements on the engine.
SC allows for a multi-fuel use platform. It could use gas, metahnol, diesel fuel, and jet fuel without any engine adjustments. Additionally, it can produce a lower misfire levels, more stable combustion and higher combustion speed.
05-25-06, 04:03 PM
#2
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05-25-06, 08:13 PM
#3
Mazda did make an experimental stratified charge rotary dubbed ROSCO that used little p-port primaries and semi-direct injection (fuel injector where oil injector is in rotor housing).
I think the reason stratified charge and other lean burn stratagies haven't been tried since the pre-catylitic 1st gen (there was a lean burn 1st gen) is that they all raise EGTs so high the catylitic converters won't last the 10 years the manufacturer has to warranty them.
This is also a reason why the RX-8 made less power/worse gas mileage over here-they had to richen the mixture to make the cats last.
That said, Mazda has teased us with the possibility of a direct injection rotary in there press releases.
If you want to play with lean burn/stratified charge yourself, ditch the cat and break out the die grinder.
My latest ports don't seem to mind running as lean as 16:1 at cruise without surging whereas the Pineapple ports didn't like much below 14:1.
You can see I also directed primary port flow up over the rotor toward the rear of the rotor and kept it high velocity as Mazda did in their ROSCO engine.
From the thread on my engine-
https://www.rx7club.com/rotary-car-performance-77/pics-blue-tiis-engine-build-new-type-primary-port-489429/
You should be able to get over 30mpg freeway w/ a leaned out 2nd gen as my '86 base/lightweight used to do 26mpg on the freeway w/ mods.
I think the reason stratified charge and other lean burn stratagies haven't been tried since the pre-catylitic 1st gen (there was a lean burn 1st gen) is that they all raise EGTs so high the catylitic converters won't last the 10 years the manufacturer has to warranty them.
This is also a reason why the RX-8 made less power/worse gas mileage over here-they had to richen the mixture to make the cats last.
That said, Mazda has teased us with the possibility of a direct injection rotary in there press releases.
If you want to play with lean burn/stratified charge yourself, ditch the cat and break out the die grinder.
My latest ports don't seem to mind running as lean as 16:1 at cruise without surging whereas the Pineapple ports didn't like much below 14:1.
You can see I also directed primary port flow up over the rotor toward the rear of the rotor and kept it high velocity as Mazda did in their ROSCO engine.
From the thread on my engine-
https://www.rx7club.com/rotary-car-performance-77/pics-blue-tiis-engine-build-new-type-primary-port-489429/
You should be able to get over 30mpg freeway w/ a leaned out 2nd gen as my '86 base/lightweight used to do 26mpg on the freeway w/ mods.
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05-26-06, 11:58 AM
#8
Also, do you think there's any way we can add a 3rd spark plug?
(4) 3-PLUG IGNITION SYSTEM
The trailing side of the rotary engine’s combustion chamber develops a squish which pushes back the flamefront as shown in Fig. 16.(2) With the conventional two-plug system, this squish prevents the flame from propagating to the combustion chamber’s trailing and in the mid and high engine speed ranges. As a result, the mixture in the squish area is expelled in an unburned state.
The 3-plug ignition system (Fig. 17) used in the R26B engine has an additional plug mounted toward the trailing side, positioned above the two original plugs. This extra plug ignites the mixture in the trailing side before the squish is generated, causing the mixture to burn completely and, also speeding up flame propagation, which improves fuel consumption. The far trailing (FT) plug hole was made as small in volume as possible, within the range where combustion would not be affected, because when the apex seal is partially across the plug hole, and if the hole is large there would be a direct path for the gas to flow from the high pressure area to the low pressure area. The effectiveness of the 3-plug system is plotted in Fig. 18. Note that both the engine output and fuel consumption benefit from the new system. Improvement in output, however, is not as great as in fuel consumption, probably due to some amount of gas blowing through the FT plug hole, thus causing some drop in volumetric efficiency.
The trailing side of the rotary engine’s combustion chamber develops a squish which pushes back the flamefront as shown in Fig. 16.(2) With the conventional two-plug system, this squish prevents the flame from propagating to the combustion chamber’s trailing and in the mid and high engine speed ranges. As a result, the mixture in the squish area is expelled in an unburned state.
The 3-plug ignition system (Fig. 17) used in the R26B engine has an additional plug mounted toward the trailing side, positioned above the two original plugs. This extra plug ignites the mixture in the trailing side before the squish is generated, causing the mixture to burn completely and, also speeding up flame propagation, which improves fuel consumption. The far trailing (FT) plug hole was made as small in volume as possible, within the range where combustion would not be affected, because when the apex seal is partially across the plug hole, and if the hole is large there would be a direct path for the gas to flow from the high pressure area to the low pressure area. The effectiveness of the 3-plug system is plotted in Fig. 18. Note that both the engine output and fuel consumption benefit from the new system. Improvement in output, however, is not as great as in fuel consumption, probably due to some amount of gas blowing through the FT plug hole, thus causing some drop in volumetric efficiency.
05-26-06, 06:40 PM
#9
can you snap a pic of that port from a different angle? it's kinda hard for me to tell exactly what's going on.
I have a couple more un-helpful pics from that same thread. I can look through my other pics on my computer for the angles you want to see.
so did the injector location allow a better idle with more overlap?
The ROSCO engine used a tiny primary P-port so the overlap was likely the same as production rotaries of the era (though more than renisis). The semi direct injector location was to help atomise the fuel well as the primary P-port blew directly accross the injector discharge plume in the larger volume of the rotor housing intake "stroke" area.
Isn't the idea of stratified charging is that they reduce the need for a catalytic converter by reducing the excess hydrocarbons.
And that is exactly what it did for Honda with their Controlled Vortex Variable Combustion chamber (cvvc) and Mazda with their lean burn 12A until emmisions standards were so strict a catylitic had to be employed.
Now the exhaust has to be so clean it is often cleaner than the ambient air, not to mention close coupled cats are important for the extra fuel required for warm up and cold start emmissions regs are getting tougher.
That reminds me of another Mazda experimental rotary where a small pre-combustion chamber was added at the trailing plug location so at cruise air/fuel was introduced into this chamber only and ignited by the trailing plug- much like the cvvc system.
I suppose could make a precombustion chamber that screwed right into the trailing plug hole, though I can see it lowering effective compression ratio. Feed it air w/ air pump, vaporized fuel metered through system pressure and ignited by your trailing plug. Set your regular fuel injection maps to zero at cruise/idle but use them still for warm-up and load driving.
I have a couple more un-helpful pics from that same thread. I can look through my other pics on my computer for the angles you want to see.
so did the injector location allow a better idle with more overlap?
The ROSCO engine used a tiny primary P-port so the overlap was likely the same as production rotaries of the era (though more than renisis). The semi direct injector location was to help atomise the fuel well as the primary P-port blew directly accross the injector discharge plume in the larger volume of the rotor housing intake "stroke" area.
Isn't the idea of stratified charging is that they reduce the need for a catalytic converter by reducing the excess hydrocarbons.
And that is exactly what it did for Honda with their Controlled Vortex Variable Combustion chamber (cvvc) and Mazda with their lean burn 12A until emmisions standards were so strict a catylitic had to be employed.
Now the exhaust has to be so clean it is often cleaner than the ambient air, not to mention close coupled cats are important for the extra fuel required for warm up and cold start emmissions regs are getting tougher.
That reminds me of another Mazda experimental rotary where a small pre-combustion chamber was added at the trailing plug location so at cruise air/fuel was introduced into this chamber only and ignited by the trailing plug- much like the cvvc system.
I suppose could make a precombustion chamber that screwed right into the trailing plug hole, though I can see it lowering effective compression ratio. Feed it air w/ air pump, vaporized fuel metered through system pressure and ignited by your trailing plug. Set your regular fuel injection maps to zero at cruise/idle but use them still for warm-up and load driving.
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