Satanicusmaximus
Mechanical
- Apr 25, 2010
- 8
Why build a 4-stroke over a two stroke? Assuming both engines utilise direct injection a 2-stroke is fundamentally better is it not?
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4-strokes obsolete? 1
- Thread starter Satanicusmaximus
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LadaTrouble
Automotive
The roots blower only acted as a scavenger pump on diesel 2 strokes,there was no pressure charging.I always wondered why they didn't do the obvious - use it as a supercharger?
BrianPetersen
Mechanical
The only way a scavenging pump could give pressure in the cylinder significantly above atmospheric pressure (i.e. "supercharging") on that type of engine, is if there is significant exhaust manifold back pressure. Otherwise the extra charge pressure just blows out the exhaust and doesn't do anything.
A turbocharger creates both the extra intake pressure and the extra exhaust manifold back pressure. But, it can't be the only scavenging device, if only because the engine can't be started using the turbocharger alone.
A lot of the Detroit Diesels used both the scavenging blower (inherent in the design) and a turbocharger.
A turbocharger creates both the extra intake pressure and the extra exhaust manifold back pressure. But, it can't be the only scavenging device, if only because the engine can't be started using the turbocharger alone.
A lot of the Detroit Diesels used both the scavenging blower (inherent in the design) and a turbocharger.
The turbo-supercharged versions of the EMD 567,645 and 710 engines for locomotive/marine/stationary power applications do scavenging and intake boost with a turbocharger (only) that is gear driven at start up and at low speeds.
The turbo is gear driven through a one way sprag clutch to guarantee blow through at start up and at low rpm. Hence the name turbo-supercharger.
The intake and gear noise on these engines is impressive and very characteristic. a between the lower power
At idle there is a very characteristic pulsating gear whine as each cylinder fires on these slow turning engines. But as the rpm comes up it becomes only turbo whine.
The lower output engines are gear driven supercharger only.
The turbo is gear driven through a one way sprag clutch to guarantee blow through at start up and at low rpm. Hence the name turbo-supercharger.
The intake and gear noise on these engines is impressive and very characteristic. a between the lower power
At idle there is a very characteristic pulsating gear whine as each cylinder fires on these slow turning engines. But as the rpm comes up it becomes only turbo whine.
The lower output engines are gear driven supercharger only.
YvesLLewelyn
Mechanical
I think what Lada was referring to is two-stroke diesels where the exhaust is controlled by poppet valves not by the piston uncovering a port. The blower could build pressure against the closed valves.
LadaTrouble
Automotive
Actually I was thinking of the Commer TS3,which is the 2 stroke diesel I'm most familiar with.But now I see that if the exhaust ports open first,then of course they must close last,and so no pressure charging.It would take some complicated trickery to make the exhaust close while the intake is still open - but now we are in the 21st century,this would be child's play.
The last of the Foden 2 strokes were doubled up into V12's and turbocharged,they were used in landing craft.
The last of the Foden 2 strokes were doubled up into V12's and turbocharged,they were used in landing craft.
Lou Scannon
Automotive
"The only way a scavenging pump could give pressure in the cylinder significantly above atmospheric pressure (i.e. "supercharging") on that type of engine, is if there is significant exhaust manifold back pressure. Otherwise the extra charge pressure just blows out the exhaust and doesn't do anything."
What about the case when the scavenging pump volume per engine cycle (assuming positive displacement) is appreciably greater than the engine's swept volume?
What about the case when the scavenging pump volume per engine cycle (assuming positive displacement) is appreciably greater than the engine's swept volume?
BrianPetersen
Mechanical
Statement is still true. The excessive flow rate will only give significant pressure rise above atmospheric in the cylinder if there is excessive pressure drop going out the exhaust ...
Maybe I'm misreading the above 2 statements. I certainly understand the above would be true with ported intake and ported exhaust 2 stroke.
Are you making the statement just for ported intake and port exhaust 2 strokes, or making the same statement for ported intake, poppet valve exhaust 2 strokes?
The Detroit Diesel Series 71's and the EMD 567,645 (and other displacements) use ported intake and poppet valve exhaust. In this case it would seem that the degree that a blower can pressurize the cylinder would be dependent upon the exhaust poppet valve closure timing versus the port closure timing..
EMD cylinder head with 4 poppet exhaust valves.
EMD (removable) cylinder liner showing ported intake and with cylinder head mounted...
Chart of EMD 645 (and others) supercharged (for blow through) and turbo supercharged on same displacement, higher output engines.
Comparison of same size engines for example the 16 cylinder 16-645E supercharged (for blow through) produced 2000 hp. The same displacement, same compression ratio, at same rpm but turbo supercharged 16-645E3 produces 3000 hp.
The DD Series 71s used the same flow concept (intake port and poppet valve exhaust)as the EMDs. All DDs use superchargers for guaranteed blow through as mentioned in a prior post and additional single or twin turbos on the higher output engines.
12 cylinder twin turbo, aftercooled detroit diesel
Are you making the statement just for ported intake and port exhaust 2 strokes, or making the same statement for ported intake, poppet valve exhaust 2 strokes?
The Detroit Diesel Series 71's and the EMD 567,645 (and other displacements) use ported intake and poppet valve exhaust. In this case it would seem that the degree that a blower can pressurize the cylinder would be dependent upon the exhaust poppet valve closure timing versus the port closure timing..
EMD cylinder head with 4 poppet exhaust valves.
EMD (removable) cylinder liner showing ported intake and with cylinder head mounted...
Chart of EMD 645 (and others) supercharged (for blow through) and turbo supercharged on same displacement, higher output engines.
Comparison of same size engines for example the 16 cylinder 16-645E supercharged (for blow through) produced 2000 hp. The same displacement, same compression ratio, at same rpm but turbo supercharged 16-645E3 produces 3000 hp.
The DD Series 71s used the same flow concept (intake port and poppet valve exhaust)as the EMDs. All DDs use superchargers for guaranteed blow through as mentioned in a prior post and additional single or twin turbos on the higher output engines.
12 cylinder twin turbo, aftercooled detroit diesel
Wonder if we will see a resurgence of uniflow 2 strokes in heavy trucks again? 2 strokes definatly have an advantage of smaller and lighter weight. It is a real shame such engines as the Napier Nomad wasn't refined more and used.
I think the EMD 710 is still being produced, and meeting the emissions requirements just fine. 4 strokes do offer better control over inlet and exhaust events, well easier to change I should say. Much easier to over come limitations like spring surge and valve float using a 2 stroke.
I think the EMD 710 is still being produced, and meeting the emissions requirements just fine. 4 strokes do offer better control over inlet and exhaust events, well easier to change I should say. Much easier to over come limitations like spring surge and valve float using a 2 stroke.
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globi5
Mechanical
- Oct 10, 2005
- 281
"Any engine that utilized oil in the fuel for lubrication would be flat out for automotive applications, and soon for almost any other application."
---
That's not entirely true: The Mazda RX-8 with its rotary engine uses oil for lubrication to lubricate the rotor seals and combustion chamber and is still being sold. (Granted oil is injected and not mixed with the fuel but the injected oil does take the same path).
And there may or may not be more applications for rotary engines (which will always depend on oil lubrication):
There was some talk about Honda possibly going back to employing 2-strokes a few years ago:
But then again: Even racing karts with 4 stroke engines are becoming increasingly popular (where 2 stroke engines have always been predominant).
---
That's not entirely true: The Mazda RX-8 with its rotary engine uses oil for lubrication to lubricate the rotor seals and combustion chamber and is still being sold. (Granted oil is injected and not mixed with the fuel but the injected oil does take the same path).
And there may or may not be more applications for rotary engines (which will always depend on oil lubrication):
There was some talk about Honda possibly going back to employing 2-strokes a few years ago:
But then again: Even racing karts with 4 stroke engines are becoming increasingly popular (where 2 stroke engines have always been predominant).
The RX-8 is an emissions headache for Mazda. It will require some form of emissions banking and trading, low-sulfur oil, or sulfur-resistant catalyst in future years. I have no specific information, but it wouldn't surprise me if they weren't using credits for it already. You can run a model or two like this, but you can't run an entire brand on it.
BrianPetersen
Mechanical
The RX-8 is being cancelled in Europe because it won't meet the next generation of their emission standards.
Regarding achieving a "supercharging" effect using the Detroit Diesel layout (ported intake and cam operated exhaust valves), of course it would be possible if the exhaust valves opened before the intake ports opened and closed before the intake ports closed. Possible, yes. But, this would either result in the effective expansion stroke being shorter than the effective compression stroke (unfavorable if taken too far), or require the exhaust valves to open and close in an even fewer number of crankshaft degrees (already a problem in those engines, and it would limit valve lift), or require the intake ports to take up a much greater portion of the cylinder thus reducing "trapped volume" i.e. the effective displacement (unfavorable).
Detroit Diesel got it right by using the scavenging blower to just scavenge, and a separate turbocharger to both "supercharge" and create exhaust system back-pressure to trap the extra charge in the cylinder ...
Regarding achieving a "supercharging" effect using the Detroit Diesel layout (ported intake and cam operated exhaust valves), of course it would be possible if the exhaust valves opened before the intake ports opened and closed before the intake ports closed. Possible, yes. But, this would either result in the effective expansion stroke being shorter than the effective compression stroke (unfavorable if taken too far), or require the exhaust valves to open and close in an even fewer number of crankshaft degrees (already a problem in those engines, and it would limit valve lift), or require the intake ports to take up a much greater portion of the cylinder thus reducing "trapped volume" i.e. the effective displacement (unfavorable).
Detroit Diesel got it right by using the scavenging blower to just scavenge, and a separate turbocharger to both "supercharge" and create exhaust system back-pressure to trap the extra charge in the cylinder ...
Anyone know what emissions are at issue for the RX-8? IIRC it was HCs that felled the RX-7s. Mazda cleaned these up in the RX-8, but if it's CO2 then that may be a tougher nut to crack.
Usually I figure everyone should have to play by the same rules, but perhaps the Wankel deserves a separate regulatory category since it's development seems to be interrupted by bars set for what's 'technologically feasible' for piston engines.
Usually I figure everyone should have to play by the same rules, but perhaps the Wankel deserves a separate regulatory category since it's development seems to be interrupted by bars set for what's 'technologically feasible' for piston engines.
SomptingGuy
Automotive
I thought it was mainly UHCs from the total loss oil system.
- Steve
- Steve
All of the emissions are challenging because of it, although UHC may be the current specific cause. Almost any level of UHC can be dealt with if you want to pay enough for the required catalyst. However, those catalysts are vulnerable to sulfur, making the combination of high UHC and sulfur very difficult to fix. It also doesn't take a genius to estimate that some nasties that engines currently emit that are not regulated will be in the not-too-distant future, including some of the heavy metals that are primarily present from the oil. Expensive oil can relieve some of that, but at some point you are not going to be commercially competitive, or you will not be able to convince regulators that you can tell when someone has not used the special fluids required for your engine.
globi5
Mechanical
- Oct 10, 2005
- 281
I'm not sure about the sulfur and the CO2 (and I don't think that the RX-8 has been getting a special treatment just because it has a Wankel engine), but the unburned hydrocarbons in the RX-8 exhaust are taken care of by a hydrocarbon-burner/converter fed by a secondary air pump (which is located in front of the catalytic converter).
But the main reason why the RX-8 has better emissions than the RX-7 is because the exhaust ports are located on the side-walls which increases the probability that the unburnt gases are being recycled: (Also, the RX-8 engine may be the world's only internal combustion engine which doesn't have an inlet/outlet overlap).
But the main reason why the RX-8 has better emissions than the RX-7 is because the exhaust ports are located on the side-walls which increases the probability that the unburnt gases are being recycled: (Also, the RX-8 engine may be the world's only internal combustion engine which doesn't have an inlet/outlet overlap).
Banking and trading is not special treatment, it's used all the time for various engines. CO2 is not an emission special to a rotary engine, it is determined almost exclusively by the fuel economy of the vehicle - although the 18 mpg of the RX-8 is uninspiring.
globi5
Mechanical
- Oct 10, 2005
- 281
Well I certainly hope that everybody was aware that CO2 emission (which drwebb was referring to) means g_CO2 per km and is directly related to the fuel economy of the vehicle and the fuel used.
Anyway the major difference between Euro 4 and Euro 5 is apparently a 25% reduction in NOx. Hydrocarbons and CO remain unchanged and CO2-emissions or fuel economy is not even part of Euro 5.
So at least according to this, the RX-8 must have problems reaching the required NOx limits or this car is simply not selling well enough and Mazda decided to stop selling the RX-8 in Europe and blamed someone else. Who knows.
Anyway the major difference between Euro 4 and Euro 5 is apparently a 25% reduction in NOx. Hydrocarbons and CO remain unchanged and CO2-emissions or fuel economy is not even part of Euro 5.
So at least according to this, the RX-8 must have problems reaching the required NOx limits or this car is simply not selling well enough and Mazda decided to stop selling the RX-8 in Europe and blamed someone else. Who knows.
Slightly off topic, but here's a link to Ricardo's 2/4 stroke switching engine:
I have no association with Ricardo!
I have no association with Ricardo!
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